    [From the U.S. Government Printing Office, www.gpo.gov]

                                                    NOV     1987

                                          FINAL REPORT ON THE EFFECTS OF

                              ON-S.ITE SEWAGE D1ISPOSAL SYSTEMS ON NUTRIENT RELATIONS

                             OF GROUNDWATER AND NEARSHORE WATERS OF THE FLORIDA KEYS

                                                  Prepared for:

           0"

           Lr\
                                                                               COASTAL ZONE

                                                                           INFORMATION CENTER

                                                   Prepared by:

                                             Brian E. Lapointe, Ph.D.
                                       International Marine Research, Inc.
                                     Rt. 3, Box 297A, Big Pine Key, FL 33043
                                                   305-872-2247

                Funds for this project were provided by the Department of              Enviornmental
                Regulation, Office of Coastal Management, through funds made available
                by the National Oceanic and Atmospheric Administration under the
                Coastal Zone Management Act of 1972, as amended.

               TD
              771.5
              .L37
              1987

                                            TABLE OF CONTENTS

                 LIST OF TABLES  -----------------------------------------------------------    ii

                 LIST OF FIGURES ---------------------------------------------------------      iii

                 PROJECT SUMMARY  ----------------------------------------------------------    iv

                 INTRODUCTION  --------------------------------------------------------------     I

                 BACKGROUND ----------------------------------------------------------------      I

                 MATERIALS AND METHODS   -----------------------------------------------------    6

                 RESULTS  ------------------------------------------------------------------    14

                                                                                  -----------
                 DISCUSSION ---------------------------------------------------                --19

                 CONCLUSIONS AND RECOMMENDATIONS  ----------------------------------   --------- 30

                 REFERENCES ---------------------------------------------------------------     33@

                 APPENDIX TABLE I ------------------------------------------------------------

                 APPENDIX TABLE II ------------------------------------------------------------

                                                 LIST OF TABLES

                   Table                                                                            Page

                    1. List of groundwater    monitoring stations in the Florida Keys       .......... 33

                    2. List of hydrographic monitoring stations in nearshore waters of
                        Big Pine Key, FL   ......................................................     34

                    3. Mean values and ranges for nutrient concentrations, temperature
                        and salinity of groundwaters and adjacent surface waters in winter,
                        1986/1987 and summer, 1987    ...........................................     35

                    4.  Comparison  of nitrate concentrations    of groundwater and adjacent
                        surface waters in winter, 1986/1987 versus summer, 1987        .............. 36

                    5.  Comparison of ammonium concentrations of groundwater and adjacent
                        surface waters in winter, 1986/1987 versus summer, 1987        .............. 37

                    6.  Comparison of soluble reactive phosphate concentrations of
                        groundwater and adjacent surface waters in winter, 1986/1987
                        versus summer, 1987   ..................................................      38

                    7.  Comparison of nutrient concentrations in groundwaters from
                        residential stations versus the control station at the Key Deer
                        National Wildlife Refuge    .............................................     39

                    8.  Mean values for nutrients and salinity at Halcyon Trailer Park
                        and Key Deer National Wildlife'Refuge     ..........................   ...... 40

                    9.  Rate and direction of   groundwater flow at Port Pine Heights,
                        Big Pine Key, during ebbing and flooding tides      .......................   41

                   10.  Rate and direction of groundwater flow at Halcyon Trailer Park
                        and Key Deer National Wildlife Refuge.during high and low tides        ...... 42

                   11.  Mean values and ranges for concentrations of nutrients and
                        chlorophyll in seawater sampled at hydrographic stations along an
                        orishore-offshore transect in nearshore waters of Big Pine Key, FL.... 43

                   12,  Correlation matrices of chlorophyll     and nutrient concentration
                        data collected at hydrographic stations along an onshore-offshore
                        transect in nearshore waters of Big Pine'Key, FL       ...................... 44

                                                  LIST OF FIGURES

                  Figure                                                                              Page

                    1. Location of groundwater monitor stations on Key Largo, FL         ............ 50

                    2. Location of groundwater monitor stations on Plantation Key,.FL          ....... 51

                    3. 'Location of groundwater monitor stations on Marathon, FL        .............. 52

                    4. Location of   groundwater monitor stations on Big Pine Key, FL        ......... 53

                    5. Calibration   curve for GeoFlo groundwater flow meter      ..................  54

                    6.  Location of hydrographic stations in nearshore waters of Big Pine
                        Key, FL  .........................    ....................................    55

                    7.  GroundwaLer flow rate in Port Pine Heights, Big Pine Key; ebbing
                        tide  ..................................................................      56

                    8.  Groundwater flow rate in Port Pine Heigh     ts, Big Pine Key; flooding
                        tide  .................................................................       57

                    9., Seasonal trends in hydraulic head based on monthly average
                       'groundwater table height and mean sea level      ..........................   58

                                             PROJECT SUMMARY

                     The effects of on-site sewage disposal systems (OSDS; septic tanks and

                aerobic treatment units) on nutrient concentrations of upland groundwaters and

                adjacent inshore waters of the Florid a Keys, Monroe County, was studied between

                December, 1986 and September, 1987. Monitor wells designed to sample

                groundwater at 8-10 ft below grade were installed at four residential stations

                in the Upper Keys (Key Largo Limestone substrate) and four residential stations

                in the Lower Keys (Miami Oolite substrate) to determine the effects of septic

                tank systems,on groundwater quality. A deeper monitor well clu ster, co"sisting

                of three wells of different depths (15-, 30-, 60' below grad e), was installed

                adjacent to the injection well of an aerobic treatment unit. Control monitor

                wells (15' and 30- below grade) were located in the pristene environs of the Key

                Deer National Wildlife Refuge (KDNWR) and remote from potential sources of

                contamination. All the monitor wells, as well as the most adjacent inshore

                surface water (i.e. canal), were sampled monthly for determination of ammonium,

                nitrate, soluble reactive phosphate (SRP), salinity, and temperature.

                     The results indicated that septic tank/drainfield systems cause extreme

                nutrient enrichment of groundwaters, which apparently seep into adjacent  surface

                waters through natural groundwater flow.patterns. The highest concentrations of

                nutrients were found in groundwaters adjacent to drainfields and the effluent of

                the aerobic treatment units  where concentrations as high as 2.5 mM for

                ammonium, 2.3 mM for nitrate, and 120 pM for SRP occurred. Annual mean

                concentrations of ammonium and nitrate in residential groundwaters were

                approximately 350-fold higher than the control, whereas concentrations of SRP

                were approximately 60-fold higher. The reduced level of SRP enrichment of

                groundwaters in the Keys appears to be due to mineral formation associated with

                carbonate geologies (i.e. fluoroapatite) and scavenging by oxides of iron and

                                                   iv

                alumiaum. A significant seasonality was evident-for the concentrations of all

                nutrients in the groundwaters and surface waters; maximum concentrations of

                groundwater nutrients occurred during winter (minimum during summer), whereas

                maximum concentrations in surface waters occurred during summer (and minimum in

                winter). This suggests that maximum  discharge of groundwater nutrient loads into

                surface waters occurrs during summer, which may be due to increased groundwater

                recharge, hydraulic head (and groundwater flow), and mixing processes during the

                higher sea levels that occur in summer compared to winter. Approximately

                three-fold higher concentrations of chlorophyll also occurred in inshore surface

                waters during summer, apparently in respone to groundwater nutrient enrichment.

                     Direct determiaations of groundwater flow rate at several locations on Big

                Pine Key during summer 1987 indicated an average flow rate of 2.8 f t/day.

                However, increased flo w was observed in response to ebbing tides (up to 5

                ft/day) and rain events (up to 12 ft/day). Direction of groundwater flow could

                not be pred icted as based solely on the decreasing grade elevations to the most

                adjacent surface water, and explains previous failures of rhodamine dye to trace

                septic effluents in to adjacent surface waters. Based on an average travel path

                to the down stream receiving waters of 350' for one canal residence on Big Pine

                Key, an average of 6 months would be required for discharge of nutrients into

                surface waters. Considering the expanded tourist and resident population of the

                Keys during winter, the resulting nutrient load might be expected to reach

                surface waters during the following summ er. Such a "delayed discharge" would be

                facilitated by increased sea level, groundwater recharge, hydraulic head, and

                groundwater flow during late spring and summer.

                                                    v

                                                         INTRODUCTION

                           The marine environment of the Florida Keys is one of the most important

                               the economy of Monroe County. The clear, oligotrophic waters of the
                     assets to

                     Keys support extensive gr owth of corals and   seagrasses that are linked directly

                     or indirectly, to tourism, commercial and sport fisheries, and the distinctive

                     "Key s" way of life. To determine potential impacts on the marine environment by

                     increasing use  of on-site sewage disposal systems (OSDS), a one year study was

                     conducted to quantify effects of OSDS on nutrient concentrations of upland

                     groundwaters and adjacent inshore waters. Twenty groundwater monitor wells were

                     installed and, together with adjacent inshore waters, sampled for nutrient

                     concentrations (ammonium, nitrate, soluble reactive phosphate) as wellas

                     salinity and temperature. Rate and direction of groundwater flow was determined

                     at several sites on Big Pine Key to determine subsurface flow patterns and

                     quantify potential dispersion   of septic leachate associated with OSDS in Miami

                     Oolite limestone substrate. Concentrations of nutrients and chlorophyll-a were

                     also measured at hydrographic stations in inshore and nearshore waters along a

                     transect extending from canal waters on Big Pine Key to offshore waters at Looe

                     Key National Marine Sanctuary-

                                                          BACKGROUND

                          The Florida Keys are truly unique in North America in Inaving the most

                     biologically diverse and productive shallow water (<10m) tropical marine

                     ecosystem. The archipelago  island chain of the Keys separates the marine

                     environments of Florida Bay  and the Gulf of Mexico from that of the Florida

                     Straits and Atlantic Ocean,  with numerous tidal passes between the Keys

                     providing water exchange between these water bodies. The most unique feature of

                     the Keys marine environment is the extensive coral reef f   ormations  that extend

                 for 220 miles between Soldier Key and Dry Tortugas that include patch and bank

                 reef systems ranging from 25m to 1.3 km offshore and collectively referred to as

                 t
                 he Florida Reef Tract (Vaughn, 1914; Jaap, 1984). Coral reef ecosytems are the

                 most biologically diverse and productive ecosystems on earth (Goreau, t979) and

                 make tourism and recreation a major factor in the local and regional economy.

                 Several species of tropical seagrasses also form extensivemeadows in the

                 shallow Keys marine environment and are important as sources of food and habitat

                 for marine organisms, stabalization of sediments, and recycling and storage of

                 nutrients (Zieman, 1982).

