Nutrient-chlorophyll relationships: an evaluation of empirical nutrient-chlorophyll models using Florida and north-temperate lake data

Nutrient-chlorophyll (CHL) relationships were developed using a large data set collected in Florida over the last 10 years consisting of monthly total phosphorus (TP), total nitrogen (TN), and CHL concentrations from 360 lakes. The precision of these and five additional published relationships was examined. The 95% confidence interval for the best available TP-CHL model is 30-325% of the calculated CHL value. Analysis of associated Florida monthly nutrient and CHL data indicate that the TP-CHL relationship is sigmoid, although a linear response is found for TP concentrations in the range of 3-160 mu g.L-1. The maximum CHL responses for a sigmoid curve and straight line are similar for TP concentrations of 3-100 mu g.L-1. Both relationships describe P limitation when the CHL response falls on or near the line and provide a benchmark to evaluate other limiting or colimiting factors that are indicated when the CHL response falls below the line. Florida and global data are similar, exhibiting a lessening of slope above a TP concentration of 100 mu g.L-1. A global median line is derived from a large population of lake data for use in general lake management.