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Research about Florida

Source-linked reports with geographic coverage including Florida.

At least 1,117 records · Page 62Linked to original sources
USGS2003

Interplay of late Cenozoic siliciclastic supply and carbonate response on the southeast Florida platform

High-resolution seismic-reflection data collected along the length of the Caloosahatchee River in southwestern Florida have been correlated to nannofossil biostratigraphy and strontium-isotope chemostratigraphy at six continuously cored boreholes. These data are interpreted to show a major Late Miocene(?) to Early Pliocene fluvial-deltaic depositional system that prograded southward across the carbonate Florida Platform , interrupting nearly continuous carbonate deposition since early in the Cretaceous. Connection of the platform top to a continental source of siliciclastics and significant paleotopography combined to focus accumulation of an immense supply of siliciclastics on the southeastern part of the Florida Platform . The remarkably thick (> 100 m), sand-rich depositional system, which is characterized by clinoformal progradation, filled in deep accommodation, while antecedent paleotopography directed deltaic progradation southward within the middle of the present-day Florida Peninsula. The deltaic depositional system may have prograded about 200 km southward to the middle and upper Florida Keys, where Late Miocene to Pliocene siliciclastic form the foundation of the Quaternary carbonate shelf and shelf margin of the Florida Keys. These far-traveled siliciclastic deposits filled accommodation on the southeastern part of the Florida Platform so that paleobathymetry was sufficiently shallow to allow Quaternary recovery of carbonate sedimentation in the area of southern peninsular Florida and the Florida Keys.

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USGS2003

Copepod communities from surface and ground waters in the everglades, south Florida

We studied species composition and individual abundance of copepods in the surficial aquifer northeast of Everglades National Park. We identified the spatial distribution of subsurface habitats by assessing the depth of the high porosity layers in the limestone along a canal system, and we used copepods to assess the exchange between surface water and ground water along canal banks, at levels in the wells where high porosity connections to the canals exist. Surface- and ground-water taxa were defined, and species composition was related to areal position, sampling depth, and time. Subsurface copepod communities were dominated by surface copepods that disperse into the aquifer following the groundwater seepage along canal L-31N. The similarities in species composition between wells along canal reaches, suggest that copepods mainly enter ground water horizontally along canals via active and passive dispersal. Thus, the copepod populations indicate continuous connections between surface- and ground waters. The most abundant species were Orthocyclops modestus, Arctodiaptomus floridanus, Mesocyclops edax, and Thermocyclops parvus, all known in literature from surface habitats; however, these species have been collected in ground water in ENP. Only two stygophiles were collected: Diacylcops nearcticus and Diacyclops crassicaudis brachycercus. Restoration of the Everglades ecosystem requires a mosaic of data to reveal a complete picture of this complex system. The use of copepods as indicators of seepage could be a tool in helping to assess the direction and the duration of surface and ground water exchange.

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USGS2003

Lower survival probabilities for adult Florida manatees in years with intense coastal storms

The endangered Florida manatee (Trichechus manatus latirostris) inhabits the subtropical waters of the southeastern United States, where hurricanes are a regular occurrence. Using mark-resighting statistical models, we analyzed 19 years of photo-identification data and detected significant annual variation in adult survival for a subpopulation in northwest Florida where human impact is low. That variation coincided with years when intense hurricanes (Category 3 or greater on the Saffir-Simpson Hurricane Scale) and a major winter storm occurred in the northern Gulf of Mexico. Mean survival probability during years with no or low intensity storms was 0.972 (approximate 95% confidence interval = 0.961-0.980) but dropped to 0.936 (0.864-0.971) in 1985 with Hurricanes Elena, Kate, and Juan; to 0.909 (0.837-0.951) in 1993 with the March "Storm of the Century"; and to 0.817 (0.735-0.878) in 1995 with Hurricanes Opal, Erin, and Allison. These drops in survival probability were not catastrophic in magnitude and were detected because of the use of state-of-the-art statistical techniques and the quality of the data. Because individuals of this small population range extensively along the north Gulf coast of Florida, it was possible to resolve storm effects on a regional scale rather than the site-specific local scale common to studies of more sedentary species. This is the first empirical evidence in support of storm effects on manatee survival and suggests a cause-effect relationship. The decreases in survival could be due to direct mortality, indirect mortality, and/or emigration from the region as a consequence of storms. Future impacts to the population by a single catastrophic hurricane, or series of smaller hurricanes, could increase the probability of extinction. With the advent in 1995 of a new 25- to 50-yr cycle of greater hurricane activity, and longer term change possible with global climate change, it becomes all the more important to reduce mortality and injury from boats and other human causes and control the loss of foraging habitat to coastal development.

