ancient runoff farming and soil aggradation in terraced wadi fields negev israel obliteration of sedimentary strata by ants scorpions and humans abstract ancient terraced fields in ephemeral stream valleys in the negev desert enabled farming based on runoff water from local rainfall the runoff was captured by stone terrace walls which were built across suitable wadis in various archaeological periods runoff floods added not only water to the fields but also fine sediment however alluvial stratification is usually absent in such terraced wadi fields why we addressed this question at the rural archaeological site of horvat haluqim in the central negev highlands our geoarchaeological excavations in area 3 of terraced field 12 revealed the existence of laminar alluvial stratification but only in the upper 5 cm micromorphology showed a gradual decline in the preservation of laminae with depth radiocarbon dating showed that the upper 50 cm of the terrace soil accumulated during the past 1300 years therefore the average aggradation rate seems about 0 4 mm year similar to modern sedimentation measurements we found evidence for bioturbation particularly by ants and scorpions in the terraced wadi fields at horvat haluqim scorpions evict the soil crumbs excavated from the subsoil on one side of the crescent shaped entrance to their burrows ants on the other hand place the excavated soil crumbs all around the entrance to their underground nest besides bioturbation human soil disturbance by farming is far more destructive to alluvial stratification hoeing and ploughing tillage can erase alluvial laminae from the surface to a depth of about 10 cm in one farming season clear evidence of ancient farming activities in area 3 was found in darker soil layers from a depth of 45 cm 92 cm laminar alluvial strata have not survived in these layers micromorphology revealed fine charcoal bone and pottery fragments interpreted as kitchen household refuse added as fertilizer to the aggrading soil surface in addition non burned dung fragments and non charred spherulites were found indicating also the use of animal dung as manure darker soil layers have a lower bulk density and a high porosity with an extremely large amount of fine pores probably ancient root channels of barley or wheat though runoff flows kept adding laminated alluvial layers to the aggrading terraced wadi fields the fine laminae initial facies did not endure the tooth of time they were gradually obliterated by bioturbation and or rapidly erased by human farming activities tillage and manuring so that laminae are non existent in the ultimate facies of the aggrading sediment soil in agricultural terraced wadi fields

soil seal development under simulated rainfall structural physical and hydrological dynamics this study delivers new insights into rainfall induced seal formation through a novel approach in the use of x ray computed tomography ct up to now seal and crust thickness have been directly quantified mainly through visual examination of sealed crusted surfaces and there has been no quantitative method to estimate this important property x ray ct images were quantitatively analysed to derive formal measures of seal and crust thickness a factorial experiment was established in the laboratory using open topped microcosms packed with soil the factors investigated were soil type three soils silty clay loam zcl sandy silt loam szl sandy loam sl and rainfall duration 2 14 minutes surface seal formation was induced by applying artificial rainfall events characterised by variable duration but constant kinetic energy intensity and raindrop size distribution soil porosities derived from ct scans were used to quantify the thickness of the rainfall induced surface seals and reveal temporal seal micro morphological variations with increasing rainfall duration in addition the water repellency and infiltration dynamics of the developing seals were investigated by measuring water drop penetration time wdpt and unsaturated hydraulic conductivity kun the range of seal thicknesses detected varied from 0 6 5 4 mm soil textural characteristics and om content played a central role in the development of rainfall induced seals with coarser soil particles and lower om content resulting in thicker seals two different trends in soil porosity vs depth were identified i for sl soil porosity was lowest at the immediate soil surface it then increased constantly with depth till the median porosity of undisturbed soil was equalled ii for zcl and sl the highest reduction in porosity as compared to the median porosity of undisturbed soil was observed in a well defined zone of maximum porosity reduction c 0 24 0 48 mm below the soil surface this contrasting behaviour was related to different dynamics and processes of seal formation which depended on the soil properties the impact of rainfall induced surface sealing on the hydrological behaviour of soil as represented by wdtp and kun was rapid and substantial an average 60 reduction in kun occurred for all soils between 2 and 9 minutes rainfall and water repellent surfaces were identified for szl and zcl this highlights that the condition of the immediate surface of agricultural soils involving rainfall induced structural seals has a strong impact in the overall ability of soil to function as water reservoir

a high resolution micromorphological record of changing landscapes and climates on the western loess plateau of china during oxygen isotope stage 5 abstract the micromorphological characteristics of a continuous set of block samples from 24 38 m depth in a well section on jiuzhoutai mountain lanzhou china are described the shape of the magnetic susceptibility curve together with previously published radiocarbon luminescence and geomagnetic dates indicates that this sample set encompasses the whole of the last interglacial s1 palaeosol complex and extends into the overlying and underlying loess l1 and l2 units seven pedosedimentary units are recognised on the basis of trends in the bulk properties and the key micromorphological indicators excrements textural concentrations shell fragments and calcite and gypsum features high rates of loess deposition with significant cryogenic activity gypsum precipitation and only weak bioturbation characterised oxygen isotope stage ois 6 and ois 4 at lanzhou depositional rates were moderately high in ois 5d and 5b with slightly higher bioturbation and no significant cryogenesis or gypsum precipitation ois 5e 5c and 5a were marked by low rates of accretion more extensive bioturbation and limited leaching this reconstruction reflects the pedosedimentary responses to fluctuating dominances of monsoonal controls during this period of global climatic change comparison of earlier micromorphological results from sites to west and east of lanzhou along a dry to humid climatic gradient indicate a clear regional pattern with reduced loess accumulation rates and enhanced bioturbation and leaching in the humid east tianshui and xian clay translocation occurred only in ois 5e at xian the warmest and most humid site on the transect

mechanisms of aggregate stabilization in ultisols from subtropical china abstract the quantification and interpretation of aggregate stability depend on internal soil properties and external factors such as measurement method and aggregate size the objectives of this study were to i determine the aggregate stability in ultisols from subtropical china applying the le bisssonais method ii determine the effect of initial aggregate size on its stability and iii interpret mechanisms of aggregate stabilization in the soils three aggregate size ranges 5 3 3 2 and 2 1 mm were obtained by dry sieving after the wetting treatments the dominant fraction of fragments for each soil was 2 1 mm or 0 63 0 2 mm the mechanisms of aggregate breakdown was in the order slaking mechanical breakdown micro cracking they differed with soil type and composition the normalized mean weight diameter nmwd of the aggregates after fast wetting and wet stirring were more correlated with soil properties such as degree of micro aggregation doa cation exchange capacity cec k 2 o fe 2 o 3 or al 2 o 3 rather than clay and soil organic carbon soc content the binding force by soil organic matter was smaller than the force caused by entrapped air or the force of combination of mechanical stress by stirring and differential swelling of minerals the smaller the aggregate the larger was the aggregate stability according to nmwd the rankings of the soils differed with the soil aggregate sizes and the wetting treatments sandy loams from sandstone sc and sw were the weakest soils while the purple mudstone pp was the strongest all the cultivated soils decreased in aggregate stability compared with the comparable uncultivated soils or parent materials irrespective of the cultivation time and the changes in soc content after cultivation

effects of different spatial distributions of physical soil crusts on runoff and erosion on the loess plateau in china the response of runoff and erosion to soil crusts has been extensively investigated in recent decades however there have been few attempts to look at the effects of spatial configuration of different soil crusts on erosion processes here we investigated the effects of different spatial distributions of physical soil crusts on runoff and erosion in the semi arid loess plateau region soil boxes 1 5 m long 0 2 m wide were set to a slope of 17 6 10 and simulated rainfall of 120 mm h 1 60 minutes the runoff generation and erosion rates were determined for three crust area ratios depositional crust for 20 33 and 50 of the total slope and five spatial distribution patterns depositional crust on the lower lower middle middle mid upper and upper slope of soil crusts the reduction in sediment loss sediment reduction was calculated to evaluate the effects of different spatial distributions of soil crusts on erosion sediment yield was influenced by the area ratio and spatial position of different soil crusts the runoff rate reached a steady state after an initial trend of unsteadily increasing with increasing rainfall duration sediment yield was controlled by detachment limitation and then transport limitation under rainfall the shifting time of erosion from a transport to detachment limiting regime decreased with increasing area of depositional crust no significant differences were observed in the total runoff among treatments while the total sediment yield varied under different spatial distributions at the same area ratio total sediment yield was the largest when the depositional crust was on the upper slope and it was smallest when the crust was deposited on the lower slope the sediment reduction of structural crust 42 5 66 5 was greater than that of depositional crust 16 7 34 3 these results provide a mechanistic understanding of how different spatial distributions of soil crusts affect runoff and sediment production copyright 2017 john wiley sons ltd

