UC Santa Cruz

Salt marshes exist at the terrestrial-marine interface, serving as hotspots for nutrient cycling of tidal and freshwater inputs and providing critical ecosystem services. Tidal inputs are understood to play a dominant role in salt marsh pore water mixing, and terrestrially derived freshwater inputs are increasingly recognized as important sources of water and solutes to intertidal wetlands. However, there remains a critical gap in understanding of the role of shallow terrestrial freshwater inputs on salt marsh hydrology, with implications for plant productivity and biogeochemical cycling. Here, we examine the hydrologic behavior, pore water salinity, and pickleweed (Sarcocornia pacifica) productivity across three marsh positions in an estuary along the central coast of California to understand how seasonal changes in terrestrial freshwater inputs impact salt marsh processes. We found that salt marsh pore water salinity, pickleweed productivity, and water level tidal signal dampening (i.e. shallow subsurface saturation) are closely coupled with elevated upland water level during the winter and spring, and dominated by tidal inputs during the summer and fall, indicating a seasonal switch in salt marsh hydrologic connectivity with the terrestrial upland. Terrestrial freshwater inputs to the salt marsh depend on water level in the adjacent upland, which fluctuates seasonally and is driven by seasonal and interannual precipitation inputs — highlighting the sensitivity of salt marsh hydrology to climate change.