Moving Sand Dunes Research Articles

Study on the Erodibility and Mechanical Resistance of Mulches Prepared from Micro Silica–Cement Mixtures

Mulching is fastest strategy to control sand dune movement in arid and semiarid areas. In the present study the effect of micro silica- cement mixture was evaluated as mulch. For this purpose, an experiment was carried out as a factorial arrangement and a completely randomized design with 3 replicates. Three studied factors included 6 micro silica rates (0 as control, 0.5, 2.5, 5, 7.5 and 12.5 percent), 2 rates of mulch thickness (one and two mm layers) and 2 time series (7 and 60 days). Prepared mulches based on different mixtures of micro silica + sand (400 g) and cement were sprayed on sand trays. Then 4 parameters including shear strength, penetration resistance, threshold friction velocity and soil losses at a wind speed of 15 ms−1 were measured on the studied treatments. Results obtained from the analysis of variances revealed that the effect of micro silica rates, thickness of mulch and time on the studied properties were significant. Mean comparisons also showed that shear strength, penetration resistance and threshold friction velocity increased and soil losses of treatments significantly decreased when the micro silica rates increased. The addition of micro silica to sand- cement mixture increased shear strength and penetration resistance by 76% and 82.5% respectively and decreased soil losses by 100%. The erodibility and mechanical properties of the treatments improved by increasing the thickness of the mulch. Moreover, in all studied treatments more improvements occurred in the mentioned properties of mulches during time. The application 7.5% of micro silica after 60 days was the optimal mulch to improve the soil erodibility and to increase the mechanical resistance against wind erosion.

The Use of SAR Offset Tracking for Detecting Sand Dune Movement in Sudan

Sand movement is one of the main environmental hazards in Northern Sudan that threaten livelihood and rural communities. This paper investigates for the first time the use of the Synthetic Aperture Radar (SAR) offset tracking technique for detecting sand movement in Northern Sudan, and distinguishes the impact of the movement influencing factors: wind speed/direction, vegetation and topography. High-resolution images from the Sentinel-1 satellite were used for the generation of displacement maps. Three different dune fields with different characteristics were investigated for a study period between 4 June and 14 October 2017 (133 days). Dune field 1 is vegetated and near a built-up area, dune field 2 is in an open environment with sand dunes overlaying rocky substrate, and dune field 3 is located near mountains. The cumulative east displacement over the study period was 1.8 m, −1.1 m and 4.8 m for the three dune fields, respectively, while the cumulative north displacement was 0.7 m, 2.9 m and 4.2 m. Large movement is detected in the non-vegetated dune fields, with an average dune velocity of 0.18 m/d, while the vegetated dune field had a velocity of 0.09 m/d, which emphasizes the fact that vegetation is an effective stabiliser of dune movement. The pixel offset results showed a positive correlation between the wind speed/direction and the dune movement. In addition to vegetation, topography also played a major role in diverting the direction of the blown sand mainly near the edges to the mountains and the vegetation barriers. This technique showed high competency in monitoring the movement of sand dunes, in addition to identifying areas exposed to large sand drifting as a risk mapping technique.

Desertification in Iraq and how to Combatit

Iraq faces many environmental challenges as a result of its geographical location within arid and semi-arid regions, as well as the economic, political and security conditions it faced. Desertification comes at the forefront of these challenges as it is considered one of the dangerous environmental manifestations because of its direct impact on food security and the impact on human health, which is the goal and main tool for development. This problem has been exacerbated during the last two decades due to several reasons, the most important of which are climate change, low rainfall rates, misuse of natural pastures, overgrazing and urban sprawl at the expense of agricultural lands in addition to unsustainable farming methods and wrong practices in irrigation operations and the increase in land areas affected by salinity and the significant deterioration in vegetation and those Covered by Moving sand dunes as a result of land degradation and erosion. In addition to the phenomenon of drying marshes, as they dried more than more than 90% of its area, and the research dealt with dividing the land of Iraq according to its production capacity into eight comprehensive sections for eight varieties.

