Average Migration Rate Research Articles

Evidence of coastal dune mobility increases over the last half century in response to historical human intervention

Given the risk of two roads being buried by the sand of two highly mobile coastal dunes (Valdevaqueros and Bolonia, SW Spain), several measures have been taken over the last half century in order to stabilize them or at least slow their progress: installation of several rows of 1-m-high concrete structures, planting of species such as Pinus pinea, Retama monosperma and Ammophila arenaria , wicker and wooden fencing, and sand mining (only performed on the Valdevaqueros dunefield). The evolution of the two dunes was investigated through the interpretation of intensive topographical monitoring and aerial photography. Average migration rates of approximately 10 m yr –1 were detected and the burial of anthropic structures has eventually occurred. This process has caused a serious regional problem, making dune management of these areas a difficult challenge. The comparison of the evolution of these two dunes has been of great importance in assessing the effect of historical human intervention and has provided a new perspective for future dune management strategies. The results obtained show that management measures based on sand removal have been proven to be unsustainable. Moreover, the monitoring methodology presented herein has proven very useful in predicting dune advance rates. For instance, the Bolonia dune could reach the nearest road in approximately 12 years.

Nitrate nitrogen accumulation and leaching pattern at a winter wheat: summer maize cropping field in the North China Plain

Excess application of nitrogen has proved to be one of the detrimental impact factors on soil and groundwater quality in the North China Plain (NCP). A 4-year (from October 2008 to September 2012) field experiment was carried out to investigate the impact of N application rate on NO3–N dynamics in soils, its leaching pattern, and movement in deep soils under different nitrogen (N) application rates in a sprinkler irrigated winter wheat (Triticum aestivum L.)- summer maize (Zea mays L.) field in the NCP. The N application rates were 0, 110, 220, and 330 kg N ha−1 per wheat or maize planting season, referred to as CK, N1, N2, and N3 treatments, respectively. The results indicate that in winter wheat season, the applied water and fertilizer N mostly accumulated in the 0–60 cm soil layer and NO3–N leaching out of the root zone (0–100 cm) was negligible under the sprinkler irrigation scheduling, while water and NO3–N leached out of the root zone during summer maize season mainly due to high rainfall event. A relatively constant NO3–N concentration in soil profile was maintained and NO3–N leaching was negligible when N application rate was 110 kg N ha−1 per crop season. While about 70 % of the applied N accumulated in 0–500 cm soil layer and about 50 % of the applied N leached out of the root zone when N application rate lager than 110 kg N ha−1 per crop season, and the NO3–N downward movement was observed to the depth of 300 cm at the end of the 4-year experiment with an average migration rate of about 50 cm year−1. Considering the potential risk of groundwater pollution, an N application rate of 110 kg ha−1 per crop season was recommend for winter wheat and summer maize under the conditions of sprinkler irrigation in the NCP and those areas with similar conditions.

Morphologic characteristics and migration rate assessment of barchan dunes in the Southeastern Western Desert of Egypt

This work explores the morphologic characteristics of aeolian dune sand in the southeastern part of Western Desert of Egypt. It aims to assess the movement of barchan dunes and evaluate their environmental influence on the Toshka Project. Morphometric investigation of barchan dunes in the Toshka area revealed that most barchans have high length/width (a/c) ratios (fat to pudgy), while one-fifth of the studied barchans have lower a/c ratios and so appear normal in their morphologic forms. Statistical analysis of the main parameters of barchan dunes in Toshka and other desert regions in the Kharga (Egypt), Kuwait, Southern Morocco, California and Southern Peru demonstrates that barchans of the Toshka area are distinctive in their appearance. They are characterized by distinct aspect with higher values of length and width and greater growth in height. The high-energy wind environment in addition to the large amount of drifting sand are principal factors responsible for the unique shape of Toshka barchans.The migration rate of barchan dunes in four chosen test locations, within the central and western Toshka area, ranges from about 3 to 10.82m/year. The calculated average migration rate of these dunes is about 6m/year in a SSW direction. Sand encroachment is more extensive in the central and western parts of the investigated Toshka area. Risk evaluation of sand dune movements in the southeastern part of the Western Desert points to medium to high sand encroachment risk values. These may represent serious hazards to the newly-established Toshka Project, threatening roads, as well as cultivated lands in the area.

