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Aeolian dune fields mantle the Earth in both vegetated (stable) and unvegetated (active) states. Changes in state are poorly understood; in particular, little is known about reactivation (devegetation) from a vegetated state. Available evidence indicates that dune reactivation can be driven by changes in aridity, increased wind speed, fire, biogenic disturbance, human disturbance, or a combination of the previous. How these controls fit together and define the reactivation potential of dune fields is presently unknown. Here we develop a framework to describe reactivation potential for a specific case: presently vegetated, supply-limited dune fields that develop blowouts under a unidirectional wind. We first define a conceptual model of blowout expansion, and then split the functions of vegetation in a stable dune field into: (i) maintenance of a protective skin, and (ii) blowout suppression. We model reactivation as disturbance breaking through the protective skin, which forms a blowout that is either (i) suppressed by colonizer species, or (ii) capable of advancing downwind and reactivating part of the dune field. The capacity for disturbance to break through the protective skin is a function of disturbance magnitude, area, and resistance of the skin. The blowout suppression capacity of a dune field is a function of sediment flux, blowout depth (related to geomorphology), and colonizer species vitality. By plotting a given dune field with two variables (protective skin breach rate and blowout suppression capacity) we define four states: (i) stable, (ii) blowout dominated, (iii) reactivating, or (iv) stable but disturbance susceptible. We reinforce the conceptual model with qualitative examples and discussion of experiments on grassland-stabilized dunes in Canada. Overall, our framework provides a starting point for quantifying the reactivation potential of vegetated dune fields.

Small unmanned aircraft systems (sUAS) are a relatively new type of aerial platform for acquiring high-resolution remote sensing measurements of Earth surface processes and landforms. However, despite growing application there has been little quantitative assessment of sUAS performance. Here we present results from a field experiment designed to evaluate the accuracy of a photogrammetrically-derived digital terrain model (DTM) developed from imagery acquired with a low-cost digital camera onboard an sUAS. We also show the utility of the high-resolution (0.1 m) sUAS imagery for resolving small-scale biogeomorphic features. The experiment was conducted in an area with active and stabilized aeolian landforms in the southern Canadian Prairies. Images were acquired with a Hawkeye RQ-84Z Areohawk fixed-wing sUAS. A total of 280 images were acquired along 14 flight lines, covering an area of 1.95 km2. The survey was completed in 4.5 h, including GPS surveying, sUAS setup and flight time. Standard image processing and photogrammetric techniques were used to produce a 1 m resolution DTM and a 0.1 m resolution orthorectified image mosaic. The latter revealed previously un-mapped bioturbation features. The vertical accuracy of the DTM was evaluated with 99 Real-Time Kinematic GPS points, while 20 of these points were used to quantify horizontal accuracy. The horizontal root mean squared error (RMSE) of the orthoimage was 0.18 m, while the vertical RMSE of the DTM was 0.29 m, which is equivalent to the RMSE of a bare earth LiDAR DTM for the same site. The combined error from both datasets was used to define a threshold of the minimum elevation difference that could be reliably attributed to erosion or deposition in the seven years separating the sUAS and LiDAR datasets. Overall, our results suggest that sUAS-acquired imagery may provide a low-cost, rapid, and flexible alternative to airborne LiDAR for geomorphological mapping.

Changes in surface conditions on cold-climate aeolian dunes are pronounced; during winter dunes are wet, snow covered, and/or frozen for extended periods of time. It is unknown how the critical wind speed for sediment transport (“threshold”) varies and how threshold may influence sediment transport predictions. Although the impact of surface conditions on threshold has been examined in synthetic experiments (wind tunnels), complicated feedbacks between threshold, sand transport, and surface conditions that occur in natural environments suggest that a ground-based empirical approach may provide enhanced insight. In this study we investigate threshold variability for 73 days during fall–winter–spring surface conditions from 18 November 2008 to 30 May 2009 in the Bigstick Sand Hills of Saskatchewan, Canada. Simultaneous measurements of threshold and atmospheric variables (air temperature, relative humidity, solar radiation, wind speed and direction) were used to examine the extent to which surface erodibility was regulated by meteorology. Time‐lapse images of the surface from a co-located camera were used for quality control and interpreting changes in the surface affecting threshold. Results reveal that threshold varied throughout the deployment (25–75% quartiles: 6.92–8.28 m s− 1; mean: 7.79 m s− 1). Threshold variability was especially evident at two scales: (i) event timescale and (ii) seasonal timescale. Event-scale variability peaked during mid-winter; in one event the threshold varied by 6 m s− 1 in 2 h with freezing and re-freezing of the surface and relatively constant atmospheric conditions. The causes of event-scale variability are complex though qualitatively related to changes of wind direction, antecedent meteorological conditions, and vertical variations of grain-scale bonding agents such as pore ice and moisture. Seasonal-scale changes manifested as an increase in threshold during fall, peaking in mid-winter, and decreasing in spring. Increased threshold in mid-winter was linked to lower insolation and air temperature, suggesting low erodibility due to the presence of pore ice. Correlation coefficients of threshold versus atmospheric variables yielded relatively weak correlations (air temperature: r = − 0.322; relative humidity: r = 0.388; solar radiation: r = − 0.309) that also varied according to wind direction, suggesting that the link between atmospheric conditions and surface erodibility on cold‐climate dunes is complex. This contrasts with results from field-based studies in warmer climates and controlled wind tunnel experiments, which show a more direct link between atmospheric variables (temperature and humidity) and surface erodibility. Nevertheless, our results do show a seasonal pattern of threshold that could be important for modeling cold-climate aeolian sediment transport.

