Geology topics
Research about Florida Keys
Source-linked reports with geographic coverage including Florida Keys.
Spatial patch occupancy patterns of the Lower Keys marsh rabbit
Reliable estimates of presence or absence of a species can provide substantial information on management questions related to distribution and habitat use but should incorporate the probability of detection to reduce bias. We surveyed for the endangered Lower Keys marsh rabbit ( Sylvilagus palustris hefneri ) in habitat patches on 5 Florida Key islands, USA, to estimate occupancy and detection probabilities. We derived detection probabilities using spatial replication of plots and evaluated hypotheses that patch location (coastal or interior) and patch size influence occupancy and detection. Results demonstrate that detection probability, given rabbits were present, was <0.5 and suggest that naïve estimates (i.e., estimates without consideration of imperfect detection) of patch occupancy are negatively biased. We found that patch size and location influenced probability of occupancy but not detection. Our findings will be used by Refuge managers to evaluate population trends of Lower Keys marsh rabbits from historical data and to guide management decisions for species recovery. The sampling and analytical methods we used may be useful for researchers and managers of other endangered lagomorphs and cryptic or fossorial animals occupying diverse habitats.
Pleistocene carbonate stratigraphy of South Florida: Evidence for high-frequency sea-level cyclicity
Pleistocene carbonates of south Florida and islands of the Florida Keys are currently divided into five marine sequences designated, from oldest to youngest, the Q1–Q5 units. The units include a mosaic of freshwater and shallow marine deposits that accumulated on the Florida platform during high sea-level stands. The units are separated by regional-scale subaerial-exposure surfaces that formed during glacioeustatic lowstands. Analyses of cores recovered at Grossman Ridge Rock Reef and Joe Ree Rock Reef in the Florida Everglades reveal additional subaerial-exposure surfaces that are used to delineate subdivisions within units Q1 (Q1a–Q1b), Q2 (Q2a–Q2d), and Q4 (Q4a–Q4b). Units Q1–Q5 preserve evidence of at least 10 separate sea-level highstands, rather than 5 as indicated by previous studies. Compilation of available uranium-series dates on corals recovered from the Florida Keys indicates that the Q4 unit accreted during sea-level maxima associated with marine oxygen-isotope Stage 9 (Q4a) and isotope Stage 7 (Q4b). The Q5 unit formed during isotope Stage 5. No reliable dates are available for units Q1–Q3. We infer that unit Q3 was formed during the extended sea-level highstand of isotope Stage 11 and that units Q2 and Q1 predate isotope Stage 11.
Analysis of multiple enteric viral targets as sewage markers in coral reefs
Water and coral mucus samples were collected from throughout the Florida Keys National Marine Sanctuary and the Dry Tortugas for three years and were analyzed for human enteric viruses (enteroviruses, noroviruses, hepatitis A virus and adenoviruses) as conservative markers of human sewage using molecular methods. Of the 100 coral and water samples collected, 40 contained genetic material from one or more human enteric viruses. DNA-based adenoviruses were detected widely, in 37.8% of samples and at 91% of stations, including ‘pristine’ reefs in the Dry Tortugas; however, the detection rate was ⩽12% for the RNA-based enteroviruses and noroviruses (hepatitis A virus was never detected). The disparity between the prevalence of RNA- and DNA-based viruses suggests the need for additional work to determine the utility of adenovirus as marker of human sewage.
Systematic mapping of bedrock and habitats along the Florida Reef tract — Central Key Largo to Halfmoon Shoal (Gulf of Mexico)
The fragile coral reefs of the Florida Keys form the largest living coral reef ecosystem in the continental United States. Lining the shallow outer shelf approximately 5 to 7 km seaward of the keys, the reefs have national aesthetic and resource value. As recently as the 1970s, the coral reefs were the heart of a vibrant ecosystem. Since then, the health of all ecosystem components has declined markedly due to a variety of environmental stressors . Corals are succumbing to bleaching and diseases. Species that are the building blocks of solid reef framework are increasingly being replaced by species that do not construct reef framework. Algal proliferation is increasing competition for space and hard surfaces needed by coral larvae for settlement. Decline of the coral reef ecosystem has significant negative implications for economic vitality of the region, ranging from viability of the tourism industry attracted by the aesthetics to commercial fisheries drawn by the resources. At risk of loss are biologic habitats and reef resources, including interconnected habitats for endangered species in shoreline mangroves, productive nearshore marine and wetland nurseries, and economic offshore fisheries. In 1997, the U.S. Geological Survey's Coastal and Marine Geology Program undertook a comprehensive 7-year-long mission to consolidate, synthesize, and map new (1997) and existing geologic and biologic information into a digitized regional database and one-volume reference source on the geologic history of the Florida Keys reef tract (this report). The project was conducted in cooperation with the National Oceanic and Atmospheric Administration's National Marine Sanctuary Program. The purpose was to examine the natural evolution and demise of several coral reef ecosystems over the past 325,000 years, with an eye toward gaining a better understanding of the cause of the reef decline observed today. Scientific data and datasets presented in this report are intended for use by others in ongoing efforts to delineate which components of reef decline in the Florida Keys may be natural and which may be a result of human activities. Beyond scientific baseline datasets, this report also incorporates environmental, social, and historical aspects of the Florida Keys, including the impact of exploratory oil wells on benthic habitats off Florida.