on the nonuniqueness of sediment yield at the catchment scale the effects of soil antecedent conditions and surface shield the understanding of reasons leading to nonuniqueness of soil erosion susceptibility is still inadequate yet indispensable for establishing general relations between runoff volume and sediment yield to obtain relevant insights we performed a series of numerical simulations with a detailed hydrodynamic model using synthetic storms of varying intensity duration and lag time between events as representations of different hydrologic response conditions in a zero order catchment the design targeted to generate surface flow and perturb soil substrate by a first rainfall event creating a set of initial conditions in terms of flow and deposited sediment prior to the onset of a subsequent rainfall event due to the differential effect of re detachment and re entrainment processes on soil particles of varying sizes the deposited sediment mass formed shielding layer one of the essential results is that unless the initial condition of flow and sediment is identical the same volume of runoff can generate different total sediment yields and their variation can reach up to 200 the effect is attributed to two major conflicting effects exerted by the deposited initialization soil antecedent condition sediment mass erosion enhancement because of supply of highly erodible sediment and erosion impediment because of constrain on the availability of lighter particles by heavier sediment consistently with this inference long term simulations with continuous rainfall show that a peculiar feature of sediment yield series is the existence of maximum before the steady state is reached the two characteristic time scales the time to peak and the time to steady state separate three characteristic periods that correspond to flow limited source limited and steady state regimes these time scales are log linearly and negatively related to the spatially averaged shields parameter the smaller the rainfall input and the heavier a given particle is the larger the two scales are the results provide insights on how the existence of shield operates on erosion processes possibly implying that accurate short term predictions of geomorphic events from headwater areas may never become a tractable problem the latter would require a detailed spatial characterization of particle size distribution prior to precipitation events

rainfall runoff properties of tephra simulated effects of grain size and antecedent rainfall abstract rain triggered lahars rtls are a significant and often persistent secondary volcanic hazard at many volcanoes around the world rainfall on unconsolidated volcaniclastic material is the primary initiation mechanism of rtls the resultant flows have the potential for large runout distances 100 km and present a substantial hazard to downstream infrastructure and communities rtls are frequently anticipated in the aftermath of eruptions but the pattern timing and scale of lahars varies on an eruption by eruption and even catchment by catchment basis this variability is driven by a set of local factors including the grain size distribution thickness stratigraphy and spatial distribution of source material in addition to topography vegetation coverage and rainfall conditions these factors are often qualitatively discussed in rtl studies based on post eruption lahar observations or instrumental detections conversely this study aims to move towards a quantitative assessment of rtl hazard in order to facilitate rtl predictions and forecasts based on constrained rainfall grain size distribution and isopach data calibrated simulated rainfall and laboratory constructed tephra beds are used within a repeatable experimental set up to isolate the effects of individual parameters and to examine runoff and infiltration processes from analogous rtl source conditions laboratory experiments show that increased antecedent rainfall and finer grained surface tephra individually increase runoff rates and decrease runoff lag times while a combination of these factors produces a compound effect these impacts are driven by increased residual moisture content and decreased permeability due to surface sealing and have previously been inferred from downstream observations of lahars but not identified at source water and sediment transport mechanisms differ based on surface grain size distribution a fine grained surface layer displayed airborne remobilisation accretionary pellet formation rapid surface sealing and infiltration excess overland flow generation whilst a coarse surface layer demonstrated exclusively rainsplash driven particle detachment throughout the rainfall simulations this experimental protocol has the potential to quantitatively examine the effects of a variety of individual parameters in rtl initiation under controlled conditions

surface crusting in two alluvial soils of northen niger valentin c 1991 surface crusting in two alluvial soils of northen niger geoderma 48 201 222 surface crusting was studied in a sandy soil and a clay loam soil in northern niger in a subdesert to desert environment light microscopy electron microscopy image analysis and soil physics were used to study and explain different crusting processes in experimental plots two 1 m2 plots on each soil were subjected to rainfall simulation in the field under natural and tilled surface conditions this study demonstrates that kinetic energy of rainfall is the major crusting factor for the sandy soil waterlogging and subsequent slaking led to the formation of structural and depositional crusts in the tilled clay loam plot in this case a surface crust can be formed regardless of kinetic energy of the rainfall this was substantiated through double ring infiltrometer measurements in both soils infiltration was severely hindered by crusting the relationships of crusting to water and wind erosion were more ambiguous four types of crusts could be defined from this study in terms of structure genetic processes and properties it could also be demonstrated that crust control practices should take into account the texture of the original soil materials

multi temporal uav data for automatic measurement of rill and interrill erosion on loess soil the fragile landscape of the north european loess belt is prone to soil erosion due to soil properties and intense land use of the fertile region exact measurement of surface changes with high temporal and spatial resolution over large areas is necessary to quantify and understand rill and interrill erosion processes high resolution aerial imagery acquired by an unmanned aerial vehicle uav is used to automatically generate precise digital surface models dsms of high spatial resolution by applying structure from motion image processing tools during an investigation period of ten months a 600 m2 field plot is observed during four field campaigns a stable reference system is established for multi temporal comparison the overall accuracy of the dsms generated from uav images is less than 1 cm verified by comparison with terrestrial laser scanner tls data furthermore a method for automatic rill extraction and rill parameter calculation is developed which enables objective rill description with cm accuracy and resolution soil surface roughness and rill development as well as volumetric quantifications are analysed for multi temporal change detection surface changes during winter season are controlled by soil consolidation crusting and sheet erosion during rainy spring season sheet erosion and rill incision occur two thunderstorms in summer season cause dominant rill erosion erosion rills are more dominantly deepening than widening from to 2 to 4 cm depth and from 17 to 23 cm width resulting in average per rill erosion values of 0 03 and 0 07 m3 respectively an orientation dependent lateral rill shift is revealed implying rill widening in eastern direction due to dominant winds from the west volumetric quantifications indicate high erosion volumes reaching up to 121 tha 1 during the summer events highest erosion volumes are due to rill erosion rather than interrill erosion copyright 2014 john wiley sons ltd

morphology and influencing factors of rills in the steep slope in yuanmou dry hot valley sw china abstract it is very important to understand rill morphology in order to understand its dynamics to reveal the morphology and influencing factors of rills in the steep slope rss in the yuanmou dry hot valley the total station photogrammetric technique and microtopographic profiler were used to obtain the parameters of the cross sections and longitudinal profiles of the rss and 12 parameters were used to characterize the rill morphology the results show that the morphology of rills clearly varied between each layer the topography soil properties and ferruginous cemented layer all exerted important influences on the rill morphology the average depth decreased with increasing slope length and the depths dominated by silt and sand were larger than that dominated by clay the average width and average width depth ratio increased with increasing slope length and the width and the width depth ratio that was dominated by clay was larger than that dominated by silt and sand the shape ratio of the rill cross section ranged from 0 50 to 0 58 and the shape of the cross section gradually changed from narrow and deep to wide and shallow with increasing slope length concave convex degree tended to be larger in the segment with ferruginous cement in the longitudinal profile the gradient gradually decreased with decreasing slope gradient and increasing slope length the presence of the ferruginous cemented layer and topsoil crust resulted in abnormal changes in the shape of the rill it is helpful to further understand the mechanisms of rill erosion under different conditions

