Sedimentology and Shallow Groundwater Responses of a Coastal Marsh Along a Salinity Gradient: A Case Study In Grand Bay National Estuarine Research Reserve, Mississippi

<p>Climate change and relative sea level rise is resulting in saltwater intrusion and inundation of coastal marshes. This study investigates factors affecting marsh hydrology, including sediment composition, seasonal variability, and coastal storms in Grand Bay National Estuarine Research Reserve (NERR) near Pascagoula, Mississippi. Analysis of sediment includes color, organic matter, carbonate, magnetic susceptibility, and particle size. Shallow groundwater hydrologic trends between Summer 2015 and Fall 2016 are established along a salinity gradient at four sites using water levels, temperature, and conductivity monitored at the surface and in piezometers at depths of 0.75m, 1.5m, and 2.25m.</p> <p>Sediment analysis indicates reducing conditions throughout with redoximorphic concentrations of iron oxides and oxidation colors. Sediment is typically high in organic matter (avg 4.6% and up to 18.5%) and below 5% carbonate. Magnetic susceptibility increases seaward. The relative abundance of sand particles is a controlling factor for permeability in the clay and silt rich marsh sediments. Shallow groundwater levels fluctuate corresponding to diurnal tidal cycles, seasonal cycles, and short-term storm influences. Temperature and salinity fluctuate slowly, and do not have strong tidal signals indicating a distinction between the marine surface and terrestrial subsurface. The salinity gradient generally follows expected trends. However, the salinity gradient shifts to the middle of the marsh in drier periods such that salinity is higher than in outer marsh areas. Salinity generally decreases with depth suggesting that seaward flow of fresher water in the shallow subsurface coupled with low permeability fine-grained sediments resists the seepage of higher density saline surface water.</p>

Name thesis:degree_name

Master of Science (MS)

Level thesis:degree_level

Masters Thesis

Year dc:date.available

2021

Author dc:creator

• Thompson, James

Contributors dc:contributor

• Franklin Heitmuller
• Patrick Biber
• Kevin Kuehn

• groundwater
• carbonate
• organic matter
• piezometer
• conductivity
• temperature
• Geology

Repository record dc:identifier

https://aquila.usm.edu/masters_theses/847

OAI identifier oai:identifier

oai:aquila.usm.edu:masters_theses-1908