丘陵地区流域土地利用对氮素径流输出的影响

氮素是地表水体富营养化的一个限制因子,土地利用对农业非点源污染的氮素输出具有重要的影响.以位于亚热带低山丘陵地区的安徽省南部宣城市梅村流域为实例,通过航空遥感图像解译、GIS分析和实地定位动态监测方法,研究了具有不同土地利用结构的农-林生态系统地表径流水的氮素含量和输出通量及其与土地利用的定量关系.结果表明:氮素的输出以NO₃^--N的输出为主,土地利用类型或土地利用格局对径流水中氮素的含量和输出具有非常显著的影响.在同一种土地利用结构系统下,NO₃^--N与T-N的含量间具有极显著的正线性关系;而只有林地-水塘系统下,NH₄⁺-N与T-N的含量间有极显著线性关系.而各类氮素的输出量间都具有极显著正的线性相关关系.各类氮素的输出量都与土地利用类型具有指数相关性,林地、水塘对氮素输出具有负效应,而水田和村庄则具有正效应.同时,土地利用类型对径流中氮素的含量也有影响.

The Impact of Land Uses on Watershed Runoff Nitrogen Discharge in Hilly Regions

Nitrogen is a crucial factor in causing the eutrophication of water body. Land use has an important impact on agricultural non-point sources (NPS) nitrogen discharge. This study on quantitative relationship of runoff nitrogen discharge and land use was conducted in Meicun watershed of Xuancheng County, Anhui Province, in the subtropical low hill area, by the dynamic monitoring of stream water and nutrient discharge, integrating interpretation of aerial image and GIS analysis. The results showed that, land use significantly affect nitrogen concentration and discharge in which nitrate nitrogen was the main component. There was a significant linear relationship between nitrate and total nitrogen concentration in the given land use system. However, statistically significant relationship between ammonium and total nitrogen concentration was found only in forest-pond system. Moreover, positive linear relationship existed between different forms of nitrogen discharge. It was found that there were exponential relationship between the discharge of nitrate, ammonium and total nitrogen and the area percentages of forest, pond, paddy and village. Forest and pond had a negative impact on nitrogen discharge while the paddy and village had positive effect. At the same time, land use types had important effect on nitrogen concentration.