兴安落叶松林降雨再分配特征

以兴安落叶松人工林为研究对象,通过冠层结构稳定时期20场降雨数据,分析了落叶松林冠层对降雨的截留再分配规律。结果表明:(1)观测期内落叶松林穿透雨量、树干径流量和冠层截留量依次为198.9mm,12.6mm,127.6mm,分别占同期林外降雨的58.65%,3.72%,37.63%;(2)根据模型估算,当降雨量超过4.2mm落叶松林开始出现穿透雨,降雨量超过7.2mm才能产生树干径流;(3)穿透雨、树干径流及林冠截留的绝对量均随降雨量的增大而显著增加,但其占林外雨的比例却表现出不同的变化趋势;(4)穿透雨量的空间变异随降雨量的增大显著减小,二者呈显著负相关(p<0.05);(5)本研究林冠层截留率处于兴安落叶松林冠截留(13.04%~39.89%)的较高水平,高于全国主要森林平均林冠截留(14.7%~31.8%)。     

祁连山青海云杉林苔藓层降雨再分配特征及其影响因素

研究苔藓层的降雨再分配对于认识其实际截持降雨过程及水文循环机理具有重要意义。本文以祁连山排露沟小流域青海云杉林苔藓层为研究对象,利用室内实验和野外观测相结合的办法,对祁连山苔藓层蓄积量、持水量(率)、林外(内)降雨量和苔藓穿透雨量进行测定,分析青海云杉林苔藓层持水特征、降雨再分配特征及其与影响因素的关系。结果表明:(1)苔藓层的厚度为2.8~12.6 cm,蓄积量为18.6~65.7 t·hm~(-2),最大持水率为218.6%~536.1%,最大持水深为8.6~19.2 mm,且苔藓层的最大持水量约为自身干重的3.5倍。(2)青海云杉林苔藓层的穿透雨总量和截留总量分别为156.5 mm和100.0 mm,分别占林内降雨总量的61.0%和39.0%,并在不同降雨量等级之间存在明显的差异。(3)苔藓层降雨再分配各组成要素(穿透雨和截留)与林内降雨量、林外降雨量、降雨历时和空气相对湿度呈极显著的相关性。林内降雨量、林外降雨量和降雨历时与苔藓穿透雨量均呈线性正相关关系(P0.01),而与穿透雨率、截留水量和截留率均呈对数函数关系(P0.05)。因此,苔藓层的持水性能及再分配特征,除与苔藓层的厚度、蓄积量和初始含水量相关外,也与林外各气象因子相关。     

大青山区油松人工林降雨分配特征研究

以大青山区30 a生油松人工林为研究对象,系统观测了林分对降雨的再分配作用,根据2006年的观测结果显示,油松人工林林冠穿透雨量、林冠截留、树干茎流所占降雨的比例分别为65.83%、33.04%、1.13%,枯枝落叶层有效拦蓄量为0.62mm,截留率为8.9%,地表径流率为2.6%;林冠穿透雨量、树干茎流量与林外降雨量均呈显著的线性正相关,而林冠截留量与降雨量呈幂函数关系。     

谷子冠层下的土壤溅蚀速率特征

为研究种植谷子(Setaria italica Beauv)条件下农地土壤溅蚀速率的变化特征,评价谷子冠层对土壤溅蚀的影响,采取室内模拟降雨手段,利用溅蚀杯法分别测定了叶面积指数为0.86、1.54、2.18和3.11四个生长阶段的谷子冠层下以及裸地上的溅蚀速率。谷子冠下溅蚀速率测定的设计雨强为40 mm/h和80 mm/h,裸地试验的设计雨强为20、406、0、80、1001、20 mm/h及140 mm/h。试验结果表明:与裸地相比,在各生长阶段,谷子冠下的平均溅蚀速率在40 mm/h雨强下平均降低24%,在80 mm/h雨强下降低约52%,特定条件下冠下溅蚀速率会高于相同雨强下裸地的溅蚀速率;冠下平均溅蚀速率的变化与冠层发育之间的关系不明显;谷子冠下各地点的溅蚀速率与该地点对应的冠下雨强之间的关系不显著,而裸地上溅蚀速率与雨强之间呈幂函数相关关系。     

