variations in spatial patterns of soil vegetation properties over subsidence related ground fissures at an arid ecotone in northeastern iran this study examines variations in the spatial patterns of soil vegetation properties in the vicinity of subsidence related ground fissures caused by groundwater over pumping over an arid ecotone situated in northeastern iran it was assumed that subsidence related fissures have a possible effect on the soil vegetation structures vegetation metrics mean canopy area mean volume vegetation cover percentage and soil properties ec ph caco3 particle size distribution were measured for locations with differing spatial expanses of ground fissures including surface ground fissures deeper ground fissures as well as those exhibiting no signs of ground fissure statistical analyses indicated significant differences p 0 05 in the spatial patterns of vegetation and soil properties for locations with different expanses of ground fissures greater degradation of soil vegetation presenting as mortality of plants and the formation of impermeable layers on the soil surface was observed around deep fissures linked to groundwater over pumping in comparison with other locations these findings confirm the relationship between heterogeneities in patterns of vegetation and soil properties and variations in structure and extent of ground fissures as well as indicating that the expansion of groundwater over pumping induced surface ground fissures can promote soil vegetation degradation over time leading ultimately to barren soils

40ar 39ar thermochronology of the southern gawler craton australia implications for mesoproterozoic and neoproterozoic tectonics of east gondwana and rodinia 40ar 39ar thermochronology of the southern gawler craton australia reveals a protracted history of slow cooling with local crustal heating rapid cooling and fault reactivation between 1700 and 700 ma hornblendes from most of the southern part of the craton including the kalinjala mylonite zone yield ages 1580 1610 ma with younger more discordant samples showing evidence of retrogression these results indicate that the region cooled below 500 c 100 m y after the kimban orogeny and coincident with the gawler range hiltaba suite magmatism to the north perhaps associated with postorogenic extension biotite and k feldspar data indicate that regional cooling after this time was more gradual with a few exceptions locally in the southeastern eyre peninsula rapid cooling at 1425 ma is indicated by nearly concordant hornblende and biotite ages and may record a phase of regional extension other exceptions include areas of lower grade archean rocks that cooled to 350 c by 1700 1640 ma greenschist facies reactivation of shear zones occurred at 1100 ma during the musgravian orogeny on the basis of biotite single grain data and retrogressed amphiboles k feldspar age spectra record cooling at 700 800 ma following regional intrusion of the gairdner dike swarm and or denudation during rifting along the pacific margin of east gondwana and breakup of rodinia tectonothermal events revealed by these results previous geochronological and geological studies and available paleomagnetic data are comparable to other cratons and mobile belts in australia east gondwana and laurentia providing evidence that southeastern australia and north america were adjacent during much of proterozoic time

estimates of electromagnetic and turbulent energy dissipation rates under the existence of strong wind shears in the polar lower thermosphere from the european incoherent scatter eiscat svalbard radar observations 1 turbulent and electromagnetic energy dissipation rates in the altitude range of 98 116 km have been estimated using data obtained from the european incoherent scatter svalbard radar esr observations on 22 september 1998 and 12 march 1999 solar and geomagnetic activities were moderate and quiet during the observational periods respectively the horizontal neutral wind fields derived from the esr observations show strong vertical shears and temporal variations the richardson numbers for the wind fields sometimes show values less than 0 25 the turbulent energy dissipation rates estimated from the wind shears have wavy structures depending on the shear distributions and decrease with height rapidly from 110 km the turbulent energy dissipation rates also have maxima which sometimes exceed 1 w kg in the region 102 108 km the electromagnetic energy dissipation rates are strongly controlled by the neutral wind in the region below 110 km while the pedersen conductivity affects the energy dissipation above 110 km on average the two energy dissipation rates change their relative importance at 109 km on 22 september 1998 and at 112 km on 12 march 1999 depending on the wind shear the electric field and the pedersen conductivity when the electromagnetic energy fluxes are small the contribution of the neutral wind to the electromagnetic and turbulent energy dissipation becomes large and the region where turbulent energy dissipation is dominant also expands upward the magnitude and the dissipation height of the energy poured from the upper and lower regions seem to be strongly dependent on the neutral wind particularly below 110 km the variations of the two energy dissipation rates may have significant effects on energetics in the polar lower thermosphere