Effect of Reactant Injection Rate on Solidifying Aeolian Sand via Microbially Induced Calcite Precipitation

Aeolian sand is a type of special soil with a loose structure, fine and uniform particles, and poor self-stabilization ability. These characteristics easily lead to sand dune movement and wind erosion in dry desert conditions. Therefore, reinforcement technology for aeolian sand is an important research topic. Microbially induced calcite precipitation (MICP) is a novel microbial soil-strengthening technique considered in this study with a focus on the effect of the reactant injection rate on the microbial solidification of aeolian sand. The aeolian sand was solidified using MICP with different injection rates of the cementing solution. The physical and mechanical properties as well as the microstructure of the solidified aeolian sand samples were analyzed. The experimental results show that using Sporosarcina pasteurii and the cementing solution (a mixture of urea and calcium chloride) can effectively solidify aeolian sand using the MICP technology. The engineering performance of the sand was effectively improved with an unconfined compressive strength that approached 14.01 MPa. The permeability coefficient of the solidified aeolian sand was significantly reduced, and the injection rate of the cementing solution significantly affected its uniformity. When the injection rate of the cementing solution was too low, most of the calcium carbonate was generated and accumulated at the top of the sand sample. Therefore, the upper part of the sample was relatively dense and strong, while the lower part had the opposite properties. When the injection rate of the cementing solution was too high, the roles of the upper and lower parts of the sample were reversed. When the injection rate of the cementing solution was 0.278 mol L−1 h−1, the solidified aeolian sand sample was relatively uniform and had a moderate unconfined compressive strength of 4.58–5.03 MPa. The uniform and high strength of the solidified aeolian sand was obtained by controlling the reactant injection rate. The optical microscope and SEM analyses indicated that the calcium carbonate crystals were rhombic hexahedral with sizes of approximately 5–10 μm. The calcium carbonate crystals were generated from the MICP in the solidified aeolian sand, which cemented the sand particles together, filled the pores between particles, increased the density and strength of the sand, and reduced its permeability coefficient.

Burial Process of a Seismic Station by Moving Dunes in Tarim Basin

AbstractA temporary seismometer vault was buried by a moving sand dune in the Taklimakan Desert at northwestern China in October 2019. The dune gradually covered the solar panel and the power supply to the seismic station was subsequently cut off. Here, we show that the burial process can be diagnosed according to the temperature record from the thermometer in the data-logger, an ultra-low-frequency seismic signal, and the change of high-frequency noise level from the continuous seismograms recorded by the broadband seismometer. The ultra-low-frequency seismic signal reflects the thermoelastic effect of the suspension spring in the seismometer corresponding to the temperature gradient in the sensor vault. At the same time, the variation of high-frequency noise level correlates well with the temperature profile and the ultra-low-frequency seismic signal, indicating the ground wind intensity. The peak frequency shifts and their different responses on three-component waveforms for the high-frequency noise might reflect the distance from the moving dunes to the station and their moving directions. This observation shows a potential usage of continuous seismograms to study rapid environment change around a temporary seismic station.

Measuring the effect of wind-driven processes on coastal dunes: a study of the Atlantis and Geelbek dune fields along the West Coast of South Africa

Dunes are dynamic features that can change location, shape or extent depending on wind direction and strength, the vegetation cover, temperature and moisture. This study focus on the primary factors impacting the change dynamics of sand dunes which are wind direction and wind strength. Two methods exist for measuring and detecting sand dune movements, namely, in situ surveys and change detection through remote sensing. This study applied change detection through remote sensing by using satellite imagery as methodology to monitor the movement and extent of change of two prominent coastal sand dunes located along the West Coast of South Africa. The significance of this study is to highlight the changes that occurred in the Atlantis and Geelbek coastal dune fields over the period 1998 to 2018 ascribable to the effect of wind-driven processes. The results showed that both these two dunes experienced more or less the same extent of movement and the direction of movement correlated well with the direction of the stronger summer wind-driven processes on the West Coast. However, it was also recorded that the extent of change of the dune fields were irregular.

