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