首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 46 毫秒
1.
Y. Avni   《CATENA》2005,63(2-3):185
Gully incision has been eroding the alluvial sediments and loess soils deposited and developed along the valleys in the arid and semiarid regions of Israel. This phenomenon is critical in the arid regions of the Negev Highlands where the agricultural fields, the main floral biomass and the areas which have the highest grazing value, are limited to narrow valleys filled with redeposited loessial sediments. The headcut migration and gully development in the region were studied between 1990 and 2001 in three representative drainage basins (Zipporim, Revivim and Sekher). During flood events, the runoff penetrates the alluvial cover of the valleys, forming vertical headcuts, which gradually retreat up the valley. The runoff is channeled into narrow gullies, preventing the floodwater from spreading over the whole width of the valley. The change in irrigation efficiency along the valleys is reflected in a sharp estimated drop of 70–90% in the floral biomass, causing the reduction of the range value by 83–99%. During the monitoring time interval (1990–2001), the linear gully retreat in the study area ranged between 12.3 and 250 m an average rate of 1.12–22.7 m year− 1 for each gully head. The process is accompanied by erosion of soil, which has high agricultural and range value. The total soil losses in these sites ranged between 800 and 9000 m3 at an average rate of 81–818 m3 year− 1 for each gully head, which is equivalent to 121–1227 Mg year− 1. During the monitoring period, approximately 0.11–0.87 ha of land lost its agricultural and range value in each basin under study, at an average rate of 0.01–0.079 ha year− 1. Since the Byzantine period (1400 BP), approximately 6.5 ha, which is 10% of the land that had high agricultural and range value in the Zipporim valley, lost its value due to gully erosion. No recovery effects of the gully channels were found in the nearby region. The soil erosion is generated by a long-term natural dynamic change in the soil / rock ratio evolving within the drainage basins through time since the termination of the last glacial phase. The loessic sediments, originally deposited within the drainage basins during the late Pleistocene glacial stage, are being removed under the present Holocene climate in several erosion stages. This ongoing phenomenon is causing degradation of soil and biomass and is severely reducing the agricultural and range potential of the region. These parameters indicate that an ongoing process of desertification is active in the arid environment of the Negev Highlands, and is advancing in proportion to the headcut retreat rates in the region. The soil erosion and headcut retreat have been active in the Negev Highlands for the last few millennia. If these processes continue in the future, the Negev Highlands region will lose its agricultural potential within a few millennia. However, the fact that the ancient inhabitants of the region implemented successful long-term land conservation techniques already 3000 years ago, implies that a sustainable land management policy can be adapted to the Negev Highlands, as well as to other semi-arid regions in the Middle East.  相似文献   

2.
This study was carried out to obtain a representative set of data on long-term erosion rates from a pilot area located close to the Jaslovske Bohunice village, in western Slovakia using the 137Cs-method. The study area chosen was representative of the hilly loess cultivated areas of Slovakia. The sampling strategy was based on a multiple transect approach. Analyses of the samples for 137Cs activity were made at the Nuclear Power Plant Research Institute, Jaslovske Bohunice. The 137Cs-method was used to obtain long-term estimates of soil erosion in the Jaslovske Bohunice site, a representative hilly loess cultivated area of Slovakia. The estimated reference 137Cs inventory was 2910 Bq m−2, with a coefficient of variation of 4.3%.Examination of the 137Cs redistribution in relation to the topography of the study area revealed that, within individual transects the 137Cs inventories were closely related to major landforms. The 137Cs inventories were considerably lower on the slopes than on the plateau and they were highest in the valley. However, when plotted against a selection of individual quantitative slope parameters, i.e. the S and the LS factors of the USLE or slope inclination, the correlations obtained were weak.Three conversion models, i.e. the proportional model (PM), the simplified mass balance model (MBM1) and the standard mass balance model (MBM2), from the set of models developed at Exeter University, Great Britain were selected to interpret the resulting 137Cs measurements into soil erosion/deposition rates. The mean erosion rates estimated with the PM were 22.4, 35.6 with MBM1 and 17.3 t ha−1 per year with MBM2. There was a good agreement between the average of these mean erosion rates (25.1 t ha−1 per year) for the Jaslovske Bohunice site and the estimated mean soil erosion rate obtained for small erosion plots (15 t ha−1 per year) for conditions similar to the study site. Nevertheless, further research on the application of the 137Cs-method, in particular the independent validation of the results obtained, is needed. Several issues requiring further study have been highlighted.  相似文献   

