3rd UF Water Institute Symposium Abstract

Submitter's Name Marie Kurz
Session Name Posters - Nutrient dynamics and enrichment impacts in aquatic ecosystems 2
Category Nutrient dynamics and enrichment impacts in aquatic ecosystems
Poster Number 41
Author(s) Marie J. Kurz,  UF Department of Geological Sciences (Presenting Author)
  Jonathan B. Martin,  UF Department of Geological Sciences
  Matthew J.  Cohen, UF School of Forest Resources and Conservation
  Rachel L.  Douglass, UF School of Natural Resources and Environment
  Chad  Foster, UF School of Forest Resources and Conservation
  Influence of Autotrophic Assimilation on Diel Elemental Cycling in a Spring-Fed River
  Ecosystem respiration and photosynthesis by submerged aquatic plants result in diel (24-hr) cycles in dissolved oxygen (DO) concentrations, pH, redox conditions and mineral saturation states in streams, which in turn drive diel variations in elemental concentrations. Direct assimilatory uptake of micronutrients by aquatic plants may also contribute to diel elemental cycles. The objective of this study is to quantify the importance of biotic assimilation relative to abiotic controls on diel elemental cycling in streams by analyzing primary producer tissue stoichiometry, environmental element availability, and the magnitude and phase of diel variations. We deployed in-situ sensors and used ICP-MS to analyze elemental concentrations in the water and dominant algal and vascular plant species of the Ichetucknee River and its five main source springs. The entirely spring-fed Ichetucknee River, in north-central Florida, is a model system for distinguishing between the multiple drivers of diel chemical cycles due to its stable discharge, known input spring chemistry, and high primary productivity. Five kilometers downstream of the source springs, diel cycles were observed in DO, pH, NO3, and PO4, reflecting aquatic primary production. Thirteen major and trace elements exhibited diel cycling. Concentrations of Mg, K, Fe, Cu, As, U, Cr, V, and Co peaked in the afternoon, in phase with DO and pH, while Ca, Mn, Ba, and Sr concentrations peaked in the morning. Elemental concentrations in both plant species were similar to concentrations in terrestrial leaves but varied considerably between collection sites. Concentrations of V, Cr, Mn, Co, Ni, Sr, Ba, and U in plants from the springs correlated well (r2 > 0.6) with spring water concentrations. Differences between assimilation estimates and observed diel elemental cycles should reflect the magnitude and timing of abiotic drivers of diel elemental cycles and provide insight into the interactions between micronutrient availability and acquisition within aquatic ecosystems.