Spatial performance assessment of reed bed filtration in a constructed wetland

Constructed wetlands (CW) are implemented to improve water quality through filtration by plants (macrophytes), which sequester nutrients and contaminants. Macrophyte beds in CWs reduce the speed of water flow, aiming to improve the water quality by sedimentation and filtration with increasing distance from the inflow. Few studies have assessed spatial distribution and accumulation concentrations of nutrients and contaminants in CW macrophytes as a performance indicator for wetland functionality and management. Macrophytes and water were analysed for nutrient and contaminant accumulation in-situ at a stormwater-fed CW and water remediation site in South Australia. During the austral summer, macrophytes were sampled at 36 sites and water at 46 sites selected by a systematic GIS produced grid covering the entire wetland, which determined distance from the inflow for each site. A total of 144 Schoenoplectus validus (stems and roots) macrophyte samples (i.e. carbon-C, nitrogen-N, Trace elements) and 183 water samples (i.e. total suspended solids-TSS, total nitrogen-TN, total carbon-TC, nitrate-NO₃^-/ nitrite-NO₂^- and ammonia-NH₄⁺) were analysed. Concentrations of water chemistry parameters that significantly increased with distance away from inflow included; TC (P = 0.0008), TN (P = 0.0001), and NH₄⁺ (P = 0.0001), while there was significant decrease in TSS (P = 0.0001). The macrophyte S. validus significantly decreased in height (P = 0.0001) and biomass (P = 0.03) with distance from the inflow. Spatial mapping of nutrients and contaminants with distance from inflow identified increasing TC and C characteristics from inflow to outflow and identified where TSS were removed from the water column. Through this spatial assessment approach of the Oaklands CW, management has identified problem areas with flow regimes that require further investigation to enhance macrophyte water filtration performance which can be used in CWs elsewhere in the world.