Bare Sand Area Research Articles

Evolution and morphodynamics of the large braided river Brahmaputra during the last four decades of the Quaternary epoch: a spatio-temporal assessment using geoinformatics

ABSTRACT Spatio-temporal assessment of the evolution and morphodynamics of the Brahmaputra River (BR) can contribute significantly in mitigating challenges offered by rapid urbanisation and climate change. The present remote sensing and geographic information system (RS and GIS) based analysis of the BR revealed an increased Braiding Intensity (BI) from 1976 to 2000, which declined in 2010, and re-emerged in 2020. The average maximum width of the river has generally widened over time and sandbar distribution has exhibited fluctuations. The overall active channel area increased by 1.5 times, and the sandbar area expanded by 1.2 times between 1976 and 2020. The interplay between braiding intensity and width reveals a positive relationship. The sandbar-water ratio reveals a significant prevalence of sandbars in the Brahmaputra River. Furthermore, the study highlights changes in the Bar Development Index (BDI), showing a significant increase in micro-bars and meso-bars but a decrease in macro-bars. With the approach of change detection, key factors observed within the river driving the changes are erosion, channel bifurcations, sandbar formation due to sediment deposition, and sandbar loss due to shifts in channel course. These characteristics are potentially influenced by high water and sediment influx, climate change, and anthropological activities.

A preliminary study of carbon dioxide and methane emissions from patchy tropical seagrass meadows in Thailand.

Seagrass meadows are a significant blue carbon sink due to their ability to store large amounts of carbon within sediment. However, the knowledge of global greenhouse gas (GHG) emissions from seagrass meadows is limited, especially from meadows in the tropical region. Therefore, in this study, CO2 and CH4 emissions and carbon metabolism were studied at a tropical seagrass meadow under various conditions. CO2 and CH4 emissions and carbon metabolism were measured using benthic chambers deployed for 18 h at Koh Mook, off the southwest coast of Thailand. The samples were collected from areas of patchy Enhalus acoroides, Thalassia hemprichii, and bare sand three times within 18 h periods of incubation: at low tide at 6 pm (t0), at low tide at 6 am (t1), and at high tide at noon (t2). Seagrass meadows at Koh Mook exhibited varying CO2 and CH4 emissions across different sampling areas. CO2 emissions were higher in patchy E. acoroides compared to patchy T. hemprichii and bare sand areas. CH4 emissions were only detected in vegetated areas (patchy E. acoroides and T. hemprichii) and were absent in bare sand. Furthermore, there were no significant differences in net community production across sampling areas, although seagrass meadows were generally considered autotrophic. Koh Mook seagrass meadows contribute only slightly to GHG emissions. The results suggested that the low GHG emissions from Koh Mook seagrass meadows do not outweigh their role as significant carbon sinks, with a value 320 t CO2 -eq. This study provided baseline information for estimating GHG emissions in seagrass meadows in Thailand.

Potential environmental implications of sandbar afforestation: Insights from ecosystem restoration initiatives in a sandbar of Brahmaputra River Assam, India

