by David J. Toth, Ph.D., P.G. St Johns River Water Management District Brian G Katz, Ph.D., P.G

THE ORIGIN AND AGE OF SPRING WATERS IN THE ST

JOHNS RIVER WATER MANAGEMENT DISTRICT,

CENTRAL FLORIDA

by

David J. Toth, Ph.D., P.G.St Johns River Water Management

District

Brian G Katz, Ph.D., P.G.U. S. Geological Survey

PURPOSE

Determine the origin and age of water discharging from 11 springs in the St. Johns River Water Management District

Study Area (In SJRWMD)

Fig. 1 Study Area

D U

D

U

Spring Nitrate-N (mg/l) Delta nitrogen-15 (ppt)Wekiwa 0.89 8.6Palm 0.52 7.8Sanlando 0.25 11.7Starbuck 0.22 12.9Rock 1.29 5.8Juniper 0.07Ponce de Leon 1.14 8.9Alexander 0.03Silver Glen 0.03Blue 0.24Salt 0.09

Fig. 2 Thickness of the Confining Unit

Fig 3. Elevation of the Floridan Aquifer

Fig 4. Thickness of the MSCU

Fig 5. Elevation of the Top of the Lower Floridan Aq.

SODIUM CHLORIDE

CALCIUM BICARBONATE

SODIUM CHLORIDE,CALCIUM BICARBONATE

Fig 6. Water Quality

Fig 7. May 2001 Pot Surface

REACTIONSCALCIUM BICARBONATE

SPRINGS

Rain Water + a CH2O + b CaCO3 + c CaMg(CO3)2 + d O2 =

Spring Water

REACTIONSSODIUM CHLORIDE SPRINGS

Rain Water + Lower Floridan Water + a CH2O + b CaCO3 + c CaMg(CO3)2 + d O2 = Spring Water

Upper Floridan Water + Lower Floridan Water + b CaCO3 = Blue Spring

Upper Floridan Water + Lower Floridan Water = Salt Springs

REACTIONSSODIUM CHLORIDE,

CALCIUM BICARBONATE SPRING

Rain Water + Lower Floridan Water + a CH2O + b CaCO3 + c CaMg(CO3)2 + d O2 = Spring Water

Spring Computed C-13 Observed C-13 Observed-ComputedWekiwa -10.54 -10.52 0.02Palm -11.43 -11.2 0.23Sanlando -11.41 -10.87 0.54Starbuck -10.93 -10.84 0.09Rock -9.25 -9.44 -0.19Juniper -9.5 -10 -0.50Ponce de Leon -9.88 -8.4 1.48Alexander -10.24 -9.57 0.67Silver Glen -6.98 -8.15 -1.17Blue -11.25 -10.61 0.64Salt -8.75 -8.73 0.02

Spring Percent Lower FloridanAlexander 9.5Silver Glen 15.7Blue 15.7Salt 53.0Ponce de Leon 3.5

Spring Average Residence Time (yrs)Wekiwa 14Starbuck 18Palm 19Rock 21Blue 22Ponce de Leon 22Sanlando 23Juniper 25Alexander 25Silver Glen 26Salt 32

Error + or - 1

CONCLUSION

Water discharging from these springs are locally derived and contain variable amounts of recently recharged water.