Automated measurement of sand dune migration using multi-temporal lidar data and GIS

Remote sensing has been used for coastal and desert sand dune studies over the past four decades, yet few methods have been developed for automated detection and measurement of dune migration directions and migration rates in large dune fields. Using high-resolution, high-accuracy, and multi-temporal light detection and ranging (lidar) data acquired in the White Sands Dune Field in New Mexico (USA) on 24 January 2009 and 6 June 2010, an automated method named Pairs of Source and Target Points (PSTP) was developed in a geographical information system (GIS) environment for automated detection and measurement of dune migration directions and migration rates. As markers for dune movement, dune slip faces were automatically extracted from lidar-derived digital elevation models (DEM), based on the range of the angle of repose, and converted into source lines and target lines through vectorization. Random target points were then generated on target lines and used to search for source points on source lines to form PSTP, thereby obtaining source direction, migration distance, and migration rate for each target point. Continuous raster data sets for dune migration rates were also created through spatial interpolation and point statistics to show dune field scale spatial patterns of dune migration rates. A total of 5936 PSTP were identified, producing dune migration directions and migration rates at 5936 locations in the study area of 9 km × 2.4 km. Histogram analysis revealed that a majority of the 3025 target points with source direction in the range 225°–285° (direction of prevailing winds) have a migration rate of 4–7 m year−1 and an average migration rate of 5.56 m year−1. The applicability of the PSTP method in special cases, and its potential as a generic method for change detection and measurement, are also discussed. The study obtained important results both in methodology development and in the study area.

Bi-module sensing device to in situ quantitatively detect hydrogen peroxide released from migrating tumor cells.

Cell migration is one of the key cell functions in physiological and pathological processes, especially in tumor metastasis. However, it is not feasible to monitor the important biochemical molecules produced during cell migrations in situ by conventional cell migration assays. Herein, for the first time a device containing both electrochemical sensing and trans-well cell migration modules was fabricated to sensitively quantify biochemical molecules released from the cell migration process in situ. The fully assembled device with a multi-wall carbon nanotube/graphene/MnO2 nanocomposite functionalized electrode was able to successfully characterize hydrogen peroxide (H2O2) production from melanoma A375 cells, larynx carcinoma HEp-2 cells and liver cancer Hep G2 under serum established chemotaxis. The maximum concentration of H2O2 produced from A375, HEp-2 and Hep G2 in chemotaxis was 130±1.3 nM, 70±0.7 nM and 63±0.7 nM, respectively. While the time required reaching the summit of H2O2 production was 3.0, 4.0 and 1.5 h for A375, HEp-2 and Hep G2, respectively. By staining the polycarbonate micropore membrane disassembled from the device, we found that the average migration rate of the A375, HEp-2 and Hep G2 cells were 98±6%, 38±4% and 32 ±3%, respectively. The novel bi-module cell migration platform enables in situ investigation of cell secretion and cell function simultaneously, highlighting its potential for characterizing cell motility through monitoring H2O2 production on rare samples and for identifying underlying mechanisms of cell migration.

Invasion and Anti-Invasion Research of Glioma Cells in An Improved Model of Organotypic Brain Slice Culture

Although glioblastomas infiltrate diffusely into adjacent brain, it is difficult to unequivocally identify the solitary invading glioma cell. It is necessary to develop coculture models to study the motility of glioma cells, and to monitor the cellular morphology, movement direction, migration area and invasion rate. Cerebral slices were cultured on Millicell-CM membrane inserts in a petri dish. The neuronal viability and organizational structure of the brain sections were well maintained by experimental verification. C6 cell clones with persistent enhanced green fluorescent protein (EGFP) expression were established. EGFP-expressing glioma cells were cultured to form aggregates, which were implanted on the brain slices. The invasion area and migration rates of C6 cells on brain slices were measured. We evaluated the invasion area and depth after C6 cells were treated with the Rac1 inhibitor NSC23766. We successfully established the glioma cell-brain slice coculture model. In coculture, the average migration rate of C6 glioma cells within brain slices reached 11.36-15.27 μm/hour. The polarity of C6 glioma cells was parallel to the white matter tracts after 7 days. The invasive ability of C6 cells (depth: 105.3 ± 10.3 μm) treated with NSC23766 was weakened compared with the control group (depth: 198 ± 9.2 μm) within the white matter of brain slices (t = 16.26, p<0.05). We developed the model to analyze the invasion features of glioma cells. The significant suppression of glioma cell invasion by NSC23766 in brain slices indicates that anti-Rac1 treatment may represent an important future therapeutic strategy for glioblastoma.

