Optimizing Watershed Land Use to Achieve the Benefits of Lake Carbon Sinks while Maintaining Water Quality

Greenhouse gas emissions and water quality decline are two major issues currently affecting lakes worldwide. Determining how to control both greenhouse gas emissions and water quality decline is a long-term challenge. We compiled data on the annual average carbon dioxide (CO2) flux and water quality parameters for 422 global lakes, revealing that 82.42% of the lakes act as carbon sources and that 66.56% have experienced water quality deterioration. Carbon sources and eutrophication trends were observed for lakes from the 1990s to 2020s, with further deterioration expected over the next 80 years. Unmanaged land use change in lake watersheds could exacerbate the CO2 flux into lakes and water quality degradation. In this study, a watershed land use planning (WLUP) framework was established, and a 24.83% reduction in the CO2 flux into lake water, a 5.07% reduction in chlorophyll a (Chl-a), a 4.70% reduction in total phosphorus, and a 12.92% increase in Secchi depth were achieved. The WLUP framework identifies Asia and Europe as the regions experiencing the greatest demands for land use transformation, where optimization leads to the most significant improvements. Metagenomic analysis revealed that forests enhance carbon fixation and that grasslands reduce carbon degradation and phosphorus metabolism in lake watersheds, explaining and supporting the possibility of WLUP. This work provides a win-win solution for improving CO2 fluxes and water quality in global lakes to mitigate the effects of climate change and promote lake protection.