Hydrology

1995 Abstracts

Submarine Groundwater Discharge

Jeffrey Chanton, William Burnett, Jaye Young, Glynnis Bugna, Department of Oceanography, Florida State University, Tallahassee, Florida 32306-3048, 904-644-6700

The purpose of our study is to evaluate the significance of groundwater discharge into Florida Bay. We have attempted to locate areas in the bay where groundwater seepage is more pronounced by reconnaissance surveys of the concentrations of radon and methane in the bay waters. These trace gases are thought to be good natural indicators of seepage of groundwaters into standing bodies of water (see below and Young et al., 1995). We have observed a wide range in 222Rn and CH4 concentrations in the bay waters with systematically higher values in the "back-key" basins investigated relative to the northern bay sites and especially the mid-bay stations (Figure 1). Using this information as a guide, we returned to Florida Bay to make direct measurements of groundwater seepage using an instrument design modified from Lee (1977). The "seepage meter" is basically a chamber implanted in the sediments which has an open port where a plastic bag can be positioned to collect seepage over measured time intervals. We used 4-liter plastic bag "collectors" which were prefilled with 1000 mL of bay water to prevent short-term artifacts (Shaw and Prepas, 1989) and to allow for measurements of negative seepage, i.e., recharge into the underground aquifer. The lower reliable measurement limit for seepage meters depends upon the length of deployment and the conditions under which the sampling occurs-based on our experience using these meters, we normally expect a lower useful limit of 3-5 mL/m2.min. Over two hundred seepage measurements were conducted on sampling trips in February and July, 1995. Our seepage sampling sites are shown (Fig. 2), for three geographic groupings: (1) open bay; (2) northern Florida Bay; and (3) back-key areas. Seepage can be highly variable, both on a temporal and spatial basis, even within small areas. Often seepage decreases as one moves away from shore. Many of our transects were arranged perpendicular to shore and so high spatial variability should be expected. Standard deviations were often of the same magnitude as the means. Numbers of replicates ranged from 4 to 8 meters.

The "mid bay" sites included a circular seagrass bed off Buchanan Keys, two transects along the western and eastern edge of Rabbit Key Basin, and one in Whipray Basin. The seepage rates from Rabbit Key Basin and Whipray Basin were low; daily means of 9, 5 and 6 ml m-2 min-1 were obtained. The results from the circular bed near Buchanan Key were somewhat greater and means of 20, 7 and 18 mL/m2.min. were obtained. Two measurements in the western transect at Rabbit Key showed significant seepage at about 30 and 40 mL/m2.min. These single measurements, however, were taken in shallow water during a period of high winds and should thus be viewed cautiously. The circular seagrass bed off Buchanan Keys did show some relatively high seepage values (up to about 40 mL/m2.min) which were verified on subsequent visits. Pairs of measurements made at this site showed reasonably good precision for measurements made within a time span of a few hours.

In northern Florida Bay (Long Sound, Snipe Point, and two sites in Madeira Bay), the seepage rates were generally low. Although a large variation existed between the two days when measurements were made, the seepage at Snipe Point appeared higher (daily means of 24 and 4 mL/m2.min. Measurements were only made on a single day at both Madeira Bay and Madeira Beach.

Some of the most interesting measurements were taken in the "back-key" areas, i.e., those areas just on the Florida Bay side of the Keys. This area generally had greater tracer concentrations in the December 1994 survey. The areas where measurements were conducted included the Key Largo Ranger Station, Tavernier Basin, Hammer Point, and Little Buttonwood Sound. Measurements off the Ranger Station were low and variable, even when made within a short time frame. Seepage in Little Buttonwood Sound, on the other hand, was moderate (daily means of 12 and 14 mL/m2.min, highest value = 56 mL/m2.min) although there was still considerable spatial variability between the meters which were all placed within a relatively small area (approximately 50 x 100 meters). The measurements made at Tavernier Basin were the highest and spatially most consistent we have measured to date in Florida Bay. The mean of 6 meters placed in a seagrass bed within an area of about 500 m2 was 68±5 mL/m2.min. This area had also produced one of the highest concentrations of radon and methane in our December measurements (see Figure 1). Six seepage meters installed in a 500-m line at Hammer Point, another site of high tracer concentrations based on our initial sampling trip, were measured repeatedly over a several day period. These repetitive measurements turned out to be a productive strategy as a clear pattern developed which showed a relationship to the tidal cycle on the Atlantic side of the Keys (Fig. 3). This pattern, which shows a trend towards higher seepage on the Florida Bay side of the Keys when the Atlantic tide is high, and lower (negative) seepage when the Atlantic level is low illustrates that tidal forcing may be of paramount importance in terms of controlling seepage into (and out of) Florida Bay (see also Halley et al., 1994).

Analysis of the monitor well waters (of Dr. Gene Shinn) showed that the underground waters were fairly uniform in 222Rn while the CH4 concentrations were more variable. Out of 19 samples, all 222Rn values except 1 were in the range of 300-650 dpm/L and most CH4 values were in the range of 100-1000 nM with 3 lower concentrations and one sample (KL5) that was spectacularly higher at about 15,000 nM. Note that these concentrations are significantly enriched relative to concentrations in surface waters, suggesting that the tracers may be good indicators of groundwater intrusion. Interestingly, the Key Largo (KL1-KL5) transect showed a general trend of increasing radon in an offshore direction (perhaps indicating an increase associated with increased residence time) and a general decrease in methane offshore (with the exception of the extremely high value at KL5). Sulfide concentrations (measured by Dr. Paul Carlson) showed a similar pattern as CH4 in these wells.

Halley, R.B., Vaciler, H.L., Shinn, A. and Haines, J.W. Marine Geohydrology: Dynamics of subsurface seawater around Key Largo. 2nd Coastal Wetalnd Ecology and Management Symposium, Key Largo, 1994.

Lee, D.R., 1977. A device for measuring seepage flux in lakes and estuaries. L&O, 22, 140-147.

Shaw, R.D. and E.E. Prepas, 1989. Anomalous, short-term influx of water into seepage meters. L&O, 34, 1343-1351.

Young, J., Bugna, G., Burnett, W. and Chanton, 1995. J. Application of Radon and Methane for assessment of groundwater discharge in coastal and offshore waters. submitted to Limnology and Oceanography.

Geophysical Mapping of Fresh/Saltwater Interface

David V. Fitterman, U.S. Geological Survey.

Introduction

Water quality in coastal areas of South Florida such as Everglades National Park (ENP) and the discharge of fresh water into Florida Bay are closely tied to water use and water management policies. Determination and monitoring of water quality is essential to restoration of the South Florida ecosystem (SFE). Increased domestic water use, drainage of land to allow farming, increased farming and subsequent nutrient loading of runoff, and changes in water management practices over the years have had a profound effect on the SFE. Monitoring of these effects is made difficult by the inaccessibility of much of this area. Airborne geophysical methods provide a means of rapidly and economically monitoring large areas where access is difficult.

Project Objective and Scope

This project addresses the question of determining the location of the fresh-water/salt-water interface (FWSWI) in the coastal regions of southern Dade and Monroe Counties, synoptic monitoring of changes in water quality associated with changes in water management practices, and looking for geophysical evidence of subsurface discharges of fresh water to Florida Bay.

