Potomac Highlands Watershed School

From Cacapon December 2001

Why Sediment Matters

The sediment found in rivers is the product of erosion: runoff and high water naturally washes soil particles into rivers. But poor land management practices, such as failing to stabilize construction sites, can greatly accelerate erosion. Excess sediment in a river harms aquatic life in many ways and also poses a  problem to people.

West Virginia's high gradient mountain streams are naturally clear and have naturally rocky bottoms with little silt. The animals and plants that live in these streams are adapted to these conditions. Many do not readily adapt to silt; some will simply drift with the current from affected areas, others will be buried and die.  Suspended sediment reduces the amount of sunlight that penetrates the water, retarding growth of  aquatic plants, which are important sources of food, shelter and nesting habitat for fish and aquatic insects. Sediment also suffocates nesting grounds for fish and fills the homes of insects and other invertebrates that  live in the tiny spaces between pebbles and rocks. Reproductive success may decline with an increase in fine sediment. Many animals living in high gradient streams deposit their eggs in gravel or on rocks. Burial with fine sediment prevents the circulation of water around these eggs, which decreases oxygen levels. Eggs may suffocate or may be poisoned by their own metabolic wastes.

Many of the invertebrates in our streams are filter-feeders, and the number of filter feeding invertebrates tend to decline if their filter feeding mechanisms be-come clogged with suspended sediment. Fish may also suffer clogging and abrasive damage to gills. By altering habitat and preventing reproduction by both fish and invertebrates, sediment alters the composition of river-bottom animal communities. Areas once occupied by gravel loving species, such as trout and many mayflies, may be replaced by mud loving fish and worms.

Excess sediment can also have serious implications for people. It can increase the frequency and severity of flooding, the cost of doing business, and the avail-ability of safe drinking water. The risk of flooding increases because as sediment piles up, the river becomes shallower and wider. The riverbed's capacity to contain high water is reduced.  Industry and water treatment plants that use river water are impacted because suspended sediment can clog, scour or otherwise damage industrial pipes, machinery and water treatment systems. This drives up maintenance costs and makes the water source less economical to use which costs us all in the long run.