退耕还林措施对滇中尖山河坡地氮磷流失的削减效应

[目的]探究滇中尖山河流域退耕还林措施下不同地类侵蚀性降雨、氮磷流失浓度、流失量的动态变化特征，对评价退耕还林生态工程对流域水体保护和面源污染的削减效应具有重要的指导意义。[方法]选择抚仙湖湖区典型流域尖山河小流域为研究区，以流域内退耕还林/坡耕地、人工林、灌木林和次生林为研究对象，对流域不同土地利用类型径流小区进行连续三年(2017—2019年)雨季(5—10月)定量监测。[结果]退耕还林后年侵蚀性降水量和年径流量分别降低37.16%和42.75%,产流量降低95.88%和94.29%。各态氮磷输出浓度分别削减：总氮34.32%、硝态氮32%、铵态氮61%、总磷73.4%和磷酸盐70.4%;各态氮磷输出量分别减少了总氮70.40 mg/m²,硝态氮41.24 mg/m²,铵态氮20.56 mg/m²,总磷162.16 mg/m²和磷酸盐107.38 mg/m²,削减率分别为：79.29%,80.48%,88.20%,95.66%和97.06%。未退耕还林前坡耕地总氮、硝态氮、...

Reduction Effect of Returning Farmland to Forest on the Losses of Nitrogen and Phosphorus on the Slope of the Jianshan River in Central Yunnan

[Objective]It is of great guiding significance for evaluating the reduction effect of the ecological project of returning farmland to forests on the protection of water environment and non-point source pollution in the river watershed to explore the dynamic change characteristics of erosive rainfall, nitrogen and phosphorus loss concentrations and loss amounts of different land types under the measures of returning farmland to forests in the Jianshan River watershed of central Yunnan Province. [Methods] Jianshan River watershed, a typical watershed in Fuxian Lake area, was selected as the study area. The main research objects were returning farmland to forest/sloping farmland, artificial forest, shrub forest and secondary forest in the watershed. Through quantitative monitoring in the different land use type runoff area in rainy season(May—October)for three consecutive years(2017—2019), the concentration, amount and dynamic characteristics of erosive rainfall, nitrogen and phosphorus losses were studied. [Results]The annual erosive precipitation and annual runoff after returning farmland to forests decreased by 37.16% and 42.75%, respectively. Runoff decreased by 95.88% and 94.29%, respectively. The export concentrations of of total nitrogen, nitrate, ammonium nitrogen, total phosphorus, and phosphate reduced by 34.32%, 32%, 61%, 73.4% and 70.4%, respectively. The non-point source pollutantoutputs of for TN, NO^-₃-N, NH⁺₄-N, TP and PO^3-₄-P decreased 70.40 mg/m², 41.24 mg/m², 20.56 mg/m², 162.16 mg/m²,and 107.38 mg/m², respectively. The reduction rates were 79.29%, 80.48%, 88.20%, 95.66% and 97.06%, respectively. The output concentrations of TN, NO^-₃-N, NH⁺₄-N, TP and PO^3-₄-P of slope farmland before conversion were 156.80%, 149.57%, 173.15%, 157.42% and 153.82% of those of other land use types, respectively. After two years, they were 139.00%, 117.66%, 108.08%, 123.18% and 92.29% respectively, which were still higher than those of other land use types in the watershed, but the reduction and control effects on nitrogen and phosphorus had increased year by year. [Conclusion] The restoration of farmland to forests in the Jianshan River watershed has effectively improved the status of non-point source pollution and soil erosion in the watershed, and provided scientific basis and data support for the governance of the water environment in the lakeside watershed.