Towards understanding sea-level rise: Interactions between precipitation, ocean water intrusion, and coastal dune vegetation

Climate change is causing the redistribution of global precipitation while simultaneously driving sea-level rise at a rate of 2-3 mm/year along many US coastlines.  Here we address these factors in tandem by investigating how elevated and decreased precipitation, via seasonal and geographic distribution, impact ocean water intrusion (below ground intrusion into the fresh water table) and plant response on subtropical coastal dunes.  The dune ecotone is blocked into fore (5-12m inland) and back (35-50 m inland) dune positions to examine how distance from the ocean impacts hydrology and plant physiology.  The results show the role of precipitation in ecosystem function differs spatially across the dune.  The fore dune is vulnerable to ocean water intrusion.  The extent of the intrusion increases with decreasing seasonal and annual rainfall.  In response to ocean water intrusion, the vegetation alters water harvesting strategies to minimize osmotic stress.  Ocean water intrusion does not occur on the back dune; however the water table sinks in response to decreased precipitation. In response, most plants become more rainfall dependent when the sinking groundwater table falls deep enough to preclude recharge to the upper soil layers.   The results demonstrate a dynamic relationship between rainfall, ocean water and vegetation indicating the impacts of sea-level rise on coastal ecosystems will be exacerbated by diminished precipitation.