Chlorophyll maxima and chlorophyll: Total phosphorus ratios in Missouri reservoirs

Abstract

Reducing the magnitude and frequency of peak algal biomass is a common goal of lake management. To better quantify such conditions in Missouri reservoirs, an upper boundary delineating maximum algal chlorophyll (Chlmax) across the range of total phosphorus (TP) was developed using summer monitoring data (n = 8839) and compared with 2 other Missouri datasets (n = 8188 and 5151). Typically, other factors constrain Chl below the maximum, and most samples contained a fraction of Chlmax. Near maximum conditions (Chlnm) were provisionally defined as 70% of Chlmax; individual reservoirs differ in their history of supporting Chlnm measurements (from 0 to 43% of samples) irrespective of nutrient status or the duration of summer monitoring. There was a rapid increase in the yield of Chlmax per unit TP across the oligo–mesotrophic range, while within the eutrophic range Chlmax varied with changes in TP in a near-unity response. This general pattern was similar for Chlnm and provides a basis for predicting how high Chl levels would change with nutrient management. Values of Chlmax in Missouri reservoirs are lower than lakes in Florida and larger than values in an international dataset, but the rate of change in Chl across the TP range is quite similar among these datasets, suggesting this pattern applies to different lake types.