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

photo of scientists and equipment in the field
Project Investigator: Judson Harvey

Project Personnel: Jim Krest, Jessica Thomas Newlin, Eric Lerch, Jungyill Choi, David P. Krabbenhoft, Steven L. Krupa, Chris Langevin, William H. Orem, Mike Reddy, James E. Saiers

Project Start Date: 1995 End Date: 2003


The objective of this project is to quantify hydrologic exchange fluxes between groundwater and surface water and its effects on transport of contaminants in the Everglades.

For more information, please see the Tides and Inflows in the Mangrove Ecotone (TIME) Model Development Project Webpage.

At present there are few reliable estimates of hydrologic fluxes between groundwater and surface water in the Everglades. This gap in hydrological investigations not only leaves the water budget of the Everglades uncertain, it also hampers progress in understanding the processes that determine mobility and transformation of contaminants, such as mercury, sulfate and nutrients. The objective of this project is to quantify hydrologic exchange fluxes between groundwater and surface water and its effects on transport of contaminants in the Everglades. The research furthermore relates surface water and ground-water interactions to past, present, and proposed management of surface-water levels and flows in the Everglades. The specific research sites are the Everglades Nutrient Removal Project (ENRP), Water Conservation Area 2A (WCA-2A), and Everglades National Park. Results are being used to estimate contributions from ground-water discharge to surface flow, and to identify sources and fate of contaminants in the Everglades.

Key Findings of Phase I Research:

  1. Water management has increased recharge and discharge in the north-central Everglades above pre-drainage conditions. Recharge from surface water to groundwater in the Everglades Nutrient Removal Project (ENRP) accounted for 31% of the water pumped into ENR for treatment during the years 1994 - 1998. Recharge varied over time by about a factor of 2 and was positively correlated with the surface water level and the rate of pumping of surface water into ENRP. Groundwater discharge into ENRP was a much smaller proportion of surface water inflow (2.8 % compared with 31% for recharge). We used two independent approaches - a water/chloride mass-balance approach and seepage-meters. Those approaches produced self-consistent results that differed from previous estimates by other researchers. Our recharge and discharge estimates (published in Wetlands, 20(3): 500-511) are being used by the SFWMD to compute final nutrient budgets for ENRP (contacts: Mike Chimney and Martha Nungasser - SFWMD). Our data and methodologies are also being used by consultants Robert Kadlec and D.B. Associates in their reassessment of Stormwater Treatment Areas (STA) design.
  2. Mercury is being recharged from surface water to groundwater and stored in the Surficial aquifer. We determined that recharging water in ENRP is transporting total dissolved mercury downward through peat into the Surficial aquifer. 10% of the mercury entering ENRP by pumping of surface water and atmospheric deposition is recharged to the underlying aquifer. In contrast, the mercury that eventually discharges to the seepage canal (a perimeter canal separating ENRP from agricultural areas) equals only 2.8% of the total mercury input to ENRP. We conclude that recharged mercury is being stored in the aquifer as a result of hydrological and biogeochemical processes. How long mercury (and other contaminants such as phosphate) will be stored in the Surficial aquifer is currently unknown. Further research is necessary because the timescale of storage has important implications for managing the Stormwater Treatment Areas (STA's) and the Water Conservation Areas (WCA's). Results described above are posted on the SOFIA web site in the form of poster presentations and data reports. The work has also been presented in invited talks at the Society of Wetland Scientists and Geological Society of America. Written reports are being prepared for journals and a circular about water quality in the Everglades.
  3. Ungaged freshwater flows discharging from groundwater into Taylor Slough were quantified for the first time. We used chloride and radium as environmental tracers to detect shallow groundwater discharge into Taylor Slough. The ultimate source of water is recharge on the Pine Islands of the Rocky Glades to the north and west of Taylor Slough. Fresh groundwater discharge was found to augment surface flow in Taylor Slough by approximately one-third in both wet and dry seasons. Our estimate of groundwater discharge into Taylor Slough is important because it represents a significant contribution to freshwater flow affecting the ecology of eastern Florida Bay and because it was previously ungaged. Our estimates were used as a basis for calibrating the SICS hydrology model (contacts: Eric Swain, USGS, Miami) and will also be used for comparison with extended modeling of the SICS area using the TIME model that incorporates a full groundwater model (contact: Chris Langevin, USGS, Miami). Our results were published as part of the 2000 GEER proceedings (USGS OFR 00-449) and in a poster presentation on the SOFIA site. The data were published in USGS OFR 00-483.
  4. Significant recharge and discharge occurs by vertical flow through Everglades peat in areas that are far from boundaries with levees and canals. Our research has shown that vertical water fluxes passing through peat are a significant component of Everglades water budgets, accounting for fluxes that are between 10 and 30 percent of surface water fluxes through the wetlands. This finding is counter to previous ideas that Everglades peat was essentially impermeable and that the hydraulic driving forces were too small to cause recharge and discharge except in the vicinity of levees and canals. A new method for quantifying recharge and discharge through peat is under development by Jim Krest. The method uses inverse modeling to match measurements of the natural activity of Ra-223 and Ra-224 in vertical profiles in peat pore water. This technique provides two independent determinations of the vertical exchange rate, and promises to be useful for obtaining high-quality estimates of vertical exchange rates in the Florida Everglades and elsewhere. Our results are currently documented in fact sheets, poster presentations, USGS reports, and as data available on the SOFIA web site. Results above are documented in abstracts and poster presentations and are being prepared for publication in journals.
  5. Discharge of deep groundwater from relict seawater origin beneath WCAs cannot explain the contaminant-level concentrations of sulfate in Water Conservation Areas. In the past our colleague Bill Orem (USGS-GD) speculated that the contaminant-level concentrations of sulfate in the central Everglades wetlands originate in the canals and fields of agricultural areas to the northwest of the present-day Everglades. Our groundwater investigations had also suggested the possibility that discharge of relict saltwater from lower layers of the Surficial aquifer was contributing to high levels of sulfate in Everglades wetlands. Through collaborative research we evaluated groundwater contributions of sulfur more carefully, concluding that groundwater discharge from the directly beneath the Water Conservation areas is not the source of excess sulfate in the WCAs. Results of our collaborative effort are in press at the Journal of Environmental Quality, as well as in USGS OFR 01-7, and in a chapter on sulfur for a circular about water quality in the Everglades (contacts: Bill Orem, USGS, Reston, VA and Dave Krabbenhoft, USGS, Middleton, WI).

Past Project Personnel

  • Eric Nemeth, Eco-associate
  • Katherine Randle, student
  • Jungyill Choi, post doctoral associate, 1999-2001, now at S.S. Papadopulos and Associates, Bethesda, MD
  • Bob Mooney, research associate, 1996-1998, now at USGS, Miami, FL
  • Jonah Jackson, Eco-associate, 1999-2000, now at Camp Dresser and McKee, Chantilly, VA
  • Cynthia Gefvert, Eco-associate, 1997-1999, now at SFWMD, West Palm Beach, FL


Work Plans

Project Summaries


Data Sets from the SOFIA Data Exchange Page

(Includes supplemental information such as data, metadata, methodology, and site listing)

Data Sets from Publications and Other Websites





Fact Sheets

Interpretive Reports and Journal Papers

Journal Articles

Open File Reports


Scientific Investigations Reports

Water Resources Investigations Reports


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Script last updated: 23 October 2018 @ 12:03 PM by THF. Record creator: BJM. Record last updated by: LJT.