the position of hydraulic fracturing to initiate vertical fractures in hard hanging roof for stress relief abstract a strong and hard hanging roof causes high underground stress in underground mines leading to rock burst coal and gas outburst or large deformations in roadways to address these problems hydraulic fracturing can form hydraulic cracks in strong hanging roofs and promote fractures in the hanging roof however it is difficult to ensure that hydraulic cracks propagate vertically through rock strata therefore a novel method has been proposed that uses hydraulic fracturing to generate vertical fractures in hard hanging roofs for roof cutting and stress relief the method exploits the additional horizontal tensile stress produced by the bending deformation of the roof so that the fracturing point occurs in a desirable tensile stress area and therefore to promote the vertical expansion of hydraulic cracks that cut off the rock strata in this paper the position of the maximum additional horizontal tensile stress is taken to be the reasonable fracturing position given by a mechanical model solving this model indicates that a shorter hanging roof equates to a thicker hanging roof a larger elastic modulus a smaller elastic cushion coefficient and a fracturing position that is deeper in the coal wall the various factors that affect the reasonable fracturing position may be ordered in terms of their impact as follows hanging roof length hanging roof elastic modulus hanging roof thickness elastic cushion coefficient horizontal stress the proposed method has been applied to roadway 5103 of the majiliang coal mine of datong coal mine group co ltd the results show that hydraulic fracturing forms vertical hydraulic cracks at the point of maximum additional horizontal tensile stress which can effectively control the deformation in the surrounding rock the fracturing position calculated by using this model is reasonable and reliable and can be used to guide the on site construction

importance of organic fe complexing ligands in the mississippi river plume abstract as part of a larger program focused on understanding the biogeochemistry of large river plumes we participated in two expeditions during 2000 to sample the mississippi river plume surface water samples were collected using a trace metal clean towed fish and analyzed for total dissolved fe organic fe complexing ligands and their associated conditional stability constants the ligands in the river plume have conditional stability constants log k fel between 10 5 and 12 3 with an average of 11 2 and standard deviation of 0 6 very similar to ligands found in the open ocean comparison of high flow and low flow regimes indicates that variability in flow may be the main cause of the variability in fe concentrations in the plume the organic fe complexing ligands are in greatest excess during a time of higher flow these ligands are responsible for maintaining very high 5 nm fe concentrations throughout the plume due to complexation with these organic ligands the concentration of fe remains above the fe hydroxide solubility level until a salinity above 35 is reached where there appears to be a sink for fe in the less productive waters therefore fe is transported a great distance from the river source and is available for biological utilization in the coastal zone

laboratory experimental study of soil crusting relation between aggregate breakdown mechanisms and crust stucture abstract crusts formation on cores of air dry and prewetted aggregates was studied using a laboratory rainfall simulator samples were taken out during the experiment in order to study changes in water content and aggregates size distribution inside the crust and under the crust pore space geometry of the crusts is described using light optical microscopy and mercury porosimetry in the case of air dry aggregates aggregates become micro cracked macropores at the surface are quickly closed and ponding occurs rapidly with prewetted aggregates microcracking does not occur and only a very slow abrasion of the aggregates is observed porosity remains high and no ponding excess occurs the discussion of these results shows that it is the way of the wetting and the initial water content which determine the breakdown mechanism and therefore the behaviour of the aggregates submitted to rainfall

runoff and interrill erosion on sandy soils under cultivation in the western paris basin mechanisms and an attempt at measurement measurements made on different scales such as rainfall simulations on 1 m2 and 20 m2 experimental plots and water sampling at the outlet of a watershed enable the analysis of the mechanisms of pluvial erosion and therefore the importance of runoffs and soil losses in the hilly and sandy parts of the western paris basin interrill erosion accounts for slow transfer of materials towards the lower part of plots and slopes the overland flow caused by restructuring of the surface tertiary and cenomanian soils erodes some 150 to 200 kg ha 1 during the month following sowing only a part of these deposits reach the river which carries away less than 50 kg ha 1 each month interrill erosion makes slopes still more uneven fills in valley bottoms and so paves the way to catastrophic erosion which scoops out rises in the ground and colluvial deposits in the lower part of slopes and valley bottoms copyright 2001 john wiley sons ltd

aggregation and sedimentation of iron phosphorus and organic carbon in experimental mixtures of freshwater and estuarine water abstract the importance of salinity and suspended minerogenic particles on the aggregation and sedimentation processes of iron phosphorus and organic carbon was studied in experimental procedures with waters from the river ore and from the ore estuary northern sweden the aggregation of dissolved iron and phosphorus reached at least 40 90 and 30 60 respectively at salinities between 4 and 6 only a few percent less than 10 of the dissolved organic carbon aggregated rapid and nearly complete sedimentation of iron and phosphorus aggregates was found at high salinities 4 5 and in the presence of clay particles mineral particles increase sedimentation by sorption of formed iron and phosphorus aggregates only a small amount of the organic carbon sedimented

investigation of non explosive expansion material in roof caving field application abstract effective roof caving plays a significant role in mining safety a spatiotemporal coupling fracturing method using a non explosive expansion material neem is proposed in this paper this method depends on the high fracturing capacity of the neem and a change from vertical charging to inclined charging aimed at producing new free surfaces step by step until the integrity of the entire rock is destroyed from a space time perspective the expansion stress and water adsorption of the neem were studied to determine the optimum stress increase interval and soak time with respect to the space aspect the charging sequence of boreholes was negatively correlated to their incline angles bringing the neem s superiority into full play based on the generation of new free surfaces in steps with respect to the time aspect the charging intervals of the inclined boreholes were designed to obtain the best stress compensation and highest fracturing efficiency a field trial was carried out in pingdingshan no 2 mine the results of which showed that some radial cracks were produced around the charging boreholes and that they propagated to the pilot boreholes moreover four main cracks were formed and were approximately parallel to the direction of the borehole rows in a fracturing group a fracture network was eventually generated which verified the expansion capacity of the neem and the feasibility of the spatiotemporal coupling fracturing method for field application

holocene sediment fluxes in a fragile loess landscape saxony germany abstract the loess region of the central saxon hill country is characterized by a relief of gently rolling hills whose most distinctive landscape elements are well defined shallow valleys called dells the aim of this research is to gather morphodynamic information on the dells in a qualitative and quantitative way by means of high resolution field mapping and laboratory based analyses the intensity of sediment shifting has been modelled via sediment budgeting on a small catchment scale research objectives are to determine the character and magnitude of geomorphic processes for a holocene time frame concerning the absence of currently obtainable dating this study represents a reflection which summarises all sediment shifting related to anthropogenic land use during the holocene as a specific parameter in terms of landscape development the relief is considered to be strongly associated with varying process intensities agrarian land use of the loess region since the late neolithic has resulted in severe soil erosion lower middle slope positions are the apparent spots were soil erosion processes take place in terms of rill erosion a detailed survey of three dells provided a very heterogeneous pattern of the relocation of soil material dell 1 zehren shows medial holocene soil profile truncation of 1090 mm in contrast dell 3 lobschutz shows soil loss of around 660 mm all systems have similarly high slope gradients up to 12 actually the deepening of the dell s depth contours and therewith the extent of erosive slope lengths is varying thus a higher longitudinal decline of the valley floors and a more intensive incision lead to enlarged erosive slope lengths which causes increasing sediment transport hence land use patterns trigger the process of material displacement whereas relief modifies the intensity of geomorphic processes

