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1.
Degraded gypsic soils in the centre of Spain can be rehabilitated with organic amendment and shrub revegetation. Erosion has been measured on plots of 2×0·5 m2 under simulated rainfall of 70 mm h−1 and a kinetic energy of 18 J mm−1 m−2. Samples of water runoff and sediments were studied in the summer of the years 2002 and 2003. The presence of shrub Atriplex halimus (Chenonodiaceae) significantly reduces runoff from 16·9 to 6·7 ml m−2 min−1 and sediments from 0·16 to 0·02 g m−2 min−1. When sewage sludge is applied the differences among plots with and without bushes disappear. Although both treatments independently applied are efficient as erosion control measures, the combined use of revegetation and organic amendment allows a reduced dose of sewage sludge with the same effect on erosion. A low dose of sludge is desirable in view of the accumulation of toxic chemicals. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

2.
In this study, we used a pair of optical disdrometers, one under and one outside the maize canopy, to measure the drop-size and the velocity distribution of hydrometeors during 12 storms and identified four distinct regions by examining how the fraction of drops recorded on the throughfall changed with respect to the drop diameter. The first region, containing drops with diameters smaller than 0.5 mm, showed an elevated number on the throughfall. Their numbers were comparable to the numbers of drops that lacked enough energy to adhere to the leaf. The second region, featuring drops with diameters larger than 0.5 mm and smaller than 3 mm, had a number ratio very close to the canopy gap fraction, indicating that their most likely origin was direct throughfall. The third region entailed drops with diameters ranging from 3 mm to 5.5 mm that featured a high throughfall to rainfall count ratio, with one of the diameter classes having higher counts under the canopy than outside of it. Through simplified calculations, we showed that drop weights in this region should exceed surface tension forces and lead to their detachment. In the fourth and final region, the throughfall to rainfall ratio decreased converging to the canopy gap fraction. By comparing the number of drops on each of the 440 diameter/velocity classes under and outside of the canopy, we were able to identify preferential drop sizes on the throughfall, i.e. classes of drop diameters with higher drop-size distributions under the canopy. The drop classes presenting higher counts under the canopy had diameters ranging from 3.25 mm to 5.75 mm with velocities between 1.4 m s−1 and 5 m s−1. We were able to trace the origin of those drops to heights of between 0.10 m and 1.05 m within the canopy, confirming that these drops constitute the indirect throughfall. The capability to estimate the detachment height of drops allows us to reconstruct the drop-size distribution at different levels of the canopy and offers unique insight into the mechanics of interception, indirect throughfall formation and re-interception of raindrops by the maize canopy.  相似文献   

3.
To evaluate the spatial variability of throughfall amount, raindrops, and erosivity under a single canopy during calm meteorological conditions, indoor experiments were conducted using a 9.8-m-tall transplanted Japanese cypress (Chamaecyparis obtusa) and a large-scale rainfall simulator. Drop size distribution, drop velocity, and kinetic energy of throughfall varied spatially under a single canopy as did throughfall amount and rain rate. Compared with throughfall rain rate, the variability was similar in drop size distribution, lower in drop velocity, and higher in kinetic energy. The results suggest that the spatial distribution of throughfall amount was dominated by the canopy shape and position of branches inside the canopy, and thus the spatial distribution was correlated with the radial distance from the trunk. Throughfall amount and rate were lower at the midway point between the trunk and the canopy edge. Throughfall drop size indices (drop size distribution, drop velocity, and unit kinetic energy) varied spatially while did not differ significantly. On the other hand, time-specific throughfall kinetic energy was correlated with the radial distance from the trunk. The dependence the throughfall kinetic energy on the radial distance from the trunk was dominated by the spatial distribution of throughfall amount. The trend in the spatial distribution of throughfall revealed in this study will aid in modelling canopy water processes and in predicting soil erosion on the bare forest floor.  相似文献   

