Purification effect and stability of water quality of different functional units in Laoyuhe Wetland Park of Dianchi Lake

Taking Laoyuhe Wetland Park (WP_lyh) in Dianchi Lake as the research object, sampling points were set up in different functional units of the wetland to analyze the removal effects of COD_Cr, N ${\mathrm{H}}_4^{+}$ -N and TP by different functional units in the testing operating period from April 15 ^th, 2015 to May 14 ^th, 2015. Sampling points were also set up at the inlet and outlet of wetlands and the long term operation effects in the period from April, 2015 to March, 2017 were monitored and analyzed. It revealed that during the WP_lyh test run, the COD_Cr, N ${\mathrm{H}}_4^{+}$ -N and TP concentrations in the outlet were significantly lower than those in the inlet, with the removal rates of 40.07%, 48.48% and 40.38%, respectively, while the treatment effect was still unstable. Among the functional units, the surface flow wetland at the entrance of the lake had the best removal effect on COD_Cr with removal rate of 10.36%, the front part of the inter-forest shallow-water wetland had the best removal effect on N ${\mathrm{H}}_4^{+}$ -N with the removal rate of 17.59%, and the back part of the inter-forest shallow-water wetland had the best removal effect on TP with the removal rate of 9.44%. It means that the decontamination rate of the inter-forest shallow-water wetland accounted for 53.15% of WP_lyh total decontamination rate, which could be regarded as the best purification unit in the wetland parks. WP_lyh's monthly reductions and removal rates for COD_Cr, N ${\mathrm{H}}_4^{+}$ -N, and TP during long term operation and the removal rates of the three characteristic pollutants showed a downward trend with time. Especially after one year of operation, the downward trend was most obvious.