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Erosion Processes (erosion + process)
Selected AbstractsSoil detachment and transport on field- and laboratory-scale interrill areas: erosion processes and the size-selectivity of eroded sedimentEARTH SURFACE PROCESSES AND LANDFORMS, Issue 8 2006O. Malam Issa Abstract Field- and laboratory-scale rainfall simulation experiments were carried out in an investigation of the temporal variability of erosion processes on interrill areas, and the effects of such variation upon sediment size characteristics. Poorly aggregated sandy soils from the semi-arid environment of Senegal, West Africa, were used on both a 40 m2 field plot and a 0·25 m2 laboratory plot; rainfall intensity for all experiments was 70 mm h,1 with a duration of 1 to 2 hours. Time-series measurements were made of the quantity and the size distribution of eroded material: these permitted an estimate of the changing temporal balance between the main erosion processes (splash and wash). Results from both spatial scales showed a similar temporal pattern of runoff generation and sediment concentration. For both spatial scales, the dominant erosional process was detachment by raindrops; this resulted in a dynamic evolution of the soil surface under raindrop impact, with the rapid formation of a sieving crust followed by an erosion crust. However, a clear difference was observed between the two scales regarding the size of particles detached by both splash and wash. While all measured values were lower than the mean weight diameter (MWD) value of the original soil (mean 0·32 mm), demonstrating the size-selective nature of wash and splash processes, the MWD values of washed and splashed particles at the field scale ranged from 0·08 to 0·16 mm and from 0·12 to 0·30 mm respectively, whereas the MWD values of washed and splashed particles at the laboratory scale ranged from 0·13 to 0·29 mm and from 0·21 to 0·32 mm respectively. Thus only at the field scale were the soil particles detached by splash notably coarser than those transported by wash. This suggests a transport-limited erosion process at the field scale. Differences were also observed between the dynamics of the soil loss by wash at the two scales, since results showed wider scatter in the field compared to the laboratory experiments. This scatter is probably related to the change in soil surface characteristics due to the size-selectivity of the erosion processes at this spatial scale. Copyright © 2006 John Wiley & Sons, Ltd. [source] Mineral soil surface crusts and wind and water erosionEARTH SURFACE PROCESSES AND LANDFORMS, Issue 9 2004Michael J. Singer Abstract The ,rst few millimetres of soil largely control the soil's response to the eroding forces of wind and water. The tendency of soils to form surface seals and crusts in,uences the processes of wind and water erosion differently. For wind, dry particle size distribution and particle organization determine the shear strength and threshold wind velocity necessary to initiate particle movement. In loams and clay loams, seals and crusts decrease roughness but increase surface soil strength, generally decreasing wind erosion. Conversely, in sand and sandy loams, loose erodible sandy material may either deposit on the crust and is subject to erosion or it may disrupt the crust, accelerating the erosion process. For water erosion, particle size distribution and structure determine in,ltration rate, time to ponding, and energy required for soil particle detachment. Seals and crusts tend to decrease in,ltration rate and time to ponding thus increasing overland ,ow and soil erosion. This paper brie,y reviews how permanent and time-dependent soil properties in,uence surface seals and crusts and how these affect soil erosion by wind and water. The tendency of a soil to form a seal and crust depends to some degree on the time-dependent property of soil structural stability, which tends to increase with increasing clay content and smectitic mineralogy which are permanent properties. These permanent properties and their effect on structure are variable depending on dynamic properties of exchangeable sodium percentage and soil solution electrical conductivity. Antecedent water content prior to irrigation or rainfall, rate of wetting before an erosive event and aging, the time between wetting and an erosive event, greatly in,uence the response of soil structure to raindrop impact. The effect of these dynamic processes is further in,uenced by the static and dynamic properties of the soil. Weak structure will be less in,uenced by wetting rate than will a soil with strong structure. Process-based models of wind and water erosion need to consider the details of the interactions between soil static and dynamic properties and the dynamic processes that occur prior to erosive events. Copyright © 2004 John Wiley & Sons, Ltd. [source] Porous Structures: In situ Porous Structures: A Unique Polymer Erosion Mechanism in Biodegradable Dipeptide-Based Polyphosphazene and Polyester Blends Producing Matrices for Regenerative Engineering (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 17 2010Mater. Abstract Synthetic biodegradable polymers serve as temporary substrates that accommodate cell infiltration and tissue in-growth in regenerative medicine. To allow tissue in-growth and nutrient transport, traditional three-dimensional (3D) scaffolds must be prefabricated with an interconnected porous structure. Here we demonstrated for the first time a unique polymer erosion process through which polymer matrices evolve from a solid coherent film to an assemblage of microspheres with an interconnected 3D porous structure. This polymer system was developed on the highly versatile platform of polyphosphazene-polyester blends. Co-substituting a polyphosphazene backbone with both hydrophilic glycylglycine dipeptide and hydrophobic 4-phenylphenoxy group generated a polymer with strong hydrogen bonding capacity. Rapid hydrolysis of the polyester component permitted the formation of 3D void space filled with self-assembled polyphosphazene spheres. Characterization of such self-assembled porous structures revealed macropores (10,100 ,m) between spheres as well as micro- and nanopores on the sphere surface. A similar degradation pattern was confirmed in vivo using a rat subcutaneous implantation model. 