Nutrient couplings between on-site sewage disposal systems, groundwaters, and nearshore surface waters of the Florida Keys

BRIAN E. LAPOINTE, JULIE D. O'CONNELL, & GEORGE S. GARRETT

Abstract
We performed a one-year study to determine the effects of on-site sewage disposal systems (OSDS, septic tanks) on the nutrient relations of limestone groundwaters and nearshore surface waters of the Florida Keys. Monitor wells were installed on canal residences with OSDS and a control site in the Key Deer National Wildlife Refuge on Big Pine Key. Groundwater and surface water samples were collected monthly during 1987 and analyzed for concentrations of dissolved inorganic nitrogen (DIN = NO3- + NO2- + NH5-), soluble reactive phosphate (SRP), temperature and salinity.

Significant nutrient enrichment (up to 5000-fold) occurred in groundwaters contiguous to OSDS; DIN was enriched and average of 400-fold and SRP some 70-fold compared to control groundwaters. Ammonium was the dominate nitrogenous species and its concentration ranged from a low of 0.77 uM in control wells to 2.75 mM in OSDS-enriched groundwaters. Concentrations of nitrate plus nitrite were also highly enriched and ranged from 0.05 uM in control wells to 2.89 mM in enriched groundwaters. Relative to DIN, concentrations of SRP were low and ranged from 30 nM in control wells to 107 uM in enriched groundwaters. N:P ratios of enriched groundwaters were consistantly > 100 and increased with increasing distance from the OSDS suggesting significant, but incomplete, adsorption of SRP by subsurface flow through carbonate substrata.

Nutrient concentrations of groundwaters also varied seasonally and were approximately two-fold higher during the winter (DIN = 1035 uM; SRP = 10.3 uM) compared to summer (DIN = 470 uM; SRP = 4.0 uM). In contrast, surface water nutrient concentrations were two-fold higher during the summer (DIN = 5.0 uM; SRP = 0.50 uM) compared to winter (DIN = 2.5 uM; SRP = 0.15 uM).

Direct measurement of subsurface groundwater flow rate indicated that tides and increased groundwater recharge enhanced flow some two-fold and six-fold respectively. Accordingly, the observed seasonal coupling of OSDS-derived nutrients from groundwaters to surface water waters is maximum during summer because of seasonally maximum tides and increased hydraulic head during summer wet season. The yearly average benthic flux of anthropogenic DIN into contiguous canal surface waters is 55 mmolm day value some five-fold greater than the highest rate of benthic N-fixation measured in carbonate-rich tropical marine waters.

Back to the Scientific Studies Index

Back to Reef Relief's Main Web Site

Dilution Study - Key West POTW Discharge KEY WEST, FL (May 9-16, 1994)

Introduction:
The Environmental Protection Agency as part of their NPDES permit review process evaluating the impacts of several municipal discharges to the coastal environment. This initiative includes a determination of appropriate measurement techniques for identification of effects to both the water column as well as the benthic communities.

As part of this process, the Water Management Division (WMD) requested the assistance of the Environmental Services Division (ESD) to identify the circulation/dilution patterns in the vicinity of the wastewater plume migration.

In processing with this request, the ESD, in conjunction with the WMD planned and subsequently conducted a hydrographic study during the period of May 9 through May 16, 1994. The study focused on defining the dilution and dispersion patterns of the Key West POTW effluent as it mixes with the maritime waters.

Conclusions:

• The outfall line appears to have separated at approximately 1000 meters from shore. In its existing configuration the discharge is through a single port at the 6 meter contour as opposed to a reported design which featured a diffuser at the 10 meter contour.
• Currents measured north of the outfall are aligned with the navigation channel paralleling the western shore of Key West. South of the outfall the current regime is dominated by the easterly flowing Florida current.
• Effluent from the Key West POTW was diluted 6:1 at the effluent boil, 93:1 750 meters from the boil ad, to 1900:1 at 4300 meters from the boil.
• Flood tides carried the traced wastewaters along te western shore of Key West via the navigation channel and continued through Garrison Bight above Flemming Key.
• On the ebb tide, currents directed the plume southeasterly for approximately 1000 meters, then the Florida current directed the flow in a more easterly direction paralleling the southern shoreline of Key West.
• Mathematical model simulations were in close agreement with the field tracer data.
• Simulation of the dilution afforded by use of a diffuser section indicates that levels of dilution at 200 meters from the outfall could be an order of magnitude greater than with the existing single port configuration.
• Nutrient levels measured in the boil and within the plume reflected enrichment above background within the fist 200 meters from the outfall.
• Algal growth potential to indicate nutrient enrichment is moderate 200 meters from the biol. The limiting nutrient was nitrogen.
• Semi-diurnal tides with a mean range of 1.3 feet was recorded during the survey.
• Winds were from the east-southeast and averaged 5 knots.

