Land use changes around 26 karstic cave-spring systems in Florida were evaluated using geographic information system. Located in the unconfined or semiconfined zones of the Floridan aquifer, some of the cave-spring systems are directly connected to the surficial land use processes by sinking streams, whereas others receiving diffuse recharge are still vulnerable to contamination due to a thin sandy cover overlying the aquifer. Comparison of nitrate-producing land use practices between 2004 and 2013-2014 shows increasing risks of groundwater contamination in the Floridan aquifer. Proliferation of septic systems and wastewater treatment sites due to growing residential areas, increased use of fertilizers for farming and landscaping stand out as major causes of nitrate overload in the both surface and groundwater.
Collapse sinkholes commonly form in karstic limestones of the Floridan aquifer of southern Georgia, USA. The limestones are capped by impermeable strata that can obscure developing sub-surface voids and catastrophically collapse when too much of their underlying support has been removed. We investigated the overnight appearance of an island in a Georgian lake and its possible relationship to the underlying Floridan aquifer using ground-penetrating radar and global-positioning-satellite spot elevations. The island is adjacent to a submerged sinkhole with an arcuate depression and whose development included convergent downward slumping. Compression created by the convergence probably squeezed lake-bottom sediments upward to form the unusual island. Our methodology can be applied to other lakes in karst regions and may prove useful for diagnosing existing or future subsidence risks.
A pipeline, known as Sabal Trail Pipeline, for natural gas transport has been proposed to extend from Alabama to Florida, passing through a very fragile and mostly uncovered karst terrain in Florida. There is considerable concern as to the structural integrity of the pipeline as well as its potential impacts on the environment, particularly on groundwater quality of the Floridan aquifer. Using Geographic Information Systems, this study examines the extent of karst in the proposed trail route and suggest two new alternative routes with significantly less karst development. Mean depression density within 5 km of the proposed Sabal Trail route is 5.2 depressions per km 2 , with a spatial coverage of 12.2%. Depressions within the alternative route have significantly lower density -2.1 depressions per km 2 and much smaller spatial coverage; 5.7%. The routes were also compared with respect to intersected land cover categories.
Occurrences of surficial karstic depressions in south-central Georgia are generally attributed to the dissolution within the Floridan aquifer even though it is overlain by a confining unit of varying thickness. This study explores the karst development within the carbonate layers of the confining unit using geophysical investigation techniques, namely electrical resistivity tomography (ERT), and ground penetrating radar (GPR). Surveys at sites of observed surficial depressions reveal shallow karst development which is unrelated to the deeper karst processes within the Floridan aquifer. The overlying unit, generally comprised of impermeable siliciclastic sediments, appears to have lower degrees of confinement at sites of increased karst development where carbonate layers are present. This has important implications not only for structural stability of the area, but also for the environmental sensitivity of the Floridan aquifer.
The Tri-County Agricultural Area (TCAA) project area contains approximately 154,000 hectares of which 15,569 hectares, or roughly10 percent, is irrigated vegetable cropland comprised of predominantly potato and cabbage farms. A diagnostic assessment was conducted from 1991-1993 to quantify and qualify nutrient loading from 10 representative area farms. The results of this study revealed that nutrient loading was primarily associated with the growing season (Jan.-June) and storm events. The study showed that nonpoint source (NPS) loading rates associated with agricultural row crop landuse are 4 to 5 times greater than other land use activities. Subsequently, costeffective BMPs were identified and their ability to reduce nutrient and sediment loading to receiving waters evaluated (1994)(1995)(1996)(1997).The TCAA Watershed Assessment Model (TCAA WAM), a GIS-based tool for determining the spatial influence of land uses and soils on water quality and quantity in a watershed (SWET, Inc., 1998), was employed to simulate the cumulative effects that BMP implementation would have on watershed nutrient and sediment loads. These results were imported into ArcView and used to generate maps and summary tables. ArcView was then used to identify and rank watersheds, or subbasins, as high, medium and low priority based upon nitrogen and phosphorous loadings. Those subbasins with high N and P loads were ranked as high priority for water quality treatment.Both in-field BMPs and wetland treatment were evaluated for their ability to remove nitrogen and phosphorous. A spreadsheet model, RtMod, was used to calculate the wetland sizing and performance efficiencies.The effects of implementing both in-field BMPs and RST on the total nitrogen and phosphorus loads conveyed from the TCAA project area were determined and their efficiency evaluated at three spatial scales: 1) within 18 high priority subbasins; 2) within 41 agricultural subbasins and 3) TCAA-wide (60 subbasins). While the TCAA project area consists of 60 individual hydrological subbasins, row crop agriculture is only present in 41 of them and occupies only 10% of the total project area. Eighteen of these subbasins were identified as high priority and contain 51% of the TCAA row crop agriculture. The maximum achievable load reduction after in-field BMPs are implemented on all row crop land in the 41 basins is estimated to be 26 % for N and 18% for P. By targeting only the high priority subbasins within the TCAA for in-field BMP implementation, nearly half of the maximum potential load reduction can be achieved. Implementation of RST in the 18 high priority subbasins was estimated to reduce the 2 TCAA agricultural TN load by approximately 22% and the TP load by approximately 50%. Total reductions following the implementation of both in-field BMPs and RST in the high priority subbasins, though not expected to equal the sum of the reductions achieved individually, are expected to be greater than those achievable by either methodology employed separately.While targeting treatment i...
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