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USGS2003

Measuring and mapping the topography of the Florida Everglades for ecosystem restoration

One of the major issues facing ecosystem restoration and management of the Greater Everglades is the availability and distribution of clean, fresh water. The South Florida ecosystem encompasses an area of approximately 28,000 square kilometers and supports a human population that exceeds 5 million and is continuing to grow. The natural systems of the Kissimmee-Okeechobee-Everglades watershed compete for water resources primarily with the region's human population and urbanization, and with the agricultural and tourism industries. Surface water flow modeling and ecological modeling studies are important means of providing scientific information needed for ecosystem restoration planning and modeling. Hydrologic and ecological models provide much-needed predictive capabilities for evaluating management options for parks, refuges, and land acquisition and for understanding the impacts of land management practices in surrounding areas. These models require various input data, including elevation data that very accurately define the topography of the Florida Everglades.

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USGS2003

Effects of recharge, Upper Floridan aquifer heads, and time scale on simulated ground-water exchange with Lake Starr, a seepage lake in central Florida

Lake Starr and other lakes in the mantled karst terrain of Florida's Central Lake District are surrounded by a conductive surficial aquifer system that receives highly variable recharge from rainfall. In addition, downward leakage from these lakes varies as heads in the underlying Upper Floridan aquifer change seasonally and with pumpage. A saturated three-dimensional finite-difference ground-water flow model was used to simulate the effects of recharge, Upper Floridan aquifer heads, and model time scale on ground-water exchange with Lake Starr. The lake was simulated as an active part of the model using high hydraulic conductivity cells. Simulated ground-water flow was compared to net ground-water flow estimated from a rigorously derived water budget for the 2-year period August 1996-July 1998. Calibrating saturated ground-water flow models with monthly stress periods to a monthly lake water budget will result in underpredicting gross inflow to, and leakage from, ridge lakes in Florida. Underprediction of ground-water inflow occurs because recharge stresses and ground-water flow responses during rainy periods are averaged over too long a time period using monthly stress periods. When inflow is underestimated during calibration, leakage also is underestimated because inflow and leakage are correlated if lake stage is maintained over the long term. Underpredicted leakage reduces the implied effect of ground-water withdrawals from the Upper Floridan aquifer on the lake. Calibrating the weekly simulation required accounting for transient responses in the water table near the lake that generated the greater range of net ground-water flow values seen in the weekly water budget. Calibrating to the weekly lake water budget also required increasing the value of annual recharge in the nearshore region well above the initial estimate of 35 percent of the rainfall, and increasing the hydraulic conductivity of the deposits around and beneath the lake. To simulate the total ground-water inflow to lakes, saturated-flow models of lake basins need to account for the potential effects of rapid and efficient recharge in the surficial aquifer system closest to the lake. In this part of the basin, the ability to accurately estimate recharge is crucial because the water table is shallowest and the response time between rainfall and recharge is shortest. Use of the one-dimensional LEACHM model to simulate the effects of the unsaturated zone on the timing and magnitude of recharge in the nearshore improved the simulation of peak values of ground-water inflow to Lake Starr. Results of weekly simulations suggest that weekly recharge can approach the majority of weekly rainfall on the nearshore part of the lake basin. However, even though a weekly simulation with higher recharge in the nearshore was able to reproduce the extremes of ground-water exchange with the lake more accurately, it was not consistently better at predicting net ground-water flow within the water budget error than a simulation with lower recharge. The more subtle effects of rainfall and recharge on ground-water inflow to the lake were more difficult to simulate. The use of variably saturated flow modeling, with time scales that are shorter than weekly and finer spatial discretization, is probably necessary to understand these processes. The basin-wide model of Lake Starr had difficulty simulating the full spectrum of ground-water inflows observed in the water budget because of insufficient information about recharge to ground water, and because of practical limits on spatial and temporal discretization in a model at this scale. In contrast, the saturated flow model appeared to successfully simulate the effects of heads in the Upper Floridan aquifer on water levels and ground-water exchange with the lake at both weekly and monthly stress periods. Most of the variability in lake leakage can be explained by the average vertical head difference between the lake and a representative Upper Floridan aquifer well. Simulated lake leakage was correlated (r2 = 0.86) to the average head difference between the lake and a representative Upper Floridan aquifer well, suggesting that leakage was largely a linear function of this head difference. The best estimate of weekly or monthly ground-water inflow can be derived using the water budget and simulated lake leakage. Ground-water inflow is calculated as a new residual to the water budget for Lake Starr after substituting the simulated values of lake leakage into the equation. Using this combined approach to calculate the ground-water inflow to Lake Starr gave gross inflow estimates of 15,689,000 and 20,778,000 cubic feet for the first and second years of the study, respectively (33 and 42 inches per year, respectively). Ground-water inflow was about 42 percent of the total inflow to the lake for the 2-year time period. Lake leakage was estimated to be 14,389,000 and 12,115,000 cubic feet per year for the first and second years, respectively (29 and 24 inches per year, respectively), and was 31 percent of the total outflow during the 2 years. The linear regression between simulated lake leakage and average head difference between the lake and an index well provides a method for estimating leakage from Lake Starr beyond the modeled time period. Leakage estimates from the relation with head difference could be used along with a lake water budget to estimate ground-water inflow over any period that water budget and average head measurements in the index well are available.