Barchan Sand Dunes Collisions Detection in High Resolution Satellite Images based on Image Clustering and Transfer Learning

Desertification is a core concern for populations living in arid and semi-arid areas. Specifically, barchans dunes which are the fastest moving sand dunes put constant pressure over human settlements and infrastructure. Remote sensing was used to analyze sand dunes around Tarfaya city located in the south of Morocco in the Sahara Desert. In this area, dunes form long corridors made of thousands crescent shaped dunes moving simultaneously, thus, making data gathering in the field very difficult. A computer vision approach based on machine learning was proposed to automate the detection of barchans sand dunes and monitor their complex interactions. An IKONOS high resolution satellite image was used with the combination of a clustering algorithm for image segmentation of the dunes corridor, and a Transfer Learning model which was trained to detect three classes of objects: Barchan dunes, bare fields and a new introduced class consisting of dunes collisions. Indeed, collisions were very difficult to model using classical digital image processing methods due to the large variability of their shapes. The model was trained on 1000 image patches which were annotated then augmented to generate a larger dataset. The obtained detection results showed an accuracy of 84,01%. The interest of this research was to provide with a relatively affordable approach for tracking sand dunes locations in order to better understand their dynamics.

Effects of temperature and light on seed germination of ephemeral plants in the Gurbantunggut Desert, China: implications for vegetation restoration

Seed germination is a key transitional stage in plant life cycle and is strongly regulated by temperature and light. Therefore, research on the effects of temperature and light on seed germination is extremely meaningful for vegetation restoration, especially in desert ecosystems. Seeds of 28 ephemeral plants collected from the Gurbantunggut Desert of China were incubated at different temperatures (5°C/1°C, 15°C/5°C, 20°C/5°C, 25°C/10°C and 30°C/15°Q in 12-h light/12-h darkness or continuous darkness regimes, and the responses of seed germination to temperature and light and the germination speed were studied in 2016. Results showed that seed germination percentage of the 28 ephemeral plants significantly differed to temperature and light. We classified the studied plants as the following groups based on their responses to temperature: 1 low temperature responsed plants, 12 moderate temperature responsed plants, 7 high temperature responsed plants, 4 non-responsed plants and 5 plants of no germination. It should be noted that Corispermum lehmannianum Bunge is sensitive to moderate and high temperatures. There were 4 groups of plant in response to light, i.e., 7 light responsed plants, 10 dark responsed plants, 6 light non-responsed plants and 5 plants of no germination. Based on seed germination speed of the 28 ephemeral plants, we divided them into 4 patterns of germination, i.e., very rapid, moderately rapid, moderate and slow. Combining variations of temperature, precipitation and sand dune types in the study area, we suggested that very rapid and moderately rapid germinated plants could be used to moving sand dunes in early spring during vegetation restoration, moderate germinated plants could be used to semi-fixed sand dunes in late autumn, and slow germinated plants could be used to sand plain in summer. Thus, seedling establishment and vegetation restoration would be improved by considering seed germination characteristics of these ephemeral plants in the Gurbantunggut Desert, China.

Measuring Sand Dune Migration Rates with COSI-Corr and Landsat: Opportunities and Challenges

It has been over a decade since COSI-Corr, the Co-Registration of Optically Sensed Images and Correlation, was first used to produce a raster map of sand dune movement, however, no studies have yet applied it to the full Landsat archive. The orthorectified and geolocated Landsat Level-1 Precision Terrain (L1TP) products offer the opportunity to simplify the COSI-Corr pre-processing steps, allowing an automated workflow to be devised. In the Bodélé Depression, Chad, this automated workflow has calculated average dune speeds of 15.83 m/year and an increase in dune movement of 2.56 m/year ±12.58 m/year from 1987 to 2009. However, this increase does not stem from a systematic increase in dune mobility. The fastest 25% of dunes from 1987 to 1998 reduced their speed by 18.16%. The overall increase stems from the acceleration of features previously moving under 13.30 m/year. While successfully applied to the Bodélé Depression, the automated workflow produces highly variable outputs when applied to the Grand Erg Oriental, Algeria. Variations within path/row scene pairings are caused by the use of mobile features, such as dune crests, as ground control points (GCPs). This has the potential to warp Landsat scenes during the L1TP processing, potentially obfuscating dune migration. Two factors appear to be crucial in determining whether a Landsat scene is suitable for COSI-Corr analysis. Firstly, dune mobility must exceed the misregistration criteria. Secondly, GPCs should be located on static features such as bedrock outcrops.

