May 2007
INTEGRATION OF THE NUTRIENT REDUCTION
FUNCTION IN RIVERINE WETLAND
MANAGEMENT
GUIDANCE DOCUMENT
PROJECT COMPONENT 4.3: MONITORING AND ASSESSMENT OF
NUTRIENT RETENTION CAPACITIES OF RIVERINE WETLANDS
AUTHORS
PREPARED BY:
University of Natural Resources and Applied Life Sciences, Vienna
WasserCluster Lunz GmbH
Technical University, Vienna
Geological Institute of Hungary (MAFI)
AUTHORS:
Elisabeth Bondar
Oliver Gabriel
Gyozo Jordan
Verena Kucera-Hirzinger
Peter Whalley
Matthias Zessner
& Thomas Hein
with contributions from
Dumitru Drumea
Misha Nistrenko
Marietta Stoimanova
Istvan Zsuffa
Iulian Nichersu
Laszlo Mrekva
University of Natural Resources and
Applied Life Sciences, Vienna
Gregor Mendel Straße 33
A-1180 Wien, Österreich
PREFACE
Growing interest in the use of wetlands for nutrient retention (e.g. World Bank projects in
Bulgaria and Hungary) was one of the main driving forces to prepare the Technical Guidance on
Nutrient Retention Capacities of Wetlands. Scientific evidence, based on experience and
understanding of nutrient processes across the Danube River Basin is needed for further steps
in integration of wetlands in the programme of measures of the European Union Water
Framework Directive.
This Guidance Document serves as an extended summary to the main Technical Report.
The main intention of this document is to emphasize nutrient retention services in riverine
wetlands in concert with other services (e.g. flood protection) and link these ecosystem services
to ecosystem functions and foster thereby the restoration and conservation of natural wetlands
in the Danube River Basin. Benefiting from this linkage also the implementation of the Water
Framework Directive will be supported and will have positive effects on the achievements of the
goals set therein.
The target audience for this document is wetland and river basin managers and thereby
providing a linkage between the environmental conservation and the water management sector.
Furthermore the guidance document is an additional tool to implement one special wetland
function the nutrient retention service into the river basin management plan.
Wetlands are generally recognized for benefits such as water storage (flood protection,
groundwater recharge), hot spots of biodiversity, local and regional water quality control
(riverbank filtration, nutrient storage of inputs from diffusive and point sources), ecosystem
production (timber, agriculture). Considering these benefits the exploitation and alterations of
riverine landscapes has led to a drastic reduction of natural wetland areas, which has been
experienced in the last decades. In context with a sustainable ecosystem perspective
considering the basic ecosystem values related to biodiversity, more innovative and integrated
management approaches are needed to use the benefits without risking a further degradation of
valuable ecosystems in the Danube River basin.
Important to note is that this document is focusing on riverine wetlands. These ecosystems are
defined as frequently connected (annually wetted areas close to river channels), while a
common border for floodplains is an inundation frequency of one in a hundred years - meaning
also a high portion of terrestrial environments.
An important step to emphasize the nutrient retention function of riverine wetlands is the
integration of this topic in wetland and also river basin management. Important to note is that
optimization of one ecosystem function can lead to a reduction of other functions and thus,
needs often a harmonization step. In consequence a prioritization and trade off analysis are
important steps in a decision process.
This guidance document compiles current knowledge and provides a guideline how to implement
the nutrient retention function. The technical background information to that guidance
document is given in the technical report, to be found at http://www.undp-
drp.org/drp/themes_wetlands.html. Detailed and more technical information about the scientific
state-of-the art and the methodological approach and calculation of the case studies are
described therein.
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TABLE OF CONTENTS
1.
Rationale and objectives...................................................................................... 7
1.1.
Rationale....................................................................................................... 7
1.2.
Objectives ..................................................................................................... 7
2.
Wetland policy and International framework........................................................... 8
3.
Current knowledge on Nutrient dynamics in riverine wetlands ..................................10
3.1.
Basic processes of nutrient dynamics in wetlands ...............................................10
3.2.
The role of wetlands and their nutrient retention capacity within river networks ......10
3.2.1.
Nitrogen removal .......................................................................................11
3.2.2.
Phosphorus retention..................................................................................11
3.3.
Hydrology and retention capacity .....................................................................12
4.
Nutrient dynamics in the Danube River BAsin ........................................................13
4.1.
Long term nutrient trends in the Danube River...................................................13
4.1.1.
Phosphorus ...............................................................................................13
4.1.2.
Nitrate .....................................................................................................13
4.2.
Impact of hydromorphology on nutrient retention in wetlands ..............................14
4.2.1.
Total phosphorus .......................................................................................14
4.2.2.
Nitrate .....................................................................................................14
4.3.
Nutrient retention in two different floodplain types as analysed in the case study ....14
4.3.1.
Connected / restored wetland (Regelsbrunn)..................................................14
4.3.2.
Disconnected wetland (Lobau) .....................................................................15
5.
Risks for wetlands related to nutrient retention functions ........................................17
5.1.
Sedimentation...............................................................................................17
5.2.
Accumulation of toxic substances .....................................................................17
6.
Inventory of Nutrient Retention Capacities of Riverine Wetlands within the Danube River
Basin ......................................................................................................................18
7.
Examples for integrated nutrient reduction measures in wetland management ...........19
8.
Recommendations .............................................................................................20
9.
Future prospects for the nutrient retention in wetlands ...........................................28
10.
References .......................................................................................................29
LIST OF TABLES
Table 1: Ranking of nitrate retention of literature values and the case study sites .....................22
Table 2: Ranking of total phosphorus retention of literature values and the case study sites ..22
Table 3: Summary of the monitoring recommendations of DRP 4.3 part 1 ...................................26
LIST OF PICTURES AND GRAPHS
Figure 1 Schematic graphic about the integrative position of the nutrient retention function with
flood protection and habitat protection ..................................................................................................20
UNIVERSITY OF NAT. RESOURCES AND APPL. LIFE SCIENCES, VIENNA
Guidance Document on the Integration of the Nutrient Reduction Function
in Riverine Wetland Management
page 5
ABBREVIATIONS
DRB
Danube River Basin
DRP
Danube Regional Project
EG Expert
Group
EU European
Union
EU WFD
EU Water Framework Directive
GEF
Global Environment Facility
HQ
High discharge (floods of different probability)
ICPDR
International Commission for the Protection of the Danube River
UNDP
United Nations Development Programme
WB
World Bank
EC European
Commission
N nitrogen
P phosphorus
TP Total
phosphorus
DIN
Dissolved inorganic nitrogen
WWTP
Waste water treatment plant
NO3-N
Nitrate - nitrogen
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INTRODUCTION
River ecosystems control the transport of nutrients and organic matter from terrestrial sources,
produce organic material within aquatic environments, degrade organic matter while
transporting it downstream and carry the fingerprint of human activities. Floodplains and other
retention zones are the key components of river ecosystems controlling these functions and act
as biogeochemical hot spots. They also represent functional retention areas, which control and
maintain river water quality. In the line with the water framework directive many efforts and
improvements have been done, mainly in the implementation of waste water treatment plants.
While these measures help to reduce surface water pollution from point sources other non point
source emissions from diffuse sources, like atmospheric decomposition and fertilization of crop
land can still lead to serious water quality problems. Here, riparian zones and wetlands play an
important role in the control of the water quality of surface water systems, by reducing nutrient
input from the catchment as well as reducing nutrient loads already transported in the river
system.
This potentially important role that riverine wetlands can play in improving water quality
through retention and modification of dissolved and suspended nutrient pollution has been
documented by a number of studies and reports, including several that refer to the Danube
River Basin.
In a 1999 report prepared under the UNDP/GEF Danube Pollution Reduction Programme (DPRP)
the significant loss of wetlands in the Danube River Basin, and the potential effect this had on
water quality in the Danube River and Black Sea, was extensively investigated. The report
concluded that, "it is an uncontested fact that recent, inundated floodplains have a positive
effect on water quality improvement and nutrient input reduction if they are not subjected to
intensive agricultural use." The historical loss of riverine wetlands was assumed therefore to
have had a negative effect on the water quality in the Danube River and Black Sea. The
potentially important role of wetland restoration in an overall Danube River Basin nutrient
reduction strategy was noted.