3.
Although much of the recent attention on the environmental problems has focused on climatic change, there is also increasing concern that accelerated soil erosion and associated land degradation represent a major problem for sustainable development and environmental protection. There is an urgent need to obtain reliable quantitative data on the extent and rates of soil erosion worldwide to provide a more comprehensive assessment of the magnitude of the problems and to underpin the selection of effective soil conservation measures. The use of environmental radionuclides, in particular 137Cs, affords an effective and valuable means for studying erosion and deposition within the landscape. The key advantage of this approach is that it can provide retrospective information on medium-term (30–40 years) erosion/deposition rates and spatial patterns of soil redistribution, without the need for long-term monitoring programmes. Advantages and limitations of the technique are highlighted. The launching of two closely linked International Atomic Energy Agency (IAEA) research networked projects in 1996 involving some 25 research groups worldwide has made a major contribution to co-ordinating efforts to refine and to standardise the 137Cs technique. The efficacy and value of the approach has been demonstrated by investigations in a number of environments. Significant developments that have been made to exploit its application in a wide range of studies are reported in this review paper. Other environmental radionuclides, such as unsupported 210Pb and 7Be offer considerable potential for use in soil erosion investigations, both individually and complementary to 137Cs. The IAEA through research networks and other mechanisms is promoting further development and applications of these radionuclides in soil erosion and sedimentation studies for a sustainable resource use and environmental protection.  相似文献   

4.
A typification of soil catenas on slopes from the manifestations of soil erosion and accumulation processes studied at several key plots in the central part of the East European Plain and in the Mid-West of the United States is suggested. The magnetic tracer method was used for assessing the rate of lateral mechanical migration of the products of pedogenesis. The typification of soil catenas on slopes was performed with the quantitative consideration for the material loss and accumulation rates, the degree of openness of the soil catenas for the migration fluxes, and the localization of accumulation zones on the slopes.  相似文献   

5.
Soil erosion is one of the most severe global environmental problems, and soil erosion surveys are the scientific basis for planning soil conservation and ecological development. To improve soil erosion sampling survey methods and accurately and rapidly estimate the actual rates of soil erosion, a Pan-Third Pole region was taken as an example to study a methodology of soil erosion sampling survey based on high-spatial-resolution remote sensing images. The sampling units were designed using a stratified variable probability systematic sampling method. The spatiotemporal characteristics of soil erosion and conservation were taken into account, and finer-resolution freely available and accessible images in Google Earth were used. Through the visual interpretation of the free high-resolution remote sensing images, detailed information on land use and soil conservation measures was obtained. Then, combined with the regional soil erosion factor data products, such as rainfall-runoff erosivity factor (R), soil erodibility factor (K), and slope length and steepness factor (LS), the soil loss rates of some sampling units were calculated. The results show that, based on these high-resolution remote sensing images, the land use and soil conservation measures of the sampling units can be quickly and accurately extracted. The interpretation accuracy in 4 typical cross sections was more than 80%, and sampling accuracy, described by histogram similarity in 11 large sampling sites, show that the landuse of sampling uints can represent the structural characteristics of regional land use. Based on the interpretation of data from the sample survey and the regional soil erosion factor data products, the calculation of the soil erosion rate can be completed quickly. The calculation results can reflect the actual conditions of soil erosion better than the potential soil erosion rates calculated by using the coarse-resolution remote sensing method.  相似文献   

6.
PRINCIPAL KINDS OF CHRONOSEQUENCES AND THEIR SIGNIFICANCE IN SOIL HISTORY   总被引：2，自引：0，他引：2  
There are four principal kinds of chronosequences of soils that differ in age. These sequences have different combinations of isochrony and/or time-transgression of incipience and cessation of development of their encompassed soil members. A further criterion is the presence or absence of partial overlap in the history of these members. Post-incisive sequences have been commonly used for inferences on pathways and rates of development of individual soils, but their usual interpretation relies on the assumption that all soils involved developed the same way even while some of them may be polygenetic. Theoretically, pre-incisive sequences are to be preferred because they should provide time-lapse information on soil development. But, since they necessarily involve buried soils, problems of post-burial change may complicate their interpretation. The usefulness of fully time-transgressive sequences with partially overlapping soil tory depends on their predominant pre-incisive or post-incisive character. Fully time-transgressive chronosequences without overlap of soil history may provide insight into regimes of soil development throughout geologic time, but not into rates of change of individual soils. Functional soil-landscape units, such as catenas and valley basins may have internal soil age differentiation. This imposes restrictions on the systematic investigation of their evolution.  相似文献   