the effect of ponding depth on infiltration in a crusted surface depression over the past few decades the influence of surface sealing on infiltration has been the subject of numerous publications however very few of these experiments have considered the effect of spatial variability in seal hydraulic characteristics on infiltration field and laboratory observations have demonstrated that seal characteristics vary considerably within a range of a few cm and the changes are often related to microtopography the objective of this experiment was to investigate the influence on infiltration of a seal with varying hydraulic properties in a surface depression two soils of different aggregate stability were used in the experiment blosseville silt loam and villamblain silty clay loam soil columns 23 cm diameter by 30 cm length were packed with aggregates of 2 0 cm and a 6 cm depression was formed in the soil surface a sedimentary crust was formed in the centre of the depression and the sample was rained upon for 60 min at a rainfall intensity of 35 mm h 1 subsequently water outflow at the base of the column and pressure heads in the column were measured during two ponding periods corresponding to depths of 0 5 and 4 0 cm water outflow rates increased with ponding depth substantially more than could be attributed to the increases in ponding pressure head and submerged area for both soils the experiment demonstrated that where seal hydraulic conductivity varies with microtopography a significant increase in infiltration rate occurs as areas of greater hydraulic conductivity are submerged the increases in ponded pressure head and submerged area are negligible compared to the influence of spatial variability in seal hydraulic conductivity

pedosedimentary reconstruction of a thick loess paleosol sequence near lanzhou in north central china abstract a 38 m well section near lanzhou at the semiarid western margin of the loess plateau china contained a continuous high resolution loess paleosol sequence spanning the last 130 000 yr depth functions of micromorphological features magnetic susceptibility calcium carbonate organic carbon and median grain size provide the basis for pedosedimentary and associated paleoenvironmental reconstructions of three paleosol complexes s1 sm and s0 each pedosedimentary stage reflects the interaction of changing intensities of controlling monsoonal forces three periods of reduced dust inputs and enhanced pedogenic activity notably bioturbation and weak leaching can be identified from within the s1 pedocomplex these soil forming intervals were separated by phases of varying land surface instability characterized by arid dust deposition semiarid accretionary pedogenesis water reworking and crust formation or even freeze thaw modification the sm pedocomplex represents an interval of relatively rapid dust accumulation with only minimal syndepositional modification and minor pedogenic alteration at ephemeral land surfaces the s0 pedocomplex is clearly more pedogenically developed although erosion reworking and mixing by water have partly homogenized the property depth functions

response of loess materials to simulated translocation by water micromorphological observations structural differences between loess material deposits produced by splash flow without splash and by rainwash i e combined splash and flow respectively were reported earlier mucher and de ploey 1977 deposits from splash alone proved to be non layered and had incurred almost no additional particle sorting deposits from flow without splash were well layered while individual laminae displayed excellent sorting rainwash produced poorly layered deposits with poorly sorted individual laminae only horizontal and subhorizontal bedding and no cross bedding were observed similar features appeared in samples from naturally layered loess deposits collected from excavations the present paper focuses on the granulometric character of the artificially created layers experiments normally involved the combined use of an erosion and a sedimentation flume slope angles of the flumes varied mainly form 0 25 to 4 degrees precipitation intensities varied from 7 to 120 mm per hour unit discharges ranged from 0 2 to 9 2 cm3 cm s flow was laminar or smooth turbulent either subcritical or supercritical froude numbers between 0 5 and 3 8 raindrop impact had little influence on the flow velocity and thickness of the surficial water film but it significantly increased transportation capacity and flow competence savat 1976 1977 undisturbed samples were collected during the experiments and impregnated with unsaturated polyester resin thin sections of 20 m thickness were studied under a polarizing microscope comparative observations were made on naturally layered loess materials during rainwash clay size particles are removed and exported whereas laminae with particles from 10 to 50 microns are more frequently produced than those with particles from 10 to 30 microns flow without splash produced relatively more laminae with grains smaller than 30 microns diameter striking in all samples is the absence of laminae composed of 30 50 m grains aggregates were only deposited by smooth turbulent flow either disturbed or undisturbed by raindrop impact in view of the experimental results the naturally formed loess deposits may be interpreted as follows the bulk of the loess from the excavation near tongrinne belgium was reworked under influence of turbulent rainwash only one sample contained laminae consisting of clay particles smaller than 10 m and of particles from 10 30 m respectively suggesting deposition from flow without splash this was taken from a gully infilling a gully fill from the excavation heverlee near leuven belgium is characterized by poorly sorted laminae dominated by the coarser silt fractions this suggests infilling under influence of turbulent rainwash

the influence of slope angle on final infiltration rate for interrill conditions abstract despite numerous studies the relationship between slope angle and infiltration rate remains unclear under different experimental conditions new processes may be introduced which influence the relationship the presence of rills for example may significantly affect the relationship between slope angle and infiltration rate so distinct relationships may exist for rill and interrill areas the objective of this study was to investigate the influence of slope angle on infiltration rate for an interrill area with a surface crust the experiment was carried out in a laboratory using simulated rainfall and soil trays designed to limit the processes to those found in interrill areas slope angles ranged from 1 5 to 21 5 infiltration was calculated from the overland flow rate and microtensiometers and micromorphological analysis were used to characterise the seals infiltration rate decreased with increasing slope angle image analysis of pore characteristics in the affected layer and subseal pressure head measurements indicated there were no differences in seal characteristics between slope angles the results showed that sealing intensity did not vary with slope angle and the dominant influence of slope angle on infiltration rate resulted from changes in overland flow depth and surface storage the results also suggest that small changes in seal hydraulic conductivity with microrelief play an important role in the infiltration process

infiltration during soil sealing the effect of areal heterogeneity of soil hydraulic properties 1 the combined effects of soil surface sealing and areal heterogeneity of the soil hydraulic properties on the mean infiltration curve are studied here for the first time seal formation during rainfall is simulated according to the dynamic model of assouline and mualem 1997 areal heterogeneity is represented by lognormal distribution of the saturated hydraulic conductivity of the initially undisturbed soil and by related distributions of the other soil parameters the mean infiltration curve of the heterogeneous field is evaluated presuming that horizontal fluxes are negligible it is found that when soil surface sealing is taken into account in a heterogeneous field the ponding time is only slightly affected however significantly more runoff is produced compared to nonsealing field mulched with the relative area contributing to surface runoff being increased from 65 to 95 the relative effect of field heterogeneity on the infiltration curve increases for higher rainfall intensity the formation of soil surface seal apparently reduces the effect of the field areal variability on the steady infiltration rate the infiltration rate after 60 min of rainfall distributes lognormally under sealing conditions while it distributes normally in the case of the unsealed soil the final infiltration rate resulting from the assumption of a sealed uniform field is underestimated compared to sealed heterogeneous field with the relative effect being larger for a loam soil 51 than for a sandy loam soil 26 also the approximation that the infiltration curve is a unique function of cumulative rainfall independent of rainfall intensity is not valid in a sealing heterogeneous field and its application in such a case would be more erroneous than in uniform fields on the other hand one may disregard the variability of all soil parameters except the hydraulic conductivity when calculating infiltration

the implications of spatial variability in surface seal hydraulic resistance for infiltration in a mound and depression microtopography abstract soil surface crusting has a major impact on water infiltration and erosion in many soils considerable progress has been made in describing crusting processes and in modelling the impact of crusting on infiltration most studies however have neglected the high spatial variability in crust characteristics observed in the field the objective of this experiment was to determine the influence of runoff depth on infiltration rate in the presence of a surface seal varying in hydraulic characteristics with microtopography the blosseville silt loam has a low aggregate stability and forms crusts readily the villamblain silty clay loam has a greater aggregate stability due to its greater clay and organic matter contents and it is more resistant to aggregate breakdown processes under rainfall samples of the soils were sieved to retain aggregates less than 2 0 cm and packed in 50 50 15 cm soil trays the trays were surrounded by a 10 cm soil border to compensate for splash loss after molding the surface into a mound and depression microtopography the samples were subjected to simulated rainfall at an intensity of 22 8 mm h 1 hourly measurements of surface roughness showed that the original roughness was smoothed out due to the infilling of depressions by sediments detached from the mounds for the final hour runon was added to the top of the soil tray to increase the runoff rate and depth for both soils infiltration rate increased more than could be attributed to the increased ponding pressure head the change in infiltration rate was particularly great for villamblain the measurements of hydraulic resistance showed that structural crusts had a lower hydraulic resistance than sedimentary crusts they also showed that the crusts formed on villamblain were of a lower hydraulic resistance than those of blosseville it appears that small changes in runoff depth can significantly increase infiltration rate when structural crusts of lower hydraulic resistance are inundated the effect was less important in blosseville which formed seals of relatively high hydraulic resistance everywhere the results provide a suitable explanation for field observations of increasing infiltration rate with either increasing rainfall intensity or runoff rate the results also have implications for the relationships between surface roughness surface water storage and infiltration