Multi-scale remote sensing of coral reefs
In this chapter we present how both direct and indirect remote sensing can be integrated to address two major coral reef applications - coral bleaching and assessment of biodiversity. This approach reflects the current non-linear integration of remote sensing for environmental assessment of coral reefs, resulting from a rapid increase in available sensors, processing methods and interdisciplinary collaborations (Andréfouët and Riegl, 2004). Moreover, this approach has greatly benefited from recent collaborations of once independent investigations (e.g., benthic ecology, remote sensing, and numerical modeling).
Analysis of coral mucus as an improved medium for detection of enteric microbes and for determining patterns of sewage contamination in reef environments
Traditional fecal indicator bacteria are often subject to a high degree of die-off and dilution in tropical marine waters, particularly in offshore areas such as coral reefs. Furthermore, these microbes are often not associated with human waste, and their presence may not be indicative of health risk. To address the offshore extent of wastewater contamination in the Florida Keys reef tract, we assayed coral surfaces for the presence of human-specific enteric viruses. The overlying water column and surface mucopolysaccharide (mucus) layers from scleractinian corals were sampled from three stations along a nearshore-to-offshore transect beginning at Long Key in the middle Florida Keys, USA. Samples were assayed for standard bacterial water quality indicators (fecal coliform bacteria and enterococci) and for human enteroviruses by direct reverse transcriptase-polymerase chain reaction (RT-PCR). The concentration of the bacterial indicators was greatest at the nearshore station in both the water column and corals, and decreased with distance from shore; no indicator bacteria were detected at the offshore station. Whereas human enteroviruses were not detected in any of the water column samples, they were detected in 50–80% of coral mucus samples at each station. These data provide evidence that human sewage is impacting the reef tract up to ~6.5 km from shore in the middle Florida Keys and that coral mucus is an efficient trap for viral markers associated with anthropogenic pollution.
Inferences about nested subsets structure when not all species are detected
Comparisons of species composition among ecological communities of different size have often provided evidence that the species in communities with lower species richness form nested subsets of the species in larger communities. In the vast majority of studies, the question of nested subsets has been addressed using information on presence-absence, where a '0' is interpreted as the absence of a given species from a given location. Most of the methodological discussion in earlier studies investigating nestedness concerns the approach to generation of model-based matrices. However, it is most likely that in many situations investigators cannot detect all the species present in the location sampled. The possibility that zeros in incidence matrices reflect nondetection rather than absence of species has not been considered in studies addressing nested subsets, even though the position of zeros in these matrices forms the basis of earlier inference methods. These sampling artifacts are likely to lead to erroneous conclusions about both variation over space in species richness and the degree of similarity of the various locations. Here we propose an approach to investigation of nestedness, based on statistical inference methods explicitly incorporating species detection probability, that take into account the probabilistic nature of the sampling process. We use presence-absence data collected under Pollock?s robust capture-recapture design, and resort to an estimator of species richness originally developed for closed populations to assess the proportion of species shared by different locations. We develop testable predictions corresponding to the null hypothesis of a nonnested pattern, and an alternative hypothesis of perfect nestedness. We also present an index for assessing the degree of nestedness of a system of ecological communities. We illustrate our approach using avian data from the North American Breeding Bird Survey collected in Florida Keys.
