LAND-OCEAN INTERACTIONS IN THE COASTAL ZONE (LOICZ)
Core Project of the
International Geosphere-Biosphere Programme: A Study of Global Change (IGBP)
Mexico Map showing lagoons
COMPARISON OF CARBON, NITROGEN AND PHOSPHORUS FLUXES
IN MEXICAN COASTAL LAGOONS
LOICZ REPORTS & STUDIES No. 10
compiled and edited by S.V. Smith, S. Ibarra-Obando, P.R. Boudreau and V.F. Camacho-Ibar
LOICZ Core Project Office
Netherlands Institute for Sea Research (NIOZ)
P.O. Box 59, 1790 AB Den Burg
Texel, The Netherlands

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Compiled & Edited by
Stephen V. Smith
School of Ocean and Earth Science and Technology
Honolulu, Hawaii 96822
United States of America
Silvia Ibarra-Obando
Center for Scientific Research and Higher Education of Ensenada (CICESE)
Ensenada
Baja California, Mexico
Paul R. Boudreau
LOICZ Core Project Office
Texel, The Netherlands
Víctor F. Camacho-Ibar
Institución de Investigaciones Oceanológicas
Universidad Autónoma de Baja California
(IIO-UABC)
Ensenada
Baja California, Mexico
LOICZ REPORTS & STUDIES NO. 10

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Published in the Netherlands, 1997 by:
LOICZ Core Project
Netherlands Institute for Sea Research
P.O. Box 59
1790 AB Den Burg - Texel
The Netherlands
The Land-Ocean Interactions in the Coastal Zone Project is a Core Project of the "International
Geosphere-Biosphere Programme: A Study Of Global Change", of the International Council of
Scientific Unions.
The LOICZ Core Project is financially supported through the Netherlands Organisation for Scientific
Research by: the Ministry of Education, Culture and Science; the Ministry of Transport, Public Works
and Water Management; the Ministry of Housing, Planning and Environment; and the Ministry of
Agriculture, Nature Management and Fisheries of The Netherlands, as well as The Royal Netherlands
Academy of Sciences, and The Netherlands Institute for Sea Research.
COPYRIGHT © 1997, Land-Ocean Interactions in the Coastal Zone Core Project of the IGBP.
Reproduction of this publication for educational or other, non-commercial purposes is
authorised without prior permission from the copyright holder.
Reproduction for resale or other purposes is prohibited without the prior, written
permission of the copyright holder.
Citation:
Smith, S.V., S. Ibarra-Obando, P.R. Boudreau and V.F. Camacho-Ibar. 1997.
Comparison of Carbon, Nitrogen and Phosphorus Fluxes in Mexican Coastal Lagoons,
LOICZ Reports & Studies No. 10, ii + 84 pp. LOICZ, Texel, The Netherlands.
ISSN:
1383-4304
Cover:
Map of the coast of Mexico published in 1616. Note that, by this date, many lagoons
and coastal embayments were already being mapped along the Mexican coast.
Disclaimer: The designations employed and the presentation of the material contained in this report
do not imply the expression of any opinion whatsoever on the part of LOICZ or the
IGBP concerning the legal status of any state, territory, city or area, or concerning the
delimitation's of their frontiers or boundaries. This report contains the views expressed
by the authors and may not necessarily reflect the views of the IGBP.
The LOICZ Reports and Studies Series is published and distributed free of charge to scientists
involved in global change research in coastal areas.

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TABLE OF CONTENTS
Page
1. OVERVIEW OF WORKSHOP AND BUDGET RESULTS
1
2. BUDGETS FOR MEXICAN COASTAL LAGOONS
4
2.1 Arid Pacific and Gulf of California coasts
4
2.1.1) Estero de Punta Banda, Baja California
4
2.1.2) Bahía San Quintín, Baja California (a teaching example)
9
2.1.3) Bahía San Luis Gonzaga, Baja California
16
2.1.4) Estero La Cruz, Sonora
21
2.1.5) Bahía Concepción, Baja California Sur
25
2.1.6) Ensenada de La Paz, Baja California Sur
29
2.2 Humid Pacific Coast
33
2.2.1) Bahía de Altata-Ensenada del Pabellón, Sinaloa
33
2.2.2)Teacapan-Agua Brava-Marismas Nacionales, Sinaloa and Nayarit
38
2.2.3) Carretas-Pereyra, Chiapas
43
2.2.4) Chantuto-Panzacola, Chiapas
47
2.3 Gulf of Mexico
51
2.3.1) Laguna Madre, Tamaulipas
51
2.3.2) Laguna de Terminos, Campeche
56
3. CONCLUSIONS AND IMPLICATIONS FOR LAGOON COMPARISON
60
4. REFERENCES
65
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APPENDICES
I
MEXICAN COASTAL LAGOONS OVERVIEW
68
II
COMPARISON OF NET & GROSS BUDGET FOR BAHÍA SAN QUINTÍN
71
III
ECOLOGICAL SERVICES AND SOCIO-ECONOMIC SUSTAINABILITY
74

- A case study: Bahía San Quintín
IV
SOCIO-ECONOMIC SITUATION OF LAGUNA DE TERMINOS
76
V
MEXICAN LAGOONS WORKSHOP REPORT
77
VI
LIST OF WORKSHOP PARTICIPANTS AND CONTRIBUTORS
82
VII
WORKSHOP AGENDA
84
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1. OVERVIEW OF WORKSHOP AND BUDGET RESULTS
A central and essential objective of the Land Ocean Interactions in the Coastal Zone (LOICZ) Core
Project of the International Geosphere-Biosphere Programme (IGBP) is to:
· gain a better understanding of the global cycles of the key nutrient elements carbon (C), nitrogen
(N) and phosphorus (P);
· understand how the coastal zone affects these fluxes through biogeochemical processes; and,
· characterise the relationship of these fluxes to human intervention (Pernetta and Milliman, 1995).
Coastal lagoons along the 12,000 km shoreline of Mexico are numerous, diverse, and well-studied.
According to Contreras (1993) Mexico has about 180 coastal lagoons and other estuarine areas, with
about 10,000 km2 on the Pacific coast and 10,000 km2 on the Gulf of Mexico. These lagoons are
subject to extremely varied degrees and kinds of human pressure due to direct uses and indirect
insults. Considerable scientific information exists for many of these systems, and the bibliographic
information has been well summarised (see References - Section 4). All of these considerations led
to the recognition by several members of the LOICZ Scientific Steering Committee that it would be
appropriate to hold a regional workshop in order to develop budgets according to the LOICZ
Biogeochemical Modelling Guidelines (Gordon et al., 1996). Such a workshop seemed likely to yield
several useful budgets, to generate interest in the region in developing further budgets, and perhaps
to provide a formula for generating regional budgets to be compiled into the world-wide database
being developed by the LOICZ Biogeochemical Modelling Node. That database is being posted on a
World Wide Web Home Page (reachable through http://www.nioz.nl/loicz/modelnod). It was further
recognised that an understanding of the functioning of these diverse and well-studied Mexican
lagoons might be exported to other regions of the world with less well-studied lagoons.
The workshop was convened at the Center for Scientific Research and Higher Education of
Ensenada (CICESE) in Ensenada, Mexico, on June 2-3rd, 1997. Five resource persons (S. Smith, F.
Wulff, R. Buddemeier, V. Camacho-Ibar and P. Boudreau) worked with eleven scientists from a
number of different institutions in Mexico. They were all familiar with lagoons throughout Mexico and
brought with them much of the necessary data and experience required to carry out the work. It was a
highly successful meeting that exceeded expectations and has laid a good framework for continued
studies within the region.
Dr. S. Ibarra-Obando initiated the technical part of the workshop by presenting an overview of the
natural history of Mexican coastal zone. A synopsis of that overview is presented in Appendix I. Drs.
Smith and Wulff presented an overview of the LOICZ budgeting procedure and used this workshop
as the inaugural presentation of the Biogeochemical Modelling Home Page. Dr. Camacho-Ibar
presented a detailed budgetary analysis for Bahía San Quintín, Baja California, in order to guide the
workshop participants through the budgeting procedure. This budget represents an extension, based
on new (and more reliable) data, from the San Quintín budget originally presented in Gordon et al.
(1996). Dr. Ibarra-Obando presented a comparison between the system-level budgets of net material
flux and addition of components to obtain gross turnover of materials (see Appendix II).
Following these general introductory exercises, the group broke into three working groups, loosely
structured around hydrological regimes of the Mexican coastal zone:
Group 1 - Botello-Ruvalcaba, Boudreau, Camacho-Ibar, Delgadillo-Hinojosa, Lechuga-Devéze and
Poumian-Tapia - derived budgets for five coastal lagoons in the desert region of Baja California, Baja
California Sur, Sinaloa and Sonora.
Group 2 - Contreras-Espinosa, Flores-Verdugo, Ibarra-Obando, de la Lanza-Espino and Wulff -
developed budgets for two coastal lagoon systems (each with several individual lagoons) in the
region with high-runoff in Nayarit, and Chiapas states.
Group 3 - Buddemeier, Carriquiry, Gomez-Reyes and Vázquez-Botello - developed a budget for
Laguna de Terminos, Campeche, a large system lying in the transition region between the high runoff
area of the lower part of the Gulf of Mexico coast and the Yucatán Peninsula, which is dominated by
low surface runoff but high groundwater flow.
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These eight budgets were partially or wholly developed during the workshop. In the subsequent two
weeks following, details of the budgets were provided, as well as written descriptions for this report
and for eventual posting on the World Wide Web page. Two additional budgets were also provided
during that two-week period; two more were added while a draft of this report was under review; all
four are included in this final report. Table 1 and Figure 1 summarise the lagoon systems which have
been budgeted and the authorship on each.
Table 1. System for which budgets have been developed and reported in this document.
SYSTEM & STATE
Num.
Abbr.
AUTHORS
Latitude N
Longitude W
Estero de Punta Banda,
1
EPB
M. Poumian-Tapia,
31o 44'
116o 38'
Baja California
V. Camacho-Ibar,
S. Ibarra-Obando.
Bahía San Quintín,
2
BSQ
V. Camacho-Ibar,
30o 27'
115o 58'
Baja California
J.D. Carriquiry,
S.V. Smith.
Bahía San Luis Gonzaga,
3
SLG
F. Delgadillo-Hinojosa,
29o 49'
114o 23'
Baja California
J. A. Segovia-Zavala.
Estero La Cruz,
4
ELC
M. Botello-Ruvalcaba,
28o 45'
111o 53'
Sonora
E. Valdez-Holguín.
Bahía Concepción,
5
BC
C. Lechuga-Devéze.
26o 39'
111o 30'
Baja California Sur
Ensenada de La Paz,
61
ELP
C. Lechuga-Devéze.
24o 08'
110o 22'
Baja California Sur
Bahía de Altata-Ensenada
71
EP
F. Flores-Verdugo,
24o 25'
107o 38'
del Pabellón,
G. de la Lanza-Espino.
Sinaloa
Teacapan-Agua Brava-
8
TAB
G. de la Lanza-Espino,
22o 08'
105o 32'
Marismas Nacionales,
F. Flores-Verdugo,
Sinaloa and Nayarit
F. Wulff.
Carretas-Pereyra,
91
CPBB
F. Contreras-Espinosa.
15o 27'
93o 10'
Chiapas
Chantuto-Panzacola,
10
CP
F. Contreras-Espinosa,
15o 13'
92o 50'
Chiapas
S. Ibarra-Obando.
Laguna Madre,
111
LM
S. Ibarra-Obando,
24o 00'
97o 00'
Tamaulipas
F. Contreras-Espinosa.
Laguna de Terminos,
12
LT
E. Gomez-Reyes,
18o 40'
91o 35'
Campeche
A. Vázquez-Botello,
J.D. Carriquiry,
R. Buddemeier.
1These budgets were prepared subsequent to the workshop, but in sufficient time to be incorporated into the report.
At the time of printing, budgets are under active development for several additional systems in
Mexico as a result of this workshop. These will be added to the modelling world wide web page when
they are completed:
· Laguna Carmen-Machona, Tabasco, 18o 16' N , 93o 50' W;
· Laguna Mecoacan, Tabasco, 18o 20' N , 93o 10' W;
· Laguna Tampamachoco, Veracruz, 20o 18' N , 97o 30' W.
Additionally, there may be sufficient information to budget some systems in Mexico over time, in a
manner that will document the interactions between material fluxes and human intervention.
The budgetary information for each system is discussed individually and reported in units which are
convenient for that system (either as daily or annual rates). Subsequently, key aspects of the data
are summarised into Tables 10-13, with all rates presented as "annualised rates." Nonconservative
fluxes are also reported per unit area, for ease of comparison among the systems.
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As useful steps towards relating the biogeochemical fluxes to human intervention, many of the
descriptions given here include socio-economic overviews. For two of these systems the socio-
economic situations are explicitly discussed. Dr. S. Ibarra-Obando and others have laid out a brief
overview of socio-economic pressures imposed on the Bahía San Quintín and watershed system
(Appendix III). Dr. A Vázquez-Botello has provided a brief synopsis of the competing human uses
and pressures acting on Laguna de Terminos, the second largest Mexican lagoon (Appendix IV). It is
hoped that these supporting documents, together with the biogeochemical budgets which are the
main focus points of this report, will help provide framework for realistic integration between
understanding material fluxes, which is the central theme of IGBP and LOICZ, the roles that humans
play in modifying those fluxes, and the implications of those modifications with respect to humans.
As another potentially useful product of this workshop, Dr. Gomez-Reyes has agreed to provide a
simple and generalised method of dispersion analysis that can be used to estimate water exchange
in lagoons and similar systems where there is no salt gradients between the lagoons and adjacent
oceanic systems. This analysis will be added as a further link on the Biogeochemical Modelling
Home Page.
The full meeting report, participants list and contact information is given in Appendix V and VI.
And a good time was had by all!
Figure 1. Map of Mexico showing names of coastal states and locations of budgeted lagoonal
systems. See Table 1 for system numbers.
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2. BUDGETS FOR MEXICAN COASTAL LAGOONS
2.1 Arid Pacific and Gulf of California coasts
2.1.1 Estero de Punta Banda, Baja California
M. Poumian-Tapia, S. Ibarra-Obando and V. F. Camacho-Ibar
Study Area Description
Estero de Punta Banda (Figures 1 and 2, 31o N, 116 o W) is located 12 km south of Ensenada in the
Maneadero valley. The estuary receives drainage from the San Carlos and Las Animas rivers only
during rainy winters. Annual average precipitation is about 20 cm per year (Ibarra-Obando and
Poumian-Tapia, 1991). Evaporation exceeds precipitation, so the estuary functions as a negative
estuary with salinity increasing from the mouth to the inland portion of the estuary (Acosta-Ruiz and
Alvarez-Borrego, 1974; Celis-Ceseña and Alvarez-Borrego, 1975). The estuary and surrounding tidal
flats cover an area of 12 km2. The estuary has an "L" shape with a short portion extending inland in a
south-easterly direction, and a channel 7.5 km long that opens into Todos Santos Bay. The mean
depth of the system is estimated to be about 2 m, and the system volume to be 24 x 106 m3. The
position of the mouth relative to the other sites on the lagoon is considered to be an important factor
in the maintenance of the circulation regime (Pritchard et al., 1978).
Salt marshes cover an area of about 3 km2 and represent the main vegetation type, with Spartina
foliosa, Batis maritima and Salicornia virginica as the most characteristic species (Ibarra-Obando and
Poumian-Tapia, 1991; 1992). The estuary is used as spawning, nursery and feeding zone for
permanent and temporary fish species. A total of 22 species have been reported, some of which are
important for the small scale local fisheries (Ibarra-Obando and Escofet, 1987). About 80 bird species
have been reported to use the estuary either temporarily or on a permanent basis with diversity
increasing from the mouth to the head. The Clapper Rail (Rallus longirostris), the Savannah Sparrow
(Passerculus sandwichensis) and the Brown Pelican (Pelecanus occidentalis), which are considered
endangered species in the USA, are still found in the marshy habitats of Punta Banda (Ibarra-Obando
and Escofet, 1987).
The estuary has been used for industrial and tourist purposes without any management plan. In 1983,
an assembling plant for oil-drilling platform supports was installed in the south-west corner of the
estuary. Its major impact was the construction of a dike which interrupted water circulation in that
portion of the estuary, with the consequent habitat destruction (Ibarra-Obando and Escofet, 1987;
Ibarra-Obando and Poumian-Tapia, 1991).The project was never finished due to the international oil
prices crisis, otherwise the impact would have been greater. Around 1990, and a few km north of the
industrial construction, a tourist development was initiated in an abandoned hotel in the sand bar.
The original project included a marina inside the estuary and a gas station, landing field for small
aeroplanes, and habitation area in the sand bar. The major impact of this project was dune
destruction. The project was not successful because it was conceived for Southern California
residents, who were afraid of investing in it because of land-tenure problems. However, house
density along the sand bar is high with ownership mainly by United States citizens. Sport fishing is
another important activity inside and around the estuary.
The Maneadero valley, adjacent to the bay, is mainly an agricultural and cattle raising area. In a 1995
census by the Baja California State Government, the Maneadero valley permanent population was
estimated at about 13,000 inhabitants and 2,000 migrants during the agricultural crop season.
Cultivable area is about 40 km2 utilised for growing vegetables (tomatoes, peas, carrots, corn,
potatoes, lettuce, etc.) and fruits (strawberry). Olives are also characteristic of the area. A small
number of agro-industries exists in order to industrialise and commercialise these products. As in the
San Quintín valley, agriculture relies mainly on ground-water exploitation. The cattle raising business
is focused primarily on production of dairy products.
In this case, we calculated a summer budget using data from 1992-1993. Average precipitation is
about 200 mm year-1 and evaporation is about 1,000 mm year-1. For this budget, the dissolved
inorganic N and P data for this system are available from Martínez-Inostros (1994). Data for one
station located near the estuary mouth were used for ocean data. The ocean salinity data used was
estimated from several papers (Millán-Núñez et al., 1981; Segovia-Zavala et al., 1988; Bustos,
personal communication); the system salinity data used was from Céliz-Ceseña (1975).
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Figure 2. Map of Estero de Punta Banda, Baja California.
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Water and Salt Balance
The box model (Figure 3), represent the terms included in the water and salt budget for the summer
period. VP is the volume of precipitation and is zero in summer, VE is the volume of evaporation
calculated from area of water, 12 km², and the evaporation rate of 4 mm day-1. The VQ (volume of
stream runoff), VG (groundwater inflows), and VO (other inflows like sewage), are considered to be 0.
So the loss of water from the system through evaporation must be balanced to maintain the volume
system constant; this is the residual flow (VR) and is made up by seawater inflow. In this case, VR is
positive, to balance water loss due to VE.
For the salt balance, the change of salinity with time multiplied by water volume must equal zero.
That is, the system is at steady state conditions. Input of salt with the residual flow from sea water is
greater than zero (VRSR = +1,632 x 103 m3 day-1), so mixing between bay and ocean must balance
the salt (VX[SOcean-SSystem] = -1,632 x 103 m3 day-1). Mixing (VX) is the only unknown, so it can be
derived:
Vx= - VRSR / (S2 -S1)= -(4.8 x 104 m3 day-1)(34) / (33.6-34.4) = +2,040 x 103 m3 day-1
(1)
Now, the exchange time of water in the system (, in days) can be calculated, as the total volume of
the system divided by the sum of VX plus the absolute value, |VR|, the processes responsible for
adding and removing water. Thus:
= Vsys / (Vx + |VR| )= 24,000 x 103 m3 / (+2,040 x 103 + 48 x 103) m3 day-1) = 11 days
(2)
VP = +0
VE = -48
VR =
+48
VRSR =
+1,632
VQ = 0
VSystem = 24,000
SOcean =
33.6 psu
SSystem = 34.4 psu
SR =
34.0 psu
= 11 days
VG = VO = 0
VX (SOcean - SSystem) = -1,632
(assumed)
VX = 2,040
Figure 3. Water and salt budgets for Estero de Punta Banda, during the summer. System volume is
in units of 103 m3. Water fluxes in 103 m3 day-1. Salt fluxes in 103 psu m3 day-1.
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Budgets of Nonconservative Materials
The balance of any nonconservative material (Y) (also at steady state) is calculated from:
dVY/dt = 0 = VQYQ + VPYP + VGYG + VOYO + VEYE + VRYR + VX(YOcean - YSystem) + Y
(3)
where the various "V" terms involve fluxes of Y with water sources and Y represents the net internal
source or sink of element Y. In the summer, the terrigenous sources of Y to Punta Banda Estuary are
assumed to be zero. On the sand bar there is tourist development which may discharge some
sewage into the bay, but these and other sewage sources are assumed to be relatively small in the
net nutrient balances (although neither measured nor indirectly estimated). Therefore, the previous
equation is simplified and solved for Y:
Y = -VRYR - Vx (YOcean-YSystem)
(4)
This is the general equation for calculating nonconservative fluxes of dissolved materials, in our
case, and the results for DIP and DIN are illustrated in Figure 4.
P Balance
It can be seen that the system is a substantial net source of DIP (DIP = +1,574 mol day-1). The
observed flux per unit area is DIP divided by the bay area, or +0.13 mmol m-2 day-1. We do not
have winter data for comparison, but we suspect by analogy with Bahía San Quintín (Section 2.1.2; a
physiographically rather similar system 200 km to the south), that the winter DIP is lower.
Nevertheless, we use this as at least an approximation of the annual average flux.
Some of the observed DIP could be associated with direct discharge of sewage into the bay. Let us
take 20 mol person-1 year-1 as an approximation of per capita domestic sewage discharge. The
human population required to account for DIP would be about 30,000 people--far greater than the
population living immediately adjacent to the bay. We therefore assume that domestic discharge,
while possibly of local importance, is a relatively small term in the DIP budget of this system.
N Balance
By contrast with DIP, the system is a much smaller source of DIN (DIN = +365 mol day-1). Again
extrapolating over the entire bay area, the rate is equivalent to DIN = +0.03 mmol m-2 day-1. As with
DIP, we suspect that the summer value is an overestimate of the annual rate but cannot evaluate
this point with available data.
Stoichiometric Calculations of Aspects of Net System Metabolism
If the positive value for DIP represents net organic matter oxidation and if the reacting organic
matter has an N:P ratio approximating the Redfield Ratio of 16:1 (Redfield, 1934), then the expected
DIN value would be 16 x DIP, or 16 x (+1,574) = 25,184 mol day-1. We can estimate the net effect
of nitrogen fixation - denitrification (nfix - denit) as the difference between the observed and expected
values of DIN:
(nfix - denit) = + 365 - 25,184 mol day-1 = -24,819 mol day-1
(= -2.1 mmol m-2 day-1, over the estuary area).
This rate might, again, be different if data were available for an annual average.
The value for DIP can also be used to estimate net ecosystem metabolism (NEM¸ or [p - r]), again
with the assumption that organic oxidation is the primary source of nonconservative DIP flux. This
rate is estimated as the C:P ratio of the reacting organic matter (again assuming a Redfield Ratio;
C:P = 106:1) multiplied by the negative of DIP:
(p - r) = -1,574 x 106 = 166,844 mol day-1
(= -14 mmol m-2 day-1, over the estuary area).
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DIPatm = 0
(assumed)
VR DIPR = +58
VQ DIPQ = 0
DIP
DIPSystem = 1.6 mmol m-3
Ocean=0.8 mmol m-3
DIPR = 1.2 mmol m-3
DIP = +1,574
VX (DIPOcean -DIPSystem) = -1,632
VG DIPG = VQ DIPQ = 0
(assumed)
DINatm = 0
(assumed)
VR DINR = +43
VQ DINQ = 0
DINSystem = 1.0 mmol m-3
DINOcean=0.8mmol m-3
DINR = 0.9 mmol m-3
DIN = +365
V
V
G DING = VQ DINQ = 0
X (DINOcean -DINSystem) = -408
(assumed)
Figure 4. DIP and DIN budgets for Estero de Punta Banda, Baja California. Fluxes in mol day-1.
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2.1.2 Bahía San Quintín, Baja California (a teaching example)
V.F. Camacho-Ibar, J.D. Carriquiry and S.V. Smith
This system is described in some detail, because it was used as an introductory, illustrative example
of the budgeting procedure. In addition to the detailed description of the budget itself, ancillary
information about gross versus net metabolism in the system and the socio-economic status of the
watershed are presented in Appendices II and III.
Study Area Description
Bahía San Quintín (Figures 1 and 5) is a hypersaline coastal lagoon located in the western coast of
the Baja California Peninsula, Mexico (30o 27'N, 116o 00'W). This bay is a net evaporative system
and can be considered as a negative estuary since its salinity is always higher than that in the
adjacent ocean. Average salinities in the bay range from 34.7 psu in the summer to 33.8 in the
winter. In the ocean, salinity ranges from 33.8 psu in the summer to 33.6 in the winter. The bay area
is 42 km2 and has an average depth of ~ 2 m (volume 90 x 106 m3). The watershed of the bay is ~
2,000 km2, of which an important part consists of agricultural lands (see discussion in Appendix III).
Total evaporation (VE) across the area of San Quintín is the vertical water loss multiplied area of the
bay; VE averages 164 x 103 m3 day-1 during the summer and 91 x 103 m3 day-1 during the winter.
Calculated in a similar manner, total rainfall (VP) averages 4 x 103 m3 day-1 during the summer and
67 x 103 m3 day-1 during winter. Although the watershed-area: bay-area ratio may be an important
factor for land-bay hydrologic interactions, weather is dry and therefore contributions from runoff are
not important year around (VQ=0). The only significant surface flows into the bay occur during
extreme rainfall events that last for only 2 to 3 weeks. In contrast, the groundwater contribution (VG)
from the San Simón hydrological basin seems to be more important than runoff, but it also occurs
only during the cooler rainy season in winter (February to April). The estimated contribution from VG
to the bay is about 1 x 103 m3 day-1 during the winter and decreases to nearly zero during the summer
(National Water Commission Office, Ensenada, B.C., Mex.).
Figure 5. Map of Bahía San Quintín and sampling stations from August 1995.
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Seagrasses are important components of the biotic community of Bahía San Quintín. It has been
estimated that seagrasses cover up to 25% of the entire bottom of the bay (Ibarra-Obando and
Huerta-Tamayo, 1987), but phytoplankton productivity is also important (Alvarez-Borrego et al.,
1977). A recent estimate (Appendix II) indicates that phytoplankton contribute about 60% of the gross
primary production in the system (~ 38,380 tonnes C year-1). Moreover, plankton detritus seems likely
to be the dominant input of organic carbon from outside the system. Therefore, even though we do
not have data on the C, N and P composition of particulate material in Bahía San Quintín, for the
sake of this exercise we assumed that the C:N:P ratios of particulate material is similar to that of the
"Redfield molecule", i.e., molar ratios of 106:16:1 (Redfield, 1934).
It is also important to point out that Bahía San Quintín, particularly the western basin, called Bahía
Falsa (Figure 5), is an important site for aquacultural activities for oysters, clams, etc. (Appendix III).
The specific characteristics of organic loading and internal cycling may have an important
contribution to the overall ecosystem metabolism.
Sampling and Analyses
Surficial and near bottom water samples were collected at 30 stations in Bahía San Quintín (Figure
5) during August 1995, February 1996 and August 1996. Samples were filtered in the field through
0.45 µm glass fiber filters and stored frozen until analysis. Dissolved inorganic nutrient (NO -
3 + NO-2;
NH +
2-
4 ; HPO4 and SiO2) determinations were based on standard analytical procedures. Groundwater
nutrient concentrations in Table 2 represent an average of the water composition of 23 wells from the
San Simón Valley that were sampled during June 1995. Summer and winter evaporation and rainfall
data represent the daily average for the months of July and February of the last 10 years.
Table 2. Bahía San Quintín, freshwater inputs and composition.
V
NO -
(1)
3 + NO-2
DIP
(1000 m3 day-1)
(mmol m-3)
(mmol m-3)
Surface runoff (VQ)
0
-
-
(assumed)
Groundwater (VG)
0
-
-
(summer)
(assumed)
Groundwater (VG)
1
31
1.4
(winter)
Precipitation (VP)
4
0
0
(mean summer)
(assumed)
(assumed)
Precipitation (VP)
67
0
0
(mean winter)
(assumed)
(assumed)
Evaporation (VE)(2)
-164
0
0
(mean summer)
(assumed)
(assumed)
Evaporation (VE) (2)
-91
0
0
(mean winter)
(assumed)
(assumed)
Outfalls (VO)
0
0
0
(1) NH +
4 was below the detection limits
(2) Notice the minus sign for VE, as this flux represents an output from the system.
- 10 -

