impact of subsurface rock fragments on runoff and interrill soil loss from cultivated soils field and laboratory studies have indicated that rock fragments in the topsoil may have a large impact on soil properties soil quality hydraulic hydrological and erosion processes in most studies the investigated rock fragments still remain visible at the soil surface and only properties of these visible rock fragments are used for predicting runoff and soil loss however there are indications that rock fragments completely incorporated in the topsoil could also significantly influence the percolation and water distribution in stony soils and therefore also infiltration runoff and soil loss rates therefore in this study interrill laboratory experiments with simulated rainfall during 60 min were conducted to assess the influence of subsurface rock fragments incorporated in a disturbed silt loam soil at different depths below the soil surface i e 0 001 0 01 0 05 and 0 10 m on infiltration surface runoff and interrill erosion processes for small and large rock fragment sizes i e mean largest diameter equals 0 04 and 0 20 m respectively although only small differences in infiltration rate and runoff volume are observed between the soil without rock fragments control and the one with subsurface rock fragments considerable differences in total interrill soil loss are observed between the control treatment and both contrasting rock fragments sizes this is explained by a rapid increase in soil moisture in the areas above the rock fragments and

unsaturated hydraulic conductivity in limestone dolines influence of vegetation and rock fragments abstract vegetation and rock fragments have a profound impact on runoff generation in the dolines of the sierra de gador southeastern spain this study investigated the effect of vegetation and rock fragments on unsaturated hydraulic conductivity k h in three limestone dolines and examined whether variation in k h was consistent with differences in runoff from simulated rainfall tension infiltrometers were used to measure unsaturated hydraulic conductivity at three pressure heads h of 30 60 and 120 mm at 70 locations within the three dolines generally the trends of the k h were consistent with the simulated rainfall data and accounted for difference in runoff for the vegetated surfaces vegetation resulted in high infiltration with unsaturated hydraulic conductivities at 30 and 60 mm are significantly greater for the vegetated surface than for the rock fragment covered surface and bare soil surface rock fragments had no obvious effect on soil hydraulic conductivity as compared with bare soils the k h of the non crusted soil were 2 5 times higher than that of the crusted soil the k h decreased with increasing tensions k 60 and k 120 were only 8 4 and 0 89 respectively of k 30 for the vegetated surfaces and were about 30 and 8 7 respectively of k 30 for both rock fragment covered surfaces and bare soils suggesting that pores in the 0 5 to 1 mm diameter range dominate flow under unsaturated conditions there were significant differences in k h among the different topographic units of the dolines and k h tended to be higher in the upper position than in the lower position of the doline

sensitivity analysis of eurosem using monte carlo simulation ii the effect of rills and rock fragments a sensitivity analysis of the surface and catchment characteristics in the european soil erosion model eurosem was carried out with special emphasis on rills and rock fragment cover the analysis focused on the use of monte carlo simulation but was supplemented by a simple sensitivity analysis where input variables were increased and decreased by 10 the study showed that rock fragments have a significant effect upon the static output parameters of total runoff peak flow rate total soil loss and peak sediment discharge but with a high coefficient of variation the same applied to the average hydrographs and sedigraphs although the peak of the graphs was associated with a low coefficient of variation on average however the model was able to simulate the effect of rock fragment cover quite well the sensitivity analysis through the monte carlo simulation showed that the model is particularly sensitive to changes in parameters describing rills and the length of the plane when no rock fragments are simulated but that the model also is sensitive to changes in the fraction of non erodible material and interrill slope when rock fragments were embedded in the topsoil for rock fragments resting on the surface changes in parameter values did not affect model output significantly the simple sensitivity analysis supported the findings from the monte carlo simulation and illustrates the importance when choosing input parameters to describe both rills and rock fragment cover when modelling with eurosem

the effect of rock content on nutrients in a sierra nevada forest soil abstract the effects of rock content on nutrient concentrations and contents kg ha 1 in a skeletal soil derived from andesite were investigated rock content to a 60 cm depth ranged from 8 to 69 among 20 quantitative soil pits within a 10 ha area on average rocks contained 9 of total soil c 19 of total soil n 3 of total ecosystem c and 12 of total ecosystem n percent rock content also appeared to cause increases in organic matter concentrations rock content was significantly positively correlated with total c and total n concentrations in the fine earth 2 mm fraction soil c was organic no carbonates were present percent rock content was also significantly positively correlated with fine earth c n ratio suggesting that organic matter in rockier soils was in an earlier stage of decomposition at any given depth other consistent correlations with rock content included bray p positive and exchangeable mg 2 negative the decrease in fine earth mass with increasing percent rock content offsets the increase in c concentration such that there was no correlation between percent rock content and either fine earth or total soil fine earth plus rock c content kg ha 1 percent rock content was significantly negatively correlated with total n bray p inorganic n exchangeable k ca 2 and mg 2 contents however the results of this study show that high rock content can affect soil c and nutrient pools not only because of the contributions of the rocks themselves but also because high rock content appears to cause higher concentrations in the fine earth fraction

cracks in desert pavement rocks further insights into mechanical weathering by directional insolation the formation of cracks is a fundamental first step in the physical weathering of rocks in desert environments in this study we combine new field data from the mojave u s gobi mongolia and strzelecki australia deserts that collectively support the hypothesis that meridional cracks cracks with orientations not readily attributable to rock anisotropies or shape in boulders or cobbles form due to tensile stresses caused by directional heating and cooling during the sun s daily transit the new studies indicate that rock size surface age and latitude play important roles with respect to their influence on rock fracture rock size and pavement surface age exert an influence on the development of rock cracks as the average clast size of mature desert pavements may be at or below the threshold clast size for thermal cracking of rocks latitude controlled seasonal temperature variations play a key role as demonstrated by 1 tightly clustered mean resultant orientations that differ by latitude as predicted in mcfadden et al 2005 and 2 very cold wintertime temperatures and strong diurnal gradients that may favor crack development in wintertime given the likelihood for strong clast heating during early morning hours the consistent evidence for meridional cracks in surfaces of diverse age and desert environments climate vegetation and distance of clast transport indicate that directional insolation may play the key role in initially generating and propagating rock fractures rather than a secondary role as implied in recent field and modeling studies of physical weathering in deserts

quantitative assessment of the piping erosion susceptibility of loess derived soil horizons using the pinhole test abstract the pinhole test is an empirical test based on the qualitative evaluation of the dispersivity colloidal erodibility of compacted fined grained soils this paper evaluates the pinhole test device for the quantitative assessment of the susceptibility of soil horizons to piping assesses the effects of hydraulic head water quality antecedent soil moisture content and soil disturbance on the hydrological and erosion response during pipeflow and formulates recommendations for the application of the pinhole test to study piping erosion processes in total 255 pinhole test experiments were conducted the results obtained from disturbed soil samples ap horizon indicate i a significant positive linear increase in pipeflow discharge qw and sediment discharge qs with increasing hydraulic head ii no relationship between qw and antecedent soil moisture content asm but significant and negative relationship between qs and asm and iii significantly higher qs for distilled water than for tap water the use of disturbed soil samples resulted in significantly more rapid flow responses and lower sediment discharges than for undisturbed soil samples the pinhole test experiments performed on different loess derived soil horizons show that the plowed topsoil ap and the underlying clay enriched horizon bt are at least two times less susceptible to piping than the decalcified c1 and the calcareous horizons c2 this confirms field observations indicating that loess derived soil horizons are very susceptible for piping erosion especially when the c horizon crops out this study demonstrates that the pinhole test is suitable for assessing the susceptibility of soil horizons to piping in a quantitative way i e qw qs the time to outflow and the cross section of the pipe after the test we recommend the use of i two different hydraulic heads i e 180 and 1020 mm ii distilled water iii contrasting antecedent soil moisture contents of the soil samples to be tested and iv different soil sampling methods to investigate the effect of soil disturbance and particularly to obtain a better understanding of the sediment response during pipeflow

a reduced relevance of vegetation change for alluvial aggradation in arid zones a basic tenet of arid region geomorphology is that a decrease in hillslope vegetation density coupled with increases in monsoonal precipitation after a change to a warmer and drier climate is an essential factor for an increase in sediment yield and fan aggradation over the last two decades vegetative cover change is increasingly cited as a prominent factor in triggering the onset of fan aggradation in deserts of southwestern north america especially in analysis of fan deposition during the late pleistocene holocene lph climatic transition to assess this assertion we compiled paleobotanical and alluvial fan stratigraphy histories from 18 published studies broadly representing four different areas in the mojave and northern sonoran deserts instead of focusing on chronology aggregation and comparison with global or regional climate change proxies forced by orbital parameters we discriminated by altitudinal regions looking for linkages between local vegetation change and alluvial deposition results indicate that the onset of extensive alluvial fan deposition 1 began well before changes in catchment vegetative cover and 2 can occur during several possible combinations of vegetation change the ambiguous relation between vegetation change and alluvial fan aggradation indicates that vegetation had a reduced role in lph aggradation other factors such as local storm intensity and water and sediment redistribution pathways on hillslopes need to be considered in this analysis given the important role that the combined hillslope alluvial system has on arid region ecosystem functions

soil containing rock fragments effects on infiltration abstract infiltration is a very complex process rock fragments affect infiltration by their presence in the soil matrix and on the soil surface procedures for quantifying soil and surface rock fragments are reviewed within the soil the physical properties and hydraulic properties that affect infiltration are shown to be influenced by rock fragments physical properties discussed are bulk density porosity and water content hydraulic properties that affect infiltration are water retention saturated conductivity and unsaturated conductivity rock fragments on the soil surface have been reported to both increase or decrease infiltration rates and amounts

spatial variability of infiltration in a semi arid environment abstract fifty two double ring infiltrometer tests performed in a small partly urbanized catchment in northern tunisia are analyzed spatial variability is characterized by use of cross correlation functions spatial patterns of infiltration properties are shown to be governed by geomorphology and occurring vegetation different geomorphological zones and zones with equal density of vegetation tend to be oriented in a parallel pattern in relation to the wadi statistical properties of infiltration capacities depending on geomorphological zone are presented

