2nd UF Water Institute Symposium Abstract

Submitter's Name Marie Kurz
Session Name Poster Session: Hydrologic, Biogeochemical and Ecological Processes 2
Category Hydrologic, biogeochemical and ecological processes
Poster Number 226
Author(s) Marie J. Kurz,  University of Florida
  Jonathan B. Martin,  University of Florida
  Veronique de Montety, University of Florida
  Matthew J. Cohen, University of Florida
  Chad R. Foster, University of Florida
  Pore water chemistry in a spring-fed river: Implications for hyporheic control of nutrient cycling and speleogenesis
  Hyporheic exchange is important for nutrient cycling in rivers, but little is known about the magnitude of this process in karst systems or its influence on speleogenesis and the formation of river channels. We use three pore-water depth profiles to assess nutrient and carbonate processing in the hyporheic zone of the Ichetucknee River (north-central, Florida). The Ichetucknee River is sourced from six major and numerous small springs which discharge from the karstic Floridan Aquifer. Order of magnitude increases in nitrate concentrations since the mid 20th century have been implicated in a recent proliferation of algae in the river. Nitrate concentrations decrease downstream and exhibit diel variations, along with specific conductivity and calcite saturation state. These patterns reflect in-stream processing, but hyporheic exchange should also influence the overall dynamics of nutrient and Ca fluxes in the river. Our depth profiles extend through unconsolidated sediment to solid carbonate of the Floridan Aquifer at 116, 121, and 181cm below the river bed. The profiles were taken ~10m from the stream banks and midway across an ~100m wide section of the river. Dissolved organic carbon (OC) immediately decreases to values below detection limits while dissolved inorganic carbon increases. This suggests the remineralization of solid OC in the upper sediments causing observed decreases in dissolved oxygen and pH and increases in NH4+. The lower pH drives dissolution of the carbonate sediment, causing increases in specific conductivity, alkalinity and calcium concentrations. Phosphate concentrations also increase probably as a result of carbonate mineral diagenesis and/or OC remineralization. Decreases in nitrate concentrations indicate denitrification occurs in the pore water. Most of these reactions appear to occur in the upper 60cm of sediment, below which many concentrations return to groundwater levels, suggesting influence of groundwater from the Floridan Aquifer at the base of the sediment.