山地表生过程与生态调控重点实验室知识库

为揭示紫色土丘陵区小流域径流过程和氮素流失过程中迁移转化机制,同步监测了该区域内苏蓉(3.01 hm~2)、截流(35 hm~2)、大兴(480 hm~2)、万安(1 236 hm~2)4个梯级小流域径流过程与氮素迁移特征,分析了不同雨型条件下典型农业小流域中氮素迁移转化规律与尺度效应。结果表明:流域面积越小洪峰对降雨响应越快,随着面积增大,洪峰在流域中有明显的滞后和坦化现象;全氮(TN)、硝态氮(NOx-N)浓度在降雨过程中呈现出较为明显的两段式特征,降雨产流初期及径流峰前期波动较大,退水期浓度缓慢上升。相较人为影响较强的源头小流域(苏蓉)而言,尺度较大小流域的TN浓度有较为明显的削减,但NOx-N仍是氮素流失的主要形式。根据NCL-NCF曲线可知,历时短、强度大的暴雨更容易产生初始冲刷效应,梯级流域对AN负荷有明显消减作用。携带大量NOx-N的壤中流和地下水控制退水过程线,并不断补充水体中氮素负荷,表现出一定的末期冲刷效应。运用数理统计方法得出TN流失总量与流域面积之间的经验公式,可为区域内小流域氮流失通量估算提供依据。

In order to elucidate the nitrogen loss mechanisms and runoff process in agricultural catchments in hilly purple soil region. Synchronized monitoring on runoff process and nitrogen transport was carried out during three storm events at four cascading small watershed, which are Surong, Jieliu, Daxing and Wan'an catchments. In addition,we analyzed the regulation of nitrogen transportation and scales effects of runoff process. The results showed that the peak discharge had the quick response to rainfall in smaller catchments while delayed and smoothed peak discharge appeared in lower reaches at Daxing and Wan'an stations; total nitrogen (TN),nitrate nitrogen (NO_3-N) concentration in the process of rainfall showed the obvious characteristics in the two stage, the drastic fluctuations in the runoff production, and concentration rise in flow withdraw. Compared with Surong station, TN concentrations in larger catchments decreased obviously, N03-N was the main form of nitrogen loss. According to NCF-NCL curve,short and heavy rain is more likely to produce the 'first flush' effect,however, cascading small watershed showed the significant reduction in storm. The subsurface flow and groundwater flow which carries a large number of N03-N controlled receding process line,and continuously added nitrogen load in the water, showing the 'end flush' effect. Regressed empirical equations between cumulated TN load and watershed area were obtained,which could be used to provide reference for estimating nitrogen losses in the similar watersheds.