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). ꞵt ,
the transpiration factor, is a value between 0 (dry) and 1 (wet). It is
calculated by summing the product of wi, a wilting
factor for each soil layer, and ri, the fraction of
roots in each layer. ꞵt 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).