Issue 7: Suspended solids

Suspended solids in aquatic systems play an important role in the transport and fate of many chemicals in the environment. Contaminants (and also nutrients, trace elements, organic compounds, and bacteria) frequently attach themselves to suspended particles, which can travel in the suspended solid load, and settle in distant locations. Suspended solids also decrease water clarity and may inhibit photosynthesis and decrease food production. In addition, excessive suspended solids eventually settle out and may fill or smother important spawning and rearing habitats.

Suspended solids consist of an inorganic fraction (silts, clays, etc.) and an organic fraction (algae, zooplankton, bacteria, and detritus). The inorganic portion is usually considerably higher than the organic. Both contribute to the turbidity of the water.

Sources of suspended solids include:

Stormwater runoff- Excessive precipitation during storm events can significantly increase runoff and subsequently increase suspended particles from urban and rural lands.

Land alteration- Construction of residential and commercial structures, road building, logging and agricultural activities expose lands to possible erosion and land slides during rainy periods

Photosynthetic activity- Algal blooms resulting from increased sunlight in spring and summer can increase the suspended solids load

River and stream alterations- Activities affecting streambeds or riparian areas along tributary streams may increase the possibility that high flows will trigger increased erosion. Turbidity and suspended solid concentrations increase as a result

Dams and reservoirs- Dams and reservoirs trap suspended sediments and decrease or alter their downstream distribution

Irrigation returns- Waters withdrawn for irrigation purposes may erode soils and return those materials to local waterways

Indirectly, suspended solids affect other parameters such as temperature and dissolved oxygen. Because of the greater heat absorbency of the particulate matter, the surface water becomes warmer and this tends to stabilise the stratification (layering) in stream pools, embayments, and reservoirs. This, in turn, interferes with mixing, decreasing the dispersion of oxygen and nutrients to deeper layers.

GIWA definition

Suspended solids refers to the adverse effects of modified rates of release of suspended particulate matter to water bodies resulting from human activities.

Environmental impacts

1. Habitat modification

2. Changes in biological community composition

3. Changes in growth/survival/reproduction of species

4. Reduced productivity

5. Enhanced erosion of coasts and river channels

6. Increased sediment deposition and siltation

7. Destruction (blanketing) of benthic communities

8. Changes in sediment redox conditions

Indicators

The following are environmental impact indicators for suspended solids.

Select the environmental impact indicators that are relevant from the list below and input data into the appropriate indicator sheets.

HYD

Hydrological

Parameters

Biological

Miscellaneous (seagrass and coral reef)

Pollution

Proxy indicator of suspended solid pollution