7.
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.  相似文献   

8.
《CATENA》1999,36(3):205-232
The morphology and geochemistry of weathering profiles in Miocene granodiorites from the coastal lowlands of NW Kalimantan, Indonesia (1°N lat.), indicate long-term weathering rates, landform development and mechanisms for the formation of `white sands' found widely in valleys and depressions. Samples are analysed from convex hill, piedmont glacis, and valley slope profiles. All profiles above the saturated zone are strongly gibbsitic, but kaolinite minerals are dominant below the water table. The profiles are interpreted as expressions of the perhumid Equatorial climate (rainfall 3000 mm y−1) acting within a dynamic regime of landscape lowering during the Neogene, the current profiles being largely Quaternary (0.4–0.6 ka). Possible effects of Quaternary tectonic and environmental changes are considered, including those caused by a Late Pleistocene drier climate when there was greater water table fluctuation and surface erosion. Landform evolution is a form of dynamic etchplanation with a long-term rate of landscape and weathering profile lowering of ca. 50 mm ka−1. Within this regime some of the `white sands' may be residual weathering products locally redistributed by colluvial or alluvial processes. They originated in the podzolising environment of the weathering profile, and later experienced post depositional (diagenetic) changes within the hydromorphic regime of the valley floor.  相似文献   

9.
Validation of spatially distributed models using spatially distributed data represents a vital element in the development process; however, it is rarely undertaken. To a large extent, this reflects the problems associated with assembling erosion rate data, at appropriate temporal and spatial scales and with a suitable spatial resolution, for comparison with model results. The caesium-137 (137Cs) technique would appear to offer considerable potential for meeting this need for data, at least for longer timescales. Nevertheless, initial attempts to use 137Cs for model validation did not prove successful. This lack of success may be explained by the important role of tillage erosion in redistributing soil within agricultural fields and, therefore, contributing to the 137Cs-derived soil redistribution rates. This paper examines the implications of tillage erosion for the use of 137Cs in erosion model validation and presents an outline methodology for the use of 137Cs in model validation. This methodology acknowledges and addresses the constraints imposed by the need to: (1) separate water and tillage erosion contributions to total soil redistribution as represented in 137Cs derived rates; (2) account for lateral mixing of 137Cs within fields as a result of tillage translocation; (3) simulate long-term water erosion rates using the model under evaluation if 137Cs-derived water erosion rates are to be used in model validation. The methodology is dependent on accurate simulation of tillage erosion and tillage translocation. Therefore, as greater understanding of tillage erosion is obtained, the potential for the use of 137Cs in water erosion model validation will increase. Caesium-137 measurements remain one of the few sources of spatially distributed erosion information and, therefore, their potential value should be exploited to the full.  相似文献   

10.
Sedimentological connectivity within drainage systems may be controlled spatially by ‘pockets’ of intact valley fill, alluvial fans impinging laterally on mainstem rivers, floodouts impinging longitudinally on valley floors, and downstream resistant rock bands and their effect on valley width. Where local conditions favor prolonged inundation of the uppermost ~ 0.5 m of the sediment surface, these environments of deposition host wetlands that provide several ecosystem services to society. In this paper, we examine the long-term (millennia), large-scale mediation of connectivity by geological and geomorphological controls, highlighting the relationship between drainage disconnectivity and wetland origin, and appraise ongoing rehabilitation efforts in light of the long-term natural dynamic. The paper uses a wetland system in the KwaZulu-Natal Drakensberg Foothills, eastern South Africa, as a case study, focusing particular attention on part of the system in which cut-and-fill processes are evident, and proceeds, using observations from this and other similar wetland systems in the region, to discuss successive breaks in connectivity with increasing spatial scale and time. Implications for valley morphology are discussed, and channel incision is shown to play an important role in long-term valley and wetland morphodynamics in certain geomorphological settings, creating a diversity of geomorphological features and hydrological regimes. Thus, rehabilitation practitioners should focus on interventions that improve or stabilize desired functional outcomes, rather than on restoring or maintaining what is perceived to be ‘the natural dynamic’ in which erosion is absent.  相似文献   

