This study seeks to single out the individual effectiveness of specific macrophytes for water contaminant mitigation and the application of this type of nature-based solutions (NBS) as the primary methodology for targeting specific water contaminants in constructed wetlands. We built lab-scale constructed wetland models using the same wetland plant species utilized in an urban Texas lake that was historically contaminated when it was used as a terminal sewage site for the city of San Antonio until the sanitation was modernized. The initial stage had the species separated as monocultures to test for species-specific contaminant removal properties; and the second stage evaluated only the targeting macrophyte in majority-scaled density plantings. Using a comparable influent water source to Mitchell Lake, the model wetland effluent was evaluated after an 8-week period for various chemical and physical factors. A similar second 8-week stage was then tested to evaluate the extent to which the targeting macrophyte improved the water quality of the effluent. Targeting macrophyte in the second stage comprised of a 50%, 70%, and 90% comparative planting density (respectively). Overall evaluations of water quality were then made by comparing the water quality results from the second phase to the results from the Mitchel Lake Pilot Project. Three species of native wetland bulrush were planted: Olney's Bulrush (Schoenoplectus americanus), Hardstem Bulrush (Schoenoplectus acutus), and Giant Bulrush (Schoenoplectus californicus). Water quality monitored primarily included COD, turbidity, pH, DO, electrical conductivity, and ammonia. Supporting water quality analysis included carbonaceous BOD5, ammonia, and major anions. The growth and health of vegetation was also recorded as supporting evidence.
First-stage results demonstrated that Giant Bulrush outperformed the two other species in terms of the overall water quality yielded. All monoculture cells performed well in enhancing DO levels and turbidity reduction. COD and conductivity remained high but consistent through Stage 1 run, indicating leaching from the soil and underlaid gravels. As a result, we selected Giant Bulrush as the target macrophyte to mix with the other two species in equal density at the prescribed ratios for Stage 2 experiments. In addition to the monitored water quality parameters, we set up additional cells to study the removal of Escherichia coli and heavy metal (chromium III and VI).

Austin McBrady

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