Nitrogen and phosphorus recycling in Lake Sammamish,a temperate mesotrophic lake

This paper presents nitrogen and phosphorus budgets for spring and summer for the trophogenic (0–9 m) and tropholytic (9–27 m) zones of Lake Sammamish. The objective of constructing the budgets is to evaluate the efficiency of nutrient recycling and increase knowledge of the overall nutrient dynamics.The budgets reveal that uptake and solubilization are the dominant fluxes and that nutrient recycling is generally efficient, with the possible exception of early spring during the diatom bloom. This leads to greater reductions in the dissolved N and P pools in spring than summer. Sedimentation is greater in spring because of a pulse immediately following the diatom bloom.Solubilization of particulates is much less in the tropholytic zone than the trophogenic zone. This is due to slower decomposition rates there and to the efficiency of solubilization in the overlying trophogenic zone which results in a relatively small particulate influx. Turnover times for the N and P pools are therefore much faster in the trophogenic zone than in the tropholytic zone. In the trophogenic zone, however, the dissolved N pool turns over much more slowly than the dissolved P pool because of its larger size relative to algal growth requirements.Overall there is a net loss of N and P from the water column in spring primarily due to sedimentation and denitrification whilst in summer there is a small net gain because of sediment release and a slight excess of inflow over outflow.The work was supported by National Science Foundation grants DEB 74-20744, BMS 74-20744 and GB 36810F to the International Biological Program, Western Coniferous Biome (US/IBP) and grant R 008512 from the US Environmental Protection Agency. Contribution no. 373 by the Western Coniferous Biome.The work was supported by National Science Foundation grants DEB 74-20744, BMS 74-20744 and GB 36810F to the International Biological Program, Western Coniferous Biome (US/IBP) and grant R 008512 from the US Environmental Protection Agency. Contribution no. 373 by the Western Coniferous Biome.