11.
Concentrated flow experiments using a small hydraulic flume and a constant flow discharge and bed slope have been conducted in order to investigate the effects of rock fragment cover (Rc) on sediment yield for an initially wet and an initially air-dry loamy topsoil. The experimental results indicate that Rc reduces concentrated flow erosion rates (E) in an exponential way (i.e., E=e−bRc), which is similar to previously reported relations for other water erosion processes such as interrill erosion and sheet-rill erosion measured on runoff plots. The decay rate (b) of this exponential relationship increased throughout the experiments because of scour-hole development and bed armouring. The concentrated flow erosion rates and b-values also depend on the initial moisture content of the topsoil. Depending on Rc, mean concentrated flow erosion rates were 20% to 65% less on initially wet compared to initially air-dry topsoils. The mean value for b was 0.032 for the initially wet, but only 0.017 for the initially air-dry topsoil, indicating that a rock fragment cover is less efficient in reducing concentrated flow erosion rates when the topsoil is initially air-dry than when it is initially wet. The results help explain the data scatter in reported relationships between Rc and interrill–rill erosion rates. They also indicate that a given surface rock fragment cover will offer more protection to wet topsoils than to dry topsoils, which are very common in Mediterranean environments. Event-based water erosion models should incorporate effects of antecedent soil moisture content as well as those of Rc on concentrated flow erosion rates.  相似文献   

12.
陕北黄土区退耕前（1976—1997）坡面切沟发育特征   总被引：7，自引：3，他引：4  
以陕北黄土区坊塌流域内7条大切沟及其谷缘上的小切沟为研究对象,通过Arc GIS和MATLAB从基于1976、1997年1:10000比例尺地形图生成的数字高程模型(DEM)上提取沟沿线,进而获得1976、1997年大切沟的面积、周长和大切沟上小切沟沟头前进距离,并结合当时的土地利用图和植被覆盖图,定量研究了退耕前陕北黄土区切沟发育的速率,以及土地利用类型和植被覆盖度对切沟发育的影响.结果显示:在1976-1997年间,7条大切沟的面积、周长增长率分别为11.01%~180.46%和8.07%~86.75%,大切沟上小切沟沟头年均前进速率为0.26~0.84m;由溯源侵蚀导致的小切沟沟头前进是研究区内大切沟上的主要侵蚀方式,大切沟沟谷拓宽和形成新的小切沟分别是对大切沟的面积和周长增长具有较高贡献率的侵蚀方式;林草覆盖能控制切沟发育,集水区内覆盖度大于65%的植被能更加有效地控制大切沟内以沟谷拓宽为主的、多过程、多部位的综合切沟侵蚀,覆盖度大于45%的植被能更加有效地控制大切沟上小切沟沟头的溯源侵蚀.研究表明基于GIS技术和不同年份的地形图,可以确定切沟侵蚀的方式及速率,实现对切沟发育的动态监测.  相似文献   

13.
Recent awareness of the potential hazard of soil erosion on arable land in the UK has highlighted the lack of reliable data concerning actual rates of soil loss. This lack of information reflects both a low level of interest, and the lack of a simple and generally applicable method of documenting long-term rates of soil loss. Existing methods involving the use of hazard classification procedures and direct measurement techniques, including erosion plots and field surveys, all possess significant limitations. The use of 137Cs measurements to provide information on rates of soil loss and deposition averaged over the past 30 years would appear to offer considerable potential. The results of applying this approach to three arable fields on contrasting soil types in Britain are reported. These results confirm the viability of the technique and its potential for providing information on patterns and rates of erosion and deposition within individual fields and their overall sediment budgets. Limitations include the restricted size of the areas that can be investigated and the need to take account of additional inputs of 137Cs derived from the Chernobyl accident.  相似文献   

