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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.
Xiao et al. (Thu,) studied this question.