Hot spot of CH4 production and diffusive flux in rivers with high urbanization

Wei Tang; Y Jun Xu; Yongmei Ma; Damien T Maher; Siyue Li

doi:10.1016/j.watres.2021.117624

Hot spot of CH₄ production and diffusive flux in rivers with high urbanization

Water Res. 2021 Oct 1:204:117624. doi: 10.1016/j.watres.2021.117624. Epub 2021 Sep 2.

Authors

Wei Tang¹, Y Jun Xu², Yongmei Ma¹, Damien T Maher³, Siyue Li⁴

Affiliations

¹ Key Laboratory of Reservoir Aquatic Environment, Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing 400714, China.
² School of Renewable Natural Resources, Louisiana State University Agricultural Center, Baton Rouge, LA 70803, United States; Coastal Studies Institute, Louisiana State University, Baton Rouge, LA 70803, United States.
³ Faculty of Science and Engineering, Southern Cross University, Lismore, NSW 2480, Australia.
⁴ Research Center for Environmental Ecology and Engineering, School of Environmental Ecology and Biological Engineering, Wuhan Institute of Technology, Wuhan 430205, China. Electronic address: syli2006@163.com.

PMID: 34500180
DOI: 10.1016/j.watres.2021.117624

Abstract

Rivers and streams play a central role in global carbon budget, but our knowledge is limited on the magnitude and extent of urbanization influence on riverine methane (CH₄) dynamics. In this study, we investigated dissolved CH₄ (dCH₄) concentration and CH₄ diffusive fluxes in 27 river segments of two 4^th-order and three 3^rd-order tributary rivers to the Yangtze River in China, which drained land areas with varied urbanization intensities. We found that urban development was the key factor responsible for high fluvial dCH₄ concentration and diffusive flux, exceeding the influence of agricultural farming, and these headwater rivers were over-saturated in CH₄ with respect to atmospheric equilibrium. dCH₄ concentration (3546 ± 6770 nmol L^-1) in the river segments draining higher urban area (20% ≤ urban land proportion ≤ 46%) was 5-6 times higher than those (615 ± 627 nmol L^-1 and 764 ± 708 nmol L^-1) in the river segments draining less urban area (0.1% ≤ urban land proportion < 2% and 2 ≤ urban land proportion < 20%). River segments draining higher urban area also acted as important sources of CH₄ to the atmosphere (8.93 ± 14.29 mmol m^-2 d^-1). Total nitrogen (TN) concentration in river water showed the best prediction capacity when compared to other water parameters. Based on urban land use grouping, nutrient elements could predict dCH₄ well in rivers draining higher urban areas (urban ≥ 2%), which also reflected the lateral input of pollutants (TN, ammonia nitrogen, and total phosphorus). River bottom sediment fraction contributed to trapping organic matter and nutrients as well as to oxic and anoxic conditions, thereby determining reach-scale spatial patterns of dCH₄ concentration. These findings highlight that combining distal geomorphic and hydrologic drivers can be effective in determining the relationship between riverine CH₄ and the proximal controls (e.g., nutrients, dissolved oxygen, dissolved organic carbon), as well as in identifying their key drivers. Being rapid urbanization a common feature of catchments worldwide, our results suggest riverine CH₄ emissions will increase into the future.

Keywords: CH(4) diffusive fluxes; Low-order streams; Riverine dissolved CH(4); Three Gorges Reservoir (TGR) catchment; Urbanization.

MeSH terms

Diffusion
Hydrology
Rivers*
Urban Renewal
Urbanization*