CO dynamic of Lake Donghu highlights the need for long-term monitoring.

Inland freshwater lakes have been widely considered as significant sources of CO to the atmosphere. However, long-term measurements of CO dynamics in lakes are still lacking, but are necessary due to their large temporal variations. Herein, we present the long-term dynamics of water parameters in Lake Donghu from 2002 to 2016, and further calculate the partial pressure of CO (pCO) based on the measurements of pH, water temperature, and alkalinity from 2008 to 2016. The results revealed that a significantly high pCO occurred during the winter in Lake Donghu (p < 0.01), whereas no significant spatial difference was observed (p = 0.37). Statistical analysis indicated that the pCO in the lake was only positively correlated with the total phosphorus (TP) concentration (p < 0.05). A multilinear regression model provided the best predictors for the pCO; however, it only explained 16% of the observed pCO variability. This indicates the complex factors that influenced the pCO in Lake Donghu between 2008 and 2016. Our estimated CO flux revealed that Lake Donghu acted as a small CO source to the atmosphere during this period, with a mean CO flux of 10.8 ± 37.4 mg m day corresponding to a mean CO emission of 0.13 ± 0.43 Gg year. The CO emission fluxes in Lake Donghu were much lower than the mean CO fluxes reported for other lakes in China and globally. Furthermore, the long-term evolution of the CO flux indicated that Lake Donghu has shifted between acting as a CO source and sink, which highlights the need for long-term monitoring to accurately evaluate CO emissions from lakes.