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The Role of Delaware River Freshwater Tidal Wetlands in the Retention of Nutrients and Heavy Metals¹

ABSTRACT

Tidal cycle budgets for June, July, August, September, and November 1979 showed that inorganic N was imported to the wetland from the Delaware River early in the growing season and exported late in the growing season. Nitrate and organic nitrogen were imported following macrophyte dieback. Reactive P was never lost from the marsh, and was actually imported on three dates. Total P was imported in July, September, and November, but otherwise exported. The metal present in the lowest concentration, Cd, was always exported; Ni, Cu, and Zn were imported on all but one date. Lead was imported late in the growing season and following macrophyte dieback. Nonpoint-source inputs of Pb exceeded inputs from tidal waters.

The vegetation played a major role in the retention of N, P, Cu, Pb, and Ni entering the wetland through the growing season. The litter retained significant quantities of all heavy metals following macrophyte dieback, but it serves only as a temporary storage vehicle because rates of decomposition are high. The soil showed no definite seasonal pattern of nutrient or heavy metal retention. Elevated Pb levels occurred at sites near storm drains reflecting rapid sedimentation and retention of this metal as storm waters entered the wetland. It is concluded that freshwater tidal wetlands play an important seasonal role in reducing nutrient and heavy metal loading in the upper Delware River estuary.

Key Words: detritus • soil • vegetation • tidal flux budgets • nonpoint-source runoff

¹ Contribution of the Biology Dep., Rider College, Lawrenceville, NJ 08648; Biology Dep., Rutgers University, Camden, NJ 08102; and Center for Coastal and Environmental Studies, Rutgers University, New Brunswick, NJ 08903.

² Professor, Rider College, Biology Dep.; Professor, Rutgers University, Biology Dep.; Graduate Assistant, Rutgers University; Ecologist, ECTS Inc., Box 3521, Cherry Hill, NJ.

Received for publication January 27, 1982.