The human population carrying capacity of the chesapeake bay watershed: A preliminary analysis
Estimating human population carrying capacity for subglobal areas is problematic due to interregional transfers of energy, resources, pollution and waste. However, recent research on Chesapeake Bay sediment has permitted determination of time of onset of major episodes of Bay degradation, which may be used with census data to derive preliminary estimates of the watershed's carrying capacity. Chesapeake Bay, the United States' largest estuary, is experiencing increasing degradation despite a decade of studies and significant remedial activity. Since 1985, phosphorus emissions declined 18%, due mainly to a ban on phosphate detergent, but nitrogen increased at least 2%. Degrading influences, related to increasing fossil-fuel consumption and relentless population growth, include (1) overharvesting of shellfish and fish species, (2) nitrogen emissions from sewage treatment plants, agriculture, fossil-fueled power plants and motor vehicles, (3) phosphorus emissions from sewage and agriculture, (4) debris, sewage, fuel spills and exhaust from 400,000 registered watercraft, (5) storm-water runoff, (6) sedimentation from land-use changes, (7) industrial discharges, (8) construction of dams and other barriers to anadromous fish migration, and (9) disposal of dredged material. Oyster harvests have declined over 95% in Virginia since the 1950s. Submerged aquatic vegetation (SAV), essential to fish and bottom-dwelling invertebrates, is estimated to cover only 10% of its pre-1950 distribution. Where remediation efforts have resulted in recolonization of SAV, species diversity is reduced 50–90%. Anoxic conditions are persistent in the Bay's deeper waters. New sediment data allow precise determination of time of onset of degration by recognizing changes in ratio of benthic to planktonic diatoms. These data, coupled with analyses of living resource populations, indicate that the most significant episode of Bay degradation commenced in the 1950s, and suggest that the human population carrying capacity for the watershed does not exceed 8 million without substantial changes in energy consumption and lifestyle. The watershed's present population of 16 million is projected to increase at least 20% by 2020. Furthermore, registration of motor vehicles may increase by one-third over the same interval. Goals of 40% reduction by 2000 of nitrogen and phosphorus emissions into the Bay set by the Chesapeake Bay Commission are unattainable without permanent changes in behavior affecting every facet of life in the watershed. The extent to which remediation efforts are successful in the Bay's watershed will help define much of the structure and nature of U.S. society in the twenty-first century.
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