In order to strengthen the understanding of the role of riverine wetlands in nutrient reduction,
further investigations and activities were proposed as part of the UNDP/GEF Danube Regional
Project (DRP). In phase 1 of the project component 4.3 the main activities have been the
evaluation and identification of the most effective monitoring strategies and programmes for
assessing nutrient removal capacities of wetlands as a basis for Danube River Basin guidelines,
to prepare pilot activities that will be carried out in Phase 2 of the DRP and to set the basis for
identifying management measures to optimise the nutrient removal capacity of wetlands in
Phase 2 (Tickner et al. 2004).
This report sets out the results from Phase 2 of DRP Output 4.3, Monitoring and Assessment of
Nutrient Retention Capacities of Riverine Wetlands.
UNIVERSITY OF NAT. RESOURCES AND APPL. LIFE SCIENCES, VIENNA
Guidance Document on the Integration of the Nutrient Reduction Function
in Riverine Wetland Management
page 7
1. RATIONALE
AND
OBJECTIVES
1.1. Rationale
Nutrient enrichment has grown in importance over the last decades because the subsequent
eutrophication appears in increased biomass of algae, species change or loss and also dissolved
oxygen depletion, leading to severe loss of ecosystem functions. This kind of pollution is caused
due to insufficient water treatment (point sources) or non-point sources (e.g. runoff from
agriculture/irrigation) in the catchment and affected river stretches downstream of these sources,
but also delta and coastal areas, where increased loads have accumulated. In the Danube River
basin the increased nutrient loads impacted the conditions along the Black Sea coast. The ongoing
degradation of Black Sea coastal areas has led to a number of scientific and management activities
to reduce the nutrient input from the Danube (UNDP/GEF Danube Pollution Reduction Program
Report, 1999; Kroiss et al., 2005).
The report of phase 1 describes the nutrient balance of the Danube River Basin in terms of
emissions to the river system and emissions from the river system to the Black Sea and the
process for selecting pilot sites at which the nutrient removal capacity of wetlands can be assessed
in greater depth.
Based on the report of phase 1 of the UNDP/GEF Danube Regional Project (DRP) component 4.3
the explicit aim of this guideline is to list recommendations for future management decisions
concerning wetlands in the Danube River Basin (DRB). To do so we use the potential role of
wetlands in nutrient removal capacities as one of the ecological functions and societal benefits
provided by these ecosystems. The guideline gives the basic background on recent policies and
presents results on a survey of wetland projects in the DRB. State-of-the-art information on
nutrient dynamics in wetlands and examples of case studies to demonstrate a more detailed
picture on different pathways and processes involved and the factors controlling these mechanisms
is part of the Technical Guidance Document (TGD) and as result recommendations for future
wetland management actions in the DRB.
1.2. Objectives
The objectives of the DRP study were to:
o Summarizing the current policies and the role of wetlands herein and the potential to
contribute to these policies by effective wetland management (both in terms of
conservation and restoration).
o Summarizing the current knowledge on nutrient retention capacity in wetlands and
analyzing case studies from the DRB in detail.
o Identifying the potential of nutrient retention functions in riverine wetland management
approaches by evaluating recent, running and near-future projects (including the results
from a questionnaire and experience from the demo projects).
o Real world examples how nutrient retention is implemented in wetland management
projects (here summaries of 4 demonstration projects will be highlighting different aspects
of nutrient retention).
o Formulating the guideline for wetland management (motivation and catchment perspective,
implementation and evaluation monitoring of the nutrient retention functions) in concert
with other key ecosystem functions primarily related to biodiversity.
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2. WETLAND POLICY AND INTERNATIONAL
FRAMEWORK
Over the last 150 years there has been a loss of 80% of Danube wetlands due to canalisation,
drainage, etc.. . To prevent further destruction and enhance restoration measures of the Danube
River and its wetlands several documents and policies were developed, also in close connection to
the European Water Framework Directive..
Following policies and programs are of importance for DRB wetlands:
1. Danube River Protection Convention (DRPC): This document forms the overall legal instrument
for cooperation and transboundary water management in the Danube River Basin and came into
force 1998. The primary concern is the maintenance and improvement of the water quality and
environmental protection of the Danube River and to establish a unified River Basin Management
Plan (RBMP). The DRPC also takes into account the specific requirements regarding sensitive and
specially protected waters like wetlands in water quality objectives. (Convention on Cooperation for
the Protection and Sustainable use of the Danube River, ICPDR, 1994) For the basin wide
cooperation between the countries the International Commission for the Protection of the Danube
River (ICPDR) was implemented (Strategic Paper for the Development of a Danube River Basin
District Management Plan, 2002).
2. EU-Water Framework Directive (WFD): The WFD establishes a framework for water policy based
on the principles of integrated river basin management. Wetlands are included in the WFD only if
they are in close context to surface water bodies, parts of surface water bodies or a target of the
objectives for groundwater bodies. However the EU-Water Directors acknowledge pressures on
wetlands and highlight their potential important role in RBM. Due to their functions, like pollution
control, alleviation of droughts and floods, and enhancement of groundwater recharge, wetlands
can help to achieve the WFD environmental objectives more efficiently.
To achieve the aims of the WFD, a Danube characterization analysis was established and identified
four basin wide key water management issues for surface waters:
> organic pollution,
> nutrient pollution,
> pollution resulting from hazardous substances
> and hydromorphological alterations
Such pressures also affect wetlands and causes impacts on the ecological status of water bodies.
Therefore measures to manage these pressures had to be a part of the RBMP. Suggested measures
can be wetland creation and enhancement, because this delivers sustainable, cost effective and
socially acceptable mechanisms for helping to achieve environmental objectives (Issue paper on
nutrient pollution, ICPDR). By the end of 2007 also a list with GIS information of disconnected
floodplains and wetlands of basin wide relevance shall be provided and included for restoration in
the PoM (Issue paper on hydromorphological alteration, ICPDR).
3. Ramsar Convention on Wetlands: An important tool for worldwide wetland conservation and
protection is the Ramsar Convention on Wetlands. It came into force 1975 and the main aim is the
conservation, restoration and wise use of wetlands. Wise use comprises sustainable utilization for
mankind, because wetlands provide many benefits and functions, but without disturbance of the
natural properties of the ecosystem.
To achieve and enhance these functions several documents and technical guidelines were provided,
such as transboundary cooperation, groundwater management, management planning,
implementation of national wetland policies, enhance local people participation and river basin
UNIVERSITY OF NAT. RESOURCES AND APPL. LIFE SCIENCES, VIENNA
Guidance Document on the Integration of the Nutrient Reduction Function
in Riverine Wetland Management
page 9
management (www.ramsar.org). About 80 wetlands of the DRB are included in the List of Wetlands
of International Importance which is implemented by the Convention. Therefore the presented
document will also dwell on several of these Ramsar guidelines.
4. Horizontal Guidance on Wetlands (WFD CIS Guidance Document No 12): Tried to clarify the
characteristics of different wetland types and elaborated the role of wetlands in the WFD. It gives
the recommendation to integrate wetlands in the Program of Measures (PoM). Basic measures
include action directly to protect, enhance or restore wetlands, because they are linked with the
ground- and surface water aims. As part of the PoM, wetland creation, restoration and
management, may prove a cost-effective and socially acceptable mechanism for helping to achieve
the environmental objectives of the Directive, due to the numerous functions and benefits wetlands
can offer.
5. ICPDR Joint Action Program (JAP): It formulates short-term and long-term actions to improve
the water quality in the DRB and to implement a River Basin Management.
The JAP also highlights the role of wetland functions in nutrient reduction, but at the same time
pointed out the lack of knowledge about their long-term efficiency in nutrient removal (Joint Action
Programme, ICPDR, 2001).
6. UNDP/GEF Danube Pollution Reduction Program (DPRP): One of the established projects of the
ICPDR was the Danube Pollution Reduction Program (DPRP) as a basis for further actions to
improve the water quality in the DRB. The identified problems for water pollution were insufficient
waste water collection and treatment on municipal level, insufficient waste water treatment of
industrial enterprises, water pollution caused by intensive agriculture and livestock breeding and
inappropriate waste disposal sites (Danube Pollution Reduction Program, 1999). To minimize these
pollutions also the initiating of wetland restoration and creation projects were considered.