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USGS2003

Occurrence and Distribution of Pesticides in the St. Lucie River Watershed, South-Central Florida, 2000-01, Based on Enzyme-Linked Immunosorbent Assay (ELISA) Screening

The St. Lucie River watershed is a valuable estuarine ecosystem and resource in south-central Florida. The watershed has undergone extensive changes over the last century because of anthropogenic activities. These activities have resulted in a complex urban and agricultural drainage network that facilitates the transport of contaminants, including pesticides, to the primary canals and then to the estuary. Historical data indicate that aquatic life criteria for selected pesticides have been exceeded. To address this concern, a reconnaissance was conducted to assess the occurrence and distribution of selected pesticides within the St. Lucie River watershed. Numerous water samples were collected from 37 sites among various land-use categories (urban/built-up, citrus, cropland/pastureland, and inte-grated). Samples were collected at inflow points to primary canals (C-23, C-24, and C-44) and at control structures along these canals from October 2000 to September 2001. Samples were screened for four pesticide classes (triazines, chloroacetanilides, chlorophenoxy compounds, and organophosphates) by using Enzyme-Linked Immunosorbent Assay (ELISA) screening. A temporal distribution of pesticides within the watershed was made based on samples collected at the integrated sites during different rainfall events between October 2000 and September 2001. Triazines were detected in 32 percent of the samples collected at the integrated sites. Chloroacetanilides were detected in 60 percent of the samples collected at the integrated sites, with most detections occurring at one site. Chlorophenoxy compounds were detected in 17 percent of the samples collected at the integrated sites. Organophosphates were detected in only one sample. A spatial distribution and range of concentration of pesticides at the 37 sampling sites in the watershed were determined among land-use categories. Triazine concentrations ranged from highest to lowest in the citrus, urban/built-up, and integrated areas, respectively. The highest median triazine concentration was found in the cropland/pastureland area. Chloroacetanilide concentra-tions ranged from highest to lowest in the citrus, integrated, urban/built-up, and cropland/pastureland areas, respectively. Chlorophenoxy compound concentrations ranged from highest to lowest in the urban/built-up, integrated, citrus, and cropland/pastureland areas, respectively. The maximum concentrations of triazines, chloroacetanilides, and chlorophenoxy compounds were 0.63, 1.0, and 14 micrograms per liter, respectively. Organophosphate was detected once at an integrated site at a concentration of 0.20 microgram per liter. Currently, the U.S. Environmental Protection Agency has no aquatic life guidelines for atrazine and metolachlor. However, assuming that all triazine and metolachlor concentrations from ELISA and gas chromatography/mass spectrometry (GC/MS) analyses were the result of atrazine and metolachlor detections, no concentrations exceeded the Canadian aquatic life guidelines for atrazine and metolachlor. One organophosphate detection (0.2 microgram per liter) did exceed the U.S. Environmental Protection Agency aquatic life guideline for chlorpyrifos. The deethylatrazine/atrazine ratio (DAR) is an important indicator of atrazine transport in the environment. The DAR ranged from 0.25 to 0.33, indicating that postapplication runoff was the most likely source of atrazine to the environment at the time of sampling. Deisopropylatrazine is a metabolite of atrazine and structurally similar compounds, such as simazine and cyanazine. The deisopropylatrazine/deethylatrazine ratio (D2R) is an indicator of nonpoint sources of deisopropylatrazine to the environment. The ratio ranged from 1 to 3 in this study, indicating simazine was an important source of deisopropylatrazine to the environment at the time of sampling, as opposed to atrazine alone. Confirmation analyses by GC/MS for triazines detected by ELISA indicated the presence of atrazine, simazine, deethylatrazine, and deisopropylatrazine. Metolachlor, however, or any of the pesticides for which the ELISA test is cross reactive (acetochlor, butachlor, propachlor, or alachlor) were not detected by GC/MS analysis. The chloroacetanilide detections may be the result of antibody cross reactivity with two metolachlor metabolites; namely, metolachlor ethane sulfonic acid (ESA) and metolachlor oxanilic acid (OA). Metalaxyl, a fungicide also used in the watershed, cross reacts with metolachlor antibodies at low concentrations. Quality assurance efforts included the collection of duplicate samples and equipment blanks for every 10 and 20 environmental samples collected, respectively. All equipment blank test results showed concentrations below the method detection limit (MDL) for triazines, chlorophenoxy compounds, and organophosphates. Chloroacetanilide concentrations ranged from the method detection limit of 0.05 to 0.07 microgram per liter. Further results indicated statistically significant differences between triazines by ELISA and atrazine by GC/MS when ELISA results are converted to the MDL. There was, however, no statistically significant difference between triazines determined by ELISA and atrazine determined by GC/MS when ELISA results were converted to one-half the MDL.

