Kolloquium: Gil Bohrer

In the global context, wetlands are small, both in overall area, and in typical single-site extent. However, wetlands are responsible for a very large fraction of the global methane flux and for a large fraction of terrestrially sequestered CO2. Wetlands are intrinsically heterogenous, with temporal variation of water elevation and seasonal and long-term vegetation dynamics, as well as spatially, through microtopographic variation of water elevation that drives differences in vegetation within any wetland sites. This heterogeneity in hydrological dynamics and vegetation structure within wetlands leads to large differences in biogeochemical processing of carbon and extreme within-site variability of CO2 uptake and methane emission rates.

My group have been working in coastal wetlands in Louisiana, and a lake coastal wetland, at an estuary of Lake Erie in Ohio. The Ohio wetland, Old Woman Creek (OWC), has one of the highest methane fluxes ever observed with a long-term EC system, but not atypical for wetlands in agricultural watersheds. We have been combining point-scale measurements of methane and CO2 concentrations and fluxes, with site-level eddy covariance flux measurements to identify and quantify the differences between patches within wetlands. We show different patterns of regulation of methane transport through plants. We developed a remote-sensing based approach to classify the area and location of different vegetation patches and follow their decadal changes. We identify long-term and short-term effects of hydrology of greenhouse gas dynamics. Our results from the field demonstrate that any sampling of methane fluxes in a wetland must account for the areas of the ecological and hydrological patch types that each of the samples within the wetland represent. We incorporated our insight from the field into the E3SM-ELM Earth-system land-surface model, for which we developed the ELM-Wet version. ELM-Wet resolves wetland at the of eco-hydrological sub-patch scale within the wetland land-unit, to improve the global predictability of methane fluxes and carbon sequestrations from wetlands.