effects of vegetation change on interrill runoff and erosion walnut gulch southern arizona during the past 100 years grassland has been replaced by shrubland in many parts of the american southwest the effects of this vegetation change on interrill runoff and erosion are investigated by performing field experiments on small and large runoff plots located on contemporary grassland and shrubland hillslopes in walnut gulch experimental watershed the experiments indicate that the vegetation change causes runoff and erosion to increase in interrill areas by decreasing resistance to overland flow decreasing runon infiltration increasing the spatial heterogeneity of the plant canopy and possibly increasing the susceptibility of the soil to frost action increased runoff and erosion result in stripping of the soil a horizon the formation of desert pavement in intershrub areas and the development of rills fines remain and accumulate only under shrubs where they form islands of fertility shrubs are able to regenerate in these islands but it is difficult for any plants to become established in intershrub areas consequently there is an increase in the spatial heterogeneity of soil resources and this spatial heterogeneity is self perpetuating increasing spatial heterogeneity of soil resources is considered to be characteristic of the process of desertification

millimeter scale microrelief affecting runoff yield over microbiotic crust in the negev desert abstract the negative effect of microrelief upon runoff yield explained by the increase in water storage and the slowdown in flow velocity is a known phenomenon however research concerning surface roughness hitherto focused on decimeter or centimeter scale microrelief owing to the heterogeneous character of many natural plots the effect of centimeter scale microrelief was mainly shown under controlled sprinkling experiments whereas no data was yet made available concerning the possible effect of a millimeter scale microrelief upon runoff yield under natural field conditions when runoff yield was measured over crusted i e surfaces covered by 1 3 mm of cyanobacterial crust and scalped 2 6 m 2 plots at the hallamish dune field negev desert israel during 5 winter seasons 1990 1995 no runoff was generated from the scalped plots during the first year following scalping while meagre quantities were received during the second year nevertheless during the third season and onward runoff yield at the scalped plots was consistently and significantly higher than that of the crusted control plots and this was so albeit the fact that the crust chlorophyll content of the scalped plots during the third season was as low as half the amount of the crusted plots these findings appeared to contradict previous findings that showed the existence of a positive linear relationship between the crust chlorophyll content and runoff yield the apparent contradiction was explained by the differences in the plot microrelief indicating that minute differences even of a millimeter scale may greatly affect runoff yield and thus may compensate for lower crust chlorophyll content surface smoothness which characterizes many of the arid zones may thus explain at least partially the high runoff yield obtained in deserts

cryptomelane a tool to determine the age and the physical chemical regime of a plio pleistocene weathering zone in a granitic terrain hagendorf se germany abstract cryptomelane a k mn bearing oxide is widespread in the lowermost part of the weathering supergene alteration zone of the hagendorf pegmatite se germany this supergene mn mineral has been used in the present study for k ar dating of weathering and paleohydraulic processes as young as plio pleistocene different cryptomelane age data found in the same weathering and paleohydraulic system resulted from continuous hydraulic processes in the weathering system rather than from a stepwise uplift that shaped the landscape in the granitic area of the ne bavarian basement an almost pure cryptomelane mineralization is indicative of the basal zone of supergene alteration because a complete separation of mn from fe can favorably be achieved only in the infiltration zone under slightly reducing conditions or in the percolation zone under slightly oxidizing conditions cryptomelane is precipitated under slightly oxidizing conditions from alkaline solutions in the percolation zone and cast as a marker for fluctuating paleo water levels manganese oxides uranyl phosphates and silicates were found at different depths in the weathering zone of this granitic terrain they were dated by different dating methods k ar and u pb and yielded the same age of formation consequently the 4 ma signal of both groups of supergene minerals has geomorphological and paleohydraulic connotation and is related to a unique geomorphological process the pliocene peneplanation gradual hydraulic adjustments gave rise to the younger pleistocene age found at shallow depth in the weathering zone

runoff and sediment yield from topsoils with different porosity as affected by rock fragment cover and position abstract interrill runoff and sediment yield from a topsoil having essentially textural pores and from another with structural pores were measured in the laboratory under simulated rain to investigate the effects of cover and positions of rock fragments the results reveal that the relation between the cover of rock fragments and interrill runoff or sediment yield can be negative as well as positive porosity in the soil near rock fragments determines both the type of relation and the degree to which the positions of rock fragments affect this relation rock fragments increase runoff and sediment yield when well embedded in a surface seal i e a top layer with essentially textural pore spaces a negative relation occurs either where rock fragments are partly embedded in a top layer with structural porosity or where the rock fragments rest on the surface of a soil having either textural or structural pore spaces the time at which macropores at the soil surface close is crucial for then the effect of the cover of rock fragments on the generation of runoff switches from reduction to an increase since cover can have an ambivalent effect on the hydrological and erosion response descriptions of topsoils containing rock fragments should include the type of soil porosity as well as the positions of rock fragments

effects of soil surface components on soil hydrological behaviour in a dry mediterranean environment southern spain abstract various researchers have studied the spatial pattern of soil surface components such as vegetation rock fragments bare soil litter and surface crusts as a key factor of hydrological behaviour in mediterranean settings with heterogeneous patches of vegetation cover and strong human impact the studies indicate that there is a mosaic of patches that generate run off or infiltrate overland flow distributed in various ways along hillslopes few of these studies however have looked at areas underlain by metamorphic rocks such as phyllites or schists this study analysed the temporal and spatial variability of the effects of soil surface components on hydrological processes in a small dry mediterranean catchment underlain by metamorphic rocks a systematic sampling of multiple sites throughout a hydrological year was carried out we related the hydrological behaviour of soil surface components to 1 their position along the hillslope 2 the distance of existing vegetation tussocks from the line of run off 3 rainfall intensity and 4 the main physical chemical soil properties affecting infiltration processes statistical analysis was used to check the validity of the relationships the results show that soil surface components have highly variable effects in both space and time on soil hydrological behaviour these effects particularly depend on the location along the line of maximum slope and the intensity of preceding rainfall whose interaction defines soil hydrological status these results are similar to those for other mediterranean settings with different lithology in that the succession of contributing patches are hydrologically interconnected along a hillslope the variables used and the grouping of explanatory variables through principal component analyses were found to be suitable for discussing the spatial distribution of soil surface components in the hydrologically dynamic environment of the study area

hydraulics of interrill overland flow on stone covered desert surfaces the hydraulics of interrill overland flow on stone covered desert surfaces depend on the resistance to flow which may be partitioned into grain resistance form resistance wave resistance and rain resistance efforts to model large scale roughness in open channels suggest that resistance to overland flow on such surfaces is a function of grain reynolds number froude number flow depth and the size shape spacing and pattern of the roughness elements the effect of flow depth on flow resistance f is often hidden in the flow reynolds number re in laboratory and field studies alike f re relations have been found to be convex upward and negatively sloping and these shapes have been explained in terms of the progressive inundation of the roughness elements where laboratory or field based models have been developed for predicting f they invariably contain percent stone cover the prominence of this variable reflects the strong influence of stone size and spacing on flow resistance a laboratory study shows that where the froude number f 0 50 wave resistance increases with stone cover and dominates resistance to flow on all surfaces with stone covers greater than 10 a field study indicates that where f 0 50 and wave resistance is inconsequential grain and form resistance typically account for about 5 and 95 of f respectively these findings have important implications for sediment transport modeling because percent grain resistance is equal to percent grain shear stress and it has recently been suggested that in overland flow as in river flow sediment transport capacity is determined by grain shear stress rather than total shear stress a laboratory study however demonstrates that this is not the case sediment transport capacity is in fact greater than predicted by grain shear stress because energy dissipated in the wakes of roughness elements in overland flow is transformed into turbulence sufficiently close to the bed to affect sediment transport

analysis of soil surface component patterns affecting runoff generation an example of methods applied to mediterranean hillslopes in alicante spain abstract spatial patterns of soil surface components vegetation rock fragments crusts bedrock outcrops etc are a key factor determining hydrological functioning of hillslopes a methodological approach to analyse the patterns of soil surface components at a detailed scale is proposed in this paper the methods proposed are applied to two contrasting semi arid mediterranean hillslopes and the influence of soil surface component patterns on the runoff response of the slopes was analysed a soil surface components map was derived from a high resolution photo mosaic obtained in the field by means of a digital camera rainfall simulation experimental data were used to characterise the hydrological behaviour of areas with a specific pattern of soil surface components by means of the parameters of the horton equation plot runoff data were extrapolated at the hillslope scale based on the soil surface component maps and their hydrological characterisation the results show that in both slopes runoff generation is concentrated up and downslope with a water accepting area in the centre of both slopes disrupting the hydrological connectivity at the slope scale this reinfiltration patch at the centre of the slope is related to the type of soil surface component and its spatial pattern herbaceous vegetation and on top rock fragments increase the infiltration capacity of soils at the centre of the slope in contrast embedded rock fragments rock outcrops as well as crusted surfaces located in the upper and lower slopes favour runoff generation in these areas in addition a general pattern of water contribution areas downslope is apparent on both slopes the south facing slope shows a higher hydrological connectivity and more runoff 55 of the surface of the south facing slope produces runoff at the end of a 1 hour rainfall event and 17 3 of the surface is covered by a runoff depth between 0 5 and 1 mm while on the north facing slope only 38 of the surface produces runoff under the same conditions longitudinal connectivity of runoff is higher at the south facing slope where more runoff generating surfaces appear and where the vegetation pattern favours the connectivity of bare areas

soil hydraulic properties on the steep karst hillslopes in northwest guangxi china soil hydraulic properties such as soil infiltration rate and hydraulic conductivity are closely linked to runoff generation and infiltration processes but little is known about them on karst hillslopes the objectives of this paper were to investigate the change in soil stable infiltration rate q s and near saturated hydraulic conductivity k ns in different slope positions and to understand their relationship with rock fragment content and soil texture within the topsoil in subtropical karst regions of southwest china tension infiltrometers 20 cm in diameter were used to measure q s and k ns at pressure head of 20 mm on hillslopes 1 a disintegrated landslide failure and 2 an avalanche slope the change of q s and k ns was great and they mostly had a moderate variability with coefficient of variations cv between 0 1 and 1 0 in the different slope positions on average q s ranged from 0 43 to 4 25 mm min and k ns varied from 0 75 to 11 00 mm min these rates exceed those of most natural rainfall events confirming that overland flow is rare on karst hillslopes from bottom to top q s and k ns had a decrease increase decrease trend due to the presence of large rock outcrops 2 m in height on hillslope 1 but had an increasing trend on hillslope 2 with less complex landform they tended to increase with increase in total rock fragment content 5 250 mm within the topsoil as well as slope gradient on both hillslopes pearson correlation analysis suggested that higher coarse pebble 20 75 mm cobble 75 250 mm and sand 2 0 05 mm contents as well as total rock fragment content could significantly facilitate water infiltration into soils but higher clay 0 002 mm content could restrict water movement this result indicated that rock fragment sand and clay contents may remarkably affect water flow in the topsoil layers and should be considered in hydrological modeling on karst hillslopes in subtropical regions

