Influence of subaqueous processes on the construction and accumulation of an aeolian sand sheet

In aeolian sand sheets the interaction between aeolian and subaqueous processes is considered one of the principal factors that controls this depositional environment. To examine the role played by the subaqueous processes on the construction and accumulation of sand sheets, surface deposits and subsurface sedimentary sections of a currently active aeolian sand sheet, located in the Upper Tulum Valley (Argentina), have been examined. On the sand sheet surface, airflows enable the construction of nabkhas, wind‐rippled mantles (flattened accumulations of sand forming wind ripples), megaripples, and small transverse dunes. Subaqueous deposits consist of sandy current ripples covered by muddy laminae. The latter are generated by annual widespread but low‐energy floods that emanate from the nearby mountains in the aftermath of episodes of heavy precipitations. Deposits of subaqueous origin constitute 5% of the accumulated sand sheet thickness. The construction of the sand sheet is controlled by meteorological seasonal changes: the source area, the San Juan river alluvial fan, receives sediment by thaw‐waters in spring–summer; in fall–winter, when the water table lowers in the alluvial fan, the sediment is available for aeolian transport and construction of the sand sheet area. The flood events play an important role in enabling sand sheet accumulation: the muddy laminae serve to protect the underlying deposits from aeolian winnowing. Incipient cement of gypsum on the sand and vegetation cover acts as an additional stabilizing agent that promotes accumulation. Episodic and alternating events of erosion and sedimentation are considered the main reason for the absence of soils and palaeosols. Results from this study have enabled the development of a generic model with which to account for: (i) the influence of contemporaneous subaqueous processes on the construction and accumulation in recent and ancient sand sheets; and (ii) the absence of developed soils in this unstable topographic surface. Copyright © 2013 John Wiley & Sons, Ltd.     

Local erosion rates versus active tectonics: cosmic ray exposure modelling in Provence (south-east France)

Over the past decade, in situ-produced cosmogenic nuclides have revolutionised the study of landscape evolution. In particular, numerous studies have demonstrated that, in active tectonic settings, cosmic ray exposure dating of deformed or displaced geomorphic features makes it possible to quantify long-term deformation rates. In western European countries, erosion due to climatically driven processes and human activities is probably the factor that most limits the accuracy of exposure ages and landscape modification rates. In this study, we present the results of a depth-profiling technique applied to alluvial terraces located along the Rhône and the Moyenne Durance rivers. The expected decrease with depth of the measured ¹⁰Be concentrations has been modelled using a χ² inversion method in order to constrain the exposure history of the alluvial sediments. The results suggest that: (1) over the Quaternary, the local surface erosion rates including both regional uplift and climatically driven processes acting on landforms are on the order of 30 m/Myr in southeastern France, and (2) providing a fairly good bracketing of the exposure age, the modelled abandonment age of alluvial terraces affected by the Moyenne Durance Fault allows estimating incision rates, comparing the alluvial terrace elevations with topographic river profiles, and a minimum vertical slip rate value of roughly 0.02 mm/yr for the southern segment of the Moyenne Durance Fault.     

Evolution of sandstone peak‐forest landscapes – insights from quantifying erosional processes with cosmogenic nuclides

The sandstone peak‐forest landscape in Zhangjiajie UNESCO Global Geopark of Hunan Province, China, is characterized by >3000 vertical pillars and peak walls of up to 350 m height, representing a spectacular example of sandstone landform variety. Few studies have addressed the mechanisms and timescales of the longer‐term evolution of this landscape, and have focused on fluvial incision. We use in situ cosmogenic nuclides combined with GIS analysis to investigate the erosional processes contributing to the formation of pillars and peak‐forests, and discuss their relative roles in the formation and decay of the landscape. Model maximum‐limiting bedrock erosion rates are the highest along the narrow fluvial channels and valleys at the base of the sandstone pillars (~83–122 mm kyr^?1), and lowest on the peak wall tops (~2.5 mm kyr^?1). Erosion rates are highly variable and intermediate along vertical sandstone peak walls and pillars (~30 to 84 mm kyr^?1). Catchment‐wide denudation rates from river sediment vary between ~26 and 96 mm kyr^?1 and are generally consistent with vertical wall retreat rates. This highlights the importance of wall retreat for overall erosion in the sandstone peak‐forest. In combination with GIS‐derived erosional volumes, our results suggest that the peak‐forest formation in Zhangjiajie commenced in the Pliocene, and that the general evolution of the landscape followed our sequential refined model: (i) slow lowering rates following initial uplift; (ii) fast plateau dissection by headward knickpoint propagation along joints and faults followed by; (iii) increasing contribution of wall retreat in the well‐developed pillars and peak‐forests and a gradual decrease in overall denudation rates, leading to; (iv) the final consumption of pillars and peak‐forests. Our study provides an approach for quantifying the complex interplay between multiple geomorphic processes as required to assess the evolutionary pathways of other sandstone peak‐forest landscapes across the globe. Copyright © 2017 John Wiley & Sons, Ltd.     

