According to Johns Hopkins University paleoecologist Grace Brush, there are no closed ecosystems. What happens to one is likely to affect others. The Chesapeake Bay and its 64,000-square-mile watershed demonstrate this. Human activity in the watershed over the past 300 years, particularly in the last century, is the primary cause of the long, downhill slide of the Chesapeake ecological system, including the vanishing wetlands, clogged rivers and streams, agricultural and industrial runoff, polluted water, destroyed bottom habitats, diversity decline, and the local extinction of whole communities of fish, oysters, clams, crabs and other benthic organisms.

Environmental Records

Studies by Brush and others show that habitat destruction in the bay is caused primarily by the continuous flow of pollution, nutrients and soil-eroded sediment from extensive deforestation, development and agriculture in the upland watershed. From bottom core samples taken in the bay and its tributaries, Brush reconstructed a history of estuarine changes over time. Core samples contain environmental records, not only of the chemical composition of sediment layers but, like tree rings, the rates at which layers have accumulated, including during storm peaks. As long as the watershed was primarily forested, the ecology of the bay remained relatively diverse and healthy. However, from the late-1800s on, increases in sediment, nutrients and pollutants draining into the Chesapeake via its freshwater streams and tributaries followed the expanding human population within the watershed.

Sediment, in turn, diminished light needed by aquatic grasses and plants on the bottom -- the habitat of small fish, shellfish and many other benthic organisms that compose the ecosystem of the bay. As vegetation died out, the decaying biomass depleted the oxygen in the water. The process was accelerated by high levels of nutrients that encouraged surface growth of blue-green algae, blocking light still further. By the 1970s, the bottom of the upper Chesapeake, once a substrate of sand and rock, thriving with plant and animal diversity, had become a floor of lifeless mud. Environmental decline was further accelerated by over-harvesting of fish and shellfish, particularly oysters and clams essential for filtering nutrients, stabilizing pH and regulating oxygen concentrations in the water.

Decline Threatens Economic Health

Despite present conditions in the largest estuary in North America, 5 1/2 times the area of San Francisco Bay, the Chesapeake continues to be vitally important to the economies of Maryland and Virginia. Recreation anglers in Maryland spend more than $467 million annually pursuing various fin fish. In 1996, seafood contributed over $125 million to the state's economy. Boating in Maryland represents a $1 billion industry.

However, without significant reductions in pollution and sedimentation, the system cannot support oysters in numbers needed to effectively filter water in the bay. Without oysters, even existing communities of fish may not be sustainable, especially with the rapid development taking place in this part of the Atlantic Coast. In Maryland, for example, where the current rate of urban sprawl is described by Gov. Parris Glendening as a "living organism out of control," loss of farm and forest land has reached alarming proportions.

In the past six months, approximately 5,000 people have left Baltimore City; 3,000 septic permits have been issued [for new urban homes]; and nearly 10,000 acres of forests and farmlands have been lost. If these trends continue, Maryland could use as much land for development in the next 25 years as it has used in the entire history of the state.

Recovery Efforts

There is an upside to all this: Environmental awareness has made the Chesapeake the most intensely studied and monitored estuary in the world, and millions of dollars are being spent in cleanup programs.

Numerous government agencies, private groups and individual scientists are involved in efforts to restore and protect the bay's natural resources and habitats, develop pollution-reduction strategies and promote environmental awareness through a broad range of educational programs. Since 1996, Maryland has reopened 173 miles