Back to the Scientific Studies Index

Back to Reef Relief's Main Web Site

KEY WEST OCEAN OUTFALL STUDY: SYNOPSIS OF RESULTS AND CONCLUSIONS

Roland E. Ferry, Ph.D.-Water Management Division/Coastal Programs Section

Summary:
The US Environmental Protection Agency, Region4, directed and conducted a series of studies of the Key West Florida wastewater treatment plant ocean outfall from August 1993 to November 1994: The studies examined local hydrographic conditions, effluent transport and dilution in the receiving waters, geochemical and biological fate of effluent constituents, wastewater contributions to the benthos and to local eutrophication and impacts to macrobenthic communities.

Hydrodynamic conditions in the immediate area around the outfall on the ebb tides tend to transport effluent to the east, roughly parallel to the southern shorelines of the lower Keys and to the north into the Gulf of Mexico on the flood tide. High velocity tidal currents appear to confine the effluent largely to areas east of the Key West navigation channel. Effluent dilution exceeds 90:1 within 750 meters of the outfall and approaches 1000:1 within 2500 meters. Modeling results predict dilutions exceeding 32,000:1 at offshore bank reefs.

Nitrogen and carbon stable isotope studies indicate that outfall particulates are not a major component of particulate matter in benthic environments near the outfall or offshore bank reefs and that seagrass inputs are a primary source of sediment nitrogen in the area. The isoptopic dissimilarity between effluent and sediments suggest weak pelagic-benthic coupling in the area, probably due to strong currents and high rates of dilution. Outfall particulates do, however, appear to comprise a major component of the diet of some filter feeding macrobenthic organisms near the outfall, but not a major contributor of nitrogen to marine macrophyes around the outfall.

Coprostanol (fecal sterol) analysis of area sediments indicated sewage contamination of the benthos for several kilometers north and south of the outfall and along the southern shore of Key West. The outfalls relative contribution to sediment contamination cannot be distinguished from that of other likely (live-aboards mooring fields) and potential (ship discharges) sources of domestic wastes.

Benthic infaunal community analysis determined that there is no significant structural differences in macroinfaunal between communities in a sewage contaminated area by wastes and communities in an uncontaminated reference location.

The results of this series of studies indicate that wastewater effluent impacts from the Key West ocean outfall are mainly limited to localized eutrophication and contributions to some sewage contamination of the benthos in the vicinity of the outfall. The probability of transport of any significant amounts of outfall contaminants to offshore bank reefs appears to be low.

Back to the Scientific Studies Index

Back to Reef Relief's Main Web Site

INITIAL AND NEAR-FIELD SUBSEQUENT DILUTION AT THE KEY WEST OUTFALL

John J. Tsai, NOAA/AOML (NOAA/Atlantic Oceanographic and Meteorological Laboratory 4301 Rickenbacker Causeway, Miami, Florida 33149)
John R. Proni, NOAA/AOML
Hening Huang, Hazen and Sawyer
Julius F. Craynock, NOAA/AOML

ABSTRACT
A one-year field study of discharge from the Key West Outfall was conducted from June 1993 to July 1994. A towed CTD was used to measure salinity about every other month with a fixed current mooring next to the outfall. Salinity deficit was used as a tracer to estimatre the minimum surface dilution at the boil and near field subsequent dilution. The measured dilution at the boil ranged from 6:1 to 35:1, and a zone of intertidal dilution 50 m in radius was observed. Total physical dilution was rapid within 200 m and reached 100:1 at about 500 m from the boil.