Plantation in riverine sandbars offers an excellent opportunity for restoration of ecosystem with a vast potential for enhancing carbon stock. Afforestation on barren islands is challenging task; however, Padmashree Jadav Payeng has single-handedly transformed a sandbar of the river Brahmaputra into a forested landscape in India’s northeastern state of Assam. Such inspiring initiative needs more attention in terms of scientific assessment to quantify ecosystem value and services that can be enriched through such activities. This study uses remote sensing data viz., Landsat4–5TM and Sentinel 2 A data to provide a detailed information on spatio-temporal variability of land use land cover of study region from 1990 to 2021. It aims to conduct a scientific and systematic assessment of biophysical changes that have occurred in the sandbars, understand the status of afforestation, and evaluate the current levels of aboveground biomass (AGB), belowground biomass (BGB), and carbon stock in the selected sandbars. The spatial distribution of AGB, BGB and carbon stock is derived using linear regression model between SAR backscatter and field-based AGB. The results demonstrate that forest cover increased by 31.92 % and sandbar area is reduced by 26.87 % from 1990 to 2021. Spatially derived AGB ranges from 9 to 1295.89 Mg per ha, BGB from 2.35 to 290.50 Mg per ha and carbon stock from 6.18 to 763.34 Mg per ha. Ficus religiosa exhibits a high biomass, ranging from 564.7 Mg per ha to 994.7 Mg per ha, and a high carbon stock, ranging from 8 to 557.30 Mg per ha, attributed to its larger diameter at breast height (DBH). Moreover, phytosociological assessment was conducted for the studied forest, which reveal a total tree species richness of 79. The forest exhibits a total tree density of 395 individuals per hectare. Different biodiversity indices provide a comprehensive understanding of species composition; where results show a Shannon diversity index of 2.81, a Simpson's index of 0.08, a Menhinick's richness index of 2.7, and a Margalef's richness index of 5.26. The article provides detailed information on change in forest cover and present status of AGB, BGB and Carbon stock, providing evidence-based narratives on ecosystem restoration. The initiative by a single person has created a forested landscape and habitat for a large number of wild animals, contributing to better carbon stock and a healthier ecosystem. With regard to the current debate of carbon market, the study suggests the need of instrumentalization of carbon credits for such restoration activities to encourage increase in carbon stock. It also concludes that in-depth research should be taken up on long-term effectiveness of such plantation activities and the potential for scaling up these initiatives for ecosystem restoration in view of climate change mitigation and sustainable forest development.

Using sea lion-borne video to map diverse benthic habitats in southern Australia

Across the world’s oceans, our knowledge of the habitats on the seabed is limited. Increasingly, video/imagery data from remotely operated underwater vehicles (ROVs) and towed and drop cameras, deployed from vessels, are providing critical new information to map unexplored benthic (seabed) habitats. However, these vessel-based surveys involve considerable time and personnel, are costly, require favorable weather conditions, and are difficult to conduct in remote, offshore, and deep marine habitats, which makes mapping and surveying large areas of the benthos challenging. In this study, we present a novel and efficient method for mapping diverse benthic habitats on the continental shelf, using animal-borne video and movement data from a benthic predator, the Australian sea lion (Neophoca cinerea). Six benthic habitats (between 5-110m depth) were identified from data collected by eight Australian sea lions from two colonies in South Australia. These habitats were macroalgae reef, macroalgae meadow, bare sand, sponge/sand, invertebrate reef and invertebrate boulder habitats. Percent cover of benthic habitats differed on the foraging paths of sea lions from both colonies. The distributions of these benthic habitats were combined with oceanographic data to build Random Forest models for predicting benthic habitats on the continental shelf. Random forest models performed well (validated models had a >98% accuracy), predicting large areas of macroalgae reef, bare sand, sponge/sand and invertebrate reef habitats on the continental shelf in southern Australia. Modelling of benthic habitats from animal-borne video data provides an effective approach for mapping extensive areas of the continental shelf. These data provide valuable new information on the seabed and complement traditional methods of mapping and surveying benthic habitats. Better understanding and preserving these habitats is crucial, amid increasing human impacts on benthic environments around the world.

