Effects of eutrophication on maximum algal biomass in lake and river ecosystems

To further clarify empirical relationships between maximum phytoplankton biomass per unit total phosphorus (TP) and the maximum: mean phytoplankton biomass ratio, predictive models were created from a meta-analysis of datasets from lakes worldwide. Peak concentrations of planktonic chlorophyll a were on average 2.6 times greater than the mean, with most maximum: mean chlorophyll a ratios falling within less than an order-of-magnitude band (from 1.2 to 6 times the mean value). Peak concentrations of planktonic algal biovolume in 22 Organisation for Economic Co-operation and Development (OECD) lakes were on average 3.3 times greater than the mean, with maximum: mean biovolume ratios ranging from 1.2 to 6.3. By contrast, the temporal dynamics of planktonic (suspended) algal biomass in Minnesota streams and rivers were far more constrained; peak concentrations of planktonic chlorophyll a were only on average 1.8 times greater than the mean, with maximum: mean chlorophyll a ratios ranging from 1.3 to 3.8. These data suggest regional differences in maximum chlorophyll a values may exist. Parallel analyses of periphyton biomass in streams and rivers showed far greater variability in the maximum: mean chlorophyll ratio for benthic algae. Peak concentrations of attached chlorophyll a were on average 4.3 times greater than the mean, with the observed maximum: mean chlorophyll a ratios exhibiting exceptionally high variability (ranging from 1.0 to 50 times the mean value), likely reflecting differences in the temporal dynamics of planktonic and benthic algal growth in freshwater ecosystems.