Groundwater Geology (2014)
Extent and confinement of the Floridan aquifer. The Floridan is among the most productive karst aquifers in the
world and source of most of Florida’s drinking water (Miller 1990)
Spatial survey of hydrogeologic zones in the Suwannee River Water Management District (after Upchurch et al.
2007). The Cody Escarpment defines the boundary between where the Floridan is confined and
unconfined/semi-confined. The Sink-Rise system is a direct consequence of water passage from confined to
unconfined areas.
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Hydrogeologic units in the Silver Springs basin (after Phelps 2004, Scott et al. 2001)
2
Plan view of Briar Cave (Marion County) showing complex anastamosing channels that generally follow matrix
fractures (NE-SW), but include caves and lateral connections.
3
Locations of Florida’s more than 700 springs, including those visited by Scott et al. (2004).
Name
Wekiva
Madison Blue
Crystal
Owens
Ichetucknee
Fanning
Weeki Wachee
Hornsby
Conc (mg-N/L)
Early
Late
0.07
0.43
0.01
1.25
0.71
2.61
0.50
3.64
0.36
0.77
0.35
3.82
0.02
0.78
0.68
0.44
Overall (mean)
0.43
1.13
Nitrogen loading from agricultural activities such as fertilization, dairy farms, chicken farms, and hog farms has
raised groundwater nitrate levels as high as 30 ppm (mg/l). 10 ppm is limit for drinking water. High
concentrations of nitrate in drinking water are known to cause Methemoglobinemia (Blue Baby Syndrome) and
nitrate in manure and fertilizer runoff is now under suspicion as an endocrine disrupter. Forestry is also on the
list of polluters.
4
Relative vulnerability of the Floridan Aquifer System to pollution from overlying land uses (from Arthur et al.
2005). Areas in white are outside the study bounds.
5
Nitrate loading to the Gulf of Mexico from the Suwannee River. Shown are a) recent changes in total loads
between 2001 and 2005 (primarily driven by changes in water flows), b) long-time series changes in nitrate
concentrations at 5 1st magnitude springs along the Suwannee River, and c) spatial estimates of nitrate loading
by sub-basin. Basins where surface and groundwater mixing is limited by a regional aquitard are shown in
blue; sub-basins where that aquitard is absent represent less than 25% of the total area, but contribute nearly
65% of the total load. (Data Sources: Hornsby et al. 2002, 2003, 2004, 2005; Mirti and Mantini 2006).
Schematic of springshed with surface water drainage in the confined
region, a sinkhole (blue dot) capturing that flow after passage into the
semi- and un-confined regions, a historic stream channel that is the
presumed flow course of the karst conduit (the “trace”) and the spring.
Priority areas for water quality protection are shown (after Upchurch
and Champion 2004).
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Investigative techniques
The age of spring water (time it took to move from rain to spring flow) is frequently determined by comparing
long term rainfall contaminant data, for example Tritium from atomic weapons testing and
chlorofluorocarbons that were used in old air conditioning systems, to Tritium and chlorofluorocarbons in
spring water. From these data the average age of spring water is estimated to be about 20 years.
Stable isotopes of hydrogen and oxygen can also act as groundwater “tags”. Water containing 2H and 18O are
heavier than normal water and don’t evaporate as easily. Therefore groundwaters are enriched in 2H and 18O
and rain waters are mostly normal water (1H2160).
Estimated water ages for Florida springs (Katz 2001) using multiple dating techniques. While the measures are
generally poorly correlated, they are consistently suggestive of recharge dates between 5 and 35 years before
present.
Flow at Crystal Springs, Hillsborough County since 1933 (Weber and Perry 2006).
7
Total Maximum Daily Load for Alachua Sink
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