In the frame of this project an evaluation of the potential of wetlands and floodplain areas in the
DRB have been reviewed. 17 wetland/floodplain sites have been identified for rehabilitation
considering their ecological importance, their nutrient removal capacity and their role in flood
protection. The estimated nitrogen reduction by these restored floodplains ranged from 34.000 to
49.000t/year and the phosphorus reduction between 4.000 and 5.800 t/ year (Danube Pollution
Reduction Program Evaluation of Wetlands and Floodplain and Areas, 1999).
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3. CURRENT KNOWLEDGE ON NUTRIENT DYNAMICS IN
RIVERINE WETLANDS
The potentially important role that riverine wetlands can play in improving water quality through
retention and modification of dissolved and suspended nutrient pollution has been documented by
a number of studies and reports, including several that refer to the Danube River Basin. The
following section summarizes the recent literature dealing with nutrient reduction and retention in
riverine wetlands and the involved processes.
3.1. Basic processes of nutrient dynamics in wetlands
Nutrient dynamics between the main channel and the riverine wetlands are dominated by four
basic processes, affecting the nutrient content of the rivers:
Transport: Concentrations of dissolved nutrients do not change very much in relation to the
discharge. Transport of suspended solids and particulate bond nutrients is highly dependent on the
flow regime of the river.
Transformation and storage: Although nutrient transformation and/or storage often are only
temporary in riverine wetlands, the retention and the timing of subsequent nutrient releases to the
main channel may affect water quality there. The key transformation and storage mechanisms and
processes are sedimentation, precipitation, adsorption to and filtration through sediments, algal
uptake, uptake by terrestrial plants and heterotrophic growth.
Removal: In a strict sense of final elimination of nutrients from the system only denitrification and
harvest can be considered as removal. However, also the storage of nutrients over long periods of
time (e.g. decades) may be considered as removal, depending on the time horizons under
consideration in management plans.
Release: Nutrients stored in wetlands may be released over time through erosion of the
sediment/soil layer or re-suspension processes. Stored nutrients may also be transformed into
dissolved forms by mineralization, solution and desorption.
Nutrient dynamics within riverine wetlands differ between wetland types and nutrient compounds:
Nitrogen: Vegetation uptake and microbial denitrification, which results in N loss to the
atmosphere, are the primary mechanisms responsible for N removal in riverine wetland systems.
Phosphorus: Phosphorus is accumulated in wetlands soils and can not be lost in exchange with the
atmosphere. Release or storage of P depends on the overlying water column and associated
biogeochemical processes (adsorption/desorption reactions, precipitation, mineralization of organic
P, and diffusion of P from the soil to the water).
3.2. The role of wetlands and their nutrient retention capacity
within river networks
In riverine wetlands the widening and bifurcating flow channel system and adjacent not flowing
water bodies as well as the exchange with hyporheic1 zones and the groundwater provides slow
1 The hyporheic zone is a region beneath and lateral of river bed, where there is mixing of shallow groundwater
and surface water.
UNIVERSITY OF NAT. RESOURCES AND APPL. LIFE SCIENCES, VIENNA
Guidance Document on the Integration of the Nutrient Reduction Function
in Riverine Wetland Management
page 11
water velocities and large submerged surfaces in intense exchange with sediment/soil complexes.
According to the nutrient spiralling2 concept, this situation results in a high cycling rate of matter
with increased nutrient transformation and retention due to physical, chemical and biological
processes. As a consequence riverine wetlands react conservative to nutrient additions - often
referred to as a buffering capacity, thus providing stability to the running water ecosystems.
Dependent on the stream order, different riparian structures are important for nutrient retention.
Within smaller rivers (low order rivers) vegetated buffer strips along the surface waters are
predominant and form the boundaries to the catchment impacts. A riparian buffer is a streamside
area of trees or other vegetation which can intercept surface runoff, subsurface flow and deeper
groundwater flows for the purpose of removing or buffering the effects of nutrients, pesticides or
other chemicals from upland use, which could otherwise enter bodies of water. In large rivers
(higher order rivers) principally broadened wetland areas are found. Wetlands include marshes,
swamps and bogs as well as some shallow water portions of rivers, lakes and ponds. They are
landscape elements that are permanently or regularly flooded or remain saturated for extended
periods of time during the growing season. Therefore, in the following sub-chapters riparian buffer
stripes, riverine wetlands and the river channel itself are distinguished in their nutrient retention
behaviour.
3.2.1. Nitrogen
removal
Riparian buffer strips significantly remove nitrogen, where subsurface flow reduction is greater
than surface derived nitrogen reductions. Reductions can reach 100%, and often lie between 60%
and 90%. Most of the reduction is assumed to account for denitrification derived losses (resulting
in atmospheric loss); one third is due to plant uptake. Dominating forested buffer strips are
presumed to have a higher denitrification potential over a year's period than grassland ones. The
optimal calculated buffer width for efficient nitrate removal has been found in the literature to be
20-30m
Riverine wetlands have been shown to be important in storing sediment, organic matter, organic
nitrogen and phosphorus. Most of these materials are transported during flood events. Even small
inundated lowland wetlands are helpful in restricting downstream export. Thus enhancing
connectivity between rivers and their wetlands enhances overall retention and reduce N exports
from large basins. Also in wetlands of higher order rivers denitrification is often nitrate limited and
therefore the potential N reduction is driven by water transport into the wetland. Denitrification
also takes place in the riverbed itself.
3.2.2. Phosphorus
retention
Phosphorus retention strongly depends on sedimentation processes, as most of the transported
phosphorus is particle bond. Phosphorus retention appears to be maximised when buffer strips
are composed of dense herbaceous and woody vegetation where stem density and related
sediment deposition explains this P retention efficiency. Riverine buffer stripes may release P to the
groundwater during the dormant season, and may become saturated with nutrients on an annual
basis and therefore become inefficient filters. Although P retention in riparian ecosystems is not
permanent the temporal delay in release can have water quality benefit downstream.
In riverine wetlands phosphorus retention during flood events is strongly related to sediment
trapping efficiency. Most of the phosphorus is transported during flood events. There are
speculations that smaller (annual) flood events lead to the most effective P retention (sediment
2 Nutrient spiralling is formulated in a conceptual framework and applied to running waters, addressing the
nutrient cycling between the water, sediment and the biota, as they are displaced downstream.
UNDP/GEF DANUBE REGIONAL PROJECT
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trapping) because the floodplain is inundated with low water depth (velocity and shear stress is
low).
The riverbed itself may also be a site of sedimentation and phosphorus storage. At high flow
events nevertheless areas of the river sediment will get mobilized again and fine sediment will get
resuspended again.
3.3. Hydrology and retention capacity
The hydrological connectivity of riverine wetlands plays a dominant role in nutrient retention
performance. With increasing surface connectivity the sediment load and the relative inorganic
content of the suspended solids decreases. In disconnected water bodies, turbidity depends mainly
on phytoplankton; its productivity is controlled by nutrient content in the water and at the
sediment surface. Dissolved nutrient concentration increases (approaching riverine values) with
increasing connectivity to the main channel providing nutrient rich water and sediment input. In
disconnected water-bodies the nutrient content also depends on the surrounding land use and the
state of succession, which is often related to the characteristics of the fine sediment layer therein.
Alteration in river hydrology
Flood control measures influence the morphology, lower the river bed, decrease the saturated soil
zone and may permanently lower the water table below the root zone. This alters the floodplain
functions such as storage or release and the directing of water flows.
This alters the hydrological exchange and all related processes such as storage or release and the
directing of water flows. In canalized rivers with little or no buffer zones higher nitrate
concentration are found than in rivers with intact riparian wetlands. The origin of the water supply
(river, river infiltration and seepage, hill slope aquifer) depends on the water-body's location and
its surface and subsurface hydrological connectivity. The water's origin determines the water
temperature, turbidity and nutrient content, which greatly influence habitat heterogeneity, plant
and animal recruitment, and ecosystem productivity. Pulsing connectivity controls nutrient inputs
and the alternation of production and transport phases. Natural floodplains with a mosaic of habitat
and high landscape diversity have a higher potential for water and nutrient retention. Riverine
wetlands which are intensively used by humans may behave either as a source or as a sink
depending on type of organic matter and chemical compounds considered.