                     The importance of maintaining water quality with increasing upland

                 development was a major element that spurred legislation t o protect the unique

                 Keys marine environme nt. In 1974, the Florida Keys were designated as an "Area

                 of Critical State Concern" under Chapter 380 of the Florida Statutes. Section

                 380.0552, "The Principles for Guiding Development in the Florida Keys Area of

                 Critical State Concern" was adopted by the administrative Commission ten years

                 later, in 1984, to "insure a water management system that will reverse the

                 deterioration of water quality and provide optimum utilization of our limited

                 aquatic resources, facilitate orderly and well planned development, and protect

                 the health, welfare, safety, and quality of life of the residents of this

                 state." Subsequently, in 1,985, the waters of the Florida Keys were designted as

                 "Outstanding Florida Waters" under Chapter 403 of the Florida Statutes.

                     in accordance with the guidelines of Section 380.0552 cited above, the use

                 of OSDS for wastewater management in the Florida Keys remains controversial. The

                 bulk (70%) of liquid domestic waste disposal in Monroe County is met by OSDS,

                 either septic tank/drainfield systems or aerobic treatment units, such as the

                 11multi-Flo" unit, coupled with injection wells. Considering that only 20% of the

                 53,000 platted, subdivided.lots in the Florida Keys are developed at present,

                                                       2

                 cumulative effects of increasing use of OSDS could have potentialy dramatic

                 effects on  inshore water quality. While studies of septic tank systems in Dade

                 County, FL have concluded that septic leachate enters surface waters in canals

                 and causes water quality degradation (Barada, 1972) there still exists no

                 general agreement regarding the effects of OSDS on water quality in the Florida

                 Keys.

                      This lack of general agreement regarding impacts of canalization and septic

                 tank use on water quality in   the Keys results from the disparate conclusions of

                 previous studies that have addressed this issue. For example, the studies of

                 Chesher (1973) reported satisfactory water quality in virtua-11y all of the

                 canals studied and concluded that   "there were no adverse environmental

                 conditions attributable to septic   tanks." However, the.studies   of Hicks et al.

                 (1974) concluded that canal systems in the Keys have poor flushing

                 characteristics that result in frequent violations of both State and Federal

                 water quality criteria. Furthermore, although dye studies failed to demonstrate

                 septic leachate directly entering canal waters, elevated dissolved nutrients and

                 total organic carbon in developed canals appeared to be responsible for lower

                 oxygen levels in developed compared to undeveloped canals (Hicks et al., 1974).

                      An assessment of the use of OSDS on inshore water quality of the Keys will

                 necessarily have to address groundwater quality also. Groundwaters are known to

                 be important nutrient sources   to lakes (Keeney et alw, 1971; Brock et al., 1982;

                 Loeb and Goldman, 1979) but only recently have.,they been demonstrated as

                 significant@nutrient sources to inshore marine waters. For example, groundwaters

                 are an important nutrient source in salt marsh    systems on  Cape Cod,

                 Massachusetts (Valiela et al., 1978), in nearshore waters     of Long Island Sound,

                 New York (Capone and Bautista, 1985), and in back-reef habitats     on coral reefs

                 along the north shore of Jamaica    D'Elia et al., 1981). While a historical

                                                         3

                   importance of groundwater nutrient inputs on nutrient budgets of coastal waters

                   is recognized (e.g. Manheim, 1967) increasing development and agriculture in

                   upland, coastal areas are dramatically increasing the role of groundwaters in

                   nutrient budgets of nearshore marine waters (Capone and Bautista, 1985; Pye and

                   Patrick, 1983). The potential for nutrient enrichment of nearshore waters by

                   groundwaters enriched with  septic leachate is exacerbated in the Florida Keys

                   because of the high porosity and permeability of its coral-derived substrate and

                   the-ubiquitous close proximity of OSDS to oligotrophic marine ecosystems; there

                   also exists the possibility that elevated tides and cross island heads

                   accelerate flow of enriched groundwaters toward oligotrophic marine habitats.

                   Studies of groundwater flow alo ng Florida-s east coast have clearly demonstrated

                   brackish groundwater fluxes into nearshore marine waters on the order of 45

                    3
                   m /day from a strip-one meter wide (Kohout, 1966), suggesting that enriched

                   groundwaters could become a major source of nutrients to nearshore environments

                   in South Florida.

                        Special concern regarding increased nutrient availability on the ecology of

                   nearshore waters of the Florida Keys is based on the known high degree of

                   nutrient limitation that is key to maintaining outstanding water quality in

                   these oligotrophic waters. Nutrient-limitation bioassays with several species of

                   dominant macroalgae in Pine Channel and Florida Bay demonstrated severe

                   limitation of productivity by phosphorus and nitrogen (Lapointe, 1987; Lapointe,

                   1988), supporting the the contention.that limited nutrient availability

                   regulates, to a large extent, marine plant growth in these waters. Consequently,

                   increased.nitrogen and phosphorus flux to nearshore waters of the Keys marine

                   environment could lead to increased marine biomass (phytoplankton and

                   macrophytes) resulting in increased microbial decomposition, decreased submarine

                   irradiance, and cumulative water quality degradation. This process of water

                                                         4

                quality degradation, referred to as cultural eutrophication, is receiving

                increas 'ed attention by marine scientists who are in general agreement that the

                process is regulated primarily by nutrient loading (e.g. Ryther and Dunstan,

                1971; Lee and Jones, 1981). Cumulative effects of eutrophication include reduced

                water transparency, reduced dissolved oxygen Concentrations, odo    rs (hydrogen

                sulfide), fish kills, and a reduction of biological diversity. Because inorganic

                forms of dissolved nitrogen (nitrate and ammonium) and phosphorus (soluble

                reactive phosphate, SRP) are the most important forms associated with domestic

                wastewater that support algal growth (Parsons et al., 1977), a knowledge of the

                contribution of OSDS to concentrations of these nutrients in groundwaters and

                surface waters of the Florida Keys is needed.

                                             SCOPE OF THE PRESENT STUDY

                     The objectives of the present study were to:

                         1) determine if use of OSDS affects nutrient concentrations of

                            upland groundwaters and/or adjacent inshore waters.

                         2) determine groundwater flo w rates in typical geologies of the Keys to

                            quantify interaction of groundwaters with inshore marine waters.

                         3) De termine the relationship, if one exists, between dissolved

                            in organic nutrients and phytoplankton chlorophyll in nearshore waters

                            to predict potential effects of increased nutrient availabili.ty.

                                                        5

                                              MATERIALS AND METHODS

                Study Area

                     This study took place in Monroe County, FL, and included a variety of

                residential canal locations that extended from Key Largo in the Upper Keys to

                Big Pine Key in the Lower Keys. The surafce geology of the Upper Keys is

                composed primarily of coral reef rock known as Key La rgo Limestone whereas that

                of the Lower Keys is formed of small spherical grains of calcium carbonate

                cemented together and known as Miami Oolite (Hoffmeister, 1974; Multer, 1971).

                Key Largo Limestone is  ver.y porous and riddled with numerous solution features

                and voids that allow rapid vertical and horizontal groundwater flow;

                consequently, this formations retains little fresh water because of its high

                permeability and therefore, no freshwater lenses occur in the Upper Keys (Parker

                et al., 1955; Hoffmeister and Multer, 1968). Although Miami Oolite in the Lower

                Keys is also quite porous, it has fewer horizontal voids than the Key Largo

                Limestone so retention of fresh water is enhanced and results in several fresh

                water Ghyben-Herzberg lenses, most notably those of Big P ine Key (Hanson, 1980).

                Monitor Wells: Design and Installation

                     To determine potential effects of septic tank leachate on groundwater

                nutrient concentrations, nutrient concentrations were determined in groundwaters

                of-16 monitor wells on eight upland residential lots with septic tank/drainfield
                sy@tems currently in use'and.com pared to values for pristene groundwaters of the

                Key Deer National Wildlife Refuge (KDNWR) that were considered the "control"(see

                list of stations in Table 1 and location of the stations in Figs,1-4). Four

                stations were selected in the Upper Keys and four in the Lower Keys to address

                                                      6

                 the different geologies of these areas and its possible effects on nutrient

                 relations of groundwaters and inshore waters.

                      Two monitor  wells were installed on each of the eight residential lots. One

                 well was installed in the vicinity of the septic tank drainfield and the other

                 well was installed on the waterfront side of the lot, approximately halfway

                 towards the surface water closest to the septic drainfield. A portable hand-held

                 I" auger was used to bore a 10- deep borehole; initial development utilized a

                 portable well point sampler designed for groundwater plume tracking (Kerfoot,

                 1984). Following development, the boreholes were cased with 1/2 inch PVC pipe

                 that had a 2' long section of continuous slotted well screen     (0.010 of an inch

                 slot width) adjusted to a horizon 8-10 ft below grade at each location.

                 Satura.ted groundwaters were commonly reached at 3-4 ft below grade at most

                 locations, but we  believed that by sampling somewhat deeper groundwaters a more

                 representative and  consistent sample of gr oundwaters would  be realized.

                      To determine potential effects of injection well wastewater on groundwater

                 nutrient concentrations both at depth and in near-surface groundwat    ers, a site

                 in the lower Keys (Halcyon Trailer Park; See Table 1) with a "Multi-flow"

                 aerobic treatment unit coupled to a 60- injection well was monitored. At this

                 site, a cluster of three monitor wells, each sampling a different and discrete

                 depth, was installed according to guidelines outlined in Driscoll -0986). From

                 grade, three boreholes (60', 30-, and 15') were augered along a transect

                 towards the closestadjacent surface waters from the injection well. The     se

                 monitor wells were cased with 2" PVC pipe (to also allow groundwater flow

                 determinations, see below) a nd each casing had a 5' section of .010 inch

                 continuous slotted well screen at the bottom; annular space in these wells was

                 packed with with1coarse.carbonate substrate.

                                                         7

                      These monitor wells meet or exceed published guidelines for monitor well

                 installation for monitoring of dissolved inorganic nutrients as outlined by

                 Driscoll (1986) and for groundwater flow determinations as suggested by Kerfoot

                 (1986); well logs that contain details of the wells (e.g. grade and exact

                 locations of wells) are available from the Monroe County Planning Department.

                 Sampling of Groundwaters

                      The monitor wells were sampled monthly following installation, which began

                 in December 1986 and ended in September 1987. Initial groundwater samples were

                 collected with a portable well point sampler (Kerfoot-, 1984@; after casing of

                 the wells, either a submersible pump fitted with Tygon plastic tubing (for 2"

                 I.D. monitor wells) or a peristaltic pump fitted with teflon'tubing was used for

                 sample extraction. Sampling protocal consisted of initially removing

                 approximately 3-5 casing volumes prior to sample collection (Driscoll, 1986).

                 All wellpoint sampler parts, pump tubing an  d fittings were rinsed with tap

                 water between well samplings to prevent cross contaminationof different

                 groundwater samples.

                      Collection and preservation of the groundwater,samples followed the

                 methodologies suggested in Standard Methods (Greenbaum, 1975).   Specifically,

                 protoca.1 consisted of sample collection into acid-washed I liter Nalg6ne

                 polyethylene containers, immediate determination of temperature (using a mercury

                 thermometer) and salinity (using a Rausch and Lomb hand-held refractometer) and

                 subsequent preservation with a biocide (10mg/l HgCl). The samples were held on

                 ice in the dark until return'to the laboratory where they were immediately

                 filtered through a 0.45,p Gelman glass fiber filter and either analyzed

                 immediately for nutrient  analysis, or frozen for subsequent analysis (within 2

                 weeks).

                                                        8

                 Determination of Ground-water Flow Rate and Direction

                       To understand interactions of groundwaters     with inshore surface waters, a

                 knowledge of the direction and rate oE horizontal subsurface flow is needed.

