三峡库区小流域土地利用结构变化及其氮素输出控制效应：以兰陵溪小流域为例

Land Use Structure Change and Its Control Effect of Nitrogen Output in a Small Watershed of Three Gorges Reservoir Area: A Case Study of Lanlingxi Watershed

基于三峡库区兰陵溪小流域退耕还林后土地利用结构变化分析,结合2015年汛期流域氮素养分输出监测数据,利用逐步回归定量分析土地利用结构特征对氮素输出的控制效应.结果表明:1退耕还林工程小流域土地利用结构发生改变,林地、园地面积比例分别增加到76.85%和13.87%,园地多以茶园单一类型片状分布,耕地面积比例锐减至1.16%,且零星分布于林地、园地之间.2小流域部分监测点总氮浓度超过国家Ⅴ类地表水水质标准,各监测点铵态氮(NH_4^+-N)、硝态氮(NO_3^--N)和总氮(TN)输出浓度分别为0.089~0.214 mg·L^(-1)、2.925~13.203 mg·L^(-1)以及3.561~14.572 mg·L^(-1),硝态氮输出浓度占总氮比例超过80%.3集水区氮素输出浓度与园地和住宅用地极显著正相关,与林地、未利用地则成极显著负相关,住宅用地和园地类型是主要的氮素输出源.4小流域土地利用结构调整应优先增加林地,适当控制园地发展,且将住宅用地面积比例控制在5%以下,并通过林茶、林果间作等方式改变小流域部分园地单一类型片状分布格局.

The nitrogen（ N） output in Lanlingxi watershed of Three Gorges Reservoir Area in 2015 was monitored and the current land use map was investigated. Cluster analysis and correlation analysis were used to identify the major sources of pollutants and to discriminate the source and the sink land use types. The effects of land use on N exports were quantitatively analyzed by stepwise regression analysis. The results showed that： 1 After the returning farmland to forest project the land use structure of this area changed dramatically. The area proportions of forest land and garden plot increased to 76. 85% and 13. 87% respectively,and the proportion of cultivated land dropped to 1. 16%. Cultivated lands were stellate distributed and garden plots in some catchments were flake distributed. 2 The content of TN in some monitoring points surpassed the Class V standard of the national groundwater environmental quality. The ammonium-N（ NH4＋-N） concentrations ranged 0. 089-0. 214 mg·L-1,2. 925-13. 203 mg·L-1for nitrate-N（ NO3--N）and 3. 561-14. 572 mg·L-1for total-N（ TN）. And NO_3^--N accounted for more than 80% of TN. 3 There were significant positive correlations between garden plot,residential land and N loss,and negative correlations between forest land,unutilized land and N export,which indicated that the former were N sources and the latter were sinks. 4Forest land area should be increased and garden plot should be controlled,and the area ratio of residential land should be kept below 5% when adjusting land use structure of this watershed. Moreover,forest-tea and forest-fruits modes should be applied to change single land use type of garden plot in some catchments.