The characteristic of these processes point to the fact that phosphorus and nitrogen has to be seen
as two issues, treated separately to understand the functioning, but finally integrated considering
the broad interactions in all management approaches and for their overall nutrient retention
efficiency factors like hydrological exchange, morphological structure, age of the wetland and
nutrient loading are of key importance.
UNIVERSITY OF NAT. RESOURCES AND APPL. LIFE SCIENCES, VIENNA
Guidance Document on the Integration of the Nutrient Reduction Function
in Riverine Wetland Management
page 13
4. NUTRIENT DYNAMICS IN THE DANUBE RIVER
BASIN
For demonstration purposes a Danube stretch between Vienna and Medve was chosen to show
the nutrient retention/removal function in three floodplains. Results are compared to the loads
transported by the Danube considering different hydrological conditions. Consequently, two
years 2002 (wet year, characterized by extremely high Danube discharges, with two HQ10 and
one HQ
3
100 ) and 2003 (dry year, characterized by low discharges) are investigated to point out
how discharge and hydrological exchange affects nutrient dynamics
how these patterns differ between different nutrient species (TP, DIN) and
if altered (Lobau), restored (Regelsbrunn) as well as mainly "artificial" (Szigetköz)
floodplains differ in nutrient retention/removal capacity.
Results from this approach are needed to understand the broad variability of nutrient
retention/removal capacity of riverine wetlands with respect to hydrological variance, to
critically highlight results from single years or events and to give a overview concerning the
dimension of nutrient retention/ losses possibly caused by riverine wetlands on a short term
perspective. The following section summarizes the conclusions from the case study. A detailed
description and results can be found in the long version of the technical report.
4.1. Long term nutrient trends in the Danube River
4.1.1. Phosphorus
TP loads in the Danube were effectively reduced since the 1980. This reduction, was mainly
achieved by point source emission reduction (reduction of P containing laundry detergents at
the end of the 1980s in Austria and Germany and initiation of P removal at WWTPs beginning in
the 1990s).
TP-loads are highly influenced by TP transport at high flow and strongly depend on number and
intensity of high flow events.
Implication to emphasize monitoring of all phases flood events (including rising and
falling limb phases)
4.1.2. Nitrate
Nitrate loads from 1978 to 1998 do not follow the same trend like the TP loads and show only a
slight decrease. The effect of a reduction of NO3-N loads from point loads (WWTP), by a forced
implementation of a denitrification operation step during the 1990s is counteracted by NO3-N
emissions from agriculture, which is the dominant source for nitrate. The dominant pathway for
NO3-N emissions to the surface water is groundwater. Due to slow groundwater velocities
measures in agriculture (e.g. optimization of mineral fertilizer application) does led to a
reduction of NO3-N emissions to the surface water with a certain time delay (years-tenth of
years).
3 HQ10 and HQ100 define the one in 10 years and one in 100 years flood event for this Danube stretch.
UNDP/GEF DANUBE REGIONAL PROJECT
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NO3-N loads show significant variations mainly caused by hydrological conditions and seasonal
variations. Highest loads are found at high flow conditions during spring with low water
temperatures and a low denitrification4 potential.
Implication to monitor groundwater flow and groundwater quality and investigate
extreme floods
4.2. Impact of hydromorphology on nutrient retention in
wetlands
4.2.1. Total
phosphorus
TP loads strong depend on the hydrological conditions. A huge amount of the annual TP load can
be transported within a flood event, which can last only a few days. During this high flow events
in the year 2002 with two (HQ10 and HQ100) TP is effectively retained in unrestricted wetland
areas. This shows the importance of sedimentation processes during flood events caused by a
reduction of the flow velocity and the respective distribution of vegetation (e.g. forests,
grasslands, meadows) in the inundated area.
However, it has to be taken into account that this retention processes can be partly reversible.
Other flood events can remobilize solids from these fluvial areas again and uptake by terrestrial
vegetation leads to transformation of the deposited nutrients. The sedimentation also induces
aggregation processes of the floodplain area and considering former land use in the wetland.
4.2.2. Nitrate
During a flood event and raising water levels NO3-N loads are retained with inundation water.
However, this is only a temporary effect because NO3-N seems to be transported in the same
order of magnitude downstream after the flood had passed and inundation water runs off. In
case of the observed extreme flood event nitrate losses are of minor importance.Therefore the
flood event itself plays only a little role in nitrate retentions in the wetland. Effective losses of
nitrate can be expected only at favourable conditions for denitrification like low flow velocities
and high temperatures.
Summer periods, characterized by stable low flow conditions, show a continuously decrease of
NO3-N loads in the river along the passage downstream. This is caused by denitrification
processes in the main channel itself and connected riparian subsystems (adjacent landscape
elements).
4.3. Nutrient retention in two different floodplain types as
analysed in the case study
4.3.1. Connected / restored wetland (Regelsbrunn)
It is dominated by a former river channel with a total length of 10km. The connectivity with the
Danube was enhanced by lowering the embankments and by artificial dike openings in different
4 Denitrification is the process of reducing nitrate and nitrite into gaseous nitrogen at oxygen depleted
conditions, performed by heterotrophic micro-organisms.
UNIVERSITY OF NAT. RESOURCES AND APPL. LIFE SCIENCES, VIENNA
Guidance Document on the Integration of the Nutrient Reduction Function
in Riverine Wetland Management
page 15
inflow areas providing surface connection at water levels 0.5m below mean water (Schiemer et
al., 1999; Hein et al., 2004). The weirs within the former side channel of the Danube have been
lowered and broadened to produce more pristine conditions (Hein et al., 2005).
At low water level the water inflow to the sidearm system is reduced to seepage and
groundwater of the river and amounts about 0.1 % of the river discharge. The conditions in the
side-arm systems are lentic. At mean water level about 0.8 % of the main channel discharge is
flowing through the side-arm (Austrian River Authority, unpublished report).
At flooding situations the river embankment is overflown and the whole floodplain gets
inundated. Approximately 12 % of the main channel water enters the side-arm at a discharge of
5.000m3s-1. Regelsbrunn is used in this study as an example for a hydrological connected
floodplain.
The calculations for nutrient fluxes show following results:
> Retention capacity for sediment and for total phosphorus (TP) rises with discharge.
> The highest nitrate retention is found at low discharges (below mean water).
> Algal productivity is controlled by the hydrologic exchange and not the availability of
nutrients
4.3.2. Disconnected
wetland
(Lobau)
Like the floodplain segment in Regelsbrunn before restoration, also the Lobau area is dominated
by a former river channel that was severed upstream from the main channel after the main
regulation of the Danube in the 19th century. Weirs, although partly already lowered and
broadened, divide the side-arm into several basins with different connection pattern to the
Danube main channel. Seepage and groundwater supply into the basins play a dominating role
in large parts of the area. Above mean water level (~1900m3/s) the floodplain fragment is
connected to the main channel only at its downstream end. The Lobau is used in this study as
an example for a hydrological altered (isolated) floodplain.
The calculations for nutrient fluxes show following results:
> Nitrate retention peak at higher discharge (elevated mean water flow) and thus,
reduced frequency
> No extensive retention capacity, neither for suspended solids nor for TP due to
restricted surface inflow during floods
> Algal productivity is controlled by nutrient availability of water and sediment
compartments
> Similar pattern are shown for the size of inundated area and shoreline length of all
water bodies within the wetlands.
UNDP/GEF DANUBE REGIONAL PROJECT
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CONCLUSION FOR MANAGEMENT
Results imply that the annual nutrient load transported into the riverine wetland is
very variable and depends highly on the hydrological exchange condition and on the
geomorphic settings of in- and outflow areas.