variation in grain size and morphology of an inland parabolic dune during the incipient phase of stabilization in the hobq desert china abstract a significant increase in rainfall in the summer of 2012 on the southern fringe of the hobq desert inner mongolia resulted in the vegetation and thus stability of dunes in this area our research focuses on a typical parabolic dune which was active in 2011 and became stabilized after vegetation colonization topographic surveys and surface sediment analysis of the morphology and surface sands of the parabolic dune indicate that decreasing mean grain size and sorting values better sorting slightly more positive skewness and increasing kurtosis occurred over the dune surface during the incipient phase of stabilization there was a strong relationship between grain size sorting and dune mobility surface sand from the stabilized dune was generally finer and better sorted than at the same location when the dune was active during 2011 2012 the dune head had moved eastwards by approximately 2 3 m while its two arms expanded outward by approximately 3 2 m the height of the dune decreased and the dune became larger with a decreasing volume once anchored 2013 2014 the overall morphology and the grain size and sorting characteristics of the dune became more constant and quite different than when the dune was active

aeolian deposition and its effect on soil and vegetation changes on stabilised desert dunes in northern china abstract spatial and temporal patterns of aeolian deposition at shapotou northern china were studied on a chronosequence 0 12 29 and 37 years of stabilised desert dunes aeolian deposition markedly influenced soil and vegetation changes on the dunes the spatial pattern of aeolian deposition was studied using dust traps and measurements of the depth of aeolian accumulation mean deposition from august 1993 to july 1994 was 372 g m 2 and showed a complex spatial pattern determined by prevailing wind direction topography and shrub distribution contrasts between the topographic pattern of aeolian deposition trap data and accumulation thickness of aeolian deposits indicate that the measured pattern of aeolian deposition alone is insufficient to explain the pattern of accumulation an accretionary surface soil or grey sand containing much aeolian derived particles is developing on the stabilised dunes at a mean rate of 1 6 mm year rapid accumulation of aeolian particles significantly changed the surface environment increased moisture retention by the finer grey sand resulted in decreased moisture penetration and subsequent desiccation of the deeper dune sands this has led to vegetation changes with the deep rooted planted xerophytic shrubs declining from 12 to only 3 cover after 37 years of stabilisation the shrubs were replaced by a widespread microphytic crust and later by shallow rooted annual species which increased from 0 to approximately 12 cover over the same period the implications of projected increases in the dustiness of arid regions on the stability of desert dunes and vegetated desert margins are discussed stabilised dunes may become increasingly vulnerable to deflation with the progressive decline in shrub cover

the effect of surface curvature on the deposition of loess a physical model summary a physical model for the deposition of fine dusty material loess on curved surfaces is presented the model is tested in a sedimentation experiment with a symmetrical hill with length axis perpendicular to the flow direction in a wind tunnel it appears both from the model and the experiment that loess deposition will occur preferably on windward slopes and not on leeward ones in contrast to the widespread wind shadow concept below the deflation threshold loess deposition increases as wind speed increases above the deflation threshold an effective accumulation of the loess layer on the surface will occur within a well defined wind speed interval the loess layer on the surface will erode away only if wind speed has exceeded this interval for flat and dry surfaces free of roughness elements the upper limit of the interval is 7 m s free stream velocity for wet surfaces however it may be considerably higher 15 m s and more

wind tunnel simulation of aeolian sandy soil erodibility under human disturbance abstract inappropriate anthropogenic activities such as overcultivation and overgrazing of steppe and excessive collection of fuelwood are largely responsible for current desertification in china however quantitative information concerning the impacts of human disturbance on soil erosion remains sparse this study investigated aeolian sandy soil erodibility under human disturbance by wind tunnel simulation the fixed aeolian sandy soils were taken from an artificial vegetation protective system on mobile dunes at the southeastern edge of the tengger desert the results indicate that 1 human disturbance such as cultivation can accelerate the erodibility of the fixed aeolian sandy soil the ratio between total soil loss from the undisturbed soil and the cultivated soil is about 0 004 2 surface vegetation and microbiotic crust are the main factors responsible for the natural wind erodibility of the fixed sandy soil wind erosion rate increases with decreasing percent of the vegetation and crust cover 3 the grain size distribution shows a higher percentage of particles in the range 1 0 mm and a lower percentage in the range

