Evaluating Complex Hydrogeological Settings in a Constructed Wetland: An Isotopic/Chemical Mass Balance Approach

The objective of this study was to investigate the hydrogeological conditions of an artificial wetland, with four possible sources of water: (1) ground water, (2) industrial waste water, (3) seepage from a water body to the north, and (4) seepage from a water body to the south. The wetland was designed to improve the quality of municipal effluent and industrial wastewater. To evaluate and separate the impact of wetland processes from those due to dilution with water from “clean” sources (i.e., rain water or ground water), a combined isotope/chemical mass-balance approach was employed. The δD, δ18O, and Na were monitored for 18 months. Based on the data, the variation of individual proportions of each water type in the wetland and monitor wells was calculated. The isotopic composition of water in the wetland varied throughout the study period changing along the wetland flow path. The wetland contained mainly wastewater (88%–100%) during normal operations; however, hurricanes and inconsistent pumping added low conductivity water directly and triggered enhanced groundwater inflow into the wetland of up to 78%. Finally, the composition of water in monitor wells was mostly groundwater dominated; however seepage from a water body to the north was detected.