Acetate Additions Stimulate CO2 and CH4 Production from Urban Wetland Soils

Abstract

Core Ideas Carbon additions to three varied wetland soils enhanced both carbon dioxide and methane production. Methane production was negatively correlated to salinity with and without carbon additions. Microbial community representation was associated with salinity not treatment. Wetlands in close proximity to urban centers receive significant inputs of dissolved organic carbon (C) and nitrogen (N) from runoff, sewage overflow, and treated wastewater. Additions of C and N may impact greenhouse gas (GHG) production rates from temperate wetland ecosystems, which are considered a large sink for atmospheric carbon dioxide (CO2). We hypothesized that microbial activity in these anaerobic ecosystems was limited by the availability of labile C which provides electron donors to support microbial metabolism. To test this hypothesis, CO2 and methane (CH4) production rates were quantified with a series of soil incubations from three wetland sites located across a salinity gradient in the Hudson River Estuary (HRE). Acetate additions to soils enhanced CO2 (2×) and CH4 (>125×) production rates from soil slurries among all wetland soils vs. no amendment controls. Enhanced CH4 production was also inversely correlated (r2 = 0.81) to the salinity of sampled soils. In contrast, neither nitrate (NO3–) nor ammonium (NH4+) additions had a significant effect on CO2 or CH4 production rates when added alone or with acetate. Greater CO2 and CH4 production from soils with added acetate were associated with lower redox potential, increased pH, and increased hydrogen sulfide concentrations. The wetland sites had dissimilar methanogenic and sulfate reducing communities, which likely contributed to differences in CO2 and CH4 production among wetland sites. These data suggest that C loadings in wetland soils enhance both CO2 and CH4 efflux and potentially limit the capacity of wetlands impacted by anthropogenic pollution to act as C sinks.