Notable changes of carbon dioxide in a eutrophic lake caused by water diversion

Abstract

Artificial water diversion project has been increasingly implemented to control eutrophication and alleviate water shortage of lakes. Water diversion can affect the biogeochemical cycles, however, carbon dioxide (CO2) sensitivity in lakes to water diversion was poorly understood. This study addressed the issue based on the famous Water Diversion project from the Yangtze River to eutrophic Lake Taihu, which has been carried out regularly since 2002 in China. The partial pressure of CO2 (pCO2) at two regions of the eutrophic lake, water-receiving Gonghu Bay and non-water-receiving Central Zone, was investigated over 16 years (2002–2017) field measurement with high sampling frequency. Results showed the river-to-lake water diversion decreased phytoplankton biomass, increased nutrient loadings, and significantly elevated the pCO2 and associated CO2 emission. Meanwhile, the water diversion project accounted for the notable CO2 spatial heterogeneity between regions and within region. However, weak CO2 seasonal variability was observed at Gonghu Bay during water diversion period. The estimated CO2 emission flux increased averagely by 54% due to water diversion, primarily resulting from phytoplankton dilution, nutrient enrichment, and external CO2 input. Water diversion and ammonia nitrogen together explained 69% of interannual variability pCO2 at Gonghu Bay, implying water diversion should be considered to better understanding the contribution of lake CO2 emissions to C budget under a changing environment. These findings were expected to serve as a reference to evaluate the water diversion effects, further study should focus on the sources of the excess CO2 to make the project a CO2-neutral option.