12 weeks of implantation resulted in an interconnected porous structure with 82,87% porosity. Cell infiltration and collagen tissue in-growth between microspheres observed by histology confirmed the formation of an in situ 3D interconnected porous structure. It was determined that the in situ porous structure resulted from unique hydrogen bonding in the blend promoting a three-stage degradation mechanism. The robust tissue in-growth of this dynamic pore forming scaffold attests to the utility of this system as a new strategy in regenerative medicine for developing solid matrices that balance degradation with tissue formation. [source] In situ Porous Structures: A Unique Polymer Erosion Mechanism in Biodegradable Dipeptide-Based Polyphosphazene and Polyester Blends Producing Matrices for Regenerative EngineeringADVANCED FUNCTIONAL MATERIALS, Issue 17 2010Meng Deng Abstract Synthetic biodegradable polymers serve as temporary substrates that accommodate cell infiltration and tissue in-growth in regenerative medicine. To allow tissue in-growth and nutrient transport, traditional three-dimensional (3D) scaffolds must be prefabricated with an interconnected porous structure. Here a unique polymer erosion process through which polymer matrices evolve from a solid coherent film to an assemblage of microspheres with an interconnected 3D porous structure is demonstrated for the first time. This polymer system is developed on the highly versatile platform of polyphosphazene-polyester blends. Co-substituting a polyphosphazene backbone with both hydrophilic glycylglycine dipeptide and hydrophobic 4-phenylphenoxy group generates a polymer with strong hydrogen bonding capacity. Rapid hydrolysis of the polyester component permits the formation of 3D void space filled with self-assembled polyphosphazene spheres. Characterization of such self-assembled porous structures reveals macropores (10,100 ,m) between spheres as well as micro- and nanopores on the sphere surface. A similar degradation pattern is confirmed In vivo using a rat subcutaneous implantation model. 12 weeks of implantation results in an interconnected porous structure with 82,87% porosity. Cell infiltration and collagen tissue in-growth between microspheres observed by histology confirms the formation of an in situ 3D interconnected porous structure. It is determined that the in situ porous structure results from unique hydrogen bonding in the blend promoting a three-stage degradation mechanism. The robust tissue in-growth of this dynamic pore forming scaffold attests to the utility of this system as a new strategy in regenerative medicine for developing solid matrices that balance degradation with tissue formation. [source] Local Knowledge and Economic Realities Affecting Soil Erosion in the Rach Rat Catchment, VietnamGEOGRAPHICAL RESEARCH, Issue 1 2008DAO KIM NGUYEN THUY BINH Abstract Several parts of Binh Phuóc Province, southern Vietnam, suffer from degraded soils and vegetation as a result of both natural erosion of weak mud rocks and sandstones and intensive human activity, especially through land clearing for agriculture on unstable slopes, deforestation, and abandonment of poor farmland. The underlying cause of this land degradation has been the farming habits of migrants of varying ethnic groups who have settled in the area since 1980. The indigenous farming knowledge of these people and the role of that knowledge in soil erosion were examined by a series of household surveys. They enabled farming practices to be related to ground cover established from a 2002 Landsat 7 ETM (Enhanced Thematic Mapper), and erosion data from a series of erosion bridge measurements. A GIS (Geographical Information System) approach was piloted as a means of identifying areas vulnerable to erosion. This could then be combined with the understanding of farming practices to reveal the relative roles of farmer behaviour, crop cover, and slope and soil characteristics in the erosion process. Land use, local people's knowledge and economic realities are the main factors, as well as natural conditions, that drive this land degradation. [source] Stocks and dynamics of SOC in relation to soil redistribution by water and tillage erosionGLOBAL CHANGE BIOLOGY, Issue 10 2006JIANHUI ZHANG Abstract Soil organic carbon (SOC) displaced by soil erosion is the subject of much current research and the fundamental question, whether accelerated soil erosion is a source or sink of atmospheric CO2, remains unresolved. A toposequence of terraced fields as well as a long slope was selected from hilly areas of the Sichuan Basin, China to determine effects of soil redistribution rates and processes on SOC stocks and dynamics. Soil samples for the determination of caesium-137 (137Cs), SOC, total N and soil particle size fractions were collected at 5 m intervals along a transect down the two toposequences. 137Cs data showed that along the long slope transect soil erosion occurred in upper and middle slope positions and soil deposition appeared in the lower part of the slope. Along the terraced transect, soil was lost over the upper parts of the slopes and deposition occurred towards the downslope boundary on each terrace, resulting in very abrupt changes in soil redistribution over short distances either side of terrace boundaries that run parallel with the contour on the steep slopes. These data reflect a difference in erosion process; along the long slope transect, water erosion is the dominant process, while in the terraced landscape soil distribution is mainly the result of tillage erosion. SOC inventories (mass per unit area) show a similar pattern to the 137Cs inventory, with relatively low SOC content in the erosional sites and high SOC content in depositional areas. However, in the terraced field landscape C/N ratios were highest in the depositional areas, while along the long slope transect, C/N ratios were highest in the erosional areas. When the samples are subdivided based on 137Cs-derived erosion and deposition data, it is found that the erosional areas have similar C/N ratios for both toposequences, while the C/N ratios in depositional areas are significantly different from each other. These differences are attributed to the difference in soil erosion processes; tillage erosion is mainly responsible for high-SOC inventories at depositional positions on terraced fields, whereas water erosion plays a primary role in SOC storage at depositional positions on the long slope. These data support the theory that water erosion may cause a loss of SOC due to selective removal of the most labile fraction of SOC, while on the other hand tillage erosion only transports the soil over short distances with less effect on the total SOC stock. [source] Influences of grass and moss on runoff and sediment yield on sloped loess surfaces under simulated rainfallHYDROLOGICAL PROCESSES, Issue 18 2006Chengzhong