侵蚀性花岗岩坡地不同地貌部位土壤剖面风化特征研究

为揭示发育于侵蚀性风化花岗岩坡地上不同地貌部位土壤剖面的风化发育特征,在浙江省选择了典型的风化花岗岩坡地:浙江省嵊州市水土保持监测站为研究区,在监测站同一坡面不同侵蚀强度的坡顶、坡中、坡底选取3个典型的土壤剖面(140 cm),从下至上等距离(20 cm)采集土壤样品,共采集21个土样。进行了各层土壤基本理化特性和化学全量的分析,并分别计算了3个剖面不同层次的主要化学风化系数及总的风化强度,结果表明:(1)在强烈侵蚀的花岗岩风化残积坡地发育的土壤,总体发育成熟过程较弱,其进一步的发育与典型的地带性土壤的发育有很大的差异,侵蚀过程严重地影响了土壤的进一步成熟,侵蚀强度越大,则土壤发育越差。(2)土壤剖面总的风化强度不大,上下层的递变差异很小,脱硅富铝化过程随着剖面深度的增加风化程度越来越弱。(3)土壤剖面的化学分层不明显,各种风化指标均在60 cm左右形成了一个分界层,其上受水力侵蚀影响明显,其下呈现出的特性以继承残积母质为主。(4)不同地貌部位的风化发育程度排序为:坡底坡中坡顶,其与采样坡面的侵蚀强度排序正好相反。(5)风化程度与有机质和黏粒含量具有较为明显的正比关系,在侵蚀环境下,土壤的物理特性对风化的影响明显,在沉积环境下土壤有机质的影响大于黏粒含量的影响。总之,由于受侵蚀的影响,坡地土壤剖面的淀积层不发育,剖面呈现出的假淀积层不是由淋溶作用形成的,而是具有一定风化程度的风化残积层,结果导致发育于山地丘陵侵蚀性坡地的土壤层次划分不同于常规的土壤层次划分。     

Soil erosion evaluation in a small basin through the use of Cs technique

Soil erosion significantly affects the most productive lands in Argentina, particularly the region called “Pampa Ondulada”. Quantification of the actual rates and patterns of soil loss is necessary for designing efficient degradation control strategies. The aim of this investigation was to gather using the ¹³⁷Cs technique a reliable set of data of erosion and sedimentation rates, in order to describe the long-term erosive landscape dynamic in a 300 ha basin representative for the “Pampa Ondulada” region of Argentina. The general topography of the basin is undulated with slopes gradients between 0 and 2.5% and slope lengths up to 800 m long. The main land use consisted in annual cropping under conventional tillage.For the soil erosion study in the basin the ¹³⁷Cs technique was used, which is based on the comparison between the ¹³⁷Cs inventories surveyed with a local reference ¹³⁷Cs profile. The sampling strategy was based on a multiple transect approach.The estimated mean soil erosion rates obtained applying Mass Balance Model 2 for the studied hillslopes ranged between −11.5 and −36 t ha⁻¹ per year and fitted the low and moderate erosion classes according to FAO. These values ranged beyond the admitted tolerance. Sedimentation was observed at the lower landscape positions probably related to changes from convex to concave slopes. The application of the ¹³⁷Cs technique in the studied basin proved to be a useful and sensible tool for assessing erosion/deposition rates. In areas with low topographic gradients like the Pampa Ondulada region, the slope length appears to be an important property for predicting spatial patterns of erosion rates.     

侵蚀性风化花岗岩坡地土壤发育特性

采用CT扫描技术、X射线荧光光谱仪化学全量分析和实验室土壤理化特性测试方法,对浙江省典型风化花岗岩坡地土壤发育的主要物理指标、化学风化系数及风化强度进行了测量计算,分析了侵蚀环境下不同地貌部位的土壤发育特征。结果表明:坡地土壤的发育程度较弱,土壤分层不明显,不同地貌部位的土壤风化发育程度排序为坡底<坡中<坡顶,与坡面侵蚀强度的排序正好相反。土壤物理风化指标随土层深度增加的变化规律较强,脱硅富铝化过程随着剖面深度的增加越来越弱,物理风化指标和化学风化指标具有同等作用的表征效果,不同于当地地带性土壤发育中以化学风化为主的特性。水力侵蚀强烈地区的最大风化强度位于20-40 cm处,推得水力侵蚀对土壤发育的影响深度为0-40 cm。     

