Net community production and hypolimnetic nutrient regeneration in a Michigan lake1

Net community oxygen production in Third Sister Lake, Michigan, was calculated from concentration gradients, eddy diffusion, and gas flux at the lake surface. The trophogenic zone extended on average to 4.5 m from April to August. Vertical flux of dissolved P provided negligible support for the productivity during this time. Stoichiometries for biomass production from inorganic N and P were inferred from enclosure experiments and from vertical profiles. N and P accumulated in the hypolimnion at a ratio of 24 : 1 by atoms, whereas ratios in the algae averaged 9.5 : 1. On the basis of areal rates of nutrient remineralization and the oxygen budget, most of the net community production from April to August could be assigned to the open water rather than to the littoral region. Littoral production processes are relatively isolated from the open water in this small, sheltered lake during the time of thermal stratification.