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• The runoff, sediment load and runoff erosion power decreased significantly. • Compared with runoff, runoff erosion power-sediment relationship is better. • The power function of runoff erosion power and sediment is better than linear. • Erosion in particular geographic locations responds strongly to runoff erosion power. In recent years, the acceleration of urbanization in the Yangtze River Economic Belt (YREB) has brought about problems such as soil erosion, ecosystem degradation and decline in ecological service functions. Therefore, this paper selects the Fujiang River Basin (FRB) in Upper Yangtze River (UYR), and analyzes the relationship between runoff erosion power (REP) and sediment transport (ST) on the basis of analyzing the variation characteristics of hydrological elements. Based on SWAT model, a variety of scenarios are set up to quantitatively analyze the impact of different land use changes on runoff and ST and REP in the basin. The results indicated that: (1) The annual precipitation in FRB from 1960 to 2018 did not change significantly, while the annual runoff, annual ST and annual REP decreased significantly. Compared with runoff and runoff depth, the relationship between sediment transport modulus (STM) and REP is the best, especially the power function between them is better than the linear function. (2) The results of the evaluation indexes of the simulation results of the SWAT model based on the measured runoff and sediment data from 2008 to 2018 are pass and above, that is, the simulation results are considered reliable. (3) Under the five scenarios of conversion of sloping farmland to forest, conversion of dry land to paddy field and conversion of grassland to bushland and forest land, the runoff and ST in the basin decreased but the overall range was small. The simulation results of SWAT model show that the erosion of specific areas in the basin shows the greatest degree of weakening with the decrease of REP. [ABSTRACT FROM AUTHOR]

Aeolian deposits are frequently used for palaeoenvironmental change studies. Their formation depends on an array of requirements: the supply of material suitable for aeolian transport and favorable conditions of sediment availability and wind strength. In order to infer palaeoenvironmental information from aeolian sand deposits these factors need to be carefully evaluated. We present a study from northern Chinese Hexi Corridor, based on 11 optically stimulated luminescence (OSL) dated sediment sections. These represent interchanging aeolian and alluvial deposits under gravel surfaces and aeolian sand in dune fields interrupted by interdunal flood deposits. Investigations in two subareas reveal contrasting geomorphologic and sedimentary histories: (1) sediment deposition during the Pleistocene–Holocene transition (~ 12 ka) followed by deflation during the Holocene and (2) frequent sediment recycling revealed by a wide spectrum of ages throughout the Holocene. The late glacial sediment pulse recorded in the western Hexi Corridor is attributed to high sediment supply, generated by efficient (peri-)glacial sediment production during glacial times in the adjacent Qilian Shan (< 5700 m asl) and a moisture increase inducing the reworking of those (glacio-)fluvial deposits during the Pleistocene–Holocene transition. The absence of a powerful reworking agent preserved these late glacial deposits in the western Hexi Corridor in contrast to moister eastern parts where Holocene sediment reworking prevailed. Geomorphological and hydrological preconditions of the subareas are discussed and reveal the controlling influence of fluvial processes on sand supply for the aeolian system. While a perennial drainage is missing in the drier western part, the Hei River drainage is fed by higher monsoonal precipitation in the central Hexi Corridor. It maintains a sediment recycling system and has ensured a sufficient sediment supply throughout the Holocene. The study promotes closer consideration of the fluvial influence on aeolian archives in palaeoenvironmental studies from central Asian and other drylands. [ABSTRACT FROM AUTHOR]

