The inadequacy of existing chlorophyll- a/phosphorus concentration correlations for assessing remedial measures for hypertrophic lakes

Abstract

Because large reductions in phosphorus loading are required to cause small decreases in mean summer phytoplankton biomass, inaccuracies exist in (1) predicting lake phosphorus concentrations from phosphorus loading models and mean and maximum chlorophyll- a from lake phosphorus concentrations and (2) representative sampling to estimate true phosphorus loading and true mean and maximum chlorophyll- a. Remedial measures to reduce external phosphorus loads—and hence lower in-lake phosphorus concentrations from some 600 mg/m 3 to much lower values of some 100 mg/m 3—will result in the reduction of long-term (several years average) mean—and, more significantly, maximum—open-water summer chlorophyll- a concentrations. However, despite the application of these remedial measures, perturbations in phytoplankton biomass will remain such that, on any particular day during the open-water period, short-term algal blooms or scums will still be sufficiently intense for long-term improvements not to be clearly evident to the casual recreational user of the lake.