The life of a meander bend: Connecting shape and dynamics via analysis of a numerical model

Analysis of bend-scale meandering river dynamics is a problem of theoretical and practical interest. This work introduces a method for extracting and analyzing the history of individual meander bends from inception until cutoff (called “atoms”) by tracking backward through time the set of two cutoff nodes in numerical meander migration models. Application of this method to a simplified yet physically based model provides access to previously unavailable bend-scale meander dynamics over long times and at high temporal resolutions. We find that before cutoffs, the intrinsic model dynamics invariably simulate a prototypical cutoff atom shape we dub simple. Once perturbations from cutoffs occur, two other archetypal cutoff planform shapes emerge called long and round that are distinguished by a stretching along their long and perpendicular axes, respectively. Three measures of meander migration—growth rate, average migration rate, and centroid migration rate—are introduced to capture the dynamic lives of individual bends and reveal that similar cutoff atom geometries share similar dynamic histories. Specifically, through the lens of the three shape types, simples are seen to have the highest growth and average migration rates, followed by rounds, and finally longs. Using the maximum average migration rate as a metric describing an atom's dynamic past, we show a strong connection between it and two metrics of cutoff geometry. This result suggests both that early formative dynamics may be inferred from static cutoff planforms and that there exists a critical period early in a meander bend's life when its dynamic trajectory is most sensitive to cutoff perturbations. An example of how these results could be applied to Mississippi River oxbow lakes with unknown historic dynamics is shown. The results characterize the underlying model and provide a framework for comparisons against more complex models and observed dynamics.

The effect of the Wenchuan earthquake on the fluvial morphology in the Longmen Shan, eastern Tibetan Plateau: Discussion and speculation

Although large earthquakes can have significant impacts on the geomorphology of mountain rivers, the consequences of such impacts remain poorly understood. The Ms 8.0 Wenchuan earthquake of 12 May 2008 created knickpoints (waterfalls) in the river systems of the Longmen Shan, eastern Tibet Plateau, in addition to numerous landslides along rivers. In this study, we use high-resolution remote sensing images and field surveys to examine how the Baisha and Jianjiang River channels responded to the Wenchuan earthquake. The morphological response along the Baisha River was a knickpoint, with a height of 4.5 m, which was studied from 2008 to 2012. However, the river did not show rapid incision via knickpoint migration during the post-earthquake period. In fact, post-seismic flooding destroyed the face of the co-seismic knickpoint. The rapid removal of the knickpoint suggests that the abrupt vertical displacement associated with the earthquake did not exceed the adjustment threshold of the fluvial dynamic equilibrium, and so was unable to drive rapid morphological change at the local scale. Along the Jianjiang River, the average meander migration rate of the Beichuan reach was −2.8 m/yr between 2001 and 2008, but increased to 51.1 m/yr during the five years following the 2008 Wenchuan earthquake. This rapid increase in the meander migration rate is attributed to excess sediment supplied to the river as a consequence of the earthquake. These two case studies indicate that the Wenchuan earthquake caused channel aggradation rather than a significant increase in river incision by locally generating relief across the river.

Application of remote sensing and GIS for evaluation of the recent morphological characteristics of the lower Brahmaputra-Jamuna River, Bangladesh

This paper deals with the morphological changes of the lower Brahmaputra-Jamuna River (BJR) in Bangladesh. Within few decades, the planform of the river has been changed abruptly by the combined effect of natural process and human interventions. Morphological features observing in this study were river planform, channel width, bankline migration and channel bed elevation. Eighteen sets of remote sensing data series from 1973 to 2011were analyzed using ERDAS/Imagine and GIS to document the variation of geomorphic elements of the lower BJR. GIS analysis of remote sensing data showed that the changes of channel planform were quite significant over the past 40 years, occurring two major phases of channel development. The changing patterns in the first phase (i.e., between 1973 and 1992) were quite irregular. However, the second phase ranging between 1992 and 2011 was unidirectional (mostly eastward). In general, the studied river reach was widened and the average rate of migration was 225 m y–1 that was three–folds the values of the first phase. The height and slope of sand bars were gradually increasing, showing the highest value around the Jamuna Multipurpose Bridge (JMB) section. The planform characteristics of BJR at the downstream of JMB showed that the river reach was gradually widening and shifting eastwards. However, the reach at the upstream of the JMB showed westward migration. The recent trends of channel changes suggest that the river planform has lost it’s naturally condition and it may, therefore, be predicted that increasing nature of channel width likely to continue in the immediate future.

