4th UF Water Institute Symposium Abstract

Submitter's Name Amy Brown
Session Name Poster Session: Water quality protection and treatment
Poster Number 34
Author(s) Amy Brown,  University of Florida (Presenting Author)
  Jonathan Martin,  University of Florida
  Elizabeth Screaton, University of Florida
  John Ezell, University of Florida
  A comparison of the impact of diffuse and point source recharge on surface and groundwater quality
  Unconfined karst aquifers can have complex interactions with rivers that receive runoff from upstream reaches with less permeable sediments, where surface runoff after rainfall can cause a rapid rise in river stage. If river stage exceeds the hydraulic head of adjacent aquifers, surface runoff from storms can intrude into the aquifer through spring vents, resulting in point source recharge and temporary storage of surface water in the aquifer. This intrusion of river water can be moderated or eliminated if groundwater heads are elevated by diffuse recharge. To assess the influence of diffuse recharge and temporary storage of river water on water quality, we examined changes in hydraulic head and chemical composition of water during and after two storms at Madison Blue Spring in north Florida. In March 2012 rain fell mostly in the upper portion of the river drainage basin and runoff caused a rapid increase in river stage. As a result, Madison Blue spring began reversing after the river stage exceeded the hydraulic heads in the spring, the conduits, and the aquifer matrix. The river water that entered the aquifer was enriched in organic carbon (OC). The breakdown of OC during temporary storage of surface water resulted in enhanced calcite dissolution, and consumption of oxygen and nitrate in the matrix adjacent to the conduits. In contrast, rain in June 2012 fell predominantly on the unconfined springshed. The hydraulic head of the groundwater remained above river stage because of the diffuse recharge, and the spring did not reverse. Since no OC-rich river water entered the aquifer, the OC breakdown with its corresponding reactions did not occur in the aquifer. Instead, spring water continued to discharge, altering the composition of the river water. These events illustrate that distribution of precipitation across a watershed impacts the exchange of surface water and groundwater.