Terrestrial Vegetation Drives Methane Production in the Sediments of two German Reservoirs

Abstract

Inland waters and reservoirs in particular are significant sources of methane to the atmosphere. However, little information is available on the extent to which organic carbon from terrestrial vegetation or from internal photosynthesis fuels the methane production. This limits our ability to constrain methane emissions efficiently. We studied the isotopic composition (13C, 14C) of pelagic and sedimentary carbon sources in two small German reservoirs. The methane was enriched by radiocarbon with isotopic ranges (∆14C 5‰ to 31‰) near to fresh terrestrial organic carbon (OC, 17‰ to 26‰). In contrast, potential source OC produced by internal photosynthesis was characterized by negative ∆14C values (−30‰ and −25‰) as derived from signatures of inorganic carbon in the reservoirs. The particulate OC in stream supplies (terrestrial OC) was also 14C depleted in almost all cases, but highly variable in ∆14C (−131‰ to 42‰). Although the import of terrestrial OC was lower than the amount of OC produced by reservoir-internal photosynthesis, we conclude that the methane production was predominantly fuelled by catchment vegetation. The utilized terrestrial OC was of contemporary origin, fixed within years to decades before sampling and supplemented with reservoir-internal or aged terrestrial OC. Our results indicate that terrestrial biomass is an important driver of methane production in reservoirs receiving significant imports of terrestrial OC.

Identifying dominant environmental predictors of freshwater wetland methane fluxes across diurnal to seasonal time scales

“…Physical processes such as turbulent conditions and atmospheric pressure (PA) fluctuations can influence the transport of CH 4 from the soil profile into the atmosphere, particularly in porous peat soils where ebullition is often the primary CH 4 transport mechanism during the pressure‐falling phase (Nadeau et al, 2013; Sachs et al, 2008; Ueyama, Yazaki, et al, 2020). Biological factors such as plant community type and primary production also influence CH 4 production and consumption through a variety of mechanisms, including supplying labile carbon compounds that fuel methanogenesis (Christensen et al, 2003; Tittel et al, 2019); enhancing oxygen transport into anoxic soil layers via aerenchyma, thereby supporting rhizosphere CH 4 oxidation (Laanbroek, 2010); and mediating transport of CH 4 to the atmosphere via aerenchyma, allowing CH 4 to bypass potential oxidation in surface soils (Knoblauch et al, 2015; Kwon et al, 2017; Villa et al, 2020).…”

Vegetation Affects Timing and Location of Wetland Methane Emissions

“…In terms of CH 4 production and consumption, vegetation provides carbon substrates to fuel microbial processes (Christensen et al, 2003). These carbon substrates are derived from decomposition of dead plant materials or more directly through root exudates (Carmichael et al, 2014; Tittel et al, 2019). However, the lacunar air ventilation system of many wetland species that supplies oxygen (O 2 ) to the rhizosphere can also reoxidize alternative electron acceptors such as sulfate, which inhibits CH 4 production due to microbial competition for carbon substrates (Dalcin Martins et al, 2017; Neubauer et al, 2005; Sutton‐Grier & Megonigal, 2011).…”

Temperature and sediment properties drive spatiotemporal variability of methane ebullition in a small and shallow temperate lake

“…Also, the OM quality, that is, the abundance of labile OM compounds, determines CH 4 production rates in anoxic environments. Labile compounds such as polysaccharides or proteins are preferentially decomposed by microorganisms, whereas more recalcitrant structures such as cellulose, lignin, or humic substances residually enrich in the sediment (Updegraff et al 1995; Tfaily et al 2014; Tittel et al 2019). To identify such effects and to characterize OM, Fourier‐transformed infrared (FTIR)—spectroscopy provides a valuable tool to identify functional moieties of OM and can therefore provide information on the decomposition state or quality of OM (Broder et al 2012).…”