bulk density of surface crusts depth functions and relationships to texture abstract a range of soils from pleistocene deposits with sandy to sandy loam textures and a group of loess derived soils with predominantly silty textures were subjected to 60 mm of simulated rainfall to form structural seals after drying samples of the surface crusts were collected to determine their bulk densities at a high resolution of depth 0 15 mm using an immersion method the bulk density data obtained for each soil sample were plotted as a function of depth beneath the soil surface two models were fitted to these plots the first was an exponential decay type function as proposed by mualem et al 1990 and the second was a sigmoidal type of function assuming that maximum compaction had already progressed to some depth below the soil crust surface all of the results indicated a gradual decrease in the bulk density with depth below the surface until convergence with the initial bulk density of the undisturbed soil was attained the maximum bulk densities recorded for crust segments representing the uppermost 2 mm of the crusts ranged from 1 713 to 1 91 g cm 3 for soils with silty sand loamy sand or sandy loam textures crusts of loess derived soils showed lower values ranging from 1 44 to 1 65 g cm 3 the maximum surface bulk density was shown to be highly significantly correlated with the log of geometric mean diameter of the primary grain size distribution in most cases both models showed good to very good fits to the measured data the exponential decay function appeared to better represent the initial stages of surface compaction and the sigmoidal function the later stages of structural crust formation

nature formation and effects of soil crusts formed by water drop impact abstract research was conducted to investigate 1 the structure formation and nature of soil crusts which develop as a result of raindrop impact under controlled conditions of simulated rain and 2 the crust effect on infiltration rates scanning electron microscope sem observations performed on sandy sandy loam and clayey soil samples show the crust to be composed of two layers 1 a skin 0 1 mm thick and 2 a layer 2 3 mm thick with a higher bulk density in which aggregates have been destroyed a washing in zone described by earlier investigators could not be detected the soil beneath the crust maintains its original structure and particle orientation the chemical composition of the rain water was found to have a significant but not very large effect on the infiltration rate vs cumulative rain curve of the clayey soil material only final infiltration rate was about 20 lower when distilled water was applied compared to tap water electrical conductivity 0 6 mmho cm 1 an increase of the bulk density from 1 35 1 48 g cm 3 in undisturbed soil to 1 74 1 88 g cm 3 in crusts was found the amount of eroded material increased gradually with increase of runoff and decrease of infiltration at steady state the erosion rates were 0 45 1 25 and 0 76 g m 2 min 1 in the sandy sandy loam and clayey soil specimens respectively percentages of clay and silt in the eroded material were higher than in the bulk samples three stages to describe the changes in nature and effects of crusts during their formation are suggested 1 the rate of infiltration decreases to a point at which runoff beings 2 the initiation of runoff until infiltration and runoff rates become stabilized and 3 infiltration and runoff maintain steady rates

micromorphological study of slumping in a hardsetting seedbed under various wetting conditions slumping of hardsetting seedbeds upon wetting has not been extensively studied despite the likelihood that it determines the physical properties after drying slumping results from processes similar to those involved in crusting except that overburden pressure can dominate rather than rainfall kinetic energy only a few studies have dealt with the morphological description of slumping to simulate different climatic and management conditions repacked seedbeds of a hardsetting sandy loam soil were subjected to a range of wetting conditions e g capillary rise immersion and rainfall simulation slumping processes were characterized using qualitative and quantitative micromorphological observations of polished blocks and thin sections from resin impregnated samples a morphogenetical framework was proposed to help description of the complex associations of processes which can lead to structural collapse crusting and slumping on wetting three main stages were considered i e aggregate disruption or abrasion relocation of the released material and compaction in the hardsetting material studied here structural collapse under slow wetting occurred at the bottom of cores due to aggregate coalescence under overburden pressure coalescence required aggregate cohesion being reduced by microcracking therefore it differed from the coalescence previously described in unstable silty loam soils where microcracking was not necessary for aggregates to coalesce macroporosity decreased most strongly under fast wetting due to physical dispersion and aggregate breakdown under simulated rainfall compaction by raindrops could not be distinguish from aggregate breakdown the role of overburden pressure and of rainfall kinetic energy remains to be stated new data are required including measurement of total porosity in the initial wet and dry states

interactions between soil properties and moisture content in crust formation runoff and interrill erosion from tilled loess soils soil surface seals and crusts resulting from aggregate breakdown reduce the soil infiltration rate and may induce erosion by increasing runoff the cultivated loess areas of northwestern europe are particularly prone to these processes surface samples of ten tilled silty loamy loess soils ranging in clay content from 120 to 350 g kg 1 and in organic carbon from 10 to 20 g kg 1 were packed into 0 5 m2 plots with 5 slopes and subjected to simulated rainfall applied at 30 mm h 1 the 120 minutes rainfall events were applied to initially field moist soil air dried soil and rewetted soil to investigate the effect of soil moisture content prior to rainfall runoff and eroded sediments were collected at 5 minutes intervals aggregate stability of the soils was assessed by measuring particle size distribution after different treatments all soils formed seals runoff rates were between 70 and 90 by the end of the rainfall event for field moist plots there were large differences between soil runoff rates for the air dried and rewetted plots interrill erosion was associated with runoff and sediment concentration in runoff readily reached a steady state value measurements of aggregate stability for various treatments were in good agreement with sealing runoff and erosion responses to rainfall runoff and erosion were lower for air dried plots than for field moist plots and were either intermediate or lowest for rewetted plots depending on soil characteristics soils with a high clay content had the lowest erosion rate when they were rewetted whereas the soil with a high organic carbon content had the lowest erosion rate in air dry conditions the results indicate the complexity of the effect of initial moisture content and the interactions between soil properties and climate

degradation of soil structure by welding a micromorphological study abstract in 1985 a plot study was started on sloping cultivated loess soils in south limbourg the netherlands to evaluate the effects of various cropping systems of fodder maize on runoff soil loss and crop yield under natural rainfall to monitor degradation of soil structure including crust formation undisturbed vertical samples 15 7 cm for soil micromorphological analysis were taken of the top 7 cm of soil at ten dates chosen in relation to times of tillage and sowing crop stage harvest and winter frost wheel marks if present were also sampled contrary to accepted views no disintegration of structural elements by slaking or dispersion was observed freshly tilled soil exhibited a loss of its original granular structure by coalescence of the aggregates into larger units eventually leading to a structureless state of part of the top soil processes held responsible for this are mainly welding of wet aggregates and seldom fusion by silt infillings in vertical inter aggregate pores the two layer model of soil crust formation of mcintyre could not be confirmed as no important vertical translocation of fines or washed in layers were observed horizontal cracks developed in the structureless soil giving rise to a platy structure in part of the top soil transitional stages of loss of soil structure were observed characterized by the progressive reduction of compound packing voids to vughs which ultimately disappeared completely and sometimes were replaced by planar voids besides structural crusts sedimentary crusts including splash deposits were observed

