Groundwater-Surface Water Interactions and Relation to Water Quality in the Everglades

Project Proposal for 1998

Program: FRAGILE ENVIRONMENTS
Project Title: Groundwater-Surface Water Exchange Fluxes and Relation to Nutrient and Mercury Cycling in the Everglades
Location of Study Area: Everglades Nutrient Removal Area (ENR) in Palm Beach County, Water Conservation Areas 2A, 2B, and 3A (WCA's) in Broward County, and reconnaissance in Southern Inland Coastal System in Dade County.
Project Start Date: FY 1996
Project End Date: FY2000
Project Number: 4384-17800 and 4384-16700
Project Chief: Judson Harvey
Region/Division/Team/Section: Northeastern/WRD/Branch of Regional Research/Surface Water Hydrology
E-mail:jwharvey@usgs.gov
Phone: 703-648-5876
Fax: 703-648-5484
Mailing Address:
USGS
430 National Center
Reston, Virginia 20192
Program Element(s)/Task(s)
Element 3, task 3.7 (75%), Element 1 (25%)
Panel: N/A
Collaborators, Clients:
South Florida Water Management District:
(1) Resource Assessment Division/Mercury Flux Project/ Larry Fink (project chief). This project is charged with determining the fate of mercury in the Everglades Nutrient Removal Area (ENR). The ENR is a prototype for seven very large constructed wetlands called Stormwater Treatment Areas that receive runoff from the Everglades Agricultural Area (EAA). Data from WCA-2a provide other critical evaluation and planning information because the eutrophied area in WCA-2a is at least a decade older than the ENR, and because relatively unimpacted areas without agricultural nutrients exist in WCA-2a. Uncertainty in surface-subsurface exchange fluxes in ENR led to contract C-6661, which funds approximately two thirds of the present USGS project. The Resource Assessment Division also supplies substantial logistical support primarily through the arrangement of transportation by airboats and helicopters to project sites.

(2) Hydrogeology Division/Mercury Flux Project/Steve Krupa (co-project investigator with Jud Harvey). This division has assigned a senior hydrogeologist (Krupa) for 60% time to co-manage the planning/installation/data collection and interpretation of groundwater hydrology at ENR and WCA-2a to support the mercury flux project described in (1).

(3) Everglades Systems Research Division/ Nutrient Flux in ENR/Michael Chimney (project chief). Like the mercury flux project this project relies on accurate water balance at ENR and WCA-2a to evaluate the fate of nutrients in the ENR and the likely fate of nutrients in Stormwater Treatment Areas.

BACKGROUND NARRATIVES

Project Summary: Knowledge about the magnitude and direction of hydrologic exchange between surface water and groundwater is critical to understanding the fate of excess nutrients and mercury in the Everglades. At present there are few reliable estimates of exchange fluxes between groundwater and surface water in the Everglades. This gap in hydrological investigations not only leaves the water balance uncertain, it also hampers progress in determining chemical sources, chemical residence times, and chemical fates at several primary research settings (Everglades Nutrient Removal Area, Water Conservation Area 2A) where the role of nutrients and mercury in altering the Everglades ecosystem is now being investigated. The overall aim of this project is to determine exchange fluxes between groundwater and surface water, to determine changes in water quality that have resulted from surface-groundwater exchange, and to relate those changes to past, present, and proposed management of surface water-levels and surface water flows in the Everglades.

Project Justification: This project is providing critical information for improving our understanding of water and chemical balances in the Everglades and their relation to surface-groundwater exchange and surface-water management policies. Questions about the magnitude of surface-groundwater exchange and its effects on nutrient and mercury budgets are being addressed at the Everglades Nutrient Removal Area (ENR) and in Water Conservation Area 2a (WCA-2a). Results are being used to refine water and chemical mass balances at those sites, and to relate those results to factors that are unmanageable (climate, hydrogeologic properties, groundwater chemistry) and factors that possibly can be managed (surface-water levels in canals and interior wetlands) to improve surface water quality. In addition to addressing problems of immediate concern in the northern Everglades, this project is providing the basis for improved hydrologic studies in the central and southern inland Everglades systems, including the use of seepage meters in a USGS-Miami cooperative study at the L-30 levee in the USGS Miami subdistrict office. In FY97 this project expanded its effort to include sites in the central Everglades in WCA-2b and WCA-3a. In FY98 a further expansion into Taylor Slough is planned.

