Considering Coasts: Adapting Terrestrial Models to Characterize Coastal Habitats

The Energy Exascale Earth System Model (E3SM) simulates fully coupled processes and interactions between water, energy, carbon and nutrient cycles. E3SM connects vegetation and soil dynamics through nutrient uptake, plant production, litterfall and decomposition as a function of abiotic parameters (i.e. temperature and moisture). However, E3SM is designed to characterize terrestrial and freshwater habitats and connects terrestrial and open ocean ecosystems using a single transport term, ignoring coastal dynamics. The goals of our project were to: 1) Parameterize a point version of E3SM to mimic coastal wetland habitats and 2) Determine C3 and C4 marsh community responses to the interacting effects of sea level rise, increased temperature, and elevated CO₂. We adapted E3SM to coastal ecosystem using long-term data sets from field experiments conducted at Smithsonian Environmental Research Center's Global Change Research Wetland (GCREW). Tidal forcing was mimicked using a 2-column system. Column 1 simulated interactions between vegetation and soil while column 2 simulated water level (both tidal and sea level rise). We also altered biogeochemical processes to incorporate salinity, methane, and sulfur dynamics.

Plant community responses to environmental change were non-linear, non-additive and inconsistent between C3 and C4 plants. We were able to characterize the following shifts observed at GCREW: alterations to above:below ground biomass ratios only in C3 communities, positive correlation between methane production and temperature suppressed by increased CO₂, and sulfate depletion with rising temperature.