Any retention capacity is related to the exchange conditions and the existing
landscape pattern (e.g. channel complexity, length of channels and their connectivity,
vegetation patterns- contribution and distribution of different vegetation patches)
Restoring connections will allow uncontrolled water exchange related to the
riverine discharge. Connection during floods is important for TP retention and
sedimentation. Wetland connection during low river discharge is important for the
nitrate removal. For both situations the long term development (especially enhanced
aggradation of wetlands) need to be considered in all management plans.
Ecological functioning is closely linked to the nutrient retention function and
depends on many factors, like hydrologic exchange (surface and groundwater), water
age in the respective water bodies, contribution of shallow areas, sediment conditions
(boundary to the subterranean ecosystem), shoreline length (measure of the
boundary between aquatic and terrestrial landscape elements) and inundation area.
UNIVERSITY OF NAT. RESOURCES AND APPL. LIFE SCIENCES, VIENNA
Guidance Document on the Integration of the Nutrient Reduction Function
in Riverine Wetland Management
page 17
5. RISKS FOR WETLANDS RELATED TO NUTRIENT
RETENTION FUNCTIONS
5.1. Sedimentation
Vegetation in riparian buffer zones controls patterns of sedimentation and erosion where re-
suspension is seen as a process that may occur due to fluvial activity, but sedimentation is seen to
be a relatively irreversible mechanism. Fairly narrow buffer stripes can reduce sediment input to
surface waters, but the long-term effectiveness is not fully known. Wetlands play a distinct role as
a sink for fine sediments, especially during high floods large amounts of transported sediments can
be retained.
5.2. Accumulation of toxic substances
The (bio-) accumulation of toxic compounds in wetlands is one of the risks associated with natural
occurring retention processes. A complex topic involving e.g. diverse chemical processes, biological
hierarchies and food web constellations control these processes. The retention processes of heavy
metals may occur in all compartments within a wetland. The water is effectively scavenged of
heavy metals by precipitation of high molecular weight humic substances and hydrous oxides of
manganese and iron, resulting in transfer of much of the dissolved heavy metals to the sediments
due to adsorption processes which bind inorganic pollutants with varying strength to the surfaces
by sediment colloids. In organisms, biological conversion occurs through assimilation and
metabolism of micro-organisms living on and around the macrophyte and plant uptake and
metabolism.
The use of wetlands to control pollution by means of e.g. heavy metal retention is considered to
accumulate substances, leading to problems in the future because they can only be stored and not
depleted / transformed. For example, the destruction or harvesting of wetland biomass is
considered to release the stored heavy metals into the environment again. It also has to be
considered that processes such as denitrification are negatively influenced by increasing pollution
levels.
UNDP/GEF DANUBE REGIONAL PROJECT
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6. INVENTORY OF NUTRIENT RETENTION CAPACITIES
OF RIVERINE WETLANDS WITHIN THE DANUBE
RIVER BASIN
The objective of the inventory of nutrient retention capacities of riverine wetlands was the
development and demonstration of an inventory methodology to support the harmonised
assessment and monitoring of nutrient retention in the Danube River Basin. Implementation of
complete inventory and creation of a full database was not the objective but rather to keep the
approach simple for demonstration purposes. The collected information is to enable the assessment
of wetland nutrient retention capacity and to enable the comparison of wetlands in terms of
nutrient retention efficiency.
The questions to be answered by the inventory questionnaire were:
·
"Are there gaps in space, time and character in essential information, including monitoring
activities?", "
·
Is the wetland under restoration or are there planned activities that influence significantly
nutrient removal capacities?", "
·
Are there management or land use changes on-going or expected that would impact
nutrient control?" or "
·
Is nutrient removal among the main functions of the managed wetland?".
Wetlands in the DRB are recognized in their nutrient control function, but in comparison with other
wetland functions, like flood control or recreation, it is still of minor recognition and thus, not
integrated in management approaches. In this sense wetlands need a strengthening and a
quantitative aspect which can be provided by nutrient budget calculations in the wetlands.
The questionnaire was sent to 44 wetland restoration projects or wetland areas within the DRB and
17 responses were received. The detailed results are found in the detailed Technical Guidance
report.
Concluding from the results of the inventory of wetland nutrient retention capacity, the following
recommendations are made:
o Floodplain restoration activity takes place, but not all wetland functions and the catchment
context are taken into account
o Objective, design and monitoring should be optimized
o Groundwater monitoring should be integrated
o Provision of basic information in the national language should be encouraged.
o Outcome for future activities:
·
All wetland managers should receive and complete the inventory questionnaire
·
A complete database should be developed on this basis and made available by the
public and by wetland managers for comparisons, evaluation and co-operation
development
·
An internet web application should be created for data supply by the wetland
managers, and for on-line database development and presentation for the public and
interested parties.
UNIVERSITY OF NAT. RESOURCES AND APPL. LIFE SCIENCES, VIENNA
Guidance Document on the Integration of the Nutrient Reduction Function
in Riverine Wetland Management
page 19
7. EXAMPLES FOR INTEGRATED NUTRIENT REDUCTION
MEASURES IN WETLAND MANAGEMENT
This chapter deals with real world examples in the DRB. Examples from 4 demonstration sites
(Hungary, Bulgaria, Ukraine, and Moldova) underline the broad variety of context, which can cause
wetland restoration in the DRB:
> wetland restoration as a necessity (pressures from ecological degradation initiating
human health and economical risks)
> wetland restoration as a political measure (environmental protection, nutrient retention,
flood control)
Each project has a different background and therefore a different approach. The experience of
these projects is also included in the recommendations for measuring nutrient retention in wetland
management. In the following some characteristics of the demonstration sites are outlined.
Nutrient reduction and ecological revitalization on the wetlands of the Danube-Drava National Park
(Hungary, Gemenc and Bèda-Karapancsa)
primary objective: nutrient retention and removal
area: ca. 18000 ha (Gemenc in total)
measures: related to planning unit (Hydrology: e.g. building of weirs, opening of channels)
Wetland restoration and pollution reduction project (Bulgaria, Marshes on Belene Island and
Kalimok/Brushlen Marshes)
primary objectives: nutrient retention and removal; biodiversity
area: Belene Island (1500 ha) and Kalimok-Brushlen Marshes (1500 ha)
measures: management plans, farmer transition support program, development of "green"
business, strengthening of monitoring programs, rise practical awareness, biodiversity and
environmental education program, improve of water management and sustainable management
Monitoring and assessment of nutrient removal capacities of riverine wetlands (Ukraine, Katlabuh
Lake)
primary objectives: reducing salinity, general improvement of water quality
area: lake 68 km2, catchment 1290 km2
measures: reopening the old channel and reconnection to the Danube
Monitoring and assessment of nutrient removal capacity of riverine wetlands (Moldova, Yalpugh
and Cahul wetland areas)
primary objectives: improve surface water quality and groundwater quality in the
catchment
area: overall catchment area: 4300 km2
measures: implementation of nutrient reduction measures on base of nutrient balances by
conserving wetland areas, monitoring the effects on water quality in the catchment and ecological
conditions within the wetland
UNDP/GEF DANUBE REGIONAL PROJECT
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8. RECOMMENDATIONS
River riparian zones and riverine wetlands are key landscapes of strategic importance. They
provide a wide range of ecological and socio-economic goods and services, including flood retention
capacity, groundwater recharge, bioproduction, and aesthetic and recreational values. This
document and the following recommendation focus on one ecological function the nutrient
retention. These recommendations are meant to provide the basis for the next step the
integration of all wetland functions in RBM with the aim to identify them and optimize management
solutions for individual wetlands. To provide these solutions an evaluation of all wetland functions
should be done, followed by a prioritization of these functions decision in the management.
Nutrient retention is partly in contradiction with other functions, so the work needs to be included
in a wise use guideline which integrate all functions, analyze trade offs and finally prioritizes certain
functions for the managers. To assess nutrient retention function information about the
hydrological exchange and the spatial configuration, the contribution and distribution of habitats, is
necessary. Therefore nutrient retention interlinks between flood protection concerns and habitat
protection (Fig. 1).
flood protection
flood protec
habit
ha
a
bit t pr
a
ot
t pr e
ot c
e t
c ion
t
hydy
rologoic
al excx
ha
h ngn
spatial contribution
spatial contributio
e
nutrie
nut
n
rie t re
t r te
e ntion/re
te
mov
ntion/re
a
mov l
a
Figure 1 Schematic graphic about the integrative position of the nutrient retention function with
flood protection and habitat protection
From the management point of view a catchment related wetland cadastral a prioritisation scheme
should support the decision on which wetland should be restored. Obviously this prioritisation
scheme can underlie different subjects with various benefits such as, biodiversity, flood control,
nutrient retention, eco-tourism etc. but should also consider possible primary pressures as
endangerment of human health by environmental pollution or excess of nutrients due to intensive
agricultural use.