FORMATION AND EVOLUTION OF SANDBARS IN THE PADMA RIVER, BANGLADESH

Sandbars are natural formations in river channels, typically composed of sand and other sedimentary particles, created by river flow and erosion-deposition The shapes, sizes, and types of these sandbars exhibit diversity depending on factors such as river flow, sediment composition, hydrological conditions, and erosion-deposition processes. These sandbars are an integral part of the river ecosystem and influence the water flow patterns, navigation routes, aquatic habitats and even provide shelter to humans and habitats. In the context of Bangladesh, there is a considerable size of population that dwell in these sandbars. The process of sandbar formation and recession is quite dynamic, and its complexity is further accentuated within the confluence zones. The Ganges, the Brahmaputra, and the Meghna River systems together form the largest delta (GBM Delta) in the world which is characterized by numerous interlaced rivers, canals, and streams. These river systems contain numerous sandbars which contribute to its complex river morphology. These sandbars are home to many people, animals, and wildlife. However, the dynamic nature of sandbars, high monsoon discharge, flooding and erratic erosion-deposition patterns make the sandbar formation and recession process quite unpredictable and puts the lives of people living on it in danger. This paper aims to study the morphological changes in sandbars, the erosion-deposition patterns within these river systems causing the sandbar formations, compare the sandbar formations in the two confluence zones of the Padma River, determine the changes in water-sandbar surface area ratio, visualize the evolution of sandbars, and quantify the movements of sandbars. The study revealed that over the past two decades (1990-2010), the main channel of the river was dominated by sandbar area. In contrast, in the past 7 years (2016-2022), the average surface area of water within the main channel of the Padma River was approximately 73,387 ha while the sandbars covered an area of around 51,274 ha, highlighting the recent dominance of water in the main channel. Conversely, in a similar time frame (2016-2022), at the two confluence zones of the Padma River, the average surface area of sandbar was greater than that of water within a 30km radial distance from each confluence node. At the upstream confluence (Padma-Jamuna-Ganges), the average surface area of sandbars was approximately 40150 ha while water covered an area of around 28531 ha. Similarly, at the downstream confluence (Padma-Meghna), sandbars covered an area of 43696 ha on an average while water covered an area of around 40889 ha. This showed that sandbars have been rapidly accumulating at the two confluence zones. It is also observed that the sandbars are very dynamic as both lateral and longitudinal migrations are observed. It is however evident that the littoral sandbars are more stable compared to the medial sandbars and therefore more suitable for habitation. From visual inspection it is evident that the bankline of the medial sandbar (Amirabad) shifts more rapidly compared to the littoral sandbar (Harirampur within the period from 2016 to 2022. Additionally, the coefficient of variation of area for the littoral sandbar and the medial sandbar are approximately 2.11% and 5.37% respectively. This indicates that the area of the littoral sandbar is more stable over the years compared to the medial sandbar as it has a lower coefficient of variation and therefore is less active. Over the years, the confluence nodes on either side of the Padma River have constantly shifted due to rapid sandbar accumulation. Between 1990 and 2022, the maximum shifting of the upstream and downstream confluences reached approximately 7500 meters and 18000 meters respectively, both in the southeast direction.

Patterns and controls of topographic change within the deflation basins of a trough and bowl coastal blowout

AbstractIn North‐West Europe and throughout the world, dune systems are increasingly stabilised by vegetation, due to both human intervention and changes in climate. Blowouts are erosional hollows produced by wind erosion in vegetated or semi‐vegetated dune systems. Where active blowouts are present in vegetated dunes, they provide a source of dynamism and sediment in an otherwise fixed environment. The transition from a fixed vegetated dune to an active blowout is poorly understood, however, and anthropogenic attempts to reactivate areas of bare sand in dunes are often unsuccessful. In this study, we measured topographic change at a monthly resolution in the deflation basins of one bowl and one trough blowout over a 23‐month period in Ainsdale Sand Dunes National Nature Reserve, North‐West England. Our results show that monthly surface change in the blowouts did not correlate strongly with the transport capacity of winds measured at a meteorological station 10 km south of the site. Precipitation was found to have a moderate negative correlation with all indices of surface change, that is, the more it rained the less the surface changed. Inter‐annual (23 months) patterns of topographic change in the bowl and trough blowouts were distinctly different. In the deflation basin of the bowl blowout erosion predominantly took place on the erosional walls facing into the prevailing winds, while minimal change occurred on the erosional walls facing away from the prevailing wind direction. This produced a moderate negative correlation between surface change and slope, that is, the steeper the slope, the more erosion occurred. In the trough blowout, erosion took place in the centre of the deflation basin and minimal change was measured on the easternmost erosional wall, which faced the prevailing winds. Patterns of monthly topographic change were highly variable and demonstrated that changes in the direction of above‐threshold winds can cause blowout walls and floors to ‘flip’ from erosional to depositional surfaces. These findings highlight the variability and complexity of surface change in blowouts and demonstrate that patterns vary because of landform morphology and climatic conditions.

