Carbon sink and source dynamics of a eutrophic deep lake using multiple flux observations over multiple years

Recent research has shown lakes play an outsized role in carbon cycling, but long‐term continuous observations and analysis of carbon dynamics are rare, limiting our understanding of interannual variation, important timescales of variability, and drivers of efflux. Therefore, we examined lake‐atmosphere carbon fluxes with the goal of quantifying annual trends and patterns in lake carbon efflux and identifying important timescales. To do so, this study integrated 6 yr of eddy‐covariance flux tower observations of lake‐atmosphere fluxes with high‐frequency observations of in‐lake temperature, dissolved oxygen, and partial pressure of CO2, for a eutrophic lake in Wisconsin, U.S.A. While growing season fluxes are variable and switch between source and sink, annual net carbon fluxes show the lake acts as an annual sink of carbon, with the magnitude depending on climate, along with the timing and strength of fall turnover, with half of the total annual carbon uptake happening in October and November.