贺兰山蒙古扁桃灌丛穿透雨特征及影响因素

贺兰山是我国北方干旱区近南北走向的山脉，蒙古扁桃(Prunus mongolica)是区内重要的灌丛类型之一，探讨贺兰山蒙古扁桃灌丛穿透雨及影响因素，对于生态保护和生态系统管理具有重要意义。文中研究了贺兰山蒙古扁桃冠层的穿透雨特征及主要影响因素，量化蒙古扁桃冠层对土壤有效降水量的影响。研究结果表明：蒙古扁桃灌丛的平均穿透雨率为69.91%,且穿透雨具有空间异质性，冠幅边缘和中央的地面分别出现“雨极”和“旱区”现象；穿透雨与降雨量和降雨时长之间均存在显著相关性(P<0.05),与降雨强度之间没有显著相关性；降雨量是影响降雨再分配的关键因子，而降雨强度与降雨时长通过影响降雨量实现对蒙古扁桃灌丛降雨再分配的调节。     

基于i-Tree Eco模型的城市林冠雨水截留和径流削减效益研究——以北京建筑大学西城校区为例

乔木冠层雨水截留作用对降雨产流和径流削减有显著影响,而国内相关的模型研究较少。在现有城市截留效益模型比较和植被实地调查的基础上,利用i-Tree Eco模型评估2014~2018年北京建筑大学西城校区内21种乔木冠层的雨水截留和径流削减效益,推导计算径流削减量的校准方法,并结合相关性分析和回归分析探究城市林冠截留影响因素的作用规律。结果表明:近5年校区内乔木的年均截留体积1365.38m³,平均年截留率10.6%,年均径流削减量266.83m³,校准后较原结果平均增加14.5%;叶面积与年截留体积呈显著线性正相关关系;降雨因素在月尺度下对截留作用及其径流削减能力的影响更显著,月截留量与月降雨天数呈线性正相关关系;径流削减量在降雨较小时对林下不透水面占比更敏感。研究可为国内相关模型评估和城市提升绿地雨水消纳能力等提供参考。     

荒漠草原中间锦鸡儿(Caragana intermedia)冠层穿透雨的发生与分布特征

为进一步认识荒漠草原带状人工中间锦鸡儿林（Caragana intermedia）植被稳定性维持的生态水文过程机制，通过对行生和散生中间锦鸡儿冠层穿透雨的对比研究，结果表明：① 两者对降水变化响应显著，但是差异不显著。散生和行生中间锦鸡儿穿透雨百分比变化范围分别为25.6%~96.5%（Cv = 23%）和25.4%~96.1%（Cv = 19%），穿透雨量均值分别为7.55 mm和7.40 mm。穿透雨量与降雨量、降雨历时、降雨强度都具有极显著的线性回归关系，但是穿透雨百分比与降水特征参数以幂函数关系为主。② 冠层下穿透雨分布存在明显的空间异质性。穿透雨百分比普遍随距灌丛基部距离的增大而线性增大。 “旱区”集中出现在散生中间锦鸡儿灌木的基部，向外百分比逐步提高；行生中间锦鸡儿则出现了多个旱区和雨极镶嵌分布的情况。     

大兴安岭南段白桦林降雨再分配特征研究

利用2013年度赛罕乌拉地区白桦林64场有效降雨及林内再分配的野外观测数据,探讨了该地区白桦林降雨再分配特征。结果表明:白桦林的穿透降雨量、树干茎流量和林冠截留量分别占同期林外降雨量的76.0%,2.3%,21.7%。穿透降雨量及树干茎流量与林外降雨量均呈明显的线性相关(R2=0.8800),而林冠截留量与林外降雨量呈指数函数关系(R2=0.8303)。实验证明当林外降雨量大于0.3mm时,可发生穿透降雨;林外降雨量大于0.51mm时,可发生树干茎流。林冠层叶面积指数(LAI值)及独特的立地条件、生长特征对降雨再分配起着重要的影响。     

