Influence of experimental extreme water pulses on greenhouse gas emissions from soils

Abstract:

Climate models predict increased frequency and intensity of storm events, but it is unclear how extreme precipitation events influence the dynamics of soil fluxes for multiple greenhouse gases (GHGs). Intact soil mesocosms (0-10 cm depth) from a temperate forested watershed in the piedmont region of Maryland (two forested upland locations, a wetland, and a creek bank) were exposed to experimental water pulses with periods of drying, forcing soils towards extreme wet conditions under controlled temperature. We used automated measurements (hourly resolution) to monitor soil CO₂, CH₄, and N₂O fluxes, coupled with analyses of soil water chemistry (i.e., pH, Eh, Fe, S, NO₃^-), and microbial community structure characterized with polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE). The experiment showed unexpected increases in emissions up to 244% for CO₂ (Wetland), and >5x10⁴ % for CH₄ (Creek) and N₂O (Forest Site 1). The Creek soil produced the largest soil CO₂ emissions, the Wetland soil the largest CH₄ emissions, and the Forest Site 2 the largest N₂O emissions among all soils during the experiment. Using carbon dioxide equivalencies of the three GHGs, we determined that the Creek soil contributed the most to a 20-year global warming potential (GWP; 30.3%), but Forest Site 2 contributed the most to the 100-year GWP (53.7%) as a result of large N₂O emissions. These results provide insights on the influence of extreme wet conditions on porewater chemistry and the underlying controlling factors of soil GHGs fluxes following experimental water pulse events.