Project Objectives: The specific aims of this project are (1) develop and test measurement systems to obtain site-specific estimates of vertical hydrologic exchange between groundwater and surface water, (2) refine spatially-averaged water balances and chemical mass balances to reflect improved estimation of groundwater-surface water exchange, (3) use results to refine chemical mass balances of nutrients and mercury in the ENR and in WCA-2a, (4) identify relative importance of factors that influence vertical exchange fluxes of water and nutrients and mercury (factors include hydrogeologic characteristics, climatology and regional water balance, and management of water levels in canals and water conservation areas) and (5) extend studies to characterize vertical exchange of groundwater and surface water in the central and southern inland Everglades systems.

Overall Strategy, Study Design, and Planned Major Products: A combined water balance and tracer methodology is used to determine vertical exchange of water and solute at research sites in the Everglades system. The initial research in 1996/97 began at fourteen sites in the Everglades Nutrient Removal Area (ENR) and at seven sites in the eastern portion of Water Conservation Area 2A (WCA-2a). Fieldwork was expanded in 1997 to include a single site in WCA-2b and a single site in WCA-3a. Beginning in FY98 additional work will be undertaken in Taylor Slough. The design of the study includes the following benchmarks; 1) establishing interior wetland research sites on transects in ENR and WCA-2a where measurements of hydraulic properties, hydraulic gradients, and site-specific surface-subsurface fluxes are being made, 2) using site-specific flux estimates to refine area-averaged water and chemical mass balance models in ENR and WCA-2a, 3) using chemical tracers to further reduce uncertainties in area-averaged chemical mass balance models in ENR and WCA-2a, and 4) establishing a relation between surface-subsurface exchange fluxes (and resulting water quality in groundwater and surface water) to past and current water-level management strategies. Planned products include 4 USGS/SFWMD reports, and 3 journal papers.

WORK PLAN

Overall:
SCOPE: The locations of research sites are shown in Figure 1. Estimates of surface-subsurface exchange fluxes and subsurface hydraulic properties are being made on two transects across the Everglades Nutrient Removal Area (ENR) project area and on two transects in Water Conservation Area 2a (WCA-2a). In total, eleven interior wetland research sites have been established at ENR and six interior research sites have been established at WCA-2a (Figures 2 and 3). In FY97 a single site was instrumented with seepage meters in WCA-2b and WC-3a -- research wells will eventually also be installed at those sites. In FY98 several sites will also be established in Taylor Slough.

INSTRUMENTATION AND DATA COLLECTION SCHEDULES: At each research site two to four research wells (piezometers), two seepage meters, and I surface water level recorder and staff gage have been installed at the location of a preexisting research platform (sites of past and ongoing nutrient and mercury research) or in some cases new sites have been established for mercury research in areas with high surface-subsurface exchange fluxes. Monitoring of water levels in surface water and in wells is continuous. Surface water quality is analyzed biweekly in the ENR and monthly in WCA-2a. Groundwater and wetland porewater chemistry is determined seasonally. Wells and water quality monitoring are also undertaken in wells and in surface waters on either side of three new levee sites at ENR and one new levee site at WCA-2a. Determinations of surface-subsurface water exchange will be made quarterly (or more often if necessary). Comprehensive chemical sampling began after research wells were installed in ENR and WCA-2a and will continue on a quarterly or semi-annual basis until completion of the project.