Assessment of the distribution and activity of dunes in Iran based on mobility indices and ground data

Abstract Sand dune movement causes severe damage to infrastructure and rural settlements in Iran every year. Identifying active dunes and monitoring areas with migrating sand are important prerequisites for mitigating these damages. With regard to this objective, the spatial variation of the wind energy environment based on the sand drift potential (DP) was calculated from 204 meteorological stations. Three commonly used dune activity models – the Lancaster mobility index (1988), the Tsoar mobility index (2005), and the index developed by Yizhaq et al. (2009) – were used for the evaluation of Iran’s sand dune activity. The analysis of the indices showed that the dune activity was characterized by great spatial variation across Iran’s deserts. All three models identified fully active dunes in the Sistan plain, the whole of the Lut desert, as well as in the Zirkuh Qaien and Deyhook regions, while the dunes in the northern part of Rig Boland, Booshroyeh and in the Neyshabor dunefields were categorized as stabilized dunes. For other dunes, the models show a less unified activity classification, with the Lancaster and Yizhaq models having more similar results while the Tsoar model stands more apart. Based on these model results and fields observations, a modified Lancaster mobility index has been applied to show a more realistic spatial variation of sand dunes activity in Iran’s desert areas.

Responses of soil denitrifying bacterial communities carrying nirS, nirK, and nosZ genes to revegetation of moving sand dunes

Revegetation is commonly the first step to restoring degraded ecosystems in desertified regions. Large areas of plantations have been planted on moving sand dunes to control land desertification in the Horqin sandy land of Northeastern China. This method aims to recover the vegetation and improve soil nutrients thereby resulting in the change in soil microbial community and affecting soil nitrogen cycle. Denitrification is an important process of the soil nitrogen cycle. In this study, we investigated the diversities and abundances of nosZ, nirS, and nirK carrying denitrifiers in 32-year-old plantations of Caragana microphylla, Artemisia halodendron, Hedysarum fruticosum, Pinus sylvestris var. mongolica, Populus simonii, and Salix gordejevii, as well as in adjacent non-vegetated moving sand dune through clone library and real-time quantitative PCR analyses, respectively. We identified the dominant phyla of denitrifying community in the semi-arid sandy soil and determined the effects of plantation type on the soil denitrifying community. Results showed that revegetation on moving sand dunes increased the number of soil denitrifying bacteria. The structures of nosZ, nirK, and nirS bacterial communities were simple, and only one or two genera dominated the communities in the sandy soil. Pseudomonas, Mesorhizobium, and Azospirillum with the relative abundances ranged from 54.90% to 96.75%, 35.75% to 89.48%, and 58.36% to 100% in libraries, were the most dominant genus of nosZ-, nirK-, and nirS-bacterial communities, respectively, and may play important functions in soil denitrification in this area. The species diversity of nirK bacteria was relatively higher than those of the other two genes. The compositions and dominant taxa of soil denitrifying communities under different plantations were all similar to those in the moving sand dunes, and thus demonstrated that revegetation on moving sandy dune and plantation type slightly affected the compositions of nosZ, nirK, and nirS bacterial communities. However, the abundance of nosZ (ranged from 4.86 × 105 to 6.75 × 106 copies/g dry soil), nirK (ranged from 1.61 × 105 to 4.65 × 106), and nirS (ranged from 5.17 × 105 to 1.30 × 107) significantly varied with plantation type. Soil properties influenced the structures of denitrifying communities by increasing or decreasing the relative abundance of dominant taxa. Hence, the structures of nosZ, nirK, and nirS communities were affected quantitatively by plantation type and soil properties. The abundance of the three genes represents an indicator for soil denitrifying community in sand-fixation plantations.