Ecogeomorphic state variables and phase‐space construction for quantifying the evolution of vegetated aeolian landscapes

Cellular automaton modelling for the simulation of dune field formation and evolution has developed progressively in aeolian geomorphology in the last decade or so. A model that incorporates the effects of vegetation and its interactions with geomorphic landscape development – the Discrete Ecogeomorphic Aeolian Landscapes (DECAL) model – can replicate a number of important visual and qualitative aspects of the complex evolution of aeolian dune landscapes under the influence of vegetation dynamics in coastal environments. A key challenge in this research area is the analysis and comparison of both simulated and real‐world vegetated dune landscapes using objective and quantifiable principles. This study presents a methodological framework or protocol for numerically quantifying various ecogeomorphic attributes, using a suite of mathematically defined landscape metrics, to provide a rigorous and statistical evaluation of vegetated dune field evolution. Within this framework the model parameter space can be systematically explored and simulation outcomes can be methodically compared against real‐world landscapes. Based on a simplified scenario of parabolic dunes developing out of blow‐outs the resulting dune field realizations are investigated as a function of variable growth vigour of two simulated vegetation types (pioneer grass and successional woody shrub) by establishing a typological phase‐diagram of different landscape classes. The set of simulation outcomes furthermore defines a higher‐dimensional phase‐space, whose axes or dimensions can be interpreted by analysing how individual ecogeomorphic landscape metrics, or state variables, contribute to the data distribution. Principal component analysis can reduce this to a visual three‐dimensional (3D) phase‐space where landscape evolution can be plotted as time‐trajectories and where we can investigate the effects of changing environmental conditions partway through a simulation scenario. The use of landscape state variables and the construction of a 3D phase‐space presented here may provide a general template for quantifying many other eco‐geomorphic systems on the Earth's surface. Copyright © 2010 John Wiley & Sons, Ltd.     

Catchment response to lava damming: integrating field observation,geochronology and landscape evolution modelling

Combining field reconstruction and landscape evolution modelling can be useful to investigate the relative role of different drivers on catchment response. The Geren Catchment (~45 km²) in western Turkey is suitable for such a study, as it has been influenced by uplift, climate change and lava damming. Four Middle Pleistocene lava flows (⁴⁰Ar/³⁹Ar‐ dated from 310 to 175 ka) filled and dammed the Gediz River at the Gediz–Geren confluence, resulting in base‐level fluctuations of the otherwise uplift‐driven incising river. Field reconstruction and luminescence dating suggest fluvial terraces in the Geren Catchment are capped by Middle Pleistocene aggradational fills. This showed that incision of the Geren trunk stream has been delayed until the end of MIS 5. Subsequently, the catchment has responded to base‐level lowering since MIS 4 by 30 m of stepped net incision. Field reconstruction left us with uncertainty on the main drivers of terrace formation. Therefore, we used landscape evolution modelling to investigate catchment response to three scenarios of base‐level change: (i) uplift with climate change (rainfall and vegetation based on arboreal pollen); (ii) uplift, climate change and short‐lived damming events; (iii) uplift, climate and long‐lived damming events. Outputs were evaluated for erosion–aggradation evolution in trunk streams at two different distances from the catchment outlet. Climate influences erosion–aggradation activity in the catchment, although internal feedbacks influence timing and magnitude. Furthermore, lava damming events partly control if and where these climate‐driven aggradations occur. Damming thus leaves a legacy on current landscape evolution. Catchment response to long‐duration damming events corresponds best with field reconstruction and dating. The combination of climate and base level explains a significant part of the landscape evolution history of the Geren Catchment. By combining model results with fieldwork, additional conclusions on landscape evolution could be drawn. Copyright © 2016 John Wiley & Sons, Ltd.     