This project covers a 1036-square-kilometer region of the Everglades located in Everglades National Park and surrounding areas. The study area is bounded on the east by U.S. Highway 1, on the south by Florida Bay and Whitewater Sound, and on the far west by the mouths of the Harney River and Shark River Slough. From these boundaries the study area extends inland from 14 to 22 km.

Summary of Methods

This project relies upon the fact that changes in water salinity produce changes in specific conductance (SC) or water resistivity. As pore fluid resistivity strongly influences the bulk resistivity of geologic materials, geophysical methods which measure rock resistivity can be used to obtain information on ground water quality.

Airborne electromagnetic geophysical surveys are used to collect resistivity data. The interpreted data provide information on geologic and hydrologic conditions including locations of geologic boundaries and spatial changes in water quality, which are of use to ground-water modelers. Interpretation relies heavily upon the use of borehole geophysical logs, namely induction logs from monitoring wells and water quality data. Surface geophysical measurements are used to refine the interpretation. Resistivity maps and their interpretations will be of use to agencies managing water levels in South Florida and assessing their impact on the SFE.

The primary tool used in this study is helicopter electromagnetic (HEM) surveys. A large (9-m-long) cigar-shaped instrument package called a "bird" is slung 30 m below a helicopter. Electrical current flowing in transmitter coils in the bird induces current in the ground. The intensity of the induced currents increases as the ground conductivity increases. The magnetic fields generated by the induced currents are recorded by receiver coils in the bird. The transmitter coils are excited at five frequencies to obtain different depths on investigation. Flying with the bird 30 m above the ground, measurements are made every 0.1 second along flight lines. Flight lines are nominally spaced 400 m apart. Analysis of these data produces apparent resistivity maps. Using multi-frequency data sets, the data are inverted to obtain resistivity-depth information along flight lines. Resistivity-depth results are used to generate cross sections and interpreted resistivity maps, such as depth to geologic or hydrologic interfaces.

Water quality measurements from monitoring wells will be used along with borehole resistivity logs to establish the relationship between water quality and formation resistivity. Laboratory measurements of cores from wells in the area will be used to refine the water-quality-formation-resistivity correlation. This correlation is needed to convert interpreted resistivity maps into water quality maps.

Summary of Results to Date

HEM apparent resistivity data collected in December 1994 show a resistivity transition becoming more conductive in the direction of Florida Bay. This feature is interpreted to be the fresh-water/salt-water interface (FWSWI). The transition is narrowest where water from Taylor Slough forces the transition seaward and becomes more dispersed to the east of Taylor Slough and between Taylor Slough and Shark River Slough. These sloughs show up as resistive features due to the fresh ground-water flows associated with them. There are several features on the maps which are attributed to the effect of man-made structures on ground-water flow. These include: a conductive feature along the old Ingraham Highway caused by the road bed blocking fresh-water flow southward which would wash away more saline water, 2) discontinuities in the resistivity values across the Flamingo road suggesting that the road bed inhibits water flow, and 3) resistive features near the S18C control structure on the C-111 canal suggesting that water impounded by the control structure flows into the surrounding aquifer.

In the region west of the Flamingo road toward the area of Tarpon Bay, the resistivity maps are dominated by the influence of tidal flow of saline to brackish water in the streams draining west and southwestward to the coast. The resulting resistivity transition attributed to the FWSWI is just inland of the upper reaches of most of these drainages. Coastward of Tarpon Bay, the area is uniformly conductive except for a small resistive feature thought to be associated with a fresh-water lens sitting under a small topographic high. The region is marked by vegetation changes indicative of higher ground and less saline ground water than the surrounding terrain which is covered by mangrove.

Interpretation of the FWSWI in the airborne resistivity data is confirmed by borehole geophysical logs and water quality data. We have established a correlation between formation resistivity and water specific conductance in the eastern part of the study area. Wells drilled farther to the west will provide information indicating if this correlation is valid over a wider region.

Helicopter electromagnetic (HEM) surveys were flown in April 1994 and December 1994 at the end of the dry and wet seasons respectively providing information at extremes of the hydrologic cycle. Comparison of the dry season (April 1994) and wet season (December 1994) HEM surveys shows that there is an increase in apparent resistivity of nearly a factor of 2 along the main portion of the FWSWI. This is attributed to increased fresh-water flow in the surface and near-surface portions of the aquifer. There is a very pronounced increase in resistivity in Long Sound and Madeira Bay. We interpret this as being caused by these water bodies becoming fresh due to increased fresh-water discharges from the Everglades during the wet season. Conductivity monitoring in Long Sound by the National Park Service confirms this hypothesis as well as conductivity surveys conducted in Florida Bay by USGS. The resistivity changes are very encouraging as they suggest that HEM surveys can be used to monitor the long term effect of changes of water flows in the Everglades. Repeat HEM surveys are planned over the next four years to monitor temporal resistivity changes.

Borehole geophysical data including induction logs and water specific conductivity measurements were collected starting in September 1994. To date a total of 16 wells have been logged. Additional wells are planned in and near ENP. These wells will be logged on a regular basis to monitor changes in resistivity associated with changes in surface and ground-water flows. Further analysis is needed to determine required frequency of repeat logging.

Time-domain electromagnetic soundings were collected during August 1995 at 35 locations in Everglades National Park. These soundings give very detailed information about the resistivity-depth structure from the surface to a depth of about 80 m. These data are being used to calibrate the HEM survey results.

The Importance of Taylor Slough Hydrology on Salinities in Florida Bay

Robert A. Johnson, Robert J. Fennema, Everglades National Park, South Florida Natural Resources Center, 40001 State Road 9336, Homestead, Florida 33034-6733.

Taylor Slough is a freshwater wetland system which encompasses more than 158 square miles, and extends some 20 miles from its upstream end north of the Frog Pond to the coastal mangrove fringe along Florida Bay. The headwaters of the slough originate in the Rocky Glades, a transitional wetland which separates Shark Slough and Taylor Slough. The slough has historically been an important source of freshwater to the central portion of Florida Bay. Prior to the 1960's, wet season water levels in the Rocky Glades and Taylor Slough headwaters were 1.5 to 2.5 feet higher than today (Johnson and Fennema, 1989). These higher water levels kept the northern Taylor Slough marshes inundated for 2 to 3 months each year, and established a hydraulic gradient that sustained surface water and groundwater flows into Florida Bay. The higher water levels also retained much of the local wet season rainfall in the wetlands and underlying aquifer, which allowed freshwater to be releasedmore gradually, tempering salinity fluctuations in the nearshore areas of Florida Bay.

Beginning in the late 1960's, construction of the Central and Southern Florida (C&SF) Project features in southwestern Dade County led to the drainage and diversion of flows away from the slough, and into the lower C-111 basin and the east coast canals to Biscayne Bay. These changes are thought to be an important contributor to the hypersaline conditions in the nearshore embayments of central and northeastern Florida Bay. Everglades National Park has been working with the Army Corps of Engineers and the South Florida Water Management District for the last ten years on modifications to the C&SF Project features in the Taylor Slough and C-111 basin to reduce ENP drainage losses, and reestablish more natural surface water inflows through Taylor Slough and into Florida Bay. A key to these efforts is the need to quantify the relationships between upstream hydrologic conditions and salinities in the downstream estuaries, in order to establish restoration guidelines for this redesign effort. Our current project is a preliminary effort to link the long-term changes in upstream water levels to fluctuations in nearshore salinities using simple statistical models, and the results of numerical hydrologic models developed for the south Florida region.

