Seasonal variability of runoff and soil loss on forest road backslopes under simulated rainfall

Runoff and soil loss from forest road backslopes is a serious problem in Mediterranean areas. Surface runoff and sediment production on backslopes of forest roads in Los Alcornocales Natural Park (southern Spain) has been studied in this paper using a simple portable rainfall simulator at an intensity of 90 mm h^− 1. One hundred rainfall simulations were performed on bare and vegetated road backslopes during summer and winter in order to study seasonal differences. Runoff coefficients and soil loss rates were lower on the vegetated plots than on the bare ones. Runoff coefficients increased 1.7 (bare backslopes) and 3.1 times (vegetated backslopes) from summer to winter. Preserving the vegetation cover over 20% is recommended for keeping soil loss rates under low levels, especially during winter.     

模拟降雨条件下作物植株对降雨再分配过程的影响

为系统测定玉米（Zea mays L.）、大豆（Glycine max）、谷子（Setaria italica）和冬小麦（Triticum aestivum Linn.）不同生长阶段的穿透雨、茎秆流和冠层截留,研究采用室内模拟降雨法测定了不同降雨强度、不同叶面积指数作物冠下穿透雨和茎秆流,采用喷雾法测定了作物不同生长阶段的冠层截留。对其进行了量化分析,并探讨了3者与作物叶面积指数和降雨强度的关系。结果表明：在40和80 mm/h降雨强度下降雨30 min,玉米、大豆、谷子和冬小麦冠下穿透雨率分别平均为65.15%、85.52%、80.05%和72.18%;在40和80 mm/h降雨强度下降雨10～20 min,4种茎秆流率分别平均为34.59%、13.58%、19.42%和26.34%;在0.3 mm/min喷雾强度下,作物冠层截留量相对较小,冠层截留率分别为0.26%、0.90%、0.53%和1.48%。随作物生长,穿透雨量逐渐降低,茎秆流量和冠层截留量逐渐增加。降雨强度与穿透雨量和茎秆流量呈正相关关系,但是2者占总降雨量的比例与降雨强度关系不显著（p＞0.05）。随着作物生长,穿透雨冠下空间分布由均匀逐渐趋向于不均匀,具有趋于向行中汇集的趋势。该研究揭示了黄土高原地区主要作物对降雨的再分配作用特征,可为农田水分有效利用和坡耕地土壤侵蚀防治提供理论依据。     

Geographical aspects of forest litters

Litter and humus formations are considered as two interrelated processes. On the basis of analysis of geographic patterns of litter formation, we set up a hypothesis for the capacity invariance of the modern area where there is conversion of terrestrial detritus, which correlates with the level of functioning of terrestrial ecosystems measured according to the level of soil respiration. It is discovered that not only the single ecological space, which is optimal for humification, gets narrow, but also its major centers are shifted within the limits of geochemically conjugated landscapes.     

降雨-径流条件下土壤溶质迁移过程模拟

通过雨滴的打击加速土壤表面溶质迁移至地表径流过程。通过设计3种水文条件即控制排水状态（-5 cm）、土壤水分饱和状态和土壤渗流状态（5 cm）,采用人工模拟3种降雨强度（30、60和90 mm/h）,及同时外加模拟相对于降雨量的0、2、4和10倍径流量,研究土壤溶质迁移到地表径流过程中扩散过程的规律。试验结果表明降雨强度、或地表径流总量、或地表水位线的增加,均加速土壤溶质的扩散过程。渗流作用下,对流-扩散作用存在着一种交互作用,能加速分子扩散过程。土壤溶质迁移过程同降雨强度、地表径流量和地下水位高低有着重要关系。     

