Sediments

Sediment is made up of loose particles of clay, silt and sand. It is a natural part of the Bay, created by the weathering of rocks and soil. However, in excess, sediment can have a negative effect on water quality in the Bay and its tributaries.

Where does sediment come from?

There are two major sources of sediment in the Bay:

• Watershed sources, due to the erosion of land and stream banks and corridors. Watershed erosion is accelerated when land is cleared of vegetation for agriculture and development. Scientists estimate that watershed sources contribute the majority of the sediment that goes into the Bay.
• Tidal sources, from the erosion of shoreline and nearshore areas, and resuspension of previously eroded sediments. Tidal erosion is also accelerated by the removal of shoreline vegetation and a lack of underwater bay grasses, which soften wave action.

Approximately 8.5 million metric tons—or more than 18.7 billion pounds—of sediment are believed to enter the Bay each year.

How are sediments a pressure on the Bay?

Excess suspended sediment is one of the largest contributors to the Bay's impaired water quality. The culprits are the tiny clay- and silt-sized fractions of sediment. These particles are frequently suspended in the water because of their size and can be carried long distances during storms. In excess, these smaller grains of sediment cloud the water, reducing the amount of sunlight that reaches bay grasses. Without enough sunlight, these underwater grasses are not able to grow and provide habitat for young fish and blue crabs.

Large amounts of sediment can have other harmful effects on the Bay's ecosystem.

• Nutrients and chemical contaminants can be carried with sediment, impacting fish and other living things in the Bay, as well as humans and animals that swim in it.
• Oysters and other bottom-dwelling species can be smothered when sediment settles to the bottom.
• Sediment can accumulate in ports and channels, which affects commercial shipping and recreational boating.
• Sediment is the primary cause of degraded habitat in many of the Bay watershed's streams.