14.
The spatial variation of soil erosion and deposition rates was studied in a small catchment cultivated by rainfed agriculture, in the Mouriki area, Viotia Greece, using the 137Cs technique. A 25 m grid was established parallel to the slope and the 137Cs inventories were defined for the grid points. After establishing the local reference inventory, the soil erosion and deposition rates were estimated using the 137Cs residuals for individual points on the grid in conjunction with the four conversion (calibration) models described by Walling and He (2001) [Models for converting 137Cs measurements to estimates of soils redistribution rates on cultivated and uncultivated soils]. The conversion models were validated by means of sensitivity analysis and using local experimental data. The resulting estimates of soil redistribution rates were interpolated by means of kriging, using Surfer Golden software. The magnitude of the soil erosion rates depend on many factors, including the location of the sampling point, the local slope, and the soil properties. The mass balance model 2 (MBM2) and mass balance model incorporating soil movement by tillage (MBM3) conversion models predict soil redistribution rates of the same order of magnitude as the experimental data and are able to take account of Chernobyl fallout. Predicted soil erosion rates for catchment grid varied from 6.71 to 85.55 t ha−1 per year using MBM2 and from 3.54 to 95.78 t ha−1 per year using MBM3. Deposition rates varied from 1.23 to 168.19 t ha−1 per year using MBM2 and from 3.24 to 189.18 t ha−1 per year using MBM3. High correlation was apparent between erosion/deposition rates (MBM2) and soil P (P<0.001), soil K (P<0.001), soil organic matter % (P<0.05), point slope (P<0.05), clay % (P=0.053) and altitude (P=0.057). The total soil losses from the catchment have been estimated at 18.34 t ha−1 per year using MBM2 and 22.12 t ha−1 per year using MBM3.  相似文献   

15.
Abstract. Despite a growing awareness that erosion on arable land in Britain is a potential hazard to long-term productivity, there is still only limited information on the rates involved, particularly long-term values. Use of the caesium-137 (137Cs) technique to study soil erosion within arable fields on various soil types at 13 locations in southern Britain has yielded retrospective measurements of the long-term ( c. 30 years) rates of soil loss and the patterns of soil redistribution within the study fields. The range of long-term rates of net soil loss extends from 0.61 per hectare per year on clay soils in Bedfordshire to 10.5 t per hectare per year on brown sands in Nottinghamshire. The measured rates are compared with other published data for similar soil types and land use, and the implications for long-term productivity and potential environmental impacts are considered.  相似文献   

16.
The semiarid regions of Spain, including the central part of the Ebro River basin, are under threat due to desertification. Severe erosion, as a result of poor land management, has led to degradation of the soil resource, and there is a clear need for quantitative erosion rate data to evaluate the problem. This study aimed to examine the potential for using caesium-137 to identify the patterns and rates of soil erosion and redistribution within this semiarid environment. Samples for the determination of caesium-137 were collected from uncultivated slopes and cultivated valley floor sites near the head and outlet of a small representative basin in the Las Bardenas area. The measured patterns of caesium-137 mobilization, redistribution and export provide a semiquantitative indication of the variation in erosion within the study site. Calibration of the caesium-137 measurements, taking account of the differing behaviour of radiocaesium on cultivated and uncultivated land, allows estimation of the actual rates of erosion and deposition involved. The results show (1) the erosion rates on the cultivated land (1.6–2.5 kg m−2 yr−1) are typically more than five times those seen on the uncultivated land (0.2–0.4 kg m−2 yr−1), and (2) erosion on the uncultivated land is significantly less severe at the head of the basin than at the outlet. Study of the vegetation cover suggests that lower growing shrubs and grasses may be more effective in reducing erosion in this environment than trees.  相似文献   

17.
《CATENA》2001,42(1):17-38
We describe catenas developed on calcareous moraines of Pinedale (∼21–15 ka) and Bull Lake (>130–100 ka) ages at Whiskey Basin on the eastern flank of the Wind River Range, Wyoming, USA. We sampled one catena of each age from each of two separate moraine fields: the Jakey's Fork and Torrey Creek valleys. Soils of the Bull Lake catena at Jakey's Fork are more developed than those of the corresponding Pinedale catena: they have thicker sola, more horizons, more pedogenic clay, and more pedogenic carbonate presumably, because of their greater age. The Weighted Mean Profile Development Index does not distinguish between the Torrey Creek catenas. Pedogenic carbonate content is greater in the Torrey Creek Pinedale catena than the corresponding Bull Lake catena, and pedogenic clay is greater in the Bull Lake catena. Catenas on the Jakey's Fork moraines are generally more developed than corresponding catenas on the Torrey Creek moraines. We suggest that differences in catena development mostly result from the differences in slope length between the Jakey's Fork and Torrey Creek catenas. The Jakey's Fork catenas are shorter than those of the Torrey Creek, which appears to lessen the role that topographic position plays in catena development.  相似文献   