An Auto-Detection and classification algorithm for identification of sand dunes based on remote sensing images

Dunes are among the most abundant aeolian landforms found on Earth and other planets. The automatic mapping of dunes over large-scale areas is crucial for predicting, monitoring, and managing lands threatened by sand encroachment. However, the spectral similarity between dune and inter-dune areas, as well as the diverse presentations of dunes of the same type, have made it challenging to automatically classify and map dunes. In this study, we propose a two-step 'detect-then-classify' framework that enables the automatic identification of heterogeneous dune types. The first step involves dune detection. We introduce a newly developed convolutional neural network called SandUnet, which is adapted from Attention U-Net. This network is designed to preserve uncompressed input signals ensuring that minor differences in the color and texture of the dunes are retained. The second step focuses on dune-type classification. To classify dunes, a fine-tuned MobileNet was constructed to integrate the wealth of knowledge ingrained in MobileNet's pre-trained layers with the adaptations tailored specifically for the sand dune images. Subsequently, each dune image is automatically classified into six different types using this framework. By applying this framework to all the bare sand areas of the Taklamakan (or Taklimakan) Desert using Landsat-8 imagery, the final classification of dune types of the desert was achieved. Testing on randomly selected 10% image patches of whole desert, the overall accuracy of the dune-type classification is 70%. This study presents an automatic and economical solution for identifying dunes in large-scale areas.

Dune slope, not wind speed, best predicts bare sand in vegetated coastal dunes

Globally vegetation cover on coastal sand dunes has increased since at least the 1950s. With the aim of restoring or increasing biodiversity, land managers in several countries have removed vegetation and/or reprofiled dune slopes to reinvigorate geomorphic activity. However, the longevity of these interventions can be relatively short (on the order of 5 to 10 years), and further active management is required. Hypotheses for controls on geomorphic activity on dunes have frequently suggested that wind speedis the most important controlling factor. Here we show dune slope to be the best predictor of bare sand at four predominantly vegetated coastal sand dunes in England and Wales. We suggest that bare sand on steep dune slopes is maintained by three important factors: (1) Wind erosion, due to topographic acceleration (2) Granular avalanches of unconsolidated sediment and (3) Rotational slumping of unstable slopes. Our results indicate that where land managers wish to ‘rejuvenate’ areas of bare sand, efforts should focus on steep windward dune slopes and reprofiling of the dune slope should mimic the concave profiles of active slope faces on active parabolic dunes with an overall slope angle of between 18° and 23° from the dune toe to the crest.

Estimating Ground Elevation in Coastal Dunes from High-Resolution UAV-LIDAR Point Clouds and Photogrammetry

Coastal dune environments play a critical role in protecting coastal areas from damage associated with flooding and excessive erosion. Therefore, monitoring the morphology of dunes is an important coastal management operation. Traditional ground-based survey methods are time-consuming, and data must be interpolated over large areas, thus limiting the ability to assess small-scale details. High-resolution uncrewed aerial vehicle (UAV) photogrammetry allows one to rapidly monitor coastal dune elevations at a fine scale and assess the vulnerability of coastal zones. However, photogrammetric methods are unable to map ground elevations beneath vegetation and only provide elevations for bare sand areas. This drawback is significant as vegetated areas play a key role in the development of dune morphology. To provide a complete digital terrain model for a coastal dune environment at Topsail Hill Preserve in Florida’s panhandle, we employed a UAV, equipped with a laser scanner and a high-resolution camera. Along with the UAV survey, we conducted a RTK–GNSS ground survey of 526 checkpoints within the survey area to serve as training/testing data for various machine-learning regression models to predict the ground elevation. Our results indicate that a UAV–LIDAR point cloud, coupled with a genetic algorithm provided the most accurate estimate for ground elevation (mean absolute error ± root mean square error, MAE ± RMSE = 7.64 ± 9.86 cm).

