Hypolimnetic deoxygenation enhanced production and export of recalcitrant dissolved organic matter in a large stratified reservoir

Liyin Qu; Chen He; Zetao Wu; Randy A Dahlgren; Mingxing Ren; Penghui Li; Quan Shi; Yan Li; Nengwang Chen; Weidong Guo

doi:10.1016/j.watres.2022.118537

Hypolimnetic deoxygenation enhanced production and export of recalcitrant dissolved organic matter in a large stratified reservoir

Water Res. 2022 Jul 1:219:118537. doi: 10.1016/j.watres.2022.118537. Epub 2022 May 2.

Authors

Liyin Qu¹, Chen He², Zetao Wu³, Randy A Dahlgren⁴, Mingxing Ren¹, Penghui Li⁵, Quan Shi², Yan Li⁶, Nengwang Chen⁷, Weidong Guo⁸

Affiliations

¹ State Key Laboratory of Marine Environmental Science, College of Ocean and Earth Sciences, Xiamen University, Xiamen 361012, China; Fujian Provincial Key Laboratory for Coastal Ecology and Environmental Studies, Xiamen University, Xiamen 361012, China.
² State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Changping District, Beijing 102249, China.
³ Fujian Provincial Key Laboratory for Coastal Ecology and Environmental Studies, Xiamen University, Xiamen 361012, China.
⁴ Department of Land, Air and Water Resources, University of California, Davis 95616, USA.
⁵ School of Marine Sciences, Sun Yat-sen University, Zhuhai 519082, China.
⁶ National Observation and Research Station for the Taiwan Strait Marine Ecosystem, Xiamen University, Xiamen 361012, China.
⁷ State Key Laboratory of Marine Environmental Science, College of Ocean and Earth Sciences, Xiamen University, Xiamen 361012, China; Fujian Provincial Key Laboratory for Coastal Ecology and Environmental Studies, Xiamen University, Xiamen 361012, China; National Observation and Research Station for the Taiwan Strait Marine Ecosystem, Xiamen University, Xiamen 361012, China. Electronic address: nwchen@xmu.edu.cn.
⁸ State Key Laboratory of Marine Environmental Science, College of Ocean and Earth Sciences, Xiamen University, Xiamen 361012, China; Fujian Provincial Key Laboratory for Coastal Ecology and Environmental Studies, Xiamen University, Xiamen 361012, China; National Observation and Research Station for the Taiwan Strait Marine Ecosystem, Xiamen University, Xiamen 361012, China. Electronic address: wdguo@xmu.edu.cn.

PMID: 35526431
DOI: 10.1016/j.watres.2022.118537

Abstract

Global impoundment of river systems represents a major anthropogenic forcing to carbon cycling in reservoirs with seasonal thermal stratification. Currently, a quantitative and mechanistic understanding of how hypolimnetic deoxygenation in stratified reservoirs alters dissolved organic matter (DOM) cycling and lateral transport along the river continuum remains unresolved. Herein, we used optical and high-resolution mass spectrometric analyses to track seasonal and spatial compositional changes of DOM from a large, subtropical impounded river in southeast China. Aliphatic compounds were contributed by algal blooms to epilimnetic DOM during the spring/summer and by baseflow to the overall DOM pool during low-discharge periods. Deoxygenation-driven hypolimnetic mineralization enhanced in situ production of bio-refractory molecules and humic-like fluorescent DOM (FDOM_H) by utilizing bio-labile DOM and settling biogenic particles during periods of stratification. Production efficiency of hypolimnetic FDOM_H was 159-444% higher than that of the global dark ocean, and was strongly regulated by temperature and possibly substrate supply. The in situ production rate of hypolimnetic FDOM_H was four to five orders-of-magnitude higher than the dark ocean, with much faster turnover rates in dark inland waters versus the dark ocean. Collectively, these findings indicate that the hypolimnion is a hotspot for microbial carbon transformations, and hence an important source and pool of refractory DOM in aquatic systems. The lateral FDOM_H flux increased 10.8-32.1% due to hypolimnetic reservoir release during periods of stratification, highlighting the importance of incorporating hypolimnetic carbon transformations into models for carbon cycling of inland waters and the land-sea interface.

Keywords: Carbon transformation; Dissolved organic matter; FT-ICR MS; Hypolimnetic deoxygenation; Optical analysis; Stratified reservoir.

MeSH terms

Carbon
Dissolved Organic Matter*
Rivers
Seasons

Substances

Dissolved Organic Matter
Carbon