Open-File Report 2010–1021
Groundwater resources in the United States are under ever-increasing demands for potable, irrigation, and recreational uses. Additionally, aquifer systems are being used or targeted for use as storage areas for treated surface waters and (or) groundwaters via injection (for example, aquifer storage and recovery). To date, the influence that the nutrients, including carbon, in the injected water have on native microbial communities and the biogeochemistry in the subsurface zones used for storage of the injectate has not been determined. In this report, we describe a series of experiments that establishes a baseline dataset for the quantity and quality of organic and inorganic carbon and nutrients in the Biscayne Aquifer (BA) and Upper Floridan Aquifer (UFA) in south Florida.
The most significant differences between the BA (26 meters below surface) and UFA (366 meters below surface) are the average specific conductance (0.552 and 6.12 microsiemens per centimeter, respectively), dissolved oxygen (1.6 and 0 milligrams per liter, respectively), and oxidation-reduction potential (40.3 and -358 millivolts, respectively). The dissolved organic carbon from the BA is characterized by carbon originating from terrestrial sources and microbial activities, while the UFA has a distinctive microbial signature. Acetate and lactate are the dominant carbon constituents in both aquifers. Additionally, components of the dissolved organic carbon from the UFA have a total trihalomethane-formation potential that is approximately threefold greater than the maximum contaminat level of 80 micrograms per liter established by the U.S. Environmental Protection Agency.
The average native bacterial abundances in the aquifers are similar with 4.69x104 cells per milliliter in the BA and 1.33x104 cells per milliliter in the UFA. The average bacteriophage abundances are also similar with 1.15x105 virus-like particles in the BA and 1.92x105 virus-like particles in the UFA. Interestingly, ciliated protozoa are present in both aquifers. The average abundance of ciliates in the BA (2.97x103 ciliates per milliliter) is approximately twentyfold greater than abundances in the UFA (1.39x102 ciliates per milliliter). Collectively, these data indicate that microbial processes are the dominant contributor to the cycling of carbon and inorganic carbon in the BA and may be the only carbon cycling process in the UFA, as this aquifer has not had a terrestrial influx of carbon for more than 15,000 years.
The rates of carbon, in the form of acetate, utilization by the native microbial communities are significantly different between the two aquifers. Based on data from 14C-acetate-utilization experiments, the microbial communities in the BA turn over the native acetate in 2.5 years, whereas communities in the UFA turn over native acetate in 6.8 years. These data support the hypothesis derived from the microbial-abundance data, in that the carbon for bacterial maintainence and growth is recycled from bacterial biomass released during cell lysis, especially in the UFA.
An in situ diffusion chamber was designed to retain bacterial cells within the chamber while allowing native water constituents to move through the chamber. A series of 1-week deployments of chambers filled with fluorescent beads, inactivated native bacteria and laboratory grown and viable bacteria into the UFA, permitted by the State of Florida Environmental Protection Agency, was successfully completed. This was the first time this type of deployment into an aquifer system that is used for potable water supply has been permitted within the United States. This technology will allow, for the first time, in situ studies on the survival of microbial indicators of fecal pollution and true pathogens in groundwater systems.
First posted April 27, 2010
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Lisle, J.T., Harvey, R.W., Aiken, G.R., and Metge, D.W., 2010, Microbial and geochemical investigations of dissolved organic carbon and microbial ecology of native waters from the Biscayne and Upper Floridan Aquifers: U.S. Geological Survey Open-File Report 2010-1021, 33 p.
Field Data Collection
Geochemical and Nutrient Data Collection
Calculation of the Calcite and Aragonite Saturation Index
Quantification and Characterization of Dissolved Organic Carbon (DOC)
Determination of the Total Trihalomethane (TTHM) Formation Potentials
Volatile Fatty-Acid (VFA) Data Collection
Bacterial and Bacteriophage Abundance Data Collection
Ciliated-Protozoa Data Collection
Diffusion-Chamber Deployment and Bacterial Survival in the Upper Floridan Aquifer
Bacterial Respiration, Carbon Turnover, and Carbon-Dioxide Production Rates
Determination of the Frequency of Dividing Cells (FDC) in Native Groundwaters
Results and Discussion
Dissolved Organic-Carbon (DOC) Quantification and Characterization
Total Trihalomethane-Formation Potential (TTHMFP)
Volatile Fatty Acids (VFA)
Bacterial, Bacteriophage, and Ciliate Abundances
Carbon-Utilization Rates of Native Aquifer Bacterial Communities
Frequency of Dividing Cells (FDC)
Deployment of Diffusion Chambers into the Upper Floridan Aquifer
Future Research Directions