A number of scientists have developed regression models that attempt to link salinities in the nearshore areas of Florida Bay to water levels in the uplands (Tabb 1967, Sculley 1986, Bjork and Powell 1994, and Cosby 1994). These efforts use the results of univariate and multivariate regression models developed by Dr. B.J. Cosby to simulate daily and monthly salinity variations in Trout Cove, Long Sound, Joe Bay, and Little Madeira Bay, based on water levels at long-term monitoring wells in and adjacent to the Park. These statistical models were initially developed to use the 40 plus years of historical water level data in the uplands to reconstruct salinity patterns in the bay. All of these studies have shown that upland water levels are statistically linked to salinity variations in the nearshore areas of the bay, and that historical reductions in upland water levels have contributed to the hypersaline conditions in the bay. Several of these statistical models were next combined with the results of a series of regional hydrologic modeling runs using the South Florida Water Management Model, to test the hypotheses that the hydrology of Taylor Slough is of specific importance to salinities in the nearshore areas of Florida Bay, and that increasing water levels in the upper portion of the slough is an appropriate way of restoring more natural variations in downstream salinities.

Model runs with increased upland water levels in the Rocky Glades and upper Taylor Slough basins (simulating the effects of pre-drainage conditions) were found to temper the observed short term and seasonal salinity variations, reduce the occurrence and duration of hypersaline periods, and prolong the beneficial effects of wet season runoff well into the following dry season. These changes were most pronounced at the salinity monitoring sites in the nearshore areas of central Florida Bay (Madeira Bay), and less pronounced for the sites in northeastern (Florida Bay). This suggests that water management impacts have had there greatest effect on reducing inflows into the bay via Taylor Slough, and that current efforts to divert excess runoff from the Eastern Panhandle basin into Taylor Slough will likely lead to salinity problems in the nearshore embayments downstream of the C-111 canal system. For this reason, the restoration of more natural freshwater inflows into Florida Bay via Taylor Slough will most likely require redirecting the historical wet season runoff that is currently lost to Biscayne Bay, or provisions to provide supplemental inflows from the upstream regional water management system.

Reconstruction and Simulation of Episodic Meteorological Events and Local Weather Regimes Which Affect the South Florida Ecosystem

Craig Mattocks, NOAA - University of Miami Cooperative Institute for Marine and Atmospheric Studies; Mark Powell, Sam Houston, NOAA - AOML Hurricane Research Division, Miami Fl.; Mark DeMaria, NOM - NWS National Hurricane Center, Miami Fl.

Introduction

The primary objective of this research project is to reconstruct episodic/catastrophic meteorological events and local weather regimes which critically affect the South Florida ecosystem. Gridded wind, precipitation, and temperature fields will be generated from real case analyses, numerical model simulations, and idealized scenarios described by canonical systems of analytical equations to produce a catalog of datasets. Research scientists will be able to quickly retrieve data from this event/regime archive for use in circulation model simulations/predictions, hydrological modeling, natural systems restoration, and biological impact studies.

Episodic Wind Field Reconstruction

Attendees of the South Florida Atmospheric Modeling Workshop (NOON, Nov.1994) expressed the need for a catalog of meteorological events/regimes which critically affect the South Florida ecosystem. Gridded datasets from this archive could be accessed for circulation/ecological model simulations, hydrological modeling, natural systems restoration, and biological impact studies. During the next several months, events to be studied include Hurricane Andrew (August 1992), the "Storm of the Century" (March 1993), Tropical Storm Gordon (November 1994) and Hurricane Donna (1960). Next year, additional reconstructions will include the Florida Keys Hurricane of 1935 and other historical catastrophic storms. Quality control procedures, spatial/temporal averaging techniques, planetary boundary layer adjustment algorithms to account for land/water exposure, hurricane wind field models, and an objective analysis technique which minimizes the error between the analyzed field and the input observations have been developed by HRD scientists (Powell et al,1995) for such applications. "Snapshots" of the surface wind streamline and isotach fields will be generated for a regular (latitude, longitude) domain centered on Florida Bay at 6-12 hour intervals. These images and gridded surface wind datasets will be archived on a World Wide Web site for access by other Florida Bay researchers. A format will be chosen which will allow these fields to be imported by geographical information systems (GIS) so that they can be overlayed/compared with other geo-referenced datasets such as mangroves, reefs and turbidity plumes.

Mesoscale Atmospheric Modeling

A major component of this dataset construction effort is the use the Advanced Regional Prediction System (ARPS) mesoscale atmospheric numerical weather prediction model which can simulate/predict surface winds, rainfall and thermodynamic fields relevant to Florida Bay at high-resolution. These fields can be used as boundary conditions/forcing for bay and ocean circulation models. The atmospheric model can also be used to study the effect of specific processes on the freshwater input to Florida Bay, such as evaporation/precipitation under different weather regimes, as well as the transport/rainout of toxic atmospheric substances in the South Florida ecosystem. The model was initialized with a homogeneous base state from the 12 UTC 25 August 1975 Miami sounding, which corresponds to the FACE case described by Cunning and De Maria (1986) and Cunning et at., (1986) . ARPS was configured to be DRY (safe, solid run), with a horizontal grid mesh of 9 km, and 42 vertical levels using a tangential vertical grid stretching (50 meter vertical resolution in lowest 500 meters, slowly increasing to 500 meters at 700 my, then reaching a man stretched spacing of 1 km in the stratosphere). A clay- loam soil with grass/shrub vegetation was used over land in the Noilhan-Planton (2 soil-layer force/restore) surface energy budget. The horizontal motion fields for 1 pm and 4 pm local are plotted in figure 3. In order to improve computational efficiency, a longer timestep was used for the relatively uneventful morning hours. At 1 PM local (elapsed time = 5 hours) plots, surface heating (low-mid 90's F) induces a fairly strong sea breeze (SB) front, best deduced from the streamline fields. There is also a classic cold imprint and divergent flow from Lake Okeechobee. The w vertical cross sections (not shown) show that full solenoidal circulations develop at both coasts, and a very intense dry convective "cell" explodes along the SB front further north. Because of the lack of moisture/convective adjustment, this circulation is believed to be too strong and not very realistic looking late in the simulation.

The next level of complexity will be to obtain sufficient supercomputer time to run the model with the moisture/convective adjustment on the same 12 GMT 25 August 1975 case and then use the "gribit" GRIB decoder (completed in September 1995) to initialize ARPS with non-homogeneous 3-D fields from the operational Eta/Meso model. Then we will try to increase the realism of the simulations by using the high-resolution land cover/use, soil/vegetation databases from the South Florida Water Management District (SFWMD). The Center for Analysis and Prediction at the University of Oklahoma (where ARPS was developed) has offered to assist us with configuring the model for the more complex simulations later this year.

References

Cunning, J.B. and M. DeMaria,1986; An investigation of the development of cumulonimbus systems over south Florida. Part I: Boundary layer interactions, Monthly Weather Review, 114, 5-24.

Cunning, J.B., H.W. Poor and M. DeMaria,1986: An investigation of the development of cumulonimbus systems over south Florida. Part II: In-cloud structure, Monthly Weather Review, 114, 26-39.