                 Direct determinations of the rate and direction of groundwater flow were made at

                 several lo cations on Big Pine Key using a Model 30 GeoFlo groundwater flowmeter

                 (K-V Associates, Inc; Falmouth, MA). This flowmeter is a portable,

                 self -contained system that allows direct measurement of the rate and direction

                 of lateral flow of groundwater through permeable saturated geologies. The Model

                 30 GeoFlo flowmeter uses a submersible sensor consisting of a circular array of

                 thermistors arranged around a central heat source. A five v6ctor response is

                 displayed on an LCD readout which, in combination with a calibration curve and

                 vector worksheet, can allow det   ermination of groundwater flow rate in the range

                 of .03-500 ft/day (+ 15%) and direction of groundwater flow (+ 10%).

                       The accuracy and precision of the GeoFlo flowmeter is greatly affected by

                 monitor well design and calibration of the flowmeter; therefore, procedures

                 suggested by the manufacturer were closely followed (See Kerfoot, 1986). The

                 GeoFlo flowmeter was deployed in 2" I.D. PVC monitor wells that had sections of

                 slotted well screen inserted at desired depths below grade. This involved use

                 of a high quality, continuous slotted well screen (Timco, sch 40, .010 inch slit

                 width, 59  slots per foot), centralization of the well, and careful annular

                 packing with washed, coarse carbonate substrate. Groundwater flow monitor wells

                 were installed at several locations on Big Pir@e Key and include three wells at

                 Halcyon Trailer Park (HTP, see above description of.monitor well installation)

                 as well as two wells (15' and 30') in the Key Deer Nati     onal Wildlife Refuge

                 (KDNWR) and one   well (15') in Port  Pine Heights subdivision (PPH, See Table 1).

                                                           9

                     Calibration of the GeoFlo flowmeter. involved use of a flow chamber packed

                with carbonate substrate similar to that surrounding th  e monitor wells (Miami

                Oolite) and a metering pump to provide controlled and variable flow rates. A

                typical calibratio n curve for the GeoFlo flowmeter in Miami Oolite substrate is

                illustrated in Fig 5; regression of the readout of the GeoFlo versus known rates

                of lateral flow allows rapid, on-site determination of groundwater flow rates.

                The five vector response is used with a worksheet to Lest for uniform cosine

                flow and then plotted on  polar gra@ph paper to determine direction of flow. Field

                logs for all groundwater  flow determinations are available from Monroe County

                Planning Department.

                Sampling of Surface Waters

                    During the monthly sampling at the eight residential monitor stations and

                the "Multi-Flo" station on Big Pine Key, samples of adjacent surface waters were

                also collected for determination of nutrient concentrations. Samples were

                collected either by hand using a 3 liter Nalgene container or using a 3.7 liter

                Niskin bottle sampler-Surface water samples were also collected at monthly

                intervals along an onshore-offshore transect extending from an inshcre canal

                system (PPH) on Big Pine Key to Looe Key National Marine Sanctuary (LKNMS),

                located 5 miles south.of Big Pine Key; the hydrographic stations along th   .is

                transect are listed in Table 2 and locations are illustrated in Fig 6. Surface,

                water samples coll ected'from canals adjacent to the residential stations were

                handled in identical fashion to that described  above for groundwater samples;

                however,-the transect 'samples, which were also analyzed for chlorophyll-a, were

                not spiked with a biocide because of interference with the chlorophyll

                analysis.

                                                       10

                Nutrient and Chlorophyll  Analysis: Methodologies and Quality Assurance

                     Surface and groundwater samples were analyzed for dissolved inorganic

                nitrogen in the form of nitrate, nitrite and ammonium using a Technicon

                Autoanalyzer II system   Preliminary analyses indicated that nitrite was

                negligible compared to nitrate in groundwater and surface water samples at all

                stations; comparable results have also been reported for similar carbonate

                groundwaters and inshore waters of Bermuda (Simmons et al., 1984) and Jamaica

                (D-Elia et al., 1979). Therefore, we determined and report herein total nitrate

                and nitrite (referred to as nitrate, NO ) using the copper-cadmium reduction
                                                        3
                method according to standard Technicon Industrial methodology (Technicon,1.972).

                The ammonium determinations were made using a modified phenol-hypochlorite

                method described bY Slawyk and MacIssac (1972). Nutrient concentrations are

                reported in units of pM (= pg-at/1) to conform with the marine chemistry

                literature. The detection limit during these analyses was 0.10 pM for nitrate

                and 0.20,uM for ammonium.

                   Because phos phate appears to. be the primary limiting nutrient in the

                nearshore Keys marine environment (Lapointe, 1987; Lapointe, 1988) and is

                present at very low concentrations (e.g. frequently < 30-50 rLM), concentrations

                of soluble reactive phosphate (SRP) were determined using the highly sensitive

                manual method described by Strickland and Parsons (1977). This method is a

                modification of the Murphey.and Riley (1962) molybdenum blue method and utilized

                a Bausch and Lomb spectrophotometer 88 fitted with a 10 cm. cell for maximum

                sensitivity.

                     Quality assurance of our nutri ent determinations is based on known internal

                standards that we re analyzed regularly with all unknown samples. A continuous

                record of analyses of standards.and recoveries was maintained and assures that.

                our determinations were accurate and within acceptable upper and lower limits

                (EPA, 1972). Interlaboratory comparisons of unknown samples.(available from EPA)

                indicated that mean recoveries for our nutrient determinations are excellent and

                range from 95-103% of stated EPA values.

                     Chlorophyll-a concentrations of seawater were determined using a Turner

                Designs Model 10 fluorometer that was calibrated using known concentrations of

                chlorophyll. A 800 ml seawater sample was filtered through a 0.45,u   Gelman

                glass fiber filter and analyzed for chlorophyll-a using a modified dimethyl

                sulfoxide (DMSO)-acetone method (Burnison, 1979). Immediately following

                filtration, the filters were placed''in 10 mls DMSO in a cool, dark place to

                extract for one hour; following this, 15 mls of acetone was added. After two

                hours of further ex.traction, the samples were analyzed for fluorescence.

                Subsequent acidification with 10% HCL was also performed to correct for

                phaeophytin.

                Statistical Analyses

                     Several hypotheses were tested in this study. First, to consider potential

                effects of OSDS on nutrient concentrations (ammonium, nitrate, and,SRP) of

                groundwaters in the Florida Keys, groundwater nutrient concentrations of the

                eight residential monitor stations were compared to nutrient concentrations of

                the "control" station at the KDNWR. Specifically, the following null and

                alternative hypotheses were tested:

                     H : nutrient concentrations of.groundwaters adjacent to OSDS are
                      0

                equal to those of groun.dwaters of the KDNWR.

                     HA  nutri ent concentrations of groundwaters adjacent to OSDS systems

                are greater than groundwaters of the KDNWR.

                                                      12

                      Second, to consider potential seasonal seepage of nutrients from

                 groundwaters into the nearshore marine environment due to climatological

                 forcing, nutrient concentrations (ammonium, nitrate, SRP) of groundwaters and

                 nearshore marine waters (canal waters adjacent to sites) at the eight

                 residential OSDS sites during winter (December-April) were compared to those of

                 summer (May-September). Specifically, the follow   ing null and alternative

                 hypotheses were tested:

                      H0: nutrient concentrations of groundwaters during winter are equal to

                 those of summer.

                      HA  nutrient concentrations of groundwaters during summer are lower

                 than those of winter.

                      H   nutrient concentrations of inshore marine waters are the same in

                 summer and winter

                      HA  nutrient concentrations of inshore marine waters are higher

                            in summer than winter.

                      These a priori hypotheses were teste.d.using the Kruskall-Wallis test, a

                 conservative nonparametric test statistic. The experimental design involved

                 comparisons of data within individual stationsto reduce station-to-station

                 variability and increase the.power of these statistical tests. Because of the

                 sensitivity of our nutrient analyses and the randomized block experimental

                 design, we used a conserv ative alpha level of P=0.05 to represent the

                 probability of makin g a Type I error; thus, significance re  ported in the results

                                                         13

                 below indicates the probability   of making an incorrect inference is <0-05 or

                 less than 1 chance in 20.

                                                       RESULTS

                 Groundwater Nutrient Concentrations

                      Concentrations of ammonium, nitrate, and SRP as well as salinity and

                 temperature of groundwaters sampled at monthly intervals between December 1986

                 and September 1987 from groundwater monitor wells at the eight septic sites and

                 KDNWR are presented in Appendix Table 1. The highest groundwater nutrient

                 concentrations generally occurred during winter at the septic locations; lower

                 concentrations occurred at the midpoint locations and the lowest concentrations

                 typically occurred in groundwaters of the KDNWR. Over the entire study, ammonium

                 and nitrate concentrations ranged from 0.77 pM to 2.75, mM and 0.03,UM to 2.89

                 mM, respectively; SRP concentrations ranged from 0.06 pM to 107.4 PI (Table 3).

                 Salinity of the groundwater samples ranged from 0% (fresh) to 27% (saline) and

                 temperature ranged from a low of 21.01C in January to a high of 32.OOC in August

                 (Table 3).

                     Nutrient concentrations in groundwaters did not vary significantly between

                 the Upper and Lower Keys,'but an overall seasonal trend was evident.

                 Concentrations of ammonium, nitrate, and SRP in groundwaters from a majority of

                 the monitor wells decreased significantly from winter to summer, 1987 (See Table

                 3). Overall, nutrient concentrations decreased from winter to summer in 8 out

                 of 13 moni tor wells for nitrate (Table 4), 7 out of 13 wells for ammonium (Table

                 5), and 8 out of 13 wells for SRP (Table 6). The average groundwater nutrient

                 concentration (average of both septic and midpoint locations) during winter was

                 541 pM.for ammonium,.494)uM for nitrate, and 10.3 pM for SRP;. the average

                                                         14

                concentration during summer w as 145 )uM for ammonium, 125 pM for nitrate,3nd 4 10

                pm for SRP (Table 3).

                     Nutrient concentrations of groundwaters at the KDNWR "control" station did

                not vary significantly from winter to summer and were consistently lower than

                nutrient concentrations characteristic of the residential stations. During

                winter, nutrient concentrations averaged 1.91 pM for ammonium, 0.76 pM for

                nitrate, and 0.11 pM for SRP; during summer, nutrient co:lcentrations averaged
                1.40 pM for ammonium, 0.20 pM for nitrate, and 0.14,pM for SRP (Tables 4-6).

                     A comparison of groundwater nutrient concentrations fro-m the residential

                stations and the KDNWR station indicates significantly elevated nutrient

                concentrations on developed, residential lots with septic tank/drainfield

                systems. For example, concentrations of ammonium, nitrate, and SRP during winter

                were all significantly higher in residential groundwaters compared to

                groundwaters in the KDNWR in all 24 cases analysed; during summer, 17 out of 24

                cases indicated significantly elevated nutrient concentrations in residential

                groundwaters compared to groundwaters of the KDNWR (Table 7). The various

                nutrients were.enriched in residential groundwaters, relative to groundwaters of

                the KDNWR, some 625 to 650-fold for nitrat e, 246 to 283-fold for ammonium, and

                29 to 94-fold for SRP.

                     Nutrient concentrations of groundwaters adjacent to the "Multi-Flo"

                injection well were also significantly elevated compared to those of the KDNWR.

