Investigating tidal inundation, pore water seepage, and groundwater flow within a salt marsh of the Florida Gulf coast

Salt marshes are common landscapes along low relief, low-energy coastlines. They serve several valuable ecosystem services, and have potentially large carbon sequestration capability. However, the loss of salt marshes globally is estimated to be 1 to 2 % per year. Investigation of hydrologic forces maintaining these ecosystems is critical for well-grounded policy and decision-making to mitigate wetland loss and manage carbon budgets. Hydrology is the defining aspect of salt marsh environments. The input, flow, and distribution of water are the primary elements of the formation and maintenance of these coastal landscapes. This study explored the hydrological processes, including overland flow, creek bank seepage, surface runoff, and groundwater discharge, of a pristine salt marsh in the Big Bend region of the Gulf of Mexico between the Aucilla and Econfina Rivers. Light Detection and Ranging data were used to calculate inundation volumes for the study area, which ranged from 0.6 to 8.0 x 105 m3 of Gulf water. Additionally, cross-shore winds were shown to have a strong influence on water levels in this region of the Gulf of Mexico. Pressure head time series from wells and seepage collectors were used to calculate creek bank seepage velocities, which ranged between ~6 x 10-6 m s-1 and 3 x 10-5 m s-1. Numerical simulations of subsurface pore water flow produced seepage velocities ranging between 1.05 x 10-5 and 4.38 x 10-5 m s-1. Bulk seepage discharge was calculated to be 0.43 m3 of water per longitudinal meter creek bank per tidal cycle. CDOM and Radon-222 measurements were used to observe water sources and seasonal differences. CDOM was highest in Econfina River, whereas Radon-222 was highest in the spring-fed Wakulla and St. Mark’s Rivers. CDOM varied for both the Econfina River and Snipe Creek, potentially correlated to precipitation, air temperature, and fall plant senescence. Groundwater discharge estimates ranged from 472 ± 1 to 2,444 ± 12 m3 d-1 for Snipe Creek, 2,040 ± 0 to 8,180 ± 3 m3 d-1 for Econfina River, and 54,220 ± 12 m3 d-1 and 82,150 ± 25 m3 d-1 for the Wakulla and St. Mark’s Rivers, respectively.Doctor of Philosoph