洱海流域生态塘湿地氮截留特征及其影响因素

To investigate the efficiency of nitrogen interception for rural non-point source pollution and to identify the dominating factors which restrain the performance of the ecological multi pond wetlands, basic design parameters and nitrogen concentrations were collected and analyzed in Erhai Lake sub-basin. The results showed that the water quality of the effluent was significantly improved after flowing through the ecological multi pond wetlands. (1) 37.5% of the effluent nitrogen concentrations were below the standard water quality of 'the environmental quality standards for surface water'(GB 3838-2002) Ⅲ. The Spearman correlation analysis showed that the purification efficiency was closely related to the influent nitrogen concentration and high nitrogen concentration could be effectively intercepted by the ecological multi pond wetlands. η(TN) was positively correlated with ρ(NH₄⁺-N) (R=0.226, n=84) and ρ(TN) (R=0.215, n=84), while it had a weakly negative correlation with ρ(NO₃^--N) (R=-0.201, n=84). Nitrate interception could be the limiting factor for the purification efficiency. (3) The alternation of high-water level ecological in the wet season and low water level ecological in the dry season was conducive to the stabilization of nitrogen detention efficiency. Wastewater from rural non-point sources in each catchment area was almost collected, intercepted and purified in the dry season. In the wet and dry season, η(NH₄⁺-N) was 57.72% and 55.30%, respectively. η(NO₃^--N) was 49.45% and 46.73%, while η(TN) was 54.41% and 54.20%, respectively. The single factor analysis was helpful to identify the controlling factors of nitrogen purification efficiency. No significant relationship was observed between nitrogen purification efficiency and design parameters (area (<8,000 m²), storage capacity (<15,000 m³) and water depth (<2.0 m)) in this Erhai Lake basin. However, a suitable water depth (<0.4 m and >1.5 m) is beneficial to the nitrogen removal.