The influence of slope aspect on soil weathering processes in the Springerville volcanic field,Arizona

A comparison was made between soils on north- and south-facing slopes of six cinder cones in the Springerville volcanic field (SVF), Arizona, in order to determine the influence of slope aspect on soil weathering processes. Twenty-four soil pedons were sampled on different aspects of six cinder cones. To control for the influence of slope on pedogenesis, all sample sites possessed slopes of 17±2°. Soil weathering processes were characterized by solum depth, texture, and Ca:Zr chemical weathering indices. Quartz and mica were used to identify eolian additions to the volcanic soils. Accelerated rates of weathering and soil development were found to occur in soils on south-facing slopes while no trend with aspect was found for eolian additions. Accelerated rates of weathering and soil development may influence cinder cone degradation and cone morphology.     

Clay plains and geomorphic history of the central Sudan A review

The paper presents an analysis of the Sudan clay plain. Total plain area is 500,000 sq. km., but the paper focuses on an area of 90,000 sq. km.In the east-central Sudan an old erosion surface between600m× 730m above sea level is probably Miocene in age. The main plainlands lie 200 – 300 m below this and date from entertiary times. Evidence of an “African” surface may occur on skeletal volcanoes near Gedaref.Downwarping along NNW-SSE lines formed distinctive basins including the Blue Nile basin. Sediments accumulated in the basins and a sequence of arkose, paludal sandy clay, alluvial sand, silt and clay in the Blue Nile basin is capped by modern silt and clay which has weathered to form a clay soil.The clays on the plain vary in age from upper Pliocene to modern though the weathering seems in balance with a somewhat wetter climate than at present. The clays dominantly on almost level plains are alluvial or lacustrine. The remainder is residual or colluvial weathered material on flat but extremely gently sloping interfluves on higher ground.The clay of the aggradational plains in the Blue Nile basin has been reworked continuously by the rivers and is therefore, much younger than the clay on the degradational plains which is upper Pliocene to Middle Phistocene in age. The present Blue Nile flows in a wide alluvial valley with the channel incised up to 24 m below the general plain.     

Beitra¨ge zur allgemeinen geomorphologie der tropen und subtropen Geomorphodynamik und vegetation klimazyklische sedimentation panplain/pediplain-pediment-terrassen-treppen