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

the spatial and temporal variability of sand erosion across a stabilizing coastal dune field this study aimed at quantifying the temporal and spatial variability in sand erosion and deposition over a coastal dune field in israel these were measured monthly over 2 years using 315 erosion pins over four transects that were placed perpendicular to the coastline vegetation cover was estimated based on aerial photographs and landsat satellite images whereas the relative height was based on a digital elevation model these variables were calculated for the area upwind south west of the erosion pins at various lengths ranging from 15 to 400 m nine geomorphologic units were defined five related to active units and four to stabilized units in active units at least 65 of the temporal variance in the annual absolute changes in sand level was explained by the index of resultant drift potential with most of the sand movement occurring during winter storms local rainfall had no apparent impact on sand mobility due to the low coincidence of sand carrying winds and rainfall in israel during the passage of frontal cyclones as for the spatial variables only a weak correlation was found between sand mobility with the distance from the coastline r 2 18 rather sand erosion and deposition were influenced by vegetation cover and the relative height of an area of 100 200 m upwind the values of soil adjusted vegetation index were significantly negatively correlated with annual absolute changes r 2 40 whereas the relative height was significantly positively correlated r 2 36 applying a multiple regression model 68 of the spatial variability in sand mobility was explained the resulting map of sand activity clearly shows that at this stage of the stabilization process most of the dunes are now disconnected and movement of sand grains from the beach or between the dunes is very limited these methods can be applied into spatial and temporal models of sand mobility thus assessing the impact of different management practices on coastal dunes

evolution of soil properties on stabilized sands in the tengger desert china abstract the spatial and temporal patterns of pedogenesis on stabilized dunes at shapotou northwestern china were studied on the time sequences of 0 18 35 and 43 years the spatial pattern of soil formation was estimated by measuring the thickness of accumulated sand fractions on the stabilized dune surface and by analyzing the characteristics and properties of soil the results showed that the environment of soil formation and circulation of soil material were influenced in the processes of shifting sand fixation and the mean soil particle size changed from 0 2 to

aeolian processes and the biosphere ravi s d odorico p breshears d d field j p goudie a s huxman t e li j okin g s swap r j thomas a d pelt s v whicker j j zobeck t m 2011 aeolian processes and the biosphere reviews of geophysics 49 3

recovery of topsoil physicochemical properties in revegetated sites in the sand burial ecosystems of the tengger desert northern china abstract recovery in soil properties and processes after sand burial in the tengger desert northern china was documented at five different aged revegetated sites 1956 1964 1973 1982 and 1991 and at a reference site with native vegetation which had never been damaged by sand burial and was enclosed for grazing the proportions of silt and clay depth of topsoil and biological soil crusts and concentrations of soil organic c k total n and total p increased with years since revegetation most characteristics of topsoil 0 5 cm characteristics had recovered to 60 of those measured at the reference site by 50 years after sand binding vegetation had been established exceptions were electrical conductivity and contents of sand silt caco 3 and organic c which recovered to 20 40 of the values at the reference site the difference in annual recovery rates of soil properties between the two most recently revegetated sites 0 14 years was greater than the difference between the two oldest revegetated sites 43 50 years best fit asymptote models showed that the estimated times for the soil properties in the 50 year old site to reach the same levels as in the reference site i e an undisturbed native steppified desert ecosystem would be between 23 and 245 years but for some properties even maximum recovery after 50 years still fell significantly short of the level at the reference site these results suggest that soil recovery is a slow process in an extremely arid desert environment and therefore the conservation of soil habitat is a crucial issue for land managers

mathematical models of vegetation pattern formation in ecohydrology 1 highly organized vegetation patterns can be found in a number of landscapes around the world in recent years several authors have investigated the processes underlying vegetation pattern formation patterns that are induced neither by heterogeneity in soil properties nor by the local topography are generally explained as the result of spatial self organization resulting from symmetry breaking instability in nonlinear systems in this case the spatial dynamics are able to destabilize the homogeneous state of the system leading to the emergence of stable heterogeneous configurations both deterministic and stochastic mechanisms may explain the self organized vegetation patterns observed in nature after an extensive analysis of deterministic theories we review noise induced mechanisms of pattern formation and provide some examples of applications relevant to the environmental sciences

dust transport and the question of desert loess formation although contemporary dust storms are frequent in arid and semi arid areas desert loess deposits are poorly developed much of the world s loess occurs in mid latitude areas which experienced glaciation during the pleistocene ocean core evidence indicates that dust transport from sub tropical deserts increased during cold stages of the pleistocene but loess formed only on certain desert margins for reasons which have not been fully explained this paper re examines the mechanisms of dust transport and deposition and the circumstances leading to the accumulation of thick loess typical loess is composed mainly of medium silt grains which are transported in short term suspension a few metres above the ground significant thicknesses of loess form only when dust is trapped within a limited area often relatively close to the source dust particles finer than 20 m are transported mainly in long term suspension over a greater height range and may be widely dispersed the availability of silt and the frequency magnitude and direction of dust transporting winds are important factors governing the potential for loess formation but the existence of a suitable dust trap is particularly important traps may be formed by topographic obstacles areas of moist ground or vegetated surfaces vegetation adjacent to glacial outwash plains and braided meltwater streams trapped dust in mid latitudes during the pleistocene dust blown during glacial periods from certain deserts notably in sinai soviet central asia and china accumulated as loess in neighbouring semi arid regions on the margins of other deserts loess formation was inhibited partly by the absence of vegetation traps during most of the holocene net dust deposition rates in all desert marginal areas have been too low for significant loess accumulation this is mainly due to a reduction in silt availability and a tendency towards landscape stability reported dust storm frequencies during the past 50 years over estimate the longer term holocene dust flux due to the effects of human activities much modern dust owes its origin to erosion of cultivated soils in semi arid areas and is finer than typical loess