4.
Revegetation of road cuts and fills is intended to stabilize those drastically disturbed areas so that sediment is not transported to adjacent waterways. Sediment has resulted in water quality degradation, an extremely critical issue in the Lake Tahoe Basin. Many revegetation efforts in this semiarid, subalpine environment have resulted in low levels of plant cover, thus failing to meet project goals. Further, no adequate physical method of assessing project effectiveness has been developed, relative to runoff or sediment movement. This paper describes the use of a portable rainfall simulator (RS) to conduct a preliminary assessment of the effectiveness of a variety of erosion‐control treatments and treatment effects on hydrologic parameters and erosion. The particular goal of this paper is to determine whether the RS method can measure revegetation treatment effects on infiltration and erosion. The RS‐plot studies were used to determine slope, cover (mulch and vegetation) and surface roughness effects on infiltration, runoff and erosion rates at several roadcuts across the basin. A rainfall rate of ≈60 mm h−1, approximating the 100‐yr, 15‐min design storm, was applied over replicated 0·64 m2 plots in each treatment type and over bare‐soil plots for comparison. Simulated rainfall had a mean drop size of ≈2·1 mm and approximately 70% of ‘natural’ kinetic energy. Measured parameters included time to runoff, infiltration, runoff/infiltration rate, sediment discharge rate and average sediment concentration as well as analysis of total Kjeldahl nitrogen (TKN) and dissolved phosphorus (TDP) from filtered (0·45 μm) runoff samples. Runoff rates, sediment concentrations and yields were greater from volcanic soils as compared to that from granitic soils for nearly all cover conditions. For example, bare soil sediment yields from volcanic soils ranged from 2–12 as compared to 0·3–3 g m−2 mm−1 for granitic soils. Pine‐needle mulch cover treatments substantially reduced sediment yields from all plots. Plot microtopography or roughness and cross‐slope had no effect on sediment concentrations in runoff or sediment yield. RS measurements showed discernible differences in runoff, infiltration, and sediment yields between treatments. Runoff nutrient concentrations were not distinguishable from that in the rainwater used. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

5.
Rainfall simulators are an important tool in studying soil erosion, which is a key process contributing to land degradation. The kinetic energy of simulated rain is central to these studies and it is used as an indicator of the raindrops' ability to detach particles from the soil surface. The main purpose of this experimental work was to explore the usefulness of incorporating meshes underneath pressurised nozzles' rain simulators that intercept the drops sprayed out by the nozzles and change the simulated rain characteristics, namely by increasing the rainfall kinetic energy. The laboratory experiments included testing four types of spray nozzles (discharge from 2·3 to 11·9 L min−1), combined with a high‐density polyethylene mesh (square aperture of 20 mm). The effect of the mesh was studied for three vertical distances between the nozzle and the mesh (0·20, 0·40 and 0·60 m). A laser disdrometer was used to measure the diameter and fall speed of the simulated raindrops. For the mesh‐free simulations, the nozzles produced drops having on average a mean equivalent diameter of around 0·6 mm and a mean fall speed of about 1·5 m s−1. The mesh increased the formation of bigger drops (>2·5 mm) and, consequently, increased the rainfall kinetic energy of the simulated rain; the magnitude of this increase varied with the spray produced by the nozzles. Results show that meshes can be useful for increasing the kinetic energy of the rainfall simulated by nozzles within soil erosion studies. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