Because of the high infiltration capacity in natural rain forests or dry forests, there is no essential surface runoff with soil erosion and soil dislocation. At extremely poor rain forest sites one must consider that the soil chemistry is likely to induce a natural thinning of vegetation, which will lead to moderate surface runoff and a selective removal of clay, silt and fine sand. Even smaller man-made changes will cause — because of positive feedback — a considerable decrease of infiltration, as well as a corresponding surface runoff with related soil erosion and soil dislocation. Only then the recent soil erosion may be accepted as natural and climate-specific, when vegetation analyses have proven that all layers of the vegetation are undisturbed.Frequently, man-made or climatically induced regressive successions will damage preferably shallow-rooting plants. Then trees and bushes will dominate the pollen spectrum. Older erosional phases without an extensive destruction of the vegetation can thus be hidden in pollen profiles. They can be evidenced, however, by discordances, respectively by the accumulation of fine and partly also of coarse materials.Soil sediment sequences occur in all studied areas of the tropics and subtropics. They can be mainly ascribed to climatic changes. More detailed evaluations would necessitate facies- as well as frequency-analyses of these soil sediment sequences. Layers of coarse material, which are found close to, or on steep slopes, or on level surfaces, can be related to haphazardly distributed individual events of increased surface runoff. In very flat areas with predominant dense vegetation, also individual layers of coarse material, as e.g. residual debris, or shortly transported slope- respectively pediment debris, can indicate climatic periods of distinctly disturbed vegetation.Such periods can be explained by an increased frequency of randomly distributed individual events of higher rainfall intensity. The stability of the ecosystem, which depends on the “general climate” determines the threshold value, at which these individual events (miniature catastrophes) become geomorphologically active.In the presence of extreme soil moisture even the — with regard to surface runoff — very stable rain forest ecosystem can be attacked by landslides. Secondarily, then also the surface runoff can lead to increased erosion, as e.g. by slope incision. In most cases, probably a previous weakening of the ecosystem's stability will have taken place, such as a higher biopedo-climatic aridity of the “general climate”, which in turn could lead to primarily active surface runoff.It takes, however, numerous strong individual events, not to stabilize an ecosystem by progressive succession, but to destabilize it by regressive succession, so that surface runoff and the dislocation of fine and coarse material will set in, because of repeated events of less intensive rainfall. This state of an ecosystem means geomorphodynamic activity, whereas the vegetation-stabilized ecosystem stands for geomorphodynamic stability with distinct soil development. Soils and soil sediments are thus important indicators for the reconstruction of geomorphological effects of paleoclimates on slopes without concentrated surface runoff.In dry areas, which are characterized by thinner vegetation, repeated events of higher rainfall intensity can lead to geomorphodynamic activity and to regressive succession, even without a change of the “general climate”. An increase of the amount of precipitation coupled with a decreasing rainfall intensity would provoke the opposite effect: a strengthening of the ecosystem, stronger vegetation growth, and soil development.In periods of geomorphodynamic activity slopes can be entirely flooded and eroded by surface runoff, provided there is a sufficient runoff divergence due to transported coarse materials, or, in other words, when there is a high load ratio. When the load ratio is too small, then under all climates and on all geomorphologic elements, which have been shaped essentially by surface runoff, a concentration of the runoff and incision will take place. This could be so, either because the erosion capacity under a given soil protection turns out too weak, or because of too steep slope gradients related to a given catchment area.When the incision speed of such a concentrated runoff channel exceeds the lowering speed of its base level — which is frequently the case — then the following will result: its gradient, which is determined by the erosion, will become smaller, a concave longitudinal profile will develop, and finally the transport capacity will decrease, which means an increase of the load ratio. This will in turn increase the runoff divergence, and will thus lead — on all relief elements with runoff concentration — to a channel widening by lateral erosion. This process can become accelerated, when a climatic change towards higher rainfall intensities sets in, which will in turn increase the runoff divergence. In southern Brazil runoff channels of remarkable width are noticeable, not only on valley floors of smallest catchment areas, but also on steep slopes. In both cases, the high runoff divergence can be demonstrated — either in drillings, or in natural exposures — by the occurrence of coarse materials under subsequently deposited, fine sediments.In all climatic zones, this development can proceed until the interfluves are completely eliminated by lateral erosion. Then relief elements with unconcentrated runoff will develop, or rather be restored at a lower elevation, i.e. smooth slopes, respectively smooth pediments (Abtragungsfußfla¨chen). The further development is, on the one hand, characterized by a retrogressive flattening of these relief elements, and, on the other hand, by their growth, as neighbouring forms will unite. The final morphology will be one of a huge, smooth plain with a relatively small longitudinal gradient, a panplain (CRICKMAY 1933). It will develop over every substratum, and in all climatic zones. The prerequisites for such a development are, on the one hand, at least a temporary dominance of climatic conditions with geomorphodynamic activity, and, on the other hand, a relatively smaller lowering of the base level, as compared with the slope denudation. Thus, the development of panplains is favoured by areas of long-lasting tectonic stability or subsidence, or by periods without lowering of the sea level or transgression. It is, in addition, favoured by a previous deep weathering, or by a deep weathering, which continues alternatingly in periods of geomorphodynamic stability, i.e. by the development of easily removable saprolite on all types of rock.The previous stage of relief development with individual, associated plains — the