soil properties along a hillslope modified by wind erosion in the ordos plateau semi arid china abstract spatial variations of soil properties at three topographic sites along a hillslope were studied in the ordos plateau of semi arid china soil properties at the three positions of the hillside acted as disconnected values soil particles 0 5 mm in diameter decreased downslope and those between 0 05 and 0 5 mm formed a larger fraction of the soil in the midslope than in the summit or footslope total mass of c n and p in the middle slope soil was the lowest among the soils in the three topographic positions abnormality of carbonate content and of mineralogical components of the soil along the hillslope suggests wind transportation from outside sources this result indicates that the site had undergone several cycles of rapid erosion and deposition

plate tectonics model for proterozoic continental accretion in the southwestern united states proterozoic crustal provinces in the southwestern united states decrease in age south from the archean wyoming province supracrustal rocks define three major age provinces from north to south 1 72 to 1 80 1 65 to 1 72 and 1 1 to 1 2 b y successions within each province are similar and define two assemblages a bimodal volcanic assemblage commonly overlain by a quartzite shale assemblage precambrian granitic plutons intrude all three provinces geochemical and sr isotope data indicate a variably depleted upper mantle source for basalts and a short lived these observations can be explained by a plate tectonics model involving successive marginal basin closures and andean type orogenies associated with southward migrating arcs the net result is to accrete 1 300 km of continental crust to the southwestern margin of north america between 1 8 and 1 1 b y ago

holocene eolian activation as a proxy for broad scale landscape change on the gila river indian community arizona abstract eolian sediments are common within the middle gila river valley southern arizona and reflect variability in eolian and fluvial processes during the late holocene this study focuses on deciphering the stratigraphic record of eolian deposition and associated luminescence dating of quartz extracts by single aliquot regeneration sar protocols stratigraphic assessment coupled with luminescence ages indicates that there are four broad eolian depositional events at ca 3145 220 yr 1950 1360 yr 800 100 yr and 690 315 yr this nascent chronology correlated with regional archeological evidence and paleoclimate proxy datasets leads to two general conclusions 1 loess deposits transverse dune formation and sand sheet deposition in the late holocene are probably linked to flow variability of the gila river though the last two events are concordant with regional megadroughts and 2 the stability of eolian landforms since the 19th century reflects the lack of eolian sediment supply during a period of fluvial incision resulting in entisol formation on dunes the prime catalyst of eolian activity during the late holocene is inferred to be sediment supply driven by climate periodicity and variable flow within the gila river catchment

the effects of sediment transport weathering and aeolian mechanisms on soil evolution aeolian derived soils are found throughout the world soil evolution processes in aeolian dominated landscapes differ from processes in bedrock weathering landscapes by a number of key aspects including the lack of 1 soil production depth dependency 2 surface armoring and 3 grain size self organization in the soil profile we use here a soil evolution model marm5d to study the differences between aeolian and bedrock weathering dominated landscapes by analyzing soil evolution on a hillslope under various aeolian and bedrock soil supply settings subject to fluvial and diffusive sediment transport the model simulates spatial and temporal variation in soil particle size distribution psd and profile depth for each grid cell on the landscape as a function of physical weathering aeolian deposition and diffusive and fluvial sediment transport our results indicate that surface armoring plays a major role in soil evolution under bedrock weathering dominated conditions armoring reduces soil erosion and in conjunction with depth dependent soil production leads to steady state soil grading and depth and a relatively uniform soil distribution in contrast aeolian dominated landscapes tend to have considerable spatial variability in soil depth and psd our results also indicate that in contrast with diffusive transport which is assumed to be psd independent fluvial sediment transport is strongly influenced by the soil production mechanism aeolian or bedrock weathering based on the results presented here we propose that aeolian dominated landscapes are more responsive to environmental changes e g climatic and anthropogenic compared with bedrock weathering landscapes we further propose that this sensitivity may help explain the patchy soil distribution that is often observed in aeolian dominated regions

