Inorganic Nitrogen and Phosphorus Dynamics in the Water Column of the PatuxentRiver

摘要

An analysis was made of nitrogen (N) and phosphorus (P) dynamics in the watercolumn of the Patuxent River, Maryland, over a 2 year cycle. Specifically, inorganic N and P assimilation were determined by isotopic tracer methods at 3 stations along the salinity gradient of the river on a monthly basis. The authors determined the concentrations of particulate N and P and the major dissolved species. Among inorganic species, nitrate showed the greatest seasonal variation, particularly at the upstream stations. Nitrate, which increased going upstream, tended to dominate the inorganic N pools. Ammonium, nitrate and phosphate uptake varied over a wide range among and within sites. Values tended to increase moving upstream. Nitrate uptake dominated inorganic N assimilation upstream while ammonium uptake was of greater importance at the most saline station. With respect to indicies of nutrient limitation, except for the summer, dissolved inorganic N was in excess relative to inorganic P, suggestive of P limitation.