Typhoon Soudelor (2015) Induced Offshore Movement of Sand Dunes and Geomorphological Change: Fujian Coast, China

Typhoons play a significant role in the marine sedimentary dynamic process and thus could significantly change the submarine geomorphology in their influence area. In this study, a high-resolution sub-bottom profiler and a side-scan sonar were used to detect the submarine geomorphology of the southeast coastal area of Nanri Island in the Taiwan Strait before and after Typhoon Soudelor—three times in 2015. The results show that the typhoon induced seaward movement of the sand dunes up to several tens of meters, resulting in significant changes in both the shape of the sand dunes and the scale of the exposed bedrocks. The typhoon also changed the submarine geomorphology, including the smoothing of anchor traces of fishing boats and the formation of relatively small sand dunes (groups). A comparison of the results of different surveys shows that the submarine geomorphology that was changed by Typhoon Soudelor could not recover within a short period of time. The wind field simulations of the typhoon process showed that the storm wave caused by the strong wind stress of the typhoon was a key dynamic factor for changing the submarine geomorphology.

Soil bacterial community restoration along a chronosequence of sand-fixing plantations on moving sand dunes in the Horqin sandy land in northeast China

In the desertified Horqin sandy land in northern China, sand-fixing plantations covering a large area have been gradually established by planting native shrubs or semi-shrubs on moving sand dunes to improve the degraded sandy ecosystem. Given that soil bacterial community mediates the biogeochemical cycling of essential elements, the secondary progressive succession of the soil microbial community may change with the establishment of sand-fixing plantations during the restoration process. However, the mechanism underlying the restoration of a soil bacterial community is unclear. We detected the variation in diversities and structures of soil bacterial communities by using the high-throughput Illumina MiSeq sequencing technique from a chronosequence of Caragana microphylla plantations and the natural Caragana microphylla community (NC), which is widely distributed in this region. We found that soil from a 32-year-old plantation possessed almost equal species richness to that of NC, thereby showing recovery of species richness during the stabilized process of moving sand dune. Bacterial community structure from the 9-year-old plantation was more similar to NC. The relative abundance of Sphingomonas responded to plantation age and can be an indicator of the restoration level of soil bacterial community. The changes in the soil properties caused by plantation establishment shaped the bacterial community structure at the genus level. All these findings demonstrated that the soil bacterial community structure in moving sand dunes can be restored to its native state by revegetation.

Using Remote Sensing and GIS Techniques in Monitoring and Mitigation of Geohazards in Najran Region, Saudi Arabia

Many sources of data (remote sensing and meteorological data, soils and groundwater samples) were used to estimate the magnitude of geological hazards, which are confirmed with field and laboratory investigation in Najran area, Kingdom Saudi Arabia. Najran area is one of these locations. It is subjected to a range of geo-hazards due to its intrinsic physiographic and geologic nature. Najran area is a growing urban and agricultural development region; however, some infrastructures have been constructed in vulnerable locations to geo-environmental hazards. The potential geo-hazards that may occur under desert conditions include sand accumulations, dune movement, mass westing and rock fall hazards, flash floods, sand stroom and problematic soils. The current study throws more light on all these geo-hazards in Najran area. Also, remediation methods for geo-hazard should be proposed to avoid these natural hazards. The present study is a trail to calculate and evaluate the drainage basins properties and potentiality using remote sensing and (GIS) tools. Twenty morphometric parameters were measured, in order to identify and evaluate flash flood hazards. Flash flood hazards in the Wadi Najran watershed is classified into three groups based on their morphometric parameters results; namely, highly, moderately and low slightly hazard degree. Our findings indicate that Najran area needs more attention and care. The Saudi Government has to join together with other people to reduce the resulting geological hazards.