Research into aeolian dune form and dynamics has benefited from simple and abstract cellular automata computer models. Many of these models are based upon a seminal framework proposed by Werner (1995). Unfortunately, most versions of this model are not publicly available or are not provided in a format that promotes widespread use. In our view, this hinders progress in linking model simulations to empirical data (and vice versa). To this end, we introduce an accessible, graphical user interface (GUI) version of the Werner model. The novelty of this contribution is that it provides a simple interface and detailed instructions that encourage widespread use and extension of the Werner dune model for research and training purposes. By lowering barriers for researchers to develop and test hypotheses about aeolian dune and dune field patterns, this release addresses recent calls to improve access to earth surface models.

Aeolian sediment transport threshold is commonly defined as the minimum wind speed (or shear stress) required for wind-driven sediment transport. Accurate and consistent quantification of this threshold is essential because it is an input variable in models used to predict wind erosion, dune activity, and dust emissions. The majority of threshold quantification has been performed with analogs (analytical models or wind tunnels); however, in the past few decades field-based approaches to threshold parameterization have become more common. Although several methods of calculating transport threshold from field data are available, their comparability is unknown. To address this issue we collected high resolution sediment transport and wind measurements (1 Hz) on an active sand dune for 11 days and compared four different methods of calculating threshold: (i) time fraction equivalence method (TFEM); (ii) Gaussian time fraction equivalence method (GTFEM); (iii) instantaneous method; and (iv) regression method. Time-paired measurements from the two most widely used methods (TFEM and GTFEM) were strongly correlated ( r = 0.977); however, correlations between other methods varied (from r = 0.861 to r = 0.261). To demonstrate the implications of using different threshold calculation methods we predicted mass transport, which ranged from 63.6 (instantaneous method) to 126.6 kg per crosswind meter (regression method). This inconsistency suggests that the threshold calculation method could have an appreciable impact on transport predictions. Threshold values are similarly inconsistent when the measurement interval is modified. As such, we do not recommend comparing any measured threshold with another. We discuss several strategies that may mitigate the impact of this issue such as clarification of semantics and method standardization. We also discuss several criticisms of field-based threshold measurements and re-conceptualizations that could allow investigators to develop a better understanding of field-based measurements. Overall, results from this study could allow future investigators to improve threshold (and transport) predictions.

Despite an abundance of sedimentary archives of mineral dust (i.e. loess) accumulations from cold, humid environments, the absence of contemporary process investigations limits paleoenvironmental interpretations in these settings. Dust accumulations measured at Jasper Lake, a seasonally-filled reach of the glacially-fed Athabasca River in the Canadian Rocky Mountains, are some of the highest contemporary rates recorded to date. High deposition rates, including a maximum of 27,632 kg ha−1 month−1, occur during river low-flow periods, but even the lowest deposition rates, occurring during bankfull periods, exceed other contemporary rates of deposition. High rates of dust deposition may be attributed to geomorphic and climatic controls affecting sediment supply, availability and transport, and biologic factors affecting accumulation. Localized confinement of the Jasper River by tributary river alluvial fans has caused channel expansion upstream, and formation of the shallow depositional basin known as Jasper Lake. This localized sedimentary basin, coupled with large seasonal water level fluctuations and suitably high wind speeds, favors seasonal dust production. In addition, a dense source-proximal coniferous forest stand encourages high dust accumulation, via increased aerodynamic roughness and airflow deceleration. The forest stand also appears to act as an efficient dust filter, with the interception and storage of dust by the forest canopy playing a significant role with regards to secondary fallout and sediment accumulation. Overall, these results provide new insights on the environmental controls of dust entrainment and accumulation in cold, humid settings, and help clarify controls on the formation of Holocene river-sourced loess deposits.

