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Groundwater Characterization and Assessment of Contaminants in Marine Areas of Biscayne National Park


Geologic Setting
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No significant evidence of contamination from groundwater into Biscayne Bay was found during this study. Low-salinity water was identified from nearshore wells and may indicate some leakage from the Biscayne Aquifer and/or surface-water intrusion into the rocks along western Biscayne Bay. Elevated nutrients in wells along the western shore indicate surface-water exchange is more likely than groundwater flow. Both ammonium and total soluble nitrogen were greater in nearshore wells than in the Biscayne Aquifer. Nitrite and nitrate were greater in Biscayne Aquifer water than in nearshore Biscayne Bay wells, indicating the possibility of nitrogen reduction along the shore. Lack of seasonal variation in groundwater salinity points to sluggish exchange with surface water. The groundwater beneath the shelf can be characterized as reduced seawater, modified by microbial respiration to remove oxygen and interaction with sediments and minerals in the host limestone. Analyses of 109 water samples collected from wells across the Florida shelf beneath BNP between August 2002 and March 2004 show no consistent evidence of wastewater contaminants occurring in groundwater beneath BNP. In addition, no significant leakage from the Floridan Aquifer was detected in the groundwater beneath BNP. At Black Point, the western edge of Biscayne Bay is influenced by surface water and perhaps by Biscayne Aquifer water, but the bulk of BNP is underlain by uncontaminated marine groundwater.

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U.S. Department of the Interior, U.S. Geological Survey
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Last updated: 04 September, 2013 @ 02:04 PM (KP)