surface control of desert pavement pedologic process and landscape function cima volcanic field mojave desert california desert pavement is a distinctive feature widespread across arid lands of the world it plays a dynamic role in geomorphic hydrologic and ecologic processes where desert pavement predominates infiltration is limited and rainfall is delivered as runoff to nearby bare ground areas where shrubs cluster desert pavement surfaces may appear monotonously flat and barren but we have found instead that they are a complex association of landscape and hydrologic elements governed by their surface characteristics previously we identified six unique surface mosaic types that accurately capture the subtle but distinct variations in surface clast arrangements for a desert pavement landscape formed on a single aged basalt flow in the mojave desert we now report that these surface mosaics predict the spatial distribution of fundamental desert vegetation and soil characteristics characteristics of soil morphology and texture the leaching depth of soluble salts percent plant cover and shrub species diversity are remarkably consistent for each mosaic type across a 580 000 year old basalt flow even when measured 1 km apart hydrologic character is distinctly different between desert pavement and bare ground regions and vegetation distributions reflect the spatially heterogeneous soil moisture where desert shrubs cluster on the three bare ground surface mosaics leaching is deep removing most soluble salts to below the 50 cm depth where shrubs are absent or few on the three desert pavement mosaics leaching depths are shallow with soluble salt depth

linking environmental regimes space and time interpretations of structural and functional connectivity connectivity as a concept has been increasingly part of discussions or explanations in hydrology geomorphology and ecology we address recent critiques of this approach by demonstrating how a refinement which distinguishes structural connectivity from functional connectivity can be used to explain patterns observed in very different environmental systems these systems are found in linkages between surface and subsurface flowpaths and the hyporheos in the river don a temperate river channel in yorkshire uk in surface and subsurface fluxes in agricultural land in the uk and in vegetation and surface conditions in a degrading environment at the sevilleta lter site in the semi arid southwest usa first we demonstrate long term geological and structural controls mediated by in channel processes second human organization of landscape elements is a significant control on runoff and erosion so that similar events can produce very different responses and vice versa third linkages between the removal of grass vegetation and runoff and erosion produce non linear and path dependent feedbacks which control the subsequent degradation of the landscape making the process difficult to reverse as a result of these studies we argue that even in cases where connectivity cannot be directly quantified at least at present this limitation does not prevent the concept from being a useful heuristic device for exploring responses of complex systems furthermore this result implies that an increasing need exists for disciplinary connectivity to investigate such systems

the effect of rock fragment size and position on topsoil moisture on arid and semi arid hillslopes abstract rock fragments on arid hillslopes affect rainwater redistribution and overland flow through various hydrological processes the present study focuses on the evolution of topsoil moisture content under rock fragments following rain events measurement was taken under rock fragments in various sizes large and small and positions on top of the soil surface and partially embedded within the soil surface at north and south facing hillslopes in arid and semi arid areas the main findings 1 the topsoil moisture content under rock fragments was higher over time than that of bare soil areas 2 rock fragments affect the topsoil moisture content for a longer time in semi arid areas than in arid areas and 3 large rock fragments and partially embedded ones are favorable micro environments for accepting and retaining rainwater and overland flowing water this may have eco geomorphic implications regarding the mosaic like patterns of source and sink areas on arid hillslopes

runoff generation from successive simulated rainfalls on a rocky semi arid mediterranean hillslope runoff generation in a mediterranean carbonate rock environment the judaean mountains west bank and israel was studied by a 2 day sprinkling experiment on an 18 x 10 m 2 plot during the first day three spells of 24 1 mm h 1 12 3 mm 27 8 mm h 1 12 3 mm and 14 4 mm h 1 12 5 mm were applied almost saturating the runoff plot on the second day 20 h later two spells of 18 7 mm h 1 34 3 mm and 35 2 mm h 1 25 4 mm followed surface runoff was a combination of infiltration excess runoff from rocky portions of the plot and saturation excess runoff from areas covered by soil soil saturation was accelerated by lateral runoff from adjacent rocky areas once the plot was saturated 80 90 of the applied rainfall became surface runoff significantly different concentrations of chloride sulphate and nitrate ions in the sprinkled water on two successive days served as tracers during the second day a two component hydrograph separation pointed to the importance of shallow reservoirs playing active parts in runoff generation about 14 of the flow collected during the second day originated from water applied during the first day during the second day of sprinkling both water sources obviously mixed in saturated soil reservoirs and contributed in variable percentages to surface flow it is hypothesized that at least during high magnitude rainfall the steep rocky slopes investigated might be regarded as flood generating zones rather than areas of pronounced recharge into the underlying yarkon taninim aquifer

overland flow generation and continuity on stone covered soil surfaces the influence of stone cover on the generation and continuity of overland flow is a function of several variables primarily stone size distance spacing between stones and stone position on top of the soil surface or partially embedded the initial hypothesis of the present study were that stone size affects overland flow generation by inducing concentration overland flow and that the distance between stones affects overland flow continuity with respect to stone size and distance between stones opposing results have been found in the literature accordingly the present paper reports on laboratory experiments which were conducted to investigate systematically the effect on overland flow of stone size distance between stones and stone position the main conclusions were 1 stone cover tended to induce overland flow relative to bare soil small stones however especially in a low cover percentage setting and when resting on top of the soil surface produced less overland flow than bare soil 2 overland flow was positively related to stone size but inversely related to distance between stones 3 overland flow yield was always greater when stones were embedded than when on top of the soil surface 4 the effect of stone size on increasing the degree of overland flow was of greater significance than the effect of the distance between stones on reducing overland flow

fibers and cylinders of cryptomelane hollandite in permian bedded salt palo duro basin texas selected core sections from the lower san andres units 3 4 5 upper san andres lower clear fork and the salado tansill formations fibers or cylinders found from only the lower san andres formation units 4 and 5 the upper san andres formation and the salado tansill salt the fibers are inorganic light to dark reddish brown pleochroic highly birefringent filamentary single crystals 5000 1 energy dispersive analyses sem and gandolfi x ray diffraction techniques have identified the fibers and cylinders as members of the cryptomelane hollandite series the fibers can be straight and or curved can bifurcate can form loops waves or spirals and can be isolated or in parallel groups detailed petrographic analyses show no evidence for recrystallization or deformation of the enclosing salt after fiber formation suggestion that the fibers grew in situ by a solid state diffusional process at low temperatures the cylinders are pleochroic highly birefringent light to dark reddish brown hollow thin walled open ended right cylinders having a 1 to 2 mu m wall thickness and variable lengths 2 to 434 mu m and diameters 6 to 55 mu m the cylinders found in the recrystallized salt are perhaps a residue from dissolved chevron salt the observation of cylinders partially or completely enclosed by salt stratigraphically above large fluid inclusions suggests that natural downward fluid inclusion migration has occurred in response to the geothermal gradient modified journal abstract

functional ecomorphology feedbacks between form and function in fluvial landscape ecosystems abstract the relationship between form and function has been a central organizing principle in biology throughout its history as a formal science this concept has been relevant from molecules to organisms but loses meaning at population and community levels where study targets are abstract collectives and assemblages ecosystems include organisms and abiotic factors but ecosystem ecology too has developed until recently without a strong spatially explicit reference landscape ecology provides an opportunity to once again anneal form and function and to consider reciprocal causation between them this ecomorphologic view can be applied at a variety of ecologically relevant scales and consists of an investigation of how geomorphology provides a structural template that shapes and is shaped by ecological processes running water ecosystems illustrate several principles governing the interaction of landscape form and ecological function subsumed by the concept of functional ecomorphology particularly lucrative are ecosystem level interactions between geologic form and biogeochemical processes integrated by hydrologic flowpaths while the utility of a flowpath based approach is most apparent in streams spatially explicit biogeochemical processing pervades all landscapes and may be of general ecological application

spatial variations of stirring in the surface ocean a case study of the tasman sea abstract stirring in the tasman sea is examined using surface geostrophic currents derived from satellite altimeter measurements calculations of the distribution of finite time lyapunov exponents ftles indicate that the stirring in this region is not uniform and stretching rates over 15 days vary from less than 0 02 day 1 to over 0 3 day 1 these variations occur at both small 10 km and large 1000 km scales and in both cases are linked to dynamical features of the flow the small scale variations are related to the characteristics of coherent vortex structures and there are low ftles inside vortices and filaments of high ftles in strain dominated regions surrounding these vortices regional variations in the stirring are closely related to variations in mesoscale activity and eddy kinetic energy eke high values of mean ftle occur in regions of high eke highest mean values of around 0 2 day 1 occur in the east australia current separation region whereas small values occur in regions with low

spatial distribution of soil surface coverage on north and south facing hillslopes along a mediterranean to extreme arid climatic gradient four research sites were established along a climatic gradient in israel representing mediterranean xeric mediterranean arid and extreme arid climate conditions the cover percentage of eight soil surface components vegetation annual and perennial forms biogenic crust mosses lichens cyanobacteria and dwarf grass stones and bare soil patches were measured transects along hillslopes on each of two opposite aspects south and north facing slopes were established at each site altogether eight transects dominance and soil surface cover diversity indices and similarity coefficients between the transects were calculated high similarity values in soil surface cover were found between the south facing slopes located in the xeric mediterranean arid and extreme arid areas these hillslopes are dominated by stones and bare soil patches in contrast lower similarity values were found between the northern slope aspects dominated by biotic components vegetation and biogenic crusts the study along a climatic gradient together with the comparison between northern and southern aspects provide useful information that can be utilized for evaluation of changes in soil surface cover characteristics given various scenarios of future climate regimes in that region

surface stone cover on desert hillslopes parameterizing characteristics relevant to infiltration and surface runoff surface stones are a common feature of desert hillslopes they influence slope processes ranging from the interception and partitioning of rainwater to the dislodgement and transport of regolith particles the aspects of a stone mantle which relate to these various influences are diverse and include surface cover fraction dimensions of the infiltration annulus and geometric and packing effects analyses of the characteristics of stone cover at two study sites were made using photographic methods and are used to evaluate different means of reporting mean stone sizes it is found that mean diameter based on weight as conventionally employed in sieve analysis is insensitive to important stone cover characteristics and may be influenced greatly by uncommon large stones similarly mean diameters based on count become inappropriate if large numbers of small stones dominate the calculated mean concealing other site to site differences in stone cover as a more appropriate parameterization of stone geometry the use of mean diameters weighted by stone surface area and perimeter length are proposed these weighting factors have the advantage that they relate closely to stone characteristics relevant to slope hydrology and erosion processes