METHODS/APPROACH: Site-specific measurements of surface-subsurface water exchange will be made using seepage meters (at flooded sites) and by modeling chemical profiles in porewater. The purpose of combining hydraulic and chemical methods is to reduce overall uncertainty in flux estimates, and to identify the best single method to be used at additional sites at southern sites in the Everglades. Hydraulic conductivity in the surficial aquifer system will be estimated from slug test analyses. Vertical hydraulic conductivity of the restricting layer at the top of the surficial aquifer system will be calculated from measured hydraulic head gradients and estimated seepage fluxes.

Area-averaged estimates of exchange between surface water and groundwater (e.g. averaged within ENR cells or ENR project as a whole, and in north, central and south sections of WCA-2a) will be calculated independently from site specific estimates by making use of surface water flows, levels, precipitation and evapotranspiration data, and using new environmental tracer data collected in wells and surface water. The tracers that are currently being tested include chloride, other major cations and anions, radioisotopes in the uranium decay series, stable isotopes of oxygen and hydrogen in water (earlier we determined that water temperature measurements were not sufficiently sensitive to the relatively low vertical seepage fluxes to be a practical tracer). The possibility of using age-dating in groundwater (tritium, chloroflurocarbons, tritium-helium rations, etc.) is also being explored beginning in the summer of 1997.

Once site-specific and area-averaged water and mass balances have been quantified with the maximum possible reliability, the objective is to establish a relation between surface-subsurface exchange fluxes (and resulting water quality in groundwater and surface water) to past and current water-level management strategies. A statistical relation between those variables can only be developed for the relatively short period of record of this study; that period may be too short to establish statistically significant trends. Use of the extensive data collected in this study in close cooperation with groundwater flow modelers at SFWMD will be the approach used to determine relationships between surface-subsurface water fluxes and past, present, and future management of surface-water levels. Those relationships will then be used as input to drive chemical mass balance modeling scenarios to examine effects of management decisions in the restoration process on water quality in surface water and ground water.

Timeline:

FY1996/97:
96/97 Major Tasks Including Fieldwork/Analysis:
Finalize study design and finish installing well and porewater sampling equipment in ENR and WCA-2a, complete testing of equipment, begin estimating hydraulic properties by slug tests, 3) begin continuous monitoring of water levels and hydraulic head, begin chemical sampling. Refine seepage-meter and porewater chemical modeling methods to estimate site-specific surface- subsurface exchange, determine limit of detection for estimating surface-subsurface exchange fluxes by these two site-specific methods (seepage meters and porewater chemical modeling), assess evidence for temporal trends in surface-subsurface exchange fluxes at research sites and adjust sampling schedules if necessary, initiate chemical sampling and large-scale chemical mass balance modeling.
96/97 Deliverables:
Complete 1 fact sheet, 1 abstract/oral presentation at a national meeting (American Chemical Society), two poster presentations at annual meetings of USGS South Florida Studies program, metadata describing measurement locations and data types for inclusion in USGS project data base.

FY1998:
1998 Major Tasks Including Field work/Analysis:
Continue monitoring hydrologic fluxes and chemistry at established research sites in ENR, WCA- 2A, 2b, and 3a. Expand activities to include reconnaissance in Taylor Slough.
1998 Deliverables:
Present results at national meeting, publish 2 reports and submit 1 journal article outlining instrumentation, methods, QA/QC, and initial results. The first report covers research well construction details, basic lithological and geophysical data and their interpretation, and hydraulic conductivity estimates from slug tests for use by other researchers. The second report covers methods to estimate site-specific exchange fluxes between groundwater and surface water using seepage meters and chemical profile modeling and provides water flux and chemical data for use by other researchers. The journal article presents spatial and temporal variability in hydraulic heads (that drive surface-subsurface exchange), the relation of hydraulic gradients to surface water level management strategies, and resulting effects on surface-subsurface fluxes.

