Geology topics

Research about Lake Wales Ridge

Source-linked reports with geographic coverage including Lake Wales Ridge.

4 recordsLinked to original sources

USGS2014

Pesticides and nitrate in groundwater underlying citrus croplands, Lake Wales Ridge, central Florida, 1999-2005.

This report summarizes pesticide and nitrate (as nitrogen) results from quarterly sampling of 31 surficial-aquifer wells in the Lake Wales Ridge Monitoring Network during April 1999 through January 2005. The wells, located adjacent to citrus orchards and used for monitoring only, were generally screened (sampled) within 5 to 40 feet of the water table. Of the 44 citrus pesticides and pesticide degradates analyzed, 17 were detected in groundwater samples. Parent pesticides and degradates detected in quarterly groundwater samples, ordered by frequency of detection, included norflurazon, demethyl norflurazon, simazine, diuron, bromacil, aldicarb sulfone, aldicarb sulfoxide, deisopropylatrazine (DIA), imidacloprid, metalaxyl, thiazopyr monoacid, oxamyl, and aldicarb. Reconnaissance sampling of five Network wells yielded detection of four additional pesticide degradates (hydroxysimazine, didealkylatrazine, deisopropylhydroxyatrazine, and hydroxyatrazine). The highest median concentration values per well, based on samples collected during the 1999–2005 period (n=14 to 24 samples per well), included 3.05 µg/L (micrograms per liter) (simazine), 3.90 µg/L (diuron), 6.30 µg/L (aldicarb sulfone), 6.85 µg/L (aldicarb sulfoxide), 22.0 µg/L (demethyl norflurazon), 25.0 µg/ (norflurazon), 89 µg/ (bromacil), and 25.5 mg/L (milligrams per liter) (nitrate). Nitrate concentrations exceeded the 10 mg/L (as nitrogen) drinking water standard in one or more groundwater samples from 28 of the wells, and the median nitrate concentration among these wells was 14 mg/L. Sampled groundwater pesticide concentrations exceeded Florida’s health-guidance benchmarks for aldicarb sulfoxide and aldicarb sulfone (4 wells), the sum of aldicarb and its degradates (6 wells), simazine (2 wells), the sum of simazine and DIA (3 wells), diuron (2 wells), bromacil (1 well), and the sum of norflurazon and demethyl norflurazon (1 well). The magnitude of fluctuations in groundwater pesticide concentrations varied between wells and between pesticide compounds. Of the 10 pesticide compounds detected at sufficient frequency to assess temporal variability in quarterly sampling records, median values of the relative interquartile range (ratio of the interquartile range to the median) among wells typically ranged from about 100 to 150 percent. The relative interquartile range of pesticide concentrations at individual wells could be much higher, sometimes exceeding 200 to 500 percent. No distinct spatial patterns were apparent among median pesticide concentrations in sampled wells; nitrate concentrations tended to be greater in samples from wells in the northern part of the study area.

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USGS1996

Sublake geologic structure from high-resolution seismic-reflection data from four sinkhole lakes in the Lake Wales Ridge, central Florida

Seismic-reflection profiles from Lake Wales, Blue Lake, Lake Letta, and Lake Apthorp located along the Lake Wales Ridge in central Florida provide local detail within the regional hydrogeologic framework as described by litho- and hydrostratigraphic cross sections. Lakes located with the mantled karst region have long been considered to be sinkhole lakes, originating from subsidence activity. High-resolution seismic- reflection data confirm this origin for these four lakes. The geologic framework of the Lake Wales Ridge has proven to be a suitable geologic setting for continuous high-resolution seismic-reflection profiling in lakes; however, the nature of the lake-bottom sediments largely controls the quality of the seismic data. In lakes with significant organic-rich bottom deposits, interpretable record was limited to areas where organic deposits were minimal. In lakes with clean, sandy bottoms, the seismic-reflection methods were highly successful in obtaining data that can be correlated with sublake subsidence features. These techniques are useful in examining sublake geology and providing a better understanding of how confining units are affected by subsidence in a region where their continuity is of significant importance to local lake hydrology. Although local geologic control around each lake generally corresponds to the regional geologic framework, local deviations from regional geologic trends occur in sublake areas affected by subsidence activity. Each of the four lakes examined represents a unique set of geologic controls and provides some degree of structural evidence of subsidence activity. Sublake geologic structures identified include: (1) marginal lake sediments dipping into bathymetric lows, (2) lateral discontinuity of confining units including sags and breaches, (3) the disruption and reworking of overlying unconsolidated siliciclastic sediments as they subside into the underlying irregular limestone surface, and (4) sublake regions where confining units appear to remain intact and unaffected by nearby subsidence activity. Each lake likely is underlain by several piping features rather than one large subsidence feature.

