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Seasonal variation in apparent conductivity and soil salinity at two Narragansett Bay salt marshes
Citation:
Mckinney, Rick, Alana Hanson, Roxannel Johnson, AND M. Charpentier. Seasonal variation in apparent conductivity and soil salinity at two Narragansett Bay salt marshes. Coastal & Estuarine Research Federation (CERF) 24th Biennial Conference, Providence, Rhode Island, November 05 - 09, 2017.
Impact/Purpose:
This presentation will cover results of a preliminary study edaphic and biotic factors that may affect the measurement of the apparent conductivity of salt marsh sediments using electromagnetic induction (EMI). Once fully developed, EMI will be a rapid alternative to traditional methods of salinity determination, allowing us to map soil salinity across a marsh surface and gain insights into marsh processes. Salinity is important in determining the structure and function of tidally influenced marsh communities. Mapping apparent conductivity of salt marsh sediments will be useful both in documenting marsh-wide changes in salinity over time and in identifying within-marsh micro-habitats. This information will help inform coastal managers and aid in providing input to decisions regarding salt marsh protection and restoration.
Description:
Measurement of the apparent conductivity of salt marsh sediments using electromagnetic induction (EMI) is a rapid alternative to traditional methods of salinity determination that can be used to map soil salinity across a marsh surface. Soil salinity measures can provide information about marsh processes, since salinity is important in determining the structure and function of tidally influenced marsh communities. While EMI has been shown to accurately reflect salinity to a specified depth, more information is needed on edaphic and biotic factors that may affect apparent conductivity over different time scales and therefore impact the interpretation of salinity data. In this study we mapped soil salinity at two salt marshes in the Narragansett Bay, RI estuary monthly over the course of a year in order to examine spatial and temporal trends in marsh salinity. Mean monthly calculated salinity was 25.8 ± 1.5 at Narrow River marsh, located near the mouth of the Bay, and 18.4 ± 1.3 at Passeonkquis marsh located in the upper Bay. Salinity varied seasonally, with both marshes showing the lowest values (16.3 and 8.3, respectively) in April and highest values (35.4 and 26.2, respectively) in August. We found that tidal inundation appears to have less impact on mean marsh calculated salinity than biotic factors and longer-term trends in precipitation and freshwater inputs to the marsh. We also examined spatial variability within the marshes and found that while accepted patterns of marsh salinity were generally maintained (i.e., lower salinity in the high marsh and upland edge), we observed site-specific differences as well as changes in salinity patterns over time. Mapping apparent conductivity of salt marsh sediments may be useful both in documenting marsh-wide changes in salinity over time and in identifying within-marsh micro-habitats.