人工降雨模拟河南淮河流域潮土非点源氮输出

为研究淮河流域农田非点源输出、区域农业非点源污染控制与管理,以河南淮河流域典型土壤(潮土)及其是否秸秆还田为对象,人工模拟0.5、1.0、1.5、2.0、2.5、3.0 mm·min^-1降雨强度下的径流、泥沙和氮输出负荷。结果表明:降雨强度越大,相同时间段内的累积径流量、累积泥沙量、氮输出量以及三者的产出速率均越大;径流中氮元素的浓度在降雨初期的20 min内变化较大,具初期冲刷效应,随后波动并趋于相对稳定或略有降低,其平均浓度在未掺混秸秆时以2.0 mm·min^-1降雨强度时最大,其次为3.0mm·min^-1,掺混秸秆后以1.5 mm·min^-1时最大;未掺混秸秆时氮元素泥沙输出量占总输出量的98.25%以上,但掺混秸秆后输出量有所降低(最低值为65.12%)。秸秆还田后,分别可在<1.0 mm·min^-1与<1.5 mm·min^-1的低降雨强度下减少径流与泥沙流失量,高降雨强度下则增加泥沙流失量;径流氮元素浓度比未掺混秸秆的高,增加了氮元素的累积输出量。累积径流量与累积泥沙量间及两者分别与氮元素输出量之间均存在良好的幂函数与对数函数关系,相关系数均在0.900以上。研究表明,降雨强度、秸秆还田均对径流、泥沙、氮输出等产生影响,引起氮输出明显变化的降雨强度在未掺混秸秆时为1.0 mm·min^-1,在掺混秸秆时为1.5mm·min^-1;减少农田非点源氮输出负荷的重要途径包括控制产流初期氮流失与泥沙流失。

Simulated rainfall effect on non-point source nitrogen output from fluvo aquic soil in the Huaihe River watershed, Henan Province, China

To identify the effect of rainfall intensity and straw returning on nitrogen output, to provide a basis for quantifing and controlling farmland non point source nitrogen output in the Huaihe River watershed, and regional environment management, taking typical soil(fluvo aquic)with and without mixed straw in the Huaihe River watershed of Henan Province as study object, rainfall intensities of 0.5, 1.0, 1.5, 2.0, 2.5 mm·min^-1, and 3.0 mm·min^-1 were simulated to study surface runoff, sediment loss, and nitrogen loss. Cumulative runoff, sediment loss, nitrogen output, and the loss rate of each over a fixed interval increased with rainfall intensity. The nitrogen concentration in runoff changed rapidly during the first 20 minutes of rainfall, showing an early flush effect, then fluctuated, becoming relatively stable or slightly declining at the end. Its average concentration without admixed straw increased from a high concentration at a flow rate of 3.0 mm·min^-1 to even higher at 2.0 mm·min^-1. Nitrogen concentration was highest at a rainfall rate of 1.5 mm·min^-1 in soil admixed with straw. The amount of nitrogen loss through sediment accounted for more than 98.25% of total loss, but was significantly reduced by mixing with straw(lowest loss rate was 65.12%). With straw returning, surface runoff and sediment loss could be reduced under low rainfall intensity(< 1.0 mm· min^-1 and < 1.5 mm ·min^-1 respectively), but sediment loss could be increased under high rainfall intensity. Nitrogen concentration with admixed straw was higher than that without, increasing cumulative nitrogen output. There were good correlations between cumulative runoff and sediment and nitrogen output. All correlation coefficients were above 0.900. Rainfall intensity and straw returning affected surface runoff, sediment, and nitrogen output. Rainfall intensity induced an obvious change in nitrogen output, with maxima at 1.0 mm · min^-1 without admixed straw, and 1.5 mm·min^-1 with admixed straw. Two important means for controlling farmland non-point source load include controlling nitrogen and sediment loss at early rainfall stages.