Sediments

Sediment is made up of loose particles of clay, silt and sand. It is a natural part of the Chesapeake Bay, created by the weathering of rocks and soil. However, in excess, sediment clouds the waters of the Bay and its tributaries, which harms fish, oysters and underwater bay grasses.

How Does Sediment Harm the Chesapeake Bay?

Excess sediment suspended in the water is one of the leading causes of the Chesapeake Bay's poor health. The culprits are the tiny clay- and silt-sized fractions of sediment. Because of their small size, clay and silt particles often float throughout the water, rather than settling to the bottom, and can be carried long distances during rainstorms.

When there is too much sediment in the water, the water becomes cloudy and muddy-looking. Cloudy water does not allow sunlight to filter through to bay grasses growing at the bottom of the Bay's shallows. Just like plants on earth, bay grasses need sunlight to grow; without it, these underwater grasses die, which affects the young fish and blue crabs that depend on bay grasses for shelter.

Large amounts of sediment can have other harmful effects on the Chesapeake Bay and the people who use it:

• Nutrients and chemical contaminants can bind with sediments, allowing the pollutants to spread throughout the Bay and its local waterways. Fish and shellfish that live and feed near contaminated bottom sediments can themselves end up contaminated, triggering fish consumption advisories in various rivers and portions of the Bay.
• Oysters and other bottom-dwelling species can be smothered when excess sediment settles to the bottom.
• Excess sediment is the primary reason that many of the Bay watershed's streams are degraded.
• Ports and channels can become clogged by accumulated sediment, affecting commercial shipping and recreational boating.

Where Does Sediment Come From?

More than 18.7 billion pounds of sediment are believed to enter the Chesapeake Bay each year. There are two major sources of this sediment: watershed sources and tidal sources.

• Erosion of the land and stream banks are watershed sources of sediment. Watershed erosion increases when land is cleared of vegetation for agriculture and development. Scientists estimate that the majority of the sediment that flows to the Chesapeake Bay comes from watershed sources.
• Erosion of shorelines and nearshore areas, as well as the resuspension of previously eroded sediments, are tidal sources of sediment. Tidal erosion increases when shoreline vegetation is removed and there are not enough bay grasses growing in the shallows to soften wave action against the shoreline.