                During summe r, concentrations of ammonium and SRP averaged 19.1,uM and 0.67 pl,

                respectively, about 5-fold higher than concentrations of 3.35 PM and 0.12 PM*for
                ammonium and SRP, respectively (Table 8). Concentrations of ammonium and SRP

                were approximately the same at different depths.at the "Multi-Flo" site (15' to

                60') whereas ammonium concentrations appeared'to increase with depth at the

                                                      15

                 KDNWR. Salinity increased with depth at both sites and waters at '00' at the

                 "Multi-Flo" site were always hypersaline (Table 8).

                 Groundwater Flow

                     Direct measurement of groundwater flow indicates that rainfall and tides

                 affect the instantaneous lateral velocity of subsurface groundwater movements.

                 At Port Pine Heights (PPH) on Big Pine Key, gr   oundwater flow rate ranged between

                 0 and 5.0 ft/day during an ebbing tide on July 24 1987 with the lowest rates

                 occuring during peak high tide and highest rates occuring during the ebbing tide

                 (Fig 7); over the full 12 hrs of the ebbing tide, the flow    rate averaged 2.3

                 ft/day (Table 10). On October 2 1987, groundwater flow    rate at the same"site

                 during a flood ing tide ranged between 2.8 and 12.1 ft/day with.anomoulously high

                 flow rates occurring between 2130 and 2300 hrs when a major rain event occurred

                 (>1.0 inchds of rain fell in 6 hrs; Fig 8); the average flow rate during this

                 flooding tide was 5.5 ft/day (Table 9). During both groundwater flow studies,
                 the direction of groundwater flow ranged between 1.63  0 and 2220 and averaged 184 0

                 or southward (Table 9).

                      Groundwater flow rates in the KDNWR monitor wells (15' and 30' wells)

                 ranged from 0 to  4.10 ft/day and averaged 2.1 ft/day; the direction of flow at

                                                          0
                 both depths was  consistently between 71 and 104     or eastward (Table 10).

                 However, flow rates were greater in the deeper (30') Key Largo Limestone

                 formation, which averaged 3.7 ft/day and ranged from 3.38 to 4.10 ft/day; flow

                 rates in the shallowe r Miami Oolite (15-)  averaged 0.38.ft/day and ranged    from

                 0.0 to 0.75 ft/day..

                      Groundwater flow rates at the Halcyon Trailer Park monitor wells (15', 30',

                 and 60'),.@veraged 2.2 ft/day and ranged from 2.17 to 3.38 f  t/day; no differences

                 in flow rate-at different depths  were  apparent. However, at this  station,

                                                         16

                 direction of groundwater flow was different belweoii the different depths flow
                 at 15' was 1970 or southwestward whereas flow at 60' was 3050 or northwestward

                 (Table 10).

                 Surface Water Nutrient Concentrations and Chlorophyll

                     Concentrations of ammonium, nitrate, and SRP as well as salinity and

                 temperature of surface waters sampled at monthly intervals between December 1986

                 and September 1987 from inshore waters adjacent to the groundwater monitor wells

                 at the eight residential sites and KDNWR are presented in Ap pendix Table 1. A

                 significant seasonal trend opposite that of groundwaters was observed for- the

                 inshore waters; consistently, the lowest nutrient concentrations occurred during

                 winter and the highest occurred during summer (Table 4-6). For example,

                 concentrations of nitrate ranged from 0.27/iM to 4.05/iM during winter and from

                 0.28 pM to 49.02 pM during summer; ammonium ranged from 0.15 pM to 2.39,UM

                 during winter and from 0.33 pM to 6.92 pM during summer; SRP ranged from 0.03 PM

                 to 0.35 pM during winter and from 0.12 uM to 1.60,uM during summer (Table 3).

                     In all 12 surface water samplings along the hydrographic transect, nutrient

                 concentrations and chlo rophyll consistently decreased towards offshore waters.

                 Over all these samplings, concentrations of nitrate ranged from 0.08,uM (LKNMS)

                 to 3.02,uM (PPH canal), ammonium ranged from 0.02 (LKNMS) to 0.94,uM (PPH

                 canal), SRP ranged from 0.03 pM (LKNMS) to 0.29 pM (PPH canal) and chlorophyll

                 ranged from 0.04 pg/1 (LKNMS) to 0.78,ug/l,(PPH canal; Table 11;,Appendix Table

                 2). Out of the twelve samplings, chlorophyll wds'significantly and positively (r

                 > 0.70) correlated with SRP six times, with ammonium twice, and with nitrate

                 three times (Table 12).

                                                      17

                     Chlorophyll concentrations were significantly greater during summer

                compared to winter in the inshore waters during-these studies. Mean chlorophyll

                concentration in PPH canal waters during winter were 0.22 jig/l (+ 0.08, N = 16),
                about three-fold lower than the mean value of M2 jjg1l (+ 0.19, N =10) during

                summer*

                                                     18

                                                     DISCUSSION

                 OSDS as a Nutri ent Source to Groundwaters and Nearshore Waters

                     Elevated nutrient  concentrations in residential groundwaters compared to

                 pristene groundwaters in the Florida Keys indicates that OSDS represent a

                 significant source of nutrients to groundwaters of the Florida Keys. It is

                 unlikely that the high concentrations of ammonium (2.5 mM), nitrate (2.5 mM) and

                 SRP (30 jjM) observed in residential groundwaters would result from a natural

                 source such as the decomposition of leguminous matter, nitrogen fixation, or

                 rainwater (D'Elia et al., 1979). That nutrient concentrations were generally

                 higher at the septic locations compared to midpoint locations during the study

                 clearly point to a septic drainfield source for these elevated nutrient

                 concentrations. Furthermore, the highest nutrient concentrations observed in

                 groundwaters during this study are typical of secondarily-treated wastewater,

                 characterized by concentrations of 2-3 mM of inorganic nitrogen (either in the

                 form of ammonia or nitrate, depending on the degree of oxidation of effluent)

                 and 200-300,pM inorganic phosphate (Ryther et al., 1975; Goldman and Ryther,

                 1975), and are probably represent groundwater septic plumes. These nutrient

                 concentrations are also typical of effluents sampled from several aerobic

                 treatment units ("Multi-Flo") during this study.

                      Clearly, and not surprisingly, use of OSDS is resulting in increased

                 nutrient concentrations of associated groundwaters. The mean SRP concentration

                 of residential groundwaters (both midpoint and septic locations) was 10.   3,uM

                 during winter and 4.0 pM during summer, considerably higher than background SRP

                 concentrations of 0.11,,juM to 0.14,uM in the KDNWR during winter and summer,
                 respectively. Thus, SRP concentrations of enriched groundwaters on residential

                 sites of the Keys were on the order of  29- to 94-fold higher than background

                                                     19

                concentrations with an annual average of 60-fold'higher SRP concentrations. For

                nitrogen, even higher enrichment occurred. The average total nitrogen

                concentration ( IN = ammonium and nitrate) on residential stations during winter

                was 1036,uM, compared to a lower value of 471 pM during summer. Relative to

                background concentrations in the KDNWR, this represents a 370 to 346-fold

                increase during winter and summer, respectively,, with an annual average of

                358- fold increase above background concentrations.

                     Elevated N:P molar ratios of enriched residential groundwaters during this

                study suggests that SRP is, to some extent, scavenged during flow through

                carbonate geologies. The N:P ratio of groundwaters (both the septic and midpoint

                locations) ranged from 94:1 to 147:1, much higher than the 10:1 molar ratio

                typical of domestic wastewater (Ryther and Dunstan,1971). In carbonate

                geologies, SRP is well known to react and co -precipitate with calcium carbonate

                to form calcium carbonate-phosphate surface complexes and/or the mineral apatite

                (Berner, 1981); additionally, SRP can be scavenged by adsorption onto oxides of

                iron (II), iron (M), and aluminum (III).- In both.oxic and anoxic sulfidic

                sediments, apatite formation is considered the dominant mineral sink of
                phosphate. The two primary minerals are fluroapatite (Ca5(PO 4)3 F) and
                hydroxyapatite (Ca5(PO 4)3 OH), with the fluoride-rich.form being the most

                predominant form in marine sediments. Consequently, concentrations of SRP are

                often low in natuarl carbonate-rich waters because of equilibrium with carbonate

                fluoroapatite (Gulbrandsen and Robertson, 1973). However, while removal of SRP

                by calcium carbonate in upland groundwaters appears to be efficient wh6n based

                on N:P molar ratios, SRP is not complet ely removed from enriched groundwaters as

                described above by comparison of residential groundwaters to those of the KDNWR.

                                                   20

                     Accordingly, upland watersheds of the Keys enriched by OSDS appear to be

                geochemically phosphorus-limited regarding their stoichiometric impact on

                nearshore primary production. The most widely used approach to identify the

                relative importance of nitrogen versus phosphorus limitation is through

                determination of N:P ratios of seawater and comparison of these ratios with

                those of marine plant populations. This approach is based on extensive analyses

                of marine plankton and dissolved inorganic.nutrients, both of which indicate an

                average N:P ratio of 16:1 by atoms in oceanic waters (Redfield, 1958).

                Deviations of either marine plant composition or seawater nutrients from this

                ratio is then used as an indirect method to infer which nutrient element limits

                productivity; N:P ratios < 10:1 indicate N-limitation wheras ratios> 30:1

                indicate P-limitation. While enriched groundwaters are clearly P-limited in that

                N:P ratios are typically > 94, surface waters in canals during this study had

                average ratios of ranging from 11 to 17, suggesting a trend towards N limitation

                in enriched inshore receiving waters. However, frequent correlation of SRP and

                chlorophyll-a in our nearshore transect studies suggest that elevated SRP is the

                primary limiting nutrient to phytoplankton production, a conclusion also

                reported for phytoplankton on the northwest Florida continental shelf (Myers and

                Iverson, 1981). These results also concur with macrophyte bioassays in nearshore

                waters of the Keys and Florida Bay where productivity was limited primarily by

                phosphorous and secondarily by nitrogen (Lapointe, 1987; Lapointe, 1988). A

                similar predominance of P-limitation occurs in carbonate-rich waters of Shark

                Bay, Australia, (Smith and Atkinson, 1984) and contasts precepts of nitrogen

                rather than phosphorus limitation of marine productivity in clastic environments

                of temperate climes (Rythe r and Dunstan, 1971).

                     Our conclusion that elevated nutrient concentrations of groundwaters in

                residential areas of the Florida Keys are anthropogenic in origin are in

                                                   21

               agree .. ont with similar conclusions for Bermuda (Simmons et al., 1984) that were

               based on elevated concentrations of nitrate in groundwaters and use of cesspits

               as the dominant form of domestic wastew ater disposal. However, while the major

               form of inorganic nitrogen in Bermuda's groundwaters is nitrate, groundwaters of

               the Keys have higher concentrations of ammonium compared to nitrate. For

               example, the mean concentration of nitrate in Bermuda's groundwaters is 749 PM

               (ammonium is negligible) compared to the Keys where the annual mean

               concentration of total inorganic nitrogen is 753 pM and consists of 310 PM

               nitrate and 443 pM of ammonium.