pediplain, respectively the plain-facet-mosaic (Fla¨chenfacetten-Mosaik) — depends as associated form to a great extent on the former pattern of incision. This pattern depends, on the one hand, on a tectonic and petrographic weathering-conditioned differentiation, whereas on the other hand, there are distinct differences between zones of similar climate, respectively of a similar climatic sequence.In areas of the tropical savannas with wide-spread saprolite the stages of geomorpho-dynamic activity set in with a lowering of the river levels. The plains, however, are hardly dissected. When the load ratio grows because of climato-genetic reasons, then river bluffs will turn into independent slope pedimentation steps, which migrate uphill. But this will only be so, when the base level does not incise any stronger, because of the great speed of the slope denudation, which in turn results from the presence of easily removable substratum. The pediments of adjacent catchment areas will intersect near the interfluves, thus forming a pediplain. This process will be accelerated, as soon as the river incision reaches, at least in some places, the base of the saprolite. Then, any further linear erosion will be retarded.In areas of tropical savannas without saprolite, as well as in other arid areas with dominant coarse material, the slope denudation lags behind the linear incision. Incision of the rivers and dissection of older plains will be dominant. When, because of climato-genetic reasons, the load ratio grows, then relief elements with unconcentrated surface runoff will be restored, i.e. planation by lateral erosion will set in.In many areas of the nowadays perhumid tropics, the planation results from lateral erosion. At the beginning of a stage of geomorphodynamic activity, the ecosystem must probably have been stable to a great extent. Then, starting from disturbances, and also because of a low load ratio, the surface runoff must have initiated linear incision and a deep-reaching dissection of older plains.When the load ratio grows as a result of climato-genetic reasons, then new planation surfaces will develop by means of valley-floor-pedimentation processes, as in arid zones. These planation surfaces will, however, possess a much lower gradient, as there is — because of deep weathering — less coarse material involved, which consequently requires less transport work. Finally, the retrograding flattening of the longitudinal profile will also progress much faster. The system of plains consists of a mosaic of individual planation surfaces (plain-facets, Fla¨chenfacetten), which are generally sloping in the same direction. As it is an associated form of individual planation surfaces, it can be classified as a pediplain. Whereas pediplains still developed in the course of the younger Quaternary, or, respectively, developed again at lower elevations after a dissection, there is hardly any evidence of panplain development. In large parts of the world, especially in exhoric areas, a development towards increasing relief energy has occurred. The entire development can be characterized as a development sequence from panplain to pediplain, pediment, and terrace sequence. Depending on the tectonic conditions of any analysed area, on its petrographic and weathering-conditioned differentiation, and on its climate-zone-specific properties, this development has proceeded to different degrees. On the one hand, the entire development has been conditioned by the regression of the sea level since the Cretaceous period, which, although interrupted several times by transgressions, amounted up to several hundreds of meters. The development of panplains, respectively of very flat pediplains, during the older Tertiary was certainly favoured by either slow regression, or by transgression.On the other hand, a progressive planation development is possible, because of a clustering of periods of geomorphodynamic activity with especially high load ratios, i.e. with highly intensive planation processes, and with low tendencies towards dissection. The opposite is a sequence of periods of activity with small, respectively decreasing load ratios, which will favour the development of pediment sequences, and of terraces with decreasing extensions. The latter seems to be true for the younger Quaternary, which is characterized by a sequence of climatic cycles with a low potential for planation processes.With regards to the older development one must keep in mind that relief elements, which had developed during intermediate, less intensive periods of activity, were subsequently destroyed by periods with more intensive planation processes (principle of selection by intensity / Intensita¨tsausleseprinzip). Therefore, relief elements from older periods have only survived, when they either originated from very strong periods of activity, or from a sequence of equivalent periods of activity. This fact can lead to the deception that the climatic development has proceeded to ever weaker climatic cycles. The real relief development, however, can only be explained by the interference of tectonics, changes of the sea level, and the sequence of climates. The world-wide, parallel development was, to a great extent, controlled by the last two factors. A long-term shifting of the climatic zones has accelerated the relief development towards the formation of pediment-, respectively terrace sequences. Thus, for example, the Central European Quaternary valley incision can be traced to the regression of the sea level, as well as to the climatic change, which brought forth climatic cycles with less intensive processes of slope denudation, but with high intensities of linear erosion.The extremely deep-reaching weathering on panplains, respectively on pediplains, is not regarded to be responsible for planation processes, but, on the contrary, to be the result of too weak planation processes compared to the deep-reaching weathering. Very flat pediplains, but above all the panplains with their small gradients and extreme flatness are characterized — even in periods of stability with stable ecosystems — by far-reaching ground water currents and high ground water tables. Depending on the conditions of the catchment area, extreme concentrations of iron- and aluminium oxides and silica may result, whereas calcium carbonate may be deposited in arid areas. These deposits of oxides and carbonates are distinctly different from younger oxide- and carbonate concentrations, found at steeper, better-drained sites on younger surfaces. As in the case of the deep-reaching weathering, we do not regard this to be the expression of basically different process combinations, but to be the result of the different sites, which depend to a great deal on the existing relief and the relief development.     

