Investigating the Critical Role of a Wetland in Spatial and Temporal Reduction of Environmental Contaminants: a Case Study from Iowa, USA

摘要

Beaver Valley Wetland in north-east Iowa, USA, was studied to determine its effectiveness in filtering incoming contaminants from the surrounding agricultural fields. The assessment was based on temporal and spatial variations in contaminant levels as they moved from the inlet to the outlet areas of the wetland. Temporally, the average conductivity and total dissolved solids in water were higher during mid-summer (273.40 mu s/cm and 188.34 mg/L) than in early (260.70 mu s/cm and 179.91 mg/L) and late summers (247 mu s/cm and 169.70 mg/L), respectively. The findings are attributed to rainfall, algae growth and high organic loads in July and August. Most contaminants showed significant decrease (30% - 74%) in concentrations going from the inlet to the outlet. On average, high loads of erodible soils during mid-summer resulted in high turbidity (45.1 NTU), high total suspended solids (TSS, 241.5 mg/L), and thereby low dissolved oxygen (DO, 1.4 mg/L) at the inlet area. Much higher DO (11.7 mg/L), lower turbidity (11.8 NTU), and lower TSS (63.8 mg/L) were observed at the outlet. Most heavy metals accumulated and retained in 15.2 cm-deep wetland soils. Tracer tests confirmed that removal of contaminants is occurring within the wetland vegetation and the top few cms of soils.