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Constructed wetland (CW) is a promising engineering technique for removal of excess nutrients and certain pollutants from wastewaters. This study characterized shallow groundwater quality for conditions with and without a CW. A shallow groundwater monitoring network with three wells was initiated in a row-crop production area of the Lower St. Johns River Basin in Hastings, Florida in 2003. This row-crop production area was then converted into a CW for stormwater treatments in 2006 without altering the monitoring wells, which provided a unique opportunity for estimating impacts of the CW on shallow groundwater quality. A total of six years (three years for pre-CW and another three years for post-CW) data were used for statistical analysis. Results showed that based on averaged values from all of the wells, there were significant differences (a = 0.05) between the pre- and post-CW for nutrients (i.e., nitrate and nitrite, total Kjehldahl nitrogen, and potassium); for cations (i.e., total aluminum (Al), calcium, magnesium, manganese); for physical parameters and anions (i.e., oxidation-reduction potential (ORP), pH, water level, and sulfate); and for heavy metals (i.e., nickel (Ni), and zinc (Zn)). Based on comparisons from each well, there were significant differences (a = 0.05) between the pre- and post-CW for Al, ORP, water level, and Ni. Results further revealed that among the significantly different water quality parameters, most of them had higher contents after the establishment of the CW except for Al, pH (slightly), Ni, and Zn. This study suggested that CW had discernable impacts on biogeochemical processes and thereby on shallow groundwater quality. |