soil heterogeneity in mojave desert shrublands biotic and abiotic processes 1 geological and ecological processes play critical roles in the evolution of desert piedmonts feedback between fast cyclic biotic and slow cumulative pedogenic processes on arid alluvial fan systems results in a heterogeneous landscape of interspace and canopy microsites defining the spatial extent between these processes will allow a better connection to ecosystem service and climate change we use a soil chronosequence in the mojave desert and high spatial resolution infiltrometer measurements along transects radiating from canopies of perennial shrubs to assess the extent of biotic and abiotic processes and the heterogeneity of soil properties in arid shrublands results showed higher saturated conductivity under vegetation regardless of surface age but it was more conspicuous on older developed soils at proximal locations to the shrub bulk density soil structure grade silt and clay content significantly increased radially from the canopy while sand and organic material decreased soil properties at distal locations 2 5 times the canopy radius had no significant spatial correlation the extent of the biotic influence of the shrub was 1 34 0 32 times the canopy radius hydraulic properties were weakly correlated in space but 75 of the variance could be attributed to sand content soil structure grade mean particle diameter and soil organic material none of which are exclusively biotic or abiotic the fast cyclic biotic processes occurring under vegetation are clearly overprinted on slow cumulative abiotic processes resulting in the deterministic variability observed at the plant scale

rainwash experiments on the erodibility of loose sediments laboratory experiments using simulated rainfall splash boards and trays were conducted in order to obtain information on the erodibility of loose sediments as a time dependent phenomenon in all ten different sediments ranging from silt d50 24 m to coarse sand d50 593 m were studied the effect of three different initial states of the sediments namely the air dry state t1 the field capacity state t2 and the desiccated state t3 on the erodibility was also assessed variations in detachability during a rain erosion experiment can be explained by change in water content including liquefaction and the development of a water layer on the surface cohesion and granulometric composition of the top layer the coarsest sandy sediments almost always yielded the highest detachability when starting from an initial field capacity state t2 for the finer sediments the highest detachability was found for the homogeneous and not yet compacted initial air dry state t1 the effect of the initial desiccated state t3 on the detachability of the finer sediments was also a function of the rainfall duration the relationship between detachability and median grain size of the sediments was very similar to the relation between grain size and the susceptibility to runoff and wind erosion established by other investigators the highest detachability was found for a fine very well sorted sand with a median grain size of 96 m

relation between infiltration and stone cover on a semiarid hillslope southern arizona abstract a knowledge of the spatial distribution of infiltration rates is essential to the application of realistic distributed rainfall runoff models in semiarid areas one method of determining this distribution is to develop a predictive equation based on a readily observable surface property such as stone cover previous studies of the relation between infiltration and stone cover on shrub covered semiarid hillslopes have yielded both positive and negative correlations it is suggested that positive correlations result where infiltration measurements are confined to areas between large shrubs negative correlations on the other hand reflect pronounced shrub intershrub differences in infiltration and stone cover and are found where both shrub and intershrub areas are sampled in this study of a semiarid hillslope in southern arizona both shrub and intershrub areas are sampled and a negative correlation is obtained between infiltration and stone cover this correlation arises from the fact that under shrubs fine sediments have accumulated primarily as a result of differential splash whereas between shrubs such sediments have been selectively removed by a combination of rainsplash and overland flow leaving behind a gravel lag consequently infiltration rates are higher under shrubs than between them owing to the higher percentage of sand in the surface soil the larger quantity of organic matter both within the soil and on its surface and the greater digging and burrowing by animals in addition simulated rainfall experiments imply that shrubs with moderately dense canopies are more effective than adjacent surface gravels in dissipating the kinetic energy of raindrops and thereby reducing surface sealing and promoting infiltration inasmuch as the field site is typical of gentle shrub covered piedmont hillslopes over much of the sonoran desert inverse relations between infiltration rate and stone cover are probably characteristic of such hillslopes and may be used to predict the spatial distribution of infiltration rates for inclusion in rainfall runoff models

the influence of slope angle on sediment water and seed losses on badland landscapes abstract by means of simulated rainfall the influence of the slope angle on the soil water and seed erosion has been studied on badland surfaces slope angle has a clear positive effect controlling soil erodibility and erosion rates but it does not have any influence on the volume of runoff after 40 minutes of rain at an intensity of 55 mm h 1 in contrast slope angle has a clear influence on runoff initiation with cracks and crusts as the main factors controlling the time to ponding and time to runoff both ponding and runoff initiation start earlier on pediments than on slopes where more cracks exist steady state infiltration rates and seed losses have an inverse relationships with slope angle pediments have 40 times lower erosion rates and 6 times higher seed losses than slopes the different behaviour of seed losses between pediment and slope is due to the strategy of the seeds against erosion processes

significance of preferential flow at the rock soil interface in a semi arid karst environment abstract in many semi arid environments the surface materials are frequently characterized by thin soils and large proportions of bare rock both of which are expected to considerably influence infiltration and groundwater recharge processes in this study small plot scale irrigation experiments in combination with dye tracer application as well as real time and subsequent soil moisture measurements and soil particle size analysis were conducted to investigate the significance of preferential flow at the rock soil interface large scale assessments of soil depth and surface type distribution were used to upscale the findings of the irrigation experiments to the scale of a complete hillslope and further to estimate percolation properties of a hypothetical rainfall event the two experimental plots were each located in the west bank mountains close to ramallah each irrigation experiment was designed with 50 mm of precipitation applied on an area of 1 m 2 during the course of ca 2 5 h each irrigation plot had a surface share of approximately 50 rock outcrop and 50 soil surface percolation properties were investigated by subsequent soil moisture measurements at high spatial resolution on vertical soil profiles on the irrigated plot dye tracer application on the rock outcrop during the sprinkling allowed for tracking of resulting outcrop runoff in the subsurface the soil depth survey included 2100 measurement points on 7 transects which allowed the estimation of local soil depth distribution results of the irrigation experiments showed that precipitation induced runoff from rock outcrops continued below ground as preferential flow along the rock soil interface while water from the soil surface percolated mainly vertically and much more homogeneously this was evident from the high density soil moisture measurements as well as from the dye tracer patterns outcrop runoff percolated faster and to greater depths than water infiltrating directly from the soil surface thus possessing a greater potential for groundwater recharge

fine gravel controls hydrologic and erodibility responses to trampling disturbance for coarse textured soils with weak cyanobacterial crusts article i nfo we compared short term effects of lug soled boot trampling disturbance on water infiltration and soil erodibility on coarse textured soils covered by a mixture of fine gravel and coarse sand over weak cyanobacterially dominated biological soil crusts trampling significantly reduced final infiltration rate and total infiltration and increased sediment generation from small 0 5 m 2 rainfall simulation plots pb0 01 trampling had no effect on time to runoff or time to peak runoff trampling had similar effects at sites with both low and very low levels of cyanobacterial biomass as indicated by chlorophyll a concentrations we concluded that trampling effects are relatively independent of differences in the relatively low levels of cyanobacterial biomass in this environment instead trampling appears to reduce infiltration by significantly reducing the cover of gravel and coarse sand on the soil surface facilitating the development of a physical crust during rainfall events the results of this study underscore the importance of carefully characterizing both soil physical and biological properties to understand how disturbance affects ecosystem processes published by elsevier b v

volcanic materials as mulches for water conservation abstract arid regions are characterised by a limited rainfall a circumstance that acts as a barrier to dryland farming lanzarote in the canary islands spain is one of the most arid regions in europe with less than 150 mm annual rainfall and potential evapotranspiration in excess of 2000 mm a traditional farming system developed on the island has led to a diversified and productive form of agriculture that uses no irrigation the system utilizes a layer of 10 20 cm of tephra covering the natural soil the tephra acts as mulch and is highly effective for soil water conservation in this work we present the results of a 3 year monitoring of soil moisture content in three plots covered with two types of basaltic tephra with different grain sizes the results are compared to those obtained on adjacent plots that were not covered with the mulch sampling was conducted once a month every 10 cm up to a depth of 1 m compared to the noncovered soils the tephra covered soils managed to retain eight times more water in the surface layer during the driest months at a depth of 1 m twice the amount of water was retained in the tephra covered plots this positive effect was explained by the tephra s physical properties particularly its low water retention capacity and high porosity enhancing water infiltration and reducing evaporation rates differences observed in the water conservation depending on the mulch type was explained largely by grain size the pyroclastic materials proved to be very effective for soil water conservation under arid conditions

lagrangian particle transport in the indian ocean a model study lagrangian transport of passive particles in the indian ocean is diagnosed using the global modular ocean model 2 of the geophysical fluid dynamics laboratory first the model is forced by time varying monthly mean climatological wind stresses and a particle cloud released in the indonesian throughflow itf region is tracked for one year in the next experiment two separate clouds one released in the itf region and the other in the arabian sea region are followed for three years by forcing the model with weekly varying nmc9195 wind stress data in both the experiments short term liapounov exponents indicate that particle trajectories are chaotic with typical e folding stretching time about 125 days the zonal dispersion of the itf cloud is faster than the shear flow dominated transport process in the first experiment as well as for the first two years in the second experiment however at later times the zonal dispersion rate is subquadratic in the latter experiment for the arabian sea cloud zonal dispersion is diffusive when the whole time range of three years is considered however for the initial six months it is shear flow dominated and thereafter becomes even subdiffusive the meridional dispersion rate is roughly superdiffusive in both experiments when the whole time range is taken into account our estimates of correlation dimension a lower bound on the fractal dimension suggest that none of the particle clouds reach the area filling limit in the time range of the model integration we also compare the present results with those from earlier studies of chaotic stirring in the oceans

characteristics of stone covers on the surface of basalt flows in arid northeast jordan variations in the stone covers on desert surfaces have implications for the operation of hydrological processes some recent attention has been given to the difficulties of identifying and quantifying relevant characteristics of stone covers investigation of how such characteristics vary in relation to geological and topographical controls are limited results are presented of a field study of the characteristics of stone covers on four lithologies in the late tertiary to quaternary basalt plateau of northeast jordan marked variations occur in clast dimensions and the characteristics of sorting between lithologies which are likely to affect hydrological response a more subtle control relating to slope conditions is superimposed on the lithological differences r and q mode factor analysis identifies groupings within the data which demonstrate the distinctiveness of different lithologies characteristics of the stone covers on sites affected by human occupation are markedly different from undisturbed sites on the same lithology