                    We believe this difference in nitrogeno us composition of groundwaters

               between Bermuda and the Florida Keys is significant and suggests generally low

               oxygen availability in groundwaters of the Keys. Ammonium represents the most

               reduced species of inorganic nitrogen and results from decomposition of organic

               matter in oxygen-depleted waters; in the presence of oxygen, ammonium is rapidly

               oxidized to nitrite and subsequently to nitrate by nitrifying bacteria. The

               apparent lack of adequate oxic conditions needed to support oxidation of OSDS

               wastewater (e.g. ammonium) in shallow grouridwaters may be related to the limited

               vadose zone,underlying drainfields associated with OSDS in the Keys; an average

               of 12" of vadose zone (above mean high water) separates drainfield wastewater

               from the piezometric (hydrated groundwater) surface in the Keys. Considering

               that groundwaters typically have low oxygen tensions even without impacts of

               organic wastes, those impacted by organic wastewater loads will become suboxic

               or anoxic. Because microbial mineralization of wastewater is much more rapid

               under aerobic. conditions,,septic tank/drainfield systems with such limited

               vadose zones may not provide complete oxidation of their wastewater, as
               suggested by the elevate@ ammonium concentrations of residential groundwaters

               found in this study. As-a consequence of impacting low oxygen groundwaters with

                                                 22

                organic wastewater and associated oxygen demands (both BOD and COD),

                biogeochemical zones (e.g. sulfide reduction zone that produces hydrogen

                sulfide) usually restricted to deeper anoxic groundwaters will shift upward

                towards to near-surface levels, increasing the occurrence of hydrogen sulfide

                odors to the atmosphere. In contrast to ammonium that was characteristic of

                sept ic tank enriched groundwaters, effluents of the aerobic t,reatment units were

                composed primarily of nitrate, indicating a better-oxidized effluent.

                     The significant decrease of groundwater nutrient concentrations and

                parallel increase in nutrient concentrations of inshore surface waters during

                summer suggests that nutrients derived from enriched groundwaters are discharged

                to adjacent inshore waters, to a large extent, in a seasonal manner. This

                finding contrasts the view that groundwater nutrient concentrations are

                relatively constant compared to surface waters (Freeze and Cherry, 1979).

                Considering that all the residential stations used in our study were located on

                canal sytems, which effectively increase shoreline development and decrease

                groundwater dilution potential, then mixing and seepage of enriched groundwaters

                with inshore surface waters is dramatically enhanced. Based on elevated ammonium

                and total organic carbon concentrations in developed canals compared to

                undeveloped canals, Hicks et al. (1975) also concluded that septic leachate

                enters surface waters and be partially responsible for observed ecological

                imbalances in adjacent waters. Considering the dramatic seasonality in extent of

                groundwater intrusion to inshore waters, we sought to explain this phenomena by

                considering the various mechanisms that regulate groundwater seepage to inshore

                receiving waters.

                                                  23

                Mechanisms of Groundwater Seepage to Inshore Waters

                     In general, nutrients associated with fresh groundwaters enter adjacent

                surface waters primarily through horizontal groundwater flow, although inclined

                and vertical flow can also occur (Visher and Mink, 1964; Cooper, 1959; Kohout,

                1960). The general direction of flow is offshore because of decreasing hydraulic

                gradients between the piezometric surface on land  and sea level at adjacent

                inshore surface waters where seepage through canal walls or bottom sediments

                occurs.. The instantaneous rate of groundwater flow is a function of porosity

                and permeability of the substrate and hydraulic head. Direct determination of

                groundwater flow rates in the Lower Keys (PPH) during summer 1987 indicated

                average instantaneous groundwater flow rates in Miami Oolite sub strate of 2.8

                ft/day (omitting higher flow rates during rain events), a value consistent   with

                the known high porosity of this geology (bulk porosity of 40-60%; Evans, 1983).

                Distinctly lower flow rates were associated with Miami Oolite in the KDNWR on

                Big Pine Key where flow rates ranged from 0 to 0.75 ft/day, a finding consistent

                with the ability of this geology to support a Ghyben-Herzberg fresh water lens

                (Hanson, 1980).

                      Our observed decrease of dissolved nutrients in groundwater and

                simultaneous increase in adjacent surface waters during summer suggests that a

                seasonal climatic or astronomical forcing mechanism enhances flow rates of

                nutrient-rich groundwaters into surface waters. Such a dramatic discharge would

                require enhanced lateral groundwater flow during summer compared to winter, and

                would be best explained by increased hydraulic head of groundwater during summer

                compared to winter. Although freshwater recharge to groundwaters of the Keys is

                ordinarily maximum during the "wet" summer.-and early fall in the Keys and could

                explain seasonal differences in hydraulic head, such a typical rainfall pattern

                                                   24

                lid no, occur during this study (NOAA weather, Key West) and no significant

                seasonal correlation between rainfall and nutrient concentrations of

                groundwaters and surface waters was apparent.

                     However, seasonal patterns in tide height did covary significantly with

                our observed patterns for dissolved nutrients. Sea level is general ly

                acknowledged as the dominant component of fluctuations of groundwater surfaces

                on carbonate oceanic islands (Hanson, 1980; Rowe, 1984), although rainfall

                becomes the more important factor during periods of heavy rain (Hanson,1980).

                Annual variations of 0.8' in sea level occur in the Keys in response to

                astronomical, isostatic, and mass transfer effects (Marmer, 1954; Pattullo,

                1963) and results in maximum sea levels and groundwater tables during summer and

                fall at which time the minimum seasonal potential evapotranspiration from

                groundwaters occurs (the maximum evapotranspiration occurs during the "dry"

                winter months). Consequently, a seasonal maximum in hydraulic head could occur

                during summer and fall, during which the mixing rate of fresh groundwaters and

                marine surface waters would result due to increased inclined flow (Visher and

                Mink, 1964) and subsurface dispersion (Cooper, 1959; Kohout, 1960). This

                possibility is directly supported by monthly average sea level and groundwater

                table height data reported by Hanson (1980) for Big Pine Key and ill ustrated in

                Fig 9; the increased hydraulic head during summer and early fall would support

                increased lateral flow compared to reduced hydraulic head and flow during winter

                and early spring. Such a seasonal mechanism is also supported by the elevated

                salinities commonly observed in groundwaters of the Keys during summer as

                compared to.winter (Table 3).

                    While groundwater,flow rates may vary seasonally as a function of hydraulic

                head and regulate seasonal patterns in discharge of nutrients to inshore waters,

                the most dramatic increases in groundwater flow occurs on shorter time scales

                                                  25

                 (i.e. hours-days) during rain events. Lateral groundwater velocities up to 12

                 ft/day occurred during rain events, causing rapid increases in groundwater

                 discharge to inshore waters that were some 5- to 7- fold higher than background

                 flow rates. The rapid flow response and lack of long lag periods of increased

                 flow is consistent with the high porosity and permeability of carbonate

                 geologies of the Keys. This finding.also explains the algal blooms that often

                 follow major rain events in inshore waters of the Keys (personal communication).

                     The direction of lateral, shallow groundwater flow appears to be related

                 primarily to the direction of the hydraulic gradient as affected by large scale

                 natural elevation grades and not necessarily by smaller scale man made changes.

                 For example, groundwater flow at the PPH residential station on Big Pine Key was

                 consistently (14 determinations over 3 months) southerly, the direction of

                 decreases in natural grade, even though the most adjacent surface water body

                 (canal) was 50- to the west of the flow monitor well. Previous studies using

                 Rhodamine dye injections into septic tanks on Big Pine Key failed to detect

                 septic leachate entering adjacent canal waters (Hicks et al., 1975), quite

                 possibly because the surface waters sampled for dye intrusion were not

                 downstream of the groundwater flow from the septic tank drainfield. Future dye

                 studies in the Keys need to obtain preliminary information regarding natural

                 subsurface flow patterns to support the assumptions generally made in such

                 tracer dye studies.

                 Patterns and Effects of Nutrient Flux to Nearshore Waters of the Keys

                     By assuming an average groundwater flow rate and path length to probable

                 receiving waters (not n,ecessarily the closest surface water), the travel time of

                 nutrients associated with groundwaters towards surface waters can be estimated.

                 For example, assuming an average flow rate of 2.0 ft/day for nutrients

                                                   26

                associated with groundwaters and an average travel path of 350' to inshore

                waters typical of the OSDS in our study, a travel time of approximately 0.5 yrs

                would be required for discharge of new septic-derived nutrients into surface

                waters. This suggests that seasonally increased nutrient input during the winter

                tourist season would require about 6 months before discharge to inshore waters,

                resulting in "delayed discharge" that would exacerbate increased flow of

                grou ndwaters into surface waters during summer months. Considering that

                irradiance and temperature are also maximum during summer, ideal conditions

                favoring phytoplankton blooms result. A similar delayed discharge of nutrients

                occurs on Cape Cod, MA, where nutrients introduced to groundwaters during the

                summer tourist season are discharged,to surface waters during winter (Kerfoot,

                personal communication).

                     The effects of increased nutrient seepage to nearshore waters of the Keys

                will be cumulative enhancement of natural eutrophication processes that will

                result in further water-quality degradation. Because the productivity and

                nutrient dynamics of inshore waters of the Keys are controlled to a large extent

                by benthic macrophytes that are themselves nutrient limited (Lapointe, 1987;
                'Lapointe, 1988), increases in biomass of marine macrophytes, both seagrasses and

                macroalgae, will undoubtedly occurr. Quite possibly, previous nutrient

                enrichment has enhanced historic seagrass and macroalgal growth rates, resulting

                in the extensive seagrass biomass harvests that are increasingly affecting

                canals and shorelines when their harvested biomass decomposes, causing local

                reduction of dissolved oxygen and strong hydrogen sulfide odors.

                     Several examples serve to illustrate the initially subtle but often

                devastating ecological'imbalances that cultural eutrophication can have on

                benthic marine ecosystems. Reef corals in Kaneohe Bay, Hawaii slowly became

                overgrown with the green "bubble alga" Dictyospheria that bloomed in response to

                                                   27

                   nutrient enrichment from a secondary sewage,outfall; diversion of the sewage

                   outfall to an offshore location has since partially restored water quality

                   (Smith, 1981). In inshore waters of Bermuda, the green alga Cladophora prolifera

                   has increased dramatically over the past ten years in response to nutrient

                   enrichment by groundwater seepage resulting from widespread use of unlined

                   cesspits (Lapointe and O'Connell, 1988); this has resulted in water quality

                   degradation of Harrington Sound, including loss of the commercially-valuable

                   Calico clam, as well as cave systems that border Harrington Sound - some of

                   Bermuda's major tourist attractions (Ileffe et al., 1984). Phytoplankton blooms

                   resulting from sewage enrichment,of Hillsborough Bay, FL (adjacent to Tampa)

                   caused reduction of seagrass biomass and replacement by the red alga Gracilaria

                   (Taylor et al., 1973), a phenomenon that has also occurred in many other inshore

                   areas of Florida*.

                         However, effects of eutrophication will not be limited solely to enhanced

                   growth of marine macrophytes. The significant correlation of phytoplankton

                   chlorophyll and dissolved nutrients, particularly SRP, during our study suggests

                   that cumulative nutrient enrichment of inshore waters of thE Keys will also

                   result in a trend toward increased phytoplankton biomass that could cause the

                   most dramatic water quality degradation. Increased phytoplankton chlorophyll

                   concentrations are well known to degrade seagrass and coral reef ecosystems by

                   decreasing water transparency, submarine irradiance, dissolved oxygen, biotic

                   diversity and secondary production (e.g. see Zieman, 1982; Johannes, 1975).

