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
Sources of hydrologic information
Stream gaging,
gaging, groundwater
groundwater level
level
ƒƒ Stream
measurements, tracer
tracer studies
studies
measurements,
(USGS, SRWMD,
SRWMD, UF
UF studies,
studies, other
other agencies)
agencies)
(USGS,
Lake City
City sprayfield
sprayfield Study
Study
ƒƒ Lake
(Katz and
and Griffin,
Griffin, Env.
Env. Geol.,
Geol., 2008)
2008)
(Katz
Nitrogen mass
mass balance
balance study
study
ƒƒ Nitrogen
(Katz and
and others,
others, JAWRA,
JAWRA, 2009)
2009)
(Katz
Potentiometric
Surface
Map of Upper
Floridan
aquifer
and extent of
Ichetucknee
Springshed
(based on 2003
water level data from
SRWMD)
(Sepulveda and
others, 2006)
Direction of ground-water flow
Land Use in the Ichetucknee Springs Basin
Sources of N and P
• Atmospheric deposition
(rainfall and dryfall)
• Fertilizers
• Cropland
• Lawns
• Pine stands
• Septic tanks
• Animal wastes
Basin area (224,000 acres)
Columbia 227,930
Suwannee 13,595
Baker
3,820
1995 Land use (%)
Forest (52.3)
Agriculture (25.0)
Urban (12.0)
Wetland and Water (8.8)
Rangeland (1.6)
• Treated municipal
Wastewater disposal—effluent
and biosolids
Ichetucknee Springs basin
ƒ
Ichetucknee
Springs
basin
Lake City
sprayfield
Ichetucknee
Springs
Karst plain
• Sinking streams
• Sinkholes
• Conduit
networks
Nitrogen in atmospheric deposition
82 45
82 30
30 15
LC-DOF
Springshed for
Ichetucknee
Springs
30 00
CC
EXPLANATION
Location of atmospheric
deposition collector
RAINFALL NO3-N LOADING
Major roads
Springshed boundary
20000
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
18000
DOF
CCITY
16000
14000
12000
10000
8000
6000
4000
2000
0
0
5
10
15
Week (March 2006-March 2007)
20
25
Itchetucknee Spring Basin Model Grid
Cell Size 250 X 250 Meters
(155 Rows X 157 Columns)
0
0
5
5
10
10
KILOMETERS
MILES
Model grid
overlain
on land use
coverage to
calculate
N and P
loading in
each cell
$
Nitrogen inputs to groundwater
and export in springs
Spring water discharge and nitrate-N concentrations
Discharge, NO3-N,
Spring Name
ft3/s
mg/L
Ichetucknee
Head
65.2
0.83
Cedar Head
8.66
0.87
Blue Hole
143
0.76
Devil's Eye
82.7
0.59
Mill Pond
47.9
0.61
Mission
28.8
0.52
Estimated Nitrogen Loading to
Groundwater, Ichetucknee Springs Basin
Source
Atmospheric Deposition
Fertilized Cropland
Fertilized Yards
Fertilized pine stands
Sprayfield
Biosolids
Animal wastes
Septic tanks
Minimum Maximum
fraction
fraction
leaching to leaching to
ground
ground
water
water
0.05
0.30
0.10
0.50
0.10
0.50
0.10
0.50
0.10
0.50
0.20
0.30
0.10
0.60
0.20
0.70
(From Katz et al., 2009)
** These estimated
percentages are based
on arbitrary leaching
rates to groundwater
and other assumptions
Variable sources of Nitrate-N
throughout springs basin
15
Delta N-NO3, per mil
30
Sprayfield
Effluent
Reservoir
20
Nitrate associated with
waste disposal or
manure spreading
CCESW
MW-7
MB-1
Devil’s
Eye Spg
Blue
Hole
MPS
MS
IHS CHS
10
But,
most springs
in the Park
have a
nitrogen
isotope
signature
indicating a
fertilizer
source of N
May-2005
Oct-2005
Jan-2007
Nitrate associated with
synthetic fertilizer
0
0
0.5
1
1.5
Nitrate-N, milligrams per liter
2
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
82 30 00
82 45 00
30 15 00
30 00 00
EXPLANATION
1.6 Kilometer radius
Spring Basin Boundary
Vulnerability
to Contamination
LOW
LOW
MEDIUM
MEDIUM
HIGH
Fertilizer nitrogen input to surface,
kilograms per hectare
N load = 0
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
Nitrate-N
concentrations
in groundwater,
springs, and
surface water,
Ichetucknee Springs
basin
(From Harrington and others, 2010)
Conclusions
¾ 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
¾ 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.
¾ Areas most vulnerable to nitrate contamination
of ground water are located in closed depressions
containing sinkholes in the lower part of basin.
Caveats and uncertainties:
¾ Land use data were used from early 1990’s and need
updating
¾ N loads from fertilizers were based on recommended
IFAS fertilizer application rates for cropland, yards, and
pine stands, that may differ from actual rates
¾ N loading from manure needs to be updated with
current animal population data
¾ Amount of nitrogen stored in unsaturated zone
beneath various land uses needs to be quantified.
¾ Denitrification in the Upper Florida Aquifer was
assumed to be minimal
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
Questions ??
Contact Information:
Brian G. Katz, PhD
U.S. Geological Survey
2639 North Monroe St.
Tallahassee, FL 32303
[email protected]
Ichetucknee
Trace
•
Enhanced elevation map of Ichetucknee
Springs basin showing Ichetucknee trace
Katz, B.G., Sepulveda, A.A., and
Verdi, R.J., 2009. 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. 607-627.