6.
The influence of land use on runoff and soil loss was assessed on two small watersheds in the Eastern Caribbean island of St Lucia, under contrasting land management regimes. The data generated from these watersheds revealed that the soil losses from an intensively cultivated agricultural watershed were 20‐times higher in magnitude than that of a forested watershed both for peak rainfall event and for total duration of analysis. This was due to higher surface runoff rates and exposure of soil to direct raindrop impact within cultivated areas. Whereas the forest canopy cover in combination with higher infiltration capacities of the forested land reduced the erosive runoff from the forest watershed and thus the soil loss. Moreover, the energy intensities of large storms in excess of 40 mm were estimated and found to range between 400 MJ mm ha−1 h−1 and 1834 MJ mm ha−1 h−1. 1
  • 1 Megajoules‐millimeters per hectare‐hour.
    • Soil loss from the agricultural watershed was strongly correlated (R2 = 0·85) to storm energy‐intensity (EI30). However, the correlation of soil loss with the EI30 (R2 = 0·71) was poor for the forest watershed due to the effect of canopy vegetation, which significantly reduced the energy of raindrop impact. Over the study period, cumulative soil losses were 10·0 t ha−1 for the agricultural site and 0·5 t ha−1 for the forest site. 2
  • 2 Metric tons per hectare.
    • The largest storm observed during the study period resulted in erosion losses of 3·78 t ha−1 and 0·2 t ha−1 from the agricultural and forest sites respectively. The regression models were developed using the measured data for prediction of runoff and soil loss over the watersheds of St Lucia under similar conditions. This study contributed towards efficient watershed management planning and implementation of suitable water conservation measures in St Lucia. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

    7.
    To study and model the interrill erosion process in an unmanaged Japanese cypress (Chamaecyparis obtusa) plantation, soil splash detachment rates were estimated based on the quantification of throughfall raindrop indices. Throughfall drops and soil splash detachment were simultaneously observed in the field, and observed data were compared with estimates produced by previous models. Observations took place over five months in 2005, during six observation periods. Raindrop indices of kinetic energy (KE), momentum (M), and momentum multiplied by the drop diameter (MD) were calculated from drop diameters and velocities. The median volume diameter of 1.99 mm for the overall observation period was well bounded by those from other Japanese cypress plantations. Throughfall consisted of large drops, generated as drips, exceeding 3 mm in diameter. The fall height was insufficient for the drops to attain terminal velocity, with 91% of the drops reaching less than 90% terminal velocity. The observed throughfall raindrop indices had strong correlation with throughfall rainfall intensity, even though throughfall raindrops occurred in seven rainfall events with different meteorological conditions. The values of observed KE and M were lower than previous model-derived estimations. Earlier models tended to overestimate throughfall KE and M, partly because the expected velocity was greater than that observed, and partly because they did not consider the effect of the splash water component during throughfall. The splash detachment rate in forests was weakly correlated with the total-amount raindrop indices but strongly correlated with the maximum value of raindrop indices over a short time scale such as 1 h. This result indicates that continuous and concentrated raindrop impacts over a short time duration cause splash detachment in the forest floor. Development of a comprehensive model of the process of forest floor soil surface erosion requires more detailed measurement of actual throughfall drops.  相似文献   

    8.
    The aim of this paper is to assess the mechanisms of water erosion in andic soils using two tests, which in a certain way simulate the two principal mechanisms of aggregate destruction in the process of water erosion—water dispersion and raindrops impact—and compare them with the aggregation observed in material dettached by inter‐rill erosion (sediments) in experimental plots with natural rain. In accordance with the obtained results, the erosive process in these soils seems to come about through a picking off of surface material of larger aggregates, due to the impact of raindrops. The intensity of pull off and fragment size from larger aggregates depends on the kinetic energy of the drops (rain intensity), but the size generally ranges between 0ċ2 and 0ċ5 mm. Therefore inter‐rill erosion initially proceeds by a washing down of smaller aggregates (<0ċ5 mm) (of less bulk density than larger aggregates 0ċ4 Mg m−3 against 0ċ9 Mg m−3), enriching the soil in larger sized aggregates which, on being fragmented by picking off of raindrops, supply new material for washing down by inter‐rill erosion. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