                   Furthermore, blooms of the toxic red tide dinoflagellate species are increasing

                   world-wide in waters adjacent to developing coastlines, sugessting that run-off

                   derived from mans activities favor initiation of these devastating blooms. Red

                   tides of Gymnodinium breve on the east coast of Florida in 1972 originated from

                   se.ed that was carried from the west coast of Florida through the Keys to the

                                                     28

                CONCLUSIONS and RECOMMENDATIONS

                      1) Based on the demonstrated extreme nutrient (ammonium, nitrate, and SRP)

                         enrichment of residential upland groundwaters by OSDS as well as

                         observed discharge of these nutrients into inshore waters, most notably

                         during summer and early fall and during rain events, we concur with

                         conclusions of Hicks et al. (1975) that water quality of inshore waters

                         of the Keys is measurably impacted by use of OSDS. As-described by Hicks

                         et al (1975), such impacts result in frequent and gross violations of

                         established Class III water quality criteria regarding dissolved oxygen

                         and biological integrity. Our results are also in agreement with those

                         of Pitt et al (1975) that also reported septic leaching into

                         groundwaters and found that hydraulic conductivity was the primary

                         factor controlling the extent of groundwater contamination. We further

                         suggest that increased growth of marine plants, both phytoplankton and

                         macrophytes, results from this enrichment and that this biomass

                         production exacerbates background BOD arriving in inshore waters with

                         nutrient enriched groundwaters. Our results do not support the

                         conclusion of Chesher (1974) that " there are no adverse environmental

                         conditions (in canal waters) attributable to septic tanks "; in

                         assessing that study, we believe that inadequate methodology and bias

                         confounded interpretation of data and precluded valid inferences.

                         Cumulative impacts of nutrients associated with OSDS as well as

                         ancillary but relat ed sources, should be quantitatively assess6d on an

                         areal basis prior to permitting of development of upland recharge areas

                         of any inshore or nearshore waters that are to be given the highest

                         degree of environmental protection. The following standards, adapted

                                                    30

                         from the Planning Board of the Town of Falmouth, MA, are given as an

                         example:

                          a) Loading per person: 5 lbs nitrogen/person/year; .25lbs

                             phosphorus/person/year for OSDS within 300 ft of shoreline.

                             Persons per dwelling unit = 3.0

                          b) Loading from lawn fertilizers: 3 lbs nitrogen/1000 ft  2  /year

                          c) Loading from road runoff: .19 lbs nirrogen/curb mile/day;

                            .15 lbs phosphorus /curb mile/day

                          d) Critical marine eutrophic levels: 16 lbs N/40,000ft  2/yr

                      While the above loading rates represent a long-term national,average, the

                critical eutrophic levels cited above are specific to Cape Cod waters (i.e.

                nitrogen-limited marine waters compared to phosphorus limited waters in the

                Keys). We suggest that a study be performed to provide a quantitative data base

                (i.e. flushing rates, concentrations of inorganic and organic nutrients,

                dissolved oxygen, chlorophyll, etc.) that would allow development of accurate

                critical eutrophic levels specific to inshore marine waters of the Keys.

                     3) Increased use of waste treatment should be considered for high

                        density, platted subdivisions that clearly are in excess of critical

                        eutrophic levels as cited above. A study should also be conducted to

                        consider cost/benefit relationships of various types of waste

                        treatment suitable for the Keys, which needs to include assessment       of

                        improved OSDS (i.e. better drainfield designs), alternate sewers
                        (Godfrey, 1986; coupled to aerobic and/or tertiery treatment

                        facilities (assessing potential use of mangrove systems to strip

                        nutrients), ocean outfalls (Officer and Ryther, 1977), and deep

                        (below an aquiclude) well injection. In advanced waste treatment

                                                    31

                        designs, priority should be placed on phosphorus stripping as this

                        nutrient appears to limit eutrophication and, compared to nitrogen,

                        is more easily removed from wastewater effluents.

                     4) Considering the unique marine resources of the Florida Keys and the

                        importance of maintaining adequate water quality to the economic

                        well-being of Monroe County, a water quality monitoring program

                        specifically designed to address nutrient enrichment via groundwater

                        seepage, wastewater outfalls, and stormwater runoff and related

                        eutrophication of adjacent surface waters needs to be initiated. A

                        majority of experts in the water quality field believe that

                        eutrophication is potentially the most severe source of degradation of

                        natural waters (Clark et al., 1977). Such a monitoring program should

                        address the current status of water quality in Monroe County and also

                        use whatever existing historical data bases are available to document

                        any significant degradation. In addition to nutrients, groundwaters are

                        often contaminated by a spectrum of synthetic organic and metal

                        pollutants. Thus, the identification in the present study of nutrient

                        enrichment from groundwaters suggests that this is an additional route

                        that should be monitored for transfer of persistent metal and organic

                        pollutants to inshore waters of,the Keys.

                                                   32

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                                                 36

                 TABLE 1. Key to abbreviations for groundwater monitoring stations.

                 ABBREVIATION                                              STATION

                      KDNWR ------------  -------------------- Key Deer National Wildlife Refuge

                      PPH  ----------------------------------- Port Pine Heights, Big Pine Key, FL

                      EP ------------------------------------ Eden Pines, Big Pine Key, FL

                     .DA ------------------------------------ Doctor's Arm, Big Pine Key, FL

                      WP ------------------------------------ Whispering Pines, Big Pine Key, FL

                      DL ------------------------------------ Dodge Lake, Marathon, FL

                      YT ------------------------------------ Yello w Tail, Marathon, FL

                      TH ------------------------------------ Treas ure Harbor, Plantation Key, FL

                      OS ------------------------------------ Ocean Shores, Key Largo', FL

                                                          37

                 TABLE 2. Hydrographic monitoring stations and locations in nearshore waters
                            of Big Pine Key, FL.

                  STATION                          LOCATION                         LAT/LON
                      I-------------------- Port Pine Heights finger canal       24 042.88'N
                                                                                 81 023.87'W

                      2-------------------- Port Pine Hei ghts main canal        24 042.86'N
                                                                                 81 023.88'W

                      3-------------------- South Pine Channel                   24 041.58'N
                                                                                 81 024.50'W

                      4-------------------- Munson Island                        24 038.30'N
                                                                                 81 023.64'W

                      5-------------------- Hawks Channel                        24 034'13'N
                                                                                 81 023:62-W
                      6-------------------- Looe Key National Marine             24 032.90'N
                                           Sanctuary Back Reef                   81 023.46'W

                      7-------------------- Looe Key National Marine             24 031-96'N
                                           Sanctuary Fore Reef                   81 024.22'W

                                                        38

                                                                                                                                                   M vim
                TABLE 3. Mean values and ranges for nutrient concentrations (PM), temperature ('C) and salinity (o/oo) at
                             canal, midpoint and septic locations in winter vs.. summer. Groundwater represents the average of the
                             the midpoint and septic values. Values represent meanst standard deviation.

                                                                                 WINTER

                LOCATION         N                 N03                   NH4                   SRP               N:P      TEMPERATURE       SALINITY

                CANAL          32    MEAN      1.61        0.55      0.88.t     0.29      0.15 + 0.05            16.6     25.5 � 3.1        37.1 + 2.1
                                     RANGE     0.27-----4.05         0.15 ----- 2.39      0.03 ---- 0.35                  19.0--30.1        33.0--42.0

                MIDPOINT       28    MEAN    118.25 + 179.89       256.94 + 325.88        2.54 :L 2.83         147.7      25.2 + 1.9         4.7 :L3.4
                                     RANGE     0.03 --- 545.45       3.61--2750.34        0.12 --- 13.79                  21.0=30.0          0.5--12.0

                SEPTIC         32    MEAN    817.36.tIO52.80       784.89 + 808.27       17.00      26.85        94.3     26.0 + 1.9         3.3-�-3.9
                                     RANGE     6.69--2896.70         32.41--2417.79       0.14--107.39                    21.0--29.3         0.0--19.0

                GROUNDWATER          MEAN    467.81 + 494.34       520.92 + 373.32        9.77 + 10.22                    25.6 �.0.6         4.0 -:L 1.0
                                     RANGE     0.03--2896.70         3.61--2417.79        0.12-107,39                     21.0--30.0         0.0--19.0

                                                                                  SUMMER

                LOCATION         N                 N03                   NH4                   SRP               N:P      TEMPERATURE       SALINITY
                CANAL          30    MEAN      3.22 +      8.38      1.69       1.48      0.43 +     0.38        11.4     30.7_� 1.3        40.9 zt 2.1
                                     RANGE     0.28 ---- 49.02       0.33 ----- 6.92      0.12 ---- 1.60                  .28.5--33.9       37.0--45.0

                MIDPOINT       26    MEAN     30.76 + 89.91        188.45 � 306.32        1.63-t 2.78          134.5      27.9 -t 1.9       15.2 �12.4
                                     RANGE     0.04 --- 409.02       0.77--1046.95        0.09 --- 14.14                  25.5--32.0         1.0--45.0
                SEPTiC         30    MEAN 220.12.L 482.13          502.97 + 784.07        6.37 + 16.28         113-5.     28.1 � 1.7        11.6 -+11.9
                                     RANGE     0.10--1969.71         3.60--2579.00        0.06 --- 85.34                  25.5--31.5         1.0--44.5

                GROUNDWATER          MEAN 125.44 � 133-89          345.71 -t 222.40       4.00 -t 3.35         117.8      28.0      O'l     13.4@� 2.5
                                     RANGE     0.04--1969.71         0.77--2579.00        0.06 --- 85.34                  25.5--32:0         1.0--45.0

                   TABLE 4. Statistical analysis (Kruskal-Wallis test) of summer vs. winter
                              nitrate concentrations (yM) at residential sites and a control site
                              at Key Deer National Wildlife Refuge. Values represent means I
                              standard deviation.

                   STATION    LOCATION       Y SUMMER             N       WINTER            N           P

                   PPH        CANAL         2.00.t     1.41       10    1.71 ;L     1.35    10        N.S.

                              MIDPOINT     164.73.� 212@.56       6  258.46 t-   187.79     10        N.S.

                              SEPTIC        1.17 +     1.09       8     18.77-t    10.04    10        <.001

                   EP         CANAL         1.32.�     0.36       8     1.02.�      0.32    10        N.S.

                              MIDPOINT      0. 57 :L   0.36       8     4.55 -t-    2.62    10        <.001

                              SEPTIC      196.49.�  385.52        8     66.77      71.77    10        N.S.

                   DA         CANAL         14.65      23.20      8     1.31        0.73    10        N.S.

                              MIDPOINT      0.85       0.83       6  277.25 :L 303.57       10        .001

                              SEPTIC      393.91    783.84        8 1989.61.�    909.59     10        .004

                   DL         CANAL         2.21       1.99       8     0.47       0.55     10-       .047

                              MIDPOINT      2.03 +     3.13       8     9.02      11.92     10        N.S.

                              SEPTIC        2.54.�     2.42       8   350.28     527.79     10        <.001

                   WP         CANAL         0.98 +     0.49       8     2.18�      1.63     8         N.S.

                              MIDPOINT      2.93 +     2.10       8     8.58       4.89     8         .019

                              SEPTIC      340.60 +  244.70        8   197.07     249.98     8         N.S.

                   YT         CANAL         4.32 +     4.27       8     2.43       1.04     8         N.S.