Fate and Ecological Effects of Decabromodiphenyl Ether in a Field Lysimeter

Flame-retardant polybrominated diphenyl ethers (PBDEs) are environmental contaminants. Deca-BDE is increasingly used commercially, but little is known about the long-term fate and impact of its major component, decabromodiphenyl ether (BDE-209), on the soil environment. In this study, we investigated the fate and ecological effect of BDE-209 over 4 years in outdoor lysimeters in a field planted with a rice-wheat rotation. BDE-209 and six lower-brominated PBDEs (BDE-28, -47, -99, -153, -154, and -183) were detected in soil layers of the test lysimeter. We calculated an average BDE-209 migration rate of 1.54 mg·m(-2)·yr(-1). In samples collected in May 2008, November 2008, November 2009, November 2010, and November 2011, 95.5%, 94.3%, 108.1%, 33.8%, and 35.5% of the spiked BDE-209 were recovered, respectively. We predicted the major pathway for debromination of BDE-209 in soil to be: BDE-209→BDE-183→BDE-153/BDE-154→BDE-99→BDE-47→BDE-28. In plants, BDE-209 and seven lower-brominated PBDEs (BDE-28, -47, -99, -100, -153, -154, and -183) were detected. BDE-100 was mainly derived from the debromination of BDE-154 in plants, but sources of other lower-brominated PBDEs were still difficult to determine. In soils containing BDE-209 for 4 years, soil urease activity increased, and soil protease activity slightly decreased. Our results provide important insights for understanding the behavior of BDE-209 in agricultural soils.

Coastal processes and tidal flat reclamation in Cixi City, China

The geomorphic configuration of hilly land (in the southern area), sea (in the northern area) and littoral plain (in the middle area) within the overall area of Cixi was formed about 2500 BP. The Cixi tidal flat belongs to the silting-up class of tidal flat. Eleven dykes have been constructed since the Song dynasty. The average outward migration rate of the coastline before the founding of the People’s Republic was 25 m/a, and it has been increased to 50-100 m/a since the founding. The influencing factors for the formation and evolution of the Cixi tidal flat mainly include landform restriction, river runoff and human activities. The influence of human activities has become even greater in modern times. The principle for the regulation of the tidal furrow during the process of tidal flat reclamation should guide action according to circumstances as well as to reclamation of the tidal flat accompanied by the regulation of the tidal furrow. The former part of this principle means that the strike of the river channel must be in accordance with the law of stream movement and transport of sediment. The latter part means that the regulation of the tidal furrow must be closely linked to alongshore reclamation of the tidal flat.

The relationship between bank erosion, local aggradation and sediment transport in a small Carpathian stream

River bank erosion is the main process in small mountainous basins, especially those where the main channel is built of poorly resistant sedimentary rock or alluvium, exemplified by the Słomka basin.The main goal of the study, based on the field survey work and the erosion pin method, was to define the relation between river bank erosion, accumulation, and sediment transport.The investigations were carried out in the Słomka stream basin (watercourse length of 25.2km, basin area of 69.9km2) on an ~1.0-km-long stream reach, strongly anthropogenically transformed, between watercourse kilometres 5.0 and 6.0. We found that with an increase in flow the retreat bank rate increased nonlinearly. An average migration rate of the undercut banks ranged from 0.10m for the flow rate of 11.5m3s−1 to 0.92m for the flow rate of 35.5m3s−1. The maximum observed rate exceeded 0.8m for the flow rate of 11.5m3s−1 and 9.0m for the flow rate of 24.8m3s−1. With respect to the channel vertical morphology over the whole measurement section, we found that bed gradeline was raised, on average, by ~0.04m. The trend is contrary to the results of field surveys performed earlier on the Carpathian watercourses. The phenomenon is related to the abundant supply of rock rubble into the stream channel.High flow stages in the Słomka stream, which caused the stream bed material to move, had a predominant impact on stream channel morphology. Processes such as destructive activity of rain drops, aeolian erosion (sandblasting), soil expansion, and shrinkage during the rainy and dry seasons were of minor significance.