FY1999:
1999 Major Tasks Including Fieldwork/Analysis:
Complete measurements in ENR, WCA-2a, 2b, and 3a. Shift focus to field activities, acquisition of past and present flow, level, water balance, and water quality data sets in Taylor Slough, and modeling in Taylor Slough.
1999 Deliverables:
Publish 1 fact sheet and submit 1 journal article on water and chemical mass balance modeling in ENR and WCA-2a, emphasizing (1) the role of surface-subsurface water exchange and the influence of managed surface water levels in enhancing surface-subsurface exchange, and (2) the effect of surface-subsurface exchange fluxes on chemical water quality.

FY2000:
2000 Major Tasks Including Fieldwork/Analysis:
Continue field effort and intensify data acquisition and modeling effort in Taylor Slough. Emphasize development and application of a transient mass balance model for water flow and chemical transport in groundwater and surface water. This model represents a logical extension of mass balance model developed to analyze ENR and WCA-2a data. The model will be used to assess the probable effects of increased restorative flows on water quality in Taylor Slough.
2000 Deliverables:
Publish 1 report and submit 1 journal article on the mass-balance model documentation and its application in Taylor Slough.

Planned Deliverables/Products: Planned products include 4 USGS/SFWMD reports, 3 journal papers, as well as involvement in publications that result from cooperation with colleagues in the Mercury/Water Quality group. Already I am collecting or helping to collect (by providing instrumentation) major cation and anion data and water stable isotope data from peat porewaters in ENR and WCA-2a (with Reddy/Aiken), mercury samples from deep porewaters at ENR (with King/Krabbenhoft), sulfate and uranium isotopic samples from peat porewater and groundwater (with Orem/Bates/Zelinski), CFC's, tritium, and dissolved gas sampling in groundwaters in ENR and WCA-2a (with Bohlke), and assessment of the value of remote imagery in quantifying width and depth cross-sections of surface flow, assessing surface water flow paths and/or defining localized areas of groundwater inflow based on remote imaging of wetland water surface temperatures (with Desmond). I will also be making project information available to other interested researchers through outlets such as the USGS South Florida digital data base.

Planned Outreach Activities: Collaborations with USGS researchers not included in the budget are noted above. At SFWMD I am collaborating with the Resource Assessment Division (Larry Fink) and with the Hydrogeology Division (Steve Krupa). These groups are charged with quantifying the water and chemical mass balances at the ENR project as a means to predict the performance of planned Stormwater Treatment Areas. More detail on cooperator partnerships is outlined 2 sections ahead.

Prior Accomplishments in Proposed Area of Work: N/A

New Directions, Expansion of Continuing Project (if applicable): Continuation in 1999 and 2000 involves transfer of successful techniques, data analyses, and modeling to Taylor Slough area to assess the effect of increased flows following restoration efforts on long term water quality changes in Taylor Slough. My project will have a field component in Taylor Slough (site-specific measurements of surface-subsurface water exchange) which will be smaller and more focussed than the studies in ENR and in WCA-2a. The effort in Taylor Slough will emphasize the analysis of past and present data water balance and water quality data records and organization of those data in a transient, coupled surface-subsurface transport model. This effort will extend capabilities of the mass-balance model originally developed for ENR and WCA-2a and will apply the extended model to assess probable water quality changes to be expected in Taylor Slough as a result of restoration efforts. The resulting model will be fully documented as a model that can easily be transferred to other wetland systems in future studies in the Everglades or elsewhere.

ACCOMPLISHMENTS, OUTCOMES, PRODUCTS, OUTREACH

Accomplishments and Outcomes, Including Outreach:
The most significant accomplishment in FY97 was completing the emplacement of research wells at 11 research sites in the ENR and 6 sites in WCA-2a (research well sites are co-located with this projects seepage meters and SFWMD/USGS ecology and geochemical sites where research platforms, seepage meters, water level recorders, and data logging instrumentation are already installed) . These wells were deemed indispensable to project success in early in 1996 but emplacement was delayed due to extreme difficulties and high costs of working at remote sites in the Everglades interior. The work was eventually completed at minimal cost to USGS through a pooling of resources between this project and several closely related projects at SFWMD. Gene Shinn in Geologic Division was a key contributor who made drilling possible in remote sites in Water Conservation Area 2A.

