3rd UF Water Institute Symposium Abstract

Submitter's Name Amy Brown
Session Name Posters - Nutrient Dynamics and Enrichment Impacts in Aquatic Ecosystems 1
Category Nutrient dynamics and enrichment impacts in aquatic ecosystems
Poster Number 36
Author(s) Amy Brown,  University of Florida (Presenting Author)
  Jonathan Martin,  University of Florida
  Elizabeth Screaton, University of Florida
  Patricia Spellman, University of Florida
  The Impact of River Water Intrusion on Nutrient and Trace Metal Concentrations in the Floridan Aquifer System at Madison Blue Spring, Florida
  Springs located adjacent to rivers can serve as recharge points for aquifers when river stage increases above the spring stage, forcing river water into the spring. Differences in water composition of the surface water and groundwater may be important to nutrient (nitrate and phosphate) and micronutrient (trace metal) concentrations. To assess how intrusion may affect these concentrations during spring reversals, we monitored Madison Blue Spring, which discharges to the Withlacoochee River in north-central Florida, during a period of elevated river stage in April 2011. Intrusion of the river water was observed to last about 20 days with electrical conductivity, temperature and depth sensors installed within the cave system and adjacent wells. The main spring vent and Martz sink, a karst window approximately 150 meters from the spring vent, were sampled seven times over a period of 34 days during and after the decrease in specific conductivity. The samples were measured for nitrate and phosphate, as well as trace metals that serve as micronutrients, such as iron. Nitrate concentration in the river was an order of magnitude lower than the concentration of the spring water, so river water intrusion decreased nitrate concentration in the groundwater consistent with mixing of two water sources. In contrast, river water had elevated phosphate and trace metal concentrations compared with the spring and thus represented a source of these elements to the aquifer. Spring water iron concentrations are elevated following river intrusion, but mixing calculations suggest that some iron transported into the springs precipitates within the aquifer. Elevated phosphate concentrations can be explained by mixing during river water intrusion, but increased phosphate concentrations observed approximately 30 days after river water intrusion must come from another source. This increase could be due to desorption of phosphate from iron oxides which precipitated during river water intrusion.