Fate and pathways of injection-well effluent in the Florida Keys

Abstract

Conclusions 7 5 Suggestions for Future Studies 7 Acknowledgments References 7 Appendix A 29. Schematic geologic cross section of middle Key Largo and bar graph of major nutrient concentrations 69 30. Schematic geologic cross section of upper Key Largo and bar graph of major nutrient concentrations 7 0 IV 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. growths of algae. One well-documented cause of increased algal growth was the disappearance of the herbivorous sea urchin Diadema. Although Diadema suffered near extinction throughout the Caribbean in 1983 (Lessios, 1984), coral mortality and algal proliferation appeared most pronounced on Florida's reefs (Dustan, 1985). While Diadema were dying in unprecedented numbers, reefs, especially in the Florida Keys, were also experiencing accelerating human exploitation. Along wit...

Temporal and spatial variation in the δ15 N and δ13 C of coral tissue and zooxanthellae in Montastraea faveolata collected from the Florida reef tract

“…The nearshore reefs occur less than 5 km offshore and often experience extremely turbid waters. Although waters close to the Florida Keys tend to be slightly elevated in their nutrient concentrations and, based on the studies by Shinn et al (1994) and Lapointe et al (1990), might be expected to be affected by sewage derived from the Florida Keys, by 0.5 km, it has been shown that the nutrient concentrations of the reefal water are close to open marine conditions (Szmant and Forrester 1996). If the ␦ 15 N of organisms, such as corals, can be considered to be valid indicators of anthropogenic influence on the marine environment, then the data presented in this paper would suggest that the Florida reefs are relatively unaffected by anthropogenic N. Such results are in contrast with the study by Sammarco et al (1999), which examined a number of reefs stretching from the coast of Australia to the Great Barrier Reef, a distance of 120 km.…”

Pathogenic Human Viruses in Coastal Waters

“…This is of particular concern when waters such as those off the Florida Keys are heavily utilized for recreational activity in addition to being ecologically sensitive to poor water quality, a common trait of all coral reef ecosystems. Several physical factors such as tidal pumping and the porous nature of limestone contribute to the rapid groundwater migration rates observed in many of Florida's coastal communities (145).…”

Estimating the groundwater contribution into Florida Bay via natural tracers, 222Rn and CH4

“…Although little is known about groundwater input into Florida Bay, it has been shown that tidal forcing is responsible for subsurface flow and significant localized groundwater input along the Keys (Shinn et al 1994;Corbett et al 1999;Dillon et al 1999Dillon et al , 2000.…”