---

Water and Salt Budgets
From data in Table 2 we can calculate the water balance for each season from equation (5) (from
Gordon et al., 1996):
dV1/dt = VQ + VP + VG + VO + VE + VR
(5)
assuming steady state, i.e., dV1/dt = 0, then the residual volume (VR) is estimated
VR= -VQ - VP - VG - VO - VE
(6)
Substituting terms in equation (6) with data in Table 2 we obtain a VR of
VR = -(0) - (4) - (0) - (0) - (-164) = +160 x103 m3 day-1
for summer (1995 and 1996) and,
VR = -(0) - (67) - (1) - (0) - (-91) = +23 x103 m3 day-1
for winter.
Figure 6 shows the water and salt budget for the summer period.
VP = +4
VE = -164
VR =
+160
VRSR =
+5,475
VQ = 0
VSystem = 90,000
SOcean =
33.78 psu
SSystem = 34.66 psu
SR =
34.22 psu
= 14 days
VG = VO = 0
VX (SOcean - SSystem) = -5,475
(assumed)
VX = 6,222
Figure 6. Water and salt budgets for Bahía San Quintín, August 1995. System volume is in units of
103 m3 . Water fluxes in 103 m3 day-1. Salt fluxes in 103 psu m3 day-1.
- 11 -

---

Table 3 shows the chemical composition of Bahía San Quintín and the neighbouring ocean water.
The seawater end-member represents an average of the composition of surface and near bottom
samples collected at stations 1-5 (n=8; see Figure 5). The bay water concentration represents an
average of the samples collected within the bay (stations 6-30, n=43). All the bay samples had
salinities above 34.0 psu during the August 1995 campaign and all the marine samples, but one, had
salinities below this value. Figure 6 illustrates the combined water and salt budgets for August 1995.
Table 3. Chemical composition of Bahía San Quintín water samples collected in August 1995.
Standard deviations are shown in parenthesis.
Salinity
DIP
NO -
+
3 + NO-2
NH4
DIN
(psu)
(mmol m-3)
(mmol m-3)
(mmol m-3)
(mmol m-3)
Ocean
33.78
0.80
0.27
1.59
1.87
(0.20)
(0.35)
(0.14)
(2.60)
(2.61)
Bay
34.66
1.95
0.50
0.48
0.99
(0.46)
(0.39)
(0.50)
(0.48)
(0.80)
The salt balance is calculated from equation (7):
dV1S1/dt = VQSQ + VPSP + VGSG + VOSO + VESE + VRSR + VXS2 - VxS1
(7),
where VX represents the mixing or exchange volume between the ocean and Bahía San Quintín, SR
(34.22 psu) represents the salinity of the residual flow, which is an average of the salinities of the
ocean (S2) and the bay (S1). As the salinity of all of freshwater terms can be assumed as 0, then
equation (7) can be simplified to:
dV1S1/dt = + VRSR + VXS2 - VxS1 = + VRSR + VX(S2 -S1)
(8)
Assuming that S1 remains constant through time (i.e. assuming steady state)
0 = + VRSR + VX(S2 -S1)
(9)
we calculate the mixing volume (VX) from
VX = - VRSR / (S2 -S1)
(10)
substituting terms in equation (10) with salinity data in Table 3:
VX = -[(160 x 103)(34.22)]/[33.78-34.66] = -(5,475 x 103)/ (-0.88) = 6,222 x 103 m3 day-1
The exchange time () of water in Bahía San Quintín for August 1995 can be calculated from
equation (11), where |VR| is the absolute value of VR:
= Vsyst / (VX+|VR|)
(11)
where Vsys is the total volume of the system (90 x 106 m3).
= (90 x 106 m3)/ (6,222 x 103 + 160 x 103) = 14 days
The mixing volumes and exchange times for the February 1996 and August 1996 campaigns were:
February 1996: VX = 3,230 x 103 m3 day-1 and = 28 days
August 1996: VX = 5,536 x 103 m3 day-1 and = 16 days
- 12 -

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Budgets of Nonconservative Materials
The balance of nonconservative materials is calculated from equation (12):
dV1Y1/dt = VQYQ + VPYP + VGYG + VOYO + VEYE + VRYR + VXY2 - VxY1 + Y
(12)
where Y represents the net internal source or sink, that is, nonconservative flux, of element Y.
As groundwater is the only potentially important terrigenous source of Y in Bahía San Quintín (Table
2), equation (12) can be reduced to:
dV1Y1/dt = + VGYG + VRYR + VX(Y2 - Y1) + Y
(13)
Again assuming steady state, the general equation for calculating nonconservative fluxes of
dissolved materials (without gaseous phase) is:
Y = - VGYG - VRYR - VX(Y2 - Y1)
(14)
P Balance
The nonconservative flux of P, P, in Bahía San Quintín for the August 1995 campaign is calculated
from data in Tables 2 and 3 and illustrated in Figure 7:
P =-(0) - [(160 x 103)(1.38)] - [(6,222 x 103)(0.80-1.95)] = 6,934 x 103 mmol day-1 =+6,934 mol day-1
In order to establish comparisons with other systems, P can be reported as a rate by normalising by
the area of the system (42 x 106 m2), thus,
P = +0.17 mmol m-2 day-1
P values for the other campaigns were:
February 1996:
+586 mol day-1 (+0.01 mmol m-2 day-1)
August 1996:
+7,767 mol day-1 (+0.19 mmol m-2 day-1)
N Balance
Separate budgets may be calculated for the different nitrogen species analysed in this study (NO -
3 +
NO-
+
2 and NH4 ), however, we only show here the budget for the total dissolved inorganic nitrogen
(DIN) which is needed for looking at the stoichiometric linkages among nonconservative budgets and
for the estimation of N metabolism in the system.
The nonconservative flux of N, N, in Bahía San Quintín for the August 1995 campaign is calculated
from data in Tables 2 and 3 and Figure 6, and illustrated in Figure 7:
N =-(0) - [(160 x 103)(1.43)] - [(6,222 x 103)(1.87-0.99)] = -5,704 x 103 mmol day-1= -5,704 mol day-
1
The N normalised by the area of the system was,
N = -0.14 mmol m-2 day-1
N values for the other campaigns were:
February 1996: -21,906 mol day-1 (-0.52 mmol m-2 day-1)
August 1996:
+12,623 mol day-1 (+0.30 mmol m-2 day-1)
- 13 -

---

DIPatm = 0
(assumed)
DIPQ = 0 mmol m-3
VR DIPR = +221
VQ DIPQ = 0
DIP
DIPSystem = 1.95 mmol m-3
Ocean=0.80 mmol m-3
DIPR = 1.38 mmol m-3
DIP = +6,934
VX (DIPOcean -DIPSystem) = -7,155
VG DIPG = VQ DIPQ = 0
(assumed)
DINatm = 0
(assumed)
VR DINR = +229
DINQ = 0 mmol m-3
VQ DINQ = 0
DINSystem = 0.99 mmol m-3
DINOcean=1.87mmol m-3
DINR = 1.43 mmol m-3
DIN = -5,704
V
V
G DING = VQ DINQ = 0
X (DINOcean -DINSystem) = +5,475
(assumed)
Figure 7. DIP and DIN budgets for Bahía San Quintín, August 1995. Fluxes in mol day-1.
- 14 -

---

Stoichiometric Calculations of Aspects of Net System Metabolism
P values in Bahía San Quintín are positive both in summer and in winter. This observation indicates
that there is a net "production" of DIP within the system. If phosphate desorption from sediments
does not contribute significantly to P, then this DIP production probably results from organic matter
oxidation.
Based on the Redfield N:P molar ratio, if the positive P values in San Quintín are a measure of the
net organic matter oxidation in the system, the expected N value (Nexp) would be 16 P. For
August 1995:
Nexp = 16 x 6,934 mol day-1 = +110,944 mol day-1
There is a discrepancy of -116,647 mol day-1 between Nexp and the N calculated with the DIN
balance (Nobs). Assuming that N cycling in Bahía San Quintín is comparable to that of Tomales Bay,
where a relatively small proportion of the "missing" DIN can be accounted for by the DON balance
(Smith and Hollibaugh, 1993), then the difference between Nobs and Nexp represents the difference
between the nitrogen fixation and denitrification, i.e.,
(nfix-denit) = Nobs - Nexp
(15)
or
(nfix-denit) = Nobs - Px (N:P)part
(16)
The (nfix-denit) calculations for the three sampling dates:
August 1995: -116,647 mol day-1 (-2.8 mmol m-2 day-1)
February 1996: - 31,282 mol day-1 (-0.7 mmol m-2 day-1)
August 1996: -111,649 mol day-1 (-2.7 mmol m-2 day-1)
suggest that Bahía San Quintín is a coastal system where denitrification exceeds N fixation
throughout the year and is, therefore, an important sink of nitrogen.
The calculation of the net ecosystem metabolism, that is, the difference between organic carbon
production (p) and respiration (r) within the system (p-r) , is made through equation (17):
(p - r) = - P x (C:P)part
(17)
Based on the Redfield C:P ratio (106:1) the estimates of (p-r) for each campaign was:
August 1995: -735,004 mol day-1 (-17 mmol m-2 day-1)
February 1996: - 62,116 mol day-1 ( -1 mmol m-2 day-1)
August 1996: -823,302 mol day-1 (-20 mmol m-2 day-1)
These results indicate that Bahía San Quintín is a net heterotrophic system throughout the year, and
that the net metabolism during winter is approximately an order of magnitude lower than the
metabolism of the system during summer. Annual average (p-r) is about 10 mmol m-2 day-1, and p is
estimated to be about 200 mmol m-2 day-1 (Smith and Ibarra-Obando, Appendix II). It follows that r is
approximately 210 mmol m-2 day-1, and p/r is about 0.95. That is, the system consumes about 5%
more organic matter than it produces.
- 15 -

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2.1.3) Bahía San Luis Gonzaga, Baja California
F. Delgadillo-Hinojosa and J. A. Segovia Zavala
Study Area Description
Bahía San Luis Gonzaga is located in Baja California, Mexico (29 o 49' N and 114 o 23' W) (Figures 1
and 8). It is a small, rapidly exchanging bay covering an area of approximately 3 km2. It has a
permanently open mouth 1 km length and 10 m deep and the average depth is 4 m. The north end is
a rocky shore and sandy beaches predominate at the southern end. The system is macro-tidal with
semi-diurnal tides. Tidal amplitudes at the entrance range from about 1 m at neap tide to about 4.8 m
at spring tide. At high-water about 17.6 x 106 m3 of water are contained within the area, and the tidal
prism is in the order of 13 x 106 m3. Water exchange time based on the tidal prism/bay volume
ranges from an average of 2.6 days at neap tide to about 0.7 days at spring tides. Tide is the main
force driving water exchange with the adjacent Gulf of California. Although we do not have a great
deal of information on the biotic community composition, we assume that it is a plankton-dominated
system. Bahía San Luis Gonzaga has little macroalgal biomass for most of its length; there is a small
salt marsh at the southern end.
The bay is located in a region with two pronounced seasons: the summer condition, from May to
October with high temperatures and the winter season from November to April with low temperatures.
The temperature ranges from 5 to 45 o C in winter and summer, respectively. The rainfall is scarce
and the monthly average is less of 4 mm. Thus, the evaporation exceeds precipitation throughout the
year.
The budget presented here is based on data collected between May 1985 and February 1986
(Mendoza-Espinosa, 1994). Four complete tidal surveys were made covering at least a tidal cycle.
Water surface samples were collected at 2 stations located at the mouth (A) and inside (B) of the bay
(Figure 8). Each value used represents an average of 9 to 13 samples for each sampling period. In
particular, DIN represents NO -
-
+
3 + NO2 + NH4 . We assumed that a very small proportion of missing
DIN can be accounted for by the DON balance, that is DON = 0. Similarly, DOP was assumed
equal 0. Thus, with this general background, the fluxes of water, salt, phosphorus, and nitrogen can
be calculated using a simple box model following Gordon et al. (1996).
Figure 8. Map of Bahía San Luis Gonzaga, Baja California (also known as Bahía Willard). "A" and "B"
show locations of sampling stations
- 16 -

---

Water and Salt Budgets
Direct rainfall (VP) and groundwater discharge (VG) are small contributors to the water budget,
because Bahía San Luis Gonzaga is located in the desert of Baja California. The catchment has a
population of approximately 30 people in scattered places. There are no industries, agriculture and
no sewage treatment plants (VO) in the catchment with the total population using septic tanks. Thus,
VP = VG = VQ =VO = 0. On the other hand, evaporation (VE ) exceeds freshwater inputs. The water
lost is balanced by a net water input from the Gulf of California, that is VR = VE . The residual water
flow (VR) is into the bay year round. Figure 9 shows the summer data. The exchange flow (VX) was
calculated using the salinity gradients between the bay and the adjacent Gulf of California. This flow
was the main route of transport of nutrients in Bahía San Luis Gonzaga throughout year. Figure 9
illustrates the water and salt budgets for the summer sampling period; Tables 10-13 summarise the
data for each of the sampling periods. Note that the water exchange rate in this system is very fast,
with the exchange time ranging between 1 and 4 days. As expected, the net exchange is somewhat
smaller than the exchange volume calculated from the tidal prism, because tidal exchange is not
100% efficient in flushing the system.
VP = + 0
VE = - 19
VR =
+19
VRSR =
+692
VQ = 0
VSystem = 10,765
SOcean =
35.74 psu
SSystem = 35.89 psu
SR =
35.82 psu
= 2.4 days
VG = VO = 0
VX (SOcean - SSystem) = 669
(assumed)
VX = -4,466
Figure 9. Water and salt budgets for Bahía San Luis Gonzaga, Summer 1985. System volume is in
units of 103 m3 . Water fluxes in 103 m3 day-1. Salt fluxes in 103 psu m3 day-1.
- 17 -

