Assessment of Water Quality Characteristics and Purification Efficiency of Constructed Wetlands with Different Operation Duration in the Northern Erhai Lake

The Luoshijiang wetland and the Jiangqian Wetland in the north of Erhai Lake have been operating for 11 years and 6 years, respectively. Three sampling points were set up at the inlet and outlet of the wetlands and the middle section of the wetlands from August 2019 to July 2020, to investigate the pollutant purification efficiency of constructed wetlands. The results showed that TP and NH₃-N in the Luoshijiang wetland and the Jiangqian wetland were in the class of Ⅰ～Ⅱ, TN and COD were in the class of Ⅰ～Ⅲ. Both wetlands still had a certain water purification capacity. The average removal rates of NH₃-N, TN and TP in the Jiangqian wetland was better than that in the Luoshijiang wetland. After 11 years of operation, the pollutant removal rate of the Luoshijiang wetland decreased significantly, which suggests that it is necessary to carry out environmental dredging or wetland function transformation.