18.
Gully erosion and environmental change: importance and research needs   总被引：29，自引：0，他引：29  
Assessing the impacts of climatic and, in particular, land use changes on rates of soil erosion by water is the objective of many national and international research projects. However, over the last decades, most research dealing with soil erosion by water has concentrated on sheet (interrill) and rill erosion processes operating at the (runoff) plot scale. Relatively few studies have been conducted on gully erosion operating at larger spatial scales.Recent studies indicate that (1) gully erosion represents an important sediment source in a range of environments and (2) gullies are effective links for transferring runoff and sediment from uplands to valley bottoms and permanent channels where they aggravate off site effects of water erosion. In other words, once gullies develop, they increase the connectivity in the landscape. Many cases of damage (sediment and chemical) to watercourses and properties by runoff from agricultural land relate to (ephemeral) gullying. Consequently, there is a need for monitoring, experimental and modelling studies of gully erosion as a basis for predicting the effects of environmental change (climatic and land use changes) on gully erosion rates.In this respect, various research questions can be identified. The most important ones are:
What is the contribution of gully erosion to overall soil loss and sediment production at various temporal and spatial scales and under different climatic and land use conditions?
What are appropriate measuring techniques for monitoring and experimental studies of the initiation and development of various gully types at various temporal and spatial scales?
Can we identify critical thresholds for the initiation, development and infilling of gullies in different environments in terms of flow hydraulics, rain, topography, soils and land use?
How does gully erosion interact with hydrological processes as well as with other soil degradation processes?
What are appropriate models of gully erosion, capable of predicting (a) erosion rates at various temporal and spatial scales and (b) the impact of gully development on hydrology, sediment yield and landscape evolution?
What are efficient gully prevention and gully control measures? What can be learned from failures and successes of gully erosion control programmes?
These questions need to be answered first if we want to improve our insights into the impacts of environmental change on gully erosion. This paper highlights some of these issues by reviewing recent examples taken from various environments.  相似文献   

19.
Quantitative assessment of soil redistribution in landscapes remains a challenging task. In this study we used radioactive soil redistribution tracer 137Cs together with soil morphological characteristics and empirically-based modeling for quantitative assessment of long-term soil conservation effectiveness. Three pairs of arable slopes were selected, all located within the territory of the Novosil experimental station (the Orel Region, central European Russia). One slope in each pair undergone creation of artificial terraces with forest shelter belts located parallel to topography contour lines and spaced at approximately 100 m from each other.Preliminary results have shown that slopes with soil-protective measures are characterized by a 11–80% reduction of average soil redistribution rates, as shown by soil profile morphology and 137Cs methods. Discrepancy in values obtained can be attributed to differences in temporal resolution of methods as well as possible influence of individual extreme events on results yielded by the 137Cs method. On the other hand, more significant decrease in average soil degradation rates on slopes with soil conservation (62–75% for each pair of slopes) was predicted by the model.The 137Cs method overestimates gross and net soil redistribution rates, as a result of the influence of extreme erosion prior to tillage mixing of a fresh fallout isotope, not accounted for by calibration models used. Another shortcoming of the estimations obtained is that sediment redeposition directly within forest belts was not taken into account. Therefore, net erosion rates obtained for slopes with forest belts should be regarded as overestimation. Nevertheless, it can be generally concluded that the multi-technical approach has allowed acquiring much more detailed information on temporal and spatial variability of soil redistribution rates than single method-based studies.  相似文献   

20.
The different erosion responses derived from two contrasting post-fire management approaches were evaluated: the clear-cutting and immediate removal of the burnt trees and; the non-intervention, that is, leaving the vegetation untouched and the burnt trees standing. Erosion rates were obtained from 200 m2 experimental plots, large enough to include the complete processes of rill and inter-rill erosion. Erosion rates of the clear-cut plot were very similar to those of the non-modified plot. Part of the burnt trees was still economically usable. The trees left in situ gradually decayed and were tumbled by the wind; the fire risk incremented. The opening of timber track networks without conservation measures was one of the most important erosion problems associated with clear-cutting. The complementary practice of brushwood dike-construction would need a preliminary study before being applied.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号