                              SEPTIC      496.33.�  982.26        8 2742.03      150.83     8         .001

                   TH         CANAL         1.05 +     0.63       8     1.65       1.00     8         N.S.

                              MIDPOINT     53.92 +  105.97        8     6.93      10.88     8         N.S.
                              SEPTIC      194.35 +  385.22        8   506.59    842.36      8         .034

                   KDR        CONTROL       0.20 +     0.23       8     0.76       1.20     12        N.S.

                   N.S.   P>0.05

                                                               40

                   TABLE 5.   Statistical analysis (Kruskal-Wallis test) of summer vs. winter
                              ammonium concentrations (pM) at residential sites and a control
                              site at Key Deer National Wildlife Refuge. Values represent means
                              + I standard deviation.

                   STATION    LOCATION           SUMMER          N       X WINTER           N          P

                   PPH        CANAL         1.88       1.33      10     0.62.�    0.21 10             .003

                              MIDPOINT     11.18       9.95      6     16.38-�-   12.41 10            N.S.

                              SEPTIC       37.73       3.46      8     83.89 �    59.62 10            .001

                   EP         CANAL,        1.74 +     0.45      8      0.84 +    0.13      10        <.001

                              MIDPOINT     16.49 �     11.13     8     23.63      9.99      10        N.S.

                              SEPTIC    2311.19 +   252.22       8   2146.90    473.46      10        N.S.

                   DA         CANAL         2.69 �     2.95      8      0.81      0.51      10        .035

                              MIDPOINT 200.71 +     132.34       6     62.86      43.89     10        .016

                              SEPTIC      743.08 +1175.76        8   1415.57    778.03      10        N.S.

                   DL         CANAL         0.83       0.83,     8      0.50 :L   0.23      10        N.S.

                              MIDPOINT     19.21  + 13.22        8     27.71  +   10.29     10        N.S.

                              SEPTIC       28.99  +    7.09      8   201.57   + 224.91      9         .007

                   WP         CANAL         2.24  +    1.72      8      1.03  +   1.03      8         N.S.

                              MIDPOINT 188.10     +   59.39      8   137.80       51.25     8         .018

                              SEPTIC      507.51  + 191.99       8   259.79@    176.84      8         N.S.

                   YT         CANAL         1*35  +    1*32      8      0.96      0.75      8         N.S.

                              SEPTIC      156.0    274.36        8   254.50 +   169.63      8         N.S.

                   TH         CANAL         1.55       0.75      8      1.40'�    0.67      8         N.S.

                              MIDPOINT    939.86    109.74       8   146.12 +     9.00      8         N.S.

                              SEPTIC      603.54 + 198.55        8  1588.40 �   400.84      .8        .001

                   KDR                      1.40 +     0*48      8      1.91 +    1.39      12        N.S.

                   N.S.    P>0.05

                                                               41

                 TABLE 1*     Statistical analysis (Kruskal-Wallis test)        of summer vs. winter
                              soluble reactive phosphate (,uM) concentrations at residential
                              sites and a control site at the Key Deer National Wildlife
                              Refuge. Values represent means -t I standard deviation.

                 STATION      LOCATION          7 SUMMER          N         7 WINTER         N      P

                 PPH          CANAL            0.32    0.21       8        0.08 :L 0.02      10 <.00i

                              MIDPOINT         0.43    0.17       8        0.97 -t 0.78      10  N.S.

                              SEPTIC           0.15    0.07       8        0.92    0.81      10 <.001

                 EP           CANAL            0.30    0.18       8        0.13    0.03      10  .008

                              MIDPOINT         0.23    0.17       8        0.86    0.97      10  .016

                              SEPTIC           18.16 + 7.62       8        65.82   38.07     10  .029

                 DA           CANAL            0.94  + 0.66       8        0.19    0.09      10  .008

                              MIDPOINT         2.14  + 0.65       8        4.92    3.05      10  .031

                              SEPTIC           2.26  � 0.86       8        5.46    2.32      10  .001

                 DL           CANAL            0.25  + 0.15       8        0.15 +  0.06      10  N.S.

                              MIDPOINT         6.05    5.40       8        7.15 +  4.08      10  .029

                              SEPTIC           0.84    0.72       8        0.77 t  0.37      10  .001

                 WP           CANAL            0.68    0.64       8        0.12 �  0.02      8   .002

                              MIDPOINT         0.70    0.18       8        0.50 +  0.18      8   N.S.

                              SEPTIC           0.23,�  0.14       8        0.51    0.21      8   .006

                 YT           CANAL            0.35 1- 0.17       8        0.15    0.07      8   .011

                              SEPTIC          24.73  + 40.54      8       44.53    32.94     8   N.S.

                 TH           CANAL            0.37  + 0.11       8             +  0.06      8   .015

                              MIDPOINT         0.44 � 0.18        8        0.76.�  0.43      8   N.S.

                              SEPTIC           0.67 + 0.88        8       :1.08    1.02      8   N.S.

                 KDR          CONTROL          0.14 �0.11         8        0.11    0.02      12  N.S.

                 N.S.= P>0.05

                                                           42

                  TABLE 7. Statistical analysis (Kruskal-Wallis        test) to determine    differences in
                             nutrient concentrations at residential stations and the         control station
                             at Key Deer National Wildlife Refuge. Values represent          the probability
                             that no difference exists between residential sites and         the control
                             station; N.S.= not significant (P >.05).

                                                              LOWER KEY@S

                                         WINTER                                            SUMMER

                  LOCATION        N03       NH4        SRP        LOCATION        N03       NH4       SRP

                  PPHM         <.001       .001    <.001          PPHM           .002      .117       .002

                  PPHS         <.001     <.001     <.001          PPHS           .012      .001       N.S.

                  EPM          <.001     <.001     <.001          EPM            N.S.      .056       N.S.

                  EPS          <.001     <.001     <.001          EPS            N.S.      .001       .001

                  DAM          <.001     <.001     <.001          DAM            .037      .002       .001

                  DAS          <.001     <.001     <.001          DAS            .001      .001       .001

                  WPM            .001    <.001     <.001          WPM            .001      .001       .001

                  WPS          <.001     <.001     <.001          WPS            .001                 N.S.

                                                             UPPER KEYS.

                                         WINTER                                          SUMMER

                  LOCATION       N03        NH4       SRP         LOCATION       N03       NH4        SRP

                  DLM           .045     <.001     <.001          DLM            N.S.      .001       .001

                  DLS          <.001     <.001       .008         DLS            .012      .001       N.S.

                  THM           .008     <.001     <-001          THM            .055      .001       .004

                  THS          <.001     <.001     <.001          THS            .003      .001       N.S.

                  YTS          <.001     <.001     <.001          YTS            .003      .001       .001

                  0SM            ---       ---        ---         OSM            .002      .006       .002

                  OSS            ---                              OSS            .019      .002       .002

                                                             43

                  TABLE 8.   Mean values for nutrients (pM) and salinity (parts per thousand)
                             for Halcyon Trailer Park and Key Deer National Wildlife Refuge.
                             Values represent + I standard deviati6lie

                  LOCATION             NO3                   NH4                   SRP         SALINITY

                  KDNWR-30-      0.07  +    0.02       5.67 +    7.00        0.12 + 0.08       2.0 + 0.0

                  KDNWR-60'      0.33  +    0 .21      1.03 +    0.46        0.13 + 0.12       0.3 + 0.6

                  HTP-MF       2691.29 +  518.15     203.29 +   342.33     117.06 + 6.46       2.9 + 2.7

                  HTP-60'        0.13  +    0.04      17.96 +    4.37        0.74 + 0.38      41.8 + 2.9

                  HTP-30'        0.29  +    0.24      19.05 +    7.34        0.93 + 0.50      39.5 + 1.1

                  HTP-15'        2.63  +    4.11      20.29 +    8.49        0.34 + 0.18      212.2 + 7.1

                  HTP-Open       0.44  +    0.19        0.91-+   0.94        0.35 + 0.17      42.6 + 3.0
                     Water

                                                             44

                  TABLE 9. Rate  and direction of groundwater flow during a flooding and
                           ebbing tide at Port Pine Heights, Big,Pine Key, FL.           Denotes
                            occurrence of a heavy rain event.

                 LOCATION           DATE        TIME          TIDE       RATE(ft/d)       DIRECTION
                    PPH           7-24-87       1215      Flooding         2.58              1990

                                                1345          High         0.00              ----
                                                1515        Ebbing         2.21              193 0
                                                1800        Ebbing         5.00              188 0
                                                1930        Ebbing         2.64              163 0
                                                2130        Ebbing         1.52              176 0

                                                2300          Low          2.08              181 0

                                                                                                 0
                    PPH    Average                          Ebbing         2.29              183

                                                                                                 0
                    PPH          10-02-87       1830          Low          2.83              190

                                                2130        Flooding      12.10*             222

                                                                                                 0
                                                2300        Flooding       9.68*             160
                                 10-03-87       0320        Flooding       4.19*             172 0
                                                1130          High         3.32              187 0
                                                1500        Ebbing         3.73              174 0
                                                2230          Low          2.83              190 0

                    PPH    Average                          Flooding       6.40              185 0

                    Heavy rain event

                                                           45

                  TABLE 10. Rate and direction of groundwater flow at Halcyon Trailer Park
                               (HTP) and the Key Deer National Wildlife Refuge (KDNWR) at
                               different depths and tides.

                  LOCATION          DATE         TIME           TIDE      RATE(ft/d)        DIRECTION

                                                                                                   0
                    HTP 15',       8-09-87       1500           High         2.17               305
                    HTP 15'       10-20-87       1830           Low          3.32               2770
                    HTP 60'        8-09-87       1330           High         2.17               1970

                                                                                                   0
                    HTP 30'       10-20-87       1730           Low          1.21               188

                    KDNWR 15'      8-08-87       1345           High         0.00

                                                                                                   0
                    KDNWR 15'     10-15-87       1710           Low          0.75                 71

                    KDNW`R 30'     8-08-87       1515           High         3.38               1040

                                                                                                   0
                    KDNWR 30'     10-15-87       1750           Low          4.10                 87

                                                            46

                 TABLE It. Mean values and ranges of nutrient concentrations (juM) and chlorphyll-a (,ug/1)
                               along an onshore-offshore transect from inshore canal waters on Big Pine
                               Key (PPH) to offshore waters at Looe Key National Marine Sanctuary (LK).
                               Values represent means + I standard deviation.

