Tuesday, December 6, 2011

The Effects of Sediment on Bay Grasses

Native grasses help ecosystems.

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The Chesapeake Bay is an estuary located along the mid-Atlantic coast. This estuary, a mix of fresh water and sea water, is more than 200 miles long and home to a diverse population of fish, plants and animals. One plant group, called bay grasses, includes varieties of underwater grasses that provide marine habitat while stabilizing the Bay. Some sediments benefit bay grasses while other sediments kill the underwater grasses.

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Bay grasses, called submerged aquatic vegetation (SAV), live underwater by rooting in sediment and filtering nutrients from the water. The plants thrive in sand or mud sediment with low organic content as they are harmed by excess nutrients such as nitrogen and phosphorous. Through photosynthesis, the plants convert carbon dioxide to oxygen in the water. The plants cover more than 40,000 acres in the vast Bay. The Chesapeake Bay is affected by watershed drainage from the District of Columbia and states including New York, Pennsylvania, Maryland, Delaware, Virginia and West Virginia.


Bay grass roots and foliage hold underwater soil in place and reduce erosion by trapping floating sediment. The buoyant grass vegetation slows wave action and water flow, providing calmer waters for bottom-dwelling clams, crabs and other species. SAV provides habitat for fish and food for waterfowl. The leafy vegetation is nursery habitat for fish and other marine life. Bay grasses such as eelgrass grow ribbon-like leaves up to 4 feet long and provide shelter for small fish and crabs hiding from predators.


When too much sediment floats in the water due to land erosion or other disturbances, it makes water cloudy and blocks bay grasses from critical sunlight needed for plant health. The suspended sediment, washed down from urban construction or agricultural use, contains excess nitrogen from fertilizer, pollution and other sources that boost algal growth. Algae further clouds the water, hindering bay grass growth. When too much sediment washes down, it suffocates bottom plants and builds deposits that destroy fragile wildlife habitat.


In addition to destroying bay grasses, sediment washed into Chesapeake Bay causes other serious problems. The sediment promotes excess algae production. High accumulations of algae absorb oxygen in the water and produce scum deposits that kill fish and shellfish. Some algae produce toxins harmful to humans and other animals. Excess sediment deposits bury bottom-dwelling plants and animals, smothering oyster and clam beds. The contaminated sediment-laden water contains toxic chemicals and human contaminants that cannot be filtered out by the bay grasses. Tons of sediment accumulate, impeding waterways and affecting boat traffic. Dredging is necessary to keep ports and boat channels clear.

ReferencesMaryland Department of Natural Resources: Bay GrassesU.S. Geological Survey; The Impact of Sediment on the Chesapeake Bay and its Watershed; Scott Phillips, et al.; June 2005Virginia Institute of Marine Science; Study Shows Bay Clean-up Helps Boost Underwater Grasses; David Malmquist; July 2010Maryland Department of Natural Resources: Harmful Algae Blooms in MarylandResourcesUniversity of Maryland Extension; Saving Your Soil and the Chesapeake Bay; Peter J. Ricciuti, et al.Photo Credit Hemera Technologies/Photos.com/Getty ImagesRead Next:

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