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Nitrate Sourcing and Nitrate Sourcing and Ground Water Age Ground Water Age for the Springs of for the Springs of
Merritt’s Mill PondMerritt’s Mill Pond
Kevin DeFossetNWFWMD
HISTORICAL NITRATE CONCENTRATIONS JACKSON BLUE SPRING
DISCHARGE MEASURMENTSJACKSON BLUE – SPRING CREEK
July 2007 Discharge Measurements
MeasurementSection
Discharge (cfs)
Spring Crk ds Hwy 90 56.0
Jackson Blue 39.1
Merritt's Mill Pond 16.9
Shangri-La 3.9
Twin Caves 1.6
Hole in the Wall 1.3
Heidi Hole 0.2
Gator Hole 0.9
Springs Total 7.9
Merritt's Mill Pond 16.9
Springs Discharge 7.9
Miscellaneous Discharge 9
RECENT NITRATE CONCENTRATIONS MERRITT’S MILL POND SPRING
Magnesium, Barium, and Strontium ConcentrationsMerritt’s Mill Pond
Range of Nitrogen Isotope Values for Inorganic and Organic Nitrogen Sources
NO3 Concentrations vs. Delta 15N-NO3
Range of Nitrogen Isotope Values for Inorganic and Organic Nitrogen Sources
NO3 Concentrations vs. Delta 15N-NO3
SF6 age 3H/3He
Jackson Blue 16.5 18.8 32.8
Shangri-La 16.5 11.2 11.6
Twin Caves 17.3 Modern 44
Hole in the Wall 14 Modern 46.4
Heidi Hole 18 15.5 31.5
Gator Hole 9 Modern >55
Dating Ground Water with SF6
• Stable, atmospheric gas
• Primarily of anthropogenic origin
• Record of atmospheric input over time
Dating Ground Water with Tritium and Helium
• Tritium results from atmospheric nuclear bomb testing
• Record of atmospheric input over time
• Helium is decay product and helps to refine age
• Atmospheric gases (N, Ar, Kr, Xe, Ne, He) needed for age determination.
What can be said?
• Based on available data, ground water sources other than Jackson Blue Spring contribute between 11 and 46 percent of the discharge of Merritt’s Mill Pond.
• Elevated levels of nitrate exist at all springs in Merritt’s Mill Pond.
• Artificial fertilizer is the predominate source of nitrate for the springs of Merritt’s Mill Pond.
• The waters feeding Merritt’s Mill Pond are of mixed age.
COMPARISON OF HYDROLOGIC CONDITIONS
EARLY 2008 – CURRENT
Date
MeasurementValue
DISCHARGE, cfs(USGS Gaging Station)
2/1/2008 50
1/12/2009 114
WATER LEVEL, ft msl(NWFWMD Monitoring Well)
2/1/2008 79
12/12/2008 84