Assessing the Past and Potential Future Impacts of Salt Water Intrusion on Tidal Swamp Habitat along the South Atlantic Coast

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Using historical aerial photogrammetry, satellite imagery, or recent vegetation mapping efforts, as well as various models, USGS investigates salt water intrusion impacts on coastal habitats along the southern Atlantic coast. 

Satellite map of the study area, Waccamaw National Wildlife Refuge

Satellite map of the study area, Waccamaw National Wildlife Refuge

The Science Issue and Relevance: Coastal habitat mosaics distributed across salinity gradients are susceptible to salt water intrusion caused by sea level rise, land surface subsidence, and decreased freshwater discharges to the coast. This project seeks to develop a widely-applicable methodology for predicting changes in coastal habitat that utilizes investigations of past changes in habitat, hydrologic simulations, and process-based models of community-level responses to fluctuating salinity and water levels. The work will focus on the Waccamaw National Wildlife Refuge (WNWR). The project addresses key goals and objectives of the USGS Ecosystems and Climate and Land Use Change Mission Areas and the National Climate Change and Wildlife Science Center. This project addresses a priority science need identified by the inter-agency scientific steering committee of the South Atlantic Landscape Conservation Cooperative (SALCC) in FY2013.

Methodology for addressing the issue: The primary objectives are: 1) to investigate past changes in the aerial extent of tidal freshwater swamps utilizing historical aerial photogrammetry, satellite imagery, or recent vegetation mapping efforts; 2) to develop a coupled hydro-dynamic and vegetation model at representative locations within the WNWR; 3) to model salinity and water levels at gauging stations located within and around the WNWR using an Artificial Neural Network (ANN) techniques; and 4) to develop a methodology for forecasting potential changes in ecotonal boundaries between tidal swamps and herbaceous oligohaline marshes utilizing predictions of sea level rise and changing freshwater inflows. Historical charts, photos and relevant satellite imagery for the WNWR will provide the basis for hypotheses regarding community-level responses to changing conditions to be tested in the process-based, dynamic vegetation model (MANTRA), which links the vegetation/vadose zone model MANHAM with the SUTRA hydrology model. The modeling takes into account abiotic processes (precipitation, tides, groundwater salinity and movement, salinity pulses from storm surges, etc.) and biotic processes (plant growth, evapotranspiration, competition, etc.), as well as both the effects of soil salinity on plant growth and the feedback effects of plant physiology on soil salinity. The modeling will include several vegetation types found along the WNWR and by improving the detail of hydrodynamics and soil salinity dynamics. This will complement the ANN approach to mapping salinity and water levels.

Hydro-dynamic and vegetation model

Hydro-dynamic and vegetation model