---

Budgets of Nonconservative Materials
Figure 10 illustrates the P and N budgets for the summer sampling period, and Tables 10-13
summarise the data for all four sampling periods.
P Balance
During three of four sampling dates, DIP concentration was higher in the bay than in the open Gulf,
indicating there must be a DIP source within the bay. Winter sampling was an exception, with lower
values within the bay than the ocean, suggesting that the bay was a DIP sink. The positive DIP
values in the Spring - Fall period indicates that there was a net production of DIP within the system,
interpreted to be the result of net organic matter remineralization. We assume that the phosphate
desorption from sediments does not contribute significantly to DIP. During the winter the bay
consumed DIP, apparently due a phytoplankton bloom.
The positive DIP values in the spring through the fall period indicates that there was a net
regeneration of DIP within the system, interpreted to be the result of net organic matter
remineralization. We assume that the phosphate desorption from sediments does not contribute
significantly to DIP. During the winter Bahía San Luis Gonzaga also consumed phosphate,
apparently due a phytoplankton bloom.
N Balance
During warmer conditions, in spring and summer, DIN was higher in the bay than in the open Gulf,
indicating there must be a DIN source within the bay. In contrast, under colder conditions (fall and
winter) lower values were found within the bay relative those the ocean, suggesting that the bay was
a DIN sink.
Stoichiometric Calculations of Aspects of Net System Metabolism
If the positive DIP values in San Luis Gonzaga are a measure of the net organic matter oxidation in
the system, and based on the Redfield N:P ratio, then the expected DIN value (DINexp) would be
16 x DIP. On the other hand, the DIN calculated using the Water and Salt balance represent the
DIN observed (DINobs). Thus, the difference between DINexp and DINobs represents the
difference between nitrogen fixation and denitrification, that is:
(nfix - denit) = DINobs - DINexp\
(18)
or
(nfix - denit) = DINobs - DIP x ( N:P)part
(19)
The (nfix- denit) estimates for Bahía San Luis Gonzaga during the 1985/86 period is shown in Table
4.
Table 4. Estimated rates of nonconservative observed DIN fluxes and (nfix - denit) in Bahía San Luis
Gonzaga.
Season/year
DINobs
DINexp
(nfix - denit)
(mmol N m-2 day-1 ) (mmol N m-2 day-1 )
(mmol m-2 day-1)
Spring/85
+0.1
+5.2
-5.1
Summer/85
+1.0
+5.1
-4.1
Fall/85
-2.1
+3.6
-5.7
Winter/86
-4.6
-8.5
+3.9
These calculations indicate that the nonconservative flux of dissolved inorganic nitrogen (DINobs)
was lower than would be predicted from decomposition of organic matter with an N:P ratio of 16
(DINexp). If the decomposing organic matter with a N:P ratio of 16 is the main source of DIP, then
there must be an additional process taking DIN from the bay. This system was denitrifying more
nitrogen than it is fixing. However, under winter conditions Bahía San Luis Gonzaga appears to be a
net nitrogen fixing system. We suspect that the variation in (nfix-denit) in this system at least partially
- 18 -

---

DIPatm = 0
(assumed)
DIPQ = 0 mmol m-3
VR DIPR = + 21
VQ DIPQ = 0
DIP
DIPSystem =1.21 mmol m-3
Ocean=0.98 mmol m-3
DIPR = 1.10 mmol m-3
DIP = +1006
VX (DIPOcean -DIPSystem) = -1027
VG DIPG = VQ DIPQ = 0
(assumed)
reflects variability associated with short water exchange times, so that each sampling period
represents a relatively brief "snapshot" of system metabolism.
DINatm = 0
(assumed)
VR DINR = + 33
DINQ = 0 mmol m-3
VQ DINQ = 0
DINSystem = 2.07 mmol m-3
DINOcean=1.38 mmol m-3
DINR = 1.73 mmol m-3
DIN = +3049
V
V
G DING = VQ DINQ = 0
X (DINOcean -DINSystem) = -3082
(assumed)
Figure 10. DIP and DIN budgets for Bahía San Luis Gonzaga, Summer 1985. Fluxes in mol day-1.
- 19 -

---

The difference between organic carbon production (p) and respiration (r) within the system (NEM) is
calculated using:
(p-r) = - DIP x (C:P)part
where (C:P)part represents the composition of particles decomposing in the system. Taking the
particle composition as the Redfield ratio (C:N:P = 106:16:1), since Bahía San Luis Gonzaga is
plankton-dominated, the estimates of DIP and NEM for each season of the year were (Table 5):
Table 5. Estimated rates of nonconservative DIP fluxes and NEM in Bahía San Luis Gonzaga.
Season/year
DIP
NEM
(mmol m-2 day-1) (mmol C m-2 day-1)
Spring/85
+0.32
-34
Summer/85
+0.32
-34
Fall/85
+0.23
-24
Winter/86
-0.53
+56
That is, the bay appears to oxidise more organic matter than it produces. Simultaneously, Merino-Paredes
(1987) measured the primary production rates in SLG using the Light/Dark bottle method. Her gross primary
production rates (GPP) ranged between 127 mmol C m-2 day-1 in fall to 193 mmol C m-2 day-1 in winter (Table
6). From this independent primary production data set, r can be estimated to be 137 mmol C m-2 day-1 in
winter to 173 mmol C m-2 day-1 in summer. As expected, the lower r values were found under colder condition
and higher values warmer conditions. Those numbers compare favourably with the respiration rates
measured with the light and Dark bottle technique by Merino-Paredes (1987). The respiration rates measured
ranged from 283 mmol C m-2 day-1 in summer to 142 mmol C m-2 day-1 in winter (Table 6). These results
support the assumption we made that the phytoplankton is the main contributor to the total metabolism in
SLG. On the other hand, the p/r ratio was estimated to be about 0.8 during summer and fall periods (Table
6). That is, the bay consumes about 20% more organic matter than it produces. These results support the
conclusion that Bahía San Luis Gonzaga is a net heterotrophic system.
On the other hand, one may expect that lower NEM rates were found under colder conditions. However, the
lower (p-r) value was found in the fall, and a positive NEM value was calculated for the winter data (Table 5).
In this sampling period phytoplankton bloom was recorded. The phytoplankton biomass, measured as
chlorophyll a, within the bay was 3 times higher those found during the precedent sampling periods. There
was a remarkable similarity between the respiration measured and the respiration estimated using the
budgetary approach to net metabolism (Table 6). The measured respiration rate using the incubation method
was 142 mmol C m-2 day-1, and the respiration estimated from GPP - NEM was 137 mmol C m-2 day-1 (Table
6). Thus, if we use the gross photosynthetic rate measured during winter as 193 mmol C m-2 day-1, then the
estimated p/r ratio for this period is calculated to be about 1.4 (Table 6). Similarly, the p/r ratio measured
using the light-dark incubation method was 1.4. These result indicates that the phytoplankton dominates the
primary production in SLG. That is, both methods indicate that SLG bay produced more organic matter than it
consumed during the winter sampling. Thus, SLG Bay was a net autotrophic system under winter conditions.
Even though we had a very limited data set, we cannot tell if this represents average conditions for the winter
or an anomaly associated with the short-term bloom. However, it is important to note the remarkable
similarity between the results given by the incubation technique and the budgetary approach to net
metabolism in SLG. We think that these results are a strong support for the NEM budgetary approach in a
plankton-dominated bay as Bahía San Luis Gonzaga.
Table 6. Gross primary production (GPP), Respiration (r) and Photosynthesis/respiration ratio
measured and estimated in Bahía San Luis Gonzaga. The rest. was calculated as GPP -
NEM. The p:rest . ratio was calculated as GPP/rest.
Season/
GPP
r measured
r estimated
p:r measured
p:r est.
year
(mmol C m-2 day-1)
(mmol C m-2 day-1)
(mmol C m-2 day-1)
Summer/85
139.3
283.3
173.3
0.50
0.80
Fall/85
127.0
168.0
161.0
0.76
0.79
Winter/86
193.3
141.6
137.3
1.36
1.41
- 20 -

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2.1.4) Estero La Cruz, Sonora
M. Botello-Ruvalcaba and E. Valdez-Holguín
Study Area Description
La Cruz is a characteristic desert coastal lagoon from the north-west of Mexico. In lagoonal systems
within this region the evaporation is an order of magnitude higher than freshwater input from
precipitation. Also, groundwater is characterised by saline intrusion, and the circulation is mainly
determined by tide and wind induced forces (Botello-Ruvalcaba and Valdez-Holguín, 1990; Valdez-
Holguín, 1994). In addition, these systems represent the northern frontier for some mangrove species
such as Avicenia germinais and Rhizophora mangle in the American pacific coast (Castro-Longoria et
al., 1989)
La Cruz is located at 28° 45´ N and 111° 53´ W, in the central-oriental coast of the Gulf of California
(Figures 1 and 11). Following the Pritchard (1967) criteria for estuary classification, the lagoon can be
classified as an anti-estuarine system. The total lagoon area is 23 km2 with an average depth of 1.4
m and a semidiurnal tide type. The population living in the basis is approximately 10,000, with
fisheries and tourism as their main activity. In the coastal lagoon itself, there are several socio-
economic activities such as fisheries, oyster culture and salt extraction that represents an income for
the people living in the area. Nevertheless, considering the low intensity of the above activities, La
Cruz can be regards as a not heavy impacted system. Therefore it offers the opportunity to obtain a
general budgetary approach before the lagoon can be heavily impacted by projected developments.
The hydrographic and biological characteristics of the lagoon are mainly related with the tide and
seasonal condition of the adjacent sea. The temperature reaches up to 34° C during summer and
12° C in winter, values for dissolved oxygen are from 2.6 to 8.6 ml l-1, and chlorophyll a is in the
range of 0.06 to 7 mg m-3 (Botello-Ruvalcaba, 1992; Valdez-Holguín, 1994). Phytoplankton primary
productivity estimations within the lagoon are from 40 to 80 mg C m-3 h-1 and seems to dominate the
primary production within the system, although mangrove contribution to primary production is also
important (Gilmartin and Relevante, 1978; Castro-Longoria et al., 1989; Botello-Ruvalcaba, 1992;
Valdez-Holguín and Martínez-Cordova, 1993). We estimate that daily primary production may be
approximately 100 mmol C m-2 day-1
In order to establish budgetary calculations, data for salinity, dissolved N and P, and other physical
characteristics were available from various sources (Gilmartin and Relevante, 1978; Botello-
Ruvalcaba, 1992; and Valdez-Holguín and Martínez-Cordova, 1993). For these desert coastal
lagoons, there is a sudden transition between summer and winter conditions (Valdez-Holguín and
Martínez-Cordova, 1993; Botello-Ruvalcaba, 1996). Therefore, a weekly one year period time series
performed from 1988 to 1989 for two stations, inside the coastal lagoon and in the adjacent sea
(Figure 11), was split in data sets representing summer and winter.
Figure 11. Study area showing the two sampling sites, , for the hydrology monitoring program in La
Cruz lagoon during 1988-1989.
- 21 -

---

Water and Salt Budgets
Figure 12 summarises the water and salt budgets for the summer, and Tables 10-13 include both the
summer and winter data. La Cruz basin has problems with saline intrusion into the groundwater, so
groundwater input (VG) can be considered to be 0. River inflow (VQ) is also 0. Precipitation is highly
seasonal and very low. Finally, evaporation dominates the freshwater budget throughout the year,
resulting in high salinity values within the system, which can be up to 4 psu above that of the
adjacent sea. The water exchange time was 21 days in the summer and 43 days in the winter.
VP = + 15
VE = - 151
VR =
+136
VRSR =
+5,111
VQ = 0
VSystem = 32,000
SOcean =
35.75 psu
SSystem = 39.40 psu
SR =
37.58 psu
= 21 days
VG = VO = 0
(assumed)
VX (SOcean - SSystem) = -5,111
VX = + 1,400
Figure 12. Water and salt budgets for Estero La Cruz, Summer. System volume is in units of 103 m3.
Water fluxes in 103 m3 day-1. Salt fluxes in 103 psu m3 day-1.
- 22 -

---

Budgets of Nonconservative Materials
The DIP and DIN budgets for the summer period are shown in Figure 13, and Tables 10-13 include
both the summer and winter nutrient budgets.
P Balance
The system is a slight net phosphorus source during both the summer and winter (summer DIP =
+563 mol day-1; winter DIP = + 199 mol day-1; average = +381 mol day-1 = +0.02 mmol m-2 day-1),
with the summer flux being substantially higher than the winter flux.
N Balance
The system is a slight net nitrogen sink during the summer (DIN = -830 mol day-1) and a nitrogen
source during the winter (DIN = +3,382 mol day-1). The average, +1,276 mol day-1 or +0.06 mmol
m-2 day-1, clearly does not differ from 0.
Stoichiometric Calculations of Aspects of Net System Metabolism
The rates of nonconservative DIP and DIN flux can be used to estimate the apparent rate of nitrogen
fixation minus denitrification (nfix-denit) as the difference between observed and expected DIN
production (DINobs-DINexp), where DINexp is DIP multiplied by the N:P ratio of the reacting
particulate organic matter. We assume that this reaction ratio is the Redfield N:P ratio of 16:1, for
plankton. During the summer:
(nfix-denit) = DINobs-DINobs = DINobs ­ (N:P)part x DIP
(20)
(nfix-denit) = -830 ­ 16 x (+563) = -9,838 mol day-1 (-0.4 mmol m-2 day-1).
And in the winter:
(nfix-denit) = +3,382 ­ 16 x (+199) = +198 mol day-1 (+0.0 mmol m-2 day-1)
Thus, the system appears to denitrify in the summer and show (nfix-denit) near 0 in the winter.
Averaged over the area of the bay for the two seasons, the bay net denitrification rate is about 0.2
mol N m-2 day-1.
In a similar fashion, DIP multiplied by the negative of the C:P ratio of the reacting organic matter
can be used to estimate net ecosystem metabolism (NEM), or production minus respiration (p-r). The
reacting organic matter is assumed to have a C:P ratio equal to the Redfield C:P ratio of 106:1.
Averaged over the annual cycle, the rate is:
NEM = [p-r] = [C:P]part x DIP
(21)
NEM = -106 x 381 = -40,000 mol day-1 (-2 mmol m-2 day-1).
The system is slightly net heterotrophic. These data are also summarised in Tables 10-13.
If p is approximately 100 mmol m-2 day-1, then r would be about 102. The p/r ratio would be 0.98; the
system appears to consume about 2% more organic matter than it produces.
- 23 -

---

DIPatm = 0
(assumed)
VR DIPR = + 165
DIPQ = 0 mmol m-3
VQ DIPQ = 0
DIPSystem = 1.47 mmol m-
3
DIPOcean=0.95 mmol m-3
DIPR = 1.21 mmol m-3
DIP = +563
VX (DIPOcean -DIPSystem) = -728
VG DIPG = VQDIPQ = 0
(assumed)
DINatm = 0
(assumed)
V
DIN
R DINR = + 830
Q = 0 mmol m-3
VQ DINQ = 0
DINSystem = 6.1 mmol m-3
DINOcean=6.1 mmol m-3
DINR = 6.1 mmol m-3
DIN = -830
V
V
G DING = VQ DINQ = 0
X (DINOcean -DINSystem) = 0
(assumed)
Figure 13. DIP and DIN budgets for Estero La Cruz, Summer. Fluxes in mol day-1.
- 24 -

---

2.1.5) Bahía Concepción, Baja California Sur
C.H. Lechuga-Devéze
Study Area Description
Bahía Concepción (26o 30' N, 111o 30" W; Figures 1 and 14), the largest and deepest coastal
embayment in the Gulf of California (282 km2; 4,553 x 106 m3), has insignificant human influences
including scarce tourist facilities. Continental runoff is absent, although small hot springs are
dispersed along the shoreline. The fluxes of these springs have not been studied; we assume that
they are refluxing seawater.
Two parts to the annual cycle are well identified. In winter (November-March), the bay is vertically
well mixed. In summer, April-October, the central basin (33 m maximum depth) develops a strong
thermocline that isolates the water below 20 m. This leads to anoxia and hydrogen sulphide
production during August and September (Lechuga-Devéze et al., 1997; Reyes-Salinas, 1994).
During this dystrophic period, high amounts of pigment are present, mainly chlorophyll b (Lechuga-
Devéze, 1994). This indicates rapid metabolic cycling, perhaps chemoautotrophic.
The water, salt, N, and P budgets developed here are only for the well-mixed period; the data were
collected by our research group. It would also be useful to establish a separate set of budgets for the
stratified period, although the long water exchange time (below) suggests that the budgets for the
well-mixed period may characterise the annual average. For now, the annual summary budgets
(Tables 10-13) are based on the data from this single period.
Figure 14. Map of Bahía Concepción, Baja California Sur.
- 25 -

---

Water and Salt Budgets
There is no runoff and apparently no groundwater or other land-derived freshwater input; evaporation
totals about 217 x 103 m3 day-1, and precipitation totals about 65 x 103 m3 day-1. Oceanic salinity at
the entrance of the bay averages 35.3 psu, while the system salinity averages 35.9 psu. Since the
system is net evaporative, residual water flow totalling about 152 x 103 m3 day-1 is into the bay.
Figure 15 summarises the water and salt budgets. According to this budget, the water exchange time
is about 500 days.
VP = + 65
VE = - 217
VR =
+152
VRSR =
+5,411
VSystem = 4,553,000
VQ = 0
SSystem = 35.9 psu
SOcean =
35.3 psu
SR =
35.6 psu
= 497 days
VG = VO = 0
VX (SOcean - SSystem) = -5,411
(assumed)
VX = + 9,018
Figure 15. Water and salt budgets for Bahía Concepción, winter. System volume is in units of 103 m3.
Water fluxes in 103 m3 day-1. Salt fluxes in 103 psu m3 day-1.
- 26 -

---

Budgets of Nonconservative Materials
P Balance
Figure 16 illustrates the P and N budgets for this system The mixing outflow of DIP from this system
is substantially larger than the residual inflow and demonstrates that there must be DIP production
(DIP) of approximately +2,637 mol day-1 in the system. We assume that this represents
decomposition of organic matter. Because of the long water residence time, we assume that this
decomposition rate is averaged over a period longer than one year.
N Balance
Similarly, the system shows strong net export of DIN (+10,371 mol day-1; Figure 16). Again, this
outward mixing represents DIN production (DIN) and is assumed to represent decomposition of
organic matter.
Stoichiometric Calculations of Aspects of Net System Metabolism
The rates of DIP and DIN production can be used to estimate the apparent rate of nitrogen fixation
minus denitrification (nfix-denit) as the difference between observed and expected DIN production
(DINobs-DINexp), where DINexp is DIP multiplied by the N:P ratio of the reacting particulate
organic matter. We assume that this reaction ratio is the Redfield N:P ratio of 16:1, for plankton.
Thus:
(nfix-denit) = DINobs-DINobs = DINobs ­ (N:P)part x DIP
(22)
(nfix-denit) = +10,276 ­ 16 x (+2,637) = -31,916 mol day-1
Averaged over the area of the bay, (nfix-denit) equals -0.1 mmol N m-2 day-1. This system appears to
be denitrifying at a relatively slow rate, although the nonconservative flux signal for DIN integrated
over longer than a year is a strong signal.
In a similar fashion, DIP multiplied by the negative of the C:P ratio of the reacting organic matter
can be used to estimate net ecosystem metabolism (NEM), or production minus respiration (p-r). The
reacting organic matter is assumed to have a C:P ratio equal to the Redfield C:P ratio of 106:1:
NEM = [p-r] = [C:P]part x DIP
(23)
NEM = -106 x 2,637 = -279,522 mol day-1.
Over the bay area, NEM equals ­1 mmol m-2 day-1; that is, the system is slightly net heterotrophic.
These data are also summarised in Tables 10-13.
- 27 -

---

DIPatm = 0
(assumed)
VR DIPR = + 68
DIPQ = 0 mmol m-3
VQ DIPQ = 0
DIPSystem = 0.60 mmol m-3
DIPOcean=0.30 mmol m-3
DIPR = 0.45 mmol m-3
DIP = +2,637
VX (DIPOcean -DIPSystem) = -2,705
VG DIPG = VQ DIPQ = 0
(assumed)
DINatm = 0
(assumed)
VR DINR = + 96
DINQ = 0 mmol m-3
VQ DINQ = 0
DINSystem = 1.2 mmol m-3
DINOcean=0.05 mmol m-3
DIN = +10,275
DINR = 0.63 mmol m-3
V
V
G DING = VQ DINQ = 0
X (DINOcean -DINSystem) = -10,371
(assumed)
Figure 16. DIP and DIN budgets for Bahía Concepción, winter. Fluxes in mol day-1 .
- 28 -