基于近景摄影测量的径流冲刷条件下冻融坡面侵蚀产沙过程

为研究冻融坡面径流冲刷条件下侵蚀产沙过程,采用2个坡度(10°,15°)、3个流量(3,6,9 L/min)、2个起始解冻深度(6,12 cm)组合进行野外冲刷试验,结合近景摄影测量技术分析不同解冻深度、不同坡度和不同流量条件下的产沙量,运用线性回归方程对近景摄影测量值和实测值进行拟合。结果表明:起始解冻深度和坡度相同条件下,冻融坡面的土壤侵蚀产沙量随着径流量和坡度的增大而增大;随着时间推移,产沙量越来越小。在流量和坡度相同时,随着初始解冻深度的增大,坡面产沙量也逐渐增大;在流量和解冻深度相同时,随着坡度的增大,坡面产沙量也逐渐增大。当流量、解冻深度和坡度最大时,坡面侵蚀产沙量达到最大。坡面产沙量实测值与近景摄影测量对比分析得到误差平均精度为90.67%,近景摄影测量技术可以在冻融条件下土壤侵蚀监测中应用。     

冻融坡面水蚀动力参数动态响应时空演化过程

为揭示冻融作用对坡面土壤水蚀的影响,探究春季解冻期坡面土壤的水蚀动力参数动态响应时空演化过程,采用2个坡度(10°,15°)、4个流量(4.5,6.5,8.5,10.5L/min)和4个起始解冻深度(2,5,10,15cm),进行野外径流冲刷试验,系统地分析冻融坡面水蚀动力参数雷诺数、弗劳德数、流速、水流剪切力、水流功率和单位水流功率在不同起始解冻深度、不同流量和不同坡度条件下的时空演化过程。结果表明:冻融坡面水蚀动力参数雷诺数、流速、水流剪切力和水流功率随流量的增加呈增加趋势;水流剪切力、水流功率与单位水流功率随坡度增加而增大;水流剪切力和水流功率随起始解冻深度的加深而增大;雷诺数、弗劳德数、流速和单位水流功率随起始解冻深度的变化趋势不明显,其起始解冻深度为5cm时,水蚀动力参数随时间变化最为剧烈;建立了冻融坡面水蚀动力参数雷诺数(R~2=0.728)、水流剪切力(R~2=0.644)、水流功率(R~2=0.721)、流速(R~2=0.533)和单位水流功率(R~2=0.553)的幂函数预测方程。     

Soil slips on weathering-limited slopes underlain by coarse-grained granite or fine-grained gneiss near Seoul,Republic of Korea

The chemical, mineral, physical, and mechanical properties of two soil layers on soil-slip scars in slopes underlain by coarse-grained granite and fine-grained granitic gneiss near Seoul, Republic of Korea, were examined. Our aim is to study the effect of the mineral grain size of the bedrock on the soil layer structure and the return period of shallow soil slips. Because of the coarser slope materials in granite resulting from weathering, the permeability is larger and the weathering front has a copious water supply; also, because of the smaller specific surface area of the minerals, restricted leaching produces grus from the bedrock, so that the rate of formation of soil (and in particular the slip plane) due to chemical weathering is faster. Since, on granite slopes, the leaching proceeds toward the surface, the sliding plane is deeper with coarser soft grus, resulting in the existence of a minimum c value in the soil layer. On gneiss slopes, by contrast, leaching cannot proceed with decreasing soil depth, and the sliding plane is deeper with finer soft grus just above hard grus and has similar c and ϕ values as the upper soft grus because the grain size of both soils is the same. In the granite soil layers, the sliding plane corresponds to the minimum shearing resistance, whereas in the gneiss soil layers, the shearing resistance increases gradually with soil depth, and the sliding plane is formed when the weathering front is located deeper. Because of the faster soil formation rate and the shallower slip depth in granite slopes, the return period of occurrence of soil slips should be shorter in granite slopes than in gneiss slopes.     

Impacts of soil erosion on organic carbon and nutrient dynamics in an alpine grassland soil

The impact of soil erosion on the nutrient dynamics in alpine grassland soils is still an essential problem. Selecting a grass-covered hillslope in eastern Tibet Plateau, the cesium-137 (¹³⁷Cs) technique was used to determine the impacts of soil erosion on soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), and total potassium (TK). The ¹³⁷Cs data revealed that there were distinct soil redistribution patterns in different hillslope positions because of the influences of slope runoff, plant coverage and grazing activity. For the upper slope, soil erosion first decreased downward, followed by soil deposition in its lower part. In contrast, for middle and toe slopes, there was an increasing soil erosion along a downslope transect. Across the lower slope, soil erosion showed an irregular variation. Influenced by the selective transport of water erosion, SOC, TN and TP storage decreased with increasing soil erosion in upper, middle and toe slopes. In contrast, SOC, TN and TP storage varied little with soil erosion in the lower slope. On the whole hillslope, TK storage also varied little with soil erosion due to the large amount of potassium elements derived from soil parent materials. Particularly noteworthy was the greatest storage of SOC, TN and TP in the lower slope where most obvious net soil erosion occurred, which is closely related to the humus accumulation combined with gravel separation as well as weathering and pedogenesis of parent rocks induced by soil freeze-thaw.     