小叶锦鸡儿灌丛不同部位穿透雨特征

2012年7-9月中旬,以科尔沁沙地小叶锦鸡儿灌从为对象,研究了其不同部位的穿透雨特征。结果表明:试验期间的总降雨量为105.99mm,其中,12.5%的降雨事件2mm,50%的降雨事件5mm。穿透雨量占同期降雨量的76.80%。小于1 mm的降雨对于灌丛下土壤不能产生补给,全部降水都被灌丛截留进而蒸发,对灌丛下土壤属于无效降水。穿透率最大值、最小值分别为85.67%、56.87%。穿透雨量与降水量之间的关系可用线性公式较好的表达(P0.01,R2=0.73)。穿透率随降雨量、降雨强度的增大而增加,两者呈显著的对数关系(P0.01)。在灌丛不同部位,穿透雨量大小表现为"冠幅边缘1/2冠幅灌丛基部"的特征,穿透雨量随降雨量增加而增大的趋势显现出冠幅边缘处快于1/2冠幅和灌丛基部处,1/2冠幅处快于灌丛基部。     

不同水分处理下冬小麦冠层温度、叶片水势和水分利用效率的变化及相关关系

小区栽培冬小麦,设计5种程度的干旱胁迫,利用防雨棚分别控制土壤重量含水量为田间持水量的45%、55%、65%、70%、80%,观测不同水分处理下冬小麦冠层温度、叶片水势和水分利用效率的变化及相关关系。结果显示,随着含水量的增加,各处理的平均和最高冠层温度整体呈下降趋势,叶水势和蒸腾速率呈上升趋势,在小麦抽穗期干旱胁迫最严重处理表现出最大水分利用效率,开花期的水分利用效率较抽穗期整体下降了50.70%;相关分析表明,抽穗期小麦的冠层温度与空气饱和差极显著正相关(P<0.01),开花期的冠层温度和叶水势呈显著负相关(P<0.05),冠层温度和空气饱和差存在着极显著正相关,空气饱和差和蒸腾速率极显著负相关,冠层温度和水分利用效率有着显著的正相关性。综上所述,冠层温度在小麦抽穗和开花期完全可以作为作物水分状况的有效监测指标之一。     

Freeze-thaw effects on erosion process in loess slope under simulated rainfall

Seasonal freeze-thaw processes have led to severe soil erosion in the middle and high latitudes. The area affected by freeze-thaw erosion in China exceeds 13% of the national territory. So understanding the effect of freeze-thaw on erosion process is of great significance for soil and water conservation as well as for ecological engineering. In this study, we designed simulated rainfall experiments to investigate soil erosion processes under two soil conditions, unfrozen slope (UFS) and frozen slope (FS), and three rainfall intensities of 0.6, 0.9 and 1.2 mm/min. The results showed that the initial runoff time of FS occurred much earlier than that of the UFS. Under the same rainfall intensity, the runoff of FS is 1.17-1.26 times that of UFS; and the sediment yield of FS is 6.48-10.49 times that of UFS. With increasing rainfall time, rills were produced on the slope. After the appearance of the rills, the sediment yield on the FS accounts for 74%-86% of the total sediment yield. Rill erosion was the main reason for the increase in soil erosion rate on FS, and the reduction in water percolation resulting from frozen layers was one of the important factors leading to the advancement of rills on slope. A linear relationship existed between the cumulative runoff and the sediment yield of UFS and FS (R²>0.97, P<0.01). The average mean weight diameter (MWD) on the slope erosion particles was as follows: UFS0.9 (73.84 μm)>FS0.6 (72.30 μm)>UFS1.2 (72.23 μm)>substrate (71.23 μm)>FS1.2 (71.06 μm)>FS0.9 (70.72 μm). During the early stage of the rainfall, the MWD of the FS was relatively large. However, during the middle to late rainfall, the particle composition gradually approached that of the soil substrate. Under different rainfall intensities, the mean soil erodibility (MK) of the FS was 7.22 times that of the UFS. The ratio of the mean regression coefficient C₂ (MC₂) between FS and UFS was roughly correspondent with MK. Therefore, the parameter C₂ can be used to evaluate soil erodibility after the appearance of the rills. This article explored the influence mechanism of freeze-thaw effects on loess soil erosion and provided a theoretical basis for further studies on soil erosion in the loess hilly regions.     

