River-Lab

Sea-level rise will have extreme impacts on coastal estuaries, including freshwater sources like rivers and creeks. Though freshwater linkages are critical to overall estuarine health, few studies have explicitly considered how sea-level rise and saltwater intrusion will impact riparian vegetation composition or community health in freshwater creeks adjacent to tidally influenced systems. Our study sought to identify the historical and current conditions as well as projected vulnerabilities for the lower section of Carneros Creek, the main freshwater source for the Elkhorn Slough, in Monterey County, California. To describe historical and current conditions of Lower Carneros Creek, we assessed historical maps, surveyed riparian vegetation using the rapid assessment method, and evaluated drinking water well data for evidence of existing saltwater intrusion. To assess future sea-level rise impacts for Lower Carneros Creek, we mapped previously modeled groundwater rise and saltwater intrusion footprints under a 0.25m sea-level rise scenario. We found that the Western lower section of Lower Carneros Creek is currently characterized by the presence of halophytic, tidal wetland species while the Eastern upper section is dominated by freshwater, riparian species. Our results also showed that even with tidal controls, sea-level rise induced groundwater rise and saltwater intrusion will impact Lower Carneros Creek’s hydrology and likely alter riparian vegetation composition. In response to these findings, we presented management considerations for Lower Carneros Creek that account for historical conditions, broader estuary-wide conservation goals, and public health concerns for communities living in the floodplain.