Tucked between Florida’s Evergladed chin and the arc of ancient coral islands known as the Florida Keys, lies majestic Florida Bay. In the best of times, this estuary is roughly 500 square miles of placid and productive, clear blue-green water. From an airplane window, the bay's unusual clarity gives it the look of a rarified fish tank, playing tricks with viewers’ depth perception.

The bay is home to more than 250 species of fish, numerous bottom-dwelling organisms such as sponges, corals, shrimp and lobster, as well as alligators, crocodiles, green sea turtles, West Indian manatees, fish-loving birds and wind-surfing humans. Therein, as ever, lies the rub.

    For most of this century, Florida Bay's history has been tied to human manipulation of the environment of the Florida Keys. Beginning in 1906 with the construction of causeways for the Overseas Railway linking Miami to Key West, the bay has been subject to relentless pressure from development. The railway beds effectively reduced the exchange of water between the Atlantic Ocean and the bay, and coral growth rates in the bay's southwestern corner began to decline.

    Over the years, dredge and fill operations have taken their toll. Much of the dredging handiwork was to create "fast land" to support a population boom beginning in the early 1950s. In the process, dozens of canals pierced ancient coral heads, inelegantly exposing their porous nature, and creating a faster highway for underground wastewater to reach Florida Bay and Atlantic waters. These manmade conduits cut into natural subsurface water routes, allowing oxygen-poor and hydrogen sulfide-rich waters to invade them. Many artificial canals became incapable of flushing themselves of pollutants as readily as natural cuts in the islands' bedrock. As a consequence, even today some of the more than 200 canals in the Keys are downright putrid.

    But the list of insults to America's only subtropical environment is a long one that begins and ends with the Keys' increasing popularity. Just from 1980 to 1998, the population of Monroe County (which incorporates most of the Keys) increased by roughly 35 percent, reaching more than 85,000. On top of the year-round residents is a healthy tourism industry that accounts for an additional 25,000 inhabitants on any given day during the winter tourist season.

Sewage Woes

    With people come the after effects of so many consumed conch fritters and piña coladas. Of all the problems posed by the influx of humans on the fragile Keys' environment, adequate treatment of human waste has been the most vexing. Primarily because of the enormous difficulty and expense of digging holes and trenches in solid rock, and stringing a sewerage system through 120 island-hopping miles of prime real estate, centralized municipal treatment facilities so common to most urban areas is as rare to the Keys as a snowstorm.

    Surprisingly, only within the last 10 years have population centers in the Keys begun to employ a system of centralized sewage treatment. Before 1989, raw, untreated waste from Key West was pumped directly into the Atlantic. Ernest Hemingway's storied and picturesque old haunt, in fact, was one of the last places in the continental U.S. to discontinue the practice of dumping untreated sewage into the environment.

    Residents have been using septic tanks routinely in the Keys since the 1950s. But in that decade, local and city governments--with no funds for centralized sewerage plants--opted for another method endorsed by federal engineers: shallow-well injection.

    Today, roughly 750 sewage disposal wells that range in depth from 30 to 90 feet are operating in the Florida Keys. In the Upper Keys, most of the injected wastewater receives what is called secondary treatment--the norm throughout Florida--by what are called "package plants." Roughly 350 are now in operation, treating wastewater before pumping it into the ground.

    In the mid-1980’s, a notable downturn in Florida Bay's water quality got the attention of the public, the media and scientists. A slime mold infection, which corresponded to an increase in salinity, killed large swaths of seagrass–some even visible by satellite--algal blooms proliferated, and shrimp and lobster fisheries began to suffer. The bay's increased saltiness was thought to be caused by a combination of drought and a reduction in the amount of freshwater reaching Florida Bay from the Everglades--a drop of up to 40 percent from development and diversion of 'Glades water to the east.

    In the past decade, the bay's levels of nitrogen and chlorophyll have generally increased, along with its turbidity–the cloudiness of the water. Nearshore waters clearly are most in jeopardy, and long-time residents of the Keys when surveyed three years ago uniformly agreed that there have been notable changes in flora and fauna – all for the worse.

    Early this year, a research study by scientists from Florida International University reported that "there is good evidence that domestic wastewater is a significant source of nutrients for the groundwater and confinded embayments and canals of the Florida Keys..."

Groundwater Spill-Over

    When coastal groundwater gets contaminated by human and animal waste, it can dump large quantities of nutrients--predominantly nitrates and phosphates--into marine ecosystems--Jamaica’s Discovery Bay, the Great South Bay of New York, and salt marshes in Massachusetts are three examples that have suffered as a result. However, as the FIU reports suggests, only recently have scientists begun to study possible groundwater contributions of wastewater nutrients into Florida Bay.

