R&D Associate Oak Ridge National Laboratory Oak Ridge, Tennessee, United States
Connections between plants and sediment dynamics or ecogeomorphic feedbacks have been modelled using variations of the Marsh Equilibrium Model (MEM) to understand the fate of terrestrial aquatic interfaces (TAIs) under altered hydrological regimes. However, many of the processes that regulate vegetation growth and nutrient and carbon cycling including sediment transport, compaction, and erosion are absent from Earth System Models. These geomorphic processes are key to accurately representing TAIs and their role within a larger landscape context including their capacity to sequester carbon and process nutrients. The goals of this study were to include ecogeomorphic processes in the Energy Exascale Earth System Model (E3SM) Land Model (ELM) to investigate connections between biogeochemical processes, vegetation growth, and sediment and the relationships between the varying temporal scales of each. Given that microbial and plant processes operate at different temporal scales than geomorphic processes, we hypothesized that biogeochemical cycling and primary production would be more influential at season-to-annual time scales while geomorphic processes would drive long-term trends. In addition, we anticipated that predictions of marsh elevation, nutrient content, and biomass production would vary significantly based on temporal resolution of data inputs (i.e. annual averages versus hourly updates). To address these hypotheses, we built on current ELM infrastructure using a multi-column framework with one column representing the tidal ch annel and other two representing the low marsh and high marsh. Using MEM equations, we varied column elevation based on vegetation growth, distance from the tidal channel (which altered sediment supply and erosion), and litter decomposition. We also altered carbon content of the static soil layers in ELM to mimic the carbon pools defined by the Cohort Theory model in age-depth soil cohorts. These modifications were preliminary steps towards the inclusion of ecogeomorphic feedbacks. We found that temporal resolution does influence predictions of marsh elevation and that the model was particularly sensitive to plant functional type parameterization and organic matter decomposition rates. In conclusion, this study suggests that incorporating ecogeomorphic feedbacks in ELM significantly alters our predictions of coastal ecosystem function with hydrologic shifts and that future simulations should include plant demography, plant-mediated transport, and dynamic root-shoot allocation.
