Surface Water Injection into the Floridan Aquifer: Biogeochemical Transformations and Ramifications

Carley Reid, University of Tampa, Tampa, FL, United States, Miranda Conley, University of Tampa, Tampa, United States, Robert Thomas Masserini Jr, University of Tampa, Chemistry Biochemistry and Physics, Tampa, FL, United States, Amy M McKenna, Florida State University, National High Magnetic Field Laboratory, Tallahassee, United States and John Lisle, USGS, United States
Abstract:
The Floridan Aquifer System (FAS) occupies an area of approximately 100,000 square miles underlying portions of Mississippi, Alabama, Georgia, South Carolina, and the entirety of Florida. This system is one of the most productive groundwater sources in the world and supplies drinking water to over ten million people. Aquifer storage and recovery (ASR) is a process by which treated surface water is injected into the sub-surface aquifer, stored, and later extracted. Injecting surface water into the FAS, an anoxic water body, and the reintroduction of this mixed water mass into surface waters has not been thoroughly evaluated. Therefore, the biogeochemical transformations associated with the ASR injection of surface water into the FAS is of interest. A time series was constructed to study the potential biogeochemical changes associated with ASR injection of Kissimmee River recharge waters into the FAS. A dilution series comprised of the two water sources was incubated under anoxic conditions to replicate the environment of the Upper Floridan Aquifer. The bacterially mediated transformations within the dissolved organic matter pool of the FAS were analyzed via Fourier Transform Ion Cyclotron Mass Spectrometry (FTICR-MS) to characterize DOM at the elemental level. The impact of nutrient injection into the suspended microbial communities of the FAS was evaluated by constructing a parallel set of microcosms and monitoring the nutrient concentrations using absorbance based colorimetric techniques. Analysis of the FTICR-MS data indicate that the DOM pool is recalcitrant and no significant change was found in the composition of the dissolved organic matter. However, utilization of nitrate and nitrite was observed by the bacterial community within the FAS. Ammonium concentrations within the FAS are on the order of 20 micromolar and the water is devoid of oxygen. This indicates that if a mixture of the native FAS and surface waters are reintroduced into the coastal system, low oxygen conditions may be induced due to the introduction of anoxic water and subsequent degradation of phytoplankton blooms stimulated by the high ammonium concentrations.
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