Powell, M.D., S. H. Houston, and T. Reinhold, 1995: Hurricane Andrew's landfall in South Florida: Part I: Standardizing measurements for documentation of surface wind fields. Accepted, Weather and Forecasting.

Baseline Information on the Quality of Nearshore Waters of the Florida Keys: Identifying Trends and Variability

William Miller, The Nature Conservancy, Florida Bay Watch Program

Nearshore waters of the Florida Keys have been little studied. A large information gap exists for this habitat in the south Florida ecosystem. The Nature Conservancy's Florida Bay Watch volunteer program initiated a project using trained volunteers to collect water quality data at canals, harbors, and other nearshore areas along the Florida Keys to help fill this void. The objectives of this ongoing project are to develop a dataset that: 1) quantifies the spatial and temporal variability of water quality in nearshore areas of the Florida Keys, 2) identifies areas of potential impact of Florida Bay water quality on resources of the Florida Keys National Marine Sanctuary (FKNMS), and areas of potential impact of Florida Keys nearshore water quality on resources of Florida Bay, and 3) provides an important baseline to monitor changes in waters quality in nearshore areas of the Florida Keys, especially as changes in sewage disposal practices of the Keys are implemented under the FKNMS management plan. The following results were expected: 1) dredged canals would contain high nutrient levels, concentrated from adjacent On-site Sewage Disposal Systems (OSDS), 2) overall, canal water quality would be degraded relative to water quality at natural/non-dredged shorelines, 3) water column nutrient levels at dredged canals would increase after rainfall events, and 4) water quality at Middle Keys sites will reflect Florida Bay influence more than sites in the Upper or Lower Florida Keys.

Volunteers for this project are trained in basic oceanographic sampling methodologies, including instrument calibration and the collection and handling of water samples for analysis of nutrients and chlorophyll. To ensure the integrity of the data, a program coordinator periodically evaluates the volunteer's sampling routine. All data is quality control checked before entry into a database.

There are currently 25 nearshore water quality stations located at the homes and workplaces of Bay Watch volunteers: 18 bayside and 7 oceanside of the Keys. Eight of the stations are at open-ended dredged canals, two are at plugged dredged canals, four are at boat basins, and eleven are at natural/non-dredged shorelines. Fifteen of the stations are in the Upper Keys, five are in the Middle Keys, and five are in the Lower Keys. Sites vary in many aspects including water depth, flushing rates, surrounding foliage, and number and type of adjacent OSDS. Most sampling is done from docks or seawalls, however, some sampling is done up to 100 meters offshore. Samples for each station are consistently taken from a marked location for which a GPS position has been recorded.

Water quality stations are sampled at the volunteer's convenience twice a week, at any one low and one high tide, year round. The following information is recorded on a standard data sheet: station number, date, time, tide, Beaufort number for wind and seastate, wind direction, current strength and direction, secchi depth, water color, sea surface temperature, specific gravity, sea surface salinity, and rainfall in the last 24 hours. In addition, volunteers collect and store water samples to be analyzed for total nitrogen, total phosphorus, and chlorophyll a content. Analysis for nutrients and chlorophyll is conducted at the Southeast Environmental Research Program's water quality laboratory at Florida International University, in Miami.

Nearshore water quality sampling began in June 1994 and is ongoing. The following ranges of water quality parameters have been observed thus far: a)secchi depth - 0.1 to 6 meters, b) temperature - 14.00 to 41.50 degrees Celsius, c) salinity - 0.0 to 59.1 parts per thousand, d) total nitrogen - 8.11 to 263.34 micromolar, e) total phosphorus - 0.06 to 4.62 micromolar, f) chlorophyll a - 0.00 to 12.89 microgams per liter. The extremes of temperature were recorded at stations with depths less than 0.50 meters. Total nitrogen tends to be higher at natural/non-dredged shorelines in the Upper Keys than at similar sites in the Lower and Middle Keys. This may possibly be from the influence of freshwater drainage into northeast Florida Bay. As expected, total nitrogen is also higher on average in dredged canals than at natural/non-dredged shorelines. Total phosphorus and chlorophyll a are typically low at most stations, with the highest average concentrations being recorded at dredged canal sites. While total nitrogen and total phosphorus concentrations increase sharply at some stations following rainfall events, this pattern is not consistent within or among stations. Overall, water quality in nearshore areas of the Florida Keys is more variable spatially than temporally.

Nearshore water quality sampling by the Florida Bay Watch program will likely continue in the Florida Keys for at least the next two years. Funding has been secured to expand the project to 30 sampling stations, and volunteers to man these stations are presently being recruited As this dataset and the spatial and temporal coverage of water quality sampling grow, we will be better equipped to characterize the spatial and temporal variability of water quality in nearshore areas of the Florida Keys, and to understand the factors that influence this variability. This dataset will also be an invaluable tool for resource managers to guage their efforts at improving water quality in the Keys.

Dynamics of Groundwater, Surface Water and Salinity Related to the Mangrove/Marsh Ecotone

William K. Nuttle, Bernard J. Cosby, University of Virginia

The coastal mangrove ecosystem in South Florida and associated nearshore areas are subjected to the mixed influences of climate, sea level and freshwater hydrology. In general, coastal hydrology is "driven" by climatic and oceanographic processes, which operate at the largest scale (i.e. the boundaries of the landscape). The effects of changes in climate and sea level cascade through the scale of hydrologically-defined landscape elements (i.e. drainage basins) to the smallest scale, ecologically-defined elements contained within them. One can conceive of hydrological conditions that vary across the landscape and in time as a hydrological "signal". Hydrological conditions experienced within an ecological element are characteristic of the ecosystem that occupies that element. Here, the meaning of the term "characteristic" includes, but is not necessarily limited to, the following: 1) hydrological conditions are integral to some maintenance function in the ecosystem; 2) succession involves the co-evolution of hydrological conditions in time; 3) infrequent, extreme hydrological conditions impose a disturbance on the ecosystem.

Hypotheses

This research tests the hypothesis that changes in coastal hydrology, caused by rising sea level and changes in freshwater discharge related to climate change and water management, contribute to changes in vegetation at the mangrove/marsh ecotone. Two corollary hypotheses guide the work. The first is that hydrological conditions that characterize the mangrove/marsh ecotone are sensitive to fluctuations in sea level and the flow of freshwater from inland areas to the coast. This hypothesis is being tested by examining historical hydrological and climatological data and by constructing and testing physically-based hydrology simulation models. The second hypothesis is that there is an unique set of hydrologic conditions that characterize the location of the mangrove/marsh ecotone. This hypothesis is being tested by an interdisciplinary investigation of conditions along several transects spanning the transition from the coast into a freshwater marsh, each of which are subject to different hydrologic endpoints and therefore having different spatial distributions of hydrologic conditions through the ecotone.

Methods

The main thrust of hydrological research so far has been aimed at testing the hypothesis that hydrological conditions characteristic of the mangrove/marsh ecotone are sensitive to fluctuations in sea level and the flow of freshwater from inland areas to the coast. This work is comprised of three major components:

- Analyze the historical record of climate, sea level and hydrology to characterize the variation within each time-series and the cross-correlations between series. Both intra-annual and inter-annual variation are being examined. Significant cross-correlations may be evidence of an underlying physical process at work.