Abstract: The delivery and transport of sediment through mountain rivers affects aquatic habitat and water resource infrastructure. While climate change is widely expected to produce significant changes in hydrology and stream temperature, the effects of climate change on sediment yield have received less attention. In the northern Rocky Mountains, we expect climate change to increase sediment yield primarily through changes in temperature and hydrology that promote vegetation disturbances (i.e., wildfire, insect/pathogen outbreak, drought-related die off). Here, we synthesize existing data from central Idaho to explore (1) how sediment yields are likely to respond to climate change in semi-arid basins influenced by wildfire, (2) the potential consequences for aquatic habitat and water resource infrastructure, and (3) prospects for mitigating sediment yields in forest basins. Recent climate-driven increases in the severity and extent of wildfire suggest that basin-scale sediment yields within the next few years to decades could be greater than the long-term average rate of 146Tkm−2 year−1 observed for central Idaho. These elevated sediment yields will likely impact downstream reservoirs, which were designed under conditions of historically lower sediment yield. Episodic erosional events (massive debris flows) that dominate post-fire sediment yields are impractical to mitigate, leaving road restoration as the most viable management opportunity for offsetting climate-related increases in sediment yield. However, short-term sediment yields from experimental basins with roads are three orders of magnitude smaller than those from individual fire-related events (on the order of 101 Tkm−2 year−1 compared to 104 Tkm−2 year−1, respectively, for similar contributing areas), suggesting that road restoration would provide a relatively minor reduction in sediment loads at the basin-scale. Nevertheless, the ecologically damaging effects of fine sediment (material<6mm) chronically produced from roads will require continued management efforts. [Copyright &y& Elsevier]

Abstract: To better understand the sedimentary history of the erosional crater of Makhtesh Hazera in the hyper-arid Negev Desert of southern Israel we have measured concentrations of in situ 10Be in alluvial sediments from the active drainage system and from abandoned alluvial terraces and dated them using optically stimulated luminescence (OSL). These sedimentary sequences suggest changes in the drainage system behavior over time and show a periodic pattern in which periods of sediment aggradation alternate with periods of degradation through incision and erosion. In alluvial terrace sediments, 10Be concentrations were combined with OSL ages to gain insight of the temporal framework of sediment deposition and shed light on the process of sediment storage. OSL and simple 10Be exposure ages of terrace sediments give deposition ages between ~340ka to ~50ka, at which time the youngest alluvial terrace was incised. Deposition was interrupted twice, at ~300ka and ~160ka, when periods of rapid incision caused the abandonment of the active fluvial surface and the stabilization of a younger and lower fluvial surface. In the active drainage system, 10Be concentrations suggest several possible quartz sources, of which the Lower Cretaceous sandstone bedrock exposed at the base of the cliff enclosing the Makhtesh is the most dominant. The results suggest that sediment eroding form these cliffs are conveyed through the active alluvial channels without significant sediment contribution from alluvial terraces or from eroded bedrock exposed within the Makhtesh. In contrast to our measurements in the active drainage system, 10Be concentrations in alluvial terrace sediments record significant storage within the Makhtesh. We suggest that the geometry of the Makhtesh, mainly the disproportion between the size of the Makhtesh and its narrow outlet, leads to significant accumulation of sediment within the Makhtesh. Episodic breaching of the barrier is followed by rapid and short-lived incision into the stored sediment. The long residence time of sediment within the Makhtesh results in high measured 10Be concentrations. At the end of each of these short incision episodes, when channels are already carved into the alluvial sediment and terraces are formed, the channels only convey sediment directly eroded from the bounding cliff of the Makhtesh; a situation presently observed. [Copyright &y& Elsevier]

Abstract: This paper describes the construction and application of a new field instrument, a Gauged Sediment Trap (GaST). Our GaST measures and captures aeolian-transported sediment, can be deployed for long periods of time (weeks), is easy to construct, and is extremely durable. The instrument consists of a water-level logger contained within an underground, water-filled sleeve, into which sediment is funneled from a surface trap. As sediment enters the sleeve water is displaced proportionally to the volume of sediment allowing for continuous monitoring of sediment accumulation. The rate of sediment transport and flux, for a given time period, is estimated through laboratory calibration using sediment from the study area and the GaST. The instrument can be affixed to almost any surface-sediment trap, whether saltation or bedload transport is the target. Data from laboratory calibration and several field tests staged in the summer and winter on Bogue Banks, NC, are presented. Using the HOBO® U20 Water-Level Logger, the GaST accurately captured sediment transport at a resolution of 5.71g (2.15cm3) of sediment per unit time, depending on sampling interval and overall sediment flux. The GaST predicted total sediment mass and volumes with less than 5% error. With an adjustable sampling interval, the GaST can be deployed for various lengths of time but may be limited by the rate of sediment accumulation (they can overflow) and the evaporation rate inside the sleeve (the water could completely evaporate in arid settings). [Copyright &y& Elsevier]

