Reservoirs change pCO2 and water quality of downstream rivers: Evidence from three reservoirs in the Seine Basin

Xingcheng Yan; Vincent Thieu; Songjun Wu; Josette Garnier

doi:10.1016/j.watres.2022.118158

Reservoirs change pCO₂ and water quality of downstream rivers: Evidence from three reservoirs in the Seine Basin

Water Res. 2022 Apr 15:213:118158. doi: 10.1016/j.watres.2022.118158. Epub 2022 Feb 4.

Authors

Xingcheng Yan¹, Vincent Thieu², Songjun Wu³, Josette Garnier²

Affiliations

¹ Sorbonne Université, CNRS, EPHE, UMR 7619 METIS, 4 place Jussieu, Box 105, 75005 Paris, France. Electronic address: xingcheng.yan@upmc.fr.
² Sorbonne Université, CNRS, EPHE, UMR 7619 METIS, 4 place Jussieu, Box 105, 75005 Paris, France.
³ Department of Ecohydrology, Leibniz Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 310, 12587 Berlin, Germany; Department of Geography, Humboldt University of Berlin, Rudower Chaussee 16, 12489 Berlin, Germany.

PMID: 35149362
DOI: 10.1016/j.watres.2022.118158

Abstract

The global increase in the construction of reservoirs has drawn attention given its documented hydrological and biogeochemical impacts on downstream rivers; however, the impact of reservoirs on downstream pCO₂ (partial pressure of carbon dioxide) is still poorly understood. To evaluate these impacts, the interactions between reservoirs and their corresponding upstream and downstream rivers were analyzed for three reservoirs in the Seine Basin based on monthly measurement during two hydrological years. The seasonal variations of water quality in the reservoirs were mainly driven by the entering water and the biogeochemical processes occurring in the reservoirs. Our results unravel the crucial role of reservoir in downstream water quality, which significantly increased DOC (dissolved organic carbon) and BDOC (biodegradable DOC) concentrations, while lowered DSi (dissolved silica) concentrations during emptying period (p < 0.01). Furthermore, the impacts of reservoirs on the annual fluxes of DOC, BDOC, and DSi were quantified and suggested that the three reservoirs respectively increased 20% and 23% of annual fluxes of DOC and BDOC, while decreased 33% of annual DSi fluxes in their downstream rivers. Additionally, the reservoirs significantly decreased downstream riverine pCO₂ (p < 0.01), and enhanced the gas transfer coefficient of CO₂ in downstream rivers by 1.3 times during the emptying period, which highlights the necessity to consider the potential impact of reservoirs on riverine CO₂ emissions. Overall, our results highlight the importance of combining biogeochemical and hydrological characteristics to understand the impacts of reservoirs on downstream rivers, and emphasize the need of similar studies under the current context of increasing reservoir constructions.

Keywords: Downstream river; Partial pressure of CO(2); Reservoirs; Seine basin; Water quality.