Intense methane diffusive emissions in eutrophic urban lakes, Central China

Liuqing Zhang; Y Jun Xu; Bingjie Ma; Ping Jiang; Siyue Li

doi:10.1016/j.envres.2023.117073

Intense methane diffusive emissions in eutrophic urban lakes, Central China

Environ Res. 2023 Nov 15;237(Pt 2):117073. doi: 10.1016/j.envres.2023.117073. Epub 2023 Sep 4.

Authors

Liuqing Zhang¹, Y Jun Xu², Bingjie Ma³, Ping Jiang³, Siyue Li⁴

Affiliations

¹ Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing, 400714, China; Chongqing School, University of Chinese Academy of Sciences, Chongqing, 400714, China; School of Environmental Ecology and Biological Engineering, Institute of Changjiang Water Environment and Ecological Security, Key Laboratory for Green Chemical Process of Ministry of Education, Hubei Key Laboratory of Novel Reactor and Green Chemical Technology, Wuhan Institute of Technology, Wuhan, 430205, China.
² School of Renewable Natural Resources, Louisiana State University Agricultural Center, Baton Rouge, LA, 70803, USA; Coastal Studies Institute, Louisiana State University, Baton Rouge, LA, 70803, USA.
³ School of Environmental Ecology and Biological Engineering, Institute of Changjiang Water Environment and Ecological Security, Key Laboratory for Green Chemical Process of Ministry of Education, Hubei Key Laboratory of Novel Reactor and Green Chemical Technology, Wuhan Institute of Technology, Wuhan, 430205, China.
⁴ School of Environmental Ecology and Biological Engineering, Institute of Changjiang Water Environment and Ecological Security, Key Laboratory for Green Chemical Process of Ministry of Education, Hubei Key Laboratory of Novel Reactor and Green Chemical Technology, Wuhan Institute of Technology, Wuhan, 430205, China. Electronic address: syli2006@163.com.

PMID: 37673122
DOI: 10.1016/j.envres.2023.117073

Abstract

Urban lakes are hotspots of methane (CH₄) emissions. Yet, actual field measurements of CH₄ in these lakes are rather limited and our understanding of CH₄ response to urban lake eutrophication is still incomplete. In this study, we measured dissolved CH₄ concentrations and quantified CH₄ diffusion from four urban lakes in subtropical China during wet and dry seasons. We found that these lakes were constantly CH₄-saturated, contributing the greenhouse gas (GHG) to the atmosphere. Nutrient enrichment significantly increased CH₄ concentrations and diffusive fluxes. Average CH₄ flux rate in the highly-eutrophic lake zones (4.18 ± 7.68 mmol m^-2 d^-1) was significantly higher than those in the mesotrophic (0.19 ± 0.18 mmol m^-2 d^-1) and lightly/moderately-eutrophic zones (0.72 ± 2.22 mmol m^-2 d^-1). Seasonally, CH₄ concentrations and fluxes were significantly higher in the wet season than in the dry season in the mesotrophic and the lightly/moderately-eutrophic lake zones, but an inverse pattern existed in the highly-eutrophic lake zones. CH₄ concentrations and fluxes increased with elevated levels of nitrogen, phosphorus and dissolved organic carbon (DOC). The accumulation of nutrients provided autochthonous substrate for methanogenesis, indicated by a negative correlation between CH₄ and the C:N ratio. Ammonium-nitrogen (NH₄⁺-N) was the best predictor for spatial fluctuation of CH₄ concentrations and diffusive fluxes in the mesotrophic and the lightly/moderately-eutrophic lake zones, while total nitrogen (TN) and total phosphorus (TP) levels showed the highest predictability in the highly-eutrophic lake zones. Based on the findings, we conclude that nutrient enrichment in urban lakes can largely increase CH₄ diffusion, and that urban sewage inflow is a key concern for eutrophication boosting CH₄ production and diffusive emission. Furthermore, our study reveals that small urban lakes may be an important missing source of GHG emissions in the global C accounting, and that the ratio of littoral-to-pelagic zones can be important for predicting lake-scale estimation of CH₄ emission.

Keywords: Aquatic CH(4) diffusive flux; CH(4) concentration; Eutrophication; Hydrological seasonality; Urban lakes.