CO2 dynamic of Lake Donghu highlights the need for long-term monitoring.

Abstract

Inland freshwater lakes have been widely considered as significant sources of CO2 to the atmosphere. However, long-term measurements of CO2 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 CO2 (pCO2) based on the measurements of pH, water temperature, and alkalinity from 2008 to 2016. The results revealed that a significantly high pCO2 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 pCO2 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 pCO2; however, it only explained 16% of the observed pCO2 variability. This indicates the complex factors that influenced the pCO2 in Lake Donghu between 2008 and 2016. Our estimated CO2 flux revealed that Lake Donghu acted as a small CO2 source to the atmosphere during this period, with a mean CO2 flux of 10.8 ± 37.4 mg m-2 day-1 corresponding to a mean CO2 emission of 0.13 ± 0.43 Gg year-1. The CO2 emission fluxes in Lake Donghu were much lower than the mean CO2 fluxes reported for other lakes in China and globally. Furthermore, the long-term evolution of the CO2 flux indicated that Lake Donghu has shifted between acting as a CO2 source and sink, which highlights the need for long-term monitoring to accurately evaluate CO2 emissions from lakes.