Understanding the entropy-based morphological variability and energy expenditure mechanism of a large braided river system

Understanding the morphological erraticism for large braided river systems is still a challenging issue in the present era of fluvial geomorphology. The present paper reports thorough spatio-temporal variability of sand bar dynamics (2000–2019) and their influence on the braided belt disorderness in the large braided Brahmaputra River. The sand bar area is detected using the modified normalized difference water index (MNDWI), and an entropy-based intensity disorder index (IDI) is further proposed to measure the spatio-temporal disorderness in the post-monsoon period. The IDI varies at a lowest value of less than 0.5 to a highest value of more than 0.9 for the selected study reach. Interestingly, IDI displays a declining trend for the first decade, followed by an increasing trend in the subsequent time slice, which signals the large-scale heterogeneity in process-form interactions for the Brahmaputra. An attempt was made to establish relationship between IDI, stream power derivatives (monsoon, peak flood, and post-monsoon), and bar area classes in order to facilitate a process-based understanding of the geomorphic adjustments. In comparison with other stream power derivatives, the peak-flood stream power showed a better correlation with the disorderness measure of the reach. Finally, this study has highlighted that smaller, highly immobile bars have significant control on the IDI variations and govern the yearly planform disorderness of the Brahmaputra. Further, the findings of this study can be used to construct a process-form-interaction framework for large braided river systems.

Assessment of land use change in riverine ecosystem and utilizing it for socioeconomic benefit.

Increasing urbanization has led to diminished agricultural mainland for food production worldwide. Riverine sandbars could be viewed as prospective landmasses which could act as additional agricultural lands. The present study emphasizes sandbar area availability and the scope of utilizing these landmasses through geospatial techniques, modelling studies and questionnaire surveys. Satellite images were derived at decadal scales to determine the change in the land-use land cover (LULC) within the Brahmaputra River in Assam, India. The fluctuations in the landmasses under different streamflow conditions were derived using a hydrodynamic model. The results showed that the percentage of vegetated sandbars has increased from ~27.36% in 1976-1980 to ~44.67% in 2016-2017, and consecutively, the percentage of non-vegetated sandbars has decreased from ~51.18 to ~30.93%. Furthermore, it was found that the area under cropland and vegetated sandbar varied seasonally. To further understand the utilization of these resources, a socioeconomic survey with a structured set of questions was conducted at various sandbars. The survey revealed various aspects of economic benefits, practices of sandbar cultivation, beneficial produce, difficulties faced, and willingness among farmers to expand sandbar cultivation. Coupling the prevailing traditional knowledge of cultivation among the farmers with scientifically derived information obtained from satellite data and mathematical model simulations can lead to a more systematic utilization of the ecosystem. Thus, the study shows the immense potential of utilizing the sandbars of large rivers to sustain food demands, alongside developing links between land-use change, ecosystem behavior, and socio-economic development.

Normalized Sand Index for Identification of Bare Sand Areas in Temperate Climates Using Landsat Images, Application to the South of Romania

The expansion of bare sand surfaces indicates a tendency towards desertfication in certain periods as a result of the improper agricultural use of sand soils and of the significant changes in the climate in the past 30 years. The Normalised Sand Index (NSI) is a new index used to identify bare sand areas and their spatio-temporal evolution in SW Romania. Landsat scenes (1988, 2001, 2019), spectral and soil texture analysis (36 samples), covariates (e.g., soil map), and field observations allowed for the validation of the results. The performance of the NSI was compared with indices from the sand index family (e.g., Normalized Differential Sand Areas Index) and supervised classifications (e.g., Maximum Likelihood Classification) based on 47 random control square areas for which the soil texture is known. A statistical analysis of the NSI showed 23.6% (27,310.14 hectares) of bare sands in 1988, followed by an accelerated increase to 47.2% (54,737.73 hectares) in 2001 because of economic and land-use changes, and a lower increase by 2019, which reached 52.5% (60,852.42 hectares) due to reforestation programs. Compared to the NSI, the bare sand areas obtained with the tested indicator were almost 20% higher. The traditional classification shows smaller areas of bare sands but uses a higher complexity of land use classes, while the producer accuracy values are lower than those of the NSI. The new index has achieved a correct spatial delimitation of soils in the interdune-dune and major riverbed-interfluvial areas, but it is limited to the transition Arenosols-Chernozems by humus content and agrotechnical works. The new spectral index favours bare sand monitoring and is a fast and inexpensive method of observing the desertification trend of temperate sandy agroecosystems in the context of climate change.

