Root, Tara

Wetlands are an essential part of the water management system in South Florida, providing many ecosystem services. However, the hydrologic connections of many wetlands, including Loxahatchee Slough in Florida, are poorly understood. Loxahatchee Slough is Palm Beach County’s most diverse natural area and a site of ongoing restoration. The primary objective of this research was to characterize the spatial and temporal variability of surface-groundwater exchange at Loxahatchee Slough. The Magnitude of groundwater seepage to the canal varied spatially. Little seasonal variability in exchange was identified in this study. Canal stage had a strong relationship with groundwater levels and slough stage indicating its important influence. This study provides more insight into the heterogeneous nature of wetland-canal exchange and the need for site-specific evaluation at wetlands for successful management.

The legacy of monosodium methanearsenate (MSMA) application to golf courses is often arsenic concentrations above the EPA’s maximum contaminant level of 10 μg/L for drinking water and the FDEP soil cleanup target level of 2.1 mg/kg for residential areas. These concentrations pose a health risk and must be remediated for residential development. The objective of this study was to determine how arsenic concentrations vary spatially at a closed golf course poised for residential development. Groundwater and sediment arsenic concentrations were quantified and the controls on arsenic (As) mobility were characterized. The presence of nitrates and iron-(hydr)oxides at the studied golf course largely influenced putting greens having the least As in groundwater whereas roughs contained the most.

A small body of saline rich water rests in the saturated zone between the foredune and the shoreline at certain beaches. This region is beneath the water table and the top of the fresher groundwater, known as the Upper Saline Plume (USP). The USP is significant because density driven flow and chemical fluxes between freshwater, rainwater, and seawater contribute to biogeochemical processes in the subterranean estuary (Duque et al. 2020). The occurrence of the USP has been observed along beaches that have a moderate to gentle slope, fine to medium grain size, and higher wave energy. The goal of this study was to determine if conditions for the presence of USP are consistent throughout different coastal beaches in southeast Florida while mapping the groundwater salinity across the beach. To identify the existence and delimit the boundary interface of the USP in the southeastern coast of Florida, multi–depth samplers were designed, built, and deployed along cross-shore transects at Jupiter and Gulfstream Beaches in Palm Beach County, FL. Groundwater samples were extracted along the transects to measure specific conductance. Although this study did not confirm the existence of the USP in South Florida beaches, an intermediate zone of water that is in-between the specific conductance ranges of relatively freshwater and relatively salty water was identified. Furthermore, the size of this intermediate zone was corresponded with beach slope, showing larger intermediate zones for steeper slopes and vice versa. Finally, temporal changes in the location and morphology of this intermediate zone were also identified in relation to a distinct disturbance event (Hurricane Isaias) which resulted in elevated ocean water levels.

Stable isotopes of water are used as tracers for characterizing surface water/groundwater interactions. Gaps in sampling protocol for these tracers in low gradient canals limits their use in studies of canal-groundwater exchanges. Several sampling methods were developed to determine the temporal and spatial isotopic variation in a canal. The influence of a flow control gate on isotopic composition and the sensitivity of isotope mixing calculations to choice of sampling method were also evaluated. There was little variability in the isotopic composition of the canal along a cross section perpendicular flow. Some variation occurred monthly and seasonally. The greatest variability occurred between the upstream and downstream side of the flow control gates when the gates were closed. Mixing calculations were not sensitive to the choice of sampling method. This study shed light on isotope sampling methods in canals for canal-groundwater interactions studies.