Shellfish and finfish production is also reduced. These problems are linked, in part, to contamination from nutrients, sediment, animal waste, and other pollutants associated with agricultural and urban runoff. These laws have done much to clean up point source contaminants by requiring states to establish and enforce water quality standards, by requiring specifications and licensing for the discharge of effluents, and by funding the installation of municipal sewage treatment plants. Nonpoint source pollutants include sediment, nutrients, pesticides, animal wastes and other substances which enter our water supply as components of runoff and groundwater flow. The streamside forest functions as a filter by removing sediment and other suspended solids from surface runoff.
Sediment is probably the most common and most easily recognized of the nonpoint source pollutants.
Sediment suspended in the water can reduce or block the penetration of sunlight, adversely affecting the growth and reproduction of beneficial aquatic plants. Sediment deposited on the stream bottom can interfere with the feeding and reproduction of bottom dwelling fish and aquatic insects, weakening the food chain. Large deposits of sediment can overfill stream channels and floodplains, greatly increasing the potential for flooding. Several mechanisms of sediment removal are at work in the streamside forest. Some sediment settles out as the speed of the flow is reduced by the many obstructions encountered in the forest litter.