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USGS1996

Analysis and simulation of ground-water flow in Lake Wales Ridge and adjacent areas of central Florida

The Lake Wales Ridge is an uplands recharge area in central Florida that contains many sinkhole lakes. Below-normal rainfall and increased pumping of ground water have resulted in declines both in ground-water levels and in the water levels of many of the ridge lakes. A digital flow model was developed for a 3,526 square-mile area to help understand the current (1990) ground-water flow system and its response to future ground-water withdrawals. The ground-water flow system in the Lake Wales Ridge and adjacent area of central Florida consists of a sequence of sedimentary aquifers and confining units. The uppermost water-bearing unit of the study area is the surficial aquifer. This aquifer is generally unconfined and is composed primarily of clastic deposits. The surficial aquifer is underlain by the confined intermediate aquifer and confining units which consists of up to three water-bearing units composed of interbedded clastics and carbonate rocks. The lowermost unit of the ground- water flow system, the confined Upper Floridan aquifer, consists of a thick, hydraulically connected sequence of carbonate rocks. The Upper Floridan aquifer is about 1,200 to 1,400 feet thick and is the primary source for ground-water withdrawals in the study area. The generalized ground-water flow system of the Lake Wales Ridge is that water moves downward from the surficial aquifer to the intermediate aquifer and the Upper Floridan aquifer in the central area, primarily under the ridges, with minor amounts of water flow under the flatlands. The water flows laterally away from the central area, downgradient to discharge areas to the west, east, and south, and locally along valleys of major streams. Upward leakage occurs along valleys of major streams. The model was initially calibrated to the steady-state conditions representing September 1989. The resulting calibrated hydrologic parameters were then tested by simulating transient conditions for the period October 1989 through 1990. A final test of model calibration was conducted by successfully simulating transient conditions for the period October 1988 through September 1989. Altitudes of the water table, base of the surficial aquifer, riverbed conductances, confining-unit leakances, aquifer transmissivities, and net recharge and discharge rates were determine during calibration. Steady-state and transient simulations reasonably approximated measured aquifer heads and lake levels. Residuals were within the established calibration criteria that required 68 percent of all simulated heads to be within + - 2 feet of observed surficial aquifer heads and lake levels and + - 5 feet of observed intermediate and Upper Floridan aquifer heads. Simulation of streamflow was poor, probably due to the scale of the model and regulated streamflow conditions. Simulation indicates a marked difference between the ground-water flow rates of September 1989 (steady-state conditions, end of wet season) and May 1990 (large pumpage, end of dry season) in million gallons per day: September May 1989 1990 Pumping rate 126 486 Donward leakage (into 367 564 Upper Floridan aquifer) Streamflow 67 13 Net lateral boundary flow 218 115 Total discharge (excluding 479 626 evapotranspiration. The calibrated flow model was used to simulate the short-term (one year) effects of 1990 water year pumpage (349 Mgal/d) on the September 1989 ground- water flow system in response to five different pumping schemes: (2) no pumpage, (2) no public supply pumpage, (3) no industrial pumpage, (4) no agricultural pumpage, and (5) no regional pumping outside the Water Use Caution Area. Simulation of no pumpage indicated maximum aquifer head rises of about 2 feet in the surficial aquifer and lakes, about 12 feet in the intermediate aquifer and about 16 feet in the Upper Floridan aquifer. The high rate recharge areas along the Lake Wales Ridge are most affected by pumping. Simulation of no agricultural pumpage resulted in a maximum recovery of about 2 feet in each aquifer. Simulation of no industrial or mining pumpage resulted in a maximum of less than one foot in the surficial aquifer and lakes, about 10 feet in the intermediate aquifer, and about 14 feet in the Upper Floridan aquifer. Simulation of no public supply pumpage indicated a maximum recovery of less than one foot in the surficial aquifer and lakes, about 4 feet in the intermediate aquifer, and about 10 feet in the Upper Floridan aquifer. Simulation of no regional pumping outside the Water Use Caution Area indicated recoveries of less than 2 feet within the Water Use Caution Area. Simulations were used to investigate long- term aquifer changes in response to two development alternatives: (1) continuation of 1990 water year hydrologic conditions and pumping rates (349 Mgal/d), and (2) increased pumpage (506 Mgal/d). Simulation of continued 1990 water year hydrologic conditions and pumping for 20 years indicated that head decline of more than 10 feet might be expected in each aquifer in the northern part of the Water Use Caution Area. Simulation of increased pumpage (an additional 45 percent) for 20 years indicated head declines of more than 20 feet in each aquifer in the northern part of the Water Use Caution Area. Because lakes are hydraulically connected to the surficial aquifer, lake levels within the Water Use Caution Area could decline substantially as a result of present and future pumping and a continuation of 1990 hydrologic conditions. These relatively large head declines were accompanied by decreased simulated lateral boundary outflow of about 40 percent and decreased simulated streamflow of about 32 percent. Equilibrium conditions at the end of the two 20-year simulations had not been attained.

