Date of Award

6-30-2016

Document Type

Open Access Dissertation

Department

Art

Sub-Department

Geological Sciences

First Advisor

Alicia M Wilson

Abstract

Tidal salt marshes are extraordinarily productive and valuable ecosystems that provide via groundwater a not insignificant portion of coastal solute and nutrient budgets. Among the many goods and services they provide are habitat for diverse wildlife, protection for coastal communities during storms, and protection for coastal surface waters by filtering anthropogenic pollutants. One threat to the health of tidal salt marshes along the East Coast have been episodes of Acute Marsh Dieback (AMD) from 1999 to 2001. Dieback was observed at North Inlet salt marsh from 2000 to 2001. Since salt marsh hydrology is dominated by the local tidal regime, it is important to understand how variations in hydrology impact marsh ecosystem health as well as how these variations impact both groundwater discharge and the distribution of solutes in the subsurface. In particular, the four naturally-occurring Ra isotopes (223Ra, 224Ra, 226Ra, and 228Ra) are considered valuable tracers of water movement and age in coastal systems but their accuracy has been hindered by their spatial and temporal variability.

From 2007 to 2011, a combined field and modeling study was performed on a marsh island in North Inlet salt marsh near Georgetown, South Carolina to better understand the impact of hydrology. A set of 21 piezometers were installed at depths of 1, 2, and 4 m below the marsh surface to measure in-situ pore pressure, temperature and salinity, and to collect water samples to measure salinity, temperature, pH, redox potential, and the activity of the four Ra isotopes. Along with publically available tide and meteorology data and conservative statistical tests, these measurements were used to (1) calculate hydraulic head, (2) determine groundwater flow paths and discharge rates, (3) calibrate a numerical groundwater flow model, (4) better understand the relationship between hydrology and AMD, and (5) determine the relationship between marsh hydrology and the temporal and spatial variations in porewater Ra activity to improve its use as a coastal groundwater tracer.

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