Toxic Chemicals: Page 10 Endangered Species Handbook

Aquatic Ecosystems

Toxic Chemicals: Page 10

Chesapeake Bay is the largest expanse of saltwater estuary in the United States. Covering 64,000 square miles, its marshes are watered by its major feeders, the Potomac, Susquehanna, Rappahannock and Patuxent Rivers, along with countless smaller feeder streams from its Maryland and Virginia shores. More than 150 rivers and streams contribute to its 650-mile-wide watershed, which extends over portions of six states (White 1982). The Bay is bordered by 8,100 miles of shoreline, including its tributaries (White 1982). The growth of Washington, D.C. and Baltimore and Annapolis, Maryland, as well as other large cities and suburbs on Chesapeake Bay, and the growth of agriculture that leeches sediments and chemicals, have been responsible for destroying large portions of this great estuary. About 140 square miles of the watershed are built on every year. Urban and suburban growth, agriculture, overfishing and industrialization have all taken a toll on the water quality of Chesapeake Bay. The raising of chickens and hogs in factory farms in the region has increased over the past few decades, producing enormous quantities of fecal material that contaminate rivers and the Bay. During storms, containment ponds have overflowed, pouring pollutants into the waterways which have been implicated in outbreaks of red tide and bacterial disease (Broad 1996). Runoff of pesticides, herbicides, sewage, fertilizer and sedimentation have turned the once clear waters murky in many parts of the Bay. The fragile ecosystem of sea grasses and marshland is damaged.

Fisheries that once produced 28 million pounds of oyster meat and 55 million pounds of blue crab have plummeted. The disappearance of 90 percent of the sea grass from Chesapeake Bay, mainly as a result of chemical pollution and sedimentation, has brought about a crash in blue crab populations, with closures in fishing seasons. Crabs lay eggs and shelter in sea grass. Oyster harvests are now 1 percent of what they were a century ago. Their populations have plummeted, and only with their absence is the role that they play in the health of Chesapeake Bay becoming clear. Originally, the billions of oysters filtered the complete volume of water in the Bay in a three-day period, clarifying the water and removing pollutants (Daily 1997). Their ecological value far outweighed the revenue they produced for fishermen. Overfishing has played a role in the decline of oysters, but the major problem is the disintegration of this once-productive estuary through losses of sea grasses and sedimentation from development and pollution. Another casualty was the Maryland darter (Etheostoma sellare), known only from a creek in the northern tributaries of Chesapeake Bay. Not seen for many years, some authorities, including the International Union for the Conservation of Nature (IUCN), consider it extinct (Baillie and Groombridge 1996). The shortnose sturgeon (Acipenser brevirostrum) historically ranged throughout the Chesapeake Bay area, where thousands were caught annually. Dams, overfishing and pollution combined to eliminate this sturgeon, and spawning no longer occurs in any of the Chesapeake's feeder rivers. The species is threatened throughout its eastern range and is listed on the Endangered Species Act.

Decades after the Clean Water Act came into effect, the Environmental Protection Agency (EPA) announced in 1996 that only 40 percent of the country's waterways are suitable for swimming or fishing because of pollution from various sources. In 1997, residents of 47 US states were warned by EPA not to eat certain types of freshwater fish after issuance of some 2,200 fish consumption advisories, a new high. These advisories list 45 contaminants in lakes and rivers, including mercury, PCBs, chlordane, dioxin and DDT. In many parts of the United States, well water has been found to be contaminated with pesticides and herbicides. This is especially severe in the farm belt of the Midwest, where the majority of these chemicals are used. According to the EPA, 1.25 billion pounds of weed and pest killers were used throughout the United States in 1995, an all-time high. Pesticide and herbicide runoff from agricultural fields was found in half of more than 500,000 miles of rivers tested by the EPA in 1995. Homeowners pouring these chemicals on their green lawns are also contributing to the contamination of streams, rivers and water supplies. A new contaminant of groundwater is a gasoline additive, methyl tert-butyl ether (MTBE). This chemical was designed to reduce air pollution to allow gasoline to burn more cleanly, but because of leakage from gasoline tanks around the country, it has entered the groundwater in every state and has been detected in 5.4 percent of wells in a US Geological Survey study. Other solvents added to gasoline were found in 47 percent of urban wells and 14 percent of rural wells (Saar 1999). The drinking-water limits set by EPA were exceeded in many of these wells (Saar 1999). This chemical is suspected to be a carcinogen.

Contamination of aquatic ecosystems has occurred throughout the world. It has played a role in endangering one of the world's rarest birds, the crested ibis (Nipponia nippon). Unlike any other ibis in appearance, the bird has white or pearl gray plumage, a shaggy mane of feathers and salmon pink tail feathers, which contrast with bare red facial skin and carmine red legs. Only 66 birds remain, up from 22 birds in the early 1990s, with a captive population in two breeding centers of over 100 birds (BI 2000). These elegant birds once ranged from southeast Siberia, Manchuria and China to as far east as Korea and Japan. For centuries they were hunted for their long nuptial plumes, nearly causing their extinction (Schreiber et al. 1989). The Japanese population of the crested ibis declined until only the tiny Sado Island held the last population; the eggs and chicks were killed by crows and jays, and the last birds were taken into captivity (Schreiber et al. 1989). Extinct in Siberia in 1917 and thought extinct in China by 1958, a pair was found nesting in Shaanxi Province in central China in 1981. This only remaining breeding population has slowly increased, but with fewer than 100 birds in the wild, it remains endangered (BI 2000).