THE IMPACTS OF STORMWATER DISCHARGES ON EUTROPHICATION IN THE FLORIDA KEYS

Brian E. Lapointe, Ph.D.
William R. Matzie, International Marine Research, Inc. Route 3, box 297A Big Pine Key, FL 33043 Phone (305) 872-2247

Estuaries, v19 n2B p422-435, June. 1996

EXECUTIVE SUMMARY
Storm water discharge is a major pathway by with land-based pollutants enter coastal waters. This project involved monitoring the effects of storm water inputs using four continuos-recording water quality monitoring instruments (Hydrolab Datasounde) along a nearfield transect extending from Big Pine Key to Looe Key National Marine Sanctuary (LKNMS); these instruments recorded dissolved oxygen salinity temperature, and tidal stage at 30 min. intervals. Water samples were also collected for nutrient determinations along this and another far-field transect (extending from Shark River on the southwest Florida shelf to LKNMS) to determine relationships between nutrient concentrations and salinity from both near-field and far-field watersheds.

Concentrations of nutrients, chlorophyll a, and turbidity increased along the near-field transect with increased freshwater inputs between the dry season (April-May, 1992) and the wet season (June-August, 1992). Freshwater discharges in early June resulted in anoxic conditions at the most inshore monitoring station (Port Pine Heights canal), a station directly impacted by septic tank leachate. High concentrations of total phosphorus correlated with freshwater inputs along both transects, indicating land-based runoff from the Keys and southwest Florida as nutrient sources. High concentrations (up to 21 uM) of ammonium followed rainfall events at the inshore stations; ammonium concentrations averaged > 1.0 uM along the entire near-field transect over the study period. Chlorophyll a and turbidity increased from the dry season into the wet season in response to the land-based storm water nutrient inputs.

A comparison of nutrient and chlorophyll-a concentrations in coastal waters of the Keys with threshold values for eutrophication on coral reefs suggests that waters of the Keys have entered a stage of critical eutrophication. Ammonium concentrations have increased several-fold at LKNMS over the past seven tears and total phosphorus, chlorophyll a and turbidity are currently 2-3 fold higher than on pristine coral reefs in the western Caribbean. The high levels of nutrients, chlorophyll a, and turbidity in coastal waters of the Keys demands that special precautions be exercised in the treatment and discharge of wastewaters and land-based runoff.

Lapointe etal 05 1 Macroalgal Blms on SE FL Crl Rfs Nut Stoich of C isthmocladum wider Carib

This leading study documents that the invasive algal blooms of codium along the Palm Beach and Broward County coasts during the summer of 1990 and thereafter were caused by increasing land-based sources of pollution, particularly sewage critical to providing the needed nutrients for such an extensive harmful event.  Published by Elsevier B.V. in Harmful Algae 4 (2005) 1092-1105.

http://www.rsmas.miami.edu/info/pressreleases/ancient-coral.html

Key To Florida Bay Locked In Ancient Coral

AUGUST 6, 1996VIRGINIA KEY, Fla.–During the past several years, the water quality of Florida Bay, part of the Everglades ecosystem, has deteriorated at a steady rate. Since 1987 large areas of sea grass have died, algae blooms have created “dead zones” in parts of the bay, and populations of birds, juvenile fish and shrimp have declined dramatically. Many people blame this ecological imbalance on high salinity in the bay caused by the diversion of freshwater from the Everglades (and ultimately Florida Bay) to the metropolitan areas on the coasts north of the bay. But a new University of Miami Rosenstiel School of Marine and Atmospheric Science-led study of coral skeletons from Florida Bay suggests that the present poor conditions of bay water were set in motion nearly 100 years ago by the construction of the Florida East Coast Railway, which connected Miami to Key West. By analyzing the oxygen and carbon isotopes in the skeleton of a 160-year-old coral head from the bay, scientists discovered that there has been no clear increase during the last 80 years in the salinity of the southern portion of Florida Bay from which the skeletons were retrieved. This finding, which is presented in the journal Palaeogeography, Palaeoclimatology, Palaeoecology, runs contrary to a widely-held belief that the decline of Florida Bay is the result of high salinities caused by a man-made diversion of freshwater from the Everglades. “There is no doubt that the flows of freshwater into Florida Bay have declined, but the geological record from this coral head shows no clear evidence that during the last 80 years this decline has substantially affected the salinity of the portion of the bay where this coral is located,” says principal investigator Dr. Peter Swart, chairman of the Division of Marine Geology and Geophysics at the Rosenstiel School. “We suggest that the railway construction combined with a reduction in the number of hurricanes over several decades has allowed a buildup of organic material within Florida Bay.” During construction of the railway, natural gaps between the keys in several locations were filled in to form causeways linking the islands. Swart and his colleagues believe that these unnatural fills reduced the natural exchange of water between Florida Bay and the open sea of the Florida Straits. “These blockages allowed Florida Bay to retain more of its organic-rich muds,” Swart says. “This organic material decays, reducing levels of free oxygen in the water and causes a build-up of nutrients. The nutrients promote algal blooms, further reducing the oxygen in the bay through the process of eutrophication.” According to Swart, this build-up of nutrients in the bay has been compounded by the fact that Florida Bay has received relatively few hurricanes during the past 47 years. “Hurricanes have a cleansing effect on the bay,” he says. “They remove organic-rich sediment to the open ocean.” By analyzing the oxygen and carbon isotopes of cores drilled from the bay corals, Swart and his colleagues determined that there has been no clear increase in the salinity in the lower part of the bay during the past 80 years. The largest change in salinity and nutrients occurred between 1905 and 1910, coincident with the construction of the Florida East Coast Railway. Salinity in that part of the bay has not changed significantly in the years since construction of the South Florida canals that have been diverting water away from the bay. “A combination of the changes brought about by the railway and the absence of hurricanes has caused this mess,” Swart says. He believes that, in addition to current efforts to redirect freshwater toward the bay, it may also be necessary to restore the natural exchange of water between the bay and the sea by replacing keys causeways with bridges. The finding does have its detractors, Swart acknowledges. “Some scientists suggest that the salinity changes in the lower bay may not be representative of other portions of the bay, particularly in those areas where the most significant sea grass die-offs are taking place. But other data suggest that salinity in one portion of the bay is strongly correlated to salinity in other parts of the bay.” Swart and his students Genny Healy and Lisa Greer, together with Richard Dodge of Nova Southeastern University are now undertaking a study for the South Florida Water Management District to correlate salinity records of corals from throughout the bay as a way to assess their current findings as a predictor of the condition of the bay as a whole. “In many ways corals can be considered to be the trees of the sea,” Swart says. “Many of them form annual bands in their skeletons comprising various densities of calcium carbonate. By counting and measuring these bands, the age and growth rate of the coral can be determined.” Corals serve as archives of environmental conditions of the past. By analyzing the chemical composition of coral skeletons, scientists can determine water salinity, water temperature and other factors that affected the growth of a coral during its history. Swart points out that coral cores are removed with minimal damage to the coral head. After drilling, cores are plugged with cement, which serves as substrate for the re-growth of corals and prevents damage from organisms that bore into corals. “There is a saying in geology that the present is the key to the past,” Swart says. “In this case, the past is very much the key to the present.”

