SUMMARY OF MAJOR FINDINGS Stream and River Highlights
Human activities associated with urban and agricultural land use are the primary factors that affect the quality of streams and the health of aquatic life throughout Long Island and New Jersey (see map on right). Although concentrations of most chemical constituents detected in stream samples generally meet Federal and State water-quality guidelines, current guidelines do not address many of these chemicals nor the combinations (mixtures) of pesticides, fertilizers, and industrial and fuel-related compounds (volatile organic compounds, or VOCs) that were commonly detected in all streams. Concentrations of trace elements and organic compounds in streambed sediment in urban areas commonly failed to meet guidelines for protection of aquatic life, but sediment quality did not appear to be as influential as other human-related factors in affecting aquatic community health. Rather, study findings indicate that urban and suburban evelopment, especially when it replaces forest and wetlands, results in changes in the natural flow of streams, habitat degradation, reduction in biological diversity, and a shift toward species more tolerant of disturbance. These factors together likely have a greater effect on impairment of aquatic life than on drinking-water quality in highly urbanized areas.
Trends in Stream Quality
About 40 percent of the domestic (household) and public drinking-water supply in the study area is obtained from ground water that is replenished by precipitation that infiltrates the soil and drains to the water-table (surficial) aquifer. Elevated concentrations of nitrate and the frequent detection of pesticides and VOCs in water samples from surficial aquifers indicate that the aquifers are vulnerable to chemicals used in agricultural and urban areas. Concentrations of nitrate in samples of shallow ground water underlying agricultural areas in southern New Jersey and agricultural and suburban areas on Long Island frequently exceeded drinking-water guidelines. The use of nitrogen fertilizers to support crop production and the use of septic systems in these areas, combined with the presence of well-drained and aerated soils, favor the formation of nitrate and its movement to ground water. Pesticide and VOC concentrations in water samples from surficial aquifers in New Jersey generally were low and rarely exceeded drinking-water guidelines; concentrations generally were greater in samples from the Long Island surficial aquifer system. Drinking-water standards or guidelines have not been established for 31 and 34 percent of the pesticides and VOCs detected, respectively. Although human activities associated with agricultural and urban land uses are the principal sources of contaminants in ground water, factors other than land use can affect ground-water quality. For example, some pesticides that are known to be used extensively were not detected in ground water because they degrade readily or are not mobile. Additionally, some constituents, such as arsenic and radium, were detected in water where surficial sediments or geologic formations are known to contain these elements.
Trends in Ground-Water Quality A computer model study of the surficial aquifer system in southern New Jersey indicates that the concentration of nitrate in streams and public-supply wells is related to the type of land use in the recharge area and the time required for the recharge water to reach the stream or well (p. 16). Model results also indicate that years or even decades will be required before reduction in nitrate use will produce substantial decreases in the concentrations of nitrate in streams and ground water. If nitrate use remains at current levels, nitrate concentrations in streams and ground water in agricultural and urban parts of the study area will continue to increase for several decades (p. 17).
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