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Fern Hammock Springs main view
Fern Hammock Springs
Fern Hammock Springs boil
Fern Hammock Springs is a second-magnitude spring and is one of the most picturesque springs in St. Johns River Water Management District. The irregularly shaped main pool measures about 160 feet from east to west and 75 feet from north to south, with a depth of 2 to 6 feet. A wooden footbridge spans the spring pool near its center. There are over 25 sand boils scattered on the bottom of the spring pool, with the largest sand boil situated under the footbridge. The bottom of the pool is mostly sand, with patches of aquatic grasses. The clear, bluish spring water has an exceptionally low concentration of dissolved solids, for a Florida spring. The spring discharges toward the northwest and flows about 600 feet down a gently meandering run to Juniper Creek, at a point about 0.25 mile east of and down the creek from Juniper Springs. Flow is then northeast down Juniper Creek about 10 miles to Lake George. Recreational activities are numerous in the Juniper Springs Recreational Area, but swimming is prohibited in Fern Hammock Springs due to ecological considerations.
Fern Hammock Springs run
Discharge at Fern Hammock Springs was measured by the U.S. Geological Survey (USGS) 42 times from 1972 to 2002. The district measured discharge 180 times from 1985 to 2010 and currently measures discharge six times per year. The difference between the minimum and maximum discharges is 7.53 cubic feet per second (cfs) over the period. The maximum discharge of 16.8 cfs was measured in April 1996; the minimum discharge of 9.27 cfs was measured in May 2000. The mean and median discharges for the period from 1972 to 2010 are 12.54 cfs and 12.40 cfs, respectively (see the table below).
Fern Hammock Springs was sampled by USGS in 1972 and 1980, with periodic field measurements through 1999. The district sampled the spring quarterly from 1985 to 2010 and continues to sample the spring four times per year. Summary statistics of the water quality data for selected variables are shown in the table below.
Summary statistics of water quality and discharge at Fern Hammock Springs
|Fern Hammock Springs||Min||Mean||Median||Max||Count||Period|
|Alkalinity, total, mg/L as CaCO3||37.0||45.4||45.0||83.0||96||1972−2010|
|Calcium, total, mg/L as Ca||11.0||12.9||13.0||15.9||85||1992−2010|
|Chloride, total, mg/L as Cl||3.0||4.7||4.4||11.7||94||1972−2010|
|Fluoride, total, mg/L as F||0.06||0.07||0.07||0.10||51||1989−2009|
|Magnesium, total, mg/L as Mg||4.0||4.7||4.7||6.5||84||1992−2010|
|Nitrate + nitrite, total, mg/L as N||0.01||0.09||0.09||0.43||92||1988−2010|
|Orthophosphate, total, mg/L as P||0.01||0.02||0.02||0.11||60||1994−2010|
|Phosphorus, total, mg/L as P||0.01||0.04||0.02||0.47||42||2003−2010|
|Potassium, total, mg/L as K||0.2||0.3||0.3||0.9||14||1995−2008|
|Sodium, total, mg/L as Na||2.0||2.7||2.7||4.4||84||1992−2010|
|Specific conductance, field, µmhos/cm at 25°C||60||119||118||193||89||1985−2010|
|Specific conductance, lab, µmhos/cm at 25°C||60||119||116||244||84||1972−2010|
|Sulfate, total, mg/L as SO4||3.0||6.7||6.0||20.0||97||1972−2010|
|Total dissolved solids, mg/L||42||69||68||152||93||1972−2010|
|Water temperature, °C||18.9||21.8||21.9||23.7||117||1972−2010|
mg/L = milligrams per liter
cfs = cubic feet per second
Age of discharge water
The age of water discharging from Fern Hammock Springs was determined by measuring the concentration of tritium, delta carbon-13, and carbon-14 in the spring discharge, which was measured in January 2001. Fern Hammock Springs had a tritium concentration of 2.45 tritium units, which suggests that the water is less than 48 years old. Fern Hammock Springs had a delta carbon-13 value of −8.40 parts per thousand and a carbon-14 concentration of 26% modern carbon, which results from the reaction of rainfall with calcite, dolomite, and sediment organic matter. The Fontes and Garnier (1979) carbon-14 age is approximately 2,000 years old.