洱海北部表流人工湿地氮截留的长效性及影响因子

Long-term effects and influencing factors of nitrogen retention in a surface flow constructed wetland in the northern part of Erhai Lake

以洱海北部正常运行10 a的罗时江河口湿地为研究对象,通过开展为期1 a的现场定点监测及文献调研,探讨洱海流域运行1、5、10 a的人工湿地氮截留动态变化及影响因子。结果表明:罗时江河口湿地上覆水无机氮浓度呈现显著干、湿季节分异,干季无机氮浓度显著高于湿季(P<0.05);从空间分异看,湿地进水口TN、NH4+-N和NO3--N浓度平均值分别为3.34、0.75、0.77 mg·L^-1,出水口浓度分别为2.01、0.42、0.45 mg·L^-1,表明正常运行10 a的罗时江河口湿地仍具备氮截留能力。正常运行1、5、10 a后的人工湿地对TN、NH4+-N和NO3--N的平均截留效率呈下降趋势,但差异未达到显著水平(P>0.05)。运行10 a后的罗时江河口湿地对TN、NH4+-N和NO3--N的平均截留效率分别为37.2%、34.6%和29.2%。冗余分析和Pearson相关分析结果显示,上覆水中DO、ρ(NH4+-N)、COD/TN及温度是罗时江湿地氮截留的重要影响因子。研究表明,处于氧化环境的上覆水有利于硝化过程,但不利于反硝化过程,后续湿地恢复、建设、管理中应重点优化湿地中的反硝化过程,以提升氮截留效果。

Taking the Luoshijiang estuarine wetland, which was constructed 10 years ago in the northern part of Erhai Lake, as the study target, the dynamic change in nitrogen retention in the restored wetland in the Erhai watershed for 1, 5, and 10 years and its influencing factors were evaluated based on one-year in-situ monitoring and literature research. The results showed that:The concentration of inorganic nitrogen in the overlying water of the Luoshijiang estuarine wetland differed significantly between the dry and wet seasons;the concentration of inorganic nitrogen in the dry season was significantly higher than that in the wet season(P<0.05). The average concentrations of TN,NH4+-N, and NO3--N in the wetland inlet were 3.34, 0.75 mg·L^-1, and 0.77 mg·L^-1 respectively, and those in the wetland outlet were 2.01,0.42 mg·L^-1, and 0.45 mg·L^-1 respectively, indicating that the Luoshijiang estuarine wetland was still capable of retaining nitrogen after 10 years of normal operation. The average TN, NH4+-N, and NO3--N retention efficiency of the restored wetlands in the northern part of Erhai Lake after 1, 5, and 10 years of normal operation showed a decreasing trend, but the difference did not reach a significant level(P>0.05).The efficiency of nitrogen retention in the restored wetlands with different operation periods also varied with dry and wet seasons. The retention efficiencies of TN, NH4+-N, and NO3--N in the Luoshijiang estuarine wetland after 10 years of operation were 37.2%, 34.6%, and29.2%, respectively. Redundancy analysis(RDA)and Pearson correlation analysis revealed that the ranges of DO, ρ(NH4+-N), COD/TN,and temperature were beneficial to the nitrification process, but detrimental to the denitrification process. Thus, subsequent restoration, construction, and management of wetlands in Erhai Lake should focus on the optimization of the denitrification process of the overlying water to enhance the efficiency of nitrogen retention.