Seasonal Terrestrial Freshwater Inputs Impact Salt Marsh Hydrology
Abstract
Salt marshes exist at the terrestrial-marine interface, serving as coastal buffers and hotspots for nutrient cycling. Shallow salt marsh hydrologic behavior and pore water mixing has been shown to be strongly influenced by tidal pumping along the intertidal zone. However, terrestrially derived freshwater inputs from adjacent uplands are increasingly recognized as important sources of water and solutes to some salt marshes. A knowledge gap still exists in understanding the role of shallow subsurface terrestrial freshwater inputs on salt marsh hydrology, with implications for plant productivity and biogeochemical cycling. As seasonal weather patterns become less predictable with climate change, it is critical to understand coastal zone responses to freshwater input variability.
To understand how seasonal changes in terrestrial freshwater inputs impact salt marsh hydrologic processes, we examined subsurface hydrology, pore water salinity, and pickleweed (Sarcocornia pacifica) productivity across three marsh positions (low, middle, and upper) in the Elkhorn Slough, an estuary located along the central coast of California. We collected monthly pore water (10-30 cm-bgs) samples for salinity, monitored high frequency water level from nested piezometers (70 cm-bgs), conducted monthly remotely sensed observations of vegetation activity, and characterized subsurface soil properties and composition through lab analyses and a geophysical survey. We found that seasonal terrestrial water inputs alter salt marsh pore water cycling by dampening the tidal signal in the shallow subsurface due to saturation during the wet season when upland water level is high. Freshwater inputs dilute pore water salinity and initiate earlier pickleweed productivity in the upper and middle marsh than in the lower marsh, which is furthest from the upland. Conversely, salt marsh hydrologic behavior is dominated by tidal inputs during the dry season when upland water level is low, indicating a seasonal disconnect in marsh hydrologic connectivity with the terrestrial upland. The duration of wet season salt marsh saturation varied between water years depending on temporal upland water levels, which were driven by seasonal and interannual precipitation inputs — highlighting the sensitivity of salt marsh hydrology to climate change.- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFM.H26C..02M