Why is sediment important?

Sediment carried in water has a variety of effects. What are they and why are they important?

Toxic chemicals

Sediment plays a major role in the transport and fate of pollutants and so is clearly a concern in water quality management. Toxic chemicals can become attached, or adsorbed, to sediment particles and then transported to and deposited in other areas. These pollutants may later be released into the environment. By studying the quantity, quality, and characteristics of sediment in the stream, scientists and engineers can determine the sources and evaluate the impact of the pollutants on the aquatic environment. Once the sources and impact are known, action can be taken to reduce the pollutants. The association of toxic chemicals with sediment is an issue of national importance.

Navigation

Deposition of sediment in rivers or lakes can decrease water depth, making navigation difficult or impossible. To ensure access, some of the sediment may be dredged from the stream or harbour, but this may release toxic chemicals into the environment. To determine how much dredging needs to be done and how often, water levels must be monitored, and the rates of sediment transport and deposition estimated. Sedimentation of navigation channels is a concern in the Fraser River (British Columbia), the Mackenzie River (Northwest Territories), and the Great Lakes - St. Lawrence system (Ontario and Quebec).

Fisheries / Aquatic habitat

Streamborne sediment directly affects fish populations in several ways:

• Suspended sediment decreases the penetration of light into the water. This affects fish feeding and schooling practices, and can lead to reduced survival.
• Suspended sediment in high concentrations irritates the gills of fish, and can cause death.
• Sediment can destroy the protective mucous covering the eyes and scales of fish, making them more susceptible to infection and disease.
• Sediment particles absorb warmth from the sun and thus increase water temperature. This can stress some species of fish.
• Suspended sediment in high concentrations can dislodge plants, invertebrates, and insects in the stream bed. This affects the food source of fish, and can result in smaller and fewer fish.
• Settling sediments can bury and suffocate fish eggs.
• Sediment particles can carry toxic agricultural and industrial compounds. If these are released in the habitat they can cause abnormalities or death in the fish.

Forestry

Some forestry practices have negative impacts on the environment. Extensive tree cutting in an area may not only destroy habitat but increase natural water runoff and accelerate soil erosion. These can lead to increased flow and sediment loads in nearby streams. They can also release chemical substances occurring naturally in forest soils, and allow them to contaminate rivers or lakes. Both the chemicals and the additional sediment can harm fish and other organisms. Sediment problems resulting from forestry practices are prevalent in British Columbia, Ontario, Quebec, New Brunswick, and Newfoundland.

Water supply

Sediment can affect the delivery of water. When water is taken from streams and lakes for domestic, industrial, and agricultural uses, the presence of sediment in the water can wear out the pumps and turbines. As this increases maintenance costs, it is important to determine the amount of sediment in the stream so that the appropriate equipment can be chosen when designing a water supply plant.

Energy production

The amount of sediment transported affects both the size and the life expectancy of reservoirs created for power generation. A dam traps sediment that would normally be carried downstream, and that sediment decreases the size of the reservoir and thus its use for power generation. Therefore, it is necessary to know the amount of sediment to ensure the effective design of reservoirs for the long term.

Agriculture

Some farming practices increase soil erosion and add toxic chemicals to the environment. Thus, productive soil is lost to farms, sediment and pollutants are added to streams, and maintenance costs of irrigation systems are increased. Sediment data and information are necessary in the evaluation of cropping practices and their environmental effects. Sediment-related problems associated with agriculture occur across the country.

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