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USGS1996

Evapotranspiration from successional vegetation in a deforested area of the Lake Wales Ridge, Florida

The suitability of three evapotranspiration models (Penman-Monteith, Penman, and a modified Priestley-Taylor) was evaluated at a site of successional vegetation in a deforested area of the Lake Wales Ridge, Florida. Eddy correlation measurements of evapotranspiration made during 22 approximately 1-day periods at a temporal resolution of 20 minutes from September 1993 to August 1994 were used to calibrate the evapotranspiration models. Three variants of the eddy correlation method that ascribe measurement error to three different sources were considered in the analysis. The Penman-Monteith and modified Priestley- Taylor models were successful in approximating measured 20-minute values of evapotranspiration (r 2 ≥0.918). The most successful approaches were the modified Priestley-Taylor model (r 2 =0.972) and a nontraditional and simplified form of the Penman-Monteith model (r 2 =0.967). The Penman approach was unsuccessful as a predictor of evapotranspiration. The evapotranspiration models were used to estimate evapotranspiration between measurements. When evapotranspiration values measured with a Bowen ratio variant of the eddy correlation method were used for model calibration, estimated daily evapotranspiration rates varied seasonally ranging from 0.2 millimeters per day (0.008 inch per day) in late December 1993 to 5 millimeter per day (0.2 inch per day) in mid-July 1994. Annual evapotranspiration (September 15, 1993, to September 15, 1994) was estimated to be about 680 millimeters (27 inches). Evapotranspiration models calibrated to the standard eddy correlation method and to an energy-balance residual variant provided estimates of annual evapotranspiration that were about 10 per cent lower and higher, respectively. These data indicate that of the 1,320 millimeters (52 inches) of precipitation during the 1-year period, about 570 to 700 millimeters (22 to 28 inches) recharged the surficial aquifer. Evapotranspiration at this study site probably defines the lower limit of evapotranspiration from vegetated surfaces in central Florida because of the shallow-rooted plants, rapidly-drained soils, and relatively deepwater table.

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