Improving Wetland Model Realism: Activating and Evaluating Sub-Grid Level Wetland Land-Unit in the E3SM Land Model (ELM)

Wetlands, and other inland water bodies, represent the highest source of uncertainty in the methane budgets from global Earth System Models (ESMs), yet wetlands are estimated to account for 20-40% of global methane emissions. Modeling challenges include the small-scale temporal and spatial heterogeneity of wetland structure and associated methane flux rates and the interactions between different underground and aboveground processes (hydrological, ecological, meteorological, and microbial) that control methane production, consumption, and transport. In this project, we aim to improve the realism of wetland representation in DOE’s Energy Exascale Earth System Model (E3SM) Land Model (ELMv1) and thereby improve simulations of methane and carbon biogeochemical processes within the wetland ecological patch-level. We developed a separate wetland land-unit, which included different patch types representing wetland ecological functional types and growth forms (e.g., floating vegetation, emergent vegetation, open water, and mud flats). We also we improved the default aerenchyma module by including a field-measured vegetation resistance to plant-mediated methane transport model. ELM’s ability to simulate the effects of the main methane flux drivers (i.e., water depth, leaf area, and plant aerenchyma conductance), among different patch types, was evaluated by a sensitivity analysis experiment. Site level simulations were performed for a freshwater and a saline marsh in Lousiana, where modeled carbon and methane fluxes matched flux observations following a Bayesian Optimization of respiration, photosynthesis, and methane production and transport parameters. Our results emphasized the ability of our model to simulate subgrid-level methane dynamics in wetlands while accounting for the different patch-type ecological and hydrological characteristics.