---

2.1.6) Ensenada de La Paz, Baja California Sur
C.H. Lechuga-Devéze
Study Area Description
The Ensenada de La Paz (24° 14' N, 110° 29' W; Figures 1 and 17), is an anti-estuarine coastal
lagoon without freshwater inputs. There are no groundwater fluxes but saline intrusion towards
underground freshwater reserves. Sewage is treated and used to irrigate small agricultural fields.
About 150,000 people live adjacent to the main entrance of the lagoon in La Paz, but it is assumed
that no sewage effluent flows directly into the lagoon. The total lagoon area is around 45 km2
(Lechuga-Devéze et al., 1986) with a depth of about 3 m and a total volume of 145 x 106 m3
(Gilmartin and Revelante, 1978).
The climate is arid, with summer showers averaging 1.15 mm day-1 and highest evaporation
averaging 5.71 mm day-1 (average for July to September). In the spring, the scarce rain averages
0.04 mm day-1, and evaporation averages about 3.56 mm day-1 (average for March to May).
During the 1970's, the natural shellfish banks (Argopecten circularis) inside the lagoon disappeared,
and to-date no new populations have developed. Primary production of the system is about 1.2 g C
m-2 day-1 (Lechuga-Devéze et al., 1986), that is, about 100 mmol m-2 day-1. Some data have shown
that the adjacent waters of the Bahía de La Paz are the main source of nitrate, phosphate and silicate
for the lagoon (Lechuga-Devéze et al., 1986; Cervantes-Duarte, 1981), meaning that the lagoon does
not support enough oxidative process to provide the inorganic nutrients for primary production.
Salinity, nitrate and phosphate data gathered by our research group (Morquecho-Escamilla and
Murillo-Murillo, 1995; Lechuga-Devéze et al., 1990) were used for the budgetary calculations to
compare the summer to spring condition, representing the wet and dry season for the system.
Figure 17. Map of Ensenada de La Paz, Baja California Sur.
- 29 -

---

Water and Salt Budgets
Figure 18 illustrates the water and salt budgets for this system for the spring, and Tables 10-13
summarise the data for both the spring and summer. The water exchange time for this system
appears to be about a month.
VP = + 2
VE = - 160
VR =
+158
VRSR =
+5,641
VQ = 0
VSystem = 145,000
SOcean =
35.0 psu
SSystem = 36.4 psu
SR =
35.7 psu
= 35 days
VG = VO = 0
VX (SOcean - SSystem) = -5,641
(assumed)
VX = + 4029
Figure 18. Water and salt budgets for Ensenada de La Paz, spring. System volume is in units of
103 m3. Water fluxes in 103 m3 day-1. Salt fluxes in 103 psu m3 day-1.
- 30 -

---

Budgets of Nonconservative Materials
P Balance
Figure 19 illustrates the P and N budgets for the spring, and Tables 10-13 summarise the data for
both spring and summer. With particular respect to DIP, there appears to be substantial variation;
DIP uptake occurs and is higher during the summer than the spring. The average DIP of the two
sampling periods is ­1,914 mol day-1. Thus the system appears to be a net sink for DIP, mostly
derived from the ocean.
N Balance
The bay appears to be a net DIN source during the spring and about neutral with respect to DIN
during the summer. The average DIN of the two sampling periods is +2,706 mol day-1.
Stoichiometric Calculations of Aspects of Net System Metabolism
Nitrogen fixation minus denitrification (nfix-denit) is calculated from the difference between observed
and expected DIN, where the expected DIN is calculated as 16 x DIP. It is assumed that the
major sink for DIP is plankton. Table 7 illustrates these calculations for Ensenada de La Paz. The
system appears to fix nitrogen in excess of denitrification, by a rate averaging about 0.8 mmol m-2
day-1.
Table 7. Estimated rates of nonconservative observed DIN fluxes and (nfix - denit) in Ensenada de
La Paz.
Season
DINobs
DINexp
(nfix ­ denit)
(mmol N m-2 day-1 ) (mmol N m-2 day-1 )
(mmol m-2 day-1)
Spring
+0.11
-0.32
+0.4
Summer
-0.01
+1.10
+1.1
The difference between organic carbon production, p, and respiration, r, within the system (NEM) is
calculated using:
(p-r) = - P x ( C:P)part
(23)
where (C:P)part represents the composition of particles reacting in the system. Taking the particle
composition as the Redfield ratio (C:N:P = 106:16:1), since Ensenada de La Paz is assumed to be a
plankton-dominated system, the estimates of P and NEM are shown in Table 8:
Table 8. Estimated rates of nonconservative DIP fluxes and NEM in Ensenada de La Paz.
Season
P
NEM
(mmol m-2 day-1)
(mmol C m-2 day-1)
Spring
-0.02
+2
Summer
-0.07
+7
This system appears to be net autotrophic by approximately 5 mmol m-2 day-1.
Primary production has been estimated to be about 100 mmol m-2 day-1, implying that respiration is
about 95 and that the p/r ratio is about 1.05. This system appears to produce about 5% more organic
carbon that it consumes.
- 31 -

---

DIPatm = 0
(assumed)
V
DIPQ = 0 mmol m-3
R DIPR = + 123
VQ DIPQ = 0
DIPSystem = 0.68 mmol m-3
DIPOcean=0.87 mmol m-3
DIP = -889
DIPR = 0.78 mmol m-3
VX (DIPOcean -DIPSystem) = +766
VG DIPG = VQ DIPQ = 0
(assumed)
DINatm = 0
(assumed)
VR DINR = + 205
DINQ = 0 mmol m-3
VQ DINQ = 0
DINSystem =1.95 mmol m-3
DINOcean=0.64 mmol m-3
DIN = +5,073
DINR = 1.30 mmol m-3
V
V
G DING = VQ DINQ = 0
X (DINOcean -DINSystem) = -5,278
(assumed)
Figure 19. DIP and DIN budgets for Ensenada de La Paz, spring. Fluxes in mol day-1.
- 32 -

---

2.2 Humid Pacific Coast
2.2.1) Bahía de Altata-Ensenada del Pabellón, Sonora
F.J. Flores-Verdugo and G. de la Lanza-Espino
Study Area Description
This site lies in Region B (as modified from Lankford, 1977; see Appendix I of this report). Within the
organisation of this report, it is included the site among systems of the "humid Pacific Coast,"
because, unlike the previously discussed systems, rainfall plus runoff clearly exceeds evaporation.
An important aspect of this system, again in contrast to the previously cited arid coast systems, this
site includes the clear influence of agricultural activities on inflowing water composition.
Agricultural development around coastal lagoons is increasing without enough consideration of the
environmental implications with respect to biodiversity and other aspects of ecological change. River
diversions by dams and the artificial channelisation for the agricultural development increase
problems of siltation inside the lagoons, erosion in the sand barriers and eutrophication and
pesticides from agriculture waste waters toward drainage channels as non-point pollution sources.
The estuarine complex of Bahía de Altata-Ensenada del Pabellón lies near 107° 38' N and 24° 25' W
(Figures 1 and 20). Bahía de Altata is a long, narrow lagoon running parallel to the coast, with sandy
sediments, mean water depth of 5 meters with mainly marine conditions (32 psu). Ensenada del
Pabellón is joined to this bay and is wider than Altata, with silt and clay sediments and a mean depth
of 1 m and display mainly estuarine conditions wit salinities between 10 to 28 psu. The annual mean
salinity for the whole system is approximately 28 psu. The adjacent marine water averages 35 psu.
Water temperature varies from 20° C in January to 32° C in August. The area of the complex is
approximately 460 km2, including 100 km2 of mangrove swamps. The Culiacan River discharge to
the lagoon has a mean annual flow of (VQ) about 3,400 x 106 m3.
The depth of the system varies from less than 25 cm in the mangroves to 15 meters in La Tonina
inlet. We estimate a mean depth of 3 meters for the whole system, giving a total volume of
approximately 1,400 x 106 m3. The system is separated from the sea by a narrow sand barrier
interrupted with two inlets: a small and relatively recent one (called La Palmita) and the main one (La
Tonina). The estuarine complex is located in the valley of Culiacan and received the agriculture
discharges of the district by several drainage channels. This district comprises more than 2,700 km2
of irrigated agricultural lands used mainly for horticultural production. The production of this district
comprises one third of the total national horticultural export. Also three sugar cane industries and a
paper mill discharges their waste into ponds connected to the system. Several authors have reported
the presence of pesticides and heavy metals in the lagoon. Relatively recent the system is receiving
a new impact from the waste waters of shrimp farms. The lagoon sustains an important fishing
activity of shrimp (Penaeus spp), oyster (Crassostrea corteziensis), clam (Chione subrugosa) and
fish such as snappers, mullets, etc. The borders of the lagoon and interior islands are covered by
mangroves (Rhizophora mangle, Laguncularia racemosa and Avicennia germinans). The latter is the
dominant mangrove species with 86% of the total density (from 4,800 to 7,600 trees ha-1). Landward
of the mangroves predominates a belt of seasonal floodplains with high salinity soils with no
vegetation at all or with patches of the terrestrial halophytes (saltworts) Salicornia spp and Batis sp.
locally known as "marismas". There is a special place where an extensive (100 km2) freshwater
marsh of cattail (Thypha spp) occurs (Chiricahueto) located in the SE of Pabellón and where several
hundreds thousands ducks from Canada and the United States of America arrive during the winter.
This freshwater swamp has increased in area as consequences of the agricultural waste waters
displacing what use to be a seasonal flood plain The mean annual rainfall of the region is 670 mm
and the mean annual evapotranspiration is 1,500 mm.
Concentrations of DIP vary in Pabellón from 3.1 (August) to 13 mmol m-3 (April) and in Altata from
2.5 to 5.8 mmol m3. We estimate a mean annual values for the whole system of 7.2 mmol m-3. In the
adjacent ocean a mean value of 0.6 mmol m-3 can be observed and in the Culiacan river a mean
value of 7.5. For DIN (nitrate + nitrite + ammonia) the values vary in Pabellón from 4.4 (February) to
6.3 mmol m-3 (August) and in Altata from 0.6 (February) to 0.8 (August). A DIN mean annual value of
3.7 mmol m-3 was estimated for the entire system, 0.6 for the ocean, 40 in the river. Nutrients are
always lower in Altata compared to Pabellón as consequences of a higher oceanic water influences in
Altata. In Ensenada del Pabellón there is more freshwater influence, mainly from the agricultural
drainage.
- 33 -

---

Nutrients cycling from the sediments to the water were estimated to be as high as 0.6 mmol m-2 day-1
for ammonium and of 0.05 mmol m-2 day-1 for phosphate. In lagoon sediments influenced by sugar
cane waste water values as high as 16 mmol m-2 day-1 for ammonium and 2,2 mmol m-2 day-1 for
phosphate were detected, demonstrating that eutrophication is a clear problem in some parts of this
system.
Plankton net annual productivity (p) was estimated to be of 267 g C m-3 year-1, equivalent to about 70
mol C m-2 year-1 The water column has a p/r ratio of 2.0 describing this part of the system as
autotrophic in general.
Figure 20. Map of Bahía de Altata-Ensenada del Pabellón.
- 34 -

---

Water and Salt Budgets
Figure 21 summarises the water and salt budgets for this system. Runoff (VQ) + precipitation (VP)
substantially exceed evaporation (VE), and groundwater input (VG) is assumed to be zero. In order to
balance the water budget, residual flow removes water and salt from the system (VR = -3,000 x 106
m3 year-1; VRSR = -94,500 x 106 psu m3 year-1). In order to maintain a steady state salinity (that is
VsystemdSsystem/dt = 0), salt must mix into the system (VX[Socean-Ssystem] = +94,500 x 106 psu m3 year-1).
Socean and Ssystem are known, so we can solve for mixing (VX = 13,500 x 106 m3 year-1). The volume of
the system is 1,400 x 106 m3, so water exchange time can be calculated as = Vsystem/(|VR| + VX) =
0.08 year. That is, the water exchange time is about 1 month.
VP = +300
VE = - 700
VR =
-3,000
VRSR =
-94,500
VQ = 3,400
VSystem = 1,400
SOcean =
35.0 psu
SSystem = 28 psu
SR =
31.5 psu
= 0.08 years
VG = VO = 0
VX (SOcean -SSystem) = +94,500
(assumed)
VX = + 13,500
Figure 21. Water and salt budgets for Bahía Altata-Ensenada del Pabellón, annual average. System
volume in 106 m3. Water fluxes in 106 m3 year-1. Salt fluxes in 106 psu m3 year-1.
- 35 -

---

Budgets of Nonconservative Materials
Figure 22 summarises the DIP and DIN budgets for the system.
P Balance
Concentration and flux of DIP in river water flowing into this system are high, apparently reflecting
the product of agricultural drainage into the system. System concentrations are also very high, and
outward transport of DIP occurs via both residual flow and mixing. These outward fluxes greatly
exceed the estimated river inflow of DIP, so there apparently is an internal source of DIP (DIP =
+75 x 106 mol year-1 = +0.19 mol m-2 year-1). We have observed that there is very high release of
DIP, especially from the sediments associated with sugar cane wastes, so this and other organic
discharges into the system are assumed to support the high nonconservative flux of DIP.
N Balance
Concentration and flux of DIN in river water are also high. While there is export of DIN both in the
residual flow and in the mixing, this outward flux is substantially lower than the river DIN import.
There must therefore be a substantial sink of DIN in this system (DIN = -118 x 106 mol year-1 = -
0.46 mol m-2 year-1). There is thus a clear discrepancy between the nonconservative fluxes of DIP
and DIN.
Stoichiometric Calculations of Aspects of Net System Metabolism
Net nitrogen fixation minus denitrification in this system (nfix-denit) is calculated as the difference
between observed and expected DIN. Expected DIN is DIP multiplied by the N:P ratio of the
reacting particulate organic matter. We do not know that N:P ratio. If this material were plankton, the
expected ratio would be near the Redfield Ratio of 16:1. Waste from sugar cane or other terrestrial
plant material might have a higher ratio, while animal wastes might be somewhat lower. Lacking a
definitive value, we assume that the appropriate N:P ratio of decomposing organic matter is near the
Redfield Ratio, and therefore that the expected value for DIN is 16 x (75 x 106) mol year-1. Thus:
(nfix-denit) = -118 x 106 - 16 x (75 x 106) mol year-1 = -1,082 x 106 mol year--1
(-2.4 mol N m-2 year-1 over the area of the system).
Thus, the system appears to be denitrifying at a substantial rate.
We can also estimate net ecosystem metabolism (NEM), that is the difference between primary
production and respiration (p-r), as the negative of the nonconservative DIP flux multiplied by the
C:P ratio of the reacting material. Again, we do not know the C:P ratio of the reacting material, but it
seems likely to equal or exceed the C:P ratio of plankton. Thus:
(p-r) = -106 x (75 x 106 mol year-1) = -7,950 x 106 mol C year-1
(-17 mol m-2 year-1 over the system area).
This is a substantial rate of net respiration, especially when compared with the estimated of primary
production (17 mol C m-2 year-1). Moreover, if the reacting material is terrigenous plant organic
matter, the likely rate of (p-r) may well exceed what is estimated here. Nevertheless, we believe that
these numbers make sense in view of the discharge of sugar cane and other agricultural waste
products into this system.
- 36 -

---

DIPatm = 0
(assumed)
DIPQ =7.5 mmol m-3
VR DIPR = -12
VQ DIPQ = +26
DIPSystem = 7.2 mmol m-3
DIPOcean=0.6 mmol m-3
DIP = +75
DIPR = 3.9 mmol m-3
VX (DIPOcean -DIPSystem) = -89
VG DIPG = VQ DIPQ = 0
(assumed)
DINatm = 0
(assumed)
VR DINR = -7
DINQ = 49 mmol m-3
VQ DINQ = +167
DINSystem = 3.7 mmol m-3
DINOcean=0.6 mmol m-3
DIN = -118
DINR = 2.2 mmol m-3
V
V
G DING = VQ DINQ = 0
X (DINOcean -DINSystem) = -42
(assumed)
Figure 22. DIP and DIN budgets for Bahía Altata-Ensenada del Pabellón, annual average. Fluxes in
106 mol year-1.
- 37 -

---

2.2.2) Teacapan-Agua Brava- Marismas Nacionales, Sinaloa and Nayarit
G. de la Lanza-Espino, F. J. Flores-Verdugo and F. Wulff
Study Area Description
Figures 1 and 23 illustrate the location and principal features of the mangrove-estuarine complex of
Teacapan-Agua Brava-Marismas Nacionales (22° 08' N, 105° 32' W). A brief historical and natural
history perspective is presented in the next paragraphs.
The region of Teacapan-Agua Brava-Marismas Nacionales has an ancient story for human
settlements. There are evidences of considerable human populations over more than 1,500 years, in
the forms of small hills of shells (Tivela sp.). Near the town of Mexcaltitan a tribal group migrated to
the upper lands and founded the city of Tenochtitlan (now Mexico city), the capital of the Aztec
empire. When the Spaniards arrived in the region in the 16th century, they estimated a population of
more than 300,000 inhabitants; this can be considered extremely high for rural standards of those
days. This high population density was sustained by the fertility of the land in the alluvial plain but
also to the richness of seafood as oyster, shrimp and fishes. The region has been a used by several
generations for multiple uses. Mangroves where mainly used for fuel and rustic construction, during
the colonial age, an important industry of tannins for cow hide treatment was developed until the 19th
century. The region was an important hunting ground up to the 1950's for jaguar and crocodile. In the
winter, more than the 20% of the total migratory birds of the Pacific arrive enroute from Alaska,
Canada and the United States. It is also possible to find areas with subhumid tropical forest and low
human impact between the mangroves on some islands. The region indirectly supports one of the
most important shark fishery in Mexico in the adjacent marine waters. Shrimp fishing is an important
economical activity and recently shrimp farming is developing. In the beginning of the 1970's an
artificial inlet was opened (Cuautla Channel) with the idea to allow the shrimp post-larvae get inside
the Agua Brava lagoon more directly, but the channel widened uncontrollably from 40 m wide 3 m
depth, as was planned, to more than 1,200 m wide and 18 m depth. The drastic change in the
hydrological pattern killed more than 50 km2 of mangroves. The aquaculture development without
planning with an environmental sound management, the river dam construction programs together
with the agricultural activities and the opening of artificial inlets, will put at risk the basic structural
functions of the ecosystem and this actual and potential resources as important cultural values.
The area comprises approximately 2,000 km2 of tidal channels, seasonal flood plains, more than 150
semi-parallel coastal lagoons formed by stranded beach ridges, big estuarine water bodies and
mangrove swamps. The mangroves, small tidal channels and the semi-parallel coastal lagoons
occupies approximately 1,100 km2. The waterways occupy 500 km2 (total area of the mangrove-
estuarine complex 1,600 km2). Water depths of the waterways vary from below 1 m to 18 m near the
inlets, with a mean depth of 2 m. The mangrove water depth varies according to the species, being
0.40 m above mean sea level for the dominant species, the white mangrove (Laguncularia
racemosa) and 0.7 m for the black mangrove (Avicenia germinans) we assume that during the
flooding periods (flows) a mean value of 0.5 m is reasonable. Obviously 0.0 m depth is assumed
during low ebb tides. A mean value (flows and ebbs) of 0.25 m is considered here to be appropriate.
The total volume (V1) of the mangrove-estuarine complex comprises 1,266 x 106 m3.
There are 5 stream flows that discharge to the system: The Cañas, Rosamorada, Bejuco, Acaponeta
and San Pedro rivers. But only the last two have flow all year around, with an annual flow of 3,000 x
106 m3 year-1 for the Acaponeta and 2,456 x 106 m3 year-1 for the San Pedro river. The other rivers
are seasonal with flows below 180 x 106 m3 year-1. Precipitation is estimated to be about 1,459 mm
year-1 and evapotranspiration of 1,991 mm year-1 (mean annual values of more than 10 years). Data
on groundwater flow and non-point agriculture waste-waters that discharge to the system are not
available.
- 38 -

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Figure 23. Teacapan-Agua Brava- Marismas Nacionales lagoon system.
Salinity: Salinities of freshwater from rivers and rainfall was assumed to be 0 psu, estuarine annual
average salinity is about 20 psu, and adjacent coastal marine water (Pacific ocean) averages 34 psu.
Nutrients and other non conservative components: Data are available for DIP, DIN (nitrate, nitrite and
ammonia) in this system Table 10. The freshwater nutrient concentration data have been weighted
according to the relative flow rates of the two major rivers.
Other: Mangrove litter-fall in three sites averages about 1,200 g m-2 year-1. If 40% of this material is
considered carbon it is equivalent to approximately 40 mol C m-2 year-1. Leaf degradation rate varied
from about 2 in the soil to 5 year-1 in the water. Humid substances (DOC) can be greater than 100 mg
l -1 with a mean value of 30 mg l -1. Mean daily net plankton productivity in the Agua Brava lagoon is
estimated to be of 0.4 g C m-2 d -1 equivalent to 12.5 mol C m-2 year -1. In general the respiration rate
in the water column is higher than the productivity so the water column is heterotrophic for most of
the year (Gross Productivity/24 hour Respiration = 0.64), a reflection of the influence of high organic
matter from rivers and mainly the adjacent mangroves swamps.
From these data we present the budgetary analysis as follows:
Table 9. Average nutrient concentration (mmol m-3) for components of the Teacapan-Agua Brava-
Marismas Nacionales mangrove-estuarine complex.
Seawater
System
Freshwater
(Y2)
(Y1)
(YQ)
DIP
0.5
0.7
32
DIN
2.5
4.0
93
- 39 -