INTRODUCTION
Initial and subsequent dilutions of waste-water discharged from municipal outfalls have been of great concern to environmentalists fo5r a long time. Different approaches have recently developed (e.g., Proni et al., 1994; Huang et al., 1994; Huang et al., 1995) for mixing zone studies to define the "worse case" criteria required by the EPA. However, field data are still inadequate. Recent study at four outfalls off the southeast coast of Florida provide excellent results of initial dilution and subsequent dilution (Proni et al., 1994)

Different approaches can be used to determine initial and subsequent dilutions of outfalls. One of the least expensive and most cost-effective ways is through conductivity measurements with current information. Salinity deficits at the boil and the surrounding area can generate easy measurements of initial and subsequent dilutions when the position associated with each measurement can be accurately determined.

This paper presents partial results of a study at the Key West Outfall using a current mooring near the outfall over a one-year period with towed CTD measurements about every two months during the same period of current mooring. A semi-empirical equation from dimensional analysis for initial dilution was derived and compared with data from SEFLOE II (Hazen and Sawyer, 1994). Subsequent dilutions as a function of distance from boil position were estimated from salinity deficits and compared with dye measurements at the same outfall.

Back to the Scientific Studies Index

Back to Reef Relief's Main Web Site

Occurrence of Fecal Indicator Bacteria in Surface Waters and the Subsurface Aquifer in Key Largo, Florida

JOHN H. PAUL, Department of Marine Science, University of South Florida
JOAN B. ROSE, Department of Marine Science, University of South Florida
SUNNY JIANG, Department of Marine Science, University of South Florida
CHRIS KELLOGG, Department of Marine Science, University of South Florida
EUGENE A. SHINN, U.S. Geological Survey Center for Coastal Geology
Received 17 January 1995/Accepted 20 March 1995

Sewage waste disposal facilities in the Florida Keys include septic tanks and individual package plants in place of municipal collection facilities in most locations. In Key Largo, both facilities discharge into the extremely porous Key Largo limestone. To determine whether there was potential contamination of the subsurface aquifer and nearby coastal surface waters by such waste disposal practices, we examined the presence of microbial indicators commonly found in sewage (fecal coliforms, Clostridium perfringens, and enterococci) and aquatic microbial parameters (viral direct counts, bacterial direct counts, chlorophyll a, and marine vibrophage) in injection well effluent, monitoring well s that followed a transect from onshore to offshore, and surface waters above these wells in two separate locations in Key Largo in August 1993 and March 1994. Effluent and waters from onshore shallow monitoring wells (1.8- to 3.7-m depth) contained two or all three of the fecal indicators in all three samples taken, whereas deeper wells (10.7- to 12.2-m depth) at these same sites contained few or none. The presence of fecal indicators was found in two of five near shore wells (i.e., those that were <1.8 miles [ <2.9 km] from shore), whereas offshore wells ( >2.1 to 5.7 miles].

Back to the Scientific Studies Index

Back to Reef Relief's Main Web Site

FLORIDA KEYS WATER QUALITY MONITORING PROGRAM

Department of Natural Resources Marine Research Institute Contract C7620

INTRODUCTION
The purpose of this project has been the development of a water quality monitoring program designed to enable assessment of the marine waters within the boundaries of Monroe County. The foci of the monitoring program are the impacts of On-Site Sewage Disposal Systems (OSDA), other system effluents, and storm water on ambient ground and surface near shore waters. These three sources of pollution are known to be the major local anthropogenic inputs to the Florida Keys National Marine Sanctuary designated in November of 1990.

In a larger perspective, it is the mandate of the Sanctuary Act, Public Law 101-605, and the responsibility of the U.S. Environmental Protection Agency (EPA) in coordination with the governor of the State of Florida (delegated to the Department of Environmental Regulation (DER)), to develop a comprehensive water quality protection program,. The Protection Plan, to be incorporated into the Florida Keys National Marine Sanctuary Management Plan, is to provide recommendations which in their implementation would "restore and maintain the chemical, physical, and biological integrity of the Sanctuary, including restoration and maintenance of a balanced, indigenous population of corals, shellfish, fish and wildlife, and recreational activities in and on the water."