- Construct hydrologic simulation model(s) to relate forcing by climate, sea level and freshwater discharge at the landscape scale to the hydrological signal at the scale of an ecological landscape element. The model(s) will be physically-based and thus represents a hypothesis about the processes chiefly responsible for determining hydrological conditions across the landscape.

- Monitor the hydrologic signal along transects through the transition from the coast into freshwater marshes. This comprises a mesoscale network as there are fewer long-term hydrological monitoring sites than ecological landscape elements. Data collected from this network will be used to test the hydrological model, and they will be used to relate the hydrologic signal to the vegetation in interdisciplinary field studies.

A fourth component is aimed at testing the hypothesis that there is an unique set of hydrologic conditions that characterize the location of the mangrove/marsh ecotone. This is basically a correlative study of hydrologic conditions and species abundance along transects through the mangrove/marsh ecotone. Data collected at mesoscale hydrological monitoring stations will be summarized into a set of candidate indices, such as hydroperiod, range of water level fluctuation, annual mean depths, mean and range of salinity, etc. The assemblage of vegetation will be characterized by data obtained from vegetation plots in the vicinity of the monitoring stations. We will examine the correlation between the hydrological and the vegetative indices for the hydrological indices that correspond most closely to the position of the ecotone, as has been done by in the freshwater marshes. The gradients of hydrologic conditions differ among the transects; therefore failure to find a common set of hydrologic indices characteristic of the ecotone argues for the null hypothesis.

Summary of Results to Date

Historical data

Retrospective analysis has begun on 40 years of monthly data related to the water budget of Shark Slough. These data include evaporation, overland flow, water levels, precipitation and sea level for the South Florida. Both intra-annual variation (i.e. hydroperiod) and inter-annual variation are being examined. From preliminary results, It appears that sea level exerts no influence on hydrology in Shark Slough, even at P35. On the other hand, neither water management nor climate predominate in their influence on hydroperiod, which implies that variability due to climate must be considered in assessing the probable effects of changes in water management.

Hydrological models

Progress in this area has been made on two separate modeling initiatives. The first is a combined surface/groundwater wetland hydrology model, mainly for use in analyzing the long term water balance data from Shark Slough (Nuttle 1993). This model is implemented as a 1-D finite element code with the one dimension oriented along the axis of Shark Slough from Tamiami Trail to the Shark River estuary. The second is FATHOM, a mass balance model of water and salt in Florida Bay, described separately.

Mesoscale hydrological monitoring

Seventeen hydrologic monitoring stations have been installed along four transects spanning the coastal mangrove/marsh complex and terminating in the inland freshwater marshes; Chatham River, Lostmans River, Shark River, and south in the C-111 area bordering on Florida Bay. The monitoring at each site includes depth of surface water, hydraulic head in the surficial aquifer, and salinity in the aquifer, the soil and surface water. These data are recorded electronically in the field and transmitted to the Beard Center by radio telemetry.

Outlook for Remaining Work

This research was initiated as part of the Global Climate Change Research program, which may not survive into the next budget year. It is uncertain at this time whether work on hydrology and climate in the estuarine areas will continue and how it will be supported if it does. Assuming that is does, there are four objectives for further work.

The first objective is to complete the retrospective analysis of historical hydrology data that has started with the Shark Slough water budget. A number of issues must be investigated, for example issues arising from non-guassian distribution of some of the data, before the statistical analysis can be considered complete. Also, it may be of interest to apply the same analysis techniques on the shorter time series in Taylor Slough and along the eastern Park boundary to examine the effects of experimental water deliveries.

The three other objectives relate to detailed, process-level studies to be conducted along the study transects now that the hydrological monitoring stations are in place. We are encouraged by the progress we have made in developing the mass balance model for Florida Bay, FATHOM, and we propose to modify and parameterize this model for the spatially complex estuarine areas along the west coast. Next and related to this objective, we are now beginning a project to collect data on salinity, tidal currents and freshwater discharge along the Shark River/Harney River transect. This effort includes detailed sampling, in conjunction with vegetation studies along a transect through the mangrove/marsh ecotone, for the purpose of investigating fluxes of water and solutes in periodically inundated areas. Finally, we propose to study groundwater flow by using geochemical techniques, including stable isotopes, to delineate flow paths and estimate residence times. This approach can be used to address questions of inter-basin flows between Shark Slough and the headwaters of Taylor Slough, beneath the Rocky Glades, and also to study groundwater discharge into estuarine areas.

Freshwater Flows into East Florida Bay

Eduardo PatinoT, U.S. Geological Survey, 9100 N.W. 36th Street, Suite 107, Miami, FL 33178.

Florida Bay, home to several endangered species, is a valuable breeding ground for marine life and an important recreational and sport fishing area. Florida Bay (fig. 1) encompasses about 850 square miles in total area with an average depth of less than 3.5 feet. It is bordered by the mainland portion of Everglades National Park to the north, the Florida Keys to the east and south, and is open to the Gulf of Mexico to the west. During the last decade, Florida Bay has experienced algal blooms and seagrass die-offs which are signals of ecological deterioration that has been attributed to an increase in salinity and nutrient content of bay water. Salinity and nutrient content are directly related to the amount and quality of freshwater that enters the bay and to flow patterns within the bay. Restoration of the Florida Bay ecosystem requires a better understanding of the linkage between the amount of water and nutrients flowing into the bay and the salinity and quality of the bay environment.

As part of the South Florida Ecosystem Program, the U.S. Geological Survey, in collaboration with Everglades National Park, the U.S. Army Corps of Engineers, and the South Florida Water Management District, is conducting a study to measure flows into east Florida Bay. Information from this study will be used in conjunction with data from other studies to help determine the effects of changes in water deliveries to Everglades National Park on the Florida Bay ecosystem. Flow into Florida Bay is closely related to sediment transport, salinity, and chemical characteristics of the bay, which in turn, determine and interact with biological characteristics. Additionally, freshwater-inflow data will be used as input to hydrodynamic models of Florida Bay, for calibration of hydrologic models of the mainland, and for water-budget determinations for south Florida--all of which are essential elements for resource management and the ecosystem restoration.

Prior to the development of currently available acoustic instruments, it was very difficult to gage flows in streams discharging into Florida Bay. Standard methods for field data collection and flow computations are impractical and inaccurate because of the low velocities, flow reversal, and bi-directional flow in which high-salinity water flows inland under freshwater flowing out to the bay (fig. 2). With today's state-of-the art acoustic instrumentation, such as the Acoustic Velocity Meter (AVM) and the Acoustic Doppler Current Profiler (ADCP), it is possible to accurately gage flows in this environment because of the ability of these instruments to quickly measure low or rapidly changing water velocities, even during stratified or bi-directional flow. AVM systems have proven to be accurate instruments in the measurement of water velocities along a horizontal plane across stream and can be permanently installed to collect continuous velocity data that, along with water-level data, are used to produce continuous records of discharge.

ADCP instruments are used to measure water velocities in three dimensions. These measurements are then used to calculate the total flow through a stream section at a given time. The ADCP uses the Doppler shift from four acoustic beams sent downward in set angles to measure the velocity of water, depth, and distance traveled across the stream transect. Field measurements made with the ADCP's are used to develop relations between AVM velocities and discharge at gaged sites.