Recreationally created footpaths as a means of preserving specific biotopes of bare sand accumulations: Evidence provided by dendrogeomorphic reconstruction

The combination of accumulation and erosion processes is the dominant geomorphic agent forming the surface of bare sand accumulations. These unique biotopes are gradually vanishing; thus, knowledge of their past dynamics is of crucial interest. This study focused on a selected locality with bare sand in the Borská Lowland (Slovakia). In total, nine buried individuals of Pinus sylvestris (L.) were used for the reconstruction of the accumulation rate of sand, and 13 exposed roots of the same tree species served as the data source for the erosion rate calculation. Detailed analysis of growth responses in trees and roots provided evidence about macroscopic and microscopic growth responses that are usable even in other studies and suggested P. sylvestris as a sensitive species for the reconstruction of accumulation and erosion processes. Reconstructed values of mean accumulation rate were higher than the mean erosion values. Finally, the obtained results were put into an anthropogenic context because the studied locality is surrounded by zones with seasonally inhabited holiday cottages. The effect of anthropogenic activities (particularly by stepping) can be associated with the wide spectrum of collected evidence: Bare sand areas were not located around other water reservoirs with the absence of recreational activities in the region. The erosion zone in the studied locality follows the zone with an increased number of forest pathways. It is possible that the increased nutrition content in transported sand due to gardening affected the occurrence of growth releases in the studied trees.

Extent, accuracy and repeatability of bare sand and vegetation cover in dunes mapped from aerial imagery is highly variable

Vegetation cover on coastal sand dunes has been increasing worldwide since at least the 1940s. Analysis of aerial and satellite imagery has been the principal source used to measure this change, however no studies have systematically evaluated the accuracy of remotely sensed estimates. Using established land cover classification methods and in-situ field measurements, we show that both the extent and accuracy of remotely sensed areas of bare sand and vegetation in dunes varies with image resolution and classification method. We found that supervised methods of classification (semi-automatic), whilst mapping a greater extent of bare sand and being more accurate than manual digitisation, had poor repeatability, exhibiting a relatively large range of bare sand and vegetation extent between classifications replicated under the same conditions. In contrast, areas of bare sand and vegetation classified by manual digitisation had high repeatability but a relatively low percentage of observed agreement with data collected in the field. For all classification methods, observed agreement with field data generally increased with image resolution. Our results demonstrate that users of land classification data in dunes should be cautious when interpreting trends of bare sand and vegetation cover due to substantial repeatability error in supervised classification methods, and relatively poor observed agreement with field data of manual classification. We recommend that analysis of bare sand and vegetation cover in dunes should be based on multiple replicates using supervised classification, employing the highest resolution imagery available and that all results presented should also include the range measured by multiple replicates.

Geomorphic response to historic and ongoing human impacts in a large lowland river

AbstractLowland coastal plain rivers are important for navigation and ecosystems, having unique concerns regarding water and sediment management. The Apalachicola River in Florida, the lower end of the ACF (Apalachicola–Chattahoochee–Flint) system, had historical modifications beginning in the 1800s. Most impacts are attributable to the Apalachicola Navigation Project in the latter half of the 20th century, which included dredging, disposal, rock and snag removal, artificial cutoffs, and wing‐dike building.As one of few studies using paired hydrographic surveys over a long reach and time (170 km, 50 years), we defined four zones of bed elevation change between 1960 and 2010 based on the cumulative thalweg elevation plots. The river has four bed change zones: (1) uppermost, marked degradation from river mile (RM) 106 to 85 because of dam construction; (2) middle, minimal degradation from RM 85 to 34; (3) artificial cutoff zone, highest degradation, from RM 34 to 27; and (4) lowermost zone, aggradation from RM 27 to Apalachicola Bay because of upstream bed and bank sediment disturbances. Artificial cutoffs and lithology influence lateral migration, with rates being highest in cutoff zones and least in areas with some bedrock upstream and finer sediments downstream. Length changes from 1941 to 2019 are stable, except for the middle reach, which lengthened nearly 10%, and the lower non‐tidal reach, where length shortened with cutoffs then regained in subsequent decades. Minimizing disturbance has led to 18% of the sand bar area revegetating since a decade of dredging ended. This framework helps in understanding historic and ongoing human activities, notably upstream water consumption, connectivity changes, sediment inputs, and climate change, that will affect the water and sediment management of the river, its floodplain, and bay, thus varying approaches for restoration.

