Integrating saltmarsh vegetation dynamics, hydrology, and biogeochemistry with the ELM-PFLOTRAN interface

The Energy Exascale Earth System Model (E3SM) simulates fully coupled processes and interactions between water, energy, carbon and nutrient cycles. However, E3SM connects terrestrial and open ocean ecosystems using a single unidirectional transport term, ignoring coastal dynamics. As a first step to incorporating estuarine habitats, we modified the land component of E3SM (ELM) to mimic both vegetation dynamics and coastal hydrology and updated biogeochemical representations. Biogeochemical reactions currently represented via the coupled ELM-PFLOTRAN interface are limited to carbon and nitrogen cycling. However, PFLOTRAN is an open-source, massively parallel, subsurface, reactive flow and transport model which can be used to incorporate additional redox reactions and track more chemical species that are important for coastal ecosystems. Our goal was to update the current reaction networks within PFLOTRAN to incorporate oxygen flux, salinity, pH, sulfur cycling, and methane production. Using porewater profile and incubation data, we were able to create depth-resolved biogeochemical soil profiles for saltmarsh habitat which mimicked the shallow oxic zone and demonstrated the balance between opposing redox reactions (e.g methane production - methane oxidation) and how this balance shifts with depth. Additionally, we designed our input files to be easily adapted to suit other ecosystems. Our next steps are to update the current ELM-PFLOTRAN interface to couple the updated vegetation, hydrology, and biogeochemical processing and conduct targeted incubation studies to resolve reaction rate constants used within our current biogeochemical module.