microanalysis of primary fluid inclusions in halite constraints for an evaporitic sedimentation modeling application to the mulhouse basin france the chemistry of the waters from which the evaporitic minerals crystallized in the lower part of the salt iv unit of the mulhouse basin france has been investigated the lithological and fluid inclusion data have been compared to the output data of the mass transfer program newequi which simulates the change in brine composition during its evaporation advancement the results show that the evolution of the composition of the brine is compatible with the calculated sequence of evaporation of a parent water corresponding to a seawater modified by cacl2 rich hydrothermal water in the studied sequence fluid inclusion data provide useful constraints for reconstructing the paleoenvironment controlling the evaporitic sedimentation they also provide data on the water stratification in the basin and on its connectivity with the open sea and important parameters controlling the productivity possible sources for the nutrients and the preservation of organic matter in the sediment

deformation of laminated silt loam due to repeated freezing and thawing cycles the effect of repeated freezing and thawing cycles on an experimentally produced laminated silt loam was studied with the purpose of obtaining more insight into the genesis of macro and microstructures observed in the loessic formations of northwestern europe the laminated silt loam was subsequently subjected to 18 cycles of alternate freezing and thawing the minimum temperature recorded after 11 days of frost was 7 c at a depth of 5 cm and 4 c at 29 cm the underlying sediments compact loam except its upper part and sand always remained unfrozen the experiment reproduced a seasonal superficially frozen ground new structures and microfabrics in the form of vesicles platy structures shear planes and micro undulations were created by ice segregation and thawing mechanical stress and subsequent frost creep the impact of the freezing and thawing cycles is very strong all the laminae being deformed or broken judging by the abundance and the diversity of the structures created freezing is a more important process than simple drying without frost as is evidenced by the range in temperature chosen for the experiment and the low number of cycles these structures do not necessarily require severe climatic conditions to develop unlike frost cracks or ice wedge casts they could develop in winter conditions similar to those present today in the french southern alps

controls of infiltration runoff processes in mediterranean karst rangelands in se spain semiarid karst landscapes represent an important ecosystem surrounding the mediterranean basin for which little is known on runoff generation knowledge of the sources and patterns of variation in infiltration runoff processes and their controls is important for understanding and modelling the hydrological functions of such ecosystems the objectives of this paper are to determine the infiltration rates and their controls in a representative mountain karst area sierra de gador se spain at micro plots and to investigate the integrated response of rainfall on a typical hillslope rainfall simulations in micro plots and natural rainfall runoff monitoring on a hillslope were carried out complementarily we investigated the role of soil surface components vegetation rock outcrop fracture and soil crust topographic position antecedent soil moisture and rainfall characteristics in regulating infiltration runoff processes results of rainfall simulation revealed the importance of vegetation cover and the presence of rock fractures in promoting the infiltration in the limestone karst landscape while bare patches and rock outcrops acted as sources for runoff all plots with 50 vegetation cover had no runoff with up to 55mmh 1 of simulated rain in contrast nearly all bare plots had runoff under the same simulated rain with runoff coefficients ranging from 3 1 to 20 6 on dry soil surface conditions and from 2 0 to 65 4 on wet soil surfaces runoff coefficients amounted to 59 0 79 5 for rock outcrops without cracks but were drastically reduced by the presence of cracks the surfaces with rock fragments resting on the soil generally located in the middle of the slopes prevented more effectively the runoff generation than those surfaces where rock fragments were embedded in the top soil antecedent soil moisture had significant impact on runoff generation with wet soil having doubled runoff coefficient shortened time to runoff and increased runoff rate compared to the same but dry soil linear regressions indicated that the main controls for constant infiltration rate were the cover percentages of vegetation and litter plus rainfall intensity while the major controls for runoff coefficient were the bare soil and vegetation coverage plus rainfall intensity high infiltration rates measured at the micro plots agreed with low intra event runoff coefficients mostly below 1 observed under natural rainfalls at the hillslope runoff depth and coefficient at the hillslope was significantly correlated with rainfall depth maximum hourly rainfall intensity and antecedent precipitation over 20days ap20 during the 1 5 year monitoring period from sep 2003 to mar 2005 the overall infiltration was 41 of the total rainfall amount and the maximum infiltration rate was almost 94 of the largest single rainfall event the results from this study contribute to improved understanding of the magnitude and controls of the surface runoff in semiarid karst mountain areas 2011 elsevier b v

lagrangian modeling of potential vorticity homogenization and the associated front in the gulf stream abstract this paper studies the water property exchange across the gulf stream the gyre scale potential vorticity homogenization and the associated property front closely aligned with the gulf stream using a double gyre jet ocean circulation model which consists of a subtropical gyre in the south a subpolar gyre in the north and a meandering jet between the two gyres a lagrangian particle modeling method is used in this study the role of the gulf stream and the annual north south shift of the wind system and their interplay in these processes are thoroughly examined the main conclusions are 1 the gulf stream could result in large water property exchange between the subtropical and subpolar gyres and the annual meridional shift of the wind pattern could further enhance the property exchange 2 most of the lagrangian transport and mixing across the jet core occurs in the interior and the eastern region whereas most of the lagrangian exchange in the western basin especially in the western boundar

surface sealing as influenced by slope angle and position of simulated stones in the top layer of loose sediments the influence of five different slope angles and two different positions of simulated stones in the top layer of a sandy and a silty sediment on surface sealing intensity is examined in the laboratory sealing intensity is assessed by studying changes of percolation rate through a sediment layer with simulated rainfall duration and by measuring cohesion of the 5 mm thick upper sediment layer a measure of seal strength by means of a torvane slope has a negative influence on sealing intensity for a constant per cent of simulated stone cover sealing intensity is lowest in the case of stones placed on the sediment surface compared to the case of stones pushed into the surface layer explanations for these findings are given and some implications are further discussed

responses of interrill runoff and erosion rates to vegetation change in southern arizona abstract vegetation change fi om grassland to shrubland has occurred over much of the sonoran and chihuahuan deserts during the past century the effect of this vegetation change on interrill runoff and erosion was examined by conducting rainfall simulation experiments on large runoff plots on contemporary grassland and shrubland hillslopes these experiments show that compared to the grassland the interrill portions of shrubland hillslopes 1 have higher runoff rates 2 experience equilibrium runoff conditions much more frequently 3 exhibit higher overland flow velocities and 4 are subject to greater rates of erosion the environmental change that has led to the vegetation change has been relatively minor but its geomorphic impact has been substantial

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

biogeomorphology of a mojave desert landscape configurations and feedbacks of abiotic and biotic land surfaces during landform evolution abstract terrestrial ecosystems can be more holistically understood by investigating the morphology of landscape mosaics the assemblage of their ecological communities and the linkages and feedbacks between the mosaics and communities the overarching objectives of this study were to 1 study the abiotic and biotic configurations of landform units as mosaics within a mojave desert chronosequence and 2 elucidate their potential feedbacks interactions and dynamics during landform evolution seven landform units distributed over three geomorphic ages were identified including young bars and swales intermediate aged flattened bars flattened swales and bioturbation units and old desert pavements and shrub zones these landform units were characterized according to abiotic and biotic land surface properties landform units were statistically distinct and predictable based on a specific suite of abiotic and biotic properties vascular plant functional group and biological soil crust community diversity varied with geomorphology with greatest diversity associated with bars and shrub zones and lowest diversity associated with desert pavements biological soil crust communities were controlled by geomorphic age surface rock size and protruding rocks with young bar units having the highest abundance and diversity perennial forbs were observed in old shrub zones with small rocks and few protruding rocks a high clast density and a finer sized clast distribution were found particularly in desert pavements and flattened swales and generally inhibited biological soil crust and plant cover evolutionary trajectories for landforms of a lower piedmont landscape can be dominated by either abiotic and biotic landform processes these two trajectories are distinctly different and are associated with their own unique linkages feedbacks and dynamics of abiotic and biotic land surface properties producing a highly diverse desert landscape

spatial patterns of soil water balance on intensively cultivated hillslopes in a semi arid environment the impact of rock fragments and soil thickness during past decades a diverse system of subsistence agriculture in south east spain annual rainfall of less than 300 mm has been overturned in favour of large scale plantations of almond trees without consideration for topography and related spatial patterns in soil hydrological properties the objective of this paper is to investigate the spatial pattern in soil physical properties induced by this cultivation system and to highlight its impacts on the water balance soil properties were recorded along hillslopes with shallow soils developed on slates and greywackes in the upper part of the guadalentin drainage basin murcia region frequent tillage of these almond plantations covering entire hillslopes has resulted in denudation by tillage erosion on the topographic convexities as well as transport of rock fragments and fine earth along the slopes these processes have created a systematic spatial pattern of soil thickness and rock fragment content shallow and stony soils on the topographic convexities and deep soils with a rock fragment mulch in the concavities at the foot of the slopes at the same time a negative relationship between rock fragment content and fine earth bulk density was observed the impact of this spatial pattern in soil properties on the water balance was evaluated using the pattern one dimensional hydrological and plant growth model the model simulates the water balance of soil profiles covering the observed variation in soil thickness stoniness and bulk density the model results indicate that the highest rates of infiltration evaporation and drainage as well as the lowest rates of overland flow are restricted to shallow soils on the hilltops in contrast the deeper soils in the valley bottoms produce a more stable moisture regime than shallower soils which tend to saturate and dry out quickly these model results are in agreement with the spatial patterns of almond productivity an asymptotic increase with soil thickness copyright c 2000 john wiley sons ltd

large near surface nitrate pools in soils capped by desert pavement in the mojave desert california we found exceptionally high nitrate levels up to 12 750 kg ha 1 at shallow depths 1 m in soils mantled by desert pavement a common land surface feature in arid regions nearby soils without desert pavement had nitrate contents that were one to two orders of magnitude lower the soil conditions coincident with desert pavement i e stability antiquity and virtually no leaching favor the retention and accumulation of nitrate delivered by atmospheric deposition or in situ fixation the nitrate stored in soils under desert pavement is a previously unrecognized pool of nitrogen that has the potential to increase the global nitrogen inventory for near surface desert soils to five times previous estimates its near surface occurrence makes this labile nitrogen pool particularly susceptible to mobilization by climate change or human disturbance risking contamination of surface and groundwaters

