Using capacitively coupled resistivity and ground penetrating radar to investigate limestone bedrock heterogeneities under different subtropical wetland communities in Big Cypress National Preserve, Florida

The Big Cypress National Preserve (BCNP) is a collection of subtropical wetlands in southwestern Florida, including extensive forested (cypress, pine, hardwood) and sawgrass ecosystems that flood annually in response to rainfall. In addition to rainfall, hydroperiod, fire regime, elevation above mean sea level, dominant vegetation type, and underlying geological controls contribute to the development and evolution of organic and calcitic soils found throughout BCNP. The Tamiami Formation, which occurs as the surface bedrock across much of BCNP, is a porous limestone with extensive dissolution and reprecipitation of minerals that create a dense authigenic caprock. Laterally heterogeneous caprock formations and bedrock topography can be an important influence on surface and subsurface water flow as well as a control on surface vegetation composition. This research implemented two near-surface geophysical techniques: capacitively-coupled resistivity (CCR) and ground penetrating radar (GPR) to identify subsurface heterogeneities related to the presence of caprock, zones of increased porosity, and how they are spatially related to the surficial environment. Instead of relying on probes hammered into the ground like a traditional resistivity survey, the CCR system uses dipoles dragged along the ground and is based on AC current acting like a capacitor. The CCR system can make resistivity measurements much faster and with increased frequency due to the lack of stationary electrodes. Ground penetrating radar (GPR) is a geophysical method that uses the propagation of electromagnetic waves to detect variations in the physical properties of subsurface materials. GPR surveys have been used extensively in South Florida to distinguish buried karstic features and image various other stratigraphic structures due to its non-invasive nature and relative ease of data collection. Using CCR and GPR surveys across cypress swamp and marl prairie communities, variations in soil thickness and structure of the underlying limestone were resolved and compared to aerial imagery of the surficial vegetation communities. This project shows the applicability of using CCR and GPR to survey 100-1000 m transects to image caprock-vegetation relationships across subtropical wetland communities.