Combined effect of micro silica with clay, and gypsum as mulches on shear strength and wind erosion rate of sands

Mulching is known as one of the fastest strategies to control wind erosion and sand dunes movement. We hypothesized that mixed micro silica with clay, gypsum and clay-gypsum as mulches will increase shear strength, threshold friction velocity and decrease soil losses of drifting sands. For this purpose, mixture of micro silica rates (0, 1, 5, 10, 15 and 20%) with clay, gypsum, and clay-gypsum applied on sand surfaces. After 60 days of mulching, shear strength, the threshold friction velocity and soil losses at a wind speed of 15 m/S at the height of 20 cm for 20 min. The results of this research revealed that the addition of 10% of micro silica in combination with clay and clay-gypsum increased the shear strength up to 10.6 and 37.5% and the threshold friction velocity up to 45.2 and 48.5%, respectively and decreased soil losses up to 100% in comparison with the samples without micro silica. Adding micro silica to gypsum had no considerable effect on shear strength, threshold friction velocity and soil losses. It was concluded that no pozzolanic reaction occurred between micro silica and gypsum and it was found that improvement in mechanical property and erodibility of clay-gypsum mulch was probably due to the pozzolanic reaction between micro silica and clay. Application of 10% of micro silica in combination with clay or clay-gypsum is therefore recommended as suitable mulch.

DETECTION OF CRESCENT SAND DUNES CONTOURS IN SATELLITE IMAGES USING AN ACTIVE SHAPE MODEL WITH A CASCADE CLASSIFIER

Abstract. Crescent sand dunes called barchans are the fastest moving sand dunes in the desert, causing disturbance for infrastructure and threatening human settlements. Their study is of great interest for urban planners and geologists interested in desertification (Hugenholtz et al., 2012). In order to study them at a large scale, the use of remote sensing is necessary. Indeed, barchans can be part of barchan fields which can be composed of thousands of dunes (Elbelrhiti et al.2008). Our region of interest is located in the south of Morocco, near the city of Laayoune, where barchans are stretching over a 400 km corridor of sand dunes. We used image processing techniques based on machine learning approaches to detect both the location and the outlines of barchan dunes. The process we developed combined two main parts: The first one consists of the detection of crescent shaped dunes in satellite images using a supervised learning method and the second one is the mapping of barchans contours (windward, brink and leeward) defining their 2D pattern. For the detection, we started by image enhancement techniques using contrast adjustment by histogram equalization along with noise reduction filters. We then used a supervised learning method: We annotated the samples and trained a hierarchical cascade classifier that we tested with both Haar and LBP features (Viola et Jones, 2001; Liao et al., 2007). Then, we merged positive bounding boxes exceeding a defined overlapping ratio. The positive examples were then qualified to the second part of our approach, where the exact contours were mapped using an image processing algorithm: We trained an ASM (Active Shape Model) (Cootes et al., 1995) to recognize the contours of barchans. We started by selecting a sample with 100 barchan dunes with 30 landmarks (10 landmarks for each one of the 3 outlines). We then aligned the shapes using Procrustes analysis, before proceeding to reduce the dimensionality using PCA. Finally, we tested different descriptors for the profiles matching: HOG features were used to construct a multivariate Gaussian model, and then SURF descriptors were fed an SVM. The result was a recursive model that successfully mapped the contours of barchans dunes. We experimented with IKONOS high resolution satellite images. The use of IKONOS high resolution satellite images proved useful not only to have a good accuracy, but also allowed to map the contours of barchans sand dunes with a high precision. Overall, the execution time of the combined methods was very satisfying.

Segmentation of Crescent Sand Dunes in High Resolution Satellite Images using a Support Vector Machine for Allometry

The study of sand dunes movement is essential to understand and prevent the desertification phenomenon, and collecting data from the field is a labor intensive task, as deserts contain usually a large number of sand dunes. We propose to use computer vision and machine learning algorithms, combined with remote sensing and specifically high resolution satellite images for collecting data about the position and characteristics of moving sand dunes. We focused on the fastest moving sand dunes called barchans, which are threatening the settlements in the region of Laayoune, Morocco. We developed a process with three stages: In the first stage, we used an image processing approach with cascading Haar features for the detection of dunes location. In the second stage, we used a support vector machine for the segmentation of contours, and in the third stage we used an algorithm to measure the allometric features of barchans dunes. We explored the collected data, and found relevant correlations between dunes length, and width, and horns sizes, which could be used as key indicators for dunes growth and progression. This study is therefore of high interest for urban planners and geologists who study sand dunes and require technical methods, based on machine learning and computer vision to allow them to collect large amount of data from satellite images to understand sand dunes progression and counter desertification problems. The use of cascading Haar feature provided a good accuracy, and the use of Support Vector Machines, along with the high resolution satellite images provided a good precision for the segmentation of barchan dunes contours, allowing the collection of morphological features which provide significant information on barchans sand dunes dynamics.