模拟降雨条件下碱性坡地土壤侵蚀试验

 采用室内人工降丨射模拟试验,研究降雨强度为50 mm/h时不问坡度（5°、15°、25°)和不同土壤（土壤的可交换钠比例ESP值分别为2.4和25)对土壤人渗率和侵蚀缺的影响。结果表明：1)不问坡度和不同土壤的径流模数随降雨历时急剧增加,后于平稳,人渗率和侵蚀产沙量随降雨历时急剧减小,趋于某一稳定值;2) 土壤ESP值水平一定时,入渗率和累计人渗量都随着坡度的增大而增加,侵蚀产沙坩随笤坡度的增大先增加后减小,在15° -25°之间存在着侵蚀的临界坡度;3)坡度一定时,径流模数随着 ESP值的增加而增加,稳定人渗率和累计人渗量随卷ESP值的增加而减小;4) 土壤的ESP值水平对侵蚀产沙量的影响随坡度不同而不同,坡度为5°和15°时,同一坡度的侵蚀产沙量随ESP值的加大而减小,当坡度为25°时,核蚀产沙量随ESP值的加大而增大,说明坡度较大时,土壤ESP值的增大更容易引起土壤侵蚀。     

模拟降雨条件下锥状工程堆积体侵蚀水动力特征

为了确定描述锥状工程堆积体坡面侵蚀动力过程较好的水力学参数,以赣北红土为主要试验材料,在人工模拟降雨条件下,系统地分析了水流剪切力、水流功率、单位水流功率以及过水断面单位能同坡面剥蚀率之间的关系。结果表明:1)除过水断面单位能外,其他各个水蚀因子无论是平均值还是瞬时值均能较好的描述坡面侵蚀动力过程;2)赣北红土工程堆积体坡面剥蚀发生的临界单位水流功率为6.8×10-3 m/s;工程堆积体坡面剥蚀发生的临界瞬时单位水流功率为3.8×10-3 m/s,由赣北红土与砾石混合而成的堆积体材料的可蚀性参数介于0.0053~0.0059 s2/m2之间,要比纯红土的可蚀性参数大20~30倍;4)瞬时过水断面单位能与剥蚀率之间相关性不密切(R2=0.130),故瞬时过水断面单位能不适合作为描述锥状工程堆积体坡面侵蚀动力过程的参数指标。4)在各个水蚀因子中,水流功率与剥蚀率相关性最好(R2=0.972),故认为水流功率是描述锥状工程堆积体侵蚀动力过程最好的水力学参数。     

Factors affecting runoff and erosion under simulated rainfall in Mediterranean vineyards

Data on surface runoff and soil loss on gentle slopes with vineyards are analysed. Using a rainfall simulator, 22 rainstorms with varied intensities from 30 to 117.5 mm h⁻¹ and return periods from 2 to 127 years were reproduced. The experimental plots were installed on vineyards planted in straight rows and oriented with the slope direction having a mean gradient of 3.8°. The texture of soils was loamy, with a very heterogeneous surface gravel cover. Values of measured surface runoff varied from 7.2 mm h⁻¹ for low rainfall intensities (30 mm h⁻¹) and short return periods (2 years) to 41.9 mm h⁻¹ with simulation experiments of higher rainfall intensity (104 mm h⁻¹) and long return periods (68 years). Runoff increased linearly with rainfall intensity resulting in soil losses that also increased with rainfall intensity (18.2 g m⁻² h⁻¹ with storms of 30 mm h⁻¹, and 93.2 g m⁻² h⁻¹ with storms of 104 mm h⁻¹); however, r² explains only 36% of the variance. It was necessary to add other factors to improve the coefficient of determination (0.74; p = 0.001) and the predictive function of the equation. These variables were rainfall intensity, kinetic energy of the storm, runoff, soil resistance to drop detachment, surface gravel cover, and gradient. The equation obtained was validated with the USLE-M. In comparison with similar experiments in other regions, the results obtained for soil loss were very moderate, especially those caused by rainstorms of intermediate and low intensity.     

Laboratory experiments on the variation of soil erosion under simulated rainfall

Samples from three Canadian Gray-Brown Luvisols were subjected to simulated rainfall in a small laboratory erosion plot. Although great care was taken to control all major factors known to influence erosion, considerable varaibility in wash loss, splash loss and runoff was observed during 60-min rainfall tests, with coefficients of variation ranging up to 28.8%. Attempts were made to isolate the source of variability by examining rainfall intensity, bulk density, various aggregate size and stability parameters and surface microrelief. The results suggest that much of the observed variability is related to complex interactions of aggregation, microrelief, runoff and rain splash. Some of these interactions were examined in detail. The experiments suggest the existence of an inherent variability in soil erosion studies which is difficult or impossible to eliminate. Results were used to plot curves showing the increase in precision of soil erosion prediction with increased test replication under controlled experimental conditions and changes in relationships with increasing test duration.     

