4th UF Water Institute Symposium Abstract

Submitter's Name John Ezell
Session Name Poster Session: Impact of changing drivers on water resources
Poster Number 19
Author(s) John Ezell,  University of Florida (Presenting Author)
  Jonathan Martin,  University of Florida
  Elizabeth Screaton, University of Florida
  Amy Brown, University of Florida
  Impacts of lowering aquifer heads on surface water-groundwater interactions: A study of spring reversals and their impact on aquifer water quality
  Water tables have decreased in regions around the world in the last century, largely due to aquifer pumping and rainfall variations. This drawdown has been linked to land subsidence, salt-water intrusion, and wetland deterioration, but one less studied topic related to drawdown is the impact on surface water-groundwater interactions. These interactions are particularly important in karst aquifers where springs may reverse flow when river stages rise above groundwater heads during flooding, directing river water into aquifers, thereby impacting groundwater chemistry. To investigate relationships between groundwater elevation, groundwater chemistry, and spring reversals, legacy records of groundwater elevations were collected from three wells in north Florida and compared to stage records from the Suwannee and Withalacoochee rivers in north Florida. Data loggers were installed in Peacock Springs (near the Suwannee River) and Madison Blue Spring (discharging to the Withalacoochee River) cave systems to measure high frequency variations in water characteristics. Low frequency water samples were also collected to measure chemical compositions during spring reversals. All three well data records show aquifer heads declining at 1 to 8 cm/yr. Elevated river stages show no change in trend over the last 80yrs. Decreasing water table elevations increase the hydrologic gradient toward the aquifer during floods of similar magnitude potentially causing an increase in the frequency of reversals. During sampled reversals, DOC concentrations in aquifer systems increased from less than 1 mgC/L pre-reversal to over 20 mgC/L at the peak of the reversal. The river water, which is more acidic than groundwater, increased dissolution rates by six orders of magnitude more than baseflow aquifer waters and thus may impact land surface movement, including sinkhole development. The decline in water tables and potentially increasing frequency of spring reversals suggest that pumping may contribute to the compromise of water quality by allowing increased intrusion of surface water.