In this section
Island Spring main view
Island Spring is a third-magnitude spring. The spring is submerged in the eastern part of the Wekiva River channel.
Discharge at Island Spring was measured four times by the U.S. Geological Survey (USGS) from 1982 to 1997. St. Johns River Water Management District measured discharge 33 times from 2001 to 2010. The difference between the minimum and maximum discharges is 4.8 cubic feet per second (cfs) over the period. The maximum measured discharge of 10.2 cfs occurred in March 2003; the minimum discharge of 5.39 cfs occurred in June 2001. The mean and median discharges for the period are 8.29 cfs and 8.34 cfs, respectively (see the table below).
Island Spring was sampled by USGS in 1982 and 1996. The district sampled the spring 27 times from 2001 to 2010. Summary statistics of the water quality data for selected variables are shown in the table below.
Summary statistics of water quality and discharge at Island Spring
|Alkalinity, total, mg/L as CaCO3||118.0||129.5||128.5||154.0||27||2001−2010|
|Calcium, total, mg/L as Ca||190.0||217.9||215.3||250.0||26||2001−2010|
|Chloride, total, mg/L as Cl||1200.0||1756.7||1780.0||2098.5||29||1982−2010|
|Fluoride, total, mg/L as F||0.20||0.22||0.23||0.25||10||2001−2003|
|Magnesium, total, mg/L as Mg||92.0||108.3||108.0||126.0||26||2001−2010|
|Nitrate + nitrite, total, mg/L as N||0.01||0.24||0.06||1.20||6||2002−2009|
|Orthophosphate, total, mg/L as P||0.06||0.08||0.08||0.10||22||2001−2010|
|Phosphorus, total, mg/L as P||0.07||0.11||0.09||0.51||17||2001−2010|
|Potassium, total, mg/L as K||21.0||24.8||25.0||28.0||26||2001−2010|
|Sodium, total, mg/L as Na||793.0||924.1||930.3||1100.0||26||2001−2010|
|Specific conductance, field, µmhos/cm at 25°C||5420||5900||5900||6380||2||2001−2003|
|Specific conductance, lab, µmhos/cm at 25°C||4500||5947||5870||6910||21||1982−2010|
|Sulfate, total, mg/L as SO4||350.0||489.2||496.0||580.0||29||1982−2010|
|Total dissolved solids, mg/L||2680||3760||3767||4500||28||1982−2010|
|Water temperature, °C||22.3||23.6||23.7||24.1||11||1982−2003|
mg/L = milligrams per liter
cfs = cubic feet per second
Age of discharge water
The age of water discharging from Island Spring was determined by measuring the concentration of tritium, delta carbon-13, and carbon-14 in the spring discharge, which was measured in March 2001. Island Spring had a tritium concentration of 0.55 tritium units, which suggests that the water is about 48 years old. Island Spring had a delta carbon-13 value of −8.45 parts per thousand and a carbon-14 concentration of 23% modern carbon, which results from the mixing of Upper and Lower Floridan aquifer water. The Fontes and Garnier (1979) carbon-14 age of Island Spring is 2,932 years old.