PNNL

Abstract

Rewetting of dry soils and thawing of frozen soils are short-term, transitional phenomena in terms of hydrology and thermodynamics in soil systems. The impact of these short-term phenomena on larger-scale ecosystem fluxes has only recently been fully appreciated, and a growing number of studies show that these events affect various biogeochemical processes including fluxes of biogenic gases such as carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), ammonia (NH3) and nitric oxide (NO). Global climate models predict that future climatic change is likely to alter the frequency and intensity of drying-rewetting events and thawing of frozen soils, highlighting the importance of understanding how rewetting and thawing will influence biogenic gas fluxes. Here we summarize findings in an acquired database from 338 studies conducted from 1956-2010, and propose future research questions. Studies have reported conflicting results, ranging from large increases in gas fluxes to non-significant changes following rewetting and thawing in various terrestrial ecosystems. An analysis of published data revealed that CO2, CH4, N2O, NO and NH3 fluxes increase 7.6 (± standard error 1.1) times following rewetting and thawing with no significant difference between these events. We explore possible mechanisms and controls that regulate flux responses, and note that there is a lack of studies on variation of CH4, NO and NH3 fluxes following rewetting and thawing events. High temporal resolution of flux measurements is critical to capture rapid changes in the gas fluxes after these soil perturbations. Finally, we propose that future studies should investigate the interactions between biological (i.e., microbial community) and physical (i.e., gas production, flux, and dissolution) changes in biogenic gas fluxes, and explore synergistic experimental and modelling approaches.