The catchments where wetland restoration seems to be most promising with respect to nutrient
loss or retention will be regions with high nutrient emissions which will, in relation to their specific
runoff, lead to high nutrient concentration in surface water. A spatial aspect is that degraded or
modified wetlands in the catchment are situated at strategically important points (e.g. nutrient rich
UNIVERSITY OF NAT. RESOURCES AND APPL. LIFE SCIENCES, VIENNA
Guidance Document on the Integration of the Nutrient Reduction Function
in Riverine Wetland Management
page 21
rivers) and that these wetlands or a sequence of wetlands can retain an appreciable volume of
water, especially during flood events. In the long version of the technical report nutrient emission
situation is shown based on MONERIS5 model calculations.
Which types of wetland in the DRB provide good conditions for nutrient retention?
On base of three different modelling approaches considering i) 388 subcatchments of the DRB
(MONERIS) ii) the Danube and its large tributaries (Danube Water Quality Model) (Kroiss et al.,
2005) and the Danube Delta (Danube Delta Model) (Kroiss et al., 2005) nutrient loss or retention
capacity including all surface water bodies was found to vary over a broad range. Although, these
result stem from different models with different approaches a comparison, as following is helpful to
underline some common but crucial aspects. Results from these models show that wetlands in the
vicinity of low order6 running waters in general provide a higher potential of nutrient retention than
wetlands of large tributaries of the Danube due to favourable conditions in the adjacent surface
water (small watersheds with high nutrient concentrations and a high discharge dynamic).
The Danube Delta provides also good conditions (e.g. low flow conditions and thus extended
residence times, structural diversity) for nutrient retention, but unfortunately, due to river
engineering actually 90% of the Danube discharge flows through three main channels, while only
10% of the discharge enters the Delta complex and its favourable conditions for nutrient
transformation and retention. As a consequence the retention of nutrients in the Danube Delta
seems to be reduced with respect to former times, but its potential for nutrient reduction and
transformation is still very high.
In general adjacent wetlands shall provide following conditions to show a high nutrient retention
potential:
> High share of surface waters in the wetland
> Partly high nutrient concentrations and accumulation of organic matter
> Morphological diversity (e.g total length of wetland channels, shoreline length)
> High diversity of habitats (vegetation types) often referred to as the habitat mosaic
> Changing flowing conditions in parts of the wetland (connection during high and low water
periods)
> Groundwater-surface water interactions
> Large surface area for sedimentation processes during floods
What retention could be expected from riverine wetlands?
Comparing different wetlands from the literature a wide range in nutrient retention could be found.
Nitrate retention range from 31 to 0.0001 t ha-1a-1, where the connected floodplain of our case
study is in the effective group, while the degraded one is found in the rather ineffective group of
floodplains. However these comparisons are only restricted because the results of the most studies
cited are nitrate losses due to denitrification and we can not quantify the different pathways of
nitrate loss in our study nevertheless it gives a good impression of the capacity of different sites.
Table 1: Ranking of nitrate retention of literature values and the case study sites (Regelsbrunn and Lobau). * the
literature values are denitrification rates.
5 Emission Model MONERIS quantifies nutrient emissions from seven main pathways (Erosion, Surface runoff,
Groundwater, Tile drainage, Atmospheric deposition, paved urban areas, Point sources).
6 Stream order refers to a simple algorithm used to define stream size based on a hierarchy of its tributaries,
proposed by Strahler 1952.
UNDP/GEF DANUBE REGIONAL PROJECT
page 22
site description
maximal nitrate retention
reference
(t ha-1a-1)
bogs and fens (drainage basin Baltic Sea)
31
Jansson et al (1998)*
grass buffer strips
5.8
Groffman et al. (1991)*
connected wetland
0.73
case study Regelsbrunn
riverine floodplain
0.597
Johnston (2001)*
floodplain forest (Morawa/Dyje)
0.224
Phare project (1997)*
restored riparian forest
0.069
Ambus & Lowrance (1995)*
floodplain siol (grass or reed)
0.0548
Venternik et al. (2003)*
degraded wetland
0.04
case study Lobau
riparian wetland
0.038
Hanson et al. (1994)*
riparian wetland
0.016
Hanson et al. (1994)*
forested buffer strips
0.0022
Groffman et al. (1991)*
riverine floodplain
0.002
Johnston (2001)*
forested area
0.0001
Groffman (1994)*
The phosphorus retention ranges from 710 to 1.5 kg ha-1a-1, but this high value came from a study
on constructed wetlands and no natural riverine one. However our case study shows that also re-
connected floodplains have a quite high phosphorus retention, but the same case study shows that
a degraded floodplain like the Lobau could be also a source of total phosphorus.
Table 2: Ranking of total phosphorus retention of literature values and the case study sites (Regelsbrunn and
Lobau). The negative value at case study site Lobau indicates phosphorus release from the system.
site description
maximal total phosphorus retention
reference
(kg ha-1a-1)
constructed wetlands
710
Braskerud et al. (2002)
connected wetland
50
case study Regelsbrunn
palustrine wetland
30
Reinelt & Horner (1995)
hardwood forest (CZ)
18
Klimo (1985)
restored wetland receiving agricultural runoff
18
Jordan et al (2003)
Fisher
floodplain meadows (UK)
17.4
Van Oorschot (1996)
and
constructed wetland
8.5
Kovacic et al (2000)
Acreman
restorated prairie pothole wetland
3
Magner et al. (1995)
floodplain forest (USA)
1.5
Richardson (1990)
degraded wetland
-5.5
case study Lobau
(2004) suggest in a review that N and P retention requires different wetland types and it is not of
great use to use mean estimation for both nutrient fractions in wetland management. For example
to enhance phosphorus retention wetland sediments should be oxidized and do not show reducing
conditions, which may be in contrast to the conditions required for denitrification.
These aspects should be taken into account when considering the hydrological, sediment and
vegetation conditions in riverine wetlands.
How to identify and assess the nutrient retention function in riverine wetlands?
UNIVERSITY OF NAT. RESOURCES AND APPL. LIFE SCIENCES, VIENNA
Guidance Document on the Integration of the Nutrient Reduction Function
in Riverine Wetland Management
page 23
In order to maintain or enhance the role of wetlands in water resource management, it is
necessary first to identify and assess the benefits which a particular wetland provides. Three steps
are needed in this process:
o - inventory and description of the wetlands (refer to RAMSAR Resolution VII.20);
o - identification of the particular attributes and functions that may play a role in water
management;
o - quantification of such functions.
The following, recommendations are made on how a monitoring of the nutrient removal capacity
can be implemented at selected restoration sites. It is obvious that a monitoring programme
depends on the available resources, availability of time and the local situation (focus of
investigation) as well as on the scale under investigation and cannot be designed on a general
level. However, it is possible to give some remarks for a draft guideline, using an iterative
approach starting with minimum requirements and a stepwise increase of complexity and validity
of results but also effort and costs which should encourage wetland managers to consider questions
of nutrient retention and losses and point out that even simple measures can be a first step to
provide helpful information.
The following four phases are a stepwise approach to implement the nutrient retention topic into
RBM. These phases include:
> Objective
> design and implementation of nutrient monitoring
> linkage of wetland functions with the catchment scale
> evaluation
Phase I: Estimating the nutrient retention potential
First it is necessary to evaluate the actual nutrient retention/ removal potential of the wetland and
therefore to clarify the Objective for nutrient management.
Following topics should be evaluated:
1 Is the wetland continuously or temporally connected (groundwater or surface water
connected)?
A good potential for nutrient retention or removal capacity is given, if the wetland is
continuous connected to the river at different discharge conditions.
