An index for assessing salt-water vulnerability in coastal regions

Abstract:

Low-lying coastal landscapes are at risk as sea level rises. Future projections suggest that 50 cm to 100 cm sea-level rise is imminent by the end of the century. One of the responses to increasing sea level is salt-water intrusion of freshwater-dependent ecosystems with long-term negative impacts on ecosystem services. This effect is further exacerbated by the presence of human-modified artificial drainages, which serve as gateways through which salt water penetrates inland areas. We present a novel conceptual model to investigate the vulnerability of low-lying, freshwater-dependent landscapes to saltwater intrusion. The saltwater intrusion vulnerability index (SIVI) is determined by the ratio of protected elevation above sea level to the log transformed local drainage area as a proxy for freshwater subsidies. As an index, SIVI represents the balance between vulnerability to salt-water exposure on one hand and the potential for freshwater flushing on the other. To this end, we use a high resolution Lidar-derived digital elevation model (DEM) to derive protected elevation, whereas the local drainage area is derived using a downscaled 100-m DEM to reflect the natural drainage and flushing potential in the absence of man-made structures. Thus, SIVI will serve as a guiding tool to determine the potential for salt-water intrusion, initially in coastal North Carolina, but eventually in similarly low-lying coastal regions. It will also aid understanding of the natural and human influences on observed patterns of salt-water intrusion and subsequent implications for ecosystem productivity, biodiversity and associated ecological processes.