Impairment Issues in the Ichetucknee Springs Basin Potential Research Questions and Hypotheses

Transcription

1 Impairment Issues in the Ichetucknee Springs Basin Potential Research Questions and Hypotheses Brian G. Katz U.S. Geological Survey Ichetucknee Springs Research Meeting February 10, 2011

2 Sources of hydrologic information Stream gaging, groundwater level measurements, tracer studies (USGS, SRWMD, UF studies, other agencies) Lake City sprayfield Study (Katz and Griffin, Env. Geol., 2008) Nitrogen mass balance study (Katz and others, JAWRA, 2009)

3 Potentiometric Surface Map of Upper Floridan aquifer and extent of Ichetucknee Springshed (based on 2003 water level data from SRWMD) Direction of ground-water flow (Sepulveda and others, 2006)

4 Land Use in the Ichetucknee Springs Basin Sources of N and P Basin area (224,000 acres) Columbia 227,930 Suwannee 13,595 Baker 3, Land use (%) Forest (52.3) Agriculture (25.0) Urban (12.0) Wetland and Water (8.8) Rangeland (1.6) Atmospheric deposition (rainfall and dryfall) Fertilizers Cropland Lawns Pine stands Septic tanks Animal wastes Treated municipal Wastewater disposal effluent and biosolids

5 Ichetucknee Springs basin Ichetucknee Springs basin Lake City sprayfield Ichetucknee Springs Karst plain Sinking streams Sinkholes Conduit networks

6 Nitrogen in atmospheric deposition Springshed for Ichetucknee Springs LC-DOF CC EXPLANATION Location of atmospheric deposition collector Major roads RAINFALL NO3-N LOADING Springshed boundary Constituents analyzed by USGS laboratory: NO3-N, NH4-N, PO4, Ca, Mg, Na, K, Cl, SO4, TOC Annually, we estimated that about 220,000 pounds (99,980 kg) of N enter ground water from atmospheric deposition KILOGRAMS NITRATE-N Week (March 2006-March 2007) DOF CCITY

7 Itchetucknee Spring Basin Model Grid Cell Size 250 X 250 Meters (155 Rows X 157 Columns) Model grid overlain on land use coverage to calculate N and P loading in each cell MILES KILOMETERS $

8 Nitrogen inputs to groundwater and export in springs

9 Spring water discharge and nitrate-n concentrations Discharge, ft 3 /s NO 3 -N, mg/l Spring Name Ichetucknee Head Cedar Head Blue Hole Devil's Eye Mill Pond Mission

10 Estimated Nitrogen Loading to Groundwater, Ichetucknee Springs Basin Minimum fraction leaching to ground water Maximum fraction leaching to ground water Source Atmospheric Deposition Fertilized Cropland Fertilized Yards Fertilized pine stands Sprayfield Biosolids Animal wastes Septic tanks (From Katz et al., 2009) ** These estimated percentages are based on arbitrary leaching rates to groundwater and other assumptions

11 Variable sources of Nitrate-N throughout springs basin 15 Delta N-NO 3, per mil CCESW Sprayfield Effluent Reservoir Devil s MB-1 Eye Spg Blue Hole MPS MS IHS CHS Nitrate associated with waste disposal or manure spreading Nitrate-N, milligrams per liter May-2005 Oct-2005 Jan-2007 MW-7 Nitrate associated with synthetic fertilizer But, most springs in the Park have a nitrogen isotope signature indicating a fertilizer source of N

12 Increased vulnerability of aquifer to contamination from closed depressions and sinkholes Total area of closed depressions represents 11% of total basin area Digitized from 1:24,000 topographic maps

13 Vulnerability to Contamination LOW LOW MEDIUM MEDIUM HIGH N load = 0 EXPLANATION 1.6 Kilometer radius Spring Basin Boundary Fertilizer nitrogen input to surface, kilograms per hectare N load > 0 and <= 34, no closed depressions N load > 34, no closed depressions N load > 0 and <= 34, closed depressions N load > 34, closed depressions Vulnerability of springs to nitrate contamination from fertilizers applied to cropland and pine stands in Ichetucknee Springs basin

14 Nitrate-N concentrations in groundwater, springs, and surface water, Ichetucknee Springs basin (From Harrington and others, 2010)

15 Conclusions Fertilizers contribute over 50% of the nitrogen load to ground water in the Ichetucknee springs basin; this is consistent with nitrogen isotope data for spring waters Possible decreases in nitrate concentrations in spring waters may not track reductions in N loading due to long ground-water residence times (20-30 years) and continual release of N from storage in the unsaturated zone. Areas most vulnerable to nitrate contamination of ground water are located in closed depressions containing sinkholes in the lower part of basin.

16 Caveats and uncertainties: Land use data were used from early 1990 s s and need updating N loads from fertilizers were based on recommended IFAS fertilizer application rates for cropland, yards, and pine stands, that may differ from actual rates N loading from manure needs to be updated with current animal population data Amount of nitrogen stored in unsaturated zone beneath various land uses needs to be quantified. Denitrification in the Upper Florida Aquifer was assumed to be minimal

17 Research Issues Refine loading estimates to ground water using most recent land use information and more precise information on fertilizer application rates Determine the amount of nitrate (N) stored in the unsaturated zone beneath fertilized cropland and pine stands, animal grazing fields, and waste disposal sites (septic tanks and STP effluent). Determine the extent of denitrification occurring in the subsurface in various parts of the springshed. Assess how future changes in land use in the basin may impact springs

18 Questions?? Contact Information: Brian G. Katz, PhD U.S. Geological Survey 2639 North Monroe St. Tallahassee, FL Ichetucknee Trace Katz, B.G., Sepulveda, A.A., and Verdi, R.J., Estimating nitrogen loading to ground water and assessing vulnerability to nitrate contamination in a large karstic springs basin, Florida. Journal of the American Water Resources Association, v. 46, pp Enhanced elevation map of Ichetucknee Springs basin showing Ichetucknee trace