pedogenetic interpretations of particle size distribution curves for an alpine environment abstract the qilian mountains are generally capped by a productive silty soil layer wherever the environment allows as holocene loess is prevalent across the qilian mountains we assume that at least some of these fine sediments are derived from loess deposition and that soils across the region may be genetically linked to test these hypotheses nine pedons in different landscapes within a typical alpine watershed of the qilian mountains were sampled we also collected fine earth samples from glacier surfaces and crevices of glacial debris in the moraine zone the particle size distribution psd is used as a proxy for identifying aeolian fractions in soils the psd curves of all of the fine earth fractions examined are polymodal although three modal sizes of roughly 16 m 35 m and 80 m are found in almost all sediments in varying proportions these modal sizes have been identified as three sources of aeolian sediments in different transport systems the composition and thickness of loess sediments are related to local site conditions and may be related to the paleoenvironmental history of the site clastic debris and vegetation cover serve as dust traps during different stages of soil formation in this alpine environment and soils grow upward with accumulating loess sediment our study demonstrates that psd curves can be used to determine the origins and especially aeolian origins of soils furthermore this study provides insight into the pedology ecology and paleoenvironmental history of loess affected ecosystems in alpine areas of the qinghai tibetan plateau

u pb geochronological constraints on the genesis of the olympic dam cu u au ag deposit south australia the olympic dam cu u au ag deposit is hosted by the olympic dam breccia complex a high level hematite rich hydrothermal breccia system which occurs entirely within and clearly postdates the roxby downs granite the u pb zircon age of the roxby downs granite is well constrained at 1588 or 4 ma field evidence indicates that brecciation hydrothermal alteration and cu u au ag ree mineralization in the olympic dam breccia complex were penecontemporaneous but this is inconsistent with differing ages from previous u pb and rb sr isotopic data on pitchblende and sericite new shrimp u pb zircon data for three olympic dam breccia complex igneous rock units confirm that cu u au ag ree mineralization was contemporaneous with brecciation and alteration and directly followed cooling of the roxby downs granite by as little as several 8 million years two of the dated olympic dam breccia complex rock units are interpreted as autobrecciated felsic dikes one crosscuts laminated hematite quartz sandstones and the other crosscuts cu u mineralized hematite rich breccias zircons from these dikes yielded ages of 1592 or 8 and 1584 or 20 ma respectively the third unit dated is a disrupted ash fall tuff horizon from within a diatreme which crosscuts hematite quartz breccias near the center of the deposit the northern extremities of this diatreme also crosscut hematitic breccias containing a substantial cu u ore zone zircons from this tuff horizon have an age of 1597 or 8 ma the tuff and associated subaerial or subaqueous volcaniclastics were unconsolidated or only weakly lithified at the time of their incorporation into the diatreme so the age of the tuff also reflects the age of diatreme activity these new isotopic data indicate that the olympic dam breccia complex has an age of approximately 1590 ma and therefore imply that brecciation closely followed emplacement and cooling of the roxby downs granite because these breccias contain sulfide fragments and polyminerallic ore fragments exhibit penecontemporaneous sulfide oxide textural relationships and show a close association between cu or u or ag or ree mineralization and fe rich breccias we argue that the metals of economic interest were introduced

land degradation in drylands interactions among hydrologic aeolian erosion and vegetation dynamics article i nfo land degradation in drylands is one of the major environmental issues of the 21st century particularly due to its impact on world food security and environmental quality climate change shifts in vegetation composition accelerated soil erosion processes and disturbances have rendered these landscapes susceptible to rapid degradation that has important feedbacks on regional climate and desertification even though the role of hydrologic aeolian erosion and vegetation dynamic processes in accelerating land degradation is well recognized most studies have concentrated only on the role of one or two of these components and not on the interactions among all three drawing on relevant published studies here we review recent contributions to the study of biotic and abiotic drivers of dryland degradation and we propose a more holistic perspective of the interactions between wind and water erosion processes in dryland systems how these processes affect vegetation patterns and how vegetation patterns in turn affect these processes notably changing climate and land use have resulted in rapid vegetation shifts which alter the rates and patterns of soil erosion in dryland systems with the predicted increase in aridity and an increase in the frequency of droughts in drylands around the world there could be an increasing dominance of abiotic controls of land degradation in particular hydrologic and aeolian soil erosion processes further changes in climate may alter the relative importance of wind versus water erosion in dryland ecosystems therefore acquiring a more holistic perspective of the interactions among hydrologic aeolian erosion and vegetation dynamic processes is fundamental to quantifying and modeling land degradation processes in drylands in changing climate disturbance regimes and management scenarios