NUTRIENTS, PATHOGENS AND BIOTOXINS
The addition of excessive nutrients from agricultural runoff, atmospheric deposition, and sewage treatment plants continue to threaten the health of coastal, estuarine, and riverine systems.�

As shown below, each year an area off Louisiana the size of New Jersey becomes a "Dead Zone" - depleted of oxygen.� Fish, shrimp and other fishery resources are eliminated.� The cause: excess nutrient loading.� Fertilizer and manure from farms throughout the Mississippi River drainage (covering 2/3 of the lower 48 states) needs to be cut sharply to repair this oxygen-deprived area.� In 1999, a White House study concluded the most cost-effective way to protect the Gulf would be to reduce fertilizer use by 20% and restore 5 million acres of wetlands to trap nutrients before they reach the Mississippi R. and its tributaries.� The Gulf's Dead Zone doubled in size to 7,000 sq. mi. after widespread Mid-west flooding in 1993, and has fluctuated annually since then depending on flows of the Mississippi.� The problem stems from algae that thrive on the excess nutrients.� As they die their decomposition robs the water's dissolved oxygen needed by fish and other marine life.�

Shellfish bed closures due to sewage loading exist coast-wide.� On any given day, one-third of the nation's 17.8 million acres of shellfish waters are closed, and in the Gulf of Mexico, 52% are restricted (USDC 1991) due, in part, to water quality degradation caused by inadequate septic systems, sewage discharges, and urban runoff.� Excessive additions of nutrients can stimulate nuisance and toxic growths of algae and deplete oxygen when these growths decay, frequently causing kills of fish and other resources.� Like the Dead Zone off Louisiana, nutrient over-enrichment is believed responsible for the loss of Chesapeake Bay's native seagrasses, a primary habitat for many juvenile fish and shellfish.� However, Federal grants for upgrading municipal sewage treatment systems have improved water quality in many areas, compared to pre-Clean Water Act conditions.� In 1991, beaches were closed or advisories issued against swimming on more than 2,000 occasions in states that monitor beach quality (only four states monitor the entire length of their shoreline).� Humans can contract a variety of diseases of bacterial and viral origin, such as gastroenteritis and hepatitis, if they become infected with pathogens associated with human sewage, through ingestion during water-based activities or through the consumption of contaminated raw or lightly cooked molluscan shellfish.� Shellfish growing waters may be affected by blooms of several species of diatoms and dinoflagellates that can cause a variety of human illnesses.� For example, some of Maine's productive shellfish growing waters have been closed for most years since 1958 because of the presence of dinoflagellate blooms responsible for paralytic shellfish poisoning.� The occurrence of these blooms is now affecting all productive shellfishing waters of the U.S. and at an increasing frequency, potentially stimulated by coast-wide nutrient over-enrichment.
"Dead Zone" off Louisiana
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Habitat
Habitat Protection Division
Inshore-Dependent Fish and Shellfish
Primary
Causes of Fishery Population Declines
Dams and Flow Diversions

Wetland Destruction

Toxic Contaminants

Cumulative Effects

Economic Benefits of Effective Habitat Protection

References


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