Quantifying hillslope erosion rates and processes for a coastal California landscape over varying timescales

The Earth's surface erodes by processes that occur over different spatial and temporal scales. Both continuous, low‐magnitude processes as well as infrequent, high‐magnitude events drive erosion of hilly soil‐mantled landscapes. To determine the potential variability of erosion rates we applied three independent, field‐based methods to a well‐studied catchment in the Marin Headlands of northern California. We present short‐term, basin‐wide erosion rates determined by measuring pond sediment volume (40 years) and measured activities of the fallout nuclides ¹³⁷Cs and ²¹⁰Pb (40–50 years) for comparison with long‐term (>10 ka) rates previously determined from in situ‐produced cosmogenic ¹⁰Be and ²⁶Al analyses. In addition to determining basin‐averaged rates, ¹³⁷Cs and ²¹⁰Pb enable us to calculate point‐specific erosion rates and use these rates to infer dominant erosion processes across the landscape. When examined in the context of established geomorphic transport laws, the correlations between point rates of soil loss from ¹³⁷Cs and ²¹⁰Pb inventories and landscape morphometry (i.e. topographic curvature and upslope drainage area) demonstrate that slope‐driven processes dominate on convex areas while overland flow processes dominate in concave hollows and channels. We show a good agreement in erosion rates determined by three independent methods: equivalent denudation rates of 143 ± 41 m Ma^?1 from pond sediment volume, 136 ± 36 m Ma^?1 from the combination of ¹³⁷Cs and ²¹⁰Pb, and 102 ± 25 m Ma^?1 from ¹⁰Be and ²⁶Al. Such agreement suggests that erosion of this landscape is not dominated by extreme events; rather, the rates and processes observed today are indicative of those operating for at least the past 10 000 years. Copyright © 2006 John Wiley & Sons, Ltd.     

Transient hillslope erosion in slow evolution landscapes

Transient evolution and adjustment to changing tectonic and climatic boundary conditions is an essential attribute of landscapes, and characterizing transient behavior is a key to understanding their dynamics and history. Developing new approaches to detect such transience has been explored by various methods, in particular to identify landscape response to Late Cenozoic and Quaternary climatic changes. Such studies have often focused on regions of high relief and/or active tectonic activity where interferences between tectonic and climatic signals might complicate the interpretation of the observations. We investigated the case of the hillslopes of the Serra do Cipó quartzitic range in SE Brazil in order to detect and quantify transience in a tectonically quiescent landscape over 100-ka timescales. We determined hilltop curvature from a high-resolution digital surface model derived from Pléiades imagery and measured cosmogenic nuclide (¹⁰Be and ²⁶Al) concentrations at these hilltop sites. We compare both observations with predictions of hillslope diffusion theory, observing a distinctive signature of an acceleration of denudation. We performed a joint inversion of topographic and isotopic data to retrieve an evolution of the hillslope sediment transport coefficient through time. The timing of the increase in denudation cannot be unequivocally associated with a single climatic event but is consistent with important, climatically modulated fluctuations in precipitation and erosion in this area during the Middle and Late Pleistocene.     

A new chronology for the age of Appalachian erosional surfaces determined by cosmogenic nuclides in cave sediments

The relative chronology of landscape evolution across the unglaciated Appalachian plateaus of Kentucky and Tennessee is well documented. For more than a century, geomorphologists have carefully mapped and correlated upland erosional surfaces inset by wide‐valley straths and smaller terraces. Constraining the timing of river incision into the Appalachian uplands was difficult in the past due to unsuitable dating methods and poorly preserved surface materials. Today, burial dating using the differential decay of cosmogenic ²⁶Al and ¹⁰Be in clastic cave sediments reveals more than five million years of landscape evolution preserved underground. Multilevel caves linked hydrologically to the incision history of the Cumberland River contain in situ sediments equivalent to fluvial deposits found scattered across the Eastern Highland Rim erosional surface. Cave sediments correlate with: (1) thick Lafayette‐type gravels on the Eastern Highland Rim deposited between c. 5·7 and c. 3·5 Ma; (2) initial incision of the Cumberland River into the Eastern Highland Rim after c. 3·5 Ma; (3) formation of the Parker strath between c. 3·5 Ma and c. 2·0 Ma; (4) incision into the Parker strath at c. 2 Ma; (5) formation of a major terrace between c. 2·0 Ma and c. 1·5 Ma; (6) shorter cycles of accelerated incision and base level stability beginning at c. 1·5 Ma; and (7) regional aggradation at c. 0·85 Ma. Initial incision into the Appalachian uplands is interpreted as a response to eustasy at 3·2–3·1 Ma. Incision of the Parker strath is interpreted as a response to eustasy at 2·5–2·4 Ma. A third incision event at c. 1·5 Ma corresponds with glacial reorganization of the Ohio River basin. Widespread aggradation of cave passages at c. 0·85 Ma is interpreted as the beginning of intense glacial–interglacial cycling associated with global climate change. Copyright © 2006 John Wiley & Sons, Ltd.     