第四纪红色粘土侵蚀土壤水分特性研究

水土流失严重的第四纪红色粘土区,夏季因高温少雨使水土保持植物措施难以见效。为了揭示红色粘土的持水特性和水分动态变化规律,对不同地形部位、不同深度的侵蚀土壤,进行了5～11月份的定点观测和持水特性的研究。结果表明:夏季,表层土壤(0～10cm)都有不同程度的干旱,坡上部裸露红色粘土尤为严重;秋季,坡中部10～30cm土层的含水量高于30～60cm的含水量;雨季,侵蚀沟底部沉积物的含水量明显地高于田间持水量;对于有效水含量,侵蚀沟底部较高,而坡上部粘土较低。因此提出:改善土壤结构,增加土壤渗透能力,促进深层贮水和选择深根性植物等措施。     

Nonlinear responses of soil erosion to climate change: a modelling study on the UK South Downs

A modelling approach is used to estimate some effects of changed climate upon rates of soil erosion on agricultural land on the UK South Downs.Previous studies have concentrated only on estimating shifts in long-term mean erosion rate: these were found to be approximately linear. However such simple shifts mask changes in the underlying distributions of annual erosion. A first series of simulations indicated that, under a wetter climate, erosion rates in wet years will generally increase more than rates in dry years. Under a “best guess” rainfall scenario with a 10% increase in winter rainfall, annual erosion increased by up to 150%. Erosion rates for individual years were shown to change in more complex nonlinear ways however, with decreases as well as increases occurring. These could be explained by the interaction of timing of rainfall with changes in the rate of crop growth.Most earlier work also assumed an equilibrium climate for the simulations, with climatic parameters such as mean monthly rainfall having stabilised at some new value, usually for a 2 × CO₂ atmosphere. This however leads to an “initial conditions” problem: how will soil characteristics have changed by the time of CO₂ doubling? A decrease in erodibility of about 20% by the time of CO₂ doubling was indicated, resulting from changed soil profile properties. However, a second series of runs employed “transient” weather sequences (i.e. with a trend imposed). For these, present-day soil profiles could legitimately be used.     

Erosion quantification in the small marly experimental catchments of Draix (Alpes de Haute Provence, France). Calibration of the ETC rainfall–runoff–erosion model

Erosion rates measured for 15 years in the small (ranging from 0.13 ha to nearly 1 km²) and steep (30–75%) mountainous marly basins of Draix (South Alps, France) are over 100 tons/ha/year in a badland area devoid of vegetation. In a similar basin, reforested at the end of the 19th century, the sediment yield is considerably reduced (less than 3 tons/ha/year). The analysis of the sediment yield of these torrents reveals the importance of the erosion processes on slopes at the scale of the elementary gully, and the influence of deposition, transport and scouring processes as soon as the channel network of the basin is developed.These processes were modelled by a hydrosedimentologic model developed by Cemagref for flood torrent erosion and called ETC. ETC is an integrated, spatialized and global model, working at the event scale. The rainfall–runoff component and the solid transport component, which involves scouring, deposition and armouring, are well developed. On the other hand, the erosion component is not yet a physically based model as the knowledge on the elementary processes is not enough quantitative. The ETC model was used on a badland basin of 86 ha in area, the Laval, and has shown its ability to simulate both water and sediment flows in mountainous and steep basins. The erosion modelling highlighted the need for a better representation of the slope processes and for more information on the storing of sediments in the channel network. Observations carried out on the influence of the vegetation cover patterns and the links between slopes and channels should be taken into account to improve the model.     