室内小流域降雨产流过程试验

该研究采用新型的小水流流量自动观测系统,在室内小流域模型上进行了不变雨强和变雨强模拟降雨试验,实时观测了模型流域各沟道的产流过程。试验进行了不同降雨强度(25、50、75、120mm/h)和不同降雨历时(5、10、15min)组合的12次降雨试验,同时进行了30-70mm/h和70-30-70mm/h的变雨强降雨试验。在不变雨强的条件下,仪器与人工测量所得稳定流量的最大平均相对误差仅为2.02%。测量得到的流量过程线呈现出起流、稳定和退水3个明显的阶段。其中,起流和退水过程涨落的剧烈程度、稳定阶段的流量大小随雨强增大而增大,稳定阶段的持续时间与降雨历时成正比。空间上,主沟出口的产流过程明显滞后于支沟出口的产流过程,且其两者之间具有一致的流量过程。在变雨强的情况下,流量过程线没有稳定的阶段,流量随雨强变化而变化。该研究对于深入理解流域产流过程具有重要意义,可为相关的模型研究提供可靠的试验支持。     

Loss of pendimethalin in runoff and leaching from turfgrass land under simulated rainfall

A field study was undertaken to investigate runoff and leaching loss of the herbicide pendimethalin in turfgrass land of loamy sand soil. A series of plots constructed in a golf course fairway were surface-applied with pendimethalin SC formulation at the rate of 2. 25 or 4.50 kg a.i./ha and subjected to simulated rainfall at 2.0 cm/day for 10 consecutive days. Runoff losses of pendimethalin were the highest at the first rainfall and then gradually decreased with time. The first runoff event contained pendimethalin in its highest concentration, and in subsequent runoff samples the concentration decreased exponentially. The ranges of pendimethalin concentration were 80.9-18.2 and 177.4-48.6 microgram/L in the standard and double doses, respectively. Total losses by 20 cm of rainfall for 10 days reached 0.81 and 1.22% of the initial deposits at 2.25 and 4.50 kg a. i./ha, respectively. Pendimethalin concentration in the leachate collected at 30-cm soil depth was quite lower than that in the runoff, and the concentration rapidly decreased from 4.3-4.7 to 0. 2-0.4 microgram/L during the 10 days of rainfall treatment. Soil residue analysis at 45 and 90 days after pendimethalin treatment showed that more than 90% of the residue remained at the top 10 cm of soil depth. Low runoff and leaching confirmed that lateral and downward movement of the herbicide should be limited in turf soil. The half-life of pendimethalin under field conditions was 23-30 days and was not affected by application dose and rainfall treatment, but longer persistence was observed under laboratory conditions. Considering low runoff and leaching, as well as relatively short persistence in soil, it is concluded that little environmental carryover of pendimethalin would be expected in turfgrass land.     

The influence of heating on organic matter of forest litters and soils under experimental conditions

The specific features of changes in the content and mobility of organic matter in litters and cryogenic soils under heating were revealed. The thermal stability of the organic matter and litters is different. In the soils, the maximal loss of matter was recorded at a temperature of 300°C. In the litters, the maximal losses were found at 300, 400 and 550°C and depended inversely on the carbon content in them. The heating to 200°C caused insignificant changes in the mass of the litters and soils but increased the content of the water-soluble fraction of organic matter and the concentration of the water-soluble mineral nitrogen forms.     

