A relation between lake morphometry and primary productivity and its use in interpreting whole‐lake eutrophication experiments

Abstract

Rates of primary production during the ice‐free season expressed per unit volume of epilimnion were linearly related to the ratio of epilimnion sediment area to epilimnion volume in unfertilized lakes in the Experimental Lakes Area (ELA), northwestern Ontario. This ratio is mathematically equivalent to the probability of retention of sedimenting particles in the epilimnion of a lake divided by the mean depth of the epilimnion and is a measure of the nutrient recycling rate of a lake. Evidence indicates that epilimnetic nutrient recycling in ELA lakes is dominated by processes occurring at the sediment‐water interface and not within the sediment. The relationship between the ratio of sediment area to epilimnion volume and primary production is used as the basis for interpreting whole‐lake eutrophication experiments. In comparison to control lakes, the ratio of production to chlorophyll in the experimental lakes was high when chlorophytes dominated and low when cyanophytes dominated. Lakes that were fertilized with both nitrogen and phosphorus had much higher chlorophyll concentrations and productivities than control lakes. Lakes that received either of these nutrients alone showed weaker responses. Both elements appear to be in short supply relative to the metabolic requirements of phytoplankton. Phosphorus control is still the key to controlling eutrophication.