The EPA and DER have initialized a multi-phase project in order to complete their obligations under the Sanctuary mandate. The first phase, completed in July of 1992, sought to identify existing data concerning water quality within and adjacent to the Sanctuary; to identify known monitoring and research programs, to define shortfalls in our knowledge of Sanctuary resources relative to water quality issues, and to develop a series of problem statements (research and management questions) which would serve as guidance in the development of future research and monitoring strategies.

Phase two of the EPA/DER effort is underway and nearing completion. It seeks to develop a coherent monitoring and research program which would provide Sanctuary and aligned resource managers with the additional knowledge necessary to make competent decisions in furtherance of the goal of resource restoration and maintenance. Information provided through implemation of the Phase II analysis may simply provide baseline data around which changes in the Sanctuary ecosystem may be assessed. Inn other cases, such information may be used to address identified and immediate resource protection needs. The development of the Phase II program will also provide an analysis and economic impact assessment of the cost of engineering options for known sources of water quality degradation and resource loss.

Finally, the EPA and DER will initiate existing public and academic efforts. It is clear that much is yet to be learned about the resources of the Sanctuary, in the face of considerable degradation, before we can properly monitor changes in the system or implement new management policy or law. Thus, basic research will be a significant component of the management agenda which will seek to maximize personnel resources and minimize regulatory and management gaps and overlaps.

Back to the Scientific Studies Index

Back to Reef Relief's Main Web Site

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

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.

Back to the Scientific Studies Index

Back to Reef Relief's Main Web Site

Nutrient Inputs From The Watershed And Coastal Eutrophication Of The Florida Keys

Brian E. Lapointe
Harbor Branch Oceanographic Institution, Inc.
Division of Estuarine, Coastal, and Ocean Sciences
Route 3, Box 297A
Big Pine Key, Florida 33043

Mark W. Clark
Florida Keys Land & Sea Trust
P.O. Box 536
Marathon, Florida, 33050

Abstract:
Widespread use of septic tanks in the Florida Keys increase the nutrient concentration of limestone in the groundwaters that discharge into shallow nearshore waters, resulting in coastal eutrophication. This study characterizes watershed nutrient inputs, transformations, and effects along a land-sea gradient stratified into four ecosystems that occur with increasing distance from land: man-made canal systems (receiving waters of nutrient inputs), seagrass meadows, patch reefs and offshore bank reefs. Soluble reactive phosphorus (SRP), the primary limiting nutrient, was significantly elevated in canal systems compared to the other ecosystems, while dissolved inorganic nitrogen (DIN; NH4+ and NO3-), a secondary limiting nutrient, was elevated both in canal systems and seagrass meadows. SRP and NH4+ concentrations decreased to low concentrations within approximately 1km and 3km from land, respectively. DIN and SRP accounted for their greatest contribution (up to 30%) of total N and P pools in canals, compared to dissolved organic nitrogen (DON) and dissolved organic phosphorus (DOP) that dominated (up to 68%) the total N and P pools at the offshore bank reefs. Particulate N and P fractions were also elevated (up to 48%) in canals and nearshore seagrass meadows, indicating rapid biological uptake of DIN and SRP into organic particles. Chlorophyll a and turbidity were also elevated in canal systems and seagrass meadows; chlorophyll a was maximal during summer when maximum watershed nutrient input occurs, where as turbidity was maximal during winter due to seasonally maximum wind conditions and sediment resuspension. DO was negatively correlated with NH4+ and SRP.