2 Are there possibilities to estimate the discharge to the wetland considering different
hydrological conditions?
This question evaluates, if a quantification of the connection is possible.
3 Does the river stretch adjacent to the riverine wetland show morphological heterogeneity
(e.g. meander), or is it canalized?
If the former river system in the wetland complex is heavily modified by drainage, ditches
and channels, significant amounts of phosphorus can be emitted via groundwater.
4 Are there significant nutrient sources within the wetland area or close by (intensive
agricultural activities-former/actual, settlements, industry, etc.)?
Often the P-enriched and degraded soils (e.g. due to intensive agricultural use) show a
tendency to release phosphorus especially under a temporally shift of redox conditions
UNDP/GEF DANUBE REGIONAL PROJECT
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(mineralisation processes when falling dry and remobilisation from iron bound P when
flooded). Other nutrient emissions can stem from point sources (e.g. industry).
5 Are groundwater or soil data available?
Possible autochthonous nutrient sources, which can be remobilised at special process
conditions and thus counteract retention or removal of nutrients or even lead to additional
nutrient emissions from the system.
This underlines that further information from surface soils, riverbed sediments and groundwater
can offer information to estimate the remobilisation potential of nutrients in a wetland.
Phase II: Minimum requirements for nutrient retention calculations basis for design and
implementation
Black box approach
The simplest approach to calculate nutrient retention in a riverine wetland is input-output
measurements considering discharge, water retention time and water quality data. On base of load
calculations nutrient retention or mobilisation at different hydrological conditions can be estimated.
The results from this monitoring concept depend on:
o Frequency of sampling
o Number of sampling sites
o Time period under investigation
o Evaluation of different hydrological conditions, especially flood events.
This simple monitoring scheme does not consider the influence of potential emission pathways like
groundwater, subsurface flow etc. to or within the system.
Phase III: Emission and balance models as Decision Support Systems (DSS) for specified nutrient
reduction in large wetland regions link to larger scale (and also the screening of additional
pressures)
Using results from emission and balance models like MONERIS (http://danubs.tuwien.ac.at/),
SWAT (http://www.brc.tamus.edu/swat/), SWIM (http://www.wiz.uni-
kassel.de/model_db/mdb/swim.html) or "material account" can lead to additional information
because internal sources, mass flows and the dominant pathways of nutrient emissions, which can
heavily influence net retention or loss of nutrients in a huge wetland area, are considered.
In the case of using the material account approach or the emission model MONERIS, the source
(e.g. formerly fertilised agricultural soils) will be evaluated, the mobilisation calculated and the
flows or emissions will be related to a pathway (e.g. drainage). A rough calibration of the emission
model MONERIS can be achieved by a comparison of the total emissions in the region and the
loads transported at the outlet of the region using different approaches to consider nutrient
retention in the river system (see final report DRP 4.3, phase I). On base of model results,
measures can be implemented to reduce internal nutrient flows (e.g. more stable or higher
groundwater levels by weir regulations) as well as to reduce the source itself (e.g. harvest,
improvement of Waste Water Treatment).
UNIVERSITY OF NAT. RESOURCES AND APPL. LIFE SCIENCES, VIENNA
Guidance Document on the Integration of the Nutrient Reduction Function
in Riverine Wetland Management
page 25
Phase IV: Specific Monitoring for evaluation
From results of phase III a more specific monitoring can be implemented, considering the specific
situation of the wetland. Thus, beneath surface water monitoring other subjects like groundwater,
soils, sediments, inundation water, plants can be included into the programme. A summary of
monitoring parameters and approaches are listed in table 1.
General remarks to the phases suggested
It should be emphasized, that monitoring of the nutrient situation in a restoration site is not useful
only for the calculation of the nutrient retention, but to understand the functioning of the
ecosystem and to derive nutrient management strategies for adjacent point sources and diffuse
sources either, which is helpful for wetland as well as river, river basin and environmental
management in general. The stepwise approach of these phases is needed to fully integrate this
function in the particular wetland management. By the use of these steps an additional benefit is
highlighted and this provides also a support for local and regional acceptance.
Based on sound information a full appreciation and integration of this function interlinked with
other functions is possible.
UNDP/GEF DANUBE REGIONAL PROJECT
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Table 3 Summary of the monitoring recommendations of DRP 4.3 part1
Parameters
sampling site
sampling frequency
note
water level, discharge, flow velovity
normally beweekly, at
Hydrology of surface
all relevant inflow and
and residence time can be
high flow or flood events
waters
outflow channels
deduced
daily
between the main river
and wetland channels
conductivity of the aquifer is
Hydrology of
groundwater slope, groundwater
or between the wetland
nevertheless a factor of uncertainty
groundwater
depth and conductivity
channels and the
so tracer tests might be considered
catchment
nutrient loads : TN, DON, NO3-N, in all relevant surface
sampling strategy should be
(NO2-N), NH4-N, TPfiltered, TPnot water connections
designed so that discharge to load
filtered, PO4-P
between the main river
(or concentration) functions can be
retention/transformation processes:
normally beweekly, at
Transport by surface
and the wetland and as
derived for the different locations as
SS, POM (FPOM, CPOM), TOC,
high flow or flood events
waters
reference in the main
a basis for the calculation of yearly
DOC, Chlorophyll a, O2, pH, T,
daily
river (at the same
loads. This means that event-
conductivity, HCO3 qualitative
places where discharge
oriented sampling at high flow/flood
detection of transformation
is measured)
conditions is necessary
processes: Isotopes as N15 or O18
nutrient loads: TN, DON, NO3-N,
(NO2-N), NH4-N, TP, PO4-P
retention/transformation processes: wel s where main
Transport by
TOC, DOC, O2, pH, T,
groundwater discharge every 1 2 month
groundwater
conductivity, (Fe, Mn) , HCO3
takes place
qualitative detection of
transformation processes: Isotopes
as N15 or O18
Normal y it wil be sufficient to estimate nitrogen inputs by deposition and N-fixation based on information on regional
Deposition, N-fixation
nitrogen depositions and information on the number of N-fixating plants, in order to check the relevance of this inputs. Only
in exceptional cases more detailed investigations will be necessary.
UNIVERSITY OF NAT. RESOURCES AND APPL. LIFE SCIENCES, VIENNA
Guidance Document on the Integration of the Nutrient Reduction Function
in Riverine Wetland Management
page 27
Parameters
sampling site
sampling frequency
note
More detailed monitoring for quantitative assessment of specific transformation processes is not of major importance. If
Storage/Transformation
possible, these indicators should be measured at additional locations inside the wetland as well.
Denitrification has to be derived from the quantification of the nutrient budget of input minus output flows over longer
Removal by
periods of time. Thus all other input and output flows must be known as well as changes in stock. Achieving this must be
denitrifcation
the main emphasis of monitoring. Indicators such as oxygen, DOC, Fe or Mn content or change in 15N contents will help
the interpretation of results and transformation of results to wetlands with similar conditions for denitrifcation.
harvested areas, the harvested
plants, the number of cuts in case
the relevance of removal by harvest
Removal by harvest
of meadows and nutrient uptakes
will be small
of these plants
long-term monitoring: changes of
morphology/relief of the wetland
monitoring the area
(e.g. silting of surface waters) and
sediment samples soon
Long term storage
affected by
the observation of P (and N and
after flood events
sedimentation
organic matter) contents in soils
and sediments of wetlands.
Wetland typology and
classification scheme contained in the project report DRP 4.3 phase 1
wetland vegetation
The use of hydrological models to
Representative sampling
Flood events
discharge
address this issue should be considered
(daily)
UNDP/GEF DANUBE REGIONAL PROJECT
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9. FUTURE PROSPECTS FOR THE NUTRIENT RETENTION
IN WETLANDS
Natural riverine wetlands are key landscape elements and provide multiple functions also for the
benefit of humankind. A well defined and integrated wetland management support the nutrient
reduction function and could be linked to other issues like flood protection.
Results from the EC-daNUbs project imply that a reduction of nutrient loads in the Danube River
Basin found for the last years is to a large extent related to the economical breakdown of the east
European countries. Decreasing nutrient loads transported by the Danube caused a distinct
increase of the water quality in the Danube influenced costal area of the Black Sea.