Simulated soil erosion from a semiarid typical steppe watershed using an integrated aeolian and fluvial prediction model

Total soil erosion is a result of both aeolian and fluvial processes, which is particularly true in semiarid regions. However, although physically interrelated, these two processes have conventionally been studied and modelled independently. Recently, a few researchers highlighted the importance and need of considering both processes in concert as well as their interactions, but they did not give specific modelling approaches or algorithms. The objectives of this study were to (1) formulate an integrated aeolian and fluvial prediction (IAFP) model, (2) parameterize the IAFP model for a semiarid steppe watershed located in northeastern China by using literature and historical data and (3) use the model to predict soil erosion in the watershed and assess the sensitivity of predicted erosion to environmental factors such as soil moisture and vegetation coverage. The results indicated that the IAFP model can capture the dynamic interactions between aeolian and fluvial erosion processes. For the study watershed, the model predicted a higher occurrence frequency of fluvial erosion than that of aeolian erosion and showed that these two processes almost equivalently contributed to the average total erosion of 0.07 mm year^?1 across the simulation period. The ‘existing’ vegetation cover can provide an overall good protection of the soils, although the vegetation cover was predicted to play a larger role in a drier than a wetter year as well as in controlling aeolian than fluvial erosion. In addition, soil erosion was predicted to be more sensitive to soil moisture than land coverage. A soil moisture level of 0.23–0.25 was determined to be the probable switch point from aeolian‐to fluvial‐dominant process or vice versa. Copyright © 2012 John Wiley & Sons, Ltd.     

Stone-line formation processes documented by in situ-produced Be distribution, Jardim River basin, DF, Brazil

Concentrations of in situ-produced cosmogenic ¹⁰Be (T_1/2=1.5 Myr) were measured in quartz samples from a quartz vein and its connected stone line from the Jardim River basin, Distrito Federal, Brazil, in order to quantify the processes involved in the landscape evolution of that region. The exponential decrease of the ¹⁰Be concentrations along the quartz vein, as well as their systematic increase along the stone-line away from the quartz vein, suggests an autochthonous development. Two models allow to estimate the lateral displacement rate. A plugs model assuming that the sample depth, and hence the production rate, is constant, and a burial model assuming that the sample depth, and hence the production rate, varies through time, yield lateral displacement rate of 37±5 and 68±6 m Myr⁻¹, respectively.     

The impact of storm-triggered landslides on sediment dynamics and catchment-wide denudation rates in the southern Central Range of Taiwan following the extreme rainfall event of Typhoon Morakot

Extreme erosion events can produce large short-term sediment fluxes. Such events complicate erosion rates estimated from cosmogenic nuclide concentrations in river sediment by providing sediment with a concentration different from the long-term basin average. We present a detrital ¹⁰Be study in southern Taiwan, with multiple samples obtained in a time sequence bracketing the 2009 Typhoon Morakot, to assess the impact of landslide sediment on ¹⁰Be concentrations (N¹⁰Be) in river sediment. Sediment samples were collected from 13 major basins, two or three times over the last decade, to observe the temporal variation of N¹⁰Be. Landslide inventories with time intervals of 5–6 years were used to quantify sediment flux changes. A negative correlation between N¹⁰Be and landslide areal density indicates dilution of N¹⁰Be by landslide sediment. Denudation rates estimated from the diluted N¹⁰Be can be up to three times higher than the lowest rate derived from the same basins. Observed increases imply that, 3 years after the passage of Typhoon Morakot, fluvial channels still contain a considerable amount of sediment provided by hillslope landslides during the event. However, higher N¹⁰Be in 2016 samples indicate that the contribution from landslide sediment at the sampled grain size has decreased with time. The correlation between changes in N¹⁰Be and landslide area and volume is not strong, likely resulting from the stochastic and complex nature of sediment transport. To simultaneously evaluate the volume of landslide-derived sediment and estimate the background denudation rate, associated with less impulsive sediment supply, we constructed a sediment-mixing model with the time series of N¹⁰Be and landslide inventories. The spatial pattern of background erosion rate in southern Taiwan is consistent with the regional tectonic framework, indicating that the landscape is evolving mainly in response to the tectonic forcing, and this signal is modified, but not obscured by impulsive sediment supply. © 2019 John Wiley & Sons, Ltd.     