With the assistance of Everglades National Park, discharge measurements were made with ADCP's near the mouths of the major streams flowing into Florida Bay. Results of these measurements verified the applicability of ADCP's for discharge measurements under these environmental conditions, provided data on high flows into the bay, and helped in the understanding of flow patterns for each of the measured streams.

Project plans are to instrument selected streams flowing into Florida Bay with AVM's and temperature and specific conductance sensors in order to measure most of the total freshwater flow from the mainland into the bay. Sites are located along the mainland coast of east Florida Bay and represent most of the freshwater flowing south into the bay from Taylor Slough and the C-111 Canal basins. Three of these sites (Trout Creek Canal station and two C-111 Canal stations) are instrumented and maintained by Everglades National Park (fig. 1). Monthly ADCP discharge measurements are planned for rating AVM systems, and monthly collection of water samples are planned for total nutrient analysis. This work will be coordinated with activities from other agencies and institutions who need simultaneous flow data during biological or chemical samplings.

A Comprehensive Groundwater Modeling System for Evaluating the Impacts of the C-111 Canal on Regional Water Resources

David R. Richards, Hsin-chi J. Lin, US Army Engineer Waterways Experiment Station.

Introduction

The Jacksonville District (SAJ) of the US Army Corps of Engineers is interested in studying surface and groundwater hydrology in the area of south Florida affected by the operations of the C-111 drainage canal. The area of interest extends from the Tamiami Canal south to Florida Bay and spanning the entire width of Florida. Water resources in the area consist of coupled surface and groundwater systems that, depending on the hydroperiod, could be dominated by either system individually. There are a wide variety of local concerns that have mutually exclusive interests in the future operations of Corps projects in south Florida, so solutions to the water resources problems will have to be optimized against competing interests. A highly viable means of achieving this goal is the development of a comprehensive modeling system that includes all of the critical hydrologic processes in south Florida.

A multi-year effort is under way to develop such a system for south Florida. The size of the problem is quite large and the complexity of the hydrologic processes are significant. However, a significant amount of work has already been accomplished in the development of the Surface water Modeling System (SMS-formerly FastTABS) and the Groundwater Modeling System (GMS). Each modeling system addresses in great detail the needs of the separate parts of the hydrologic cycle. Indeed, a significant effort was made in their development to ensure that each application used consistent data structures so that the models could be combined or connected at a later data. The C-111 project presents an opportunity to apply all of this technology on a project that requires a thorough modeling effort throughout the hydrologic cycle.

Prototype

Current knowledge of the C-111 region indicates that the hydrologic system is quite complicated with large portions of the water existing in either the surface or groundwater form depending on the hydroperiod. There is also a free exchange of salinity between certain surface and groundwater systems that varies with hydroperiod. As a result, a meaningful application of surface and groundwater models in this region must have flow and salinity transport coupled as it passes between surface and groundwater. Since there are active withdrawals and rediversions by man-made structures and practices, a truly state-of-the-art modeling system is required. Given the geometric and hydrologic complexity of the problem, coupled multi-dimensional models of both surface and groundwater resources are necessary for meaningful tools that will address the important water resource issues.

Comprehensive Modeling Approach

Due to the geographic, climatological, and hydrologic attributes of the C-111 project, each portion of the hydrologic cycle needs to be addressed in the modeling in great detail. At a minimum this requires a system that can route riverine discharges throughout the C-111 canal system, a density-driven hydrodynamic modeling system capable of multi-dimensional riverine and estuarine analysis, and a three-dimensional density driven groundwater modeling system. Additionally, there is a need for specific, intensive field data that will be used in the verification of the surface and groundwater models. This study involves the collection of such data and the verification of the surface and groundwater models.

Groundwater Processes

Groundwater processes in south Florida have a significant impact on regional water resources. When water levels are maintained at lower than historical levels, it is possible to provide the maximum level of flood protection. However, lower groundwater levels can result in large groundwater recharge rates that almost entirely eliminate surface water runoff into estuarine areas such as Florida Bay. This can have significant negative impacts in Florida Bay due to the high evaporation potential. With a large evaporation potential and suppressed freshwater runoff into Florida Bay, it is possible to create hypersalinity problems. Hypersalinity is currently a problem in Florida Bay but it is not yet known how much of this is a natural phenomenon or what impact the management of C-111 has on the degree of the problem. Numerical models of surface and groundwater processes are the most effective means of evaluating if C-111 management strategies can be developed to maintain flood protection and allow sufficient runoff to enter Florida Bay to minimize the hypersalinity problem.

Groundwater Modeling Objective

The objective of the groundwater modeling effort is to create a regional groundwater model that can be used to study various C-111 management strategies. The developed groundwater model will be able to predict regional groundwater flow and salinity transport. The model will be constructed so that all of the major users of water in south Florida (cities, agriculture, the Everglades, etc.) are included.

Groundwater Modeling Approach

A regional groundwater model of south Florida will be constructed using the Department of Defense Groundwater Modeling System (GMS). GMS is the standard groundwater modeling system within the Department of Defense for conducting hazardous and toxic waste contamination investigations associated with the environmental restoration of military bases. As such, the system has a high degree of sophistication for modeling a wide variety of groundwater flow and transport problems. The GMS contains all of the necessary ingredients required to successfully model groundwater in south Florida. These include a comprehensive graphical user interface, a complete database management system for storing and accessing surface and subsurface data, a suite of subsurface conceptualization tools for developing solid models of the stratigraphy, and a variety of flow and transport models with pre- and post-processing capabilities including an extensive suite of visualization tools. While the GMS is available for both personal computers and UNIX workstations, this application will require the use of a fast UNIX workstation.

Based on available surface and subsurface data, a complete hydrogeologic conceptualization of the region will be performed. This will include an analysis of the subsurface stratigraphy, estimation of hydrogeologic parameters, identification of groundwater recharge areas and rates, and an analysis of pumping data from a variety of sources. Once this is completed, a 3-D finite element model (FEMWATER) will be constructed. FEMWATER is a variably-saturated model that includes density-driven (salinity) transport. During this project, FEMWATER will be improved by directly coupling flow and transport between the surface and groundwater. This will be accomplished by accounting for mass transfers of water and salinity between the surface and subsurface within the model. The improved FEMWATER will address the problem frequently encountered in the canals of south Florida where pumped groundwater is used to maintain canal levels which tend to drain back into the aquifers depending on hydrologic conditions. This is an essential feature that is not available in other modeling systems and is required to get accurate answers in this region.

Groundwater Model Coverage

The groundwater model will extend from the Tamiami Canal south including the entire tip of south Florida. This will include both Florida and Biscayne Bays. The Tamiami Canal is identified because it is an area of well documented water levels that can serve as boundary conditions. The mesh will extend offshore to areas where salinity conditions are well known. For the existing and plan conditions, the groundwater model will take salinity boundary conditions from available surface and subsurface data and numerical surface water models.

Surface Water Model Connections

A connection between surface and groundwater models is essential to correctly model South Florida physical processes. This connection will occur in two ways. First, there is a connection between the open coastal areas which will be defined by the surface water models. These models will provide spatially distributed salinity values that will be used as boundary conditions for the groundwater model. Second, the canal areas in the interior of Florida will connect surface and groundwater within the FEMWATER model. In the first case, surface and groundwater models will be run separately but connected through boundary condition passing. In the second case, the interaction will be directly coupled within a single model. At this stage of model development, it is not necessary to directly couple all models in a single model.