However, economic restructuring forced by the expansion of the EU with a huge cash flow for
establishing a higher economic status, will lead to increasing nutrient emissions particularly from
the region of the middle and lower course of the Danube.
Implementations of further policies and measures, which significantly can reduce nutrient
emissions and retain or transform nutrients, are of outstanding importance to guarantee the
advancement or even the confirmation of the favorable present status.
Thereby a mix of measures (e.g. construction of Waste Water Treatment Plants, reconstruction and
restoration of riverine wetland sites) seems to be most promising to satisfy the complex socio
economical as well as ecological requirements which have to be considered in the future
development presumably in the Danube River Basin.
With regard to the natural wetlands in the DRB it has to be emphasized that wetland area is
drastically reduced throughout the DRB, remaining wetlands are under risks to loose their basic
ecosystem values. In consequence, all suggestions regarding nutrient retention need to be seen as
an additional benefit for conservation and restoration activities of natural wetlands without leading
to any further degradation of nature conservation values as these are already appreciated to be of
major importance, especially in natural wetlands.
Nutrient retention in restored wetlands can play an important role in sustainable management
approaches - as results from the case study sites underline - but seems to be a proper measure in
particular, because nutrient retention is one positive effect in combination with other ecological and
socio economical benefits especially useful in developing, rural regions.
The integration of wetland management in RBM is urgently needed, as well as the catchment
perspective for a sustainable management of wetlands.
For a future RBMP for the Danube river basin we suggest following points:
> Continuation of monitoring programmes of the demonstration sites (long term
effects)
> Development of an integrated management approach (what are the next steps
to be implemented?)
> Combined efforts in wetland management in the light of the WFD
UNIVERSITY OF NAT. RESOURCES AND APPL. LIFE SCIENCES, VIENNA
Guidance Document on the Integration of the Nutrient Reduction Function
in Riverine Wetland Management
page 29
10. REFERENCES
Ambus P. and R. Lowrance (1995): Comparison of denitrification in two riparian soils. Soil. Sci.
Soc. Am. J. 55: 994
Braskerud, B.C. (2002): Factors affecting nitrogen retention in small constructed wetlands
treating agricultural non-point source pollution. Ecol.Eng. 18: 351-370
Fisher, J. and M.C. Acreman (2004): Wetland nutrient removal: A review of the evidence.
Hydrology and Earth System Science 8(4): 673-685
Groffman, P.M. (1994): Denitrification in freshwater wetlands. In Current topics in wetland
biogeochemistry, Wetland Biogeochemistry Inst. Baton Rouge, LA, 1994; as citied in Lowrance
et al., 1995
Groffman, P.M., E.A. Axelrod, J.L. Lemunyon and W.M. Sullivan (1991): Denitrification in grass
and forested vegetated filter stripes. J. Environ. Qual. 20: 671
Hanson, G.C., P.M. Groffman and A.J. Gold (1994): Denitrification in riparian wetlands receiving
high and low groundwater nitrate inputs. J. Environ. Qual. 23: 917
Hein T., C. Baranyi, W. Reckendorfer and F. Schiemer (2004): The impact of surface water
exchange on the hydrochemistry and particulate matter dynamics in floodplains along the River
Danube, Austria. Sci. of the Total Envir., 328, 207-218.
Hein T., W. Reckendorfer, J. Thorp and F. Schiemer (2005): The importance of altered
hydrologic retention in large regulated rivers: examples from the Austrian Danube. Archiv f.
Hydrobiologie, Large Rivers 15: 425-442
Jansson A., C. Folke and S. Langaas (1998): Quantifying the nitrogen retention capacity of
natural wetlands in the large-scale drainage basin of the Baltic Sea. Landscape ecology. 13(4):
249-262
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Relation to Geomorphology of Riverine Wetlands. Soil Sci. Soc. Am. J. 65: 577588
Jordan, T.E., D.F. Whigham, K.H. Hofmockel and M.A. Pittek (2003): Nutrient and sediment
removal by a restored wetland receiving agricultural runoff. J. Environ. Qual. 32: 1534-1547
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VSICEK,F. (eds.): Floodplain forest ecosystem. I. Before water management measures,
Academia Praha: 425-459
Kovacic, D.A., M.B. David, L.E. Gentry, K.M. Starks and R.A. Cooke (2000): Effectiveness of
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Kroiss H., C. Lampert, M. Zessner, C. Schilling and O. Gabriel (2005): "DANUBS - Nutrient
Management in the Danube Basin and its Impact on the Black Sea, EVK1-CT-2000-00051, Final
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UNIVERSITY OF NAT. RESOURCES AND APPL. LIFE SCIENCES, VIENNA
Guidance Document on the Integration of the Nutrient Reduction Function
in Riverine Wetland Management
page 31
GLOSSARY
Autochthon Material or organic matter which is produced in the river/ water body itself e.g.
phytoplankton which is the food basis for zooplankton. The contrary is allochthon e.g. leaves /
litter from the surrounding trees.
Bifurcation - The separation of a stream into two parts. The creation of distributaries is the
consequence of bifurcation
Constructed Wetlands Constructed wetlands are wetlands specifically built to act as natural
pollution control plants and are not directly comparable to natural wetlands.
HQ 1 HQ 100 Statistic expectation for the discharge at flood events, based on long term
monitoring. The numbers stand for the annularity and the probability that this event takes
place.
Hyporheic zone - Defined as a subsurface volume of sediment and porous space adjacent to a
stream through which stream water readily exchanges. Although the hyporheic zone physically
is defined by the hydrology of a stream and its surrounding environment, it has a strong
influence on stream ecology, stream biogeochemical cycling, and stream-water temperatures.
Thus, the hyporheic zone is an important component of stream ecosystems.
Mineralization A process where a substance is converted from an organic substance to an
inorganic substance caused by microorganisms. Two important mineralization processes are the
ammonification and the nitrification.
Nutrient Retention The term nutrient retention is often used as a substitute for storage and
has a similar meaning.
Nutrient Removal - In contrast to "storage", "removal" is the final elimination of nutrients out
of a river by wetland system in a way that no future release from the wetland system to the
river will happen. In this sense only denitrification and harvest can be considered as "removal"
out of the river and wetland system. Storage (retention) of nutrients over long periods of time
(e.g. decades) may also be considered as removal, depending on the time horizons under
consideration.
Nutrient spiraling concept - A concept to explain the transport and transformation of
nutrients along river stretches
Nutrient Storage - Storage can be considered as temporary (although often long lasting i.e.
years or decades) retention in the wetland system. Main mechanisms and processes that lead
to storage are: sedimentation, precipitation, adsorption and filtration to sediments, algae and
plant uptake, as well as heterotrophic growth.
Nutrient Transformation Are the processes by which nutrients are altered in their state i.e.
denitrification or incorporation into plant matter.
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Redox potential (reduction potential) - In aqueous solutions, the reduction potential is the
tendency of the solution to either gain or lose electrons when it is subject to change by
introduction of a new species. A negative redox potential indicates reducing conditions whereas
a positive indicates oxidizing conditions. Reducing condition lead e.g. also to phosphorus re-
solution from the sediment into the water column which may enhance eutrophication processes.
Riverine Wetlands - Riverine wetland are those wetlands situated by channels with moving
water, and also near deepwater habitats. In some parts the average depth of the channel is at
least 2 meters. Here we concentrate on riverine wetlands with connected (currently or formerly)
palustrine and/or lacustrine systems in the whole catchment. In this sense it is including also
floodplain, even former. We can call it riverine wetland system sensu lato.
Shear stress a parallel or tangential force to the surface of the river bed with an abrasive
effect
Stream Order The stream order system is a simple method of classifying stream segments
based on the number of tributaries upstream. A stream with no tributaries (headwater stream)
is considered a first order stream. A segment downstream of the confluence of two first order
streams is a second order stream. Thus, a nth order stream is always located downstream of
the confluence of two (n-1)th order streams.
Water age Number of days the water of the river is in the wetland. River water = day 0
UNIVERSITY OF NAT. RESOURCES AND APPL. LIFE SCIENCES, VIENNA