INFLUENCE OF WATERSHED RUNOFF ON NUTRIENT DYNAMICS IN A SOUTHERN CALIFORNIA SALT-MARSH

The effect of freshwater runoff on nutrient loading and dynamics was s tudied in Carpinteria Salt Marsh, a typically small (93 ha) southern C alifornia, U.S.A., estuary adjoining a watershed supporting extensive agricultural and urban development. Concentrations of dissolved nitrat e, but not ammonium or phosphate, were elevated in stream flow and per ched groundwater in the watershed, relative to marsh surface waters. L oading of nitrate and particulate organic nitrogen (PON) from the wate rshed, but not ammonium or phosphate, increased as a function of strea m discharge. Estimates of net nutrient exchange over selected tidal cy cles suggested that the marsh exported nitrate, ammonium and PON to th e Santa Barbara Channel. Nitrate and PON were advected from the waters hed through the marsh while ammonium was produced within the marsh and exported. The availability of imported nitrogen for primary productio n may be limited by marsh tidal elevation as most nitrogen inputs are throughput to the Santa Barbara Channel. (C) 1995 Academic Press Limit ed