Monitoring Rock Desert Formation Caused by Ice–Snow Melting in the Qinghai-Tibet Plateau Using an Optimized Remote Sensing Technique: A Case Study of Yushu Prefecture

The rapid and effective identification of the spatial distribution of rock deserts in ice–snow melting areas can provide useful information for the prevention of natural disasters. In this study, Landsat TM/OLI were used to track the evolution of snow lines in the snow melting areas of Yushu Tibetan Autonomous Prefecture of the Qinghai-Tibet Plateau (hereinafter referred to as Yushu Prefecture) during the last 30 years. A total of seven extraction schemes were used to classify the rock desert in the ice–snow melting area by remote sensing. Our results show that: (1) The accuracy of the multi-index factor compound analysis and object-oriented classification compound method was the highest. This method can provide a rapid and efficient reference scheme for rock desert extraction in the plateau ice–snow melting area. (2) The combinations of two single methods with higher accuracy can further improve the total accuracy. If a single method with lower accuracy is involved in the multi-method fusion, the accuracy of the method with lower accuracy can be improved. (3) In the past 30 years, there has been a large amount of ice–snow melting in Yushu Prefecture. The ice–snow melting area accounts for 53.78% (1451.04 km2) of the ice–snow area, and the bare rock and bare stone in the rock desert account for 63.77% of the total area of the ice–snow melting area. Bare sand and bare soil area account for 30.27% of the total area of ice and snow melting area.

Stabilization of the Lower Jamuna River in Bangladesh—Hydraulic and Morphological Assessment

This paper presents a hydraulic and morphological analysis of the Lower Jamuna in Bangladesh with a focus on two key bifurcations that are important for stabilization of the Lower Jamuna reach. We used ground measurements, historical data, multispectral satellite images from various sources as well as numerical models. We carried out hydraulic analyses of the changes and their peculiarities, such as flow distributions at the bifurcation and hysteresis of the stage–discharge relationships. We supplemented our analysis by using numerical models to simulate discharge distribution at the bifurcations under various flow and riverbed conditions. We developed an advanced and automated satellite image processing application for the Lower Jamuna, referred to as Morphology Monitor (MoMo), using the Google Earth Engine. MoMo was found to be an effective tool for a rapid assessment and analysis of the changes in deep-channel and sandbar areas. It is also useful for monitoring and assessing riverbank and char erosion and accretion, which is important not only for morphological but also ecological impact assessment. The application can be adapted as an operational tool as well. Furthermore, we assessed the evolution of deep channels at the bifurcations based on regularly and extensively measured bathymetry data. The analysis was carried out in complement with morphological modeling, particularly for short-term prediction. In this paper we present the major findings of the analysis and discuss their implications for adaptive river management.

Sandy riverbed shoal under anthropogenic activities: The sandy reach of the Yangtze River, China