Pan Abstract It is important to evaluate the impacts of grasses on soil erosion process so as to use them effectively to control soil and water losses on the Loess Plateau. Laboratory-simulated rainfall experiments were conducted to investigate the runoff and sediment processes on sloped loess surfaces with and without the aboveground parts of grasses and moss (GAM: grass and moss; NGAM: no grass and moss) under slope gradients of 5°, 10°, 15°, 20°, 25° and 30°. The results show that runoff from GAM and NGAM plots increased up to a slope gradient of 10° and decreased thereafter, whereas the runoff coefficients increased with gradient. The average runoff rates and runoff coefficients of NGAM plots were less than those of GAM plots except for the 5° slope. This behaviour may be due to the reduction in water infiltration under moss. The difference between GAM and NGAM plots in average runoff rates varied from 1·4 to 8%. At the same gradients, NGAM plots yielded significantly (, = 0·05) more sediment than GAM plots. Average sediment deliveries for different slopes varied from 0·119 to 3·794 g m,2 min,1 from GAM plots, and from 0·765 to 16·128 g m,2 min,1 from NGAM plots. Sediment yields from GAM plots were reduced by 45 to 85%, compared with those from the NGAM plots. Plots at 30° yielded significantly higher sediments than at the other gradients. Total sediments S increased with slope gradients G in a linear form, i.e. S = 9·25G , 39·6 with R2 = 0·77*, for the GAM plots, and in an exponential model, i.e. S = 40·4 exp(0·1042G) with R2 = 0·93**, for the NGAM plots. In all cases, sediment deliveries decreased with time, and reached a relative steady state at a rainfall duration of 14 min. Compared with NGAM plots, the final percentage reductions in sediment delivery from GAM plots were higher than those at the initial time of rainfall at all slopes. Copyright © 2006 John Wiley & Sons, Ltd. [source] The role of seepage in erodibilityHYDROLOGICAL PROCESSES, Issue 1 2001L. O. Owoputi Abstract This paper describes a laboratory experimental study to examine the role of seepage in the soil-water erosion process. The study utilized a laboratory flume, which was subjected to both seepage and rainfall in order to determine the exact character of the influence of seepage on erosion rates. The results from the experimental tests performed on sand and sandy clay till are reported. The experimental results show that seepage, by itself, has little effect on erosion rates. However, the erosion caused by rainfall is increased when seepage is present. The increased erosion was not caused by an increase in the total runoff from the seepage. It was found that seepage has an effect on the erodibility of the sand and sandy clay till. The results also show that the impact of seepage on the erodibility of the sand is greater than that of the sandy clay till. Copyright © 2001 John Wiley & Sons, Ltd. [source] Factors affecting the ability of dental cements to alter the pH of lactic acid solutionsJOURNAL OF ORAL REHABILITATION, Issue 12 2000M. Patel Two related studies have been carried out to determine the effect of (a) powder:liquid ratio and (b) relative amounts of cement on the extent of buffering of a lactic acid storage solution using zinc polycarboxylate and glass,ionomer cements (both water-activated). The effect of varying the powder:liquid ratio was found to be slight and not statistically significant. On the other hand, increasing the numbers of specimens in a given volume of storage solution was found to have a significant influence on the final pH (at the 0·0005 level of significance). The fact that powder:liquid ratio did not affect the final pH led to the conclusion that attack occurs mainly at the matrix of these cements, confirming previous findings about the acid erosion process. The finding that increasing the relative amount of cement to acid storage solution strongly influenced pH suggested that, under clinical conditions, buffering would be important. When five specimens were used, the final pH corresponded to that of arrested caries, from which it was concluded that these cements have the ability to be cariostatic in vivo. [source] Conservation of gullies in susceptible riparian areas of alluvial soil regionsLAND DEGRADATION AND DEVELOPMENT, Issue 3 2002R. C. Yadav Abstract The problem of gully erosion is very severe in the riparian areas of the alluvial deep soil region in India. Research and development have progressed in response to the change in social needs. The earlier strategy of maintenance of law and order has changed to one of reclamation and restoration of the productive capacity of riparian areas. Watershed management in the ravines has been adopted for development of food security, eco-restoration and pollution control. Case studies on the watershed management in watersheds projects initiated in the mid-1980s revealed the scope for bringing increased prosperity through crop diversification and eco-restoration. In consideration of the erosion process, new concepts of management zones and improved conservation and reclamation practices have been developed. The sociological factors have been rationally analysed, as they applied to watershed management in the ravines. A new paradigm of watershed management by group action is necessary in the future. Since the ways of combating the ravine problem and enhancing the productivity of ravine-degraded lands were made on rational process-based approach, there is scope for it to be implemented in other countries with similar land and socio-economic situations. Copyright © 2002 John Wiley & Sons, Ltd. [source] Dependency of Tritium Retention in Graphite on Temperature Control of Molecular DynamicsCONTRIBUTIONS TO PLASMA PHYSICS, Issue 3-5 2010A. Ito Abstract We have investigated the carbon plasma facing material and hydrogen atom interaction by the use of molecular dynamics simulation to clarify chemical erosion processes on divertor plate. The present paper is our first try at elucidation of temperature dependence by the molecular dynamics. Temperature was controlled by using Langevin thermostat method. As a result, the retention of hydrogen atom achieve steady state, and the CH4 was generated, which was not found MD simulations without a temperature control method. About 30 percent of injected hydrogen atoms are retained. CH4 yields has a peak at 600 K, which accords with experimental results. A dominant path of CH4 generation found by the present molecular dynamics simulation is as follows: a CH is detached from eroded surface and then it grows into CH4 adsorbing hydrogen atoms via CH2 and CH3. In