Carbon dioxide emissions from cascade hydropower reservoirs along the Wujiang River, China

Currently, CO₂ emissions from cascade hydropower reservoirs are not well understood. In this study, we investigated the seasonal carbon dioxide partial pressure (<i>p</i>CO₂) and related environmental factors in 4 cascading reservoirs (Hong Jia Du, Dong Feng, Suo Feng Ying, and Wu Jiang Du) of Wujiang River, southwest China. The results showed that <i>p</i>CO₂ in the surface water of these reservoirs had obvious spatiotemporal changes and generally decreased from the riverine zone to the lacustrine zone in each reservoir. In summer, <i>p</i>CO₂ was highest downstream of the dam because of stratification and deep water discharge for hydropower generation, whereas <i>p</i>CO₂ was much lower in the surface water of the lacustrine zone because of carbon removal by photosynthesis. When water temperature was low, however, <i>p</i>CO₂ was higher in the surface water of the lacustrine zone because of respiration and organic decomposition. Among these reservoirs, only Suo Feng Ying had CO₂ emissions higher than the average value of natural lakes. In addition, CO₂ emission flux showed an exponentially negative relationship with hydraulic retention time of reservoirs, based on this work and other reports of reservoirs in the Yangtze River basin.