Collaborative Research: Hydrogeophysical monitoring and modeling of heterogeneity in salinization processes across the marsh-upland transition

Rising sea levels driven by climate change threaten to transform coastal landscapes with profound, global economic implications. Within the coastal zone, increased flooding of soils with saline water disrupts the natural cycling of nutrients and carbon between soils, the atmosphere and the ocean. Coastal marshes are an important sink of terrestrial carbon, and carbon accumulation rates in coastal marshes exceed those of temperate forests. Whereas gradual sea-level rise results in slow, lateral inland movement of saline groundwater, storms and large tides cause rapid inundation of soils with saltwater, driving vertical transport of salt into soils. The ecological consequences of these processes are visible to the naked eye, particularly across the transition between coastal marshes and forested uplands, where increasing soil water salinity results in tree mortality and the formation of ‘ghost forests’. However, the patterns of salinity change beneath the subsurface in soils and groundwater are unclear, particularly as numerous positive and negative feedback mechanisms may exist. For example, the death of individual trees may locally enhance vertical transport of salt if dead roots and surrounding soil serve as preferential pathways for the transport of saline water. Variations in soil texture (e.g., grain size) across the marsh-upland transition may also result in variability in rates of salinization both during short-term storm events and in response to gradual sea-level rise. This project will apply electrical geophysical imaging technologies and hydrological models of saltwater transport to improve understanding of the role of subsurface heterogeneity (both geology and vegetation induced) in regulating gradual and rapid (storm surge) hydrological processes across multiple marsh-upland transition zones. Electrical geophysical imaging methods provide spatially continuous, non-invasive information of variations in salinity. In this project, these methods will be deployed to monitor the evolution of salinity changes in response to major storm events. The work will [1] produce data and simulations to improve conceptual models for salinization resulting from storm events by incorporating the role of subsurface heterogeneity; [2] develop strategies to improve the predictive capabilities of hydrological models of saltwater transport by incorporating spatially and temporally rich geophysical observations; [3] promote awareness of geophysical imaging technologies for investigating coastal landscapes within a broad community of interdisciplinary scientists; [4] engage a diverse body of students and early career scientists in workshops studying the marsh-upland transition. This project is jointly funded by Hydrologic Sciences and the Established Program to Stimulate Competitive Research (EPSCoR). This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.