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Interaction Between Oxygen Consumption and Carbon Dioxide Emission in a Subtropical Hypoxic Reservoir, Southeastern China
Author(s) -
Yan Jing,
Chen Nengwang,
Wang Fenfang,
Liu Qian,
Wu Zetao,
Middelburg Jack J.,
Xie Yuyuan,
Guo Weidong,
Zhang Xin
Publication year - 2021
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1029/2020jg006133
Subject(s) - hypolimnion , environmental science , hypoxia (environmental) , oxygen , eutrophication , carbon dioxide , hydrology (agriculture) , environmental chemistry , ecology , chemistry , nutrient , geology , biology , geotechnical engineering , organic chemistry
Abstract It is well recognized that dam construction aggravates eutrophication and hypoxia in river reservoirs, but the interaction between oxygen dynamics and carbon cycling is often unclear. Here we investigated the external and internal controls on oxygen consumption and effects of hypoxia on carbon dioxide (CO 2 ) emission in a subtropical reservoir in southeast China based on detailed field measurements during 2017 and 2018. Hypoxia lasted 4 months starting in mid‐July and expanded from the bottom to near surface water. Rainstorm hyperpycnal flow and unusual hydraulics (outflow exit 40 m from the bottom) resulted in two thermoclines and enhanced the oxygen deficit in deeper water. Microbial respiration accounted for 67.4%–96.5% of total oxygen consumption in the bottom water. The increased supply of organic matter from storm runoff and to a lesser extent primary production in summer enhanced subsequent oxygen consumption. We observed an imbalance between excess CO 2 production and oxygen depletion in summer and winter which was likely associated with other processes in the hypolimnion (e.g., chemoautotrophy, anaerobic degradation of organic matter, proton buffering, and nitrification). The water‐air CO 2 fluxes suggest that the surface reservoir usually served as a CO 2 source, but was a sink in summer due to high primary productivity. CO 2 was always oversaturated in the hypolimnion; this layer was at the depth of the dam outflow and ultimately released 68% of annual CO 2 efflux to the atmosphere. This research confirmed that construction of a hydropower dam has substantially altered reservoir metabolism and regulated the CO 2 emission pathway.