land use effects on soil crusting and hydraulic response of surface crusts on a tropical alfisol soil surface crusting a common phenomenon on cultivated soils has major implications for agriculture and the environment because of its effects on soil hydrological properties erosion and crop establishment the objectives of this study were to evaluate land use controls on crust formation and the hydraulic response of soils to crust development for a patancheru series soil clayey skeletal mixed isohyperthermic udic rhodustalf in south central india soil aggregates obtained from cultivated pl and naturally vegetated fallow nv land were packed into sample trays and subjected to laboratory rain simulation to form crusts thin sections and visual observation indicated that crust development reached a more advanced stage in the pl case compared with nv following 90 min of rain at 40 80 mm h 1 intensity this was reflected in a thicker crust layer with fewer voids in the former and a less smooth surface with partially disintegrated aggregates in the latter the hydraulic response of the soil surface with the progression of crust development indicated a more permeable and less dense crust formed on nv than on pl soil the results suggested that nv soil aggregates were more stable and that crust formation is more gradual for stable aggregates compared with the less stable pl aggregates a structural crust type formed on the patancheru soil by means of parallel subprocesses involving translocation and illuviation of aggregate disruption by products and raindrop compaction and particle rearrangement copyright 1999 john wiley sons ltd

effects of crust and cracks on simulated catchment discharge and soil loss sealing crusting and cracking of crusts of the soil surface has been observed in many parts of the world in areas with sandy silty and loamy soils sealing and crust formation occurs under the influence of rain storm and drying weather with prolonged drying surface crusts might crack leading to complex situations with respect to infiltration and runoff generation cracking of crusted loamy soils appears to be a general process this study aims to measure the hydraulic properties of fully crusted and cracked crusted areas and to evaluate the effects of these measurements on catchment discharge and soil loss in a loess region of the netherlands using the lisem soil erosion model samples with minimum infiltration rates fully crusted and with maximum infiltration rates cracked crusted surfaces were taken from fields with bare soil or winter wheat and their soil hydraulic functions were measured the results of these measurements were used as input in the lisem soil erosion model simulations of discharge and soil loss were done for each of these two land uses and for two rain events additionally simulated discharge and soil loss under actual recorded land use were calculated in all cases soils with no surface cracks produced higher figures for discharge and soil loss than those where 10 of the surface crust was cracked for a good interpretation of the results for soil loss the spatial distribution of cracked crusted areas and fully crusted areas has to be investigated in detail to deal with cracked crusted and fully crusted areas in simulation modelling care has to be taken to accurately measure the soil physical functions representing the maximum and minimum infiltration rates an assignment of these functions to calculation grids has to be made as the lisem model is capable of assigning different soil physical functions to each calculation grid an improved prediction of the soil physical behaviour of the catchment can be simulated

iron isotope systematics in estuaries the case of north river massachusetts usa abstract recent studies have suggested that rivers may present an isotopically light fe source to the oceans since the input of dissolved iron from river water is generally controlled by flocculation processes that occur during estuarine mixing it is important to investigate potential fractionation of fe isotopes during this process in this study we investigate the influence of the flocculation of fe rich colloids on the iron isotope composition of pristine estuarine waters and suspended particles the samples were collected along a salinity gradient from the fresh water to the ocean in the north river estuary ma usa estuarine samples were filtered at 0 22 m and the iron isotope composition of the two fractions dissolved and particles were analyzed using high resolution mc icp ms after chemical purification dissolved iron results show positive 56 fe values with an average of 0 43 0 04 relative to the irmm 14 standard and do not display any relationships with salinity or with percentage of colloid flocculation the iron isotopic composition of the particles suspended in fresh water is characterized by more negative 56 fe values than for dissolved fe and correlate with the percentage of fe flocculation particulate 56 fe values vary from 0 09 at no flocculation to 0 1 at the flocculation maximum which reflect mixing effects between river borne particles lithogenic particles derived from coastal seawaters and newly precipitated colloids since the process of flocculation produces minimal fe isotope fractionation in the dissolved fe pool we suggest that the pristine iron isotope composition of fresh water is preserved during estuarine mixing and that the value of the global riverine source into the ocean can be identified from the fresh water values however this study also suggests that 56 fe composition of rivers can also be characterized by more positive 56 fe values up to 0 3 relative to the crust than previously reported in order to improve our current understanding of the oceanic iron isotope cycling further work is now required to determine the processes controlling the fractionation of fe isotopes during continental run off

microgeometrical characterisation and percolation threshold evolution of a soil crust under rainfall abstract an experiment has been carried out in order to both measure the unsaturated hydraulic conductivity of a soil crust when it is developing and to characterize its macro and microstructural evolution five stages of a structural crust developing in a loamy clay soil have been identified mercury intrusion experiments and micromorphological descriptions have provided information on the structural evolution of the crust at the microscale quantitative image analysis from images of the crust microstructure has led to the definition of a particle erosion index at the microscopic scale which is the mean chord length calculated in the solid phase this index decreases from 60 to 11 m during the whole experiment the lowest value being recorded at the fourth stage specific measurements of the percolation threshold in the soil crust at different stages during its formation have given quantitative data to interpret the modifications of the unsaturated hydraulic conductivity of this crust when it develops the percolation threshold decreases from 130 m at the second stage down to 40 m at the fifth stage between the same stages the unsaturated hydraulic conductivity at 5 kpa decreases from 12 2 to 4 7 cm h both the structural information given by the chord size distribution and the functional information obtained from the percolation threshold can be related to propose a new model of soil crusting

interrill erosion of carbon and phosphorus from conventionally and organically farmed devon silt soils abstract globally between 0 57 and 1 33 pg of soil organic carbon soc may be affected by interrill processes also a significant amount of phosphorus p is contained in the surface soil layer transformed by raindrop impact runoff and crust formation in the eu the p content of a crusted 2 mm surface layer corresponds to 4 to 40 kg ha 1 of p on arable land 1 094 mil km2 therefore the role of interrill processes for nutrient cycling and the global carbon cycle requires close attention interrill erosion is a complex phenomenon involving the detachment transport and deposition of soil particles by raindrop impacted flow resistance to interrill erosion varies between soils depending on their physical chemical and mineralogical properties in addition significant changes in soil resistance to interrill erosion occur during storms as a result of changes in surface roughness cohesion and particle size as a consequence erosion on interrill areas is selective moving the most easily detached small and or light soil particles this leads to the enrichment of clay phosphorous p and carbon c such enrichment in interrill sediment is well documented however the role of interrill erosion processes on the enrichment remains unclear enrichment of p and c in interrill sediment is attributed to the preferential erosion of the smaller lighter soil particles in this study the p and organic c content of sediment generated from two devon silts under conventional cs and organic os soil management were examined artificial rainfall was applied to the soils using two rainfall scenarios of differing intensity and kinetic energy to determine the effects on the p and c enrichment in interrill sediment interrill soil erodibility was lower on the os irrespective of rainfall intensity sediment from both soils showed a significant enrichment in p and c compared to the bulk soil however sediment from the os displayed a much greater degree of p enrichment this shows that the net p export from organically farmed soils is not reduced by a similar degree than soil erosion compared to conventional soil management the enrichment of p and c in the interrill sediment was not directly related to soc p content of the soil and soil interrill erodibility a comparison of soil and sediment properties indicates that crusting p and c content as well as density and size of eroded aggregate fragments control p and c enrichment due to complex and dynamic interactions between p soc and interrill erosional processes the nutrient and c status of sediments cannot be predicted based on soil p content soc or interrill erodibility alone clearly further research on crust formation and the composition of fragments generated by aggregate breakdown and their transport in raindrop impacted flow under different rainfall conditions is required attaining this critical missing knowledge would enable a comprehensive assessment of the benefits of organic farming on nutrient budgets off site effects of interrill erosion and its role in the global c cycle