addition, we propose the problem that the hydrogen atom retention and CH,, yields depend on the thermal relaxation time in MD simulation using temperature control methods (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Estimation of temporal variation in splash detachment in two Japanese cypress plantations of contrasting ageEARTH SURFACE PROCESSES AND LANDFORMS, Issue 9 2010Y. Wakiyama Abstract To elucidate splash erosion processes under natural rainfall conditions, temporal variations in splash detachment were observed using a piezoelectric saltation sensor (H11B; Sensit Co., Portland, ND, USA). Preliminary laboratory tests of Sensit suggested that they were suitable for field observations. Field observations were conducted between July and September 2006 in 21- and 36-year-old Japanese cypress (Chamaecyparis obtusa) plantations with mean stand heights of 9·2,m and 17·4,m, respectively. Splash detachment (in g m,2) was measured seven times using splash cups, and raindrop kinetic energy (in J,m,2,mm,1) in both stands was measured using laser drop-sizing (LD) gauges. Sensit was installed to record saltation counts, which were converted to temporal data of splash detachment (splash rate; in g m,2 10,min,1) using the relationship between splash detachment and saltation counts. Surface runoff was monitored using runoff plots of 0·5,m width and 2·0,m length to obtain temporal data of flow depth (in millimeters). Both total splash detachment and raindrop kinetic energy were larger in the older stand. Increased splash rates per unit throughfall were found in both stands after rainless durations longer than approximately one day in both stands. However, a lower splash rate was found in the 21-year stand after rainfall events. During extreme rainstorms, the 21-year stand showed a low runoff rate and a decline in the splash rate, while the 36-year stand showed a higher splash rate and increased flow depth. The piezoelectric sensor proved to be a useful means to elucidate splash erosion processes in field conditions. Copyright © 2010 John Wiley & Sons, Ltd. [source] SCALES: a large-scale assessment model of soil erosion hazard in Basse-Normandie (northern-western France)EARTH SURFACE PROCESSES AND LANDFORMS, Issue 8 2010P. Le Gouée Abstract The cartography of erosion risk is mainly based on the development of models, which evaluate in a qualitative and quantitative manner the physical reproduction of the erosion processes (CORINE, EHU, INRA). These models are mainly semi-quantitative but can be physically based and spatially distributed (the Pan-European Soil Erosion Risk Assessment, PESERA). They are characterized by their simplicity and their applicability potential at large temporal and spatial scales. In developing our model SCALES (Spatialisation d'éChelle fine de l'ALéa Erosion des Sols/large-scale assessment and mapping model of soil erosion hazard), we had in mind several objectives: (1) to map soil erosion at a regional scale with the guarantee of a large accuracy on the local level, (2) to envisage an applicability of the model in European oceanic areas, (3) to focus the erosion hazard estimation on the level of source areas (on-site erosion), which are the agricultural parcels, (4) to take into account the weight of the temporality of agricultural practices (land-use concept). Because of these objectives, the nature of variables, which characterize the erosion factors and because of its structure, SCALES differs from other models. Tested in Basse-Normandie (Calvados 5500,km2) SCALES reveals a strong predisposition of the study area to the soil erosion which should require to be expressed in a wet year. Apart from an internal validation, we tried an intermediate one by comparing our results with those from INRA and PESERA. It appeared that these models under estimate medium erosion levels and differ in the spatial localization of areas with the highest erosion risks. SCALES underlines here the limitations in the use of pedo-transfer functions and the interpolation of input data with a low resolution. One must not forget however that these models are mainly focused on an interregional comparative approach. Therefore the comparison of SCALES data with those of the INRA and PESERA models cannot result on a convincing validation of our model. For the moment the validation is based on the opinion of local experts, who agree with the qualitative indications delivered by our cartography. An external validation of SCALES is foreseen, which will be based on a thorough inventory of erosion signals in areas with different hazard levels. Copyright © 2010 John Wiley & Sons, Ltd. [source] Gully erosion processes: monitoring and modellingEARTH SURFACE PROCESSES AND LANDFORMS, Issue 14 2009Javier Casalí Guest editors No abstract is available for this article. [source] Evaluation of the SWEEP model during high winds on the Columbia Plateau ,EARTH SURFACE PROCESSES AND LANDFORMS, Issue 11 2009G. Feng Abstract A standalone version of the Wind Erosion Prediction System (WEPS) erosion submodel, the Single-event Wind Erosion Evaluation Program (SWEEP), was released in 2007. A limited number of studies exist that have evaluated SWEEP in simulating soil loss subject to different tillage systems under high winds. The objective of this study was to test SWEEP under contrasting tillage systems employed during the summer fallow phase of a winter wheat,summer fallow rotation within eastern Washington. Soil and PM10 (particulate matter ,10 µm in diameter) loss and soil and crop residue characteristics were measured in adjacent fields managed using conventional and undercutter tillage during summer fallow in 2005 and 2006. While differences in soil surface conditions resulted in measured differences in soil and PM10 loss between the tillage treatments, SWEEP failed to simulate any difference in soil or PM10 loss between conventional and undercutter tillage. In fact, the model simulated zero erosion for all high wind events observed over the two years. The reason for the lack of simulated erosion is complex owing to the number of parameters and interaction of these parameters on erosion processes. A possible reason might be overestimation of the threshold friction velocity in SWEEP since friction velocity must exceed the threshold to initiate erosion. Although many input parameters are involved in the estimation of threshold velocity, internal empirical coefficients and equations may affect the simulation. Calibration methods might be useful in adjusting the internal coefficients and empirical equations. Additionally, the lack of uncertainty analysis is an important