The Alachua Sink
The posted coordinates are to an area that is an important geologic feature of Alachua County. You do not need to, and should not leave the trails. As with all nature areas in Florida, please be aware of potentially dangerous wildlife.
The Alachua Sink is located on the north rim of Paynes Prairie and is part of Paynes Prairie Preserve State Park. The prairie is made up of many sinkholes, but the Alachua Sink is significant because it is connected to the Floridan Aquifer, our primary source of drinking water in Florida. This earthcache describes some of the hydrogeology of the area.
The geology of the Alachua Sink is Ocala Group limestone which is often characterized by irregular erosion patterns on the surface as well as subterranean levels. These erosional features lead to sinkholes. Notice the exposed limestone and irregular edges surrounding the body of water in front of you. That body of water is actually the Alachua Sink, and is a unique sink hole that extends far below the ground level of Paynes Prairie. The Alachua Sink is actually a series of interconnected sink holes of varying ages, and new sink holes continue to form in the area, indicating that the limestone is still being actively dissolved.
The Paynes Prairie Basin is approximately 16,000 acres, and water from the surrounding areas flows down into the prairie as part of the local watershed. The main areas of inflow are Prairie Creek, which connects Newnan’s Lake to Paynes Prairie, and Sweetwater Branch, which includes stormwater and discharged treated water from the City of Gainesville. The appearance of the area varies significantly by season in terms of vegetation as well as the water levels as the inflow to the sink changes based on rainfall.
The Alachua Sink acts as a conduit between the surface water in Paynes Prairie and groundwater in the Floridan Aquifer. The average elevation of the prairie basin is between 50 and 60 feet above sea level; the bottom of the Alachua Sink is approximately 80 feet below sea level. The Floridan Aquifer is one of the largest sources of potable water in the United States, and it supplies the northern half of Florida with nearly all of its potable water. The Alachua Sink and the Paynes Prairie Basin play a critical role in recharging the aquifer, and thus providing potable water for the people and ecosystems that depend on it.
To log this earthcache, please visit the posted coordinates and the added waypoint (in the sheltered area on the boardwalk), continue along the trail overlooking the sink and email the answers to the following questions to the cache owner through the profile above. Do not place your answers in your log, even if encrypted.
- Looking at the interpretive panel titled “Sculpted From the Bones of an Ancient Sea”, which can be found in the pavilion overlooking the Alachua Sink, what is the average height of the bluff surrounding the Sink?
- The Paynes Prairie Watershed covers approximately how many total acres? (Hint, the answer is NOT 16,000)
- At peak flow, approximately how many gallons of water will enter the Floridan Aquifer through the Alachua Sink?
- If the outflow of the Alachua Sink were to become blocked as it has occasionally in the past, how do you think your experience at Paynes Prairie would be affected or changed?
- Observe the water entering the sink. Knowing that this will be entering the Floridan Aquifer and become drinking water, what everyday things could you do to improve the quality of the water?
- OPTIONAL – Post a picture of yourself from along the La Chua trail with the sink in the background.
References:
A Hydrogeologic Studey of Alachua Sink, Alachua County, Florida Utilizing Ground Penetrating Radar and Other Geophysical and Hydrologic Methods. Michael N. Ritter, Dames and Moore, Inc.
http://www.dep.state.fl.us/water/tmdl/docs/tmdls/final/gp1/alachuasink-nutr-tmdl.pdf
http://www.afn.org/~pprairie/aboutPrairie/natural.html