Epilimnetic oligotrophication increases contribution of oxic methane production to atmospheric methane flux from stratified lakes

Fan Xun; Muhua Feng; Cheng Zhao; Wenlei Luo; Xiaotong Han; Zhen Ci; Yifan Yin; Rong Wang; Qinglong L Wu; Hans-Peter Grossart; Peng Xing

doi:10.1016/j.watres.2024.122602

Epilimnetic oligotrophication increases contribution of oxic methane production to atmospheric methane flux from stratified lakes

Water Res. 2024 Oct 10;268(Pt A):122602. doi: 10.1016/j.watres.2024.122602. Online ahead of print.

Authors

Fan Xun¹, Muhua Feng², Cheng Zhao¹, Wenlei Luo³, Xiaotong Han², Zhen Ci⁴, Yifan Yin⁴, Rong Wang³, Qinglong L Wu⁵, Hans-Peter Grossart⁶, Peng Xing⁷

Affiliations

¹ Key Laboratory of Lake and Watershed Science for Water Security, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China; State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China; College of Resources and Environment, University of Chinese Academy of Sciences, Beijing 100049, China.
² Key Laboratory of Lake and Watershed Science for Water Security, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China; State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China.
³ Key Laboratory of Lake and Watershed Science for Water Security, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China; State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China; The Fuxianhu Station of Deep Lake Research, Chinese Academy of Sciences, Chengjiang 652500, China.
⁴ Key Laboratory of Lake and Watershed Science for Water Security, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China; State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China; College of Hydrology and Water Resources, Hohai University, Nanjing 210008, China.
⁵ Key Laboratory of Lake and Watershed Science for Water Security, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China; State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China; The Fuxianhu Station of Deep Lake Research, Chinese Academy of Sciences, Chengjiang 652500, China; Center for Evolution and Conservation Biology, Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou 511458, China; Sino-Danish Center for Education and Research, University of Chinese Academy of Sciences, Beijing 100039, China.
⁶ Department of Plankton and Microbial Ecology, Leibniz- Institute of Freshwater Ecology and Inland Fisheries (IGB), Stechlin 16775, Germany; Institute of Biochemistry and Biology, University of Potsdam, Potsdam 14476, Germany.
⁷ Key Laboratory of Lake and Watershed Science for Water Security, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China; State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China; The Fuxianhu Station of Deep Lake Research, Chinese Academy of Sciences, Chengjiang 652500, China. Electronic address: pxing@niglas.ac.cn.

PMID: 39454273
DOI: 10.1016/j.watres.2024.122602

Abstract

Although considerable attention has been paid to the effects of eutrophication on aquatic methane (CH₄) emissions to the atmosphere, the ecosystem-level effects of oligotrophication/re-oligotrophication on aquatic CH₄ production and subsequent ecological responses remain to be elucidated. It has been hypothesized that dissolved inorganic phosphorus (DIP)-deficient conditions drive the ecosystem to utilize poorly bioavailable organic phosphorus for biomass formation, thereby generating CH₄ as a by-product. To test this hypothesis, a mass balance approach was used to estimate in situ oxic methane production (OMP) in an oligotrophic, deep Lake Fuxian. The isotopic signature of dissolved ¹³C-CH₄, the potential substrates for OMP, and the phnJ/phnD genes associated with microbial demethylation of organic phosphorus compounds were analyzed. Our results indicate that CH₄ accumulation was maximal in the surface mixed layer (SML, i.e., Epilimnion) during lake stratification, and ∼ 86 % of the total CH₄ flux to the atmosphere was due to OMP. Decomposition of methylphosphonate (MPn) by Alphaproteobacteria (genera Sphingomonas and Mesorhizobium) contributed significantly to OMP. Furthermore, water temperature (Temp), chlorophyll a (Chla), and DIP were the most critical predictors of water OMP potential. Meta-analysis of currently available global data showed that OMP had a negative exponential distribution with DIP (OMP = 2.0 e^-0.71DIP, R² = 0.57, p < 0.05). DIP concentrations below a threshold of 3.40 ∼ 9.35 μg P L^-1 triggered OMP processes and increased the atmospheric CH₄ emissions. Under future warming scenarios, stratification and catchment management induced oligotrophication or re-oligotrophication may systematically affect the biogeochemical cycling of phosphorus and the OMP contribution to CH₄ emission in stratified lakes.

Keywords: Oligotrophication; atmospheric CH(4) emissions; mass balance; methane paradox; methyl-phosphonate (MPn); phosphate deficient.