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Water and Salt Budgets
Figure 24 illustrates the average annual water and salt budgets for Teacapan-Agua Brava-Marismas
Nacionales. Freshwater flow (VQ ) is estimated by adding the flows of the Acaponeta and San Pedro
rivers (5,456 x 106 m3 year-1). Direct precipitation (Vp) and Evaporation (VE) are estimated as 2,412 x
106 m3 year-1 and 3,223 x 106 m3 year-1, respectively, considering the area of the complex (1,619 x
106 m2 ). The other components (VG and Vo) are assumed to be small. The system shows substantial
net residual outflow of water, as expected from the freshwater inputs to the system. It can be seen
from these calculations that the water exchange time in this system is about a month.
VP = + 2,400
VE = - 3,200
VR =
-4,400
VRSR = -118,800
VQ = 5,500
VSystem = 1,266
SOcean =
34 psu
SSystem = 20 psu
SR =
27 psu
= 0.10 years
VG = VO = 0
VX (SOcean - SSystem) = +118,800
(assumed)
VX = + 8,486
Figure 24. Water and salt budgets for Teacapan-Agua Brava-Marismas Nacionales, annual average.
System volume is in units of 106 m3. Water fluxes in 106 m3 year-1. Salt fluxes in 106 psu
m3 year-1.
- 40 -

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Budgets of Nonconservative Materials
Figure 25 illustrates the DIP and DIN budgets for these systems. The data are also listed in Tables
10-13.
P Balance
Substantial DIP comes in from terrigenous runoff into this system, but very little P exchanges with
the ocean with either residual flow or exchange flow. Clearly the system takes up most of the DIP
delivered to it. The system is a sink for virtually all of the land derived DIP (Figure 25). Thus, DIP =
-170 x 106 mol year-1 = -0.11 mol m-2 year-1 over the mangrove-estuary area.
N Balance
Similarly to DIP, DIN comes in from land and is mostly trapped in the system (Figure 25). Thus, DIN
= -452 x 106 mol year-1 = -0.28 mol m-2 year-1 over the mangrove-estuary area.
Stoichiometric Calculation of Aspects of Net System Metabolism
We can calculate net nitrogen fixation minus denitrification (nfix-denit) as the difference between
observed and expected DIN. Expected DIN is DIP multiplied by the N:P ratio of the reacting
particulate organic matter. In a mangrove-dominated system, it is not entirely obvious what the
dominating reactive organic matter is, so we use two N:P values. First, we employ the Redfield N:P
ratio of plankton (16:1). Then we use a reactant which has an N:P ratio of 30:1, more typical of
various land plants. Thus, with plankton:
(nfix-denit) = -452 x 106 ­ 16 x (-170 x 106) = +2,268 x 106 mol N year-1
(+1.4 mol N m-2 year-1 over the estuary-mangrove area).
With land plants:
(nfix-denit) = -452 x 106 ­ 30 x (-170 x 106) = +46,448 x 106 mol N year-1
(+2.9 mol N m-2 year-1 over the estuary-mangrove area).
Note that, with either material, the system appears likely to be fixing nitrogen in excess of
denitrification.
Similarly, we can estimate net ecosystem metabolism (NEM = p-r) as the negative of the
nonconservative DIP flux multiplied by the C:P ratio of the reacting organic matter. If the net reacting
material is plankton, the particulate C:P ratio is about 106:1. If it is mangrove litter, then the ratio may
be as high as 1000:1. With plankton:
(p-r) = -106 x (-170 x 106) = +18,020 x 106 mol C year-1
(+11 mol C m-2 year-1).
With mangroves dominating the net production:
(p-r) = -1,000 x (-170 x 106) = +170,000 x 106 mol C year-1
(+106 mol C m-2 year-1).
This latter figure is about double the rate of mangrove litter production, and that production should
approach an upper limit of net primary production. We therefore suggest that the lower figure more
accurately reflects the likely rate of net ecosystem production. In either case, if the DIP uptake
primarily represents net organic metabolism, rather than inorganic sorption or precipitation of P, this
system is strongly net autotrophic.
We assume that the lower value more accurately reflects (p-r). Primary production was estimated
above to be about 30 mol C m-2 year-1, implying that respiration is approximately 30. These numbers
suggest that the p/r ratio of the system is about 1.3.
- 41 -

---

DIPatm = 0
(assumed)
V
DIPQ = 32 mmol m-3
R DIPR = -3
VQ DIPQ = +175
DIPSystem = 0.7 mmol m-3
DIPOcean= 0.5 mmol m-3
DIP = -170
DIPR =
0.6 mmol m-3
VX (DIPOcean -DIPSystem) = -2
VG DIPG = VQ DIPQ = 0
(assumed)
DINatm = 0
(assumed)
VR DINR = -15
DINQ = 93 mmol m-3
VQ DINQ = 480
DINSystem = 4.0 mmol m-3
DINOcean=2.5 mmol m-3
DINR = 3.3 mmol m-3
DIN = -452
V
V
G DING = VQ DINQ = 0
X (DINOcean -DINSystem) = -13
(assumed)
Figure 25. DIP and DIN budgets for Teacapan-Agua Brava-Marismas Nacionales, annual average.
Fluxes in 106 mol year-1.
- 42 -

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2.2.3) Carretas-Pereyra, Chiapas
F. Contreras-Espinosa
System Description
The Carretas - Pereyra coastal system (15° 27' N, 93° 10' W; Figures 1and 26), is formed by 4 small
lagoons (Pereyra, Carretas, Bobo and Buenavista). Total size of system is about 35 km2. The depth
is about 1.5 m, so the volume is estimated to be 53 x 106 m3. Rainfall is about 2.3 m year-1, and
evaporation is about 0.8 m year-1. Runoff totals about 240 x 106 m3 year-1. The system has a rates of
primary production that measured as ranging from 288 to 764 mg C m-3 hour-1 (Contreras, 1993).
Ecological conditions are similar to Chantuto system (Section 2.2.4), because the two systems are
close to one another (seasonal variations by wet and dry seasons with strong influences over
productivity and fisheries; mangrove vegetation is dominant). Both systems are within "La
Encrucijada" Biosphere Reserve. Social and economic consideration from Chantuto are same for this
system. Shrimp fisheries is the principal economic activity and the problem of excessive
sedimentation is similar to Chantuto.
Figure 26. Map of the Carretas-Pereyra System.
- 43 -

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Water and Salt Budgets
Figure 27 summarises the water and salt budgets for this system. Runoff into this system is about
230 x 106 m3 year-1; rainfall is about 80 x 106 m3 year-1; and evaporation is about 20 x 106 m3 year-1.
Therefore residual flow out of this system totals about 300 x 106 m3 year-1. We assume that
freshwater inflow has a salinity of 0 psu. Oceanic salinity adjacent to the lagoon is estimated to have
a salinity of about 21.6 psu, and the average lagoon salinity is about 10.8 psu. With these figures a
water exchange time of about 0.07 years (~ 26 days) is calculated.
VP = + 79
VE = - 24
VR =
-297
VRSR =
-4,682
VQ = +234
VSystem = 53
SOcean =
21.6 psu
SSystem = 10.8 psu
SR =
16.2 psu
= 0.07 years
VG = VO = 0
VX (SOcean - SSystem) = +4,682
(assumed)
VX = + +434
Figure 27. Water and salt budgets for Carretas-Pereyra, annual average. System volume is in units
of 106 m3 . Water fluxes in 106 m3 year-1. Salt fluxes in 106 psu m3 year-1.
- 44 -

---

Budgets of Nonconservative Materials
Figure 28 summarises the DIP and DIN budgets for this system.
P Balance
DIP concentration in the Carretas-Pereyra lagoonal complex is relatively high and riverine input is
low. As a result, the calculations indicate that DIP is positive (+3 x 106 mol year-1). This is
equivalent to a flux of 0.09 mol m-2 year-1.
N Balance
Similarly, there is a positive nonconservative flux of DIN within this system (DIN = 3 x 106 mol year-
1; 0.09 mmol m-2 year-1).
Stoichiometric Calculations of Aspects of Net System Metabolism
Net nitrogen fixation minus denitrification (nfix-denit) is calculated as the difference between
observed and expected DIN. Expected DIN is DIP multiplied by the N:P ratio of the reacting
particulate organic matter. In a mangrove-dominated system, it is not entirely obvious what the
dominating reactive organic matter is, so we use two N:P values. First, we employ the Redfield N:P
ratio of plankton (16:1). Then we use a reactant which has an N:P ratio of 30:1, more typical of
various land plants. Thus, with plankton:
(nfix-denit) = +3 x 106 ­ 16 x (+3 x 106) = -45 x 106 mol N year-1
(-1.2 mol N m-2 year-1 over the estuary area).
With land plants:
(nfix-denit) = +3 x 106 ­ 30 x (3 x 106 ) = -87 x 106 mol N year-1
(-2.5 mol N m-2 year-1 over the estuary area).
Note that, with either material, the system appears likely to be a net denitrification system.
Similarly, we can estimate net ecosystem metabolism (NEM = p-r) as the negative of the
nonconservative DIP flux multiplied by the C:P ratio of the reacting organic matter. If the net reacting
material is plankton, the particulate C:P ratio is about 106:1. If it is mangrove litter, then the ratio may
be as high as 1000:1. With plankton:
(p-r) = -106 x (+3 x 106 ) = -318 x 106 mol C year-1
(-9 mol C m-2 year-1)
With mangroves dominating the net metabolism:
(p-r) = -1,000 x (+3 x 106) = +3,000 x 106 mol C year-1
(+86 mol C m-2 year-1).
This latter figure is about double the likely rate of mangrove litter production (based on data from
Agua Brava), and that production should approach an upper limit of net primary production. We
therefore suggest that the lower figure more accurately reflects the likely rate of net ecosystem
production. In either case, if the DIP uptake primarily represents net organic metabolism, rather than
inorganic sorption or precipitation of P, this system is net heterotrophic.
- 45 -

---

DIPatm = 0
(assumed)
DIPQ = 8.7 mmol m-3
VR DIPR = -3
VQ DIPQ = +2
DIPSystem = 14.0 mmol m-3
DIPOcean= 8.7 mmol m-3
DIPR = 11.4 mmol m-3
DIP = +3
VX (DIPOcean -DIPSystem) = -2
VG DIPG = VQ DIPQ = 0
(assumed)
DINatm = 0
(assumed)
VR DINR = -3
DINQ = 13 mmol m-3
VQ DINQ = 3
DINSystem =12.7 mmol m-3
DINOcean=6.6 mmol m-3
DIN = +3
DINR = 9.7 mmol m-3
V
V
G DING = VQ DINQ = 0
X (DINOcean -DINSystem) = -3
(assumed)
Figure 28. DIP and DIN budgets for Carretas-Pereyra, annual average. Fluxes in 106 mol year-1.
- 46 -

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2.2.4 Chantuto-Panzacola, Chiapas
F. Contreras-Espinosa and S. Ibarra-Obando
Study Area Description
The Chantuto-Panzacola estuarine system (15° 13' N, 92° 50' W; Figures 1 and 29), is located in the
state of Chiapas, The system is formed by five major lagoons: Chantuto, Campon, Teculapa, Cerritos
and Panzacola and received drainage from six rivers: San Nicolas (Payacal), Ulapa, Cacaluta, Dona
Maria, Cintalapa and Vado Ancho. The drainage basin is about 300 x 106 m3 and the average flow
(VQ ) is about 725 x 106 m3 year-1. Rainfall averages about 3,000 mm year-1, and evaporation about
800 mm year-1. About 20,000 people live in the municipality where the system is located
(Acapetahua). The total estuary + mangrove extension is about 180 km2; of this, approximately 30 x
106 m2 is open water. The open water area averages only about 1.5 m in depth. The mouth is
permanent and communicates with the sea and there is also a long estuarine belt parallel to the sand
bar.
The biotic community is dominated by mangroves (Rhizophora mangle) and during the rainy season
freshwater vegetation is characteristic in the Cerritos lagoon (Nymphae blanda, Cabomba sp., Pistia
stratiotes, Salvinia sp., Azola sp. Eichornia crassipes and Neptunia sp.). Primary production values
range from about 50 to 260 mg C m-3 h-1 and chlorophyll a values from 8-35 mg m-3.
Information on the physico-chemical variables is available in Contreras (1993) and, for purposes of
this exercise is spelled out in the box diagrams.
The upper basin still has native vegetation, as these areas are protected under a Biosphere Reserve
status. Inhabitants in these areas are largely isolated therefore have few basic services. Recent road
construction has accelerated erosion processes. Adjacent areas include precious wood forests that
are exploited (red cedar, mahogany) and areas where secondary vegetation and agricultural fields
have replaced the original vegetation. Coffee represents an important crop from the economic point
of view but it is grown in areas where the soil layer is very thin, causing lost of vegetative cover
during the rainy period. Areas of the basin devoted to both agriculture and cattle raising have lost
their original vegetation as a result of erosion processes. Erosion is presently a major threat to the
area, and no management plan exists to control the situation.
The main activities in the coastal zone of Chiapas include agriculture, cattle raising and fisheries.
Among the fisheries, prawn fisheries inside the estuaries is the most important activity to such a
degree that 70% of the local annual income is due to this activity.
Figure 29. The Chantuto-Panzacola estuarine system
- 47 -

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Water and Salt Budgets
Figure 30 summarises the water and salt budgets for the system. Freshwater inflow is assumed to
have a salinity near 0 psu. Salinity in the system averages about 14 psu, and salinity of the coastal
ocean exchanging with this system average about 22 psu over the year. Runoff is estimated to be
690 x 106 m3 year-1; rainfall is about 90 x 106 m3 year-1; and evaporation is about 24 x 106 m3 year-1.
With these values, the estimated water exchange time is about 0.02 year, or about a week.
VP = + 90
VE = - 24
VR =
-353
VRSR =
-5,507
VQ = +287
VSystem = 45
SOcean =
18 psu
SSystem = 13.2 psu
SR =
15.6 psu
= 0.013 years
VG = VO = 0
VX (SOcean - SSystem) = +5,507
(assumed)
VX =+1,147
Figure 30. Water and salt budgets for Chantuto-Panzacola, annual average. System volume is in
units of 106 m3 . Water fluxes in 106 m3 year-1. Salt fluxes in 106 psu m3 year-1.
- 48 -

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Budgets of Nonconservative Materials
Figure 31 summarises the P and N budgets for the Chantuto- Panzacola lagoonal system, Chiapas.
P Balance
This system appears to be approximately neutral with respect to DIP, perhaps reflecting the
relatively short water exchange time.
N Balance
The system is a very slight net producer of DIN (DIN = +4 x 106 mol year-1 = +0.14 mol m-2 year-1
across the open-water area of the system.
Stoichiometric Calculations of Aspects of Net System Metabolism
These rates are too near 0 to be confident of stoichiometric calculations. However, the system
apparently has a net organic production rate near 0 and suggests a rate of (nfix-denit) of +4 x 106 mol
year-1, or about +0.15 mol m-2 year-1. At least qualitatively, the system seems to be a net nitrogen
fixer, although we are not confident of the absolute rate.
- 49 -

---

DIPatm = 0
(assumed)
DIPQ =9.2 mmol m-3
VR DIPR = -2
VQ DIPQ = +3
DIPSystem = 6.6 mmol m-3
DIPOcean= 5.7 mmol m-3
DIPR =
6.2 mmol m-3
DIP = +0
VX (DIPOcean -DIPSystem) = -1
VG DIPG = VQ DIPQ = 0
(assumed)
DINatm = 0
(assumed)
DINQ =+3 mol m-3
VR DINR = -4
VQ DINQ = 6
DINSystem =11.4 mmol m-3
DINOcean=8.6 mmol m-3
DIN = +4
DINR = 10.0 mmol m-3
VG DING = VQ DINQ = 0
(assumed)
VX (DINOcean -DINSystem) = -3
Figure 31. DIP and DIN budgets for Chantuto-Panzacola, annual average. Fluxes in 106 mol year-1 .
- 50 -

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2.3 Gulf of Mexico
2.3.1) Laguna Madre, Tamaulipas
S. Ibarra-Obando and F. Contreras-Espinosa
Study Area Description
Laguna Madre (Figures 1 and 32, 23-25o N, 97o W) is located on the Gulf of Mexico shoreline. Its
northern limit is the Rio Bravo delta, and its southern limit the mouth of the Soto La Marina river. It
occupies a shallow basin that has an average depth of 0.7 m, and an area of about 2,000 km2; it is
the largest Mexican lagoon. It is separated from the sea by a sand bar. The San Fernando river
mouth divides the lagoon into two sub-basins, known as North and South. The lagoon presents 13
mouths that communicate with the sea only on a temporal basis, as sediment accumulation after
cyclones and hurricanes promotes their closure (Contreras, 1993).
Climate is arid with evaporation being far more important than freshwater input from rivers. As a
consequence, the lagoon is drying out, with increasing salinity in the remaining water body, and salt
deposition in its margins. Average evaporation is 1,900 mm year-1, and average precipitation 600
mm year-1. River freshwater input which might flow into the system is diverted for agricultural and
urban purposes, so none gets into the lagoon (Estado de Tamaulipas, 1996).
Dune vegetation exists at the lagoon margins, being represented by the following species: Uniola
paniculata, Ipomoea pescaprae and Croton punctulatus. Halophytes like Spartina spartinae, Suaeda
nigrica, Salicornia ambigua and Distichlis spicata, are also found. Upland areas present both spiny
shrubs and low forest spiny species, like mesquite and ebony. Submerged vegetation consist of
algae and seagrasses, which have been greatly reduced by the desiccation process and hypersaline
conditions. Only after heavy rains and mouth openings, salinity decreases, but this effect is only
temporary (Contreras, 1993). Halophytes are also disappearing from the lagoon margins, promoting
erosional areas that also contribute to lagoon infilling (Estado de Tamaulipas, 1996).
The icthyofauna comprises 78 species, among which prawns, croakers, snooks, mullets and
houndsharks are the most representative (Contreras, 1993). Oyster and prawn aquacultural projects
have failed due to poor water quality conditions (lack of freshwater input, and lack of a free water
exchange with the ocean). For the same reasons, crab harvest has declined. The lagoon is also well
known for being a resting, feeding and reproductive site for migratory waterfowl, mainly ducks:
Aythya americana and Anas discors (Estado de Tamaulipas, 1996).
Urban wastewater, as well as pesticides, herbicides and fertilisers residues represent the main
pollution source. Boat traffic contributes to pollution by oil and fuel spill, as well as boat washing.
Pollutant products are spilled in the open ocean without any regulation. All these products are carried
away by currents and end up in the lagoon (Tamaulipas State Government, 1996).
About 80,000 people inhabit the area around the lagoon. The coastal plain represents one of the
most important agricultural areas of the country, being among the most important crops: cotton,
cereals, leguminous and oily crops. Cattle raising is also an economically important activity. Besides
the artesanal fishery, large scale fisheries are represented by tuna and prawn fisheries. For the
Laguna Madre area, fisheries represent the most important economic activity, although the volume
captured is small (Estado de Tamaulipas, 1996).
Phytoplankton primary production for this system has been estimated to be about 600 g C m-2 year-1
(i.e., about 50 mol C m-2 year-1).
- 51 -

---

Figure 32. Map of Laguna Madre.
- 52 -

---

Water and Salt Budgets
Figure 33 summarises the water and salt budgets for Laguna Madre. Like the systems for the arid
Pacific (Section 2.1) and unlike the humid Pacific (Section 2.2), Laguna Madre is a net evaporative
system and shows penetration of water from the ocean. This seawater penetration delivers salt, so
salt mixing is outward in order to maintain a steady-state salinity in the system. The estimated water
exchange time () is determined as has been discussed in other sections and is about 0.09 year, that
is, about 1 month.
VP = + 1,200
VE = - 3,800
VR =
+2,600
VRSR = +104,000
VQ = +0
VSystem = 1,400
SOcean =
36 psu
SSystem = 44 psu
SR =
40 psu
= 0.09 years
VG = VO = 0
VX (SOcean - SSystem) = -104,000
(assumed)
VX =+ 13,000
Figure 33. Water and salt budgets for Laguna Madre, annual average. System volume is in units of
106 m3 Water fluxes in 106 m3 year-1. Salt fluxes in 106 psu m3 year-1.
- 53 -