gap in providing reliable output from this model. Published in 2009 by John Wiley & Sons, Ltd. [source] Solution of the linear diffusion equation for modelling erosion processes with a time varying diffusion coefficientEARTH SURFACE PROCESSES AND LANDFORMS, Issue 10 2008Georgios Aim. Abstract In the present paper the differential equation of the temporal development of a landform (mountain) with a time dependent diffusion coefficient is solved. It is shown that the shape and dimensions of the landform at time t are independent of the specific variation of the diffusion coefficient with time; they only depend on the mean value of the diffusion coefficient in the time interval where the erosion process takes place. Studying the behaviour of the solution of the differential equation in the wave number domain, it is concluded that Fourier analysis may help in estimating, in quantitative terms, the initial dimensions, the age or, alternatively, the value of the diffusion coefficient of the landform. The theoretical predictions are tested on a hill of the southern part of the Ural mountainous region, in order to show how the results of the mathematical analysis can be used in describing, in quantitative terms, the morphological development of landforms due to erosion processes. Copyright © 2007 John Wiley & Sons, Ltd. [source] Dynamics of soil erosion rates and controlling factors in the Northern Ethiopian Highlands , towards a sediment budgetEARTH SURFACE PROCESSES AND LANDFORMS, Issue 5 2008Jan Nyssen Abstract This paper analyses the factors that control rates and extent of soil erosion processes in the 199 ha May Zegzeg catchment near Hagere Selam in the Tigray Highlands (Northern Ethiopia). This catchment, characterized by high elevations (2100,2650 m a.s.l.) and a subhorizontal structural relief, is typical for the Northern Ethiopian Highlands. Soil loss rates due to various erosion processes, as well as sediment yield rates and rates of sediment deposition within the catchment (essentially induced by recent soil conservation activities), were measured using a range of geomorphological methods. The area-weighted average rate of soil erosion by water in the catchment, measured over four years (1998,2001), is 14·8 t ha,1 y,1, which accounts for 98% of the change in potential energy of the landscape. Considering these soil loss rates by water, 28% is due to gully erosion. Other geomorphic processes, such as tillage erosion and rock fragment displacement by gravity and livestock trampling, are also important, either within certain land units, or for their impact on agricultural productivity. Estimated mean sediment deposition rate within the catchment equals 9·2 t ha,1 y,1. Calculated sediment yield (5·6 t ha,1 y,1) is similar to sediment yield measured in nearby catchments. Seventy-four percent of total soil loss by sheet and rill erosion is trapped in exclosures and behind stone bunds. The anthropogenic factor is dominant in controlling present-day erosion processes in the Northern Ethiopian Highlands. Human activities have led to an overall increase in erosion process intensities, but, through targeted interventions, rural society is now well on the way to control and reverse the degradation processes, as can be demonstrated through the sediment budget. Copyright © 2007 John Wiley & Sons, Ltd. [source] Physical modelling of fault scarp degradation under freeze,thaw cyclesEARTH SURFACE PROCESSES AND LANDFORMS, Issue 14 2006M. Font Abstract Physical modelling has been developed in order to simulate the effects of periglacial erosion processes on the degradation of slopes and scarps. Data from 41 experimental freeze,thaw cycles are presented. They attest to the efficiency of periglacial processes that control both erosion and changes in scarp morphology: (i) cryoexpulsion leads to an increase of scarp surface roughness and modifies significantly the internal structure of the active layer; (ii) combined effects of frost creep and gelifluction lead to slow and gradual downslope displacements of the active layer (0·3 cm/cycle); (iii) debris flows are associated with the most significant changes in scarp morphology and are responsible for the highest rate of scarp erosion; (iv) quantification of the erosion rate gives values close to 1 cm3 cm,2 for 41 freeze,thaw cycles. These experimental results are consistent with field data acquired along the La Hague fault scarp (Normandy, France) where an erosion rate of 4·6 ± 1 m3 m,2 per glacial stage has been computed from the volume of natural slope deposits stored during the Weichselian glacial stage. These results show that moist periglacial erosion processes could lead to an underestimation of Plio-Quaternary deformation in the mid-latitudes. Copyright © 2006 John Wiley & Sons, Ltd. [source] Soil detachment and transport on field- and laboratory-scale interrill areas: erosion processes and the size-selectivity of eroded sedimentEARTH SURFACE PROCESSES AND LANDFORMS, Issue 8 2006O. Malam Issa Abstract Field- and laboratory-scale rainfall simulation experiments were carried out in an investigation of the temporal variability of erosion processes on interrill areas, and the effects of such variation upon sediment size characteristics. Poorly aggregated sandy soils from the semi-arid environment of Senegal, West Africa, were used on both a 40 m2 field plot and a 0·25 m2 laboratory plot; rainfall intensity for all experiments was 70 mm h,1 with a duration of 1 to 2 hours. Time-series measurements were made of the quantity and the size distribution of eroded material: these permitted an estimate of the changing temporal balance between the main erosion processes (splash and wash). Results from both spatial scales showed a similar temporal pattern of runoff generation and sediment concentration. For both spatial scales, the dominant erosional process was detachment by raindrops; this resulted in a dynamic evolution of the soil surface under raindrop impact, with the rapid formation of a sieving crust followed by an erosion crust. However, a clear difference was observed between the two scales regarding the size of particles detached by both splash and wash. While all measured values were lower than the mean weight diameter (MWD) value of the original soil (mean 0·32 mm), demonstrating the size-selective nature of wash and splash processes, the MWD values of washed and splashed particles at the field scale ranged from 0·08 to 0·16 mm and from 0·12 to 0·30 mm respectively, whereas the MWD values of washed and splashed particles at the laboratory scale ranged from 0·13 to 0·29 mm and from 0·21 to 0·32 mm