Abstract
To better understand the decreases observed in pH levels downstream from the associated hydroelectric dam, the impounded Wujiang River in Southwest China was investigated. Study results indicate that the average pH decrease from upstream to downstream of the hydroelectric dam could be up to 0.47 units, and pH differences were particularly apparent during water thermal stratification. Notably, pH was controlled by [CO2]/[CO3 2−] ratios in this impounded river. The decrease in [CO2]/[CO3 2−] ratios and associated increases in pH at the surface of the reservoirs were mainly due to the prevalence of photosynthesis, while the reverse phenomenon was observed at the bottom due to respiration. The evidence from δ13CDIC clearly demonstrated these processes. The increase in phytoplankton biomass enhanced this pH decrease, while dissolved organic carbon had limited impacts on the pH variation. The decrease in pH downstream from the hydroelectric dam resulted from the development of pH stratification in the water profile and the dam operations that release bottom waters for hydropower generation. Consequently, the cascade in hydropower development could increase the risk of river acidification.
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Acknowledgments
We are grateful to Ganrong Li, Zhiwei Han and Chipeng Zhang for their assistance in sample collection in the field. This study was financially supported by the Foundation of Chinese Academy of Sciences (Grant Nos: kzcx2-ew-102), National Key Basic Research Program of China (Grant No: 2013CB956703) and National Natural Science Foundation of China (Grant Nos. 41021062 and 41173096).
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Wang, B., Liu, CQ., Wang, F. et al. A decrease in pH downstream from the hydroelectric dam in relation to the carbon biogeochemical cycle. Environ Earth Sci 73, 5299–5306 (2015). https://doi.org/10.1007/s12665-014-3779-3
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DOI: https://doi.org/10.1007/s12665-014-3779-3