---

Budgets of Nonconservative Materials
Figure 34 summarises the DIP and DIN budgets for this system.
P Balance
This system is a clear net source for DIP. Even though the rate of nonconservative DIP flux is
relatively small (DIP = +31 x 106 mol year--1 = 0.02 mol m-2 year-1), this rate results in a strong
concentration gradient between the system and the coastal ocean. The first consideration was that
this DIP production is consistent with the production seen for the various arid systems of the arid
Pacific coast (section 2.1). That analogy seems to be an unlikely explanation for this phenomenon in
Laguna Madre, because the oligotrophic coastal ocean waters seem unlikely to be a major source of
oceanic organic matter delivery to the lagoon. The next alternative considered was direct discharge
of human wastes. This source would deliver both organic and inorganic P; as long as the organic P
decomposed to inorganic material, the two would be indistinguishable in the budget. If we consider
the human population living adjacent to the lagoon (80,000) and use an approximate per capita P
discharge of 20 mol person-1 year-1, then this P source would amount to only approximately 2 x 106
mol DIP year-1. It therefore seems certain that there are other sources of either direct discharge of
DIP into this system or organic P discharge and decomposition of that organic matter. Hydrocarbon
pollutants and agricultural waste seem the most plausible sources. In either case, the decomposition
of these materials would constitute DIP sources to sustain the apparently net heterotrophic conditions
of this system.
N Balance
This system is also a source of DIN (DIN = +61 x 106 mol year--1 = 0.03 mol m-2 year-1). Both NO3
and NH4 are elevated well above oceanic values (NO3System = 2.8; NO3Ocean = 0.3; NH4System = 4.6;
NH4Ocean = 1.5; all units in mmol m-3). The relatively high concentrations of NH4 also tend to suggest
that the nutrient source is at least partially the result of organic decomposition.
Stoichiometric Calculations of Aspects of Net System Metabolism
Estimation of nitrogen fixation - denitrification (nfix-denit) is made from the difference between
observed and expected DIN, where the expected value is given by DIP x N:P ratio of the
decomposing organic matter. Although we do not know the source of this material, we assume that it
has an N:P ratio approximating the Redfield Ratio (16:1). Therefore:
(nfix-denit) = +61 x 106 - 16 x (+31 x 106) = -435 x 106 mol year-1
(-0.2 mol m-2 year-1 averaged over the entire lagoon).
This value is obviously uncertain, because we cannot readily predict the nature of the decomposing
organic matter. Nevertheless, the calculated rate seems reasonable.
Net ecosystem metabolism (NEM = [p-r]) can also be estimated from DIP, again with the
uncertainty as to the nature of the primary organic matter which is apparently decomposing. This
quantity is estimated as the negative of DIP multiplied by the C:P ratio of the reacting organic
matter. For the sake of this calculation, we assume that the reacting organic matter has an
approximately Redfield C:P ratio of 106:1. Thus:
(p-r) = -106 x (+31 x 106) = 3,286 x 106 mol year-1
(-2 mol m-2 year-1 over the lagoon area).
That is the system appears to be net heterotrophic by approximately 2 mol m-2 year-1. This value is
about 4% of the estimated annual primary production; thus the p/r ratio of this system is about 0.96.
- 54 -

---

DIPatm = 0
(assumed)
VR DIPR = +4
VQ DIPQ = 0
DIPSystem = 2.8 mmol m-3
DIPOcean= 0.1 mmol m-3
DIPR =
1.5 mmol m-3
DIP = +31
VX (DIPOcean -DIPSystem) = -35
VG DIPG = VQ DIPQ = 0
(assumed)
DINatm = 0
(assumed)
VR DINR = +12
VQ DINQ = 0
DINSystem = 7.4 mmol m-3
DINOcean=1.8 mmol m-3
DIN = +61
DINR = 4.6 mmol m-3
V
V
G DING = VQ DINQ = 0
X (DINOcean -DINSystem) = -73
(assumed)
Figure 34. DIP and DIN budgets for Laguna Madre, annual average. Fluxes in 106 mol year-1.
- 55 -

---

2.3.2) Laguna de Terminos, Campeche1
E. Gomez-Reyes, A. Vázquez-Botello, J. Carriquiry and R. Buddemeier
Study Area Description
Laguna de Terminos (Figures 1 and 35; 18-19o N, 91-92o W), is located in the southern portion of the
Gulf of Mexico and in the south west side of the Yucatan peninsula. The northern limit of the lagoon
is the Del Carmen Island in whose ends are located the two mouths that assure permanent
communication with the sea: Puerto Real in the east side and El Carmen in the west side. The lagoon
is in the transition zone between the low-lying limestone topography and the alluvial plains of the Gulf
of Mexico (Coll de Hurtado, 1975). The lagoon has an ellipsoidal shape in an east- west direction; is
70 km in length and 30 km in its widest portion; its area is 1,700 km2. The Terminos lagoon receives
drainage mainly from the Candelaria-Panlau system and the Chumpan-Balchacah system. The
Candelaria-Panlau system is formed by the confluence of the Candelaria and Mamantel rivers. The
Candelaria river itself represents an input of 700 x 106 m3 year-1. The Chumpan-Balchacah system is
formed by the Chumpan river and the Balchacah lagoon. The river bed of the Chumpan river
occupies an area of about 1,900 km2 and its annual runoff volume is of about 1,400 x 106 m3. Other
inputs are represented by the Palizada river, the Sabancuy river and the streams Colax, Lagartero,
Chivoj Chico and Chivoj Grande. The Palizada river and its arms form inner lagoons known as the
East Palizada system and the Pom-Atasta system (Contreras, 1993). The mean annual total river
discharge to the Terminos lagoon has been estimated to be 6 x 109 m3 (Phleger and Ayala-
Castañares, 1971).
Ocean water enters the lagoon through the Puerto Real mouth and exits via the Del Carmen mouth
with a net flux of up to 1,350 m3 s-1 in an East-West direction (Mancilla and Vargas, 1980).
Physico-chemical and biological characteristics of the lagoon can be found in Contreras (1993). In
general, it can be mentioned that the margins are covered by mangroves. In those sectors of the
lagoon characterised by its high salinity (south-west, east and in the south-south-east section of the
Del Carmen Island), the red mangrove Rhizophora mangle, is more abundant. In areas with high river
influence, the black mangrove is characteristic. Vegetation distribution is a function of water
transparency and CaCo3 content in the sediments. In clear waters seagrasses are abundant:
Thalassia testudinum, Halodule wrightii and Syringodium filiforme. Among the fauna, prawns,
echinoderms, decapodes, and fish (103 species) have been reported. Commercially important
species include: oysters (Crassostrea rhizophora and C. virginica), fish (Rangia cuneata) and sharks.
Net phytoplankton production in the estero averages about 300 g C m-2 year -1 and in the lagoon
about 200 g C m-2 year -1 (i.e., 25 and 17 mol C m-2 year-1, respectively) (Day et al., 1988)
Figure 35. Map of Laguna de Terminos showing major circulation pattern and percentage of river
inputs into the Bahía.

1 This initial draft budget was prepared at the workshop. A more recent budget has been prepared that is more accurate and
detailed. The reader is advised to contact the authors or the LOICZ WWW home page at : http://www.nioz.nl/loicz/modelnod for the
more recent information.
- 56 -

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The Terminos lagoon is located in front of an extensive continental platform fringe known as Sonda
de Campeche, that has an average width of 120 km from its shoreline to its inner margin (Gutiérrez-
Estrada, 1967). This zone represents one of the most important marine fisheries areas in the country.
It is also a place where oil extraction activities take place, and has therefore been impacted by oil-
spills. During the 1976 oil-spill, Vázquez-Botello (1980) documented that although hydrocarbons
accumulated in the sediment and their values were quadrupled, the oysters beds were not impacted.
This lagoon is the most studied system in the whole country, with more than 300 references
(Contreras, 1993). The socio-economic situation is described in Appendix IV.
Water and Salt Budgets
The mean climatic conditions of Laguna de Terminos can be separated into a 5-month dry season,
which extends from approximately January to June, and a 7-month wet season from June to January.
The data which were available for budgeting were for the wet season, during which about 88% of the
river inflow into the lagoon occurs. Approximately 5 x 109 m3 of runoff occurs during this period; three
rivers dominate this flow (Figure 35). For budgeting purposes and comparison with other sites, we
have expressed this wet season flow as an annual rate of 9 x 109 m3 year-1. In a similar manner, we
convert 7-month rainfall and evaporation rates to annualised water fluxes of +3 x 109 and ­2 x 109 m3
year-1, respectively, for the wet season.
A modification of the standard budget calculations is required. There are two entrances to Laguna de
Terminos. Water flows into the lagoon through the eastern entrance; there is an east-to-west net
circulation, with most outflow through the western entrance (Figure 35). Therefore, for calculation of
residual fluxes and exchange fluxes, oceanic composition is based on water composition near the
eastern entrance and both lagoonal and residual composition is based on water in the western portion
of the lagoon. It is useful for the calculations to characterise the inflowing water as Vin and the
outflowing water as Vout. These terms can be related to the "standard" exchange terms of residual
flow and exchange flux (VR, VX) for ease of comparison with other systems.
If we represent all of the freshwater inputs minus evaporative output as VQ* (i.e., VQ* = VQ + VP ­ VE +
VG + VO), we can write the steady-state water and salt balance equations as follows:
VR = -VQ* = Vin- Vout
(14)
Vin Socn = Vout Ssyst
(15)
By rearrangement:
V S
V =
*
(16)
in
( Q syst
S
- S
ocn
syst )
It follows that Vin is the equivalent of VX, and Vout is VX + VQ*.
Figure 36 illustrates the water and salt budgets for Laguna de Terminos, as derived according to this
procedure. Lagoon water exchange time is calculated as the lagoon volume divided by Vout,. For this
system, the exchange time is 0.22 year, or almost 3 months. We recognise that there is one
shortcoming in the budget as we have developed it. That shortcoming is that the Yucatán peninsula
is a major site of groundwater flow, and this volume flux may be significant in the budget (Perry and
Velazquez-Oliman, 1996). We suspect that this is not a serious problem for the water budget during
the wet season, but it may well be significant during the dry season.
Budgets of Nonconservative Materials
The mass balance equations for any material Y are modified in a manner analogous to the salt
balance equation, with some significant differences. First, the various freshwater sources are
explicitly identified, because they would be likely to have different concentrations of Y. Second, the
unknown in the equation is the biogeochemical flux, Y:
Y
= V Y
- V Y - V Y - V Y - V Y - V Y
out syst
in ocn
Q Q
P P
G G
o O
(27)
Figure 37 summarises the DIP and DIN budgets for Laguna de Terminos.
- 57 -

---

VP = + 3,000
VE = - 2,000
Vout =
21,176
VQ = 9,000
VSystem = 5,000
SOcean =
36 psu
SSystem = 19 psu
= 0.24 years
VG = VO = 0
V
(assumed - probably
in = + 11,176
incorrect for VG )
Figure 36. Water and salt budgets for Laguna de Terminos based on data for the wet period (June -
January), but expressed as annual rates. See text for details of flux calculations. System
volume is in units of 106 m3 . Water fluxes in 106 m3 year-1. Salt fluxes in 106 psu m3
year-1.
P Balance
It can be seen that the system is net sink for DIP, based on the loading data that we have (DIP =
146 x 106 mol year-1). It is possible that there are local inputs of DIP associated with agricultural
activities and not included in the budget, and there might be some groundwater input of DIP. These
inputs are judged not to be large, at least during the wet season when runoff-derived DIP seems
likely to dominate. In general, DIP flux in groundwater flowing through carbonate terrain is low.
N Balance
The system is also a net sink for DIN (DIN = -1,400 x 106 mol year-1). DIN is often very high in
groundwater, so it seems plausible that this additional DIN source is significant. If there is such
additional DIN loading, then we have underestimated DIN.
Stoichiometric Calculations of Aspects of Net System Metabolism
These P and N fluxes can be used to calculate nitrogen fixation minus denitrification (nfix-denit)
according to the procedures laid out in the previous sections. We calculate (nfix-denit) as the
difference between observed and expected DIN. Expected DIN is DIP multiplied by the N:P ratio
of the reacting particulate organic matter. We assume that the appropriate ratio is the Redfield N:P
ratio of plankton (16:1). Thus:
(nfix-denit) = -1,400 x 106 ­ 16 x (-146 x 106) = +936 x 106 mol N year-1
(+0.6 mol N m-2 year-1 over the lagoon area).
Note that the system appears likely to be fixing nitrogen in excess of denitrification.
Similarly, we can estimate net ecosystem metabolism (NEM = p-r) as the negative of the
nonconservative DIP flux multiplied by the C:P ratio of the reacting organic matter. If the net reacting
material is plankton, the particulate C:P ratio is about 106:1:
(p-r) = -106 x (-146 x 106) = +15,476 x 106 mol C year-1 = (+9 mol C m-2 year-1)
The system appears to be net autotrophic.
- 58 -

---

DIPatm = 0
(assumed)
Vout DIPout = - 6
DIPQ = 17 mmol m-3
VQ DIPQ = + 150
DIPSystem = 0.3 mmol m-3
DIPOcean= 0.3 mmol m-3
DIP = -147
Vin DIPin = + 3
VG DIPG = VQ DIPQ = 0
(assumed; may not be
correct for VG DIPG)
DINatm = 0
(assumed)
DINQ =144 mmol m-3
Vout DINout = - 42
VQ DINQ = 1,300
DINSystem = 2 mmol m-3
DINOcean=15 mmol m-3
DIN = -1,426
Vin DINin = + 168
VG DING = VQ DINQ = 0
(assumed; may not be
correct for VG DING)
Figure 37. DIP and DIN budgets for Laguna de Terminos based on data for the wet period between
June and January, but expressed as annual rates. See text for details of flux calculations.
Fluxes in 106 mol year-1 .
- 59 -

---

3.
CONCLUSIONS AND IMPLICATIONS FOR LAGOON COMPARISONS
Tables 10-13 summarise key data for the lagoons budgeted during the workshop and post-workshop
exercises. The diversity of sites, in terms of size, hydrological and hydrographical regime, and net
biogeochemical function is evident. Not evident in these tables but described in the site write-ups is
the range of variation in biotic composition of the sites (plankton-dominated, major seagrass
component, major mangrove communities). The degree of human impact on these systems also
varies tremendously.
Within the strict context of the biogeochemical budgeting, some features appear to be emerging. In
general, there seems to be a trend from systems which release DIP at the northern end of the Baja
California peninsula and mainland side of the Gulf of California, to systems which take up DIP to the
south and across into the wet lagoons of the Mexican tropical Pacific coast. Laguna Madre and
Laguna de Terminos, on the Gulf of Mexico, seems to fit this trend of DIP release in the north and
uptake in the south. If the nonconservative DIP flux is accepted as an index of net organic carbon
metabolism, then this trend can be interpreted as a general shift from systems which are net
heterotrophic to the north, to net autotrophic systems to the south.
A similar latitudinal trend exists with respect to the nonconservative flux comparison between DIN
flux which is observed and DIN flux which is expected from the DIP flux. The more northerly sites
show evidence of net denitrification, at rates which are ecologically reasonable. The southern sites
generally appear to be sites of net nitrogen fixation--again at reasonable rates.
It would be very useful to test these trends further, with additional budgets. Looking at the map of
coastal Mexico (Figure 1), we can recognise other areas in which coastal lagoons do exist and for
which budgets would be very useful: the coasts of Tamaulipas through Tabasco, and most of the
Yucatan peninsula; the Pacific mainland coast between Jalisco and Oaxaca; southern Sonora; and
the Pacific coast of Baja California Sur.
If the trends which are noted here stand up to further examination, then the next obvious step in
comparison among coastal lagoons world-wide would be to collect selected data from other
geographic regions which might be represented by a few sites amenable to budgets. How well do
these Mexican systems represent warm temperate and tropical coastal lagoons biogeochemically? If
the match looks good, then this study provides the framework for extrapolating from Mexico to other
regions.
An interesting reminder arose in the case of an attempted budget of Laguna Alvarado, a large system
in the State of Veracruz (~ 120 km2; 200 x 106 m3; 18° 45'N, 95° 45' W). This lagoon receives flows
from the Papaloapan River (one of the largest rivers in Mexico) as well as other large rivers. The
water flow through that system was sufficiently large (~50 x 109 m3 year-1) that the estimated water
exchange time was less than 0.5 days. For a system like that, the water and salt approach simply will
not work. With such a rapid water exchange, slight mismatches between nutrient concentrations and
freshwater inflow result in extreme (and clearly unreasonable) estimates of nonconservative nutrient
fluxes. This example provides an important cautionary note that the budgetary approach employed
here is not universally applicable.
- 60 -

---

Table 10. Freshwater discharges and nutrient loadings to Mexican coastal lagoons. All rates
expressed as annual rates, for ease of intercomparison. The numbers in the table reflect
the different accuracies used for the different systems.
System1 Season
VP
VE
VQ
VQPQ
VQNQ
VG
VGPG
VGNG
(Num.)
(106 m3 (106 m3 (106 m3 (106 mol (106 mol (106 m3 (103 mol
(103 mol
year-1)
year-1)
year-1)
year-1)
year-1) year-1)
year-1)
year-1)
EPB (1) Summer
+0.0
-17.5
+0
+0
+0
+0
+0
+0
BSQ (2) Summer
+1.5
-59.9
+0
+0
+0
+0
+0.0
+0
Winter
+24.5
-33.2
+0
+0
+0
+0
+0.4
+11
SLG (3) Spring
+0.0
-4.9
+0
+0
+0
+0
+0
+0
Summer
+0.0
-7.0
+0
+0
+0
+0
+0
+0
Fall
+0.5
-3.3
+0
+0
+0
+0
+0
+0
Winter
+0.1
-3.5
+0
+0
+0
+0
+0
+0
ELC (4) Summer
+5.5
-55.1
+0
+0
+0
+0
+0
+0
Winter
+1.5
-25.6
+0
+0
+0
+0
+0
+0
BC (5)
Winter
+23.7
-79.2
+0
+0
+0
+0
+0
+0
ELP (6) Spring
+0.7
-58.4
+0
+0
+0
+0
+0
+0
Summer
+19.0
-93.8
+0
+0
+0
+0
+0
+0
EP (7)
Average +300
-700
+3,400
+26
+167
+0
+0
+0
TAB (8) Average +2,100
-3,200
+5,500
+175
+480
+0
+0
+0
CPBB
Average
+79
-24
+234
+2
+3
+0
+0
+0
(9)
CP (10) Average
+90
-24
+287
+3
+3
+0
+0
+0
LM (11) Average +1,200
-3,800
+0
+0
+0
+0
+0
+0
LT (12)
June-
+3,000
-2,000
+9,000
+150
+1,300
+0
+0
+0
January
1See Table 1 for system abbreviations and Figure 1 for system locations.
- 61 -

---

Table 11. Salinities and inorganic nutrient concentrations in lagoon waters (syst) and adjacent ocean
(ocn) of Mexican coastal lagoons. The numbers in the table reflect the different
accuracies used for the different systems.
System1
Season
Socn
Ssyst
DIPocn
DIPsyst
DINocn
DINsyst
(Num.)
(psu)
(psu)
(mmol m-3) (mmol m-3) (mmol m-3) (mmol m-3)
EPB (1)
Summer
33.6
34.4
0.8
1.6
0.8
1.0
BSQ (2)
Summer
33.78
34.66
0.80
1.95
1.87
0.99
Winter
33.59
33.84
1.09
1.28
13.54
6.84
SLG (3)
Spring
35.26
35.32
1.24
1.36
1.35
1.39
Summer
35.74
35.90
0.98
1.21
1.38
2.07
Fall
35.50
35.59
1.38
1.60
7.88
5.89
Winter
35.34
35.39
1.74
1.26
6.23
2.32
ELC (4)
Summer
35.75
39.40
0.95
1.47
6.1
6.1
Winter
37.45
41.33
0.27
0.61
8.6
14.8
BC (5)
Winter
35.3
35.9
0.3
0.6
0.05
1.2
ELP (6)
Spring
35.7
36.4
0.87
0.68
0.64
1.95
Summer
34.7
36.2
0.70
0.11
0.50
0.45
EP (7)
Average
35
28
0.6
7.2
0.6
3.7
TAB (8)
Average
34.0
20.0
0.5
0.7
2.5
4.0
CPBB (9) Average
10.8
21.6
11.4
14.0
6.6
12.7
CP (10)
Average
22
14
5.7
6.6
8.6
11.4
LM (11)
Average
36
44
0.1
2.8
1.8
7.4
LT (12)
June-January
36
19
0.3
0.3
15
2
1See Table 1 for system abbreviations and Figure 1 for system locations
- 62 -

---

Table 12. Water and salt budget calculations for Mexican coastal lagoons. All rates are expressed as
annual rates, for ease of intercomparison. The numbers in the table reflect the different
accuracies used for the different systems.
System1 Season
Area
Volume
VR
VX
Exchange
(Num.)
(106 m2) (106 m3) (106 m year-1) (106 m3 year-1) Time (year)
EPB (1)
Summer
12
24
+18
+745
.03
BSQ (2)
Summer
+58
2,271
0.04
Winter
+8
1,179
0.08
Average
42
90
SLG (3)
Spring
+5
3,005
0.004
Summer
+7
1,553
0.007
Fall
+3
1,152
0.009
Winter
+4
1,288
0.009
Average
3
11
ELC (4)
Summer
+50
511
0.06
Winter
+24
245
0.12
Average
23
32
BC (5)
Winter
282
4,553
+55
3,292
1.36
ELP (6)
Spring
+58
1,471
0.10
Summer
+75
1,766
0.08
Average
45
145
EP (7)
Average
460
1,400
-3,000
13,500
0.08
TAB (8)
Average
1,600
1,266
-4,645
8,958
0.09
CPBB (9) Average
35
53
-297
434
0.07
CP (10)
Average
30
45
-353
1,147
0.013
LM (11)
Average
2,000
1,400
+2,600
13,000
0.09
LT (12)
June-January
1,700
5,000
-10,000
11,176
0.24
1See Table 1 for system abbreviations and Figure 1 for system locations
- 63 -