The fate of wastewater-derived nitrate in the subsurface of the Florida Keys: Key Colony Beach, Florida
Shallow injection is the predominant mode of wastewater disposal for most tourist-oriented facilities and some residential communities in the US Florida Keys National Marine Sanctuary. Concern has been expressed that wastewater nutrients may be escaping from the saline groundwater system into canals and surrounding coastal waters and perhaps to the reef tract 10 km offshore, promoting unwanted algal growth and degradation of water quality. We performed a field study of the fate of wastewater-derived nitrate in the subsurface of a Florida Keys residential community (Key Colony Beach, FL) that uses this disposal method, analyzing samples from 21 monitoring wells and two canal sites. The results indicate that wastewater injection at 18–27 m depth into saline groundwater creates a large buoyant plume that flows quickly (within days) upward to a confining layer 6 m below the surface, and then in a fast flow path toward a canal 200 m to the east within a period of weeks to months. Low-salinity groundwaters along the fast flow path have nitrate concentrations that are not significantly reduced from that of the injected wastewaters (ranging from 400 to 600 μmol kg −1 ). Portions of the low-salinity plume off the main axis of flow have relatively long residence times (>2 months) and have had their nitrate concentrations strongly reduced by a combination of mixing and denitrification. These waters have dissolved N 2 concentrations up to 1.6 times air-saturation values with δ 15 N[N 2 ]=0.5-5‰, δ 15 N[NO 3 - ]=16-26‰, and calculated isotope fractionation factors of about −12±4‰, consistent with denitrification as the predominant nitrate reduction reaction. Estimated rates of denitrification of wastewater in the aquifer are of the order of 4 μmol kg -1 N day -1 or 0.008 day -1 . The data indicate that denitrification reduces the nitrate load of the injected wastewater substantially, but not completely, before it discharges to nearby canals.
Key Largo Limestone revisited: Pleistocene shelf-edge facies, Florida Keys, USA
New dates and analysis of 12 deep and 57 shallow cores allow a more detailed interpretation of the Pleistocene shelf edge of the Florida Platform as found in various facies of the Key Largo Limestone beneath the Florida Keys. In this study a three-phase evolution of the Quaternary units (Q1-Q5) of the Key Largo is presented with new subdivision of the Q5. (1) In the first phase, the Q1 and Q2 (perhaps deposited during oxygen-isotope stage 11) deep-water quartz-rich environment evolved into a shallow carbonate phase. (2) Subsequently, a Q3 (presumably corresponding to oxygen-isotope stage 9) flourishing reef and productive high-platform sediment phase developed. (3) Finally, a Q4 and Q5 (corresponding to oxygen-isotope stages 7 and 5) stabilization phase occurred with reefs and leeward productive lagoons, followed by lower sea levels presenting a sequence of younger (isotope substages 5c, 5a) shelf-margin wedges, sediment veneers and outlier reefs. The Key Largo Limestone provides an accessible model of a carbonate shelf edge with fluctuating water depth, bordering a deep seaward basin for a period of at least 300 ka. During this time, at least four onlaps/offlaps, often separated by periods of karst development with associated diagenetic alterations, took place. The story presented by this limestone not only allows a better understanding of the history of south Florida but also aids in the interpretation of similar persistent shelf-edge sites bordering deep basins in other areas.
Rapid movement of wastewater from on-site disposal systems into surface waters in the lower Florida Keys
Viral tracer studies have been used previously to study the potential for wastewater contamination of surface marine waters in the Upper and Middle Florida Keys. Two bacteriophages, the marine bacteriophage ϕHSIC and the Salmonella phage PRD1, were used as tracers in injection well and septic tank studies in Saddlebunch Keys of the Lower Florida Keys and in septic tank studies in Boot Key Harbor, Marathon, of the Middle Keys. In Boot Key Harbor, both phages were detected in a canal adjacent to the seeded septic tank within 3 h 15 min of the end of the seed period. The tracer was then detected at all sampling sites in Boot Key Harbor, including one on the opposite side of U.S. Highway 1 in Florida Bay, and at an Atlantic Ocean beach outside Boot Key Harbor. Rates of migration based on first appearance of the phage ranged from 1.7 to 57.5 m h −1 . In Saddlebunch Keys, ϕHSIC and PRD1 were used to seed a residential septic tank and a commercial injection well. The septic tank tracer was not found in any surface water samples. The injection well tracer was first detected at a site most distant from the seed site, a channel that connected Sugarloaf Sound with the Atlantic Ocean. The, rate of tracer migration from the injection well to this channel ranged from 66.8 to 141 m h −1 . Both tracer studies showed a rapid movement of wastewater from on-site sewage treatment and disposal systems in a southeasterly direction toward the reef tract and Atlantic Ocean, with preferential movement through tidal channels. These studies indicate that wastewater disposal systems currently in widespread use in the Florida Keys can rapidly contaminate the marine environment.
