Ecosystem-Scale Oxygen Manipulations Alter Terminal Electron Acceptor Pathways in a Eutrophic Reservoir
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Ecosystem-Scale Oxygen Manipulations Alter Terminal Electron Acceptor Pathways in a Eutrophic Reservoir Ryan P. McClure,1* Madeline E. Schreiber,2 Mary E. Lofton,1 Shengyang Chen,3 Kathryn M. Krueger,2 and Cayelan C. Carey1 1
Department of Biological Sciences, Virginia Tech, Blacksburg, Virginia 24061, USA; 2Department of Geosciences, Virginia Tech, Blacksburg, Virginia 24061, USA; 3UNSW Water Research Laboratory, UNSW Sydney, 110 King St, Manly Vale, New South Wales 2093, Australia
ABSTRACT Lakes and reservoirs globally are experiencing unprecedented changes in land use and climate, depleting dissolved oxygen (DO) in the bottom waters (hypolimnia) of these ecosystems. Because DO is the most energetically favorable terminal electron acceptor (TEA) for organic carbon mineralization, its availability controls the onset of alternate TEA pathways (for example, denitrification, manganese reduction, iron reduction, sulfate reduction, methanogenesis). Low DO concentrations can trigger organic carbon mineralization via alternate TEA pathways in the water column and sediments, which has important implications for greenhouse gas production [carbon dioxide (CO2) and methane (CH4)]. In this study, we experimentally injected supersaturated DO into the hy-
Received 16 June 2020; accepted 22 October 2020
Electronic supplementary material: The online version of this article (https://doi.org/10.1007/s10021-020-00582-9) contains supplementary material, which is available to authorized users. Author contributions CCC conceived the original research project. RPM and CCC worked closely together to develop the original research ideas addressed in this paper. RPM and MES led the overall synthesis and interpretation of the data and writing with many contributions from CCC. RPM, MEL, SC, and KMK collected field data, and RPM, SC, MEL, KMK, and CCC compiled and analyzed data. All authors approved the final version of the manuscript. *Corresponding author; e-mail: [email protected]
polimnion of a eutrophic reservoir and measured concentrations of TEAs and terminal electron products (TEPs) in the experimental reservoir and an upstream reference reservoir. We calculated the electron equivalents yielded from each TEA pathway and estimated the contributions of each TEA pathway to organic carbon processing in both reservoirs. DO additions to the hypolimnion of the experimental reservoir promoted aerobic respiration, suppressing most alternate TEA pathways and resulting in elevated CO2 accumulation. In comparison, organic carbon mineralization in the reference reservoir’s anoxic hypolimnion was dominated by alternate TEA pathways, resulting in both CH4 and CO2 accumulation. Our ecosystemscale experiments demonstrate that the alternate TEA pathways that succeed aerobic respiration in lakes and reservoirs can be manipulated at the ecosystem scale. Moreover, changes in the DO dynamics of freshwater lakes and reservoirs may result in concomitant changes in the redox reactions in the water column that control organic carbon mineralization and greenho
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