ELM-Wet: A new wet-landunit patch-level approach for modeling carbon and methane fluxes from wetlands

We intoduce the development of a new wetland-focused version of the Energy’s Exascale Earth System Model (E3SM) Land-surface Model (ELM). The updated version, ELM-Wet, activates a separate wet-landunit for simulation of wetlands. This Wet-landunit handles multiple eco-hydrological functional type patches. We introduced wetland-specific hydrology through prescribing site-level (whole wetland) constraints on surface water elevation and including a patch-level characteristic maximal inundation depth that enables resolving different sustained inundation depth for different patches, and if data exists, prescribing inundation depth at the site and patch levels. We modified the calculation of methane transport through palnt aerenchyma based on observed conductance for different vegetation types. We use BOA, a new Bayesian Optimization toolpack, to parameterize the processes controlling CO2 and CH4 fluxes in the wetland landunit. Site-level simulations of a coastal freshwater wetland in Louisiana (US-LA2) were performed with the updated model. Eddy covariance observations of CO2 and CH4 fluxes from 2012-2013 were used to train the model. Flux data from 2021 were used for validation. Patch-specific chamber flux observations and observations of CH4 concentration profiles in the soil porewater from 2021 were used for evaluation of the model performance in terms of soil concentration profiles at the patch level. Our results show that ELM-Wet with BOA optimization was able torepresent inter-daily and seasonal CO2 and CH4 fluxes and concentration dynamics across the wetland’s eco-hydrological patches.