Mulching mode and planting density affect canopy interception loss of rainfall and water use efficiency of dryland maize on the Loess Plateau of China

High and efficient use of limited rainwater resources is of crucial importance for the crop production in arid and semi-arid areas. To investigate the effects of different soil and crop management practices(i.e., mulching mode treatments: flat cultivation with non-mulching, flat cultivation with straw mulching, plastic-covered ridge with bare furrow and plastic-covered ridge with straw-covered furrow; and planting density treatments: low planting density of 45,000 plants/hm~2, medium planting density of 67,500 plants/hm~2 and high planting density of 90,000 plants/hm~2) on rainfall partitioning by dryland maize canopy, especially the resulted net rainfall input beneath the maize canopy, we measured the gross rainfall, throughfall and stemflow at different growth stages of dryland maize in 2015 and 2016 on the Loess Plateau of China. The canopy interception loss was estimated by the water balance method. Soil water storage, leaf area index, grain yield(as well as it components) and water use efficiency of dryland maize were measured or calculated. Results showed that the cumulative throughfall, cumulative stemflow and cumulative canopy interception loss during the whole growing season accounted for 42.3%–77.5%, 15.1%–36.3% and 7.4%–21.4% of the total gross rainfall under different treatments, respectively. Soil mulching could promote the growth and development of dryland maize and enhance the capability of stemflow production and canopy interception loss, thereby increasing the relative stemflow and relative canopy interception loss and reducing the relative throughfall. The relative stemflow and relative canopy interception loss generally increased with increasing planting density, while the relative throughfall decreased with increasing planting density. During the two experimental years, mulching mode had no significant influence on net rainfall due to the compensation between throughfall and stemflow, whereas planting density significantly affected net rainfall. The highest grain yield and water use efficiency of dryland maize were obtained under the combination of medium planting density of 67,500 plants/hm~2 and mulching mode of plastic-covered ridge with straw-covered furrow. Soil mulching can reduce soil evaporation and retain more soil water for dryland maize without reducing the net rainfall input beneath the maize canopy, which may alleviate the contradiction between high soil water consumption and insufficient rainfall input of the soil. In conclusion, the application of medium planting density(67,500 plants/hm~2) under plastic-covered ridge with bare furrow is recommended for increasing dryland maize production on the Loess Plateau of China.     

雨强和植被覆盖度对典型坡面产流产沙的影响

应用先进的UGT水蚀测量仪,研究黄土高原祖厉河流域雨强和植被覆盖度对典型坡面产流产沙的影响。结果表明:黄土高原半干旱区间隔为15min的产流量、径流含沙量和产沙量与15min雨强具有相同的增减趋势,呈三次曲线关系y=b0+b1x+b2x2+b3x3。7种雨强条件下,人类扰动撂荒地的产流量、径流含沙量和产沙量均明显大于植被自然恢复的撂荒地,覆盖度20%的撂荒地是覆盖度35%撂荒地的平均径流系数的2.35倍,径流含沙量的4.48倍,产沙量的14.06倍。相对于受到扰动的撂荒地,植被自然恢复的撂荒地水土保持效益显著。     

陕北黄土高原降雨侵蚀力时空变化研究

陕北地区是典型的黄土高原水土流失严重区,降雨侵蚀力是表征水蚀地区降雨侵蚀潜力的复合指标。系统分析降雨侵蚀力国内外研究现状,采用陕北及其周边地区27站日降雨资料及降雨侵蚀力简易计算方法,分析陕北地区降雨侵蚀力季节差异、年际变化,绘制了陕北地区多年平均及其20世纪各年代降雨侵蚀力空间分布等值线,研究结果对进一步认知陕北地区水土流失规律、指导水土保持工作具有重要意义。     

