4th UF Water Institute Symposium Abstract

Submitter's Name Alexis Johnson
Session Name Poster Session: Water quality protection and treatment
Poster Number 33
Author(s) Alexis Johnson,  University of Florida Department of Environmental Engineering Sciences (Presenting Author)
  David Kaplan,  University of Florida Department of Environmental Engineering Sciences
  Robert Hensley, University of Florida School of Forest Resources and Conservation
  The Effect of Variable Hyporheic Exchange on Nitrate Removal in Florida Springs: A Smart Tracer Approach
  One of the most pressing issues facing the waterways of Florida is anthropogenic nitrate pollution due to more than fifty years of rapid population growth and increased agricultural activity. In light of recently declared numeric nutrient criteria, a full understanding of nutrient cycling processes is crucial for proper water quality and quantity management. In-stream nitrate removal due to denitrification is thought to be positively correlated with high velocity gradients and increased hyporheic exchange. However, previous studies in tidally influenced springsheds have noted greater nitrate retention at lower velocities, possibly due to increased residence times. This study aims to identify the connection between velocity gradient and nitrate removal rate using the biologically reactive tracer resazurin to directly measure the amount of spring discharge subject to hyporheic exchange under varying flow conditions. Tracer studies will be performed during various tidal stages, and breakthrough curves of resazurin and its byproduct resorufin will be analyzed and compared to in-situ nitrate measurements to determine the contribution of hyporheic exchange to denitrification. Greater reduction of resazurin is expected during low tide due to the high velocity gradient and subsequently increased water-sediment exchange. The use of this “smart” tracer for hydrologic studies is a relatively new application, and this work will not only contribute to a greater understanding of nutrient cycling, but will also aid in the development of direct methods for quantifying the role of the hyporheic zone in the biogeochemical processing of contaminants of concern in aquatic ecosystems.