Hydrogeochemistry of the New Jersey Coastal Plain: 1. Major-element cycles in precipitation and river water

The New Jersey Coastal Plain (Pine Barrens) is an extensive region where inorganic interactions between the soils and shallow groundwater are at a minimum. This study compares the geochemistry of precipitation and surface water to analyze transport mechanisms of major elements and to evaluate hydrogeochemical balances in this relatively unusual system. Precipitation composition is controlled by proximity to the ocean and seasonal variability of storm movements. Total dissolved solids in precipitation are high (11.5 ppm) but decrease inland; Na + and Cl − are more abundant in winter precipitation whereas K +, SO 2− 4, Ca 2+, and NO 3 − exhibit greater concentrations during the summer months. Na + and Cl − are derived from marine aerosols; SO 2− 4 is a product of SO 2 pollution in the atmosphere; other ions have significant contributions from continental aerosols. Dissolved solids in rivers are low (20 ppm) compared with average river water and pH is acidic (4.5). Both reflect paucity of mineral-water reactions in the uppermost aquifer (Cohansey Formation — quartz sand and gravel). However, regional variations in river-water geochemistry suggest cross-aquifer migration of deep groundwaters into the Mullica River basin. Mass balances confirm that river-water composition is controlled principally by precipitation. However, Ca 2+, PO 3− 4, and SO 2− 4 are depleted in river waters, probably as a result of removal by biota or cedar swamp processes. Mg 2+ shows an excess in the rivers, suggesting a contribution from deep groundwater. The poor chemical buffering in the waters of this region render them highly susceptible to contamination.