黄土丘陵沟壑区草地径流和泥沙拦截效率及其影响因素

Efficiency of runoff and sediment interception by grass strips and their influencing factors in a hilly Loess Plateau region

植被措施是控制水土流失的重要手段,拦截效率反映植被对上方来水来沙的拦截能力,厘清拦截效率的影响机制是科学布设植被拦截带的理论基础.针对黄土丘陵沟壑区撂荒1年草地、撂荒7年草地、柳枝稷(Panicum virgatum)3种植被拦截带,通过自然降雨条件下持续3年的单一植被配置及其组合的径流小区观测试验,设计了一种新的拦截率确定方法.通过方差分析、冗余分析、回归分析揭示拦截效率的差异及其影响因素.结果表明:(1)径流与泥沙拦截率的整体趋势为撂荒7年草地>柳枝稷>撂荒1年草地,5度坡面>15度坡面>25度坡面;撂荒7年草地与柳枝稷的径流与泥沙拦截率在坡度之间的相对差异较小,说明两种草地的拦截功能相对稳定.(2)径流拦截率主要受降雨特征和上方来水量影响(简单效应在7.8%-26.7%之间);泥沙拦截率主要受土壤与植被特征影响(简单效应在6.9%-32.1%之间),降雨和径流的影响相对较小;降雨与径流特征对径流与泥沙拦截率具有负效应,土壤性质(土壤容重除外)与地表覆盖具有正效应.(3)拦截效率对降雨和径流特征呈现非线性响应关系,其中5度坡面上方来水量<3 mm、前期降雨指数<10 mm时径流拦截率随两者快速降低,超过阈值后径流拦截率缓慢降低;植被与土壤因素的相互关联、降雨与径流因素的复杂多变引起拦截率预测的不确定性.总之,达到一定年限的撂荒草地和人工草地柳枝稷适宜作为黄土丘陵沟壑区的植被拦截带,调控地表覆盖与土壤性质可以改善草地的拦截功能,降雨条件是影响草地拦截功能发挥的重要外部因素.

Vegetation measures are crucial for controlling soil and water loss,and interception efficiency reflects the ability of vegetation to intercept runoff and sediment.Clarifying the mechanism driving the interception effect can provide an important theoretical basis for designing vegetation interception strips.Runoff plots were designed with three different grass interception strips(7-year abandoned land,1-year abandoned land,and Panicum virgatum inhabited land)in a hilly Loess Plateau region.Runoff,soil loss,and environmental factors were observed under natural rainfall for 3 years.A new formula was proposed for calculating the intercept rate.Variance,redundancy,and regression analyses were used to explore the differences in intercept efficiency and driving factors.The results showed that:(1)the general trend in runoff and sediment interception rate was ranked as 7-year abandoned land>P.virgatum inhabited land>1-year abandoned land,and for different topographies,it was ranked as 5°slope>15°slope>25°slope.The relative differences among the three slope gradients for runoff and sediment interception rates of 7-year abandoned land and land comprising P.virgatum were small,indicating that the interception functions of the two grasslands were relatively stable.(2)The runoff interception rates were mainly affected by rainfall characteristics and upslope runoff(simple effects were between 7.8%and 26.7%),while sediment interception rates were mainly affected by soil and vegetation characteristics(simple effects were between 6.9%and 32.1%);however,the effects of rainfall and runoff were relatively small,and the rainfall and runoff characteristics had negative effects on interception rates.Soil properties(except for soil bulk density)and surface coverage exerted positive effects.(3)The response of intercept efficiency to rainfall and runoff showed a nonlinear relationship.For the upslope runoff<3 mm or the antecedent precipitation<10 mm on a 5°slope,the runoff interception rate decreased rapidly,but if it exceeded the threshold,the runoff interception rate decreased slowly.The interactions between vegetation and soil factors as well as the complex variations in rainfall and runoff factors resulted in uncertainty in the interception rate prediction.In conclusion,natural grasslands with a certain period of abandonment and plantation of P.virgatum are suitable for vegetation interception strips in the Hilly Loess Platean region.The regulation of soil surface coverage and soil properties can improve grassland interception.Rainfall conditions are important external factors driving interception.