Default land surface model description
The Exascale Energy Earth System Model (E3SM)’s land model (ELM) represents energy, water, carbon, and nutrient balances in terrestrial ecosystems, as well as processes that control the movement of energy and matter between soil layers, vegetation, and the atmosphere (Golaz et al., 2019; Lawrence et al., 2019). In the model, carbon uptake by plants is closely coupled with water uptake by roots via stomatal conductance; greater stomatal conductance is associated with both higher water and carbon uptake.
Soil water stress limits stomatal conductance through a transpiration function (Equation 1, Oleson et al. 2013). t , the transpiration factor, is a value between 0 (dry) and 1 (wet). It is calculated by summing the product of w, a wilting factor for each soil layer, and ri, the fraction of roots in each layer. t is multiplied by the minimum conductance to apply soil water stress.
\(\beta_{t}=\ \sum_{i}{w_{i}r_{i}}\) (Equation 1)
The current study builds from salt marsh processes that have been recently implemented in ELM, including tidal hydrology and parameterization of salt marsh graminoids (O’Meara et al., 2021). Water level is represented with a two-column approach, with one column representing a tidal channel and the other representing an adjacent, hydrologically-connected marsh. The water level in the tidal channel varies according to the tide pattern. When the water level in the tide channel is elevated above the marsh surface, water is transported laterally to the second column representing a marsh or other vegetated wetland type. In our simulations, which focus on salt marsh systems, we use the C4 grass PFT previously parameterized for Spartina patensbased on literature values and measurements from the Global Change Research Wetland in Chesapeake Bay (O’Meara et al., 2021).