influence of soil surface features and vegetation on runoff and erosion in the western sierra madre durango northwest mexico abstract in mountainous areas runoff and soil erosion are closely linked to soil surface features particularly stoniness depending on the size of rock fragments gravel pebbles stones and or blocks and especially the way they are integrated into the soil matrix they may facilitate or hinder infiltration and promote soil losses the present study examines the role of different soil surface features and their influence on runoff formation and on soil erosion in an area seriously affected by overgrazing based on measurements made on hillslopes for 2 years at the plot scale the results show that grass cover pebbles and sand content increase runoff and erosion inversely slope value tree cover percentage structural stability and organic matter content are negatively correlated with runoff and soil losses it is shown that the correlations can be explained by the major role played by the surface features on hydrologic behaviour of the hillslopes two main surface features were identified and hydraulically characterised namely i crusted surfaces with embedded gravel widespread on gentle slopes which induce high runoff and erosion rates and ii stony surfaces where free pebbles and blocks protect the top soil against raindrops and overland flow kinetic energy and lead to reduce runoff and soil losses

hydraulics of interrill overland flow on a semi arid hillslope southern arizona parsons a j abrahams a d and luk s h 1990 hydraulics of interrill overland flow on a semi arid hillslope southern arizona j hydrol 117 255 273 simulated rainfall experiments were conducted on an 18 m wide by 35 m long runoff plot located in southern arizona by using a wide plot that extended from the divide to beyond the rill heads it was possible to examine the full range of lateral variability and downslope changes in interrill overland flow on a shrub covered semi arid piedmont hillslope the mean depth d mean velocity v and reynolds number re of overland flow were computed for two measured sections situated 12 5 and 21 m from the top of the plot at a section d vs re and v vs re relations show that increases in re are accomodated largely by increases in d these hydraulic relations are principally the result of resistance to flow increasing with re as overland flow spreads into new areas inasmuch as the maximum equilibrium discharge simulated in these experiments has a return period of about 7 yr increasing resistance to flow as re increases may be considered typical of most overland flow events on shrub covered piedmont hillslopes in southern arizona downslope hydraulic relations differ strikingly from at a section relations under equilibrium runoff conditions resistance to flow decreases rapidly as re increases permitting increases in re to be accomodated entirely by increases in v the decrease in resistance to flow is due to progressive downslope concentration of flow into fewer deeper threads under non equilibrium conditions downslope hydraulic relations may be quite different from those obtaining at equilibrium but resistance to flow always decreases downslope this is the result of low flows following pathways formed by higher flows that concentrate downslope analyses of overland flow hydraulics at the scale of interrill areas produce results that are quite different from those obtained from small plots a knowledge of the hydraulics at this scale is essential if models of interrill overland flow are to become more realistic and hence better predictors of runoff hydrographs and sediment yield

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

evaluating the life expectancy of a desert pavement abstract this paper integrates prior scholarship on desert pavements with a case study of pavements on stream terraces in the sonoran desert to analyze the processes and site conditions that facilitate the survival of ancient desert pavements this synthesis identifies vital factors key factors and site specific factors promoting pavement stability hyperaridity is the vital factor in pavements surviving for 106 years or more aided by minimal bioturbation and clast size reduction three key factors aid in pavements surviving for 104 to 105 years accumulation of allochthonous dust underneath pavement cobbles a flat topography and a lack of headward retreating swales or gullies a unified explanation for pavement longevity however did not emerge from a literature review because a variety of site specific factors can also promote pavement antiquity including resistant bedrock beneath the pavement disk shaped cobbles to promote dust accumulation and microclimatological and ecological reasons for minimal bioturbation both key and site specific explanations for pavement longevity apply well to a case study of pavements on stream terraces in the sonoran desert central arizona the buildup of cosmogenic 10be and in situ 14c optically stimulated luminescence and varnish microlamination ages reveal stable pavements range in age between 30 and 332 ka with conditions for longevity including flat surface topography pavements underlain by consolidated granitic bedrock a lack of headward retreating gullies and swales 87sr 86sr analyses indicating the infiltration of allochthonous dust floating disk shaped pavement cobbles and a quartzite lithology resistant to disintegration however 10be ages also indicate evidence for the instability of desert pavements on stream terraces underlain by unconsolidated playa clays and unconsolidated fanglomerate these weaker materials allowed the growth of headward retreating swales that in turn promoted exposure of newer gravels by surface erosion

influence of relative surface age on hydraulic properties and infiltration on soils associated with desert pavements abstract av horizons found in desert pavement environments are known to evolve pedogenically over geologic time this study was conducted to determine whether increased pedogenic development of the av vesicular horizon over relative time impacts the hydraulic properties of individual soil peds and the mechanism of infiltration as inferred by dye patterns we examined peds from the av horizons associated with desert pavements that mantled three different alluvial deposits with different relative surface ages qf5 10 ka qf3 50 100 ka and qf2 10 50 ka and included an additional surface qf6 4 ka for the dye studies we hypothesized that increases in the development of the av over time would lead to a more structured soil surface with greater potential flow between soil peds and lower hydraulic conductivity of the soil peds themselves results showed that average k s and of the qf5 peds were significantly greater than estimated for the qf2 and qf3 peds although k s was greater for the qf5 peds the steady state infiltration rate was equal for the qf3 qf2 and qf5 surfaces perhaps indicating a reduction in matrix flow through soil peds and an increase in interped flow between soil peds studies were also conducted using dyed water and a tension disc infiltrometer set to saturation following the tests the soil was excavated in 2 cm increments and photographed the dye patterns for the qf6 indicated that the water moved rapidly through the soil matrix into deeper soil and without any preferential flow around peds the qf5 exhibited more dye stained soil at depth than seen in the qf2 and qf3 perhaps due to higher ped conductivity qualitative observations on the qf2 and qf3 suggest that water flowed primarily along the ped faces and then toward the ped interiors the results suggest that infiltration through av horizons evolves from a matrix dominated process on the younger soils to a preferential flow dominated process on older surfaces

rock fragments and soil hydrological processes significance and progress abstract in this review we explore the significance of rock fragments in studies of soil hydrological processes because according to research the effects of rock fragments on soil hydrological processes are inconsistent positive negative rock fragments play a critical role in the biosphere as the primary filter for water and solutions containing contaminants and heavy metals rock fragments have a complex influence on soil hydrological processes e g soil erosion runoff generation water infiltration solute transport and water flow and are highly relevant in a typical system in the soil plant atmosphere continuum cracks related to rock fragments provide preferential flow paths through which pollutants are transported into groundwater in this paper the published literature is reviewed concentrating on rock fragments and their effects on soil hydrological processes systematic studies and examples illustrate the effects of rock fragments architecture i e coverage content size position spatial heterogeneity morphology weathering and topography on soil hydrological processes methods and models applied to evaluate the effects of rock fragments on soil hydrological processes are examined in detail we conclude that the relationship between rock fragments and soil hydrological processes is complicated and requires more international research efforts this review concludes with a discussion of perspectives on areas of research that can improve understanding of the effects of rock fragments on soil hydrological processes with insights and suggestions also being provided regarding potential research trends requirements and solutions

can rock fragment cover maintain soil and water for saline sodic soil slopes under coastal reclamation abstract seeking a potential erosion control method for saline sodic soil slopes under coastal reclamation is essential we investigated the effect of rock fragment covers rc on the rainfall partitioning infiltration and runoff processes and the erosion processes for saline sodic slopes of 15 and 30 subjected to a 50 min simulated rainstorm with an intensity of 92 mm h 1 six rock fragment covers 0 10 20 40 60 and 80 were investigated soil was packed in 200 cm 100 cm 30 cm flumes divided into two to create two replicates for each treatment two sequential soil erosion events e1 followed by e2 were induced under two rainstorms that were 24 h apart results showed that in general rc had a positive effect on the runoff rate for both slopes a logarithmic relationship existed between the steady state infiltration rate and the rc for the gentler slopes an rc between 40 and 60 could protect the soil from erosion for e2 and e1 e2 events but did not do so for the e1 events alone for the steeper slopes the rc had no effect on soil losses for the e2 and e1 e2 events but increased the soil losses for the e1 events as the situation of rock fragment changed from situation 1 well embedded into the soil surface to situation 4 submerged in water the relationship between rc and soil loss became more complex and might change over time from a positive to a negative one the results suggested that the effect of rc on runoff and soil losses was influenced by the change of rock fragment situations over time during individual rainstorms the benefits of rc might be augmented by using them in combination with another protective measure

hydric properties of some spanish soils in relation to their rock fragment content implications for runoff and vegetation abstract physical and hydric characteristics of the upper three horizons average depth of sampling 0 0 25 0 25 0 60 and 0 60 1 20 m of 92 soil profiles of spain grouped according to the geological nature of the rock fragments on the soil surface or in the soil profile were studied mathematical relations were developed to separate the contributions of the fine earth fraction and of the fraction above 2 mm indexes were obtained that relate gravitational water and available water in the fine earth fraction with the values from total soil a multiple comparison statistical study was performed for the mean values of 1 rock fragment content 2 organic matter content 3 silt plus clay content 4 gravimetric water content at different suction values the linear correlations of the gravitational and available water indexes with the rock fragment content by volume as independent variable were studied they showed positive or negative effects of the increase of rock fragment content on both indexes depending on their petrographical composition finally conclusions related tothe development of vegetation and to the production of runoff have been drawn when rock fragment content increases the results show positive effects for the development of vegetation and for the production of saturation overland flow

effects of drainage ditches and stone bunds on topographical thresholds for gully head development in north ethiopia abstract gully erosion is an extreme process of land degradation operating in different regions of the world a common way to quantify the susceptibility of land to gully incision is the use of topographical thresholds for different land use types however the impact of various management practices in cropland on these thresholds has not been studied to date although land management may significantly affect runoff production erosion processes and rates here the impact of different land management practices on gully head development in cropland is studied based on a standardized procedure for topographical threshold analysis s ka b where s represents the slope gradient of the soil surface a the drainage area at the gully head b an exponent and k a coefficient reflecting the resistance of the land to gully head development a case study area was chosen around wanzaye north ethiopia where three different cropland management practices were studied in 75 catchments i the catchment wide use of stone bunds on the contour ii the use of slightly sloping drainage ditches feses and iii the combined use of stone bunds and feses the lowest k values 0 078 0 090 are found for catchments treated with feses the highest k values 0 198 0 205 are observed for stone bund catchments and medium k values 0 092 0 099 are found for mixed catchments this finding implies that catchments with the exclusive use of drainage ditches are the most vulnerable to gully head development compared with mixed catchments and stone bund catchments however on site sheet and rill erosion rates are reduced by feses as they lower the gradient of the overland flow lines three trends in cropland management around wanzaye and the wider region are observed i feses are exclusively made on rather steep slopes where small drainage areas lead to the rapid development of gully heads ii stone bunds are constructed on both steeper and gentle sloping cropland and iii larger and gently sloping catchments seem to be most suitable for the combined use of drainage ditches and stone bunds

