Trade-offs Between Light and Nutrient Availability Across Gradients of Dissolved Organic Carbon Lead to Spatially and Temporally Variable Responses of Lake Phytoplankton Biomass to Browning

Abstract Northern lakes are experiencing widespread increases in dissolved organic carbon (DOC) that likely to lead changes pelagic phytoplankton biomass. Pelagic biomass responds trade-offs between light and nutrient availability. However, the influence of DOC absorbing properties carbon–nutrient stoichiometry on across seasonal or spatial gradients has not been assessed. Here, we analyzed data from almost 5000 examine how carbon–phytoplankton relationship is influenced by availability, (carbon-specific visual absorbance, SVA 420 ), DOC–nutrient [total nitrogen (TN) total phosphorus (TP)] stoichiometry, using TOC as a proxy for DOC. We found evidence availability [chlorophyll (chl)- ], with shape varying season. A clear unimodal was only fall, particularly subsets highest TOC:TP. Observed trends increasing TOC:TP decreasing TOC:TN suggest effects future browning will be contingent stoichiometry. If continues, increase most northern lakes, up 76% 1.7 mg L −1 expected subarctic regions, where DOC, , DOC:TN, DOC:TP all low. In boreal regions higher thus lower may experience moderate even decreases browning.