Abstract: The channel head, defined as the upstream boundary of concentrated water flow and sediment transport between definable banks, represents the transition from hillslope processes to fluvial processes. The ability to delineate the location along a slope at which channels initiate is important for understanding hydrologic and geomorphic processes governing headwater streams. Studies demonstrating an inverse relationship between either contributing drainage area (A) and local valley slope (θ) or basin length (L) and θ for channel heads come primarily from regions with humid climates. Seventy-eight channel heads were mapped in the headwaters of rivers in the semiarid Colorado Front Range. Multiple field sites were chosen to account for variability from aspect and elevation. Surface topographic parameters were measured in the field and analyzed to test the hypothesis that surface processes control channel initiation in this region. Although simple linear regressions indicate a poor inverse relationship between A and L and no relationship between L and θ, multiple regressions indicate that surface topographic parameters explain over half the variability in the location of channel heads. This suggests that surface processes exert an influence on channel initiation, but do not explain as much of the variability as observed in previous studies from wetter regions. A threshold of erosion necessary to initiate a channel was observed at ~10,000m2 for A, although values as high as 600,000m2 were mapped for some channel heads. Variation within the study area correlated with elevation, which is a proxy for differences in volume and type of precipitation; sites at lower elevation with less precipitation, but more intense convective rainfall, tend to have smaller contributing area and basin length. Aspect did not influence surface topographic parameters. We interpret the results to reflect surface and subsurface influences on channel initiation. Nearly 70% of the mapped channel heads coincide with constrictions created by weathered bedrock knobs, suggesting that local factors strongly influence channel initiation once the threshold for contributing area is exceeded. Field-mapped channel head locations plot at or downslope from the inflection point of a regional slope–area curve generated from 10m DEMs, although some extend well downslope into the region assumed to be dissected by alluvial channels. Most actual drainage areas for channel initiation are thus an order of magnitude larger, and plot in a significantly different portion of the slope–area graph, than would result from the widespread practice of assuming channel heads are located at the gradient reversal in such curves. [Copyright &y& Elsevier]

Abstract: Alluvial fan surfaces in the Atacama Desert of northern Chile preserve evidence of recent, precipitation-driven, surface flows. Determining the hydrologic characteristics of these flows is important for understanding the effects of rare yet significant storms in the region. Flow reconstruction, runoff analysis, and comparison with climatological data yield surface activation recurrence intervals of ∼1–20years for three small fans and their associated catchments proximal to Iquique and Antofagasta, Chile. Modeled discharges provide minimum constraints on the precipitation rates required to resurface fans in the hyper-arid region and suggest that relatively short-lived and intense precipitation events (1–3h, >4mmh−1) are capable of producing surface flows that mobilize and transport the largest grains found in channelized portions of the fan surface. The results of this study provide an indication of the ability of a particular storm event, i.e., precipitation rate, to activate a geomorphic surface and contribute to our understanding of the controls on surface evolution in hyper-arid environments. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: In this study, two small experimental catchments were selected in semi-arid grassland in Mongolia. The Kherlen-bayan Ulaan (KBU) catchment has been subjected to intensive grazing as a wintering shelter for domestic livestock animals, and the number of livestock animals in the Baganuur (BGN) catchment has been increasing over the last few decades. The rates and patterns of soil erosion within the catchments were estimated based on cesium-137 (137Cs) and lead-210 (210Pbex) inventories in bulk soil core samples. The medium-term (~40 years) soil erosion rates based on the 137Cs measurements indicated that annual soil loss from the KBU catchment was approximately three times greater than that from the BGN catchment. The 137Cs-derived rates and patterns of soil erosion indicated that soil in the KBU catchment was susceptible to surface erosion, with facilitated transport of eroded sediment to the catchment outlet. The 210Pbex-derived soil erosion rates were generally greater than those derived from 137Cs in both catchments. If we assume that the soil erosion rate has been increasing with increasing domestic livestock numbers, the most plausible explanation is that the 210Pbex-derived estimates represent recent increases in soil erosion. Furthermore, the 210Pbex/137Cs inventory ratio showed a tendency to increase with downslope distance on the eroded hillslope in the BGN catchment. Assuming that the increase in inventory ratio is a result of constant fallout input of 210Pbex on the eroded sediment during its transportation along the hillslope, the 210Pbex inventory may not be suitable to estimate soil erosion rates at sites where downslope movement of sediment is slow. Further discussion regarding interpretation of 210Pbex-derived soil loss is required, and the applicability of the 210Pbex technique on semi-arid hillslopes remains to be determined. [Copyright &y& Elsevier]