Climate and relief-induced controls on the temporal variability of denudation rates in a granitic upland

How soil erosion rates evolved over the last about 100 ka and how they relate to environmental and climate variability is largely unknown. This is due to a lack of suitable archives that help to trace this evolution. We determined in situ cosmogenic beryllium-10 (¹⁰Be) along vertical landforms (tors, boulders and scarps) on the Sila Massif to unravel their local exhumation patterns to develop a surface denudation model over millennia. Due to the physical resistance of tors, their rate of exhumation may be used to derive surface and, thus, soil denudation rates over time. We derived soil denudation rates that varied in the range 0–0.40 mm yr^-1. The investigated boulders, however, appear to have experienced repositioning processes about ~20–25 ka bp and were therefore a less reliable archive. The scarps of the Sila upland showed a rapid bedrock exposure within the last 8–15 ka. Overall, the denudation rates increased steadily after 75 ka bp but remained low until about 17 ka bp . The exhumation rates indicate a denudation pulse that occurred about 17–5 ka bp . Since then the rates have continuously decreased. We identify three key factors for these developments – climate, topography and vegetation. Between 75 and 17 ka bp , climate was colder and drier than today. The rapid changes towards warmer and humid conditions at the Pleistocene–Holocene transition apparently increased denudation rates. A denser vegetation cover with time counteracted denudation. Topography also determined the extent of denudation rates in the upland regime. On slopes, denudation rates were generally higher than on planar surfaces. By determining the exhumation rates of tors and scarps, soil erosion rates could be determined over long timescales and be related to topography and particularly to climate. This is key for understanding geomorphic dynamics under current environmental settings and future climate change. © 2019 John Wiley & Sons, Ltd. © 2019 John Wiley & Sons, Ltd.     

Geological constraints and 26Al–10Be burial dating isochrons

The ²⁶Al–¹⁰Be burial dating method has been applied to a range of problems in geochronology. This technique allows us to determine the burial age of quartz‐containing sediments, by measuring the concentration of cosmogenic ¹⁰Be and ²⁶Al in the quartz. In its most basic form, the method assumes a simple history (single exposure episode followed by burial) for the quartz clasts. Balco and Rovey have recently developed an innovative isochron version of this method, which can take into account a more complicated exposure history for the quartz, and used it to date a series of glacial tills. There can be constraints on the slope and intercept of the isochron, depending on how we model the geology of the Balco–Rovey approach. We show how to take these constraints into account when fitting the slope and intercept; we apply a Bayesian approach, in which there is a straightforward way to implement constraints. We discuss the important issues that arise; a variety of choices must be made in choosing the prior, both in what geological insights to include and in how to include them. Copyright © 2011 John Wiley & Sons, Ltd.     

Aeolian landform processes since the last deglaciation revealed by OSL chronology and stratigraphy in the Hulunbuir dune field in NE China

The Hulunbuir dune field (HLB) is situated near the northern limit of the East Asian summer monsoon (EASM), and vulnerable to climate change. The aeolian sand–paleosol sequences of this region are crucial for understanding the past landform processes in response to climate change, but not yet understood well due to chronological controversies. Here, we presented 20 optically stimulated luminescence (OSL) ages from five aeolian sand–paleosol profiles in the HLB, and reconstructed the aeolian landform processes since 18 ka. The findings of this study suggested that the HLB was probably dominated by mobile dunes before 18 ka, as 10 out of 11 aeolian samples were dated to 18–12 ka. Two strong sandy paleosol layers were found and dated to ∼9 ka and 5–0.5 ka, indicating that strong in situ pedogenic process on the accumulative sand could occur during the Holocene. The OSL ages of samples near the top of three profiles were >9.5 ka, indicating two possible surface processes. First, the land surface was stable since 9.5 ka after stabilization, with no accumulation or erosion. Alternatively, the surface could have been erosive with the eroded sediments feeding downwind active dunes. The latter explanation is consistent with the current local landforms, which has widespread blowout pits, indicators of strong wind erosion. We emphasized that the OSL age of a sand layer sample in fossil dunes implied the onset of mobile dune stabilization, not the age of dune activity, as previously stated.     

