The ‘Mississippi River Delta Transition Initiative’: An Eco-hydrological model to assess the impacts of extreme droughts and salt-water intrusion in the Mississippi River Delta Region.

The Mississippi River Delta (MRD) is a complex and dynamic eco-region that is essential for biodiversity and coastal protection. Yet, the MRD is increasingly vulnerable to climate change, salt intrusion, and extreme drought events, which threaten its ecological stability. This study developed and applied an eco-hydrological model to analyze the combined effects of these stressors on wetland vegetation. Specifically, it focused on the increase in salinity during the 2022 drought and its negative impact on plant productivity. The original eco-hydrological model, Photo3 (Hartzell et al. 2018; publicly available at: https://github.com/samhartz/Photo3) was modified to account for soil saturation and the effects of salinity on plant transpiration. Meteorological and micrometeorological data for the model were obtained from the United States Geological Survey (USGS) Eddy Covariance stations located in the Barataria basin. Information on salinity, water level, and plant types was sourced from the Coastwide Reference Monitoring System (CRMS). This setup enabled realistic simulations of the environmental conditions and physiological responses of vegetation. The study focused on two species: Spartina patens, which dominates coastal brackish marshes, and Sagittaria lancifolia, which is prevalent in freshwater areas not affected by salt stress. The results underscored the critical role of salinity as a major limiting factor during the 2022 drought. In saline areas, salinity levels surpassed the tolerance thresholds of Spartina patens, leading to prolonged stress and significant reductions in transpiration and carbon assimilation rates. Nonetheless, several limitations persist, including the oversimplification of salinity effects and the omission of dynamic processes such as water redistribution, submergence, and groundwater variation. Future developments should incorporate stochastic forcing, soil-water-salinity interactions, and a water balance that accounts for water table variation rather than relying solely on soil moisture. This study provides new insights into wetland resilience and lays the groundwork for sustainable management strategies in deltaic ecosystems that are increasingly at risk from global change.