Salinity causes widespread restriction of methane emissions from inland waters

Abstract

Inland waters are the largest natural source of methane (CH4), a potent greenhouse gas, but models and estimates of aquatic CH4 cycling and emissions were developed in soft-water ecosystems and may not apply to globally abundant salt-rich inland waters. Here we show that elevated salinity constrains microbial CH4 cycling restricting aquatic emissions at large scales. Our survey of the Canadian Prairie ecozone demonstrates that salinity interacts with organic matter availability to shape CH4 patterns across aquatic networks (rivers, lakes, wetlands, and agricultural ponds). Current empirical models, biased toward solute-poor surface waters, overestimated CH4 concentrations and emissions measured in hardwater systems by up to several orders of magnitude, with discrepancies strongly linked to salinity. Models were particularly inaccurate for bubble-mediated emissions from small lentic systems, one of the largest sources of aquatic CH4 globally. Elevated salinity reduced aquatic CH4 emissions by an estimated 81 % in the Canadian Prairies, and could result in a 7.8 % overestimation of global lentic emissions. Widespread salinization of inland waters under future land use and climate regimes could further restrict methane emissions.

Methane Emissions From the Qinghai‐Tibet Plateau Ponds and Lakes: Roles of Ice Thaw and Vegetation Zone

“…Most ponds and lakes in desert zones and some in steppe zones are hydrologically terminal, exhibiting higher water salinity. Higher water salinity can inhibit methanogens' abundance (Liu et al., 2016) and enhance CH 4 anaerobic oxidation by sulfate (Avrahamov et al., 2014), leading to a reduction in annual CH 4 flux from these saline waterbodies (Soued et al., 2024; Xun et al., 2022). There was no relationship between water pH and annual CH 4 flux, but sediment pH exhibited a significant negative correlation with annual CH 4 flux (Figures 5b and 5c).…”

“…The contribution of CH 4 emissions during ice thaw to annual CH 4 emissions varies substantially among different high‐latitude freshwater lakes (4%–74%) (Denfeld, Baulch, et al., 2018) due to variability in carbon availability and dissolved oxygen (Michmerhuizen et al., 1996; Sepulveda‐Jauregui et al., 2015). However, only a few studies on annual CH 4 emissions included fluxes during the ice thaw period in alpine and saline waterbodies (water salinity over three parts per thousand), although these waterbodies are abundant in the Northern Hemisphere and may exhibit different CH 4 emission patterns (Messager et al., 2016; Soued et al., 2024).…”

New perspectives on the potential of temperate freshwater wetlands as natural climate solutions based on different CO2 equivalent metrics

“…Second, the ionic concentrations of restored wetland should be monitored, which has been found to regulate dominant anaerobic metabolism pathway. For instance, high abundance of sulfate associated with wetland salinization could suppress CH 4 production by altering the dominant anaerobic metabolism pathway from methanogenesis towards pathways that yield higher energy (e.g., SO 4 2− reduction) 7,32 . Third, plant community composition of restored wetland should be optimized, since cutting and/or grazing Typha within restored wetland could bene t the reduction of CH 4 production and emission 33 .…”

Examining the impacts of salt specificity on freshwater microbial community and functional potential following salinization

“…These dynamics were corroborated by Duan and Kaushal (2015), in which several additional biogeochemical modifications were also attributable to increased salinization, including the elevated release of various carbon and nitrogen constituents from impacted soils. In contrast, increasing salinity decreased CH 4 emissions (Soued et al, 2024) and impacted other microbe‐mediated nutrient cycling functions (Ho et al, 2023).…”