室内模拟降雨条件下土壤水分入渗及再分布试验

降雨入渗对城市绿化、防洪排涝、农业生产等方面有着重要的意义。采用室内模拟降雨,使用时域反射仪采集相关数据,从土壤含水率变化特征和湿润锋运移特点等方面,研究了在垂向一维条件下不同雨强降雨对水分入渗的影响,探讨在降雨条件下土壤水分的再分布情况,从而确定试验所用砂壤土保水性最优土层范围。结果表明：降雨结束后,土壤水分的再分布主要受土水势控制,随着时间的延长,蒸发作用逐渐占据主导地位;试验所用砂壤土的最佳保水性土层深度为20～35 cm,可为植物的选栽提供参考。     

Effect of compost on erodibility of loamy sand under simulated rainfall

Three types of composts [vegetable, fruit and yard waste compost (VFYW), garden waste compost (GW), and spent mushroom compost (SM)] were applied at a rate of 30 m³ ha⁻¹ for 10 years to loamy sand, to determine its effect on the aggregate stability and susceptibility to water erosion. Aggregate stability was measured using the stability index derived from the wet sieving method while a laboratory rainfall simulator was used to measure runoff, sheet and splash erosion. Only GW recorded a significant increase (45%) in aggregate stability. Runoff, sheet erosion, and splash erosion did not show significant improvement for any of the compost types. SM application resulted in a significant increase (51%) in the shear strength of the soil after rainfall. Long term compost application does not appreciably improve the resistance of loamy sand to water erosion.     

The effect of nickel and copper deposition from a mining and smelting complex on coniferous regeneration in the boreal forest of northern Manitoba

Airborne pollutants in the form of SO₂ and heavy metals have been dispersed over the boreal forest in the Thompson area of northern Manitoba since 1961. Metal deposition has been found in soils and plant material to a distance of 35 km from the Inco nickel smelter. Studies were initiated in 1979 to determine effects of Ni and Cu on coniferous regeneration of jack pine (Pinus banksiana Lamb.) and black spruce (Picea mariana (Mill) BSP.).Studies included metal accumulation in cones, effects on seed quality, seed germination and seedling response in metal contaminated soils. Nickel and Cu accumulation in cones of both species declined rapidly with distance from the smelter. Seed quality and germination potential was not related to metals in cones or air pollutant influence in general. Nickel and Cu accumulation in surface organic soils was inversely related to distance from the smelter. A significant inverse correlation was determined between seedling growth and Cu/Ni concentrations in surface organic soils. Metal accumulation in soils within 5 km of the nickel smelter inhibited root growth of conifer seedlings.     

Soil losses under simulated rainfall in semi-arid shrublands of the Ebro Valley, Spain

Abstract. Runoff and soil loss were measured using simulated rainfall at nine shrubland sites on gypsiferous soils in the Ebro Valley. The sites represented diverse physiographical situations, including three soil types, three slopes and different percentages of rock outcrop and vegetation cover. Soil type, slope and vegetation cover significantly affected runoff and soil losses. An average of 40% of the simulated rainfall (48 mm/h) appeared as runoff and amounts were positively correlated with soil losses. The greatest runoff and soil losses were from plots with the steepest slopes. Rock outcrops decreased soil losses.     

Nomographic estimation and evaluation of soil erodibility under simulated and natural rainfall conditions

To evaluate soil erodibility under different land uses and to study the applicability of nomograph for estimation of soil erodibility a field experiment was conducted under both natural and simulated rainfall conditions under four land uses viz. barren, cultivated, grassland, and forest in the sub‐mountainous tract of Punjab (India). Measured soil erodibility (K) values varied from 0·33 to 0·67 under natural rainfall conditions and from 0·23 to 0·40 under simulated rainfall conditions. Among different land uses, measured K was in the order of barren > cultivated > grassland > forest soils. The values of the K estimated by nomograph were very low as compared to the observed values. The trends were also in contrast to these observed values of K under simulated and natural rainfall conditions. To modify nomograph equation, different ranges of aggregate sizes were correlated with soil loss. It was observed that water stable aggregates (WSA) <2 mm size had a significant correlation with soil loss under both natural (r = 0·88) and simulated (r = 0·76) rainfall conditions. So the nomograph equation was modified to include the M parameter based on WSA <2 mm size. The value of K estimated from the modified nomograph had a significant correlation with measured values of K under both the natural and simulated rainfall conditions. Copyright © 2009 John Wiley & Sons, Ltd.     