the relation between surface rock fragment cover and semiarid hillslope profile morphology abstract rock fragment covers veneer hillslopes in many parts of the world and influence the operation of hydrologic and geomorphic processes on those surfaces the purpose of this investigation was the examine the spatial variability of rock fragment cover on morphological units of hillslopes in southeastern arizona u s a simple statistical models based upon hillslope gradient as well as a soil slope factor ssf were developed and validated for the estimation of percent rock fragment covers rfc on these units although reasonably accurate estimates were made using either hillslope gradient or the ssf it appears more efficient to utilize hillslope gradient alone likewise reasonably accurate estimates of rfc can be made using either a composite model for the entire hillslope or unit specific models however it appears more efficient to utilize the gradient composite model

spatial distribution of rock fragments in dolines a case study in a semiarid mediterranean mountain range sierra de gador se spain abstract rock fragments rfs at the soil surface have great effects on the intensity of various hydrologic and geomorphic processes however little information is available on the spatial distribution of rock fragments rf in the dolines which may be of importance in understanding overland flow and subsequent recharge in limestone karst landscapes this study analysed spatial variability of rf cover and size in different topographic positions top upper middle and lower position in three dolines in sierra de gador almeria province south east spain the results indicated that cover percentage of small rfs 5 20 mm increased but large rf cover 250 600 mm and 600 mm decreased from the upper position to the lower position of the dolines small rfs were usually resting on the soil surface while most large rfs tended to be partly embedded in the soil surface total rf cover and d 50 median diameter of the surface rfs greater than 5 mm tended to increase with slope gradient

can ash control infiltration rate after burning an example in burned calcareous and gypseous soils in the ebro basin ne spain abstract fire is a long established ecological factor that has shaped the life history hydrogeomorphological processes soil formation and landforms of mediterranean environments soil infiltration is one of the properties affected by fire as a consequence of litter and vegetation removal and heating of and changes to the biological chemical and physical soil properties in this context ash can play an important role in soil infiltration behavior and therefore affect sediment and runoff yield the aim of this work is to determine the effect of ash cover on infiltration rates a single ring infiltrometer was used immediately after a wildfire and before the first storm events to determine the soil infiltration rate a total of 24 infiltrations were made 2 soil types 2 treatments 6 replicates in each infiltration experiment the soil wetting front the bulk density and stoniness were also measured the results show that the final infiltration rate fc values are higher in calcareous soils than in gypseous soils the ash cover in calcareous burned soils only temporarily decreases the bulk density of topsoil and enhances infiltration

soil surface characteristics influence on infiltration in black marls application to the super sauze earthflow southern alps france soil surface characteristics sscs have a strong influence on the infiltration properties at the soil surface they can explain spatial variations in the infiltration processes observed under natural rainfall for relatively little differentiated material and can help us to understand the surface and subsurface hydrology of landslides representative of some of black marls landscapes of the french southern alps this paper presents the results of investigations into the influence of sscs using careful morphological description in situ tension disc infiltrometry and statistical analysis hierarchical ascending classification and stepwise discriminant analysis the site studied is the super sauze earthflow the selected infiltration and runoff variables were described for 233 microplots chosen all over the earthflow the results show that an approach based on a description of relevant variables influencing water infiltration can validate a typology based on expert knowledge hydraulic conductivity at saturation was measured on 36 undisturbed soil cores and at low negative pressure heads on 83 microplots the dispersion exceeds three orders of magnitude at each pressure head a statistical analysis of the data set obtained by describing selected variables showed the relevance of the black marl descriptors when defining types of ssc that enable us to distinguish significant hydrodynamical behaviour this leads us to suggest a distribution of hydraulic conductivity curves near saturation for each ssc type which can be used as a key to distribute local hydraulic conductivity values adapted to black marl hillslopes as well as the types of ssc at a microplot scale leading to types of hydrodynamic properties the typology of combinations of sscs at a coarser scale should lead to types of hydrological response and to identification of hydrological and geomorphological response units copyright 2003 john wiley sons ltd

slope form and associations with ground boulder cover in arid environments northeast jordan abstract many studies of slope form and sediment transfer dynamics use either bounded field plots or laboratory physical hardware models to study associations between morphology and process results are presented here of a study which examines spatial variations in slope form changing ground surface boulder cover between sites and at different points along slope profiles and evidence for the movement of fine grained sediments which underlie the boulder cover the study site is located in northeast jordan an arid landscape characterised by a late tertiary to early quaternary basalt plateau spreading across the foot slopes of the druz mountains basalt age ranges from approximately 8 9 ma to recent scoracious deposits from local eruptive centres which are no more than 100 000 years old the study considers whole slope profiles rather than a representative section of a slope and accounts for form differences by quantifying slope shape using a length height integral slope form differs with basalt age gradually changing from concave to convex shapes the boulder cover can be used to examine the mobility and redistribution of underlying fine grained sediment by establishing the degree of clast burial at points along slope profiles twenty five slope profiles were surveyed and five plots distributed between crest and toe located at similar points on thirteen the axial dimensions of boulders within each plot were recorded sorting and the preferential movement of smaller clasts is a characteristic of the steepest part of slopes while mean clast size increases downslope for older basalts and decreases downslope for younger basalts the degree of wadi network evolution and the development of sediment pans known as qa and marab varies with flow age links can be established between the age and physical nature of individual lava flows differences in slope form and their spatial distribution associations also exist between changes in boulder dimensions basalt type and the extent of clast burial between topographic highs and lows

effects of rock fragment covers on erosion and transport of noncohesive sediment by shallow overland flow rock fragments on soil surfaces can have a variety of contrasting effects on the hydraulics of overland flow and soil erosion this makes modeling soil erosion difficult systematic studies are needed to assess the effects of rock fragments on the hydraulics of overland flow and to specifically relate these hydraulics to sediment yield therefore flume experiments were conducted in which overland flow was applied to a highly erodible sediment surface covered by various percentages of rock fragments high local turbulence was caused by horseshoe vortex erosion around individual rock fragments for a given discharge and slope the dimension of the scour was affected by the space between the rock fragments for low cover percentages the scour can develop undisturbed and sediment yield increases with percent of rock fragment cover up to about 20 sediment yield then declines as percent cover increases above 20 beyond a cover threshold value of 20 the larger opportunity for scour hole development is counteracted by limited inter rock fragment space that does not allow scour holes to develop to their full extent as sediment yield varies nonmonotonically with rock fragment cover percent sediment yield cannot be predicted by spatially averaged flow hydraulics

effect of antecedent conditions and fixed rock fragment coverage on soil erosion dynamics through multiple rainfall events the effect of antecedent conditions and specific rock fragment coverage on precipitation driven soil erosion dynamics through multiple rainfall events was investigated using a pair of 6 m 1 m flumes with 2 2 slope four sequential experiments denoted e1 e2 e3 and e4 involved 2 h precipitation rates of 28 74 74 and 28 mm h 1 respectively and 22 h without rainfall were conducted in each experiment one flume was bare while the other had 40 rock fragment coverage the soil was hand cultivated and smoothed before the first event e1 only and left untouched subsequently sediment yields at the flume exit reached steady state conditions over time scales that increased with sediment size experiments were designed such that both steady and non steady effluent sediment yields were reached at the conclusion of e1 results from subsequent experiments showed that short time soil erosion was dependent on whether steady state erosion was achieved during the preceding event although consistent steady state effluent sediment yields were reached for each sediment size class steady state erosion rates were however dependent on the rainfall intensity and its duration if steady state sediment yields were reached for a particular size class that class s effluent sediment yield peaked rapidly in the next rainfall event the early peak was followed by a gradual decline to the steady state condition on the other hand for size classes in which steady state was not reached at the end of the rainfall event i e e1 in the following event e2 the sediment yields for those classes increased gradually to steady state i e the sharp peak was not observed the effect of rock fragment cover 40 on the soil surface was also found to be significant in terms of the time to reach steady state i e their presence reduced the time for steady conditions to be attained effluent sediment yields for the bare and rock fragment covered flumes e1 showed steady conditions were reached for the latter in contrast to the former we used the hairsine rose h r model to simulate the experimental data as it explicitly models soil particle size classes experiments e1 and e2 involved soil compaction by raindrops and in this case the model predictions were found to be unsatisfactory however compaction was effectively completed by the end of experiment e2 and the model provided reasonable predictions for experiments e3 and e4

the hydrological response of soil surfaces to rainfall as affected by cover and position of rock fragments in the top layer rainfall experiments have been conducted in the laboratory in order to assess the hydrological response of top soils very susceptible to surface sealing and containing rock fragments in different positions with respect to the soil surface for a given cover level rock fragment position in the top soil has an ambivalent effect on water intake and runoff generation compared to a bare soil surface rock fragments increase water intake rates as well as time of runoff concentration and decrease runoff volume if they rest on the soil surface for the same cover level rock fragments reduce infiltration rate and enhance runoff generation if they are well embedded in the top layer the effects of rock fragment position on infiltration rate and runoff generation are proportional to cover percentage micromorphological analysis and measurements of the saturated hydraulic conductivity of bare top soils and of the top layer underneath rock fragments resting on the soil surface reveal significant differences supporting the mechanism proposed by poesen 1986 i e runoff generated as rock flow or as horton overland flow can partly infiltrate into the unsealed soil surface under the rock fragments provided that they are not completely embedded in the top layer hence rock fragment position beside other rock fragment properties should be taken into account when assessing the hydrological response of soils susceptible to surface sealing and containing rock fragments in their surface layers a simple model based on the proportions of bare soil surface soil surface occupied by embedded rock fragments and soil surface covered with rock fragments resting on the soil surface describes the runoff coefficient data relatively well