    9.
    《Biosystems Engineering》2003,84(3):315-329
    A model for fan-ventilated greenhouse cooling is presented in which the primary heat transfer surfaces (cover/structure, canopy and floor) are represented as three parallel planes. Validation of the model was accomplished using data collected over 14 days. Agreement was good, with canopy temperatures over-predicted by only 0·1%, air temperatures in the canopy under-predicted by 0·5%, humidity of the canopy air under-predicted by 1·6% and transpiration rates under-predicted by 1·4%. Simulation runs suggest that when evaporative pad cooling is not used, little advantage is derived from increasing airflow rates beyond about 0·05 m3 m−2 s−1. When evaporative pad cooling is used, however, both air and canopy temperatures decline with increasing airflow rates up to 0·13 m3 m−2 s−1, the highest level considered. Increasing canopy size is predicted to be more influential in reducing air temperatures when evaporative pad cooling is used than when it is not, but its effect on canopy temperature is expected to be approximately the same whether or not evaporative pad cooling is used. With no evaporative pad cooling, the evapotranspiration coefficient (i.e., the ratio of energy used for transpiration to incoming solar energy) is predicted to range from 1·75 for an outside temperature of 36·8°C and an outside humidity ratios of 3·3 g kg−1 to 0·8 for an outside humidity ratio of 29·9 g kg−1 at the same temperature. With evaporative pad cooling, the coefficient is predicted to range from 0·6 to 0·8 at the same outside temperature and the same range of outside humidity ratios.  相似文献   

    10.
    Soil erosion is a severe problem on China's Loess Plateau due to its fine‐grained soils and the increasing frequency of extreme rainfall events. Accordingly, this study used a 100‐year frequency rainstorm dataset to analyse sediment deposition and sources in a 27‐km2 catchment with a dam field area of 0·14 km2 based on the hypothesis that sediments were intercepted by the dam (before collapse) during the rainstorm event and deposited in the dam field. This study applied composite fingerprinting, which revealed the sediment source contributions and estimated sediment deposition. Sediment deposition (626·4 kg m−2) decreased linearly or exponentially with increasing distance from the dam. Composite fingerprints based on the optimal parameters revealed relative sediment contributions of 44·1% ± 25·5%, 37·7% ± 35·0%, 9·0% ± 11·4% and 9·2% ± 11·5% by bare ground, croplands, grassland and forests, respectively. The 5‐year cumulative sediment deposition from normal rainfall was 2·3 × 104 t less than the extreme rainstorm. Bare grounds and croplands were the dominant sediment sources following both the extreme rainstorm and normal erosive rainfall events but varied at different areas of the check‐dam. Erosion patterns and start times depended on land use type, thereby affecting sediment profiles in the dam field. Furthermore, severe erosion from bare ground that were all gully slopes and gully walls occurred throughout the rainfall, whereas grasslands and forest erosion occurred earlier and croplands later. Finally, extreme rainfall promoted mass wasting on slopes, gully slopes and gully walls, which are important in determining extreme rainstorm erosion pattern variation. This study aimed to reveal erosion pattern variation under extreme rainstorm events. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

    11.
    Soil and surface water runoff are the major causes of cropland degradation in the hilly red soil region of China. Appropriate tillage practices are urgently needed to reduce erosion and protect the soil surface. In this study, five tillage systems [manure fertiliser (PM), straw mulch cover (PC), peanut–orange intercropping (PO), peanut–radish rotation (PR) and traditional farrow peanut (PF)] were compared in terms of soil infiltration and the capacity to generate runoff. Based on field‐plot monitoring and simulated experiments, this study revealed that the organic content of the soil in the PO (19.43 g kg−1), PC (18·63 g kg−1) and PM (18·18 g kg−1) treatments increased compared with those of the PF (15·64 g kg−1) and PR (17.17 g kg−1) treatments. Moreover, the three tillage practices also enhanced the soil's aggregate stability and infiltration capacity. The average annual runoff generation rates of the treatments were as follows: PR (3,141 m3 ha−1 a−1) > PF (2,189 m3 ha−1 a−1) > PC (755 m3 ha−1 a−1) > PM (514 m3 ha−1 a−1) > PO (388 m3 ha−1 a−1). The PO treatment reduced the runoff generation rate by approximately 82·3% compared with that of the PF treatment. Among the treatments, the PO treatment had the highest threshold rainfall depth (22 mm) for runoff generation. Regression analysis revealed that the threshold rainfall depths linearly increased with the infiltration rates. The results of this study could benefit local soil management and cropland conservation. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