Sedimentary and OSL dating evidence for the development of the present Hobq desert landscape, northern China

The sedimentary sequence and landscape of the Hobq desert was observed through twelve profiles along five N-S sections extending through the entire desert. Aeolian sands were found to overlie the alluvial, diluvial, and lacustrine sediments in this desert. Optically stimulated luminescence (OSL) dating results were obtained from post-IR OSL signals of quartz fractions of sand samples at the bottom of sand dunes and hills by using the Double-SAR protocol. The OSL ages reveal that the latest sand accumulation began around 19 ka in the northwestern part and 9 ka in the eastern part of the Hobq Desert. Around 7 ka, the sand accumulation was strengthened and extended southward and northward 2 ka to develop the present desert landscape. Our study suggests that the aeolian sand accumulation around 19, 9 and 7 ka resulted from the weakening of the Asian summer monsoon over this region. However, the rapid development of the present Hobq desert landscape since 2 ka was likely triggered by human activities in this desert.     

Relations between rainfall–runoff‐induced erosion and aeolian deposition at archaeological sites in a semi‐arid dam‐controlled river corridor

Process dynamics in fluvial‐based dryland environments are highly complex with fluvial, aeolian, and alluvial processes all contributing to landscape change. When anthropogenic activities such as dam‐building affect fluvial processes, the complexity in local response can be further increased by flood‐ and sediment‐limiting flows. Understanding these complexities is key to predicting landscape behavior in drylands and has important scientific and management implications, including for studies related to paleoclimatology, landscape ecology evolution, and archaeological site context and preservation. Here we use multi‐temporal LiDAR surveys, local weather data, and geomorphological observations to identify trends in site change throughout the 446‐km‐long semi‐arid Colorado River corridor in Grand Canyon, Arizona, USA, where archaeological site degradation related to the effects of upstream dam operation is a concern. Using several site case studies, we show the range of landscape responses that might be expected from concomitant occurrence of dam‐controlled fluvial sand bar deposition, aeolian sand transport, and rainfall‐induced erosion. Empirical rainfall‐erosion threshold analyses coupled with a numerical rainfall–runoff–soil erosion model indicate that infiltration‐excess overland flow and gullying govern large‐scale (centimeter‐ to decimeter‐scale) landscape changes, but that aeolian deposition can in some cases mitigate gully erosion. Whereas threshold analyses identify the normalized rainfall intensity (defined as the ratio of rainfall intensity to hydraulic conductivity) as the primary factor governing hydrologic‐driven erosion, assessment of false positives and false negatives in the dataset highlight topographic slope as the next most important parameter governing site response. Analysis of 4+ years of high resolution (four‐minute) weather data and 75+ years of low resolution (daily) climate records indicates that dryland erosion is dependent on short‐term, storm‐driven rainfall intensity rather than cumulative rainfall, and that erosion can occur outside of wet seasons and even wet years. These results can apply to other similar semi‐arid landscapes where process complexity may not be fully understood. Published 2015. This article is a U.S. Government work and is in the public domain in the USA     

Quantifying erosional equilibrium across a slowly eroding,soil mantled landscape

The textbook concept of an equilibrium landscape, which posits that soil production and erosion are balanced and equal channel incision, is rarely quantified for natural systems. In contrast to mountainous, rapidly eroding terrain, low relief and slow-eroding landscapes are poorly studied despite being widespread and densely inhabited. We use three field sites along a climosequence in South Africa to quantify very slow (2-5 m/My) soil production rates that do not vary across hillslopes or with climate. We show these rates to be indistinguishable from spatially invariant catchment-average erosion rates while soil depth and chemical weathering increase strongly with rainfall across our sites. Our analyses imply landscape-scale equilibrium although the dominant means of denudation varies from physical weathering in dry climates to chemical weathering in wet climates. In the two wetter sites, chemical weathering is so significant that clay translocates both vertically in soil columns and horizontally down hillslope catenas, resulting in particle size variation and the accumulation of buried stone lines at the clay-rich depth. We infer hundred-thousand-year residence times of these stone lines and suggest that bioturbation by termites plays a key role in exhuming sediment into the mobile soil layer from significant depths below the clay layer. Our results suggest how tradeoffs in physical and chemical weathering, potentially modulated by biological processes, shape slowly eroding, equilibrium landscapes. © 2019 John Wiley & Sons, Ltd.     