physical characterization spectral response and remotely sensed mapping of mediterranean soil surface crusts abstract soil surface crusting and sealing are frequent but unfavorable processes in mediterranean areas soil crust and seals form on bare soil subject to high intensity rainfall resulting in a hard impenetrable layer that impedes infiltration and hampers the germination and establishment of plants the adverse consequences of overland flow and reduced fertility can lead to erosion and ongoing degradation therefore information on the distribution of surface crusts and their physical properties is essential to combat the undesired effects of crust formation in e g soil erosion and soil compaction we studied the occurrence of crusts in a study area in mediterranean southern france our objectives were to compare the physical and hydrological properties of the crusts and underlying soil to identify the spectral characteristics 400 to 2500 nm of the crusted and non crusted soil surfaces using high resolution field spectra and to investigate the potential of mapping crust occurrence using airborne hyperspectral hymap images the differences in some physical properties between crusted and non crusted surfaces are significant while others are only marginal crusting markedly reduces the infiltration capacity and crust strength varies between the different soil types spectral differences are small mainly in albedo values overall reflectance and in absorption band depth and shape albedo differences range from 8 to 40 differences in absorption band features in the spectra of crusts and non crusted surfaces are small sixty percent of the crusted soil surfaces showed stronger absorption features in the clay mineral absorption bands at 2200 nm than non crusted soils increased absorption is due to a relative enrichment in fines spectral feature fitting and linear spectral unmixing algorithms were applied to airborne hymap images to evaluate the possibilities of mapping surface crusts crusts could be mapped in fallow agricultural fields but the spectral response of natural badlands was too fragmented for crust mapping

influence of rock fragment coverage on soil erosion and hydrological response laboratory flume experiments and modeling two laboratory flume experiments on the effect of surface rock fragments on precipitation driven soil erosion yields were carried out the total sediment concentration the concentration of seven individual size classes and the flow discharge were measured digital terrain models dtms were generated before and after one of the experiments the results revealed that the rock fragments protected the soils from raindrop detachment and retarded the overland flow therefore decreasing its sediment transport capacity rock fragments were found to affect selectively the different size classes in a manner that changed according to the time scale for short times the rock fragment coverage reduced erosion of the finer particles 100 m was unaffected at long times the rock fragment cover decreased the concentration of the individual size classes in proportion to effective rainfall intensity and the area exposed to raindrops an area based modification of the hairsine and rose h r soil erosion model was employed to analyze the experimental data the h r model predictions agreed well with the measured sediment concentrations when high rainfall intensity and low rock fragment cover were used predictions were instead less accurate with low rainfall intensity and high rock fragment cover the dtm results showed that the presence of rock fragments on the soil surface led to increased soil compaction perhaps due to higher soil moisture content from greater infiltration within the rock fragment covered flumes

the influence of groundwater on surface flow erosion processes during a rainstorm surface erosion rates on a disturbed natural soil in a 10 m indoor flume increased by an order of magnitude when a water table developed at a 10 cm depth during simulated rainstorms erosion rate increases did not correlate well with surface hydraulic flow conditions and all significant erosion increases began before the full soil depth was saturated before the water table reached the soil surface and before seepage was possible groundwater influenced erosion processes primarily by increasing unsaturated pore water pressures and decreasing soil shear strength in surface rainflow rather than through the direct entrainment of soil particles by seepage flow there was no unique morphologic expression of the influence of groundwater during a rainstorm subsurface processes influencing surface erosion were detected only by appropriate subsurface instrumentation which included micropiezometers tensiometers and time domain reflectometry erosion rate increases occurred all along the slope and were not concentrated at the base of slope due to a seepage zone soil depth was crucial to determining surface erosion increase it is likely that confusing trends in surface flow erosion rates in past studies have occurred due to unrecorded groundwater development or an emphasis on seepage effects groundwater must be monitored along hillslopes under all moisture and soil conditions in order to avoid misleading and inconsistent conclusions derived solely from surface flow or seepage data copyright 2002 john wiley sons ltd

effect of microrelief on water erosion and their changes during rainfall soil surface roughness contains two elementary forms depressions and mounds which affect water flow on the surface differently while depressions serve as temporary water storage mounds divert water away from their local summits although roughness impacts on runoff and sediment production have been studied almost no studies have been designed explicitly to quantify the evolution of depressions and mounds and how this impacts runoff generation and sediment delivery the objectives of this study were to analyze how different surface forms affect runoff and sediment delivery and to measure the changes in surface depressions and mounds during rainfall events a smooth surface was used as the control both mounds and depressions delayed the runoff initiating time but to differing degrees and slightly reduced surface runoff when compared to the runoff process from the smooth surface surface mounds significantly increased sediment delivery whilst depressions provided surface storage and hence reduced sediment delivery however as rainfall continued and rainfall intensity increased the depression effect on runoff and erosion gradually decreased and produced even higher sediment delivery than the smooth surface depressions and mounds also impacted the particle size distribution of the discharged sediments many more sand sized particles were transported from the surface with mounds than with depressions the morphology of mounds and depressions changed significantly due to rainfall but to different extents the difference in change had a spatial scale effect i e erosion from each mound contributed to its own morphological change while sediments deposited in a depression came from a runoff contributing area above the depression hence a much greater source area than a single mound the results provide a mechanistic understanding of how soil roughness affects runoff and sediment production copyright 2015 john wiley sons ltd

permanence of soil surface crusts on abandoned farmland in the central ebro basin spain abstract surface crusts are frequently found on fallow land in the semi arid ebro basin spain and are an important factor in land degradation soil surface sealing leads to a decrease in infiltration rates and a consequent increase in runoff thereby accelerating sheet wash and rill erosion thin sections were used to analyse the development and structures of the different crusts found across the ridge furrow field pattern rainfall simulations experiments and infiltration measurements show the runoff generation and the soil erosion rates on the crusts the spatial distribution of crusts was documented using large scale aerial photographs taken from a remote controlled hot air blimp splash and slaking cause structural crusts to form on the ridges while eroded material leads to a build up of sedimentary crusts in the furrows a platy structure as well as vesicles then develop in these crusts depending on the amount of time that has elapsed since ploughing and the frequency of wetting and drying cycles alluvial fan crusts develop on material accumulated at the end of erosion rills the increase in the runoff of up to 81 and the decrease in infiltration rate up to 4 6 mm h 1 on surface crusts were quantified

concentrated flow erosion as a main source of sediments in galicia spain knowledge of soil loss rates by water erosion under given climate soil topography and management conditions is important for establishing soil conservation schemes in galicia a region with atlantic climatic conditions in spain field observations over the last decade indicate that interrill rill and ephemeral gully erosion may be an important sediment source the aim of this work was to assess concentrated erosion rates describe types of rills and ephemeral gullies and determine their origin evolution and importance as sediment sources soil surface state and concentrated flow erosion were surveyed on medium textured soils developed over basic schists of the ordenes complex series coruna province spain from 1997 to 2006 soil surface state was characterized by crust development tillage features and roughness degree soil erosion rate was directly measured in the field concentrated flow erosion took place mainly on seedbeds and recently tilled surfaces in late spring and by autumn or early winter during the study period erosion rates were highly variable and the following situations could be distinguished a no incision or limited rill incision i e below 2 mg ha 1 year 1 b generalized rill and ephemeral gully incision in the class of mean values between 2 5 and 6 25 mg ha 1 year 1 this was the most common erosion pattern and c heavy erosion as observed during an extremely wet winter period between october 2000 and february 2001 with erosion figures that may be about ten orders of magnitude higher up to 55 60 mg ha 1 year 1 therefore low values of soil losses are dominant but also large values of rill and ephemeral gully erosion occurred during the study period copyright 2009 john wiley sons ltd

morphology genesis and classification of surface crusts in loamy and sandy soils abstract in an attempt to organize the knowledge of soil crusting processes and to group soil crusts on the basis of common morphological features and physical properties we synthesized and reinterpreted information from previous publications as a result we propose a classification system for surface crusts formed by rainfall in loamy and sandy soils although this system does not aim to be comprehensive it was designed from the study of a great number of crust samples collected in the temperate and tropical zones thus corresponding to a wide range of environmental and land use conditions three main classes of crusts structural erosion and depositional were distinguished each with subclasses where possible correspondence has been made with former systems this system helps predict infiltrability in accounting not only for total porosity of surface crusts but also for pore shape and continuity since crust classes are genetically related this classification system also supplies some insight into predicting soil degradation and selecting the most suitable control techniques