    12.
    As the basic unit of erosion and sediment yield, it was critical to determine the amount of soil erosion and sediment yield in the small watersheds for sustaining a reasonable water resource and sediment regulation system. In this study, we determined the sediment yield from the dams‐controlled watershed on the North Loess Plateau. Three check dams in the watershed were investigated by drilling ten‐hole sedimentation cores. The corresponding flood couplets were dated according to thickness of deposition layers, distribution of sediment particle size and historical erosive rainfall events. On the basis of the check dams capacity curve, the soil bulk density and the thickness of couplets, the deposit mass of check dams, and then the sediment yield of watershed at different temporal and spatial scale were deducted. In total of the 33, 60 and 55 couplets were corresponded to individual flood events in the dam MH1# from 1976 to 1984, the dam MH2# from 1985 to 2007, and the dam MH4# from 1981 to 2009, respectively. The specific sediment yield for flood events was 1,188.5–11,527.9 Mg km−2, 1,278.6–17,136.7 Mg km−2, and 3,395.9–33,698.5 Mg km−2, and the annual average sediment yield was 10,728.6 Mg (km2 · a)−1, 12,662.9 Mg (km2 · a)−1, and 16,753.3 Mg (km2 · a)−1 in dam MH1#, MH2# and MH4# controlled watershed, respectively. The sediment yields were inversely proportional to the dams – controlled areas. For the whole watershed, the annual average sediment yield was 14,011.1 Mg (km2 · a)−1 from 1976 to 2009. There were large amounts of sediments (42.3–50.5%) were intercepted gradually along the way from small watersheds to the river channel. And the minimum rainfall for sediment deposited in the dams was greater than 20 mm in this watershed. The results of this study suggested that the sediments retained behind check dams were helpful to quantifying the amount of erosion sediment yield and understanding the soil erosion evolution in the small and ungauged watersheds. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

    13.
    Soil erosion is a serious problem in the Loess Plateau of China, and assessment of soil erosion at large watershed scale is urgently need. This study used RUSLE and GIS to assess soil loss in the Yanhe watershed. All factors used in the RUSLE were calculated for the watershed using local data. RUSLE‐factor maps were made. The mean values of the R‐factor, K‐factor, LS‐factor, C‐factor and P‐factor were 970 209 MJ km−2 h−1 a−1, 0·0195 Mg h MJ−1 mm−1, 10·27, 0·33359 and 0·2135 respectively. The mean value of the annual average soil loss was found to be 14 458 Mg km−2 per year, and the soil loss rate in most areas was between 5000 and 20 000 Mg km−2 per year. There is more erosion in the centre and southeast than in the northwest of Yanhe watershed. Because of the limitations of the RUSLE and spatial heterogeneity, more work should be done on the RUSLE‐factor accuracy, scale effects, etc. Furthermore, it is necessary to apply some physical models in the future, to identify the transport and deposition processes of sediment at a large scale. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

    14.
    种植大豆地表土壤溅蚀效应及其空间分布特征   总被引：4，自引：0，他引：4  
    马波  吴发启  马璠 《土壤学报》2013,50(1):50-58
    为系统研究种植大豆条件下农地溅蚀速率变化特征并建立简单易用的模型,评价大豆种植对土壤溅蚀的影响,采用室内模拟降雨的方法,测定了不同降雨强度(40 mm h-1和80 mm h-1)、不同大豆生长阶段(始花期、盛花期、结荚期和始粒期)下的穿透雨强度和溅蚀速率,分析了大豆冠下溅蚀速率与叶面积指数和穿透雨强度的关系,探讨了冠下溅蚀速率的空间分布特征.结果表明:与裸地相比,在大豆全生育期,大豆冠下平均溅蚀速率在设计雨强40 mm h-1和80 mm h-1下,分别减少了62.85％和60.74％.冠下平均溅蚀速率随叶面积指数增加呈显著的增加趋势,且随降雨强度的增大而显著增加.冠下各点溅蚀速率受相应各点的穿透雨强度影响在80 mm h-1设计雨强下较为显著,随穿透雨强度的增加而增加.大豆冠下溅蚀速率的空间分布与穿透雨的分布具有一定的对应性,即冠下穿透雨较为集中的区域会在一定程度上增加溅蚀的发生,并导致冠下溅蚀速率分布不均,大豆冠下穿透雨是冠下溅蚀产生和分布的主要能量来源.该研究提出的大豆冠下溅蚀速率模型可为坡耕地土壤侵蚀防治和农田灌溉有效利用提供理论支持.  相似文献   

