Northern lakes are experiencing widespread increases in dissolved organic carbon (DOC) that are likely to lead to changes in pelagic phytoplankton biomass. Pelagic phytoplankton biomass responds to trade-offs between light and nutrient availability. However, the influence of DOC light absorbing properties and carbon–nutrient stoichiometry on phytoplankton biomass across seasonal or spatial gradients has not been assessed. Here, we analyzed data from almost 5000 lakes to examine how the carbon–phytoplankton biomass relationship is influenced by seasonal changes in light availability, DOC light absorbing properties (carbon-specific visual absorbance, SVA₄₂₀), and DOC–nutrient [total nitrogen (TN) and total phosphorus (TP)] stoichiometry, using TOC as a proxy for DOC. We found evidence for trade-offs between light and nutrient availability in the relationship between DOC and phytoplankton biomass [chlorophyll (chl)-a], with the shape of the relationship varying with season. A clear unimodal relationship was found only in the fall, particularly in the subsets of lakes with the highest TOC:TP. Observed trends of increasing TOC:TP and decreasing TOC:TN suggest that the effects of future browning will be contingent on future changes in carbon–nutrient stoichiometry. If browning continues, phytoplankton biomass will likely increase in most northern lakes, with increases of up to 76% for a 1.7 mg L⁻¹ increase in DOC expected in subarctic regions, where DOC, SVA₄₂₀, DOC:TN, and DOC:TP are all low. In boreal regions with higher DOC and higher SVA₄₂₀, and thus lower light availability, lakes may experience only moderate increases or even decreases in phytoplankton biomass with future browning.

北部湖泊的溶解性有机碳（DOC）普遍增加，这很可能导致浮游浮游植物生物量的变化。中上层浮游植物的生物量对光和养分的可利用性之间的权衡做出反应。但是，尚未评估DOC的吸光特性和碳营养素化学计量对跨季节或空间梯度对浮游植物生物量的影响。在这里，我们分析了将近5000个湖泊的数据，以研究碳与浮游植物生物量之间的关系如何受光的季节性变化，DOC光吸收特性（特定于碳的视觉吸收率，SVA _{420）的影响。}）和DOC-营养物[总氮（TN）和总磷（TP）]化学计量，使用TOC代替DOC。我们发现在DOC和浮游植物[叶绿素（叶绿素） -之间的关系之间的光和养分有效性折衷证据一个]，与季节的关系变的形状。仅在秋季，特别是在TOC：TP最高的湖泊子集中，才发现明显的单峰关系。观察到的TOC：TP增加和TOC：TN减少的趋势表明，未来褐变的影响将取决于碳营养素化学计量的未来变化。如果继续褐变，则大多数北部湖泊的浮游植物生物量可能会增加，1.7 mg L ^-1的浮游植物生物量最多可增加76％在DOC，SVA ₄₂₀，DOC：TN和DOC：TP都较低的北极地区，预计DOC会增加。在DOC较高和SVA ₄₂₀较高的北方地区，因此光的利用率较低，湖泊可能会出现浮游植物生物量仅适度增加甚至减少的情况，并且将来会变褐。