respectively. Thus only at the field scale were the soil particles detached by splash notably coarser than those transported by wash. This suggests a transport-limited erosion process at the field scale. Differences were also observed between the dynamics of the soil loss by wash at the two scales, since results showed wider scatter in the field compared to the laboratory experiments. This scatter is probably related to the change in soil surface characteristics due to the size-selectivity of the erosion processes at this spatial scale. Copyright © 2006 John Wiley & Sons, Ltd. [source] Testing etching hypothesis for the shaping of granite dome structures beneath lateritic weathering landsurfaces using ERT methodEARTH SURFACE PROCESSES AND LANDFORMS, Issue 10 2003Anicet Beauvais Abstract An Erratum has been published for this article in Earth Surface Processes and Landforms 28(13) 2003, 1491. Granite domes, boulders and knobs buried within saprolite have been detected beneath lateritic weathering landsurfaces using 2D electrical resistivity tomography (ERT). This technique provides a valuable means of mapping the bedrock topography and the regolith structures underneath landsurfaces, as it is intrinsically very sensitive to the electrical properties of superimposed pedological, hydrological and geological layers, allowing the determination of their relative geometry and spatial relationships. For instance, 2D inverse electrical resistivity models including topographic data permit the de,nition of lithostratigraphic cross-sections. It shows that resistive layers, such as the more or less hardened ferruginous horizons and/or the bedrock, are generally well differentiated from poorly resistive layers, such as saprolite, including water-saturated lenses, as has been corroborated by past and actual borehole observations. The analysis of the 2D geometrical relations between the weathering front, i.e. the bedrock topography, and the erosion surface, i.e. the landsurface topography, documents the weathering and erosion processes governing the development of the landforms and the underlying structures, thus allowing the etching hypothesis to be tested. The in,ltration waters are diverted by bedrock protrusions, which behave as structural thresholds compartmentalizing the saprolite domain, and also the regolith water table, into distinct perched saturated subdomains. The diverted waters are thus accumulated in bedrock troughs, which behave like underground channels where the saprolite production rate may be enhanced, provided that the water drainage is ef,cient. If the landsurface topography controls the runoff dynamics, the actual bedrock topography as depicted by ERT imaging in,uences the hydrodynamics beneath the landsurface. In some way, this may control the actual weathering rate and the shaping of bedrock protrusions as granite domes and knobs within thick saprolite, before their eventual future exposure. Copyright © 2003 John Wiley & Sons, Ltd. [source] Testing of the SIBERIA landscape evolution model using the Tin Camp Creek, Northern Territory, Australia, field catchmentEARTH SURFACE PROCESSES AND LANDFORMS, Issue 2 2002G. R. Hancock Abstract The SIBERIA landscape evolution model was used to simulate the geomorphic development of the Tin Camp Creek natural catchment over geological time. Measured hydrology, erosion and geomorphic data were used to calibrate the SIBERIA model, which was then used to make independent predictions of the landform geomorphology of the study site. The catchment, located in the Northern Territory, Australia is relatively untouched by Europeans so the hydrological and erosion processes that shaped the area can be assumed to be the same today as they have been in the past, subject to the caveats regarding long-term climate fluctuation. A qualitative, or visual comparison between the natural and simulated catchments indicates that SIBERIA can match hillslope length and hillslope profile of the natural catchments. A comparison of geomorphic and hydrological statistics such as the hypsometric curve, width function, cumulative area distribution and area,slope relationship indicates that SIBERIA can model the geomorphology of the selected Tin Camp Creek catchments. Copyright 2002 © Environmental Research Institute of the Supervising Scientist, Commonwealth of Australia. [source] Stocks and dynamics of SOC in relation to soil redistribution by water and tillage erosionGLOBAL CHANGE BIOLOGY, Issue 10 2006JIANHUI ZHANG Abstract Soil organic carbon (SOC) displaced by soil erosion is the subject of much current research and the fundamental question, whether accelerated soil erosion is a source or sink of atmospheric CO2, remains unresolved. A toposequence of terraced fields as well as a long slope was selected from hilly areas of the Sichuan Basin, China to determine effects of soil redistribution rates and processes on SOC stocks and dynamics. Soil samples for the determination of caesium-137 (137Cs), SOC, total N and soil particle size fractions were collected at 5 m intervals along a transect down the two toposequences. 137Cs data showed that along the long slope transect soil erosion occurred in upper and middle slope positions and soil deposition appeared in the lower part of the slope. Along the terraced transect, soil was lost over the upper parts of the slopes and deposition occurred towards the downslope boundary on each terrace, resulting in very abrupt changes in soil redistribution over short distances either side of terrace boundaries that run parallel with the contour on the steep slopes. These data reflect a difference in erosion process; along the long slope transect, water erosion is the dominant process, while in the terraced landscape soil distribution is mainly the result of tillage erosion. SOC inventories (mass per unit area) show a similar pattern to the 137Cs inventory, with relatively low SOC content in the erosional sites and high SOC content in depositional areas. However, in the terraced field landscape C/N ratios were highest in the depositional areas, while along the long slope transect, C/N ratios were highest in the erosional areas. When the samples are subdivided based on 137Cs-derived erosion and deposition data, it is found that the erosional areas have similar C/N ratios for both toposequences, while the C/N ratios in depositional areas are significantly different from each other. These differences are attributed to the difference in soil erosion processes; tillage erosion is mainly responsible for high-SOC inventories at depositional positions on terraced fields, whereas water erosion plays a primary