                 STATION                           N03              NH4              SRP             EN:P       Chl-a

                 1--- PPH-BEL          MEAN     1.60 +   0.92   0.57 +    0.23   0.09 +    0.07      24.1     0.34 + 0.22
                                       RANGE    0.39 --- 3.02   0.22 --- 0.94    0.03 --- 0.29                0.09 --- 0.78

                 2--- PPH-MAIN         MEAN     1.67 + 0.57     0.49 + 0.18      0.07 + 0.05         30.8     0.19 + 0.09
                                       RANGE    0.38 --- 2.36   0.18---0.79      0.03 --- 0.22                0.07 --- 0.42

                 3 --- PINE CHANNEL    MEAN     0.84 + 0.32     0.32 � 0.12      0.05 � 0.02                  0.14 � 0.06
                                       RANGE    0.26 --- 1.29   0.12 --- 0.48    0.03 --- 0.10                0.06 --- 0.21

                 4--- LITTLE           MEAN     0.78 � 0.42     0.27 + 0.11      0.05 + 0.02         21.0     0.22 :t 0.11
                      MUNSON   IS.     RANGE    0.27---l.75     0.09 --- 0.49    0.03 --- 0.08                0.08 --- 0.50

                 5--- HAWKS            MEAN     0.40 � 0.34     0.16 + 0.07      0.05 + 0.03         11.2     0.24 + 0.13
                      CHANNEL          RANGE    0.13 --- 1.05   0.05 --- 0.31    0.03 --- 0.11                0.09 --- 0.50

                 6 --- LK-BACK  REEF   MEAN     0.40 + 0.32     0.21 � 0.16      0.05 + 0.02         12.2     0.18 � 0.09
                                       RANGE    0.14 --- 0.94   0.02 --- 0.06    0.03 --- 0.10                0.10 --- 0.43

                 7S--LK-FORE    REEF   MEAN     0.38 + 0.33     0.23 + 0.14      0.04 � 0.02         15.3     0.13 t 0.07
                      SURFACE          RANGE    0.08---0.96     0.02 --- 0.53    0.03 --- 0.08                0.05 --- 0.32

                 7B--LK-FORE    REEF   MEAN     0.52 � 0.38     0.22 + 0.09      0.06 � 0.04         12.3     0.19 � 0.10
                      BOTTOM           RANGE    0.14 --- 1.35   0.02 --- 0.33    0.03 --- 0.16                0.07 --- 0.37

                  TABLE 11,   Correlation matrices ol nutrlenL concentrations and c     410 rophyll-a
                              data along and onshore-offshore transect from inshore canal waters
                              on Big Pine Key to offshore waters of Looe Key National Marine
                              Sanctuary (LK). Data were collected At samplings from 10/17/86 to
                              6/19/87. Values represent correlation coefficients; *r >0.70 is
                              considered significant.

                  10/17/86 LK #1          AMMONIA     PHOSPHATE      CHLOROPHYLL

                           NITRATE          .82         .67             .52

                           AMMONIA                      .66             .82 *

                           PHOSPHATE                                    .80 *

                  11/15/86 LK #2          AMMONIA     PHOSPHATE      CHLOROPHYLL

                           NITRATE          .68         .52             .86

                           AMMONIA                      .47             .49

                           PHOSPHATE                                    .76

                  11/23/86 LK #3          AMMONIA     PHOSPHATE      CHLOROPHYLL

                           NITRATE          .96         .35             .78

                           AMMONIA                      .41             .68

                           PHOSPHATE                                    .13

                  12/06/86 LK #4          AMMONIA     PHOSPHATE      CHLOROPHYLL

                           NITRATE          .89         .66

                           AMMONIA                      .82             .05

                           PHOSPHATE                                    .39

                  12/21/86 LK #5          AMMONIA     PHOSPHATE      CHLOROPHYLL

                           NITRATE          .96         .94 *           .81 *

                           AMMONIA                      .93 *           .78 *

                           PHOSPHATE                                    .88 *

                   1/08/87 LK #6          AMMONIA     PHOSPHATE      CHLOROPHYLL

                           NITRATE          .91         .95 *           .27

                           AMMONIA                      .79 *           .40

                           PHOSPHATE                                    .24

                                                        48

                   .-TABLE 12. CONTINUED

                      1/28/87 LK #7         AMMONIA     PHOSPHATE      CHLOROPHYLL

                              NITRATE         .91         .72            .59

                              AMMONIA                     .81.*          .47

                              PHOSPHATE                                  .70

                      2/18/87 LK #8         AMMONIA     PHOSPHATE      CHLOROPHYLL

                              NITRATE         .84         .27            .34

                              AMMONIA                     .37            .43

                              PHOSPHATE                                  .12

                      3/20/87 LK #9         AMMONIA     PHOSPHATE      CHLOROPHYLL

                              NITRATE         .81         .29

                              AMMONIA                     .21            .39

                              PHOSPHATE                                  .31

                      4/09/87 LK #10        AMMONIA     PHOSPHATE      CHLOROPHYLL

                              NITRATE         .85           18           .04

                              AMMONIA                     .11            .30

                              PHOSPHATE                                  .49

                      4/26/87 LK #11        AMMONIA     PHOSPHATE      CHLOROPHYLL

                              NITRATE         .68         .02            .31

                              AMMONIA                     .45            .36

                              PHOSPHATE                                  .86

                      6/19/87 LK #12        AMMONIA*    PHOSPHATE      CHLOROPHYLL

                              NITRATE         .63         .55            .37

                              AMMONIA                     .93            .65

                              PHOSPHATE                                  .79

                                                             49

                                                                          LIME

                                                                             BLACIMArER
                                                                                                        &A RWS   SOUNAD
                                                                              SOUND

                                                                                                                              PT.

                                                                                                                              0 M

                                                              SCALE IN FEET

                                                                                                     CROSS Us
                        LOCATION MAP                                                 SHELL            KEY
                                                                                     KEY

                                                                                                                 INAKE Pl-
                                                                                     8LALWWA7*.WR 504VIV

                                                                                                              T---T  11

                                                                            BOGGY KEY

                                                                                 C:.

                                                                          Burromwoo
                                                                           $0110                                     5d*5 40

                                                                                        rAll0N 8AS.

                                                           &V770N;JlO0D
                                                              SOUND                                                               *S

                                                                                                    10*  --l-
                                                                Xe                   rl-
                                                                                                  OCEAN
                                                                                                  SHORES

            FiEure 1. Location of groundwater monitor stations                 on  Key Largo.

                                                                                                                                                                                          P t CIARLES

                                                                                                         S.CALI it, FEE-.

                                                                                                                                                                                            TREASURE
                                                                                                                                                                                                 HARBOR

                                         LOCATION MAP

                                                                                                                                           (9                                           RWRKWU     KEY

                                                                                                                                             A           41

                                                                                                                     S

                                             CURRIE
                                                COVE

                     Figure         2. Location of groundwater monitor                                           stations on Plantation Key.

                                                                            'T
                                         rI
                                                  j

                                                                                                   (ND
                                                                                            noo            7.-

                                                                                              SCALE IN FEET

                                  LOCATION      MAP

                                                                                                                                                                                   YELLOW
                                                                                                                                                                                     TAIL          STIPP

                                                                                                                                                                  DODGE
                                                                                                                                                                   LAKE

                                                                                                                           KNIGHT
                                                                                                       US                    KE

                                                                                           PIGEON
                                                                                            KEY

                                                                                                                              BOOT
                                                                                                                               KEY

                                                      @DLASSES ET
                                                                                                                                                    W SISTER 'ROCK          E, SWER RO.CK
                                                                                           tiArKS       CjiAVX0

               Figure 3. Location of                        groundwater monitor                     stations                   ra".
             m            m            m                                                    m            = Oak

                                                                                          PORT PINE
                                                                                            HEIGHTS

                                    f, 8:G TORCH
                                                                                                 PINE  K; f
                                                                                                        KEY DEER
                                                                                                            REFUGE
                                                                                                                            DOCTORS
                                                                                                                                ARM

                     Tcp I@EE                                                                                                      NO  NAME. KEY
                      KA@

                                                                 TORCH
                                                          WDLE
                                                                        EDEN
                                                                         PINES

                                                                        0
                                                                                      C,                                       HALCYON
                                                                                                                               TRAILER
                                                                                                                                  PARK
                                 ;SUMMERLAND
                                     KEY                                                                                               WHISPERING
                                                                                                                                           PINES

                                            us@-j
                                                                                                                                                 SPANISH

                                                                                                           NiWFOUND     HARSOR
                                                                                 LITTLE  I C R CH

                                                     RAMROD KEY
                                                                                                                                T@p -

                       Figure 4. Location of g-roundwater monitor                                     stations on Big Pine Key.

                                  Figure 5. Cal-ibiatJon Curve. for GeoFlow groundwater flow meter.!,'

                              12

                      Uj      10

                      0                    r2=0.92
                      0
                              8             b=O-28

                      z       6
                                                                                                                                           Ln
                      Uj

                              4                                            0
                      0

                      U-

                              2

                                                   25                 50                 75                 100                125

                                                  INSTRUMENT READOUT IN COLUMN             "F" (Relative Units)

                                         PORT PINE HEIGHTS CA
                            r            FINGER CANAL
                             @FIIG TORCH
                                                 q@j@jjl     I   BIG PIPIF kFy
                                                                                                P
                                                       @i 11119rud
                                        T" PINE    %."
                                  3 sou           PORT PINE HEIG Tq
                                      CHANNEL   2MAIN CANAL

                                                                                        tIn IIAMf.
                                           MIDDLE TORCH

                                                   0

                           "'."ERLAND
                        p    KEY

                                 US.%,

                                                                                               $PA)V;SH jj4A-30.,

                                                        LITTLE TORCH    AWWFOuNa HAR80.9

                                      RAMROD KEY

                                        4   MAVER
                    _-----@-@@@MLINSON           ISLAND

                                                                               SCALE IN FEET

                                              AHAWKS CHANNEL

                                               6LOOE KEY NATIONAL
                                              jrMARINE SANCTUARY
                                                 13ACK REEF
                                                          luld

                                                       LOOE KEY NATIONAL
                                             c@@71MARINE SANCTUARY
                                                       FORE REEF

                   F19'ure 6. Location of hydrographic.stations in nearshore waters of Big Pine Key.
                                                              55

                                                TIDE HEIGHT(MSL)
                                                      (inches)

                             0                         0     N    -P.   0)   Go
                   1800

                                            ago
                                                                   Ln
                   2200

         0

                   0200

                                               0

         CD
                   0600

         0

                m

                0
                -h
                0  1000

                   1400
                                                                   16

         CD

                   1800

         CD
         Cr

         aq

         r+
                   2200

                                  0          Co

                                      LATERAL VEL06TY     of GROUNDWATER
                                                    ft-d-1

                                                     56

                                                TIDE HEIGHT (MSI.
                                                     (inches)

                                                                        +              +
                                                                 N)     41
              1200                                                      1

              1300

         0
         a    1400'

         ,D
                                                                                         010i,
              1500

              1600

                                                           00S

                                                    so
         0
         r+   1700                            so

                                       is
              1800

              1900

         CD  2000

                                                                         .%#
             2100                                                           oil
         0
         0

             2200

             2300

             2400

                                                               0

                                        LATERAL VELOCITY of GROUNDWATER
                                                     f t - d-'

                                                      57

                                                                          Well 2
                                                                               (1980)
            18.0                                                        Hanson

                                                                                  4f

                                                                                                       4.5  increased hydraulic head
                                                                                                      increased conductivity a f ow

                                                                       40'
            15.0

                                                              4f.

          >                                                40,'

                                                                                        Mean sea level
                                                                                                                                     Ln
            12.0

         E

         CU
         J@

                                     OF,

             9.0
                                  41f

             6.0                   A

                         CD                 Cr_                  z                            CL
                         LLJ       <        CL
                                                                 D
                                                          TIME
                Figure. 9.  Seasonal trends in- hydraulic head based on monthly average groundwat
                                                                                                ter.
                           table hei    and"n Ef&f evjjM
                             "M

                                                                                                                                  OAA COASTAL SERVICES CTR LIBRARY

                                                                                                                                 3 6668 14110278 2