Nitrogen Sources and Sinks In a Wastewater Impacted Saline Aquifer Beneath the Florida Keys, USA

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Coastal Sciences, Gulf Coast Research Laboratory


Groundwater wells surrounding a high volume advance treatment wastewater (ATW) disposal well in the Florida Keys were monitored for nitrate, nitrite, and ammonium concentrations over a 14 month period. Nutrient concentrations in the shallow subsurface (9 m) show a bimodal distribution between the low salinity wastewater plume and the ambient brackish to saline groundwaters. High NO3- concentrations are found 3 within the ATW plume while the highest NH4+ concentrations are found in shallow wells outside of the plume. Evidence suggests that the overlying mud layer unique to this study site contributes the bulk of the NH4+ observed in these wells. NO3- concentrations at 9 m wells varied by a factor of four in response to concurrent variations in ATW NO3- loads over the coarse of the study. Estimated NO3- uptake rates varied from 32 +/- 29 to 98 +/- 69 and did not directly correlate with ATW NO3- loading as we hypothesized. We estimate that 70 +/- 34% of the NO3- from the treatment plant is removed from solution in the subsurface of the study site. Considerable decreases in NO3- concentration and enrichment of (NO3-)-N-15 was observed in many wells, indicating significant denitrification or anaerobic ammonium oxidation is occurring in the subsurface. Dissolved inorganic nitrogen concentrations, distributions, and N-15 compositions indicate that denitrification is likely the dominant mechanism for N removal in the ATW plume at Key Colony Beach, Florida. (C) 2007 Elsevier Ltd. All rights reserved.

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Estuarine Coastal and Shelf Science





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