Production Runs

Once the groundwater model is verified to the existing conditions, a total of 10 different operational scenarios will be simulated. These may include different meshes for each to test various geometric changes to the canal system including rediversions of C-111 waters. Other simulations could include maintaining different water levels for the purposes of evaluating recharge efficiency and the ability to get freshwater runoff to Florida Bay. Some of the simulations may include projecting impacts from extreme weather conditions on the existing and plan conditions. Likely simulations include long term droughts and extremely wet conditions such as hurricanes.

Hydrodynamic Modeling for Evaluation of the Impacts of the C-111 Canal on Regional Water

Lisa C. Roig, David R. Richards, US Army Engineer Waterways Experiment Station.

Introduction

Hydrodynamic modeling, as it is defined here, is the riverine and estuarine simulation that is important to the management of various surface water systems in south Florida. For the purposes of this project, the dominant concern is Florida Bay. Florida Bay is a shallow, semi-enclosed lagoon system that has an unusual distribution of emergent and partially submerged mudflats, islands, and mangrove swamps. The bay itself is essentially an interconnected assemblage of shallow basins that are connected by narrow navigation passages, and by flow through the mangrove stands and intermittent flow over the mudbanks. Observations of water color and turbidity indicate that the circulation and mixing of water particles in the Bay are complex phenomena. Hydrologic inputs to the Bay such as freshwater releases from C-111 and storm based rainfall events have localized affects that are spatially and temporally heterogeneous. The water column is generally quite shallow and vertically well mixed throughout the Bay. Under unusual circumstances salinity stratification has been observed in some of the basins, but these isolated events probably do not have a major impact on the overall circulation of the Bay.

Objectives

The objectives of this study are 1) to develop a two-dimensional, vertically averaged model of hydrodynamics and salinity transport in Florida Bay; 2) to use the model to understand the impacts of alternative freshwater release scenarios on circulation and salinity distribution in the Bay; and 3) to provide the model data sets and user documentation to local resource agencies for in-house modeling studies.

Technical Approach

To model the effects of alternative freshwater releases on the circulation of Florida Bay, one must resolve the horizontal bathymetry of the basins, the partially submerged mudbanks, the mangrove swamps, and the coastal boundaries. Since the water column is generally well mixed, a two-dimensional, vertically averaged model of circulation in the Bay is adequate to simulate the majority of the hydrodynamic phenomena that have been observed. The equations that describe horizontal circulation and mixing in the Bay are the vertically averaged shallow water equations, the advection-dispersion equation for dissolved salts, and an equation of state relating salinity concentration to fluid density. The model to be used must be capable of resolving the complex horizontal distribution of mudflats, islands, and mangrove swamps that control circulation in the interior of the bay. The model must include an algorithm for describing the flooding and draining of the islands and mudbanks as water levels rise and fall. One modeling system that incorporates these equations and these capabilities is the TABS-MD numerical modeling system that was developed and is maintained by the U. S. Army Corps of Engineers Waterways Experiment Station (WES).

At the heart of the TABS-MD system are the finite element model for two-dimensional, vertically averaged free surface flows known as RMA2 and the finite element model for two-dimensional transport of dissolved constituents known as RMA4. These models were originally developed by Dr. Ian King at Resource Management Associates (RMA) under contract to WES. The models have been maintained and improved by the staff at WES, and are incorporated into the TABS-MD system as RMA2-WES and RMA4-WES. A sophisticated, user friendly, graphical user interface (GUI) known as the Surfaces Water Modeling System or SMS (formerly FastTABS) has been developed at WES to facilitate the pre-processing of input files and the post-processing of model outputs. This GUI allows the user to visualize model results in a variety of ways, including contour maps, vector maps, and animated displays of time dependent solutions. The user documentation and tutorial guides for these models exist and have been extensively field tested

Florida Bay is unusual because the horizontal salinity distribution may have a significant effect on the horizontal circulation in the Bay. Many vertically well-mixed estuaries are strongly driven by tidal forces and wind forces so that the density driven component of the currents is negligible when considering horizontal circulation. RMA2-WES and RMA4-WES have been widely applied to these types of estuaries. Previous versions of these models effectively decoupled the hydrodynamic calculations from the salinity calculations, which did not have any adverse effect on the accuracy of the solution for most vertically well mixed estuaries. Because Florida Bay is expected to have a significant horizontal response to salinity induced density gradients, the algorithm is being modified to couple the salinity calculations with the hydrodynamics.

Simulating the propagation of tides through the mangrove swamps is highly dependent upon the parameterization of the friction terms in the momentum equations. WES has been actively involved in the development of new formulations for frictional resistance to flow through emergent vegetation. To properly simulate the flow through the mangrove stands requires the incorporation of a dynamic friction formulation to replace the usual Mannings relationship. An initial version of this algorithm has been successfully tested in a separate study.

Offshore water level boundary conditions will be supplied by an existing numerical model of the Gulf of Mexico, Caribbean Sea, and Atlantic Ocean. Ultimately, the RMA2-WES model will extend from the west coast of Florida, throughout the Keys and stop north of the C-111 discharge. Up to three freshwater release scenarios will be simulated, including a base condition which will be verified to a data set that is yet to be selected. The simulation period will be on the order of a season (several weeks). The results of the simulations will be documented and the modeling methodology will be fully described.

Visual Mapping of Water Quality in Florida Bay and Adjacent Waters

Bill Sargent, Courtney Westlake, Florida Department of Environmental Protection, Florida Marine Research Institute, Coastal and Marine Resource Assessment Section, 100 Eighth Avenue Southeast, St. Petersburg, Florida 33701-5095, Telephone (813) 896-8626; Dave Eaken, Florida Department of Environmental Protection, Florida Marine Research Institute, South Florida Regional Laboratory, 2796 Overseas Highway, Suite 119, Marathon, Florida 33050-3513, Telephone (305) 289-2330

Since March 1994, we have conducted monthly aerial surveys of Florida Bay and adjacent regions to determine the extent and distribution of turbid or colored waters. The resultant maps are incorporated into an ARC/INFO geographic information system (GIS) for comparative analyses and production of display maps.

Each month observers fly over the study area in a small aircraft. A set of 16 subjective categories is used to identify different types of water masses from each other. As the actual number of differently colored water masses observed at any one time can be immeasurable and the subtle differences which visually distinguish them from each other can be impossible for a human to accurately detect, each color category used on the maps incorporates a broad range of related water types. Because each person has their own interpretation of color and texture, it is difficult to standardize observations based on verbal

descriptions. It is only with experience in the field that the observation team members have been able to standardize this classification. To maintain consistency among surveys the same two main observers are used each month. The observers constantly confer with each other during the survey but record their own individual observations. Water categories are assigned as a consensus among observers during drafting of a master map after each flight. Although this methodology is subjective we believe it is an effective means for obtaining a snapshot of the distribution of water color conditions in the region and portraying these distributions in a readily interpretable manner. The colors depicted on the maps are not the actual water colors observed, but are meant to be a representation of the differences in the water types observed in Florida Bay and the adjacent Keys. The objective of the aerial survey is to map the distribution of visually distinct water masses during a specific instant in time.