    "You read in the papers that EPA has determined that so many pounds of nitrogen and phosphorus are going into the ground in the Keys," says Dr. Jeff Chanton, chemical oceanographer at FSU. Chanton (Ph.D. ) has been conducting research since 1994 on nutrient-rich groundwater flows into Florida Bay, along with his colleage Dr. William Burnett, with support from the state Department of Environmental Protection as well as from federal agencies.

    The question, says Chanton, is whether current methods of disposal--primarily the shallow injection wells--are satisfactory.

    "Do they need to go to centralized sewerage (throughout the Keys)? That’s what we’re trying to determine," Chanton says.

    Chanton and Burnett, along with graduate students Kevin Dillon and Reide Corbett, are using tracers--compounds that can be introduced at the source and easily detected elsewhere downstream--to measure how quickly sewage from injection wells in the Keys makes its way to surface water.

    Their methodology builds on work done by Burnett in the 1980’s. When Burnett and FSU colleagues were working in Central Florida to analyze the environmental effects of the phosphate mining industry there they consistently found elevated levels of radioactivity in the groundwater underlying the mined sites, as well as the unmined areas. As it turns out, the element radium and its gaseous decay product, radon, commonly are associated with phosphate deposits. Burnett says radon's special characteristics, a key one being that it doesn't react with other materials, make it an excellent tracer.

    "We’re using radon and methane as prospecting tools to locate the areas where groundwater comes out. But now we’re also figuring out how fast it travels," Chanton explains. His team is mainly concerned with how much nitrogen and phosphorus is reaching Florida Bay from shallow well injection of partially treated wastewater.

    The FSU team also is collaborating with Dr. Lee Kump of the Department of Geosciences at Pennsylvania State University. The Penn State work involves drilling out columns of rock and running nutrients through them to see if nitrates and phosphates attach to the surface of the underground carbonate rock, or if they pass through. Kump is measuring nutrient distributions around these sites, and has experience with analogous conditions--much of Pennsylvania rests atop a similar type of karst, or porous limestone geology.

    Besides geology, other natural phenomena conspire to prevent scientists from getting quick-and-easy answers. For example, researchers must factor in tidal influence on groundwater flow. On average, the height of water in Florida Bay actually is somewhat greater than it is in the Atlantic, likely caused by wind out of the western Gulf "piling up" water in the eastern Gulf. That means that net groundwater flow is slightly toward the Atlantic.

    In reality, the groundwater of the Keys "sloshes" back and forth, says Chanton, complicating already difficult-to-gauge groundwater flow patterns through the underlying cracks and fissures of partially-dissolved limestone. The slight overall flow toward the Atlantic is good news for the bay, and not such good news for the offshore Atlantic reefs which have suffered greatly in recent years. The small gradient toward the Atlantic is not as important in the wider and less porous lower Keys, Chanton said.

A Happy Environmental Accident?

    In their work on septic tank fluids on Big Pine Key and shallow-well injection of wastewaters on Key Largo, the FSU researchers have reached at least one indisputable conclusion--wastewater in the ground fairly rapidly wends its way to surface waters. The Swiss cheese-like rock that underlies much of Florida is especially porous in the Keys, particularly the upper reaches from Key Largo to Long Key.

    In some places, injected wastewater can reach the surface water in a matter of just several hours, although in one injection well study on Long Key, the FSU team found that some of the wastewater can remain in the immediate vicinity of the well for several months. The high flow rates are more typical of the upper Keys which are underlain by the more porous Key Largo limestone.

    The question for all locations is whether the wastewater that emerges is "polished," says Chanton--whether the phosphate and nitrates stick to the limestone matrix through which it travels. Phosphate is the real demon in the mix--the shallow bay and the nearby Atlantic coral reefs are extremely sensitive to the stuff.

    "We can show that the water does move from the injection wells into the surface waters of the bay. But now we’re trying to determine the extent to which the nutrients are scrubbed as they move through the system. It looks like there’s good evidence that the phosphate is removed," Chanton says.

    Preliminary information suggests upwards of 90 percent of the phosphate adheres to the underground limestone, he said. The finding, if subsequent tests support it, amounts to a "happy accident" by sanitation engineers who came up with the shallow-well injection idea in the 1950s. In all likelihood, Chanton said, designers of the system had no clue about the natural affinity for Keys limestone for the phosphates in human waste when they installed their first injection pump.

    But they also had little or no appreciation for the long-term capacity of the islands' limestone foundation to keep stripping those pollutants out of wastewater constantly pumped from above. Chanton cautions that although there is heavy dilution of this dirty water at depth, nearly all of it eventually percolates to the surface.

    "If you take a cup of sewage and pour it into the canal, you dilute it by many, many factors," Chanton says. But those 'cups' are flowing in there all the time."

    Still, the absolute amount reaching surface waters is not known, nor are the effects of nitrates which apparently aren't altered very much in their journey through the limestone’s nooks and crannies. Just how much more of this injected pollution the Keys and their surrounding waters can withstand is anyone’s guess, he said.