Abstract
Atrazine fate and transport in three constructed pond and island wetlands in north east Illinois, USA, were studied in the field (1991) and modeled. The wetlands received pumped inflow from the Des Plaines River. The nominal residence time was about eight days for two, but was longer for the third. The river atrazine chemograph had two peaks that rose quickly after heavy spring rains and then subsided slowly. Maximum concentrations exceeded the United States federal drinking water standard (3 μg/l). The wetlands delayed, reduced, and spread out the peaks, removing 26 to 64% of their inflows depending on residence time. Flow and mixing models idealized the wetlands as single flow reactors or as networks of them. Atrazine reactions on biofilms with mass transfer rate limitation and when sorbed to sediments and litter were postulated. Simulation results were consistent with almost all atrazine reactions on biofilms. Mass transfer coefficients were 10–15 m/year with the wetland bottom taken as the biofilm area. The corresponding wetland half-lives were about 10 days. Best calibration resulted when most of the reaction took place near the pumping inlet. Model coefficients were similar to values for BOD and nutrients in other surface flow wetlands or to those derived from tracer data. The results suggest that observed removal rates of many pollutants in wetlands may reflect similar underlying mass transfer rate limitations.
Published Version
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