Spatiotemporal water quality variability in a highly loaded surface flow wastewater treatment wetland

This study evaluates spatiotemporal relationships between water quality parameters (WQPs), nutrients, suspended solids, and biochemical oxygen demand (BOD) concentrations within an engineered wastewater treatment wetland system in the Georgia Piedmont, USA. We explored factors related to treatment efficiency within a heavily loaded 630-m(2) surface flow wetland system over a 2-yr period. Relationships between temperature, dissolved oxygen (DO), and oxidation-reduction potential (ORP) were observed; relationships were also seen between these WQPs and nutrient concentrations. Because temperature, DO, and ORP affect nitrogen (N) cycling rates, seasonal trends in N forms were evident in the system. Organic N and inorganic/organic phosphorus concentrations correlated with solids concentrations in the vegetated system without exhibiting seasonal trends. Surface water within the vegetated section generally exhibited anoxic conditions, leading to removal of nitrate-N within the system; however, limited mineralization and nitrification occurred, which greatly limited overall N removal. Plant selection and lack of maintenance likely led to high solids and BOD contributions to treatment wetland surface water, which varied substantially between and along monitored transects. Because so few studies have investigated treatment dynamics within treatment wetland cells, focusing solely on influent/effluent characterization, radical spatiotemporal variability may be the norm as opposed to the commonly accepted assumptions of relatively uniform pollutant degradation across treatment wetland cells. This spatiotemporal variability in WQPs underscores the dynamic nature of treatment wetlands and the need for routine maintenance, including sludge removal and plant harvesting.