The value of environmental modelling languages for building distributed hydrological models

An evaluation is made of the suitability of programming languages for hydrological modellers to create distributed, process‐based hydrological models. Both system programming languages and high‐level environmental modelling languages are evaluated based on a list of requirements for the optimal programming language for such models. This is illustrated with a case study, implemented using the PCRaster environmental modelling language to create a distributed, process‐based hydrological model based on the concepts of KINEROS‐EUROSEM. The main conclusion is that system programming languages are not ideal for hydrologists who are not computer programmers because the level of thinking of these languages is too strongly related to specialized computer science. A higher level environmental modelling language is better in the sense that it operates at the conceptual level of the hydrologist. This is because it contains operators that identify hydrological processes that operate on hydrological entities, such as two‐dimensional maps, three‐dimensional blocks and time‐series. The case study illustrates the advantages of using an environmental modelling language as compared with system programming languages in fulfilling requirements on the level of thinking applied in the language, the reusability of the program code, the lack of technical details in the program, a short model development time and learnability. The study shows that environmental modelling languages are equally good as system programming languages in minimizing programming errors, but are worse in generic application and performance. It is expected that environmental modelling languages will be used in future mainly for development of new models that can be tailored to modelling aims and the field data available. Copyright © 2002 John Wiley & Sons, Ltd.     

On the development of a magnetic susceptibility-based tracer for aeolian sediment transport research

Aeolian processes – the erosion, transport, and deposition of sediment by wind – play important geomorphological and ecological roles in drylands. These processes are known to impact the spatial patterns of soil, nutrients, plant-available water, and vegetation in many dryland ecosystems. Tracers, such as rare earth elements and stable isotopes have been successfully used to quantify the transport and redistribution of sediment by aeolian processes in these ecosystems. However, many of the existing tracer techniques are labor-intensive and cost-prohibitive, and hence simpler alternative approaches are needed to track aeolian redistribution of sediments. To address this methodological gap, we test the applicability of a novel metal tracer-based methodology for estimating post-fire aeolian sediment redistribution, using spatio-temporal measurements of low-field magnetic susceptibility (MS). We applied magnetic metal tracers on soil microsites beneath shrub vegetation in recently burned and in control treatments in a heterogeneous landscape in the Chihuahuan desert (New Mexico, USA). Our results indicate a spatially homogeneous distribution of the magnetic tracers on the landscape after post-burn wind erosion events. MS decreased after wind erosion events on the burned shrub microsites, indicating that these areas functioned as sediment sources following the wildfire, whereas they are known to be sediment sinks in the undisturbed (e.g. not recently burned) ecosystem. This experiment represents the first step toward the development of a cost-effective and non-destructive tracer-based approach to estimate the transport and redistribution of sediment by aeolian processes. © 2018 John Wiley & Sons, Ltd.     

Experimental study of aeolian sand ripples in a wind tunnel

The topographic parameters and propagation velocity of aeolian sand ripples reflect complex erosion, transport, and deposition processes of sand on the land surface. In this study, three Nikon cameras located in the windward (0–1 m), middle (4.5–5.5 m), and downwind (9–10 m) zones of a 10 m long sand bed are used to continuously record changes in sand ripples. Based on the data extracted from these images, this study reaches the following conclusions. (1) The initial formation and full development times of sand ripples over a flatbed decrease with wind velocity. (2) The wavelengths of full development sand ripples are approximately twice the wavelengths of initially formed sand ripples. Both wavelengths increase linearly with friction velocity. During the developing stage of sand ripples, the wavelength increases linearly with time. (3) The propagation velocity of full development sand ripples is approximately 0.6 times that of the initially formed sand ripples. The propagation velocity of both initial and full development of sand ripples increase as power functions with respect to friction velocity. During the developing stage of sand ripples, the propagation velocity decreases with time following a power law. These results provide new information for understanding the formation and evolution of aeolian sand ripples and help improve numerical simulations. Copyright © 2017 John Wiley & Sons, Ltd.