Field observations and laboratory experiments concerning the creep process of rock blocks in an arid environment

Data on soil erosion by runoff at the Sde Boqer experimental site, northern Negev, Israel, indicate that runoff erosion is unlikely to transport coarse material over the treads of bedrock steps. Detailed field observations led to the idea that, despite the arid conditions, such material could be transported by a mass movement process, namely creep. To test this hypothesis a laboratory experiment, inspired by the situation in the field, was designed. A limestone block was laid upon a gently inclined earth pedestal derived from the Sde Boqer area. Both the pedestal and the block were submitted to the following tests which are assumed to contribute to the creep process in the field: wet-dry cycles; wet-frost-thaw cycles; variable conditions of air humidity; artificial structural disturbance of the earth pedestal.Data obtained indicate that a continuous “dry block-creep” is active for long periods when the loam pedestal is dry (1 % – 3 %) and submitted to a low relative air humidity and high air temperature. The cumulative movement over a period of 445 days amounted to 1200 microns. The dry movement was accelerated when air relative humidity was increased up to 100%. A faster downslope movement — 0.29 mm/cycle — was recorded on wet-frost-thaw tests; and a more acclerated one was obtained when structural disturbance were applied by perforating the earth pedestal, a process similar to that performed by burrowing animals. Surprisingly, once the earth pedestal stabilized, no net gain in downslope movement was recorded on wetting-drying tests. Results obtained in the laboratory, as well as their possible application to field problems are discussed.     

冻融坡面土壤剥蚀率与侵蚀因子关系分析

为确定影响冻融坡面土壤剥蚀率的主要土壤侵蚀因子,采用2个(10°、15°)坡度、2个(3、9 L/min)流量和4个(2、5、8、11 cm)起始解冻深度组合进行野外冲刷试验,分析土壤剥蚀率随坡度、流量和解冻深度变化规律,研究土壤剥蚀率与水蚀动力参数(径流水深、水流剪切力、水流功率、单位水流功率)间的相关关系,运用逐步回归分析方法,建立冻融坡面土壤侵蚀预测模型。结果表明:相同起始解冻深度条件下土壤剥蚀率随着坡度和流量的增加有增大的趋势,相同坡度条件下,流量为3 L/min时,起始解冻深度5 cm时土壤剥蚀率最大;流量为9 L/min时,随着起始解冻深度的增加土壤剥蚀率增加;土壤剥蚀率与水流剪切力、水流功率、单位水流功率分别呈显著线性正相关关系(P0.01);建立了基于水流功率和起始解冻深度的土壤剥蚀率预测方程(R~2=0.967)。     

GENESIS OF RED AND BLACK SOILS ON BASALT ON THE DARLING DOWNS, QUEENSLAND, AUSTRALIA

Shallow friable red soils (euchrozems) and shallow cracking clays (black earths) occur in close proximity on basalt hills of the Darling Downs of Queensland. The euchrozems are mainly restricted to fiat hill crests and are associated with lithosols; the shallow black earths occur on upper pediment slopes, on small convex crests and on depressions on flat crests. The euchrozems are moderately leached and contain kaolin minerals and hematite with minor montmorillonite, while the black earths are dominantly montmorillonite with minor kaolin and hematite. It is proposed that the euchrozems have developed by long continued weathering under stable well-drained conditions while the black earths have formed in sites prone to erosion and in situations with less water available for weathering. The weathering products produced in each situation have ensured continuation of the processes. The presence of two red soils in anomalous positions have been ascribed to (a) soil formation on exposed ‘bole’ (compacted red clay) layers and (b) local peculiarities of parent material controlling the course of weathering.     

遂宁组母质封禁后的土壤侵蚀规律分析

通过遂宁市水土保持试验站母质侵蚀观测场长期连续观测试验,收集1991—2000年资料,采用数据分析方法,对遂宁组紫色土母质侵蚀规律进行了研究。结果表明:(1)母质侵蚀区在封禁10 a内的年际地表径流模数与年际降雨量变化趋势一致,而土壤侵蚀模数总体呈现逐年下降趋势;(2)径流深与降雨量呈正相关,与降雨时间呈负相关。(3)降雨量和平均降雨强度两因子对土壤侵蚀量影响不显著,土壤侵蚀量与地表径流深在封禁期前4 a内能建立回归方程。由此认为,采用封禁管理来防治紫色土母质侵蚀可行,封禁至少8 a以上土壤侵蚀强度类型才由剧烈侵蚀逐渐转化为轻度侵蚀。     

The impact of environmental factors on early stage Andosol development south of Vatnajökull,Iceland

