During the 1940s, 1950s, and 1960s, the Delaware estuary was characterized by severe water quality problems, including the foul stench of hydrogen sulfide gas caused by anoxic conditions in sections of the river near Philadelphia. Uncontrolled waste-water discharges and destruction of habitat from urban and industrial growth in the Delaware watershed were responsible, along with overfishing, for the collapse of many historically important fisheries in the Delaware estuary such as American shad, striped bass, shortnose sturgeon, and American oysters. Desirable amenities such as parks, walking trails, or cafes along the riverfront were not considered for urban development because of the noxious conditions of the Delaware River.
As a result of water pollution control efforts implemented since the late 1960s in the Delaware estuary, dramatic reductions in municipal and industrial effluent discharges of ultimate CBOD, ammonia-N, total phosphorus, and fecal coliform bacteria have been achieved by upgrading wastewater treatment facilities to secondary and better-than-secondary levels of treatment. Municipal and industrial loading of ultimate CBOD to the river, for example, was reduced by 89 percent during the period from 1958 to 1995.
New construction and upgrades of municipal and industrial water pollution control facilities have resulted in significant improvements in water quality, the resurgence of important commercial and recreational fishery resources, and a renewal of economic vitality to once abandoned urban waterfronts along the Delaware River.
Assessment of long-term trends of historical water quality data at critical locations clearly documents great improvements in DO, ammonia-N, total phosphorus, and fecal coliform bacteria. DO, for example, has improved from typical summer minimum levels of less than 1 mg/L during the 1960s and 1970s along a 10-mile section of the river downstream from Philadelphia to minimum levels of 4 mg/L and higher during the 1990s. Ambient ammonia-N concentrations near Marcus Hook have declined by an order of magnitude from late 1960s levels of approximately 1.4 mg N/L to mid-1990s levels of approximately 0.15 mg N/L. Total phosphorus has exhibited a trend similar to that of ammonia-N with late 1960s levels of approximately 0.8 mg P/L dropping almost an order of magnitude to approximately 0.1 mg P/L during the mid-1990s.
A number of indicators of environmental resources of the Delaware estuary have also demonstrated tremendous improvements that can be attributed to the water pollution control efforts and associated public awareness of the importance of environmental quality initiated by the 1972 CWA. The recovery of the American shad population during the mid-1980s, for example, is a remarkable achievement. The restoration of this important fishery resource to populations that can support an extensive recreational and commercial fishery is a success story. Highly popular annual shad festivals now celebrate the seasonal migration of this fish from the ocean into the estuary as a rite of spring.
Although the restoration of valuable fishery resources is important from an economic and ecological perspective, the recreational benefits achieved by the cleanup of the Delaware River far exceed the benefits attributed to fishery improvements. Riverfront development for commercial uses and public parks, increases in sailing and boating, and numerous other economic benefits have occurred along the Delaware River. Most remarkable is that the city centers of Philadelphia, Wilmington, and Trenton, after decades of urban development activity retreating inland, are now moving back toward the riverfront. Investments in urban development along the river would simply not be feasible without the aesthetic qualities of clean water in the Delaware estuary (Albert, 1997). Urban waterfront and riverfront development activity has also been booming in many other cities (e.g., New York Harbor; Cleveland, Ohio; Boise, Idaho; Portland, Oregon; Atlanta, Georgia; Richmond, Virginia) that have successfully cleaned up polluted rivers, lakes, and harbors, making their urban waterways assets and sources of civic pride rather than disgraceful liabilities.
Despite the remarkable environmental improvements achieved by investments in water pollution control infrastructure since initiation of the 1972 CWA, challenges remain for the next generation. Water quality and resource management problems recognized only since the mid-1980s must be addressed. Contamination of the water column and sediments by heavy metals such as mercury, chromium, lead, copper, and zinc has been identified in urban-industrial areas of the river. Probable sources of heavy metals include natural geochemical processes, industrial and municipal dischargers, stormwater runoff, and atmospheric deposition (Santoro, 1998). Toxic chemicals such as PCBs, polynuclear aromatic hydrocarbons (PAHs), and pesticides have also contaminated the water column and sediments of the estuary, resulting in bioaccumulation of those chemicals in pelagic fish and benthic organisms.
Fish consumption advisories were issued in 1989 by New Jersey and Pennsylvania and in 1996 by Delaware (Santoro, 1998). Acute sediment toxicity appears to be more widespread in the estuary than previously documented, with the highest areas of sediment toxicity identified in the heavily urbanized and industrialized region between Torresdale and Marcus Hook. Chronic toxicity was also identified in the water column under particular conditions of streamflow and effluent discharges (Santoro, 1998). The design and construction of facilities to control and treat combined sewer overflow discharges of raw sewage to the tidal river during heavy rainstorms is an ongoing project. Finally, the allocations of wastewater loads for ultimate CBOD from municipal and industrial dischargers that have evolved since 1968 will need to be revised to ensure that the water quality improvements achieved since the 1970s can continue to be maintained as population and industrial activity grow during the twenty-first century (Mooney et al., 1999; HydroQual, 1998).
In 1973, a USEPA study concluded that the Delaware River would never achieve designated uses defined by "fishable standards." More than 25 years after that pessimistic pronouncement, the fishery resources of the Delaware estuary are thriving. The restoration of the vitality of the estuary is a direct result of water pollution control efforts and strong public awareness of the importance of supporting federal, state, and local environmental regulations and policies.
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