Windblown sand action on civil structures: Definition and probabilistic modelling

The accurate prediction of windblown sand effects on structures and infrastructures is fundamental for their design and performance assessment in desert and coastal regions. Windblown sand occurs in the form of moving sand dunes, sand drift, sand erosion, accumulation, and avalanching around built structures. Windblown sand is here defined as an environmental variable action, analogously to wind or snow actions. We categorize its effects into Sand Ultimate Limit States and Sand Serviceability Limit States. We propose a framework to assess windblown sand action by means of a probabilistic method because of the inborn variability of the phenomenon. The proposed method is useful for the design of both structures and infrastructures and of sand mitigation measures. It allows to evaluate characteristic values of the sand action and assess related characteristic times of failures. In order to prove its technical feasibility, the proposed framework is then applied to a desert railway because of the particular sensitivity of such kinds of infrastructures to windblown sand action.

Management and Evaluation of Sand Dunes and Their Impact on Environmental Degradation in the Eastern of Salah Al-Din Governorate

The study aimed at using RS and GIS to monitor changes in movement and stabilization of sand dunes and their effect on degradation and environmental pollution. Field work included selecting a representative area of ​​sand dunes in the east of Salah-Aldin Governorate, and then obtaining some of the samples. Laboratory work involved the preparation of samples for the determined some of the chemical and physical analysis. The library work included the acquisition of more than satellite images (1976, 2000, 2010 and 2011), and then we making at the Digital processing which involve geometric correction and spectral enhancement and then the values ​​of the indicators and plant indicators were calculated (NDVI, VI, SI, BSI, LDI, TNDVI, NDVI, MSAVI, IPVI, NDSDI, CI) by using the ERDAS and GIS program for the calculated degree of degradation and production of the NDVI maps, and calculations were active and non-active area. The results showed an increase in the area of non-active ​​sand dunes in the years(2010 and 2011) compared with the(1976 and 2000) years. The results showed that the values ​​of plant indicators (NDVI, VI, TNDVI, SAVI, MSAVI, IPVI and CI) were increased in the Non active Sand dunes. The study confirms that remote sensing techniques play an important role in monitoring the deterioration and the movement and stabilization of sand dunes from through NDVI Maps and another indicators were calculated, which require attention to limit their expansion and spread.

Threads of local continuity between centralized and decentralized causality: Transitional explanations for the behavior of a complex system

One line of research on student understanding of complex systems has tended to emphasize discontinuities between common misconceptions and relatively more sophisticated understandings. Other work has focused on instruction while acknowledging the existence of other ways of understanding complex systems, but less emphasis has been on examining the knowledge structures within these intermediate ways of understanding. This study takes a microgenetic approach to examining student’s explanations for the behavior of complex systems. Using the Knowledge-in-Pieces epistemological perspective, the analysis documents a continuity of reasoning patterns across less prototypically centralized and more prototypically decentralized (a more sophisticated causality) explanations while explaining the movement of sand dunes. The first analysis examines 31 interviews and shows that many reflected a general reasoning pattern that encompassing some combination of an initial centralized explanation, a final decentralized explanation, and transitional explanations. A second analysis examines a single student’s reasoning pattern and finds that the activation of relevant intuitive knowledge pieces (p-prims) and transitional explanations function as threads of continuity across the continuum of reasoning patterns. These findings suggest that students are able to exhibit a continuity of reasoning patterns across centralized to decentralized causality and are able to access productive intuitive knowledge about complex systems that are applicable to both the macro and micro levels of sand dune movement. Implications suggest that future research investigate these transitional explanations along with the mechanisms of shifting explanations that can account for this robust continuum.