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Table 13. Nonconservative flux calculations for P and N, and stoichiometric derivations from those
fluxes for Mexican coastal lagoons. All rates are expressed as annual rates, for ease of
intercomparison. Averages are reported only for nonconservative fluxes and metabolic
rates derived from those nonconservative fluxes.
System1
Season
Area
Vol.
DIP
DIN
DIP
DIN
nfix-denit
p-r
(Num.)
(106 m2) (106 m3) (103 mol
(103 mol
(mol
(mol
(mol
(mol
year-1)
year-1)
m-2
m-2
m-2
m-2
year-1)
year-1)
year-1)
year-1)
EPB (1)
Summer
12
20
+575
+133
+0.05
+0.01
-0.8
-5
BSQ (2)
Summer
+2,683
+1,263
+0.06
+0.03
-0.9
-6
Winter
+214
-7,996
+0.01
-0.19
-0.4
-1
Average
42
90
+1,449
-3,366
+0.04
-0.08
-0.7
-4
SLG (3)
Spring
+354
+113
+0.12
+0.04
-1.9
-13
Summer
+350
+1,100
+0.12
+0.37
-1.6
-12
Fall
+249
-2,198
+0.08
-0.73
-2.0
-8
Winter
-581
-4,710
-0.19
-1.57
+1.5
+21
Average
3
11
+93
-1,425
+0.03
-0.48
-1.0
-3
ELC (4)
Summer
+205
-299
+0.01
-0.29
-0.5
-1
Winter
+73
+975
+0.00
+0.04
+0.0
-0
Average
23
32
+139
+338
+0.01
+0.02
-0.1
-1
BC (5)
Winter
282
4,553
+963
+3,751
+0.00
+0.01
-0.0
-0
ELP (6)
Spring
-324
+1,852
-0.01
+0.04
+0.2
+1
Summer
-1,072
-124
-0.02
-0.00
+0.3
+2
Average
45
145
-699
-864
-0.02
-0.02
+0.3
+2
EP (7)
Average
460
1,400
+75,000
-118,000
+0.16
-0.26
-2.4
-17
TAB (8)
Average
1,600
1,266
-170,000
-452,000
-0.11
-0.28
+1.5
+11
CPBB (9) Average
35
53
+3,000
+3,000
+0.09
+0.09
-1.3
-9
CP (10)
Average
30
45
+0
+4
+0.00
+0.14
+0.2
0
LM (11)
Average
2,000
1,400
+31,000
+61,000
+0.02
+0.03
-0.2
+2
LT (12)
June-
1,700
5,000
-147,000 -1,426,000
-0.09
-0.81
+0.6
+10
January
1See Table 1 for system abbreviations and Figure 1 for system locations
- 64 -

---

4. REFERENCES
Acosta-Ruiz, M. and S. Alvarez-Borrego. 1974. Distribución superficial de algunos parámetros
hidrológicos y físico-químicos en el Estero de Punta Banda, B.C. en otoño e invierno.
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Ciencias Marinas, 2: 98-105.
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período de primavera-verano de 1981. Professional Thesis. Universidad Autónoma de Baja
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Contreras, F. and L.M. Zabalegui. 1988. Aprovechamiento del Litoral Mexicano. Centro de
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productivity in Terminos Lagoon, Chap. 13: 221-236. in: Yan~ez-Arancibia, A. and J.W. Day,
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F. Wulff and T. Yanagi. 1996. LOICZ Biogeochemical Modelling Guidelines. LOICZ Reports
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APPENDIX I
MEXICAN COASTAL LAGOONS OVERVIEW
S. Ibarra-Obando, S.V. Smith and F. Contreras -Espinosa
In about 12, 000 km of coastline, Mexico has about 180 coastal lagoons and other estuarine areas.
These occupy an area of approximately 16,000 km2 and span a climatic regime ranging from warm
(arid) temperate to both wet and dry tropics (Lankford, 1977; Mee, 1977; Contreras, 1985, 1993;
Contreras and Zabalegui, 1988).
Mexican coastal lagoons have been used extensively as sites of fisheries, aquaculture development,
and tourism. Activities incidental to the ecology of these systems have had profound and largely
negative impacts: for example, waste discharges, including spills associated with petroleum
exploration; disturbance associated with agriculture, deforestation, and other coastal land
development; dredging, marina development and other development activities within the lagoons
themselves; extraction industries such as salt collection, and so forth. As a result, many Mexican
lagoonal systems are under threat of damage, severely damaged, or already destroyed.
Mexico has a long tradition of research on the ecology of its coastal lagoons. Presented here is an
overview of their main characteristics, pollution status and research effort. Much of the background
information can be traced to a paper by Lankford (1977), describing Mexican coastal lagoons.
Several books by Contreras (the most recent one being 1993; with an accompanying CD-ROM
compiled by Castañeda and Contreras, 1997) summarise most of the scientific literature and much of
the data on Mexican coastal lagoons.
Lankford (1977) identified seven regions in which the Mexican coastline could be subdivided. His
divisions were based on physiography but approximated State boundaries. For the purposes of using
INEGI statistical data, we have found it convenient to modify his boundaries slightly and collapse the
regions down to 5 regions coincident with State Boundaries (Figure 38). Summary statistics by region
are presented in Tables 14-16.
Region A - Baja California and Baja California Sur States - comprises the Baja California peninsula
(human population ~2,000,000) and contains about 60 coastal lagoons and other estuarine water
bodies. The estuarine surface area represents about 19% of nation's total. Climate is hot and arid,
with winter rains to the north and summer rains to the south. Mean annual precipitation and runoff are
low. Groundwater extraction exceeds recharge, so saline intrusion occurs in some areas. Human
impacts include salt and phosphate rock extraction, excessive boat traffic, increasing tourist
activities, domestic and industrial sewage discharge, fisheries resource exploitation, locally intensive
aquaculture, structural modifications such as dredging for industrial and tourist purposes. Research
effort in these regions (as measured by the number of scientific references listed by Contreras, 1993)
has been considerable, due to the presence of research institutions and universities.
Region B - Sonora and Sinaloa States - These two states are home to approximately 4,000,000
persons. The estuarine surface area in this region represents 17% of the nation's total and includes
about 40 lagoons and estuaries. Weather is arid in the north and semi-arid in the south, with limited
runoff. Also in this region, groundwater extraction exceeds recharge, and saline intrusion occurs.
Shrimp fisheries and aquaculture represent among the most important activities that take place in
these lagoons. Resultant impacts include mangrove destruction, eutrophication and sediment
accretion. Other impact sources are agrochemical pollution, increasing human settlements, tourism,
industrial and urban wastewater discharge. Research effort in this region has been relatively minor.
Region C - Nayarite, Jalisco, Colima, Michoacan, Guerrero, Oaxaca and Chiapas States - extends
from Nayarit to Chiapas (~20,000,000 persons) and contains about 40 lagoons and estuaries. Its
estuarine surface represents 20% of the national total. Climate varies from semiarid in the north to
very humid in the south. There are numerous rivers with small drainage basins and runoff is
important. Groundwater recharge exceeds extraction. Changes in river course are promoting lagoon
water salinity increase, accretion processes and migratory waterfowl reduction. Industrial pollution,
tourism, urban and industrial wastewater discharge, road construction, human settlements, salt
extraction and fisheries are also common impacts. In its northern portion, shrimp aquaculture is an
important activity. Research effort in the region has been low.
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Region D comprises the states of Tamaulipas, Veracruz and Tabasco (~10,000,000 persons). The
estuarine area is the largest in the country, about 24% of the national total. About 30 coastal lagoons
and estuaries are present in this region. Climate is semiarid in the north and subhumid in the south.
Summer is the rainy season. There are large rivers with high flow. Precipitation and runoff are
important, as are groundwater recharge and storage. This region is well known for oil extraction and
resultant pollution. Other activities include oil refineries, natural gas extraction, cattle raising, shrimp
fisheries, tourism, untreated urban and industrial waters. The research effort in this region is the
highest in the nation.
Region E includes the states of Campeche, Yucatán and Quintana Roo (~3,000,000 persons). Its
estuarine surface represents 19% of the national total and contains about 15 coastal lagoons and
estuaries. Climate varies from arid to subhumid. Rain is present during summer but it is not heavy.
The area is characterised by low-lying limestone topography, with much of the water flow being
groundwater. There are few rivers in this region. Groundwater extraction and recharge are low and of
the same magnitude. Deleterious activities include oil and salt extraction, human settlements, urban
wastewater discharge, road construction, tourism and fisheries. A moderate amount of the national
research effort has been devoted to this area.
Table 14. Statistics about the dimensions lagoons and estuaries of Mexico, and about the number of
scientific studies. (From Contreras, 1993; Castañeda and Contreras, 1997).
Geographic
Coastline
Number of
Estuarine
Number of
Region
Length
Estuaries
Surface
References
(km2)
(km2 )
A
4,300
58
3,000
1,303
B
1,800
40
2,700
567
C
2,400
40
3,200
487
D
1,400
30
3,800
1,306
E
1,700
15
3,000
642
TOTAL
11,600
183
15,700
4,305
Table 15. Mean annual precipitation and runoff per geographic region (INEGI, 1994).
Geographic
Mean Annual
Runoff
Region
Precipitation
(10 6 m3)
(10 6 m3)
A
20,800
300
B
168,000
25,000
C
359,100
126,700
D
569,400
192,800
E
172,200
29,100
TOTAL
1,289,500
373,900
Table 16. Regional distribution of groundwater. * indicates areas with saline intrusion (INEGI, 1994).
Geographic
Extraction
Recharge
Storage
Region
10 6 m3 year-1
10 6 m3 year-1
10 6 m3
A (*)
1,700
1,200
10,600
B (*)
3,000
2,100
32,600
C
1,400
2,700
D
2,700
4,000
46,750
E
500
500
TOTAL
9,300
13,200
- 69 -

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Figure 38. Map of Mexico, showing the coastal states and the major coastal physiographic regions;
slightly modified from Lankford (1977) in his paper on classification of coastal lagoons.
- 70 -

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APPENDIX II
COMPARISON OF NET & GROSS BUDGET FOR BAHÍA SAN QUINTÍN
S.V. Smith and S. Ibarra-Obando
These calculations are intended to put the gross and net metabolism of Bahía San Quintín into
perspective, in order to illustrate the utility of direct estimates of gross metabolism for estimating
turnover of materials and the utility of direct estimates of net metabolism for estimating primary
production ­ respiration. In Tables 17-20, biomass (B) is only estimated to the nearest order of
magnitude and is intended only as a crude index of material turnover.
The first points to note are (from Table 17) that plankton and seagrass apparently dominate the
primary production (p), as derived from various literature data for San Quintín and other sites. The
plankton have relatively low primary production but occur throughout the bay. By contrast, the
seagrass occupy only about 25% of the bay area but have high rates of production. Other plants
appear minor primary producers.
Seagrass respiration (r, Table 18) is apparently likely to consume most of the seagrass primary
production. We made "direct" estimates of both plankton respiration and benthic sediment
respiration. Plankton respiration, which is difficult to measure anyway, appears too low, because a
plankton p/r ratio of 3.5 seems abnormally high. This value dominates the estimated net system
metabolism and yields a total system p/r ratio of 1.35 (Table 17). If we adjust the plankton p/r ratio to
a more realistic value of 1.4 (Table 19), we derive a system p/r ratio of 1.02. The point is that this
single, difficult-to-measure term dominates estimates of p/r by "adding up the pieces," although the
gross metabolism is relatively stable at values of about 30,000 to 40,000 tonnes C year-1.
If, by contrast, we use the estimated value for p, and the value for (p - r) from Camacho et al.
(Section 2.1.2) as 1,840 tonnes C year-1, we can calculate the p/r ratio of the whole system to be
0.95. Even assuming that the estimated value for p might be in error by a factor of 2, we only perturb
this estimate between 0.98 and 0.91. As long as the assumption that the nonconservative flux of DIP
is a measure of net system metabolism, this method gives a robust estimate for this critical
characteristic of system metabolism (Table 21).
It follows that the combination of conventional estimates of component metabolism, together with the
budgetary approach to net metabolism, allows the estimate of both the turnover characteristics and
the net reservoir characteristics of the system.
Table 17. "Measured" metabolism for Bahía San Quintín expressed per area.
Community
Area
%
B
p
r
(p-r)
p/r
(km2)
(g C m-2) (g C m-2 day-1) (g C m-2 day-1) (g C m-2 day-1)
Seagrass
Shallow
6
14
100
3.00
2.50
0.50
1.20
Deep
6
14
100
2.00
2.50
-0.50
0.80
"Bare" sediment.
Shallow
2
5
10
3.00
3.00
0.00
1.00
Deep
27
61
1
0.05
0.63
-0.58
0.08
Plankton
42
95
1
1.40
0.40
1.00
3.50
Benthic algae
1
2
100
3.00
3.00
0.00
1.00
Salt marsh
2
5
100
3.00
2.50
0.50
1.20
TOTAL
44
100
36
2.39
1.77
0.62
1.35
- 71 -

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Table 18. "Measured" metabolism for Bahía San Quintín expressed as totals and percentages for
ecosystem.
Community
Area
%
B
%
p
%
r
%
(p-r)
(km2)
(t C)
(t C year-1)
(t C year-1)
(t C year-1)
Seagrass
Shallow
6
14
600
38
6,570 17
5,475
19
1,095
Deep
6
14
600
38
4,380 11
5,475
19
-1,095
"Bare" sediment
Shallow
2
5
20
1
2,190
6
2,190
8
0
Deep
27
61
27
2
493
1
6,209
22
-5,716
Plankton
42
95
42
3
21,462 56
6,132
22
15,330
Benthic algae
1
2
100
6
1,095
3
1,095
4
0
Salt marsh
2
5
200
13
2,190
6
1,825
6
365
TOTAL
44
100 1,589 100
38,380 100
28,401
100
9,979
Table 19. "Likely" metabolism for Bahía San Quintín expressed per area.
Community
Area
%
B
p
r
(p-r)
p/r
(km2)
(g Cm-2) (g C m-2 day-1) (g C m-2 day-1) (g C m-2
day-1)
Seagrass
Shallow
6
14
100
3.00
2.50
0.50
1.20
Deep
6
14
100
2.00
2.50
-0.50
0.80
"Bare" sediment.
Shallow
2
5
10
3.00
3.00
0.00
1.00
Deep
27
61
1
0.05
0.63
-0.58
0.08
Plankton
42
95
1
1.40
1.00
0.40
1.40
Benthic algae
1
2
100
3.00
3.00
0.00
1.00
Salt marsh
2
5
100
3.00
2.50
0.50
1.20
TOTAL
44
100
36
2.39
2.34
0.05
1.02
- 72 -