Large-scale reservoirs change downstream water and sediment conditions, causing adaptive adjustments in erosion and deposition along the riverbed, ultimately impacting sandbar morphology. This study examined the sandy reaches downstream of the China Three Gorges Project along the Yangtze River for river erosion and siltation, riverbed morphology, beach evolution, and other physical processes over the past 40 years, to explain the evolution of river geomorphology under human activities, such as reservoirs, improvement projects, and sand mining. The Shashi reach is approximately 52 km in length; it is the first sandy riverbed downstream of the China Three Gorges Dam. Analysis of topographic data from 1975 to 2018 showed that decreased sediment from the basin resulted in increased riverbed erosion (93.1%, in low-water channel), with sand mining activities destroying the integrity of the central bar. Simultaneously, total sandbar area decreased, thalwegs deepened, river morphological coefficients decreased, and the riverbed became narrower and deeper. The erosion and deposition patterns of the Shashi reach beach and channel have changed from “low shoal erosion-high shoal deposition” to “both low and high shoal erosion”. Additionally, waterway engineering has changed sandbar boundaries, and impacted the evolution of interactions among beach groups. Under quasi-natural conditions, strong interactions occur in sandbar evolution, such as the development of the Taipingkou Channel Bar (TPKCB), which led to Lalinzhou Point Bar (LLZPB) erosion, tail section widening, as well as Sanbatan (SBT) shrinkage and recession of its eastward edge. Owing to the implementation of waterway engineering, the linkage between the TPKCB and the upper section of the LLZPB weakened. The widening of the lower section of the latter has caused the SBT to shrink further and shift westward. Changes in the morphologies and dynamic axes of upstream beach groups have resulted in a sharp reduction of incoming sediment causing the downstream Jinchengzhou Point Bar (JCZPB) to gradually evolve into a shrunken channel bar.

Impacts of soil disturbance on plant diversity in a dry grassland

Dry grasslands are not only amongst the most species-rich habitats in Europe but also amongst the most threatened. Threats include habitat destruction as well as modification to the historic disturbance regime under which native plants have evolved (e.g. too high or too low levels of disturbance). The aim of this study is to examine the effects of soil disturbance intensity on species composition and diversity in a dry grassland in Mols Bjerge National Park in Denmark. We recorded vascular plant species inside and just outside patches of bare sand and at the transition between bare sand and dense vegetation outside the patches. We found that species richness was highest in the dense vegetation, intermediate in the transition zone and lowest in bare sand areas. However, an analysis of plant traits showed that the number of small annual species was highest in the transition zone. High abundance of small annual species may therefore indicate intermediate disturbance regimes. Moreover, literature indicates that many threatened species are adapted to such habitats, which suggests that dry grasslands should be managed to maintain areas with intermediate disturbance intensities to improve conditions for many threatened species. High abundance of small annual species thus indicates that favourable management has been achieved.

Application of Satellite Sentinel-2 Images to Study Alternate Sandbars Movement at Lower Vistula River (Poland)

The lower Vistula River was regulated in the years 1856–1878, at a distance of 718–939 km. The regulation plan did not take into consideration the large transport of the bed load. The channel was shaped using simplified geometry—too wide for the low flow and overly straight for the stabilization of the sandbar movement. The hydraulic parameters of the lower Vistula River show high velocities of flow and high shear stress. The movement of the alternate sandbars can be traced on the optical satellite images of Sentinel-2. In this study, a method of sandbar detection through the remote sensing indices, Sentinel Water Mask (SWM) and Automated Water Extraction Index no shadow (AWEInsh), and the manual delineation with visual interpretation (MD) was used on satellite images of the lower Vistula River, recorded at the time of low flows (20 August 2015, 4 September 2016, 30 July 2017, 20 September 2018, and 29 August 2019). The comparison of 32 alternate sandbar areas obtained by SWM, AWEInsh, and MD manual delineation methods on the Sentinel-2 images, recorded on 20 August 2015, was performed by the statistical analysis of the interclass correlation coefficient (ICC). The distance of the shift in the analyzed time intervals between the image registration dates depends on the value of the mean discharge (MQ). The period from 30 July 2017 to 20 September 2018 was wet (MQ = 1140 m3 × s−1) and created conditions for the largest average distance of the alternate sandbar shift, from 509 to 548 m. The velocity of movement, calculated as an average shift for one day, was between 1.2 and 1.3 m × day−1. The smallest shift of alternate sandbars was characteristic of the low flow period from 20 August 2015 to 4 September 2016 (MQ = 306 m3 × s−1), from 279 to 310 m, with an average velocity from 0.7 to 0.8 m × day−1.