morphological characterization of soil crust development stages on an experimental field abstract crust development on a loamy aquic hapludalf near paris was studied in an experimental field to which various fertilizers and amendments had been applied these treatments over a period of 57 years had induced a range of organic matter contents and exchangeable cation percentages the macroscopic aspects of the soil surface was closely monitored during crusting and microscopic characterization was carried out at every main crust development stage crusting followed a general pattern 1 sealing of the soil surface by a structural crust 2 development of a depositional crust even in the sodic plot where the depositional crust appeared especially early the structural crust developed first the change from the first stage to the second one mainly depended on a decrease in infiltrability due to the structural crust properties that induced micro runoff and puddling under rainfall structural crust development seemed to involve a coalescing process due to raindrop impact when moistening decreased soil cohesion this process developed much faster in the sodic than in the limed plot morphology of the depositional crust in particular microbedding and sorting could be related to the hydrodynamic behaviour of the soil surface abundance size and duration of puddles

distribution morphology and influencing factors of rills under extreme rainfall conditions in main land uses on the loess plateau of china abstract rill erosion is one of the main forms of soil erosion of the hillslopes on the loess plateau of china few studies have evaluated the effects of land use on the distribution and morphology of rills under extreme rainstorms a total of 50 rill survey sites were selected in a typical watershed of the loess plateau of china to investigate the rill distribution and morphology of three land uses fallow land fl slope farmland sf and annual grassland ag under extreme rainstorm conditions called 7 26 rainstorm seven parameters rill width rill depth width depth ratio cross section area rill density degree of rill dissection and rill erosion modulus were used to characterize rill morphology and the basic soil and vegetation properties bulk density particle size distribution and vegetation coverage and topographic factors slope length gradient direction were measured it was found that rills developed on three land uses and those with widths ranging from 5 to 20 cm accounted for 80 rills developed on fl were deeper than those on sf and ag almost all rills on fl had a depth of 5 20 cm 90 3 while the depth of rills on sf and ag were mainly smaller than 15 cm 91 5 and 91 9 respectively in addition to width rill depth and cross section area of sf and ag were also significantly less than those of fl sf and fl had a relatively high width depth ratio and dissection degree however land use had no significant effect on rill density crop plantations sf and grass restoration ag significantly reduced rill erosion modulus 28 70 and 45 07 reduction respectively land use topography soil and vegetation factors significantly affected rill morphology p 0 001 based on redundancy analysis rda and can explain 48 0 of the total variability of rill morphology with slope length vegetation coverage and slope gradient having the greatest influences most of the rill morphological parameters significantly decreased as the vegetation coverage increased but they significantly increased with increasing slope length and slope gradient this study clearly illustrates the severe rill erosion caused by this rainstorm and indirectly indicates that crop harvesting fl aggravates rill erosion and that revegetation ag can effectively contain rill erosion therefore rehabilitation efforts should be focused on revegetation grassland and or woodland on steep slopes to control soil erosion

laboratory methods for the estimation of infiltration rate of soil crusts in the tabernas desert badlands soil crusting is a crucial factor for runoff generation in the tabernas desert badlands however very few methods have been developed for the measurement of infiltration in crusts which are often distributed on steep slopes where experimental devices are very difficult to install making measurement difficult we have used the trickle irrigation ti method and mini disk infiltrometers mdi in the laboratory to measure steady infiltration rate under nearly saturated condition and tensions respectively in soil crust samples removed from the field steady infiltration rate under tensions were performed at three water pressure heads h 0 5 2 0 and 6 0 cm steady infiltration rate of soil crusts in the tabernas desert badlands ranged from 21 3 to 30 7 mm h 1 measured by ti method steady infiltration rate under tensions decreased with increasing tensions it was 9 9 18 4 mm h 1 0 4 5 7 mm h 1 and 0 2 3 3 mm h 1 at 0 5 2 0 and 6 0cm pressure heads respectively steady infiltration rate measured by ti method and that at a tension of 0 5 cm by the mdi is consistent with the results from the previous simulated rainfall studies in the same soil crust surfaces suggesting that the ti and mdi methods may be potentially a useful lab measurement for approximating field infiltration rate d 2004 elsevier b v all rights reserved

characteristics of soil infiltration in the tarim river floodplain the ecology in the tarim river basin is influenced by inundation of its floodplain to date however there is limited information about the infiltration properties of floodplain soils that are inundated by this river the aim of this study was to investigate steady infiltration rates of these soils under four different hydraulic heads 5 10 20 and 30 cm results showed that the mean infiltration rates were generally high and ranged from 3 17 to 3 50 cm h 1 when the hydraulic head was between 5 and 30 cm the steady infiltration increased slightly as the hydraulic head increased the relationship between the hydraulic head and the infiltration rate can be described by the equation y 0 0122x 3 072 r2 0 739 where y is the steady infiltration rate and x is the hydraulic head there was no significant difference between the infiltration rates for the four different hydraulic heads the infiltration rate was highest for loamy sand followed by sandy loam and was lowest for silt soils infiltration was influenced by soil texture and crust and was low 1 cm h 1 hydraulic head of 5 cm for soils with thick crusts and high for soils without surface crusts mean of 6 09 cm h 1 hydraulic head of 5 cm the steady infiltration rate was not influenced by soil organic matter these results indicate that flood water can percolate into the floodplain soils and give an improved understanding of the factors that influence the ecological processes on the tarim river floodplains

the effect of slope gradient and length on the parameters of a sediment transport equation for sheetwash abstract sheetwash sediment transport q s is often expressed by q s kq m s n where s is slope gradient and q water discharge for practical reasons the length rainfall intensity product li is often used in this equation as a surrogate for discharge the estimation of the exponents m and n is biased whenever complex hillslope shapes are used and when water discharge is not linearly related to li an experiment was designed to simultaneously measure water and sediment discharges on short straight hillslopes of similar material sloping at 5 11 and 27 natural rainfalls were used throughout this study the values obtained for the exponents m and n using all the available measurements are 1 5 and 0 9 respectively the value of m lies between the boundaries proposed in literature and the exponent n is slightly under the lower limit this experiment showed that water discharge is not linearly related to the length rainfall intensity product and that the value of m calibrated with q increases with slope gradient this result is explained by the return flow occuring at the base of steeper slopes and by the contribution of rainsplash to particle detachment consequently three points will be discussed in detail i the relevancy of using li rather than q to estimate m and n or to facilitate measurement and mainipulation in hillslope simulation models ii the implications on erosion processes and simulation of hillslope evolution of the systematic effect of gradient on water and sediment discharges and iii the problem of scale in the calibration of sediment transport equations

application of image based granulometry to siliceous and calcareous estuarine and marine sediments abstract grain size analysis has long been used as a descriptor of transport and depositional processes this paper presents the possibility of using image based granulometries not yet widely used in the earth sciences to characterize granulometric composition of unconsolidated estuarine and marine sediments to test the method conventional sediment analysis of siliceous and calcareous sediments are compared to image based analysis of sediments obtained along the ore estuary northern sweden and the adriatic sea croatia and italy these grains have different textural characteristics composition roundness and specific surface area granulometric parameters are calculated using both a graphical method and the mathematical method of moments grains have been imaged using a microscope and mathematical granulometries have been applied to the digital data image based granulometric moment descriptors are compared with sieve coulter counter derived moments although it is not claimed that digital imaging should be the only method used in sedimentology the results show the potential of applying digital electronic imaging to granulometric analysis of sediments in this way sampling for granulometric analysis and sieving processes combined with coulter counter analysis of fraction