role in SOC storage at depositional positions on the long slope. These data support the theory that water erosion may cause a loss of SOC due to selective removal of the most labile fraction of SOC, while on the other hand tillage erosion only transports the soil over short distances with less effect on the total SOC stock. [source] The effect of soil type, meteorological forcing and slope gradient on the simulation of internal erosion processes at the local scaleHYDROLOGICAL PROCESSES, Issue 13 2010Guillaume Nord Abstract Numerical simulation experiments of water erosion at the local scale (20 × 5 m) using a process-based model [Plot Soil Erosion Model_2D (PSEM_2D)] were carried out to test the effects of various environmental factors (soil type, meteorological forcing and slope gradient) on the runoff and erosion response and to determine the dominant processes that control the sediment yield at various slope lengths. The selected environmental factors corresponded to conditions for which the model had been fully tested beforehand. The use of a Green and Ampt model for infiltration explained the dominant role played by rainfall intensity in the runoff response. Sediment yield at the outlet of the simulated area was correlated positively with rainfall intensity and slope gradient, but was less sensitive to soil type. The relationship between sediment yield (soil loss per unit area) and slope length was greatly influenced by all environmental factors, but there was a general tendency towards higher sediment yield when the slope was longer. Contribution of rainfall erosion to gross erosion was dominant for all surfaces with slope lengths ranging from 4 to 20 m. The highest sediment yields corresponded to cases where flow erosion was activated. An increase in slope gradient resulted in flow detachment starting upstream. Sediment exported at the outlet of the simulated area came predominantly from the zone located near the outlet. The microrelief helped in the development of a rill network that controlled both the ratio between rainfall and flow erosion and the relationship between sediment yield and slope length. Copyright © 2010 John Wiley & Sons, Ltd. [source] Fire effects on rangeland hydrology and erosion in a steep sagebrush-dominated landscape,HYDROLOGICAL PROCESSES, Issue 16 2008Frederick B. Pierson Abstract Post-fire runoff and erosion from wildlands has been well researched, but few studies have researched the degree of control exerted by fire on rangeland hydrology and erosion processes. Furthermore, the spatial continuity and temporal persistence of wildfire impacts on rangeland hydrology and erosion are not well understood. Small-plot rainfall and concentrated flow simulations were applied to unburned and severely burned hillslopes to determine the spatial continuity and persistence of fire-induced impacts on runoff and erosion by interrill and rill processes on steep sagebrush-dominated sites. Runoff and erosion were measured immediately following and each of 3 years post-wildfire. Spatial and temporal variability in post-fire hydrologic and erosional responses were compared with runoff and erosion measured under unburned conditions. Results from interrill simulations indicate fire-induced impacts were predominantly on coppice microsites and that fire influenced interrill sediment yield more than runoff. Interrill runoff was nearly unchanged by burning, but 3-year cumulative interrill sediment yield on burned hillslopes (50 g m,2) was twice that of unburned hillslopes (25 g m,2). The greatest impact of fire was on the dynamics of runoff once overland flow began. Reduced ground cover on burned hillslopes allowed overland flow to concentrate into rills. The 3-year cumulative runoff from concentrated flow simulations on burned hillslopes (298 l) was nearly 20 times that measured on unburned hillslopes (16 l). The 3-year cumulative sediment yield from concentrated flow on burned and unburned hillslopes was 20 400 g m,2 and 6 g m,2 respectively. Fire effects on runoff generation and sediment were greatly reduced, but remained, 3 years post-fire. The results indicate that the impacts of fire on runoff and erosion from severely burned steep sagebrush landscapes vary significantly by microsite and process, exhibiting seasonal fluctuation in degree, and that fire-induced increases in runoff and erosion may require more than 3 years to return to background levels. Published in 2008 by John Wiley & Sons, Ltd. [source] Predicting unit plot soil loss in Sicily, south ItalyHYDROLOGICAL PROCESSES, Issue 5 2008V. Bagarello Abstract Predicting soil loss is necessary to establish soil conservation measures. Variability of soil and hydrological parameters complicates mathematical simulation of soil erosion processes. Methods for predicting unit plot soil loss in Sicily were developed by using 5 years of data from replicated plots. At first, the variability of the soil water content, runoff, and unit plot soil loss values collected at fixed dates or after an erosive event was investigated. The applicability of the Universal Soil Loss Equation (USLE) was then tested. Finally, a method to predict event soil loss was developed. Measurement variability decreased as the mean increased above a threshold value but it was low also for low values of the measured variable. The mean soil loss predicted by the USLE was lower than the measured value by 48%. The annual values of the soil erodibility factor varied by seven times whereas the mean monthly values varied between 1% and 244% of the mean annual value. The event unit plot soil loss was directly proportional to an erosivity index equal to , being QRRe the runoff ratio times the single storm erosion index. It was concluded that a relatively low number of replicates of the variable of interest may be collected to estimate the mean for both high and particularly low values of the variable. The USLE with the mean annual soil erodibility factor may be applied to estimate the order of magnitude of the mean soil loss but it is not usable to estimate soil loss at shorter temporal scales. The relationship for estimating the event soil loss is a modified version of the USLE-M, given that it includes an exponent for the QRRe term. Copyright © 2007 John Wiley & Sons, Ltd. [source] The influence of climatic change and human activity on erosion processes in sub-arid watersheds in southern East SiberiaHYDROLOGICAL PROCESSES, Issue 16 2003Leonid M. Korytny Abstract A LUCIFS model variant is presented that represents the influence of climate and land use change on fluvial systems. The study considers trends of climatic