三峡库区小流域不同土地利用类型对氮素流失影响

作为一个独立汇水单元,小流域是三峡库区面源污染源头.在三峡库区涪陵段王家沟小流域内选择最具有代表性3种土地利用类型布设地表径流监测点,利用2014年5~12月12场自然降雨采集地表径流样品,分析不同土地利用类型及其构成的坡面、子流域氮素流失浓度时空变化特征,揭示三峡库区小流域不同土地利用类型与氮素流失关系.结果表明,不同土地利用类型春季作物时期TN平均流失浓度差异最大,旱地分别是桑树套种地、水田的1.61、6.73倍;水田3个时期TN流失浓度变化最显著.氮素流失以NO~-_3-N为主,TN与NO~-_3-N存在显著的线性相关关系.TN、NO~-_3-N流失浓度与坡面旱地作物玉米、榨菜面积比显著正相关,与水稻、桑树面积比显著负相关;NH~+_4-N流失浓度与坡面榨菜面积比显著正相关.不同土地利用类型组成坡面中,桑树套种地与水田组成的坡面3个时期TN地表径流平均流失浓度最低,分别为2.55、11.52和8.58mg·L~(-1);玉米榨菜轮作旱地坡面最高,分别为27.51、25.11和27.11 mg·L~(-1).子流域不同土地类型和空间组合方式对其TN流失浓度影响较大,合理调整流域土地利用结构和空间布局是三峡库区面源污染源头控制有效措施.

Nitrogen Losses Under the Action of Different Land Use Types of Small Catchment in Three Gorges Region

As an independent water-collecting area, small catchment is the source of non-point source pollution in Three Gorges Region. Choosing 3 kinds of the most representative land-use types and using them to lay monitoring points of overland runoff within the small catchment of Wangjiagou in Fuling of Three Gorges Region, the author used the samples of surface runoff collected through the twelve natural rainfalls from May to December to analyze the feature of spatial-temporal change of Nitrogen''s losses concentrations under the influence of different land use types and the hillslopes and small catchments composed by those land use types, revealing the relation between different land-use types and Nitrogen''s losses of small catchments in Three Gorges Region. The result showed: the average losses concentration of TN showed the biggest difference for different land use types during the period of spring crops, and the average value of dry land was 1.61 times and 6.73 times of the values of interplanting field of mulberry and paddy field, respectively; the change of the losses concentration of TN was most conspicuous in the 3 periods of paddy field. The main element was NO₃^--N, and the relation between TN and NO₃^--N showed a significant linear correlation. TN''s and NO₃^--N''s losses concentrations were significantly and positively correlated with the area ratio of corn and mustard, but got a significant negative correlation with the area ratio of paddy and mulberry; NH₄⁺-N''s losses concentrations got a significant positive correlation with the area ratio of mustard. Among all the hillslopes composed by different land use types, TN''s average losses concentration of surface runoff of the hillslope composed by interplantating field of mulberry and paddy land during the three periods was the lowest, and the values were 2.55, 11.52, 8.58 mg·L^-1, respectively; the hillslope of rotation plough land of corn and mustard had the maximum value, and the values were 27.51, 25.11, 27.11 mg·L^-1, respectively; different land use types and spatial combination ways of subcatchment had a greater influence on TN''s losses concentrations, so using a reasonable way to adjust land use structure and spatial arrangement of whole catchment was an effective measure to control the source of non-point source pollution of Three Gorges Region.