Icelandic soils develop in a dynamic environment affected by both natural processes and anthropogenic impacts. We present an extensive investigation of soil mineralogy and pedogenesis in a disturbed (i.e., by solifluction) pedon under such conditions. The study focuses on two distinct tephra layers, a rhyolitic tephra from the Öræfajökull eruption in 1362 CE (Ö1362) and a basaltic Veiðivötn tephra from 1477 CE (V1477). Both tephra layers form an important parent material in the study area south of Vatnajökull, Iceland. The Andosol developed from tephra and aeolian material, rich in volcanic glass. The pH (H₂O) values were between 5.5 and 6.6 and clay mineralogy displayed a predominance of allophanic material in both soil and tephra. The pedon can be seen in its early stage of chemical weathering and soil development. Despite the overall predominance of non- and poorly-crystalline short-range order secondary materials and Fe (hydr)oxides in the clay-size fraction, we found indication of smectite. High exchangeable Ca²⁺ and Mg²⁺ concentrations reflect enhanced aeolian input of volcanic material, while elevated exchangeable-Na⁺ concentrations are most likely caused by the oceanic composition of precipitation. The impact of erosion and aeolian processes on pedogenesis seemed to be higher between the deposition of Ö1362 and V1477, than in the soils above. Both, soil and tephra layers appeared disturbed by erosion–deposition processes over time. Characterised by a significantly coarser particle size composition, low soil organic carbon (SOC) content, and a more diverse mineralogy, a distinct fluvial sediment layer at 10–30 cm depth appeared sharply contrasting to the other soil layers in the profile. This possibly reflects the diverse composition of glaciofluvial material from a landslide originating from a Kvíárjökull moraine in the north. Changed weathering patterns and properties in the soils above the Ö1362 tephra indicated soil degradation following the deposition of the rhyolitic tephra.     

Vertical transport of decomposing spruce needles during nine years in a raw humus soil profile in southern Norway

In a podsol profile, the amount of time passed after spruce (Picea abies) needles fall from the trees is correlated with their depth position in the organic soil layer. This relationship was examined by dropping marked needles in small patches on the ground and collecting them at various intervals during the following nine years. Needles dropped in moss-covered patches mostly reached the dense needle mat at the bottom of the green moss (“zero depth”) after about one year. After two years, it was estimated that about 60% of the initial dry mass was lost. After three years, the needles had an average depth position of 1 cm below “zero”, corresponding to the transition between the O_l and O_f layer. Needles of the same age were situated at varying depths, mainly because of variation between individual patches, but also because not all needles were caught by the moss vegetation at the start. The downward transport rate slowed down with time. After nine years, the mean needle depth was 3.1 cm below “zero”, about halfway to the bleached mineral layer and in the upper part of the fine root layer. Needles situated close to roots were often almost completely disintegrated. The total vertical transport through the organic layer evidently takes many decades. Needles dropped on bare needle mats underneath large trees had a mean depth position of 1.6 cm after nine years.     

The long-term effect of tillage on soil displacement of hilly areas used for growing wheat in Greece

Abstract. Tillage displaces large amounts of soil from upper slopes and deposits soil in lower landscape positions, greatly affecting productivity in these areas. The long-term effect of tillage on soil erosion was studied in four field sites growing mainly rainfed wheat. The soil loss from landscape positions with slopes, ranging from 3 to 28%, was estimated by: (a) comparing data of horizon thickness described at the same position at different times; and (b) using soil movement tracers added to the soil. Existing empirical relationships were used for estimating soil loss by tillage and runoff water, and loss in wheat biomass production. The experimental data showed soil losses of 0.4 to 1.4 cm yr^–1 depending on slope gradient, plough depth, and tillage direction. In two of the sites, soil depth has been reduced by 24–30 cm in a period of 63 years. The mean soil displacement of the plough layer (30 cm thick), measured by soil movement tracers, ranged from 31 to 95 cm yr^–1 depending mainly on slope gradient, corresponding to a rate of soil loss of 0.3 cm to 1.4 cm yr^–1. Soil eroded from the upper slopes was deposited on the lower slopes increasing soil thickness by 0.4 cm to 1.4 cm yr^–1. The application of empirical relationships, estimating soil loss by tillage and water runoff, showed that soil erosion at the field sites can be mainly attributed to tillage. The loss in wheat biomass production due to erosion was estimated at 26% on upper slopes for a period of 63 years, while a 14.5% increase in wheat production was estimated due to deposition of soil material in the lower landscape.