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USGS2003

Potential for saltwater intrusion into the lower Tamiami aquifer near Bonita Springs, southwestern Florida

A study was conducted to examine the potential for saltwater intrusion into the lower Tamiami aquifer beneath Bonita Springs in southwestern Florida. Field data were collected, and constant- and variable-density ground-water flow simulations were performed that: (1) spatially quantified modern and seasonal stresses, (2) identified potential mechanisms of saltwater intrusion, and (3) estimated the potential extent of saltwater intrusion for the area of concern. MODFLOW and the inverse modeling routine UCODE were used to spatially quantify modern and seasonal stresses by calibrating a constant-density ground-water flow model to field data collected in 1996. The model was calibrated by assuming hydraulic conductivity parameters were accurate and by estimating unmonitored ground-water pumpage and potential evapotranspiration with UCODE. Uncertainty in these estimated parameters was quantified with 95-percent confidence intervals. These confidence intervals indicate more uncertainty (or less reliability) in the estimates of unmonitored ground-water pumpage than estimates of pan-evaporation multipliers, because of the nature and distribution of observations used during calibration. Comparison of simulated water levels, streamflows, and net recharge with field data suggests the model is a good representation of field conditions. Potential mechanisms of saltwater intrusion into the lower Tamiami aquifer include: (1) lateral inland movement of the freshwater-saltwater interface from the southwestern coast of Florida; (2) upward leakage from deeper saline water-bearing zones through natural upwelling and upconing, both of which could occur as diffuse upward flow through semiconfining layers, conduit flow through karst features, or pipe flow through leaky artesian wells; (3) downward leakage of saltwater from surface-water channels; and (4) movement of unflushed pockets of relict seawater. Of the many potential mechanisms of saltwater intrusion, field data and variable-density ground-water flow simulations suggest that upconing is of utmost concern, and lateral encroachment is of second-most concern. This interpretation is uncertain, however, because the predominance of saltwater intrusion through leaky artesian wells with connection to deeper, more saline, and higher pressure aquifers was difficult to establish. Effective management of ground-water resources in southwestern Florida requires an understanding of the potential extent of saltwater intrusion in the lower Tamiami aquifer near Bonita Springs. Variable-density, ground-water flow simulations suggest that when saltwater is at dynamic equilibrium with 1996 seasonal stresses, the extent of saltwater intrusion is about 100 square kilometers areally and 70,000 hectare-meters volumetrically. The volumetric extent of saltwater intrusion was most sensitive to changes in recharge, ground-water pumpage, sea level, salinity of the Gulf of Mexico, and the potentiometric surface of the sandstone aquifer, respectively.