Back to the Scientific Studies Index

Back to Reef Relief's Main Web Site

INFLUENCE OF DOMESTIC WASTES ON ENERGETIC PATHWAYS IN ROCKY INTERTIDAL COMMUNITIES

By Mark M. Littler and Steven N. Murray

1. The calorific contents of eighteen macroinvertebtrates and thirty-six macrophytes were determined in an unpolluted rocky intertidal habitat and in an nearby polluted.
2. Much of the variation in the calorific values of macrophytes was related to life span. The algae that characterized the unpolluted community usually contained comparatively fewer calories per unit weight. These forms had relatively more structural tissues and hence allocated relatively less energy to rapid growth and production. In the polluted habitat, fugitive or opportunistic algal species were more prevalent; these had thallus constituents with lower calorific values, suggesting that these aglae may have evolved reduced palatibility.
3. The major taxonomic groups of algae yielded the following sequence of mean calorific values: Chlorophyta, 4.78 kcal g-1 ash-free dry weight; Rhodophyta, 4.39; Cyanophyta, 4.38; Phaecophyta, 4.22.
4. In nearly every case, macroinvertebrate populations exposed to domestic sewage had higher energy contents than did corresponding populations from the unpolluted habitat.
5. Macroinvertebrates in the polluted habitat grazed greater proportions of blue-green algae and bacteria. Omnivores and suspension feeders in the polluted habitat appeared to utilize energy-rich compounds in the sewage effluent; this may explain the greater standing stocks of omnivores and suspension feeders in the peripheral regions of the outfall plume.

Back to the Scientific Studies Index

Back to Reef Relief's Main Web Site

IMPACT OF SEWAGE ON THE DISTRIBUTION, ABUNDANCE AND COMMUNITY STRUCTURE OF ROCKY-INTERTIDAL MACRO-ORGANISMS

Abstract
The biological effects of a low-volume domestic sewage discharge were studied near Wilson Cove, San Clemente Island, California (USA), from February to June, 1972. There were fewer species and less cover near the outfall (7 macro-invertebrates, 17.6%; 13 macrophytes, 91.7%) than in nearby "unpolluted" control areas (9 macro-invertebrates, 9.2%; 30 macrophytes, 103.4%). The outfall biota was less diverse than that of the controls, as shown by 5 different diversity indices.

A great reduction in community stratification (spatial heterogeneity) and, hence, community complexity occurred near the outfall; this reduction in stratification was primarily due to the absence of Egregia laevigata, Halidrys dioica, Sargassum agardhianum and Phyllospadix torreyi.

These were replaced in the mid-intertitdal near the outfall by a low turf of blue-green algae, Ulvi californica, Gelidium pusilum and a small Petrocladia capillacea, and in the intertidal by Serpulorbis squamigerus covered with Corallina officianalis var. chilensis. A statistically-based determination of assemblages or groups of organisms (i.e, cluster analysis) revealed 3 discrete control area groups; 3 assemblages contained samples from both areas. The distributional patterns of these groups indicate that near the outfall the degree of dilution of discharged sewage is more important in regulating zonation than is tidal height.

The enhancement of the suspension feeder Serpulorbis squamigerus and the omnivores Ligia occidentallis, Pachygraspsus crassipes and Anthopluera elegantissima in the outer fringe of the outer outfall plume hypothetically is due to their ability to utilize sewage as a food source. A critical effect of the outfall may be to decrease environmental stability thereby favoring rapid-colonizers and more sewage-tolerant organisms. The outfall smaller growth forms, simpler and shorter life histories, and most were components of early successional stages.

Back to the Scientific Studies Index

Back to Reef Relief's Main Web Site

Paul R. Epstein, Center for Health and the Global Environment, Harvard Medical School. Tel (617) 432-0493

An outbreak of cholera on the southern Coast of Bangladesh in 1992 may presage the risks posed to developed and less-developed countries alike from deep-sea dumping of human sewage, according to some researchers. Scientists have noted that the 1992 outbreak was accompanied by an upwelling that brought deep-sea water to the surface near the Bangledeshi coast. In recent years, researchers have discovered a variety of pathogenic microbes, many usually found only in human feces, at unexpected depths of the ocean. Marine scientist D. Jay Grimes of the University of Southern Mississippi says that a variety of viruses that infect the human gastrointestinal tract - including poliovirus and rotavirus - have been identified in ocean water samples taken below 1,0000 meters (3,300 feet). In the late 1980's, Sagar M. Goyal of the University of Minnesota isolated gut bacteria from samples obtained as sewage-sludge dumping sites more than 170 kilometers offshore from New York City, 30 months after the sites were closed to dumping. The bacteria were resistant to several antibiotics, showing that they originated from humans who were taking the drugs.

Although the scenario by which such microbes could reach the surface is unclear, Dr. Paul Epstein of the Harvard School of Medicine has expressed concern about the presence of pathogens in the deep ocean, particularly the given proliferation of projects such as miles long pipelines to take sewage out to sea.

Back to the Scientific Studies Index

Back to Reef Relief's Main Web Site