Consistent stoichiometric long-term relationships between nutrients and chlorophyll-a across lakes

Abstract Aquatic ecosystems are threatened by eutrophication from nutrient pollution1. In lakes, eutrophication causes a plethora of deleterious effects, such as harmful algal blooms, fish kills2 and increased methane emissions3. However, lake-specific responses to nutrient changes are highly variable, complicating eutrophication management4. These lake-specific responses could result from short-term stochastic drivers overshadowing lake-independent, long-term relationships between phytoplankton and nutrients5. Here we show that strong stoichiometric relationships exist between nutrients and chlorophyll a (Chla) for 5-year simple moving averages (SMAs, median R² = 0.87) along a gradient of total nitrogen to total phosphorus (TN : TP) ratios. These stoichiometric relationships are consistent across 159 shallow lakes from a cross-continental, open-access database. We calculated 5-year SMA residuals to assess short-term variability and found substantial short-term Chla variation which was weakly related to nutrient concentrations (median R² = 0.12). Our findings are robust and broadly relevant. We found consistent statistical estimates based on a rigorous bootstrap approach and included all data from lakes under six meters average depth, a category that includes 89% of global lakes. These stoichiometric long-term relationships can improve quantitative nutrient management in lakes and their catchments through a nutrient-ratio-based strategy.