黄土区土质道路径流水动力学参数的灰色关联度分析

黄土区土质道路路面侵蚀是该地区土壤侵蚀中的重要形式之一,为了探讨其土壤剥蚀率与径流水动力学参数的相关关系,以便为该地区道路土壤侵蚀预报模型的建立提供帮助,采用室内人工降雨及放水冲刷实验、灰色关联度分析方法研究了裸露土质路和植草土质路的径流水动力学参数与土壤剥蚀率间的关系,结果表明:1)在15°坡度、不同雨强条件下,可根据径流量或水流功率计算土壤剥蚀率;2)在2mm.min-1雨强、不同坡度条件下,可根据水流功率或坡度计算土壤剥蚀率;3)在降雨加放水冲刷试验条件下,裸露土质路的土壤剥蚀率可通过径流水深或径流流速计算得出,而植草土质路的土壤剥蚀率可通过过水断面单位能量或径流量计算得出。因此,在无汇水条件时,根据径流水流功率计算土壤剥蚀率较为合理;在有汇水条件时,采用径流量计算土壤剥蚀率较为合理。     

Lysimeter study to investigate the effect of rainfall patterns on leaching of isoproturon

The influence of five rainfall treatments on water and solute leaching through two contrasting soil types was investigated. Undisturbed lysimeters (diameter 0.25 m, length 0.5 m) from a sandy loam (Wick series) and a moderately structured clay loam (Hodnet series) received autumn applications of the radio-labelled pesticide isoproturon and bromide tracer. Target rainfall plus irrigation from the end of November 1997 to May 1998 ranged from drier to wetter than average (235 to 414 mm); monthly rainfall was varied according to a pre-selected pattern or kept constant (triplicate lysimeters per regime). Leachate was collected at intervals and concentrations of the solutes were determined. Total flow (0.27-0.94 pore volumes) and losses of bromide (3-80% of applied) increased with increasing inputs of water and were larger from the Wick sandy loam than from the Hodnet clay loam soil. Matrix flow appeared to be the main mechanism for transport of isoproturon through the Wick soil whereas there was a greater influence of preferential flow for the Hodnet lysimeters. The total leached load of isoproturon from the Wick lysimeters was 0.02-0.26% of that applied. There was no clear variation in transport processes between the rainfall treatments investigated for this soil and there was an approximately linear relationship (r2 = 0.81) between leached load and total flow. Losses of isoproturon from the Hodnet soil were 0.03-0.39% of applied and there was evidence of enhanced preferential flow in the driest and wettest treatments. Leaching of isoproturon was best described by an exponential relationship between load and total flow (r2 = 0.62). A 45% increase in flow between the two wettest treatments gave a 100% increase in leaching of isoproturon from the Wick soil. For the Hodnet lysimeters, a 35% increase in flow between the same treatments increased herbicide loss by 325%.     

Influence of adsorption–desorption phenomena on pesticide run-off from soil using simulated rainfall

The surface run-off of a number of pesticides (diuron, isoproturon, atrazine, alachlor, aclonifen, trifluralin, lindane and simazine), chosen for their range of adsorption behaviours, was studied using simulated rainfall applied to small plots over a short time (one hour). Pesticides were applied together onto bare soil using two different sandy loam soils from Jaillière and Coet Dan sites. The surface run-off samples were collected throughout the running of the event and concentrations of pesticides were measured in both liquid and solid phases. Sorption isotherms for isoproturon and diuron on Jaillière soil as well as eroded particles were measured under equilibrium conditions and compared to their partitioning during surface run-off. At the rainfall intensity used, both soils generated a large load of eroded particles. The average run-off flow rate increased with time for the Jalliére soil, while it remained relatively constant at a higher level for the Coet Dan soil. The concentrations of each pesticide in the run-off samples decreased as the experiments proceeded. The pesticides were classified into two types by their partitioning between the solid and liquid phases. Atrazine, simazine, diuron, isoproturon and alachlor were mainly transported in surface run-off water. By contrast, 90% of trifluralin and aclonifen was adsorbed onto eroded particles. Lindane was intermediate, with a 37% adsorption level. When the contribution of eroded particles was minor, the agrochemical concentrations were inversely proportional to the water flow rate. We have proposed a model that describes the mass of chemicals extracted from soil into surface water during a surface run-off event of a given average duration and flow rate. This model takes into account the dilution of the soil solution and the desorption of chemicals through two parameters called, respectively, the dilution factor and the extraction retardation factor. The desorption kinetic was the limiting step in the surface run-off of weakly sorbed chemicals, such as isoproturon. © 1999 Society of Chemical Industry