characteristics (air temperature, annual precipitation totals, rainfall erosion index, aridity and continentality coefficients) for the steppe and partially wooded steppe watersheds of the south of East Siberia (the Yenisey River macro-watershed). It also describes the influence of these characteristics on erosion processes, one indicator of which is the suspended sediment yield. Changes in the river network structure (the order of rivers, lengths, etc.) as a result of agricultural activity during the 20th century are investigated by means of analysis of maps of different dates for one of the watersheds, that of the Selenga River, the biggest tributary of Lake Baikal. The study reveals an increase of erosion process intensity in the first two-thirds of the century in the Selenga River watershed and a reduction of this intensity in the last third of the century, both in the Selenga River watershed and in most of the other watersheds of the study area. Copyright © 2003 John Wiley & Sons, Ltd. [source] A conditional GIS-interpolation-based model for mapping soil-water erosion processes in LebanonLAND DEGRADATION AND DEVELOPMENT, Issue 2 2008R. Bou Kheir Abstract Soil erosion by water is a major cause of landscape degradation in Mediterranean environments, including Lebanon. This paper proposes a conditional decision-rule interpolation-based model to predict the distribution of multiple erosion processes (i.e. sheet, mass and linear) in a representative area of Lebanon from the measured erosion signs in the field (root exposure, earth pillars, soil etching and drift and linear channels). First, erosion proxies were derived from the structural OASIS classification of Landsat thematic mapper (TM) imageries combined with the addition of several thematic erosion maps (slope gradient, aspect and curvature, drainage density, vegetal cover, soil infiltration and erodibility and rock infiltration/movement) under a geographic information systems (GIS) environment. Second, erosion signs were measured in the field, and interpolated by the statistical moments (means and variance) in the defined erosion proxies, thus producing quantitative erosion maps (t,ha,1) at a scale of 1:100,000. Seven decision rules were then generated and applied on these maps in order to produce the overall decisive erosion map reflecting all existing erosion processes, that is, equality (ER), dominance (DOR), bimodality (BR), masking (MR), aggravating (AR), dependence (DER) and independence (IR). The produced erosion maps are divided into seven classes ranging between 0 and more than 1·8,t,ha,1 for sheet erosion, and 0 and more than 10·5,t,ha,1 for mass and linear erosion. They are fairly matching with coincidences values equal to 43 per cent (sheet/linear), 48 per cent (sheet/mass) and 49 per cent (linear/mass). The overall accuracies of these maps were estimated to be 76 per cent (sheet erosion), 78 per cent (mass erosion) and 78·5 per cent (linear erosion). The overall decisive erosion map with 15 classes corresponds well to land management needs. The model used is relatively simple, and may also be applied to other areas. It is particularly useful when GIS database on factors influencing erosion is limited. Copyright © 2007 John Wiley & Sons, Ltd. [source] Stable carbon isotopes as an indicator for soil degradation in an alpine environment (Urseren Valley, Switzerland)RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 10 2009Monika Schaub Analyses of soil organic carbon (SOC) content and stable carbon isotope signatures (,13C) of soils were assessed for their suitability to detect early stage soil erosion. We investigated the soils in the alpine Urseren Valley (southern central Switzerland) which are highly impacted by soil erosion. Hill slope transects from uplands (cambisols) to adjacent wetlands (histosols and histic to mollic gleysols) differing in their intensity of visible soil erosion, and reference wetlands without erosion influence were sampled. Carbon isotopic signature and SOC content of soil depth profiles were determined. A close correlation of ,13C and carbon content (r,>,0.80) is found for upland soils not affected by soil erosion, indicating that depth profiles of ,13C of these upland soils mainly reflect decomposition of SOC. Long-term disturbance of an upland soil is indicated by decreasing correlation of ,13C and SOC (r,,,0.80) which goes in parallel with increasing (visible) damage at the site. Early stage soil erosion in hill slope transects from uplands to adjacent wetlands is documented as an intermediate ,13C value (,27.5,) for affected wetland soil horizons (0,12,cm) between upland (aerobic metabolism, relatively heavier ,13C of ,26.6,) and wetland isotopic signatures (anaerobic metabolism, relatively lighter ,13C of ,28.6,). Carbon isotopic signature and SOC content are found to be sensitive indicators of short- and long-term soil erosion processes. Copyright © 2009 John Wiley & Sons, Ltd. [source] Tectonics and quaternary evolution of the Northern Apennines watershed area (upper course of Arno and Tiber rivers, Italy)GEOLOGICAL JOURNAL, Issue 1 2009Marco Bonini Abstract This work examines the connection between Quaternary tectonics and erosion/incision processes in the primary Tuscan-Romagna watershed of the Northern Apennines, which essentially coincides with the topographic culmination of the Nero Unit structural ridge. Tectonic and geomorphic information were collected in the area where this ridge is crossed by the upper Tiber River course forming a deep gorge. Structural analysis and field mapping have revealed that the region experienced polyphase tectonics with superposed thrust folding events identifiable both at the map and mesoscopic scales. Hinterland-SSW-verging thrusts and thrust-related folds deformed the whole thrust pile during the latest deformation phase. Backthrusts/backfolds controlled the development of intermountain basins nearby the main watershed during the Early Pleistocene and seemingly deformed, in the Tiber gorge, a low-relief landscape developed in the Early Pleistocene (ca. 1.1,Ma). Successively, the upper Tiber River course area and Apennines axial zone underwent a generalized uplift, which is manifested by the deep incision of palaeo-morphologies. This proposed sequence of events correlates well with the major geodynamic change of the Apennines revealed by an acceleration of uplift rates in the Middle,Late Pleistocene. This latter event may also correlate with increased rates of river incision recorded in Europe as a consequence of uplift and/or climate change. Copyright © 2008 John Wiley & Sons, Ltd. [source] | ||||||||||