Coastal dunes have received growing attention in recent years because of the ecosystem services they provide and the high anthropic pressure that they have historically been subjected to and continue to endure. Such pressure especially affects arid dune fields where any changes are more noticeable due to their natural dynamics. The aim of this paper is to analyze the relationship between the degradation of an arid aeolian sedimentary system (El Médano, Tenerife, Spain) due to historical long-term land uses and its subsequent biogeomorphological evolution. The methodology combines historical sources (historical documents, aerial and common photographs and oral sources) and current ones (orthophotos, LiDAR data and field work). In order to analyze the response of the system to these uses, 8 plots were chosen in which 3 different historical land uses had resulted in the total or partial elimination of the vegetation and landforms. Biogeomorphological variables were measured on 461 nebkhas in these plots. The main results show that the historical land uses studied in this paper (aerodrome , aggregate extraction and crop cultivation) modified the entire system, with changes observed in the topography, vegetation cover and sediment availability for transport. Changes in topography and distance from shore were important factors in its recovery capacity. This research contributes to our understanding of the different aeolian sedimentary dynamics that can be detected in the same dune field (especially with nebkha landforms) and is of particular importance for making appropriate environmental management decisions to facilitate the recovery of the ecosystem. • Aggregate extractions on the foredune have an irreversible impact. • Different environmental patterns in a dunefield are responses to historical land uses. • Distance to the coast acts as a main factor in system recovery. • Historical land uses modify the natural gradients of the system. • Biogeomorphological patterns in 461 nebkhas were analyzed. [ABSTRACT FROM AUTHOR]

Aeolian sand movement contributes to evolution of surface landforms on Earth and Mars, as well as on Venus and Titan. Most natural landforms in arid regions are molded by wind with a general feature of unsteadiness. Many researches have improved our cognition of saltation in unsteady flow, but it is probably true that this issue is not yet fully analysed. In this paper, we conducted three-dimensional numerical simulations of wind-blown sand under unsteady wind conditions. The trajectories of sand particles are simulated by using a Lagrangian model. Particle motion, particle-bed interaction and wind modification have been taken into account. Results indicate that the characteristics of sand transport in unsteady and steady wind conditions profoundly differ; the sediment transport in unsteady conditions is significantly enhanced and increases with the amplitude of the sinusoidal wind fluctuations; the time series of sediment transport reveals a sine-like variation which lags behind the variation of the wind with a time delay of about 1 s (response time of saltation to wind variation). In unsteady conditions, sand transport shows an 'overshoot' which is embodied in the initial wave of the sediment transport. The impact of unsteady sediment transport should be paid more attention in future Aeolian research. Our work undertakes the key point by conducting three-dimensional numerical simulation of solid particles over unsteady wind conditions. Corresponding to different amplitudes and frequencies, the sediment transport rate reveals a sine-like variation, and the average sediment transport rate of unsteady flow is greater than that of uniform one. Unlabelled Image • 3D numerical simulations of wind-blown sand under unsteady wind are conducted in terms of LES. • Characteristics of unsteady wind have an impact on sediment transport and particle velocity. • The first wave crest of sediment transport is affected by wind period. [ABSTRACT FROM AUTHOR]