Modeling wetland's extent, their surface heat fluxes and exchange of carbon dioxide and methane
October 18, 2011
Hosted by Scott Denning (advisor), Colette Heald, Joe von Fischer (Biology)
Though wetlands cover only a small percentage of the terrestrial land surface, 3-8%, their soils contain an outsized proportion, perhaps a quarter, of the terrestrial carbon store. Wetlands are also the largest and most variable natural source of atmospheric methane. As such, wetlands form a vital component of the of the climate system, particularly given their prevalence at high latitudes and the warming trends forecast for and observed in those regions.
A method of prognostically estimating wetland extent utilizing the topographic index, ln(a/tanÎ²), is developed and assessed. The method is used to scale heat and carbon exchange in the Simple Biosphere Model (SiB), results are compared to estimates using an earlier version of the model and eddy-covariance measurements from a tower in northern Wisconsin. A model of methane exchange is implemented in SiB, with basic representation of methanogenesis and methanotrophy as temperature dependent reactions scaled by wetland area. Estimates from this model are also compared to observations from the Wisconsin location.
The technique for estimating wetland area appears viable and desirable, particularly as it permits representation of seasonal and other temporal variations in wetland extent. Modeled wetlands improve correspondence between predicted and observed heat fluxes and carbon exchanges at the Wisconsin site. Estimates of methane exchange appear promising, but varying atmospheric methane concentrations impacts the surface exchange of the gas substantially; a processes that would require coupling to an atmospheric model to resolve.