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Starbuck Spring main view
photo by R. Means, FGS
Starbuck Spring pool
Starbuck Spring is a second-magnitude spring that was formerly known as Sheppard Spring. Milky blue water apparently flows from a single limestone vent, producing a boil in the north-central part of the pool. The circular pool is about 65 to 70 feet in diameter and about 4 to 7 feet deep, with a sandy bottom. The land around the pool has been built up 2 to 3 feet with earth fill, and the pool is enclosed by a low retaining wall made of concrete sacks. Water exits the pool over a weir on the northeast side of the pool and the spring run flows about 500 feet toward the east to the Little Wekiva River.
Starbuck Spring run
Discharge at Starbuck Spring was measured by the U.S. Geological Survey (USGS) in 1944 and 1960, then frequently from 1972 to 2002. St. Johns River Water Management District measured discharge from 1993 to 2010 and currently performs bimonthly discharge measurements. The difference between the minimum and maximum discharges is 13.43 cubic feet per second (cfs) over the period. The maximum measured discharge of 21.4 cfs occurred in October 1960; the minimum discharge of 7.97 cfs occurred in November 2009. The mean and median discharges for the period from 1944 to 2010 are 13.78 cfs and 13.90 cfs, respectively (see the table below).
Starbuck Spring was sampled by USGS five times between 1944 and 1995, with periodic field measurements only at other times. The district sampled Starbuck Spring 58 times from 1993 to 2010 and currently samples 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 Starbuck Spring
|Alkalinity, total, mg/L as CaCO3||98.0||125.0||124.5||169.0||60||1944−2010|
|Calcium, total, mg/L as Ca||35.0||41.9||42.2||46.0||56||1993−2010|
|Chloride, total, mg/L as Cl||12.0||21.4||21.7||26.4||62||1944−2010|
|Fluoride, total, mg/L as F||0.17||0.20||0.20||0.22||29||1993−2003|
|Magnesium, total, mg/L as Mg||10.7||11.9||12.0||13.0||56||1993−2010|
|Nitrate + nitrite, total, mg/L as N||0.13||0.41||0.39||1.71||54||1993−2010|
|Orthophosphate, total, mg/L as P||0.12||0.15||0.14||0.41||56||1972−2010|
|Phosphorus, total, mg/L as P||0.11||0.15||0.15||0.18||32||1972−2010|
|Potassium, total, mg/L as K||1.2||1.5||1.4||2.1||56||1993−2010|
|Sodium, total, mg/L as Na||11.0||13.4||13.1||16.1||56||1993−2010|
|Specific conductance, field, µmhos/cm at 25°C||212||347||357||393||57||1993−2010|
|Specific conductance, lab, µmhos/cm at 25°C||257||421||357||3620||46||1960−2010|
|Sulfate, total, mg/L as SO4||12.0||24.4||25.1||29.2||63||1944−2010|
|Total dissolved solids, mg/L||148||203||205||250||57||1960−2010|
|Water temperature, °C||22.2||24.0||24.0||26.5||115||1944−2010|
mg/L = milligrams per liter
cfs = cubic feet per second
Age of discharge water
The age of water discharging from Starbuck Spring was determined by measuring the concentration of tritium, delta carbon-13, and carbon-14 in the spring discharge, which was measured in September 1995, and tritium and helium-3, as measured in February 2001. Starbuck Spring had a tritium concentration of 2.4 tritium units, which suggests that the water is less than 42 years old. The tritium/helium-3 age was 19 years. Starbuck Springs had a delta carbon-13 value of −10.51 parts per thousand and a carbon-14 concentration of 46% modern carbon, which results from the reaction of rainfall with calcite, dolomite, and sediment organic matter. The adjusted carbon-14 age of Starbuck Spring is recent.