Complex flow patterns and hydraulic characteristics could reduce the utilization efficiency of constructed wetland (CW), and consequently, its pollutant removal performance. Thus, it is of great importance to explore the internal flow patterns of CWs. Isotopic molecules exist naturally in CWs and have special properties under liquid conditions; using hydrogen and oxygen isotope technology cannot only reduce secondary pollution but also reflect the hydraulic characteristics of CWs. In the present study, the annual variation of isotopic composition in field-scale CW was investigated to evaluate the long-term feasibility of stable isotopic technology characterizing hydraulic flow patterns. The relationship between nutrients concentration distribution and flow pattern variation in CW under different seasons was discussed as well. Results demonstrated that isotope 18O/16O distribution could be used to determine the internal flow pattern of CW throughout the year, except for preferential flow area of CWs in winter, since more hydraulic retention time is needed to ensure the change of water isotopes due to the small evaporation in winter. Lower ammonia nitrogen concentration was observed in the stagnant area, while the total phosphorus concentration of the stagnant area increased during winter. And more attention should be paid to aquatic plants during the CW design, since it has significant influence on the hydraulic flow patterns of CW.
Keywords: Ammonia; Constructed wetland; Evaporation; Hydraulic flow patterns; Total phosphorus; Water isotopes.