The University of Miami Rosenstiel School of Marine and Atmospheric Science ranks among the world’s premier oceanographic research and teaching institutions. The Rosenstiel School is a global leader in the study of sea and air circulation, fisheries, coral reefs, climate change, and ocean conservation. The School celebrated its 60th anniversary in 2003.

 

http://www.britishecologicalsociety.org/journals_publications/journalofappliedecology/index.php

Julie P. Hawkins and Callum M. Roberts
Research Center, Sharim-el- Sheikh, Egypt
Journal of Applied Ecology 1993, 30, p.25-30.

ABSTRACT

This study investigated the effects of trampling by scuba divers and snorkelers on reef-flats of coral reefs near Sharim-el- Sheikh, a popular resort in Egypt.

There were significantly more damaged coral colonies and loose fragments of live coral rocks in heavily trampled areas. Percentage cover of bare rock and rubble was also significantly greater; conversely numbers of hard coral colonies and total percentage of live coral cover were lower.

Coral colonies were smaller in trampled compared to control areas, with average height and diameter significantly less in heavily trampled areas. An area regularly visited be snorkelers exhibited intermediate effects.

Coral species composition and the relative abundances of different coral growth forms did nor appear to be affected by the trampling.

Several of the effects detected differed between outer and middle zones of the reef flat, suggesting that some communities were more vulnerable to trampling than others.

In addition to causing biological damage, trampling reduced the aesthetic appeal of the reef-flat for tourists. An effective management strategy might therefore be to contain trampling within narrow areas rather than allowing free access by divers.

http://sofia.usgs.gov/publications/ofr/94-276/index.html\

Eugene A. Shinn, Ronald S. Reese and Christopher D. Reich
USGS Coastal Geology Center, St. Petersburg, Florida
USGS Water Resources Division Office, Miami, Florida

US Department of the Interior, US Geological Survey OFR 94-276 1994

 

EXECUTIVE SUMMARY

I. 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 (NO2 and NO3) and phosphorus were not particularly elevated in offshore ground water but were above the levels found in surface marine water.

The highest levels of nitrogen (NO2 NO3) and phosphorus were in shallow onshore groundwaters.

Sources for the nutrients in the shallow onshore groundwater 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.

II. 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 (9-12m) nevertheless remained slightly hypersaline relative to sea water throughout the year.

III. 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 and 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 phosphorus is taking place.

Ground waters were found to contain more dissolved solids that 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.

IV. 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 faces that extends only a few hundred feet seaward of the Keys.

Reef facies give way to mudstone facies within a few hundred feet seaward of the Keys.

Reef facies give way to mudstone facies within a few yard 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 facies.

V. 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 one 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 conforming 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 miles 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 (10-20m) of water, where Holocene reef and sediment accumulations are thin or absent.

IV. This study did not address direct measurements of lateral groundwater movement or a hydrologic mechanism for transplanting hypersaline groundwater away from the Florida Keys.

More recent work, however (Halley et al., 1994), shows that sea level in Florida Bay is higher 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 groundwater flow towards 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 is needed for prediction and modeling efforts in the future.