Piezoelectric sediment transport sensors (PSTSs) are commonly used to detect aeolian sediment transport. Detection of particles in the near-surface airstream can be used to derive measures of sediment transport threshold, which is an important parameter in sediment transport modeling. However, despite common usage, little comparative field data regarding the detection capabilities of PSTSs are available. This study compares the sediment transport detection of four PSTSs: Sensit H11-B, Sensit H11-LIN (10× configuration), Safire, and Sensit H11-LIN (1× configuration). These sensors were co-located on an active sand dune for 11 days with data measured and recorded at 1 Hz. During this period the relative proportion of time that sediment transport occurred was as follows: Sensit H11-B: 7.212%, Sensit H11-LIN 10×: 3.260%, Safire: 1.832% and, Sensit H11-LIN 1×: 0.089%. These relative differences demonstrate that the transport detection capabilities of the sensors are inconsistent. We find that the cylindrical design and variable sensitivities restrict straightforward prediction of field detection according to sensor specifications. From these data we demonstrate that the response of each sensor influences the estimate of sediment transport threshold. Regardless of the source of variability, the very presence of detection inconsistency is problematic. Overall, results from this investigation indicate that comparison of metrics derived from measures of sediment transport presence/absence (such as threshold) with different PSTSs is, at present, tenuous.

Topographic changes from erosion pins and on-site meteorological data document the spatial and temporal patterns of aeolian sediment transport at monthly to annual timescales across an active parabolic dune within a vegetation-stabilized inland, prairie dune field. Over two years, the sediment budget, calculated from digital elevation models, shows that the total volume of erosion (9890 m 3 ) is greater than the amount of deposition (6990 m 3 ), indicating a net loss of 2900 m 3 of sediment (or ∼ 29% of eroded sediment) from the dune. Sediment erosion occurred mainly on the stoss slope (3600 m 3 ; ∼ 36% of eroded sediment), but also on the south (2100 m 3 ; ∼ 21%) and north sides of the dune head (1700 m 3 ; ∼ 17%), the blowouts along the arms (1740 m 3 , ∼ 18%) and the crest (650 m 3 ; ∼ 7%). Erosion from the deflation basin is limited by surface roughness and armoring effects of a gravel lag deposit (100 m 3 ; ∼ 1%). Thus, the blowouts currently contribute to maintaining dune mobility because no other sediment input occurs from upwind. Sediment deposition onto the dune occurred primarily beyond the brink on the south and southeast lee slopes (5500 m 3 ; ∼ 80%), coinciding with the southeasterly resultant transport direction for November 2004–05. The net loss of about 2900 m 3 (∼ 29%) may be attributed to sediment carried in suspension over and beyond the dune. Correlation analysis between sediment transport and meteorological variables suggests that monthly to seasonal changes of surface conditions (e.g., vegetation cover, ground freezing, moisture) buffer the relative importance of temperature and precipitation on rates of sediment transport. Conversely, wind correlates well on a monthly to seasonal basis because it is a driver of transport under all types of surface conditions. Seasonal effects produce a complex interaction between wind, climate and surface conditions. This leads to a dynamic range of threshold velocities, which in turn causes spatial and temporal variations in transport-limiting and supply-limiting conditions. Collectively, these findings have implications for modeling parabolic dune morphodynamics and sediment transport in mid- to high-latitude inland settings.

A conceptual model is proposed for the activity of sand dune systems on the northern Great Plains that incorporates vegetation growth theory and geomorphic system theory. Dunefield activity is modeled as a cyclic phenomenon, alternating between active and stable states, with the latter as the system state attractor. The model is divided into two constituent parts: an activation model and a stabilization model. The activation model is qualitative and describes the transition from stable to active dunes as the result of a climatic perturbation such as drought that decreases vegetation cover. The intensity and duration of the climatic perturbation determines the rate of decline of vegetation cover. The stabilization model is quantitative and describes the transition from active to stable dunes using a logistic model of vegetation growth. Small perturbations during stabilization can prolong the duration of recovery, enabling dunes to remain active well after the initial perturbation. Despite the geographic focus of this study, the model appears applicable to a variety of environments where dune activity is limited, in part, by vegetation cover.

The historical activity of sand dunes on the southern Canadian prairies was investigated in order to determine the relation with recent climate variations. Changes in dune activity were determined from historical aerial photographs at seven sites with active parabolic dunes in Saskatchewan and Manitoba. The methodology developed combines digital image processing and geographical information system (GIS) analysis to measure changes in dune activity from the aerial photographs, as well as correlation analysis to determine the relation between dune activity and climate variations. Overall, dune activity has been decreasing since the early to mid 1900s as evidenced by greater vegetation colonization than sand dune migration or reactivation. The decrease in dune activity is significantly correlated with decadal-scale variations in aridity and is coincident with a decrease in annual wind speed. Evidence suggests that this response is superimposed on a longer trend towards stabilization, possibly in place since the late 1700s. Taken together, the effect of this complex response is that dune recovery on the southern Canadian prairies is prolonged well after an initial disturbance and therefore gives the impression of anomalous levels of activity for extended periods thereafter. For this reason, dune mobility indices predicated on short-term climate variations (years to decades) do not fully describe the present level of dune activity on the southern Canadian prairies.