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Florida's Geology Makes Wastewater Disposal a Potential Threat to Ecosystem Health in the Florida Keys
The Florida peninsula sits atop a limestone platform thousands of meters in depth. Most of the platform is overlain by a veneer of silicate sand, but in many coastal environments this cover is absent. Given the porous nature of limestone, it is in these coastal environments that the disposal of wastewater, or the use of such wastewater-disposal systems as septic tanks and shallow injection wells, presents unique problems relative to human and ecosystem health. Waste-disposal practices are of particular concern in the Florida Keys, one of the State's tourist meccas, where more than 36,000 septic systems, an estimated 5,000 to 10,000 cesspits (covered limestone holes that serve as septic tanks), and more than 600 shallow class IV injection wells (approx 30 m deep) are the dominant systems of wastewater disposal. The central problem with these systems is that wastewater is deposited directly into limestone environments, which are in close association with surface waters and the potable waters of the Biscayne aquifer. Pollutants and pathogenic microorganisms are rapidly transported to canal, nearshore, and offshore environments by the influence of tidal pumping. Several studies in the Florida Keys that used bacteriophage as tracers by flushing them down various toilets demonstrated that these microorganisms could be detected in canal surface waters in as little as 3 hours. A study that screened 19 different sites covering the full length of the Florida Keys demonstrated that specific human pathogenic viruses (Polio and Coxsackie viruses, Hepatitis A virus, Norwalk viruses, and others) were present at all but one site. This study specifically demonstrated the prevalence of human fecal-oral pathogens in canal and nearshore waters, but other constituents such as detergents, various cleaners, and whatever else might be disposed of in household sinks may pose significant threats to ecosystem health. Although many of the problems associated with these types of wastewater-disposal systems exist in Florida's coastal communities, it is the coral reefs of the keys and the susceptibility of corals to pollutants and nutrients (natural and anthropogenic) that have resulted in numerous scientific endeavors to understand the physical, chemical, and biological sources of stress to this valued ecosystem. Researchers have recently used coral mucus to demonstrate the presence of specific human viruses in nearshore reef environments in the keys. Coral mucus, which is a highly charged nutrient-rich coral biofilm, is an ideal natural "flypaper" that can trap passing viruses from the overlying water column. In a paper published in the journal EcoHealth (v. 1, p. 317-323, "Analysis of Coral Mucus as an Improved Medium for Detection of Enteric Microbes and Determining Patterns of Sewage Contamination in Reef Environments"), Erin Lipp (University of South Florida) and Dale Griffin (U.S. Geological Survey) demonstrate for the first time that human-specific wastewater-associated viruses are detectable at an outer-reef site (Alligator Reef, off Marathon) in a nearshore-to-offshore-transect water-quality study. This study and others like it will aid regional ecosystem and public-health officials in addressing management issues. (Information about the journal EcoHealth can be viewed at the EcoHealth Web site.)
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in this issue:
Drilling Monitoring Wells in the Dry Tortugas American Samoa's Resilient Coral Reefs Seepage Samplers in Ashumet Pond
Gulf of Mexico Vulnerable to Hurricanes
Exhibit Designers Interested in Hurricane Research USGS Hosts Science-Learning Session
Deep Water Coral Research Workshop
Four Publications Win Shoemaker Awards Gene Shin Wins Shifting Baselines Contest
Elena Nilsen Joins Coastal and Marine Geology Team USGS Vessel To Test Counter-Terrorism Equipment
Human Influence on San Francisco Bay Floor |
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U. S. Department of the Interior | U.S. Geological Survey
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