Research wells have already demonstrated that significant driving forces for vertical exchange of groundwater and surface water exist far away from levees, a first-time observation in the northern Everglades where groundwater and surface water have traditionally been assumed to be decoupled except near canals.

An additional accomplishment in FY97 was the successful adaptation of the seepage meter approach for use in the Everglades. The problem is estimating vertical fluxes of water in areas where hydraulic gradients indicate a potential for exchange. Using values of hydraulic conductivity derived fro slug tests in a computation using Darcy's Law is provides an estimate with orders of magnitude uncertainty. We also tested other several candidate approaches that rely on tracers, modeling chemical and temperature profiles which also provided fluxes with high uncertainty. Seepage meters required considerable development time but provided useful, repeatable measurements with acceptable uncertainty. Results indicate that exchange fluxes are as high a 20 centimeters/day in some areas, which is almost two orders of magnitude higher than annually averaged precipitation and evapotranspiration. Already this project assisted a cooperative project in the USGS Miami subdistrict by making available the meters and personnel to collect seepage data on a transect parallel to the L-30 levee in Water Conservation Area 3.

The preliminary results of our study indicate that (1) significant hydraulic forces exist to drive surface-groundwater exchange in the Everglades, (2) hydraulic forces that drive vertical exchange vary both in space and time -- spatial variation dominates at ENR whereas temporal variation is dominant in WCA-2a -- thus the proximity to canals where surface-water levels are stabilized by management appears to be important, (3) resulting vertical exchange of groundwater and surface water has substantially affected water quality in both surface water and groundwater, and (4) overall the management of surface-water levels in canals and in conservation areas appears to be enhancing surface-groundwater exchange.

Deliverables, Products Completed:
Harvey, J.W., Vertical Exchange of Ground Water and Surface Water in the Florida Everglades. U.S. Geological Survey Fact Sheet FS-169-96

Harvey, JW., Krupa, S., Mooney, R., and Fink, L., Vertical exchange between groundwater and surface water in the Florida Everglades, poster presentation at 1st Annual Meeting of USGS Investigators in the South Florida Environments Program, July 3 1 - August 2, 1996, West Palm Beach.

Harvey, J.W., Krupa, S., and Fink, L., Hydrologic exchange between groundwater and surface water in the northern Everglades, abstract number 63, Geochemistry Division, American Chemical Society, Annual Meeting, August 25-29, 1996, Orlando.

Harvey, JW., Krupa, S., and Mooney, R., Spatial and seasonal variation in surface-groundwater exchange in the northern Everglades, presentation for 2nd Annual Meeting of USGS Investigators in the South Florida Ecosystems Program, August 25-28, 1997, Fort Lauderdale.

NEEDS

Required Expertise:
FY 1998
senior hydrologist
physical science technician
eco intern contract employee
physical science aid (summer)

FY 1999
senior hydrologist
physical scientist technician
eco intern contract employee
physical science aid (summer)

FY2000
senior hydrologist
eco intern contract employee
physical science aid (summer)

Names of Key Project Staff:
FY 1998
Judson Harvey, WRD, Reston
Robert Mooney, WRD, Miami
Cynthia Greenlaw, eco contract employee, West Palm Beach
Jonah Jackson, summer student, Reston

FY 1999
Judson Harvey, WRD, Reston
Robert Mooney, WRD, Miami
Cynthia Greenlaw, eco contract employee, West Palm Beach
Jonah Jackson, summer student, Reston

FY2000
Judson Harvey, WRD, Reston
Cynthia Greenlaw, eco contract employee, West Palm Beach
Jonah Jackson, summer student, Reston

Major Equipment/Facility Needs: None. Major equipment for the project was purchased by SFWMD.

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