Quantification of methane emissions from different land-cover patches in a heterogeneous wetland

Abstract:

Methane (CH4) is the second most important greenhouse gas following carbon dioxide, and has 26-43 times greater potential effect on global warming. Wetlands are the largest contributor among all natural sources of methane and contribute 20% to 40% of the global methane emission. The large uncertainty of CH4 fluxes and the challenging aspects of modeling it are driven, to a large degree, by the small-scale spatial and temporal heterogeneity of methane fluxes, and the complexity and range of scales of meteorological, hydrological, ecological, and microbial processes that control and affect these fluxes. Wetlands are typically composed of several ecological patch types, characterized by different plant communities and hydrological regimes. Although terrestrial wetlands are typically small (few km), the difference in methane emissions from different adjacent patch types can be as high as 1-2 orders of magnitude. The objective of our study is to quantify the methane emissions from different land-cover patches of a heterogeneous wetland. We are conducting our research on Old Woman Creek wetland, which is an estuarine, mineral-soil marsh at the south shore of Lake Erie. We used high-resolution remote sensing image to classify and map the extent of each patch type of the wetland. We divided the land-cover patches into four: 1) open water, 2) mud flats, 3) Emergent vegetation, and 4) floating-attached vegetation dominated by American lotus (Nelumbo lutea). We sampled the gas exchange from each patch type on a monthly basis during the growing season using non-steady state chamber. And we combined the remote sensing data and chamber measurements to estimate the contributions of each land-cover patch type to the total methane emissions of the wetland. We found that the land-cover patches of the wetland changed over recent years. There were less cattail in the year 2018 than that of the previous year, while the American lotus has taken more area of the wetland. The water level also changed, and the area used to be covered by mud flat changed to American lotus because of the rising water level. The differences in methane emission is associated with the difference in land-cover patches, which is driven by the wetland hydrological dynamics.