    15.
    Introduced pigs (Sus scrofa ) are recognised as having significant environmental impacts. Here, we quantify the effect of feral pigs in a catchment (undisturbed by Europeans) in the monsoonal tropics of northern Australia. Field data collected over a 5‐year period showed that the areal extent of pig disturbance ranged from 0·3 to 3·3% of the survey area (average 1·2%, σ = 0·9%). Mass of exhumed material was considerable and ranged from 4·3 to 36·0 Mg ha−1 y−1 (average 10·9 Mg ha−1 y−1). The excavations produce surface roughness which acts as sediment traps. Over the 5‐year study period, there was no evidence to suggest that pigs produce any rill or gully erosion. There does not appear to be any relationship between rainfall amount and area disturbed or volume of material exhumed. However, a significant positive relationship was observed between number of disturbances and rainfall. The location of any disturbance appears to be random and has no relationship with topography or geomorphic attributes such as slope, upslope contributing area or wetness indices derived from a high‐resolution digital elevation model of the site. While pigs are disturbingly relatively large volumes of soil, there is no clear evidence to support any increase in local erosion and soil structural change may be occurring slowly and only be observable over the long term. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

    16.
    Soil organic carbon (SOC) is one of the important measures of soil fertility and sustainability in arable lands. With continuous CO2 flux measurements, this study assessed the SOC decomposition and its environmental controls at both half‐hourly and season‐long scales in a single‐crop rice (Oryza sativa L.) paddy during three fallow periods between 2004 and 2007. Measurements were made on a gray lowland soil sited in eastern Japan using the eddy covariance method. Ecosystem respiration was strongly affected by soil water content measured at 0–0·1 m depth. At 0·5 m3 m− 3 or more of soil water content, the baseline of ecosystem respiration decreased by 50% compared with that at 0·2 m3 m− 3 . The effect was quantified at half‐hourly scale using an empirical multiple regression model, together with the soil surface temperature and the time after residue incorporation. At season‐long scale, net biome production, which is equivalent to the change in the SOC pool during the fallow period, was estimated from the flux and ancillary data at 150 g C m− 2 in 2004–2005, 70 g m− 2 in 2005–2006, and 270 g C m− 2 in 2006–2007. Apparently, as much as 46 to 79% of the soil organic matter incorporated (crop residues, ratoon, and stable manure) was decomposed during the fallow period. Precipitation, or associated soil water content, was important for the carbon balance of the field at season‐long scale because of its large interannual variability and relatively low permeability of the paddy soil. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

    17.
    A localized rainfall kinetic energy (E) equation and an erosivity map were developed, and the suitability of the universal soil loss equation (USLE) for assessing the soil erosion of a non‐US region was investigated. After accurately measuring and gathering data regarding raindrop size using disdrometers in four northern Taiwan locations, this study investigated the drop size distribution under different conditions by categorizing the rainfall patterns to develop regression equations for estimating the unit volume‐specific kinetic energy (KEmm) and the unit time‐specific kinetic energy (KEtime) of northern Taiwan. Climate zoning, which is not considered in currently used designs, was then implemented along with two‐stage cluster analysis to construct a rainfall erosivity (R) distribution map using the kriging model. The binary polynomial regression function of KEtime, which had the highest correlation (R2 = 0.98), was suggested to estimate E in northern Taiwan. It was found that the pattern and intensity (I) of rainfall will slightly affect E. The climatic influence on the root mean square of the semivariogram was significant, which suggests that climate zoning can help estimate the rainfall erosivity (R). The outcomes were extended to estimate R in areas without rainfall stations.  相似文献   