模拟降雨条件下地貌发育与侵蚀产沙的关系

地貌是影响流域侵蚀产沙的关键因素之一,为了进一步研究地貌发育与侵蚀产沙的关系,该文以小流域概化模型为对象,运用模拟降雨试验方法,以高精度摄影测量和GIS技术为手段对流域地貌发育过程及侵蚀产沙强度变化规律进行了研究。结果表明,产沙速率（Gt）、降雨产沙强度（Gp）和平均输沙强度（M）都随着流域地貌发育过程呈现先增大后减小的变化趋势;在流域地貌发育过程中,存在临界地面裂度（32%左右）和临界相对体积（65%左右）,使降雨产沙强度和平均输沙强度的变化趋势由递增变化为递减。这种临界现象对更深入地研究流域地貌发育及其与侵蚀产沙的关系具有重要理论意义,同时说明地面裂度和相对体积可以作为流域发育程度的指标。     

The effects of ryegrass roots and shoots on loess erosion under simulated rainfall

Numerous studies have demonstrated that vegetation coverage is very important to control soil erosion by water. However, the combined impacts of plant roots and shoots on soil erosion by water and the relative contributions of the roots and shoots are not clearly understood. Four rainfall simulation experiments with the rainfall intensity at 1.5 mm min^− 1 were conducted at an interval of 5 weeks to investigate the effects of ryegrass (Lolium perenne L.) shoots and roots on soil erosion and runoff reductions. Ten ryegrass planted pans and four fallow pans were prepared for the experiments. The first rainfall simulation experiment was conducted after ryegrass had been planted for 12 weeks. It showed that compared with the runoffs in the fallow pans, the runoff in the planted pans decreased 25% and 70% in the 12th week and the 27th week, respectively; and the sediment decrements amounted up to 95% in the 27th week. The results also indicated that the shoot effect on runoff reduction, accounting for over 50% except in the 27th week when the shoot affect also accounted for 44%, was relatively greater than the root effect. However, the roots contributed more to soil loss reduction than the shoots, and in particular accounted for 90% of soil loss reduction at the 27th week. Both the soil erosion rate and average infiltration rate were linearly correlated with root surface area density in cm² root surface area per unit soil volume. Ryegrass planting could improve soil physical properties, especially soil aggregate stability, which increased from 33.1% in the 12th week to 38.5% in the 27th week. The study results are probably useful in evaluating the effects of plant shoots and roots on soil erosion control.     

人工模拟降雨条件下花岗岩红壤坡面侵蚀过程与特征分析简

通过室内人工模拟降雨试验,研究降雨强度、坡度及地表覆盖3因素对花岗岩红壤坡面侵蚀过程的影响.结果表明：1）起始产流时间随降雨强度和坡度的增加而有所提前,而地表覆盖能延缓起始产流时间;2）在不同降雨强度和坡度条件下,径流率从产流初期开始都快速增加,7 ～ 10 min后达到稳定,且随着降雨强度和坡度增加,径流率也显著增加;3）随着降雨强度的增大,产沙率明显增大,且降雨强度越大,坡度对产沙率的影响越明显;4）降雨强度和径流总量、产沙总量之间相关性极显著,其相关系数分别为0.892和0.799;5）地表覆盖具有良好的减沙作用,其减沙效益超过90％.     

外源铜和镍在土壤中的化学形态及其老化研究

采用连续提取法测定了外源铜和镍进入田间土壤后的化学形态分布,比较研究了这2种重金属在3种不同类型土壤(红壤,水稻土和潮土)中随老化时间的形态转化和分布.结果表明,外源铜以残留态(40%～60%)和EDTA可提取态(40%)为主;随老化时间,EDTA可提取态、易还原锰结合态及铁铝氧化态向残留态转化;外源镍在酸性红壤中以可交换态(40%)和残留态(30%～50%)为主,在中性水稻土中以EDTA可提取态(30%)和残留态(30%～50%)为主,在碱性潮土中以铁铝氧化态(20%)和残留态(40%)为主.随老化时间,水溶态、可交换态、EDTA可提取态等向残留态转化.土壤pH较低时水溶态和可交换态含量较高,但是同时随老化时间的降低量也明显;pH较高时有利于易还原锰结合态和有机质结合态的转化.