Uncertainty and dynamics of natural wetland CH4 release in China: Research status and priorities

Abstract

Natural wetlands represent the largest single source of methane (CH4), a potent greenhouse gas. China is home to the world's fourth largest wetland area, and it is facing intense climate- and human-related impacts. The scientific community in China has invested considerable effort into investigating wetland CH4 release and its dynamics. Static chamber and eddy covariance observations have verified the temperature, water regime and air pressure as factors that regulate the diurnal and seasonal variation of CH4 release. Non-growing seasons, especially freezing–thawing cycles, play a role in CH4 release. However, a knowledge gap still exists with respect to the inter-annual variability of CH4 release. Observations also suggest that water and temperature regimes control the micro- and macro-scale spatial pattern of CH4 release, respectively. Recent bookkeeping surveys, biogeochemical model simulations, and chemical transport model inversions, have narrowed the uncertainty range of national CH4 release to 2.46–3.20, 2.77–4.95 and 2.38–4.91 Tg CH4 yr−1, respectively. Wetland loss (especially cropland conversion in Northeast China), despite climate changes, decreased CH4 release by 45.2%–52.2% from the 1950s–2000s, and by 13.2%–15.4% from the 1980s–2000s. However, future warmer temperatures and rising CO2 are predicted to strengthen national CH4 release by 32% (RCP2.6), 55% (RCP4.5) and 91% (RCP8.5) by the 2080s, albeit without the variation in wetland extent having been considered. Furthermore, future research should emphasize the mechanisms involved in CH4 release during freezing–thawing cycles and interannual variability. Model–data fusion of eddy covariance and manipulative experiments, especially warming and CO2 enrichment, would benefit estimations and projections of CH4 release.