Human-induced N-P imbalances will aggravate GHG emissions from lakes and reservoirs under persisting eutrophication

Lakes and reservoirs are hotspots for emissions of atmospheric greenhouse gas (GHG) such as CO₂, CH₄, and N₂O, and their nutrient levels and stoichiometric status are significant drivers of GHG emissions. In recent decades, human-induced unbalanced inputs of nitrogen (N) and phosphorus (P) have enhanced the P-limiting state of inland lake and reservoir systems. However, it remains unclear whether this state transition involves global changes in nutrient-limiting systems and GHG emissions from lakes and reservoirs. In this study, a comprehensive model was developed to examine the relationship between GHG fluxes and total N (TN) and total P (TP) to predict future human-induced N over-enrichment and its impact on global GHG emissions. Our results show that excess N inputs amplified GHG emissions, with future water eutrophication (1.2×) projected to increase CO₂ emissions (384.66 Tg·y^-1), CH₄ (7.38 Tg·y^-1), and N₂O (0.23 Tg·y^-1) from lakes and reservoirs by 49 %, 12 %, and 25 %, respectively, amounting to approximately US$0.13 trillion ($0.08-6.91 trillion, 2015$) in social costs. A future 50 % increase in N: P will increase the relative social cost of carbon by 15 % compared to future 1.2× eutrophication levels. Given the social costs and benefits of reducing N and P pollutants in water individually and in synchronization, future long-term strategies for managing eutrophication in lakes and reservoirs need to emphasize balanced control of N and P.