Antibiotic resistance is a global concern for human, animal, and environmental health. Many studies have identified wastewater treatment plants and surface waters as major reservoirs of antibiotic resistant bacteria (ARB) and genes (ARGs). Yet their prevalence in urban karst groundwater systems remains largely unexplored. Considering the extent of karst groundwater use globally, and the growing urban areas in these regions, there is an urgent need to understand antibiotic resistance in karst systems to protect source water and human health. This study evaluated the prevalence of ARGs associated with resistance phenotypes at 10 urban karst features in Bowling Green, Kentucky weekly for 46 weeks. To expand the understanding of prevalence in urban karst, a spot sampling of 45 sites in the Tampa Bay Metropolitan area, Florida was also conducted. Specifically, this study considered tetracycline and extended spectrum beta-lactamase (ESBLs) producing, including third generation cephalosporin, resistant E. coli, and tetracycline and macrolide resistant Enterococcus spp. across the 443 Kentucky and 45 Florida samples. A consistent prevalence of clinically relevant and urban associated ARGs were found throughout the urban karst systems, regardless of varying urban development, karst geology, climate, or landuse. These findings indicate urban karst groundwater as a reservoir for antibiotic resistance, potentially threatening human health.

A gas chromatographic method for the rapid determination of aqueous carbon dioxide and its speciation into solvated carbon dioxide and bicarbonate is presented. One-half mL samples are injected through a rubber septum into 20-mL vials that are filled with 9.5 mL of 0.1 N HCl. A one mL portion of the headspace is withdrawn and injected onto a gas chromatograph equipped with a thermal conductivity detector. Using the dimensionless Henry's constant for carbon dioxide and an adaptation of the Henderson-Hasselbalch equation, carbon dioxide in the samples can be categorized among solvated, bicarbonate, and carbonate forms. Natural water samples as well as wastewater from a municipal sewage treatment plant and a swine rearing operation were analyzed by this method and the results compared favorably to those obtained by titration. Samples stored for up to 5 weeks showed no significant changes in carbon dioxide concentrations. In addition, using flame ionization and electron capture detectors, methane and nitrous oxide concentrations in the samples were also measured.

This study assesses the capability and practical applications of quasi-3 Dimensional (3D) Electrical Resistivity Tomography (ERT) for mapping air-filled conduits in eogenetic karst. A high-resolution quasi-3D ERT survey, consisting of multiple parallel 110m-long 2D profiles, was conducted over two mapped cave systems on the Brooksville Ridge, Florida. The irregularly shaped caves have diameters ranging up to 4 m and span depths from 3 m to 11 m below ground surface. Dipole-dipole array geometries with L2 (least squares) rather than L1 (robust) inversion produced the best fits of resistivity highs with the mapped cave locations. As expected, 3D inversions of sets of parallel lines produced better results than 2D inversions of individual transects. Better imaging was obtained of a cave over which cave-parallel profiles were run in addition to cross-cave profiles. However, even with the best acquisition and processing steps, there are significant misfits in the apparent size of the large cave sections, and narrower conduits are not imaged. Resolution decreased significantly with depth, as expected given the method limitations and the site constraints on profile lengths. 3D visualization techniques are explored, and found helpful in examining the data and comparing mapped caves and 3D resistivity datasets; however, when applied to eogenetic karst terrain, ERT has limited capacity to detect smaller cavities, which may require the additional use of other geophysical or subsurface investigative methods. With sinkholes continuing to be of concern to residential and urban development in west-central Florida, the results of this research present additional insight on the potential of quasi-3D ERT methods to map and characterize the potential hazards posed by karst terranes.