Urban constructed wetlands are typically designed to capture sediments and pollutants such as nutrients and heavy metals from surrounding landscapes. The hypothesis for this study is that ecotoxicological assays, based in growth inhibition of three plants (Sinapis, Sorghum and Lepidium) by sediment from wetlands can serve as predictive indicators of pollutant loadings in urban constructed wetlands. The goal is to evaluate the potential for ecotoxicological assays to serve as indicators of wetland effectiveness in mitigating ecological impacts of pollution.
The study was conducted in the Pike River watershed (Racine, WI) in six wetlands across a gradient of dominant land use types (agricultural, commercial, residential, undeveloped and industrial lands). Pollutant loadings into wetland sites were estimated based on the Source Load and Management Model (SLAMM) and studies of published literature. Sediment samples were collected from the wetlands during summer 2015 and 2017 and water quality parameters were measured using multi-parameter YSI 6600 sondes. Nitrate and orthophosphate concentrations were analyzed spectrophotometrically using HACHTMkits. Ecotoxicological tests were conducted with wetland sediments using PhytotoxkitTM, (Microbiotest Inc. 2015). The presence of metals in the sediments was estimated using X-ray fluorescence (XRF; EPA Method 6200).
Results/Conclusions
Results indicate that the percentages of industrial and undeveloped land use are positively correlated with nitrate and phosphate concentrations in wetland waters. Nitrate and phosphate concentrations were observed to be between 2-4 mg/L and 0.2 – 0.5 mg/L respectively with increasing industrial (12.1 – 20.8) land use percentage. Whereas, Nitrate and Phosphate concentrations were observed to be between 0-6 mg/L and 0.25 – 0.5 mg/L respectively with increasing undeveloped (7.41-49.3) land use percentage. In terms of the ecotoxicological test species, proportion growth inhibition of root and stem in Lepidiumand Sinapis increased withincreasing residential land use. The specific increase in the proportion growth inhibition of root and stem were from 0 to 0.6 and 0 to 0.1 respectively with increasing percentage of residential (11 -58) land use.Patterns of covariation show that ecotoxicological assays can serve as indicators of pollution loading into the wetlands.
In addition, we are also characterizing the extent to which the patterns in sediment bacterial taxonomical diversity (e.g. Proteobacteria, Firmicutes, Actinobacteria, Bacteroidetes, Chloroflexi, Planctomycetes) co-vary with eco-toxicological assay. Preliminary results will be shown and discussed.
The take home message from this study is that simple plant ecotoxicological indicators can be predictive indicators of pollutant loadings in urban constructed wetlands.