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Table 20. "Likely" metabolism for Bahía San Quintín expressed as totals and percentages for
ecosystem.
Community
Area
%
B
%
p
%
r
%
(p-r)
(km2)
(t C)
(t C year-1)
(t C year-1)
(t C year-1)
Seagrass
shallow
6
14
600
38
6,570 17
5,475
15
1,095
deep
6
14
600
38
4,380 11
5,475
15
-1,095
"Bare" sediment.
shallow
2
5
20
1
2,190
6
2,190
6
0
deep
27
61
27
2
493
1
6,209
17
-5,716
Plankton
42
95
42
3
21,462 56
15,330
41
6,132
Benthic algae
1
2
100
6
1,095
3
1,095
3
0
Salt marsh
2
5
200
13
2,190
6
1,825
5
365
TOTAL
44
100 1,589 100
38,380 100
37,599
100
781
Table 21. Summary of budget results for Bahía San Quintín expressed in terms of gross and net
metabolism.
p
r
p/r
p/r
(t C year-1)
(t C year-1)
(direct)
(from budget)
(not robust)
(robust)
gross estimate
gross estimate
(TABLE 3)
38,380
28,401
1.35
(TABLE 4.)
38,380
37,599
1.02
(p-r)
gross estimate (gross p - [p-r])
(transect budget)
38,380
40,220
0.95
-1,840
(t C year-1)
gross p x 2
(gross p - [p-r])
76,760
78,600
0.98
gross p / 2
(gross p - [p-r])
19,190
21,030
0.91
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APPENDIX III
ECOLOGICAL SERVICES AND SOCIO-ECONOMIC SUSTAINABILITY -
A case study: Bahía San Quintín
Introduction
The overall aim of IGBP is "to describe and understand the interactive physical, chemical and
biological processes that regulate the total Earth system, the unique environment that it provides for
life, the changes that are occurring in the system and the manner in which they are influenced by
human actions" (Pernetta and Milliman, 1995).
LOICZ is that component of the IGBP which focuses on the area of the earth's surface where land,
ocean and atmosphere meet and interact. The overall goal of this project is to determine at regional
and global scales: the nature of that dynamic interaction; how changes in various components of the
Earth system are affecting coastal zones and altering their role in global cycles; to assess how future
changes in these areas will affect their use by people; and to provide a sound scientific basis for
future integrated management of coastal areas on a sustainable basis (Pernetta and Milliman, 1995).
One of the ways in which the LOICZ project is achieving the required integration to reach its goal is
budgeting water, C, N and P in the coastal zone. Human populations and economic activities alter C,
N, P, water, and sediment inventories, and their fluxes within and through the coastal zone. These
same fluxes and inventories represent and control the processes that define the living resources --
terrestrial, aquatic and marine -- that provide direct and indirect economic goods and services to
humankind. This link between natural science and socio-economics has yet to be successfully
addressed by any of the IGBP core project elements. For this reason we have decided to undertake
an integrative study using Bahía San Quintín as a study case.
The San Quintín system is represented by the San Simon valley and a coastal lagoon known as
Bahía San Quintín (Figure 5). This system is located in the Baja California Peninsula (30o N); its
watershed covers an area of approximately 2,000 km2, and the surface area of the Bay itself is about
40 km2. The system is very arid, with an average annual rainfall of approximately 200 mm year-1 and
pan evaporation of 1,500 mm year-1 near the coast. There is no significant surface runoff from land
into the bay except during major storms. Groundwater represents the only freshwater source and is
heavily exploited in order to sustain agriculture. Agriculture (dominated by tomato growing)
represents the most important economic activity in the region, providing jobs for local people and
migrants coming from the southern part of Mexico (mainly Oaxaca).
This agricultural activity is far more intensive than can be sustained naturally, and virtually all of the
produce is exported. Water use is about 12 x 106 m3 year-1 greater than the recharge of 30 x 106 m3
year-1, and the aquifer is being drawn down by about 3% per year. This is causing saline intrusion
along the coast, where the human population lives and relies on the groundwater for domestic,
municipal and industrial water supplies. Further, this activity is relying heavily on the import of
inorganic fertilisers. Some of the fertiliser nutrient elements enter the aquifer, further contaminating
the remaining fresh water.
The human population of the region is readily divided into two groups: a permanent population of
about 25,000 persons, most of whom live in 3 towns in the San Quintín valley, and about that same
number of migrant labourers, who are there an average of about half the year and who mostly live in
camps. There is no sewage treatment for the wastes from either of these groups, so their discharge
largely percolates into the top of the aquifer.
The marine part of the system, known as Bahía San Quintín, is a hypersaline coastal lagoon; its area
consists of two sub-basins: Bahía Falsa (west) and Bahía San Quintín (east) (Figure 5). The bay has
a permanent mouth and exchanges nutrients and organic materials with the coastal ocean. The
system is a net exporter of dissolved inorganic phosphorus, apparently derived from the
decomposition of particulate organic matter exported from outside the system.
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Two economic activities are significant in extracting living resources from the marine system, but
both are sustained naturally. The first of these is an artesanal harvesting of the natural population of
clams. Second, since about 1970 Bahía Falsa has been used for oyster culture, with this being the
most important economic activity for the marine part of the system. There is some question as to
whether these two extractive industries compete with one another. Other relevant activities using
include tourism, especially sport fishing (outside the bay) and duck hunting.
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APPENDIX IV
SOCIO-ECONOMIC SITUATION OF LAGUNA DE TERMINOS
A. Vázquez-Botello
General
The Mexican State of Campeche covers 2.6% of the total land surface of Mexico; in 1995 its
population represented 0.7% of the total population of the country with a density of 12.4 inhabitants
km-2. The rural population is 28% of the total state population and the urban population is mainly
located in Campeche City and Isla del Carmen City.
Campeche state belongs to the 1V Region according to the classification of the fishing zones in
Mexico. There were 374 shrimp fishing boats of high level registered in 1993, and Del Carmen city is
considered as one of main fishing ports. Its land surface covers about 13,000 km2, with humid warm
climate and heavy rainy season lasting 7 months.
The county's population increased 2.3 times (234%) in 25 years, from about 80,000 inhabitants in
1979 to 180,000 in 1995; with an annual growth rate of nearly 4%.
Agriculture
The area of cultivation is 1,600 km2, 93% of which is temporal and 7% uses both irrigation and
temporal systems. Subsistence agriculture is the mainly practised type and the most important crops
are: corn, rice, sorghum and green pepper.
Cattle
Cattle ranching is practised in the Atasta peninsula, Sabancuy and Candelaria regions. It is of the
extensive type and dairy cattle is very important with 260,000 head by 1993 (45 % of the state's
participation). There are also pigs, sheep, horses, chickens and bees raised for commercial
purposes.
Forests
Forest exploitation has not been done carefully; wood production has significantly decreased, from
55,000 m3 in 1993 to 4,000 in 1997 of wood roll. There are precious woods such as cedars and
mahogany. The only products removed from the forests are gum and palm.
Fishing
There are two main fishing zones in Campeche state: Del Carmen Island and The Sonda the
Campeche. In 1993 the total fishing production was 20,000 tons. The fishing centres produced
2,000,000 oysters larvae. There are 50 co-operative societies, 19 are for shrimp fishing and 31 for
scale fish. The fishing fleet has 228 shrimp fishing boats and 2,700 shore fishing boats.
Industry
Extraction of crude oil and natural gas is truly the main industrial activity. In 1995 the Mexican oil
company had registered 10,573 workers. In the Sonda de Campeche there are 413 productive oil
wells in activity. The average daily production in the zone is 2,681,000 barrels of crude oil which is
equivalent to 75% of the country production and 30% of natural gas nation wide.
Other important industries are metal products, food and drink production, tobacco, chemical industry
as well as charcoal, rubber and plastics.
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APPENDIX V
LOICZ WORKSHOP ON MEXICAN COASTAL LAGOONS
CICESE, Ensenada, Mexico
2-3 June 1997
MEETING REPORT
1. Official Opening of the Workshop
Dr. Silvia Ibarra-Obando, Centro de Investigación Científica y de Educación Superior de Ensenada
(CICESE), co-chair of the workshop, welcomed the participants (Appendix VI) to CICESE and
graciously explained that although the working language for the meeting is English, participants
should feel free to make enquiries in Spanish.
Dr. Ibarra-Obando introduced Prof. Stephen Smith, LOICZ Scientific Steering Committee (SSC)
Member and co-chair of the workshop.
The LOICZ Scientific Steering Committee (SSC) Members who are acting as resource persons in
were identify, Dr. Robert Buddemeier and Prof. Fred Wulff. Mr. Paul Boudreau, LOICZ Core Project
Scientist was identified as providing support for the workshop. Dr. Victor Camacho-Ibar was also
identified as a resource person.
2. Administration and Organisation of the Workshop
2.1 Administrative and organisational matters
Dr. Ibarra-Obando informed the participants on a number of matters concerning the logistics of the
workshop. Ms. Amelia Chavez, CICESE librarian, was introduced and her offer to assist participants
in locating data and information in the library was gratefully accepted.
2.2 Introduction of Workshop participants
Prof. Smith invited all of the participants to briefly introduce themselves and to say a few words about
their scientific background and geographic area of interest.
2.3 Purposes, expected outcome and schedule of the workshop
Prof. Smith then summarised the purposes of the workshop. He pointed out that Mexican coastal
lagoons span a climatic regime ranging from cool arid temperate to both wet and dry tropics. They
range from relatively little to high degree of perturbation from human activities and that many of the
lagoons are relatively very well studied. This range in conditions, the large number of lagoons and
the small but active scientific community of researchers make Mexico an excellent region to develop
a core of biogeochemical budget models that can be used to investigate patterns of fluxes of carbon,
nitrogen and phosphorus in coastal lagoons.
The expected outcome of the workshop is a number of biogeochemical budgets for a number of
lagoons spanning the various regions in Mexico. It is hoped that a sufficient number of budgets
(hopefully four but at least two) will be produced to allow for a useful comparison of non-conservative
fluxes within and between regions. The workshop participants are asked to prepare as many budgets
as possible with the data available within the time of the workshop and that any additional budgets
prepared after the workshop will be considered for inclusion in the workshop report (this document).
Prof. Smith pointed out that the running of the workshop will be informal and scheduling of the
agenda items (Appendix VII) will be determined as agreed by the participants. He suggested that the
general approach should be that following the opening plenary, participants would be broken into
groups by region to carry out budgeting exercises with the help of the resource persons. The results
of these exercises would then be presented to the full group in a closing plenary as a means of
sharing the results among all participants and promoting intercomparison. This proposal was
accepted by the participants.
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3. Brief background and status of the International Geosphere-Biosphere Programme (IGBP)
and to the Land Ocean Interactions in the Coastal Zone (LOICZ) Core Project of IGBP
Mr. Boudreau provided a very brief overview of the background and status of the International
Geosphere-Biosphere Programme (IGBP) and to the Land Ocean Interactions in the Coastal Zone
(LOICZ) Core Project of IGBP. He pointed out that the main focus of the programme is the study of
global material flux related to global change. The LOICZ Project is one of eleven programme
elements in the IGBP and has as its goal the study of flux in the coastal zone. It includes research on
drainage basins, rivers, estuaries and continental shelves of the world. Although the present
workshop is primarily focused on biogeochemistry, the integration of natural and socio-economic
research in the study of changes in the coastal zone is an important component of LOICZ.
4. Natural history background of Mexican lagoons
Primarily for the benefit of the resource persons who may not be familiar with the natural history of
Mexican lagoons, Dr. Ibarra-Obando presented a brief background (Appendix I). She pointed to the
wide range in climate conditions. It was suggested that the major coastal physiographic regions as
shown in Figure 38 be used to group participants for the small workgroups.
5. Brief background and LOICZ Biogeochemical Modelling Initiative
5.1 General background and introduction
Prof. Smith provided a brief background to the LOICZ biogeochemical modelling initiative. He
pointed out that the LOICZ Biogeochemical Modelling Guidelines (Gordon et. al, 1996) that were
circulated to the participants before the workshop present a methodology for calculating budgets of
carbon, nitrogen and phosphorus flux in coastal systems in a standard way. The application of such
methodologies provides results that can then be compared among systems globally in an effort to
establish the importance of the coastal waters to the overall global flux and changes in these fluxes.
The participants were reminded that the LOICZ guidelines will not be applicable to all situations and
they were instructed to use their own experience and knowledge in generating the budget results.
A major initiative within the LOICZ Project is the compilation of as many budgets as possible for as
many regions of the world. The on-going results this compilation effort are to be made available on
the World Wide Web (WWW) home page (see next section). All budgets prepared by the workshop
participants, either during or after the workshop, will be considered for inclusion in this compilation
exercise. Submitted budgets will be reviewed for accuracy and completeness and, if they are judged
to be of sufficiently high quality, will be placed on the home page with full credit given to the original
authors. As this effort greatly benefits the global LOICZ research, assistance is offered to authors
who may require help. Budgets and or requests for additional information, assistance should be
directed to either the LOICZ CPO, Prof. Smith or Prof. Wulff (addresses in Appendix VI).
5.2 LOICZ Biogeochemical Modelling Node WWW Home Page Demonstration
In an effort to introduce the participants to the specifics of budget preparation and to the end goal of
the budgeting work, Prof. Wulff presented an introduction to the LOICZ Biogeochemical Modelling
Node WWW Home Page. He showed the participants the present status of the home page and
explained that it is a very valuable source for researchers interested in generating such budgets. The
budgets documented provide numerous examples of the data, calculations and presentation of
results that are required for use by LOICZ. The home page can be accessed through the LOICZ
Home page at http://www.nioz.nl/loicz/modnod. All participants were encouraged to review the home
page and provide comments to Prof. Wulff. Budgets provided by the participants will be considered
for addition to the home page.
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6. Budget for Bahía San Quintín
6.1 Overall (Net) Biogeochemical Budgets
Dr. Victor Camacho-Ibar presented a budget model for Bahía San Quintín, Baja California, as an
introduction to the details of the budget modelling. The presentation and associated documentation
(Section 2.1.2, above) provided an excellent description of the modelling methodology. The
documentation provided was used by the participants in the working groups in developing their
budgets. This work which updates and improves on the original Bahía San Quintín results published
in Gordon et al. (1996) will be incorporated into the LOICZ biogeochemical analysis and home page.
6.2 Component Gross budgets
Dr. Ibarra-Obando presented a component gross budget for Bahía San Quintín (Appendix II). In this
budget she attempted to estimate overall production and respiration for comparison with the values
for net flux presented by Dr. Camacho-Ibar. In her presentation she pointed out community
respiration was particularly difficult to measure directly and that this poorly estimated value had
significant impact on the gross budget results. She contrasted this with the results for the net budget
as derived following the LOICZ approach with was much more robust.
7. Application of LOICZ Modelling Approach to Mexico Lagoon Situations
Smaller working groups were set up to carry out the budget modelling for specific Mexican lagoons.
Based on the geographic areas of interest of the participants the following groups were formed to
attempt to address the budgeting in the different regions (resource persons in italics):
GROUP
REGION
AREA
CONDITIONS
(see Figure 38)
(see Figure 1)
1
A
Baja California Peninsula
Arid
B
Sonora and Sinaloa
Botello-Ruvalcaba
Delgadilla
Lechuga-Devéze
Poumian-Tapia
Boudreau
Camacho-Ibar
2
C
Nayarit to Chiapas
Humid
Flores-Verdugo
Ibarra-Obando
de la Lanza-Espino
Wulff
3
D
Tamaulipas, Veracruz &
Semiarid
Tabasco
E
Campeche, Yucatan &
Sub-humid
Quintana Roo
Carriquiry
Contreras Espinosa
Gomez-Reyes
Vázquez-Botello
Buddemeier
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The groups worked more or less independently, with the help of the resource persons. In all cases,
the groups identified lagoons with sufficient data at hand to budget and proceeded to complete as
much of the budgets as possible.
As a result of data availability, expertise and complexity of the systems chosen to budget, the
different groups were able to produce different numbers with different levels of completeness. In
summary, budgets were produced for the following areas:
GROUP
LAGOON
1
Arid Baja California and Gulf of California coasts
1.1) Bahía San Quintín, Baja California (a teaching example)
1.2) Estero de Punta Banda, Baja California
1.3) Bahía San Luis Gonzaga, Baja California
1.4) Bahía Concepción, Baja California
1.5) Estero La Cruz, Sonora
2
Humid Pacific Coast
2.1) Teacapan-Agua Brava-Marismas Nacionales, Sinaloa and Nayarit
2.2) Chantuto-Panzacola, Chiapas
3
Sub-Humid- Gulf of Mexico
3.1) Laguna de Terminos, Campeche
Four additional budgets were provided immediately following the workshop:
LAGOON
AUTHOR(S)
1) Carretas-Pereyra
Contreras-Espinosa;
2) Ensenada La Paz
Lechuga-Devéze;
3) Bahía de Altata-Ensenada del Pabellón
Flores-Verdugo and de la Lanza-Espino; and,
4) Laguna Madre
Ibarra-Obando and Contreras-Espinosa.
8. Presentation and review of budgets
Each group presented the results of their work in a closing plenary. The authors took the suggestions
from the discussion to revise and improve the initial draft budgets.
9. Workplan and timetable for future activities
The co-chairs made it clear to the participants that submission of budgets for additional lagoons not
considered during this workshop was greatly encouraged as soon as they become available. In
addition, Prof. Smith presented a number of recommendations for future action:
· each research group to furnish at least one complete budget to the LOICZ CPO by June 15th.
Additional budgets submitted within this time frame would be welcomed and included in the
report;
· the LOICZ CPO will circulate to all participants a copy of the report by July 1st for their
review, comments and corrections;
· participants to submit additional budgets to the LOICZ CPO by August 1st for possible
inclusion in the final report;
· LOICZ CPO to circulate final report to the full network of LOICZ contacts by September 1st;
· if a minimum of four budgets are submitted for each of the three regions, Prof. Smith will
take the lead in writing an article, co-authored by all participants and submitted to a refereed
journal comparing net ecosystem metabolism among Mexican coastal lagoons.

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Participants agreed with these recommendations and the timetable proposed and committed to
providing additional budgets.


In addition to these specific recommendations, a number of more general suggestions were agreed
to:

· all participants were encouraged to continue to submit budgets;
· the process of regional budgeting workshops should be used in other areas to generate within
regional comparisons; and
· results so far support the development of a typology of matching lagoonal ecosystem types with
ecosystem functions.
10. Approval of the report of the Workshop
It was agreed that the meeting report would be prepared by the workshop organisers and circulated to
the participants by July 1st. Participants agreed to review the draft meeting report and provide
corrections, comments, additions and changes to the LOICZ CPO no later than August 1st. It was
agreed that the workshop resulted in sufficient scientific results that a LOICZ Reports & Studies
document be produced. It was agreed that the workshop report be published as an appendix of the
R&S document. It was also agreed that the document should be widely circulated to the LOICZ
community as a means of supporting the LOICZ modelling approach.
11. Closure of the Workshop
Dr. Ibarra-Obando, co-chair of the meeting, thanked the participants of the workshop for their efforts
before and during the workshop. She also thanked the staff of the local organising committee for their
organisation and administrative support to the workshop and in particular Mrs. Maria Eugenia Ovies.
There being no further business Dr. Ibarra-Obando and Prof. Smith closed the meeting at 14:30
hours on 3 June 1997.
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APPENDIX VI
LOICZ WORKSHOP ON MEXICAN COASTAL LAGOONS
CICESE, Ensenada, Mexico
2-3 June 1997
PARTICIPANTS AND CONTRIBUTORS TO BUDGETS
Mr. Martín BOTELLO-Ruvalcaba
Dr. José D. CARRIQUIRY*
Depto. de Investigaciones Científicas
Inst. de Investigaciones Oceanológicas
y Tecnológicas
Universidad Autónoma de Baja California
Universidad de Sonora (DICTUS-UNISON)
(IIO-UABC)
Rosales y Niños Héroes s/n
Km. 103 Carretera Tijuana-Ensenada
Hermosillo, Sonora, MEXICO
Apartado Postal 453
E-Mail: mbotello@guayacan.uson.mx
Ensenada, Baja California, 22830 MEXICO
present mailing address:
Phone: 1-61-74 4601 Ext. 123
Dept. of Applied Biology
Fax:
1-61-74 5303
Hull University
E-Mail: jdcarriq@bahia.ens.uabc.mx
Hull, UNITED KINGDOM
Phone: 04180-465513
Prof. Francisco CONTRERAS Espinosa
Fax:
04182-465458
UAM-IZTAPALAPA
E-Mail:
Centro de Documentación sobre Ecosistemas
M.A.Botello-Ruvalcaba@appbiol.hull.ac.uk
Litorales Mexicanos
Michoacán y Purísima, Col. Vicentina
Mr. Paul BOUDREAU
Apartado Postal 55-535
LOICZ Core Project Office
México, D. F. 09340 MEXICO
Netherlands Institute for Sea Research
Phone: 52-5 724-4746
P. O. Box 59
Fax:
52-5 724-4738
1790 AB Den Burg, Texel
E-Mail: fce@xanum.uam.mx
THE NETHERLANDS
Phone: 31-2223 69404
Dr. Guadalupe de la LANZA Espino
Fax:
31-2223 69430
Instituto de Biología
E-Mail: loicz@nioz.nl
Universidad Nacional Atuónoma de México
(IB-UNAM)
Dr. Robert W. BUDDEMEIER
Apartado Postal 70-153
Kansas Geological Survey
04510 MEXICO, D. F.
University of Kansas
Phone: 525-622 5716
1930 Constant Ave.
Fax:
525 550 0164
Campus West
E-Mail: gdlle@servidor.unam.mx
Lawrence, Kansas, 66047-3720
Phone: 1-913-864-3965
Mr. Francisco DELGADILLO Hinojosa*
Fax:
1-913-864-5317
Instituto de Investigaciones Oceanológicas
(after 20/7/97 area code is 785)
Universidad Autónoma de Baja California
E-Mail: buddrw@kgs.ukans.edu
(IIO-UABC)
Km. 103 Carretera Tijuana-Ensenada
Dr. Víctor CAMACHO-Ibar*
Apartado Postal 453
Inst. de Investigaciones Oceanológicas
Ensenada, Baja California 22830 MEXICO
Universidad Autónoma de Baja California
Phone: 1-61-744601 Ext. 122
(IIO-UABC)
Fax:
1-61 74 53-03
Km. 103 Carretera Tijuana-Ensenada
E-Mail: fdelgad@faro.ens.uabc.mx
Apartado Postal 453
Ensenada, Baja California 22830 MEXICO
Phone: 1-61-74 4601 ext. 123
Fax:
1-61-74 5303
E-Mail: vcamacho@bahia.ens.uabc.mx
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Dr. Francisco J. FLORES Verdugo
Prof. Stephen V. SMITH
Instituto de Ciencias del Mar y Limnología
School of Ocean and Earth Science and
Universidad Nacional Autónoma de México
Technology
(ICML-UNAM)
University of Hawaii
Laboratorio de Trofodinámica en Lagunas
1000 Pope Road
Costeras
Honolulul, Hawaii 96822 UNITED STATES
Explanada de la Azada y Cerro del Crestón
Phone: 1-808-956 8693
Mazatlán, Sinaloa 82240 MEXICO
Fax:
1-808-956 7112
Phone: 52-69 85 28 45
E-Mail: svsmith@soest.hawaii.edu
Fax:
52-69 82-61-33
E-Mail: verduz@mar.icmyl.unam.mx
Mr. E. VALDEZ-Holguín**
Depto. de Investigaciones Científicas
Dr. Eugenio GOMEZ-Reyes
y Tecnológicas
UAM IZTAPALAPA
Universidad de Sonora (DICTUS-UNISON)
División de Ciencias Básicas e Ing.
Rosales y Niños Héroes s/n
Depto. de Ingeriería de Procesos e Hidráulica
Hermosillo, Sonora, MEXICO
Michoacán y Purísima, Col. Vicentina
E-Mail: jvaldez@guayacan.uson.mx
México, D. F. 09340 MEXICO
Phone: 52-5 724-4646, 52-5-723-6992
Dr. Alfonso VÁZQUEZ-Botello
Fax:
52-5 724-4400
Instituto de Ciencias del Mar y Limnología
E-Mail: egr@xanum.uam.mx
Universidad Nacional Autónoma de México
(ICMyL-UNAM)
Dr. Silvia IBARRA-Obando*
Apartado Postal 70-305
Centro de Investigación Científica y de
04510 México, D. F. MEXICO
Educación Superior de Ensenada (CICESE)
Phone: 52-5-622 5810
Km. 107 Carretera Tijuana-Ensenada
Fax:
52-5-616 0748
Apartado Postal 2732
E-Mail: alfonsov@mar.icmyl.unam.mx
Ensenada, Baja California 22860 MEXICO
Phone: 52-61 74 42 00
Prof. Fred WULFF
Fax:
52-61 74 5154
Department of Systems Ecology
E-Mail: sibarra@cicese.mx
Stockholm University
106 91 Stockholm SWEDEN
Dr. Carlos H. LECHUGA-Devéze
Phone: 46-8 16 42 50
Centro de Investigaciones Biológicas del
Fax:
46-8 15 84 17
Noroeste
E-Mail: fred@system.ecology.su.se
Km. 0.5 a la Telefónica
Apartado Postal 128
La Paz, Baja California, Sur 23000 MEXICO
*U. S. Mailing addresses:
Phone: 52-112-53626 Ext. 136
Instituto de Investigaciones Oceanológicas
Fax:
52-112-54710
Universidad Autónoma de Baja California
E-Mail: clechuga@cibnor.mx
(IIO-UABC)
P. O. Box 189003-099
Ms. Miriam POUMIAN Tapia*
Coronado, Ca. 92178
Centro de Investigación Científica y de
United States
Educación Superior de Ensenada (CICESE)
Km. 107 Carretera Tijuana-Ensenada
Centro de Investigación Científica y de
Apartado Postal 2732
Educación Superior de Ensenada (CICESE)
Ensenada, Baja California 22860 MEXICO
P. O. Box 43-4844
Phone: 52-61 74 4200
San Diego, Ca. 92143-4844
Fax:
52-61 74-5154
United States
E-Mail: mpoumian@cicese.mx
J. A. SEGOVIA-Zavala**
** contributor to budgets
contact through
Mr. Francisco DELGADILLO Hinojosa
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APPENDIX VII
LOICZ WORKSHOP ON MEXICAN COASTAL LAGOONS
CICESE, Ensenada, Mexico
2-3 June 1997
AGENDA
1. Official Opening of the Workshop
2. Administration and Organisation of the Workshop
2.1 Administrative and organisational matters
2.2 Introduction of Workshop participants
2.3 Purposes, expected outcome and schedule of the workshop
3. Brief background and status of the International Geosphere-Biosphere Programme (IGBP)
and to the Land Ocean Interactions in the Coastal Zone (LOICZ) Core Project of IGBP
4. Natural history background of Mexican lagoons
5. Brief background and LOICZ Biogeochemical Modelling Initiative
5.1 General background and introduction
5.2 LOICZ Biogeochemical Modelling Node WWW Home Page Demonstration
6. Budget for Bahía San Quintín
6.1 Overall (Net) Biogeochemical Budgets
6.2 Component Gross budgets
7. Application of LOICZ Modelling Approach to Mexico Lagoon Situations
8. Presentation and review of budgets
9. Workplan and timetable for future activities
10. Approval of the report of the Workshop
11. Closure of the Workshop
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