Relationships of total phosphorus and chlorophyll in lakes worldwide

Abstract Lakes around the world are sensitive to water quality degradation and eutrophication through increases in primary production. Understanding the drivers of primary production has been a fundamental question in limnology since its early days. Here, we conducted a systematic review to develop a dataset of water chemistry and lake morphometry for 3874 lakes distributed across 47 countries around the world to answer: (1) What is the global relationship between chlorophyll a (Chl a ) and total phosphorus (TP) in lakes? (2) Are there inflection points at which the TP–Chl a relationship is no longer linear? and (3) What explains the inflection points and nonlinearities in the TP–Chl a relationship? We found that a sigmoidal relationship between TP and Chl a explained 44% of the variation. We also found physical characteristics of the lake mediated the TP–Chl a relationship such as mean depth, Secchi depth, and elevation. The nonlinear segments of this relationship best described lakes located in very cold (mean annual temperature = −10°C) and hot (> 25°C) climates, which also dominated the high and low ends of TP concentrations, respectively. A positive linear TP–Chl a relationship existed at intermediate concentrations of TP (0.004–0.23 mg L −1 ). A high degree of variability in Chl a exists between lakes at similar TP levels, highlighting the difficulty in simply decreasing nutrient inputs to manage eutrophication in lakes worldwide. Moreover, as global temperatures continue to rise, the Chl a –TP relationship in lakes located in very cold or warm temperate regions of the world may shift in response to these warmer temperatures.