Geology and hydrogeology of the Florida Keys
This chapter discusses the geology and hydrogeology of the Florida Keys, and focuses on the islands formed of Pleistocene limestone. These islands, which are crossed when driving from Miami to Key West, are typically regarded as "the Florida Keys." The outstanding and fragile character of ecosystems on and around the Florida Keys has prompted State and Federal efforts to protect and preserve the remaining public portions of the region. The Florida Keys were largely ignored during the sixteenth, seventeenth, and eighteenth centuries, although the waters just offshore provided a major shipping thoroughfare to and from the New World. The Florida Keys are now recognized as one of the great recreational and environmental resources of the United States. The islands are outposts of a laid-back, tropical resort culture that has as its foundation warmth and clear water. A significant part of the attraction is fishing, diving, and boating around the area's coral reefs, which the islands protect. But the reefs were not always so highly valued. The Florida Keys that have protected the reefs for millennia, may now be the source of the agents that may accomplish what Agassiz thought was beyond man's power a century ago.
Reef fishes of the Florida Keys
The Florida Keys are a chain of islands extending 320 km (199 mi) along the southern edge of the Florida Plateau from Biscayne Bay to the Dry Tortugas (101 km [63 mi] west of Key West). The Florida Reef Tract, a band of living coral reefs paralleling the Keys, extends from Fowey Rocks to the Marquesas and includes about 130 km (81 mi) of bank reefs and 6,000 patch reefs. For convenience, the Keys can be divided into the upper, middle, and lower Keys (Fig. 1). The environmental and economic importance of the Florida Keys is indicated by the many protected or regulated areas, which include several national wildlife refuges, national parks, marine sanctuaries, and state-protected areas (Fig. 1). Because many recreational and commercial activities occur in nearshore habitats, these areas have high potential for environmental damage. Relatively high rates of human population increase (28%-44%) are predicted over the next 20 years in some parts of the Keys; Monroe County, which includes all of the Keys, had a population growth of 160% during the past 40 years. Human activities associated with increased population growth may well ultimately disrupt the Florida Keys marine ecosystem and damage the area's overall economy. In recognition of this possibility, the Florida Keys National Marine Sanctuary was designated in 1990 under the Marine Protection, Research, and Sanctuaries Act, U.S. Public Law 101-605. The sanctuary includes 9,515 km 2 (3,673 mi 2 ) of coastal waters around the Florida Keys. The Sanctuaries and Reserves Division of the National Oceanic and Atmospheric Administration was charged with developing a comprehensive management plan and regulations to protect sanctuary resources (NOAA 1995). We focus on the current status of Florida Keys reef fishes and areas where research is needed immediately.
Fate and pathways of injection-well effluent in the Florida Keys
Twenty-four wells (21 locations) were core drilled into the limestone beneath the Keys, reef tract, and outer reefs to determine if sewage effluents injected in Class V wells onshore are reaching offshore reef areas via underground flow. These wells were fitted with PVC casings and well screens and were sampled every three months for a period of one year. Analyses showed consistent hypersalinity in most wells and a marked increase in nitrogen (as ammonia) in offshore ground water. Other forms of nitrogen (NO 2 and NO 3 ) and phosphorous were not particularly elevated in offshore ground water but were above the levels found in surface marine water. The highest levels of nitrogen (NO 2 and NO 3 ) and phosphorous were in shallow onshore ground waters. Sources for the nutrients in the shallow onshore ground water consist of septic tanks and cesspools (@ 24,000 and 5,000 in the Florida Keys, respectively), agricultural fertilizers, and natural vegetation. Ammonia concentrations were low in shallow ground waters beneath the Florida Keys, probably because of oxidizing conditions. Tidal pumping is particularly active, especially nearshore. Hydraulic heads sufficient to elevate well water as much as 7 cm above sea level during falling tides were detected in all nearshore wells. During rising tides, the situation was reversed and water flowed into the wells. Tidal pumping implies considerable water movement both in and out of the upper few meters of limestone. Tidal pumping is a likely mechanism for mixing and transferring nutrient-rich ground water into the overlying marine waters. Although tidal pumping should cause rather complete mixing and dilution of any freshwater-based effluents entering the limestone via the more than 600 disposal wells in the Florida Keys, the