development of badlands and gullies in the sneeuberg great karoo south africa abstract the study aims to examine the origin and development of land degradation with particular emphasis on badland and gully systems in the sneeuberg uplands of the great karoo this is an area of semiarid extensive stock farming where land degradation in the form of rill and gully erosion has accompanied the replacement of grassland by shrub vegetation species diversity has declined and ground cover has been reduced leading to a positive feedback loop which exacerbates the degradation many foot slopes developed in shales clays and colluvium have extensive incipient badland development with closely spaced gullying up to 1 5 m deep in valley bottom and valley side depression locations gullies up to 8 m deep have developed usually cut to bedrock through valley fills of mainly holocene colluvium both badlands and gullies appear to have developed since european settlement and to be part of the same hydrological system with extensive areas of bare ground badlands feeding water to incising gullies experiments using simulated rainfall throw some light on current processes badland areas are active under high frequency low magnitude rainfall events major gullies are likely to be the result of occasional high magnitude events but these have not been observed overgrazing in the past is the most likely cause of the degradation

spatial distribution of rock fragments on steep hillslopes in karst region of northwest guangxi china abstract rock fragments 5 mm in diameter at the soil surface and within the topsoil have a large effect on the intensity of various hydrologic and geomorphic processes however little information is available on the spatial distribution of rock fragments in subtropical regions the objective of this paper was to investigate the relationship between the spatial distribution of rock fragments and landforms on two different steep karst hillslopes in northwest guangxi southwest china on the first hillslope a disintegrated landslide failure with the presence of several large rock outcrops 2 m in height the spatial distribution of rock fragment cover had no obvious relationship with topographic position except that the mean cover percentage of small rock fragments 5 20 mm decreased from bottom to top on the second hillslope an avalanche slope without the presence of large rock outcrops the mean total rock fragment cover 5 600 mm increased from bottom 5 to top 21 with decreasing variability and rock fragments with various sizes 5 20 20 75 and 75 250 mm showed a similar increasing trend the mean total rock fragment cover increased linearly with slope gradient on the second hillslope and tended to increase and then decrease with gradient but their relationship was not obvious on the first hillslope this indicated that the spatial distribution of surface rock fragment cover had a close relationship with the presence of large rock outcrops and slope gradient however the median diameter d50 of the surface rock fragments had an increase decrease trend with slope gradient but there was no obvious relationship on both hillslopes with low overland flow therefore the dominant factor for the spatial distribution of rock fragment cover and size at the soil surface might not be soil erosion by water but slope gradient vegetation and geomorphologic condition of the slope the mean total volumetric rock fragment content 5 250 mm within the topsoil 10 20 cm thick increased linearly from bottom 16 to top 39 with slope gradient on the first hillslope and had a logarithmic increase from bottom 10 to top 27 with gradient on the second hillslope this suggested that rock fragment content within the topsoil was mostly controlled by slope gradient and topographic positions and had not a close relationship with the presence of large rock outcrops

surface roughness evolution of soils containing rock fragments soil surface roughness is a dynamic property which determines to a large extent erosion and infiltration rates although soils containing rock fragments are widespread in the mediterranean region the effect of the latter on surface roughness evolution is yet poorly understood therefore laboratory experiments were conducted in order to investigate the effect of rock fragment content rock fragment size and initial moisture content of the fine earth on the evolution of interrill surface roughness during simulated rainfall surface elevations of simulated plough layers along transects of 50 cm length were measured before and after simulated rainfall totalling 192 5mm z 70mm h with a laser microreliefmeter the results were used to investigate whether systematic variations in interrill surface roughness along stony hillslopes in southeastern spain could be attributed to rock fragment cover and rock fragment size soil surface elevations were measured along the contour lines 50 cm long transects with a contact microreliefmeter roughness was expressed by two parameters related to the height and frequency of roughness elements respectively standard deviation of de trended surface elevations random roughness rr and correlation length l derived from exponential fits of the autocorrelation functions the frequently used assumption that surface roughness rr of cultivated topsoils decreases exponentially with cumulative rain is not valid for soil surfaces covered by rock fragments the rr of soils containing small rock fragments 1 72 7 cm increased with cumulative rainfall after an initial decrease during the first 17 5 mm of rainfall for soils containing large rock fragments 7 7 cm rr increased with rainfall above a threshold rock fragment content by mass of 52 per cent for a given rainfall application rr increased non linearly with rock fragment content the correlation length for soils containing small rock fragments decreases with rock fragment content and is significantly lower than for soils with large rock fragments soils covered with small rock fragments large rr and small l are thus well protected against raindrop impact by a water film in the depressions between the rock fragments on abandoned agricultural fields along hillslopes in southeastern spain rock fragments cover increases non linearly with slope owing to selective erosion of finer particles on steep slopes the increase of surface cover by large rock fragments 25 mm is even more pronounced the simultaneous increase of rock fragment cover and rock fragment size with slope explains the non linear increase of rr with slope these relationships differ for soils covered by platy misaschists and those covered with cubic andesites the variations in correlation length along the hillslopes are not clear probably owing to a simultaneous increase in rock fragment cover and rock fragment size these findings may provide a better prediction of soil surface roughness of interrill areas covered by rock fragments using slope angle and lithology

on the mixing enhancement in a meandering jet due to the interaction with an eddy abstract the interaction between a simple meandering jet such as the gulf stream and an eddy is shown to greatly enhance the mixing and dispersal of fluid parcels in the jet this enhanced mixing is quantified by calculating the rate of increase of the root mean square pair separation of lagrangian particles e g floats launched in the jet s immediate vicinity in the presence of an eddy particles can escape from the regions in which they were initially launched comparisons with observations show a markedly improved qualitative agreement when the eddy is allowed to interact with the meandering jet

assessing the impact of soil surface characteristics on vineyard erosion from very high spatial resolution aerial images cote de beaune france we describe a new method to map intra plot soil surface heterogeneities at a 5 cm spatial resolution our approach unites aerial image classification acquired at very high spatial resolution vhsr with local soil sampling vhsr aerial image processing based on image classification allows precise mapping of the spatial distribution of soil surfaces soil sampling defines soil typology by physical and chemical characteristics this method has been applied to a plot area located on the hillslopes of burgundy vineyards monthelie france where decennial erosion data were already available in order to assess the effect of soil surface characteristics and slope angle on erosion intensity and localisation from this method four classes of radiance were distinguished and interpreted as four soil surface state classes ssc defining specific areas within the studied plot these sscs have been characterised by their grain size distribution their organic carbon calcium carbonate and total nitrogen contents by allowing soil surface states to be mapped at five centimetre resolution this approach provides novel insights into the characterisation of soil patterns and into erosion analysis on cultivated hillslopes our work shows that the spatial distribution of soil erosion is related to the local slope steepness but also to the spatial distribution of stoniness that results from water and tillage erosion processes

conservation of soil moisture by different stone covers on alpine talus slopes lassen california abstract this study reports on the influence of stone covers with different clast sizes on the soil moisture of alpine talus slopes in lassen california fifteen four plot sets were sampled in the dry season july 1990 in sandy areas and in talus covered with pebbles cobbles or blocks between 2740 and 2775 m three depths 0 5 5 10 10 15 cm were sampled field moisture content increased gradually with depth in all soil profiles and also in plots covered by increasingly larger rocks surface soils in sand areas were very dry but under rocks had water contents 6 to 14 times greater differences among plots decreased with depth but subsoil samples in sand were still drier than those beneath any stone cover at similar depths blocks were most effective in conserving moisture water content below them was higher than even in deep 10 15 cm sand soils soil temperatures were recorded in sand and under blocks for an 11 day period minima were not significantly different but average maxima were 5 6 c lower under blocks than in sand which reached highs 4 4 c lower than the air differences in soil moisture among talus types are ascribed to lower evaporation losses under stones due to both disruption of capillarity by the coarse particles which prevented water flow to the talus surface and to their efficient reduction of maximum temperatures an irrigation experiment was conducted at 2110 m on a steep talus on the chaos crags from july 18 to aug 2 1993 four 100 75 cm plots with the same surface types than at lassen received 22 5 mm water moisture content was then periodically sampled watering produced similar water distributions among soil depths and talus types to those in lassen evaporation occurred quickly in bare soils due to high air and soil temperatures the sand surface was already dry 2 days after watering but stone covered plots remained moist until day 15 when soils under blocks still retained 77 97 of the water content percent by weight at the start of the test

detachment and transportation of loose sediments by raindrop splash summary laboratory experiments on sediments ejected by splash consisted of two parts quantities ejected and mean projected distances were measured since the splash tray was 100 cm long and 20 cm wide and since both measurements were made on a receiving screen of one square metre it was obvious that only part of the translocated sediment was caught it was subject to serious doubt that the measured distances were representative for all sediment translocated if it is stated that the ejected sediment is distributed according to an exponential function around any point of impact located on the tray and if by definition tray and rainfall are perfectly homogeneous the ratio of the true to the measured distance and the ratio of the caught to the translocated sediment are only a function of the exponent of the real function the apparent distance being also a function of this exponent is thus the only factor needed to solve the two questions hence all empirical data were transformed into true data

effects of interrill erosion soil crusting and soil aggregate breakdown on in situ co2 effluxes soil and carbon redistribution on arable land and the associated impacts on carbon sequestration and mineralisation may play an important role in the global carbon cycle while our insight in the process chain of erosion transport and deposition has significantly grown over recent years there are still major gaps in understanding making it difficult to make an overall assessment of erosion processes on carbon exchange between the soil and the atmosphere one issue is the potential effect soil degradation and erosion processes may have on co2 effluxes at eroding sites the major goal of this study was therefore to analyse and understand the effects of interrill erosion soil crusting and soil aggregate breakdown on in situ co2 effluxes therefore a set of rainfall simulations were carried out on bare loess burden soil with different antecedent soil moisture content all treatments were compared with controls protected from rain drop impact using a fine meshed geotextile as expected runoff and sediment delivery was significantly larger on bare compared to covered soils while surface runoff and sediment delivery increased in most cases with rising antecedent soil moisture as well as rainfall duration crust thickness increased with antecedent soil moisture and rainfall intensity and was in general smaller for the controls however variations in crust thickness did not result in significant differences in in situ measured co2 effluxes also the destruction of the soil crust after six to seven days of measurements did not have a significant effect this leads to the conclusion that crusting and interrill erosion has no or only a minor effect on in situ co2 effluxes nevertheless it should be recognised that topsoil carbon is preferentially removed due to interrill erosion which may result in additional co2 release at depositional sites or in stream and or standing water bodies