    18.
    黄土地区主要树种的林冠降雨特征分析   总被引：4，自引：0，他引：4       下载免费PDF全文
    在人工降雨条件下,采用色斑法对黄土地区4个主要树种幼树进行林冠降雨观测。结合AutoCAD、Excel数据处理软件,在0．1mm径级下分析不同树种的林冠降雨特性,并对比研究林外降雨和不同树种的林下降雨动能。结果表明：1）不同树种林冠降雨雨谱基本不受空旷地降雨强度影响;2）用正态分布函数和类卡方分布函数对林冠降雨雨谱描述和分析容易失真,应寻求更好的数学形式对林冠降雨雨谱进行表达;3）林冠降雨雨滴直径—体积分布密度图是双峰曲线,表明Best函数同样未能对林冠降雨大雨滴作出准确描述,而利用多项式函数直接表达累积体积效果更好;4）不同树种单位水体（1L）的林冠降雨动能大小为侧柏（28．18J）〉油松（26．74J）〉元宝枫（25．75J）〉刺槐（20．07J）,此结论也为在充分降雨条件下判断植被冠层是否增加了降雨动能提供了可比条件。  相似文献   

    19.
    The effect of raindrop temperatures on runoff generation and erosion on clayey soil was investigated in sprinkling experiments with a laboratory rotating disk rain simulator. The experiments were applied to Rhodoxeralt (Terra Rossa) soil with two pre‐prepared moisture contents: hygroscopic and field capacity. For each moisture content, three rainfall temperatures were applied: 2, 20, and 35 °C. Erosion was generally lower in the pre‐wetted soil than in the dry soil (12.5 and 24.4 g m−2 per 40 mm of rain, respectively). Whereas there was no significant effect of raindrop temperature on the dry soil, the soil that was pre‐moistened to field capacity was affected by rainwater temperature: runoff and erosion were high when the temperature difference between rainfall and soil surface was high, and sediment yields were 13·9, 5·2, and 18·3 g m−2 per 40 mm of rain, for rain temperature of 2, 20, and 35 °C, respectively. It is reasonable to conclude that thermophoresis caused by thermal gradients within the soil solution reduces the stability of aggregates and then increases the soil losses. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

    20.
    We investigated the erodibility of surface casts produced by an anecic earthworm of the Colombian savannahs by means of indoor rain simulations. The kinetic energy applied to samples, 21.62 J minute−1 m−2, was estimated to be equivalent to 41% of the energy of the more intense period of a local storm. The erodibility of casts was assessed at different stages of their ageing along with the effects of repeated wetting‐drying cycles. Bare soil cores and soil cores of the same size with a cast on their surface (soil + cast) were used as controls. Saturated hydraulic conductivity (HC) was measured to test whether casts enhance soil water permeability. Fresh, almost liquid, individual casts were completely dispersed by a 2‐hour rainfall simulation at a dispersion rate of 0.9 ± 0.5% of sample minute−1. After 5 hours drying at 32°C and 79% relative humidity, casts were as moist as fresh casts (non‐significant Mann–Whitney U‐test) but had a solid appearance and were no longer dispersed by raindrop impact. Under simulated rainfall, dry casts were very slowly fragmented into large aggregates (> 5 mm). The HC of casts was increased by repeated cycles of wetting and drying but unaffected by length of air‐drying and natural ageing, and averaged 7 (3, n = 6), 20 (3, n = 7) and 32 (1, n = 45) cm hour−1 for bare soil, soil + cast and all casts, respectively (standard error, sample size). Except for bare soil, these values were greater than the greatest rainfall intensities recorded locally. The consequences for soil erosion, nutrient losses and water infiltration are discussed.  相似文献   

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