ground waters in the 30- to 40-ft-depth range (9-12 m) nevertheless remained slightly hypersaline relative to sea water throughout the year. Fecal coliform and fecal streptococcal bacteria were associated with three Lower Keys offshore wells and two shallow onshore wells at Key Largo. On occasions, these bacteria were detected farther offshore, once in a well 4 miles off Key Largo. The bacterial analyses for Key Largo (both onshore and offshore) are supported by two independent bacteriological researchers using more sophisticated methods than the standard 100-ml membrane-filter method used in this study. Fecal bacteria can serve as tracers; thus, we conclude their presence is possible evidence for offshore transport of ground waters originating on Key Largo. Elevated nutrients (ammonia) and slightly elevated dissolved total phosphorous in offshore ground waters, however, cannot be tied to onshore sources with existing data. Rock analyses of material from our cores do not prove or disprove the hypothesis that limestone beneath the Keys or reef tract is serving as a sink for phosphorus or other nutrients. The data, however, do not rule out phosphorus uptake by limestone adjacent to disposal sources. For the purposes of this study, monitoring wells were not positioned sufficiently close to injection wells to determine if uptake of phosphorous is taking place. Ground waters were found to contain more dissolved solids than could be accounted for if hypersalinity resulted from simple evaporation of sea water. These data indicate that ground waters in the vicinity of our wells are dissolving solids from the rock rather than precipitating material within the rock framework; however, as mentioned above, our wells were not positioned sufficiently close to disposal wells to determine if localized uptake is occurring. Examination of rock cores from these wells revealed a general distribution of reef- and grainstone-facies belts. The Upper and Middle Keys are composed of a thin coral reef facies that extends only a few hundred feet seaward of the Keys. Reef facies give way to mudstone facies within a few yards of shore on the Florida Bay side of the Keys. On the seaward side of the Keys, beneath Hawk Channel and White Bank, the Pleistocene limestone is a mixed grainstone, packstone, and wackstone facies. Corals are rare or absent. The Pleistocene limestone beneath the outer reefs 4 to 5 miles offshore, however, consists of reef facies with the same coral fauna as that found on Key Largo. This pattern of two major reef-facies belts separated by a 2- to 4-mile-wide belt of grainstone facies may have as yet undetermined effects on groundwater circulation beneath the Florida reef tract. Grainstone is approximately an order of magnitude less permeable than the coralline Key Largo Limestone facies. The Q3 surface, a major subsurface unconformity thought to form an effective confining zone elsewhere in south Florida, was not detected in wells drilled more than 1 mile from shore. This unconformity, however, was detected in all wells drilled on or near the Keys. What was found to be a more effective and widespread confining layer is the Holocene sediment deposited on the Pleistocene limestone during the past 6,000 to 7,000 years. These relatively impermeable sediments are extensive, forming a belt up to 5 miles wide beginning about 0.5 mile offshore. Holocene sediments generally consist of low-permeability lime mud just above the Pleistocene surface, overlain by more permeable carbonate sands and reefs. Leakage of ground water by tidal pumping is not likely to occur through lime-mud-dominated areas such as Hawk Channel but is likely to occur through isolated porous and permeable Holocene reefs situated on Pleistocene limestone highs, and in places where Holocene sediment does not cover the limestone bedrock. Leakage is therefore limited to 1) a shallow-water 0.5-mile-wide nearshore belt of exposed Key Largo Limestone, 2) Holocene patch reefs, which grow on mud-free topographic rock highs, and 3) along the seaward side of the outermost reef in 35 to 65 ft (10-20 m) of water, where Holocene reef and sediment accumulations are thin or absent. This study did not address direct measurements of lateral groundwater movement or a hydrologic mechanism for transporting hypersaline ground water away from the Florida Keys. More recent work, however (Halley et al., 1994), shows that sea level in Florida Bay is higher than on the Atlantic side of the Keys more than 50% of the time. Higher sea level on the bay side of the Keys provides a potential for groundwater flow toward the Atlantic most of the time. Use of tracers (dyes or harmless bacteriological tracers) injected into the center of tightly spaced clusters of monitoring wells is a simple way to ascertain the net direction and rate of groundwater movement. Knowing the direction and rate of groundwater movement is needed for prediction and modeling efforts in the future