Primary productivity in receiving reservoirs: links to influent streams

Primary productivity and chlorophyll a concentrations were measured in 8 reservoirs in New York City drinking-water-supply watersheds. The light-and-dark bottle O2-change procedure was used to measure gross primary productivity (GPP) once each summer from 2000 to 2002. GPP normalized for photosynthetically active radiation (PAR) in the Neversink and Schoharie averaged only 0.025 and 0.035 g O2/mol quanta, respectively. Values for New Croton and Cannonsville averaged 0.118 and 0.125 g O2/mol quanta, respectively. Values in the other reservoirs (west basin Ashokan, Pepacton, Rondout, and Kensico) were intermediate. Chlorophyll a concentrations in reservoir photic zones ranged from mean values of ,10 to 100 mg/m, with highest values in New Croton and Cannonsville and lowest concentrations in Neversink, Pepacton, and Schoharie. Cannonsville was eutrophic, and New Croton was at the mesotrophic–eutrophic boundary. Neversink, Schoharie, and Pepacton were at the oligotrophic– mesotrophic boundary, and the remaining reservoirs (Kensico, Rondout, and west basin Ashokan) were mesotrophic. Reservoir conditions were related to watershed-scale land use. Gradients within reservoirs in chlorophyll a, depth of photic zone, and primary productivity indicated an influence of the major tributary on reservoir conditions in several of the reservoirs.