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Table 2 – Field Water Quality Measurements of Springs in the Choctawhatchee River Basin.
| Spring Name | Date
Sampled |
Temperature
(degrees C) |
Specific
Conductance (umhos/cm) |
Dissolved
Oxygen (mg/L) |
pH
(standard units) |
| Morrison Spring | 11/3/2004 | 20.24 |
225 |
3.14 |
7.64 |
| Vortex Spring | 1/12/2005 | 19.91 |
212 |
5.04 |
7.37 |
| Ponce de Leon Spring | 1/12/2005 | 20.03 |
219 |
3.73 |
7.36 |
| Jackson Spring | 1/12/2005 | 19.95 |
212 |
2.29 |
7.25 |
| Thundering Spring | 1/19/2005 | 16.80 |
136 |
8.80 |
7.07 |
| Natural Bridge Rise | 2/23/2005 | 17.77 |
87 |
5.52 |
7.26 |
| Pate Spring | 3/03/2005 | 15.64 |
187 |
7.80 |
7.61 |
| Holmes Blue Spring | 3/10/2005 | 20.02 |
212 |
5.76 |
7.82 |
| Wrights Blue Spring | 3/10/2005 | 13.63 |
121 |
9.98 |
7.60 |
| Hidden Spring | 3/10/2005 | 17.94 |
291 |
2.67 |
7.57 |
| Potter Spring | 6/03/2005 | 20.80 |
156 |
1.17 |
7.33 |
| Washington Blue Spring | 6/03/2005 | 20.97 |
138 |
0.96 |
7.34 |
| Blue Run Spring | 6/03/2005 | 20.65 |
162 |
4.00 |
7.13 |
| Weaver Spring (Surficial Aq.) | 2/23/2005 | 15.80 |
18 |
5.45 |
4.92 |
| Ray Hill Spring (Surficial Aq.) | 3/15/2005 | 20.21 |
31 |
5.86 |
4.97 |
| Pleasant Ridge Spring (Surficial Aq.) | 3/15/2005 | 20.17 |
24 |
3.84 |
5.12 |
Temperature can be highly variable in surface water dependent on atmospheric conditions. Ground water temperatures tend to be much more stable. For instance, long-term water temperature readings at Wakulla Springs — a first magnitude Floridan Aquifer spring in Wakulla County—reveal that the temperature typically has a median value of 20.79 degrees C (n=4120, mean=20.77, stdev=0.11). The median temperature of the Choctawhatchee River springs, 19.95 degrees C (n=13, mean=18.80, stdev=2.28) compares well with this typical Floridan Aquifer value.
A surface water body with a dissolved oxygen (DO) value of less than 5.0 mg/L is considered impaired. The longer ground water remains in the aquifer, however, the DO concentration becomes lower due to oxidation reactions with the matrix material and the lack of re-aeration from the atmosphere or biologic sources. DO values in Floridan Aquifer wells recently sampled in this area have a median value of 0.14 mg/L (n=27, mean=1.58, stdev=2.21). The median DO value for the Choctawhatchee River springs is 4.00 mg/L (n=13, mean=4.68, stdev=2.84). The higher DO values measured for the springs indicate a much shorter average residence time in the aquifer for the spring discharge compared to ground water in the Floridan Aquifer wells.
The spring pH values indicate that the water is well buffered. This is typical of water that has remained in the Floridan Aquifer for any length of time. The dissolution of limestone by acidic rain water raises the pH of the water and creates the characteristic karst topography of the Dougherty Karst Plain. The median pH value for Floridan Aquifer wells recently sampled in this area is 7.80 standard units (n=27, mean=7.88, stdev=0.85). The median value of the Choctawhatchee River Springs is 7.36 standard units (n=13, mean=7.41, stdev=0.22).
Specific conductivity is a measure of the ion content of water. Rain water and surface water not influenced by ground water input usually have a specific conductivity value less than 50 umhos/cm when not impaired by non-point sources. The median specific conductivity value for Floridan Aquifer wells recently sampled in this area is 260 umhos/cm (n=27, mean=338, stdev=224). The median specific conductivity of the Choctawhatchee River Springs is 187umhos/cm (n=13, mean=181, stdev=54.5).
The elevated DO values and lower pH and specific conductivity values in comparison to the Floridan Aquifer wells are probably the result of an influx of lower residence time, less mineralized and more acidic ground water into the Floridan Aquifer before it discharges from the springs. Because of this high local recharge and the significant surface water – ground water interaction within this highly karstic environment, the springs along the Choctawhatchee River are particularly vulnerable to proximate land use activities.
