Using Stable Water Isotopes to Estimate Source Water Contribution in a Tidal Marshland

Sea level rise due to climate change is exacerbating issues of saltwater intrusion and contamination. Identifying sources of water in coastal marshland under the influences of tides is critical in assessing vulnerability and developing strategies to protect coastal ecosystems. Mixing models such as end-member mixing, allow the contributions of salt and freshwater to be quantified using conservative tracers such as water isotopes. Using stable water isotopes as tracers to assess the impact of saltwater intrusion in coastal environments has been limited compared to their application in catchment hydrology. This study aims to explore the feasibility of using water isotopes to quantify the salt and freshwater dynamics in a tidal salt marsh at the St. Jones Reserve (39.10 ^◦N, 75.44 ^◦W) in Delaware, USA.  During a full tidal cycle, porewater samples were collected from piezometers (at 30 and 100 cm depths below the surface) at four sampling sites along a saline gradient at St. Jones Reserve.  Samples were taken at specific time intervals to capture the full effect of the tide. The isotope composition of the collected porewater samples was measured using a Liquid Water Isotope Analyzer (LWIA). End member analysis will be used to estimate the relative contributions of salt and freshwater at each point along the salt gradient. By quantifying these contributions, we hope to gain insights into the potential impacts of saltwater intrusion on the tidal marsh ecosystem. The information will allow better understanding of the hydrological conditions of the marshland and aid interpretations of an array of soil physical and chemical properties and processes being studied at the site.