The geographic region currently covered by the survey extends from Key Largo southwest to Big Pine Key, including the reef tract south of the Keys, then northward from Big Pine Key to Ponce de Leon Bay, back south to Cape Sable, and east to Barnes Sound. Most of the bays and lakes along the northern shore of Florida Bay, including Lake Ingraham are surveyed. In the future, the survey region might be expanded westward to Key West. This survey expansion will be accompanied by an expansion of a ground truthing effort.

A joint effort between the Florida Marine Research Institute and The Nature Conservancy Bay Watch volunteer program is collecting water samples and performing analyses to determine the composition of the major water masses observed. A series of 6 fixed location stations are sampled during the aerial survey. Up to 24 additional stations are sampled the following day. The locations of these stations are determined based upon locations of water masses of interest. These efforts are discussed elsewhere in these proceedings. Summarized excerpts of these water quality data are incorporated into the GIS for analyses and display on maps produced for public distribution. These data are used in comparative analyses with data from other research efforts being conducted by the Florida Marine Research Institute and discussed elsewhere in these proceedings.

GIS is proving to be an effective mechanism to promote data sharing and the combining of data from different research efforts to allow for investigation of the ecosystem from an integrated perspective. The GIS is also used to mass produce informative maps which are distributed to scientists, resource managers, environmental policy makers and the concerned public on a routine basis. In order to provide the public with information about Florida Bay, the Florida Department of Environmental Protection and The Nature Conservancy Bay Watch volunteer program are collaborating on projects to place long-term displays in public places and provide the news media with appropriate material for incorporation into news stories.

A summarized version of the colored water maps condenses the 16 water categories into five major classifications. The five classifications are; turbid water caused primarily by sediment in the water, turbid water caused by sediment and microalgae in the water, turbid water caused primarily by elevated levels of microalgae in the water, water which is stained brown due to its natural association with nearby wetlands, and water with minimal or background levels of turbidity. These five classifications represent the five major types of water quality situations observed in Florida Bay.

Both the summarized and detailed versions of the maps are made available to all individuals who request them. A mailing list is maintained to automatically provide interested individuals with new monthly maps as soon as they are available.

Hydrogeologic Aspects of Sewage Disposal in the Florida Keys

E. A. Shinn, Christopher D. Reich, Robert B. Halley, USGS, 600 4th Street South St. Petersburg, FL 33701, Ronald S. Reese, USGS, 9100 N.W. 36th Street, Miami, FL 33178.

Quarterly samples of Groundwater from 45 monitoring wells in Pleistocene limestone beneath Florida Bay, the reef tract and on the Keys, was sampled and analyzed quarterly. Well depths range from 5 to 20 m. Nutrients NO2, NO3 and NH4 in the offshore ground water were elevated about 10 times that of sea water and NH4 increased progressively up to 40 times that of seawater under coral reefs 8 to10 km offshore. Salinity, except for shallow wells onshore, ranged from 36 to 42 ppt and the waters were generally anoxic. Onshore ground waters were equally saline except in shallow near-surface wells, where salinity measured 10 ppt or less. Fecal bacteria were identified in saline ground water from both onshore and offshore wells.

Subsurface hydrology is controlled by lithology, buried subaerial unconformities, and by Holocene carbonate mud overlying karstic Pleistocene grainstones and reef deposits. Tidal pumping, sufficient to raise water 20 cm above sea level, suggests leakage of nutrients and bacteria into surface marine waters, especially nearshore where there is no overlying Holocene sediment. Higher sea level in Florida Bay causes ground water to flow through the Keys and likely incorporates nutrients and bacteria from the 30,000 septic-tank drain fields and approximately 700 shallow sewage water injection wells. Because flow is toward the reef tract, both natural and anthropogenic nutrients may cause observed blooms of benthic algae and coral diseases.

A Comparison of Mercury in Estuarine Fish: Indian River Lagoon and Florida

Douglas G. Strom, Gregory A. Graves, Florida Department of Environmental Protection, Southeast District Ambient Water Quality Section, Port St. Lucie, Florida.

Three-hundred sixty seven economically important gamefish were collected from two Florida estuaries: Indian River Lagoon in Martin and St. Lucie Counties and Florida Bay. Fish species collected were spotted seatrout, snook, gray snapper, jack crevalle, mayan cichlid, black drum, gafftopsail catfish, pompano, redfish, sheepshead, southern flounder and spadefish. Mercury tissue analyses were performed on edible filets.

Statistical analysis indicated that location was the most significant factor affecting mercury levels. Several species of fish caught in eastern Florida Bay exhibited an enrichment in mercury with respect to other sample collection areas. a significant portion of the estuarine fish collected in eastern Florida Bay exceed the 1.0 mg-Hg/Kg USFDA "no consumption" health advisory criteria. Mercury levels were especially elevated in jack crevalle from all areas, and in spotted seatrout from northeastern Florida Bay. Estimates of the percentage of fish within an area that may exceed applicable state and federal fish consumption advisory levels are presented.

Current status of project: Final report available November 10, 1995.

Monitoring and Evaluation of Radar Measured Rainfall Estimates Over Florida Bay and the Everglades

Paul T. Willis, NOAA/CIMAS, University of Miami, 4301 Rickenbacker Cswy., Miami, FL 33149.

Objective or Hypothesis

The freshwater input to Florida Bay, directly from precipitation and through flow from precipitation to the north, is a crucial factor in any analysis, or modeling, of the salinity levels in Florida Bay. Because of the convective nature of the rainfall over South Florida, sparse gage measurements only give representative rainfall measurements for long averaging periods -- a month or longer. Any study of shorter time scales requires much higher resolution precipitation measurement. The new digitized and recorded next generation Doppler weather radars (WSR-88D - NEXRAD) at Miami, and eventually Key West, will be capable of producing rainfall estimates over the entire Florida Bay area at a time and spatial resolution not previously possible. The NWS algorithms used to convert radar reflectivity to rainfall rates were developed largely for mid-latitude subtropical regimes, and are not always appropriate for the more tropical rainfall in South Florida.

To fully exploit the the capabilities of the new radars for hydrological purposes over Florida Bay and the Everglades, their rainfall estimation algorithms must be tuned for the tropical South Florida conditions. Despite its tremendous promise estimate of rainfall from radar data is not without problems. Many of these problems can be solved. It is the objective of this research project to tune these algorithms based on existing rain drop size distribution (DSD) data, and on new drop size distribution data collected with aircraft and on the ground in the Florida Bay/Everglades area. The goal is to produce the best possible high resolution radar rainfall product possible for the Florida Bay/ Everglades area for use by all Florida Bay researchers.

Methods and Timing

Funding was received, and this project commenced only in the middle of this September. The following tasks are underway:

NWS radar data are being archived for use and evaluation. Data are being collected for several case studies to evaluate whether the raw radar scan data, or a modified partially processed product is the most appropriate for an accurate Florida Bay rainfall atlas.

Flights will be conducted starting late September to collect airborne rain DSD data for input into a probability matching methodology to estimate rain rate from radar reflectivity measurements.

Existing rain DSD data are being compiled and arrangements are being made to collect surface rain DSD data in the Everglades/Florida Bay area.

The radar rain estimates will be compared and evaluated using all available gage data.

Outlook for Remaining Work

We plan to collect data at the end of this rainy season and concentrate on the transition into next summers rainy season.


Last updated: 07/15/98
by: Monika Gurnée
gurnee@aoml.noaa.gov