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Ezell, J., Martin, J., Screaton, E., Brown, A., Gulley, J., Sutton, J., Spellman, P.
Periods of elevated precipitation cause spring flow to reverse and flood water to flow into river bank sediments. This intruding water will dissolve aquifer limestone during subsurface recharge and contribute to dissolution as precipitation recharges the aquifer through the land surface. Determining the frequency of reversals and which mechanisms contribute the most dissolution is important because each shapes landscapes and regional hydrology in unique ways, yet relative reversal frequency and volumes dissolved by these three mechanisms remain unknown. We partition the amount of dissolution resulting from each of these mechanisms following a precipitation event in 2012 in north-central Florida that caused a reversal into Madison Blue Spring. Water flowing into the spring as it reversed dissolved ~3.8 x 108 mmol of calcite. Dissolution caused by intruding river water, not including the spring reversal, along the studied river reach was ~2.3 x 109 mmol of calcite. Dissolution resulting from recharge of rainfall through the land surface was ~6 x 109 mmol of calcite. Dissolution resulting from direct recharge is widespread in time and space while dissolution from river intrusions is focused at the location of conduits. Rainfall and stage data reveal that Madison Blue Spring has reversed on average ~1.5 times/year for the last ~80yrs. The frequency of reversals is controlled by precipitation patterns which appear partially controlled by climatic cycles such as El Nino and the AMO. The balance between dissolution drivers created the current geomorphology and hydrology of north Florida, including both long phreatic caves and surface rivers, and a different dissolutional balance may have been reached without climatic cycles influencing precipitation patterns. |