洱海流域生态塘湿地氮截留特征及其影响因素

Characteristics and Effects of Nitrogen Interception in the Ecological Multi Pond Wetlands in Erhai Lake Sub-Basin

为考察生态塘湿地对农村面源污染水体氮截留效果及其影响因素,以洱海子流域生态塘湿地为例,对其基本设计参数和水质进行调查分析,评估生态塘湿地对氮的截留效果,识别不同形态氮在湿地中的迁移转化特征,剖析生态塘湿地中氮截留的主控因子.结果表明:(1)污水经生态塘湿地净化处理后,出水水质显著改善.出水氮达GB 3838—2002《地表水环境质量标准》Ⅲ类标准的比例为37.5%.(2)Spearman相关分析表明,湿地净化效率与湿地氮输入密切相关,生态塘湿地可以有效实现氮的截留,η(TN)(η为去除率)分别与ρ(NH_4^+-N)(R=0.226,n=84)、ρ(TN)(R=0.215,n=84)呈显著正相关,与ρ(NO_3^--N)(R=-0.201,n=84)相关性不强,硝酸盐氮截留是其效率提高的主要制约因素.(3)丰水期、枯水期高低水位交替运行有助于氮截留效率的稳定,枯水期生态塘几乎可以截蓄汇水分区内全部农村面源污水,实现污水的收集消纳及净化.丰水期和枯水期平均η(NH_4^+-N)分别为57.72%和55.30%;平均η(NO_3^--N)分别为49.45%和46.73%;平均η(TN)分别为54.41%和54.20%.(4)单因素分析法有助于识别影响湿地氮净化效率的主控因子.研究显示,当生态塘湿地面积(<8 000 m^2)、库容(<15 000 m^3)、水深(<2.0 m)在一定范围内时,氮净化效率与面积、库容、水深响应关系不显著,但合适的水深(<0.4 m和>1.5 m)有利于氮的截留.

College of Ecological and Environmental Sciences, East China Normal University, Shanghai 200241, China Abstract: 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(NH 4^+-N)( R =0.226, n =84) and ρ(TN)( R =0.215 , n =84), while it had a weakly negative correlation with ρ(NO 3^--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(NH 4^+-N) was 57.72% and 55.30%, respectively.η(NO 3^--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 m^2 ), storage capacity (<15,000 m^3 ) 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.