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USGS2003

Interactive effects of redox intensity and phosphate availability on growth and nutrient relations of Cladium jamaicense (Cyperaceae)

Expansion of Typha domingensis into areas previously dominated by Cladium jamaicense in the Florida Everglades has been linked to anthropogenic phosphorus (P) enrichment and increased hydroperiod. The principal stress factor for plants in flooded soils is biochemical reduction, the intensity of which is measured as redox potential (Eh). The objective of this study was to assess the growth response of C. jamaicense to Eh (−150, +150, and +600 mV) and P availability (10, 80, and 500 μg P/L). Plants were grown hydroponically in a factorial experiment using titanium (Ti 3+ ) citrate as an Eh buffer. Treatment effects on growth, biomass partitioning, and tissue nutrients were recorded. Growth approximately doubled in response to a 50‐fold increase in P availability. Low redox significantly reduced growth and tissue P concentration. While plant P concentrations increased 20‐fold between the 10 and 500 μg P/L treatments, P concentrations were 50–100% higher at +600 mV than at −150 mV within each phosphate level. At high Eh, C. jamaicense appears well adapted to low nutrient environments because of its low P requirement and high retention of acquired P. However, at low Eh the ability to acquire or conserve acquired P decreases and as a consequence, higher phosphate levels are required to sustain growth. Findings of this study indicate that young C. jamaicense exhibits low tolerance to strongly reducing conditions when phosphate is scarce.

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USGS2003

Sediment dynamics of a sediment-starved, open-marine marsh embayment: Waccasassa Bay, Florida

Although the Big Bend region of Florida's Gulf of Mexico coast is considered sediment-starved, the open marine marshes that characterize the area are keeping pace with sea level rise. Waccasassa Bay, an embayment within this region, also contains unique subtidal mudbanks that thicken with increasing proximity to embayment head, while the remainder of the bayfloor is characterized by exposed carbonate bedrock or by a thin veneer of sediment. Hydro- dynamic data sets were collected to determine the primary sedimentary processes within Waccasassa Bay capable of creating such geomorphic features. Data suggest that the embayment is a flood-dominated system influenced primarily by semi-diurnal tides with flood-stage intensification towards the river-mouth. Subtidal mudbanks are believed to be the result of tidal time-velocity asymmetries and the convergence of sediment transport pathways. Flood dominance for potential bedload transport suggests a gradual infilling of the bay interior for the short time scale of this study. With no mechanism for seaward transport, Waccasassa Bay can be considered a sediment sink for the remainder of the Big Bend re

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USGS2003

Predicting coastal retreat in the Florida Big Bend region of the Gulf Coast under climate change induced sea-level rise

Many wildlife preserves and refuges in coastal areas of our nation are slowly being inundated by rising sea-level. Land elevation and tidal flooding are key factors controlling the extent and zonation of coastal habitats. Warming of our global environment threatens to speed the rate of sea-level rise and perhaps further amplify the detrimental effects of tropical storms, droughts, and lightning fires. A field and modeling study was conducted to determine the current status of emergent vegetation and surficial hydrology and to predict marsh transgression under rising sea-level. Field surveys were conducted to relate vegetation cover and ecotones to surface elevation and tidal inundation. A regional site application of a GIS-based simulation model, WETLANDS, was developed to predict ecosystem response to changing sea-level conditions on a coastal reach of the Big Bend region in northwest Florida. The WETLANDS model contains functional probabilities of community tolerance to flooding conditions that dictate the rate and process of ecological succession and coastal retreat. Map information of hypsography and bathymetry of the study area were digitized and interpolated to construct a digital elevation model. Classified thematic mapper imagery of aquatic and terrestrial habitat at a community level was used to initialize model simulation by vegetative type. Model simulations were generated to predict a likelihood index of habitat change and conversion under different scenarios of sea-level rise. The WETLANDS model was applied to track the process and pattern of coastal inundation over space and time for low, mid, and high sea-level rise projections of 15, 50, and 95 cm over the next century. Model results indicated that major portions of this coastal zone will be permanently inundated by 2100, bringing about a combined migration of marsh habitat and displacement of forest habitat. Results show that lowland pine forests will undergo retreat on the order of thousands of hectares over the 21st century. Coastal marsh extent may actually increase slightly as a function of the low lying topography. Socioeconomic implications may be nominal for this area given its remote and fairly undeveloped and protected coast-202 line. The model offers a technological tool for research and policy purposes that allows for effective land and water management, risk assessment, and cumulative impact analysis of wetland systems and landscapes.

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USGS2003

Modeling mangrove forest migration along the southwest coast of Florida under climate change

Mangrove forests dominate in the intertidal zones of the tropical extent of the coast about the Gulf of Mexico, USA. Global climate change forecasts suggest that these coastal forests will be among those ecosystems most immediately threatened by projected increases in sea level and hurricanes. The interactive effects of environmental conditions that prevail in these forests and the changes that are likely to occur in a global warming climate may lead to major shifts in forest composition, structure, and function of mangrove ecosystems.

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