Eutrophication and temperature drive large variability in carbon dioxide from China's Lake Taihu

Abstract Eutrophication and warming are changing the functioning of lake ecosystems, and their impacts on lake carbon dioxide (CO 2 ) variability have received increasing attention. However, how eutrophication and warming change lakes' carbon cycle has not been determined. Here, the surface partial pressure of CO 2 ( p CO 2 ) and CO 2 flux in Lake Taihu, a large and eutrophic lake in eastern China, was investigated based on monthly samplings over a 24‐yr period (1992–2015), during which the lake experienced profound anthropogenic and climate changes. The results showed that eutrophication caused by nutrient enrichment plays a role in three aspects: (1) nutrient concentrations controlled the CO 2 variability on decadal scales; (2) peak p CO 2 and CO 2 fluxes occurred in river mouths due to large external nutrient loading inputs; and (3) eutrophication effects on CO 2 varied among subzones, which was linked to external inputs and in‐lake primary production. Meanwhile, temperature controls the seasonal variation in CO 2 by stimulating primary production, leading to significantly lower p CO 2 and CO 2 fluxes in warm seasons with algal blooms. Further analysis suggested that temperature effects varied spatially and temporally, high nutrient loading may confound the temperature effects via stimulating CO 2 production. To our knowledge, this study presents the longest field measurements (24 yr) of CO 2 from such large and ice‐free freshwater lakes with monthly surveys, which may provide a powerful example to demonstrate that eutrophication and warming can shape CO 2 variability from a temporal perspective. Future studies should focus on the interactive warming and eutrophication effects to accurately predict future CO 2 emission.