农业小流域土地利用格局变化对氮素输出的影响——以丹江口库区胡家山小流域为例

流域土地利用格局对农业非点源污染氮素输出具有重要的影响。以丹江口库区胡家山小流域为研究对象,分析2008～2016年土地利用类型变化对流域总氮输出的影响,以期为丹江口库区生态清洁小流域建设提供参考。结果表明:2008～2016年,流域出口处总氮年平均浓度从5. 13±4. 2 mg/L降低为2. 06±0. 62mg/L;总氮输出负荷由49 025 kg/a降低至21 578 kg/a,总氮输出负荷减少56. 0%。对比分析流域生态治理工程实施情况,发现坡改梯、退耕还林等水土保持治理与植被恢复措施在有效控制水土流失的同时,还在减少流域氮素输出中发挥了重要作用。经相关分析,流域内林地、耕地、居民地的空间分布格局对流域氮素输出均有影响,其中100 m河岸带范围为流域总氮负荷输出的主要区域。有效控制胡家山小流域100 m河岸带尺度的氮素流失,可显著降低流域总氮输出负荷。

Effects of land use pattern change on nitrogen export of Hujiashan Watershed in Danjiangkou Reservoir Area

Land use pattern has important effects on nitrogen output from agricultural non-point source pollution. Taking Hujiashan watershed in Danjiangkou reservoir area as the research object, this paper analyzed the influence of land use pattern change on the total nitrogen output of the basin from 2008 to 2016 to provide reference for the construction of ecological clean watershed in Danjiangkou reservoir area. The results showed that the annual average TN concentration at the outlet of Hujiashan watershed declined from 5.13±4.2mg/L to 2.06±0.62mg/L during 2008~2016; TN output load of the watershed decreased from 49025kg/a to 21578kg/a, reduced by 56%. By comparing and analyzing the implementation of watershed ecological control project in Hujiashan watershed, it showed that the soil and water conservation and vegetation restoration measures, such as conversion of slope-to-terrace and returning farmland to forest, played an important role in effectively controlling soil and water loss and reducing nitrogen output in watershed. Correlation analysis showed that the spatial distribution pattern of forest land, farmland and residential land all had impacts on nitrogen output in the watershed, and 100m riparian zone was the main area of total nitrogen output in the watershed. Effective control of nitrogen loss in 100m riparian zone of the watershed can significantly reduce total nitrogen output load of the whole watershed.