The natural medications for wound healing – Curcumin, Aloe-Vera and Ginger – do not induce a significant effect on the migration kinematics of cultured fibroblasts

Curcumin, Aloe-vera and Ginger are popular natural medications (NMs) for treating wounds, however, the mechanisms by which these NMs apparently accelerate wound healing remain largely unknown. From a biomechanical perspective, it is specifically unclear whether fibroblast motility improves in the presence of any of these NMs. Here we use our recently developed quantitative high-precision automated assay for cell migration (Topman et al., 2012b) which is based on image processing of time lapse micrographs to determine whether kinematic parameters e.g. the maximum and average migration rates of en mass fibroblast colonies are influenced by treating the cells with the above NMs. We found no evidence that Curcumin, Aloe-vera and Ginger directly influence the en mass fibroblast migration kinematics in vitro post infliction of localized mechanical damage to the cultures. However, due to the complexity of a wound healing process in vivo, these NMs may still influence the healing through other pathways.

Are small communities at risk of population loss?

Small communities almost universally worry about out-migration and the negative effects of out-migration on community viability. Using Oregon community-level data and applying the threshold estimation method of Hansen (Econometrica 68(3):575–603, 2000), we are able to identify population thresholds that distinguish small communities from their larger counterparts based on significant structural differences in factors affecting net migration. Our results suggest that smaller communities are more at risk of population decline than larger ones. After controlling for spatial spillovers from neighboring communities, the average net migration rate is 3 % in the larger communities (roughly above 5,000 population), 2 % in the mid-sized communities (roughly between 1,250 and 5,000) and \(-3\) % in the smallest communities (roughly less than 1,250). Other things equal, geographic isolation from large cities and low wage rates provide some protection from net out-migration for the smallest communities, but even for the smallest places, a larger population base lowers the risk of net out-migration.

The distribution of the coalescence time and the number of pairwise nucleotide differences in a model of population divergence or speciation with an initial period of gene flow

This paper is concerned with a model of “isolation with an initial period of migration”, where a panmictic ancestral population split into n descendant populations which exchanged migrants symmetrically at a constant rate for a period of time and subsequently became completely isolated. In the limit as the population split occurred an infinitely long time ago, the model becomes an “isolation after migration” model, describing completely isolated descendant populations which arose from a subdivided ancestral population. The probability density function of the coalescence time of a pair of genes and the probability distribution of the number of pairwise nucleotide differences are derived for both models. Whilst these are theoretical results of interest in their own right, they also give an exact analytical expression for the likelihood, for data consisting of the numbers of nucleotide differences between pairs of DNA sequences where each pair is at a different, independent locus. The behaviour of the distribution of the number of pairwise nucleotide differences under these models is illustrated and compared to the corresponding distributions under the “isolation with migration” and “complete isolation” models. It is shown that the distribution of the number of nucleotide differences between a pair of DNA sequences from different descendant populations in the model of “isolation with an initial period of migration” can be quite different from that under the “isolation with migration model”, even if the average migration rate over time (and hence the total number of migrants) is the same in both scenarios. It is also illustrated how the results can be extended to other demographic scenarios that can be described by a combination of isolated panmictic populations and “symmetric island” models.

Labour migration in the enlarged EU: a new economic geography approach

This paper studies the impact of migration policy liberalisation on international labour migration in the enlarged European Union (EU) in a structural economic geography approach. The liberalisation of migration policy would induce an additional 1.80–2.98% of the total EU workforce to change their country of location, with most of migrant workers relocating from the East to the West. The average net migration rate is decreasing in the level of integration, suggesting that from an economic point of view no regulatory policy responses are necessary to labour migration in the enlarged EU.

DUNE MIGRATION AND SAND TRANSPORT RATES IN TIDAL ESTUARIES: THE EXAMPLE OF THE RIVER ELBE

Large parts of the tidal estuary of river Elbe (Germany) are characterized by regular patterns of sand dunes. They are presumed to evolve due to complex sand transport mechanisms and show multi-faceted migration patterns. Direction and magnitude of their migration are influenced by hydrodynamic boundary conditions such as river runoff and tides. Dune Migration can lead to residual sand transport rates, depending on its direction and magnitude and the dune's characteristics. The understanding of dune migration patterns and associated sand transport is the basis of an effective sediment management as well as an important requirement for planning offshore structures. This study focuses on methods for computing migration and sand transport rates in automated ways. In a comparison and validation of different approaches, a cross-correlation technique was found to produce best results. From a unique data set of up to six annual bathymetrical multi-beam soundings between 1995 and 2010, dune characteristics and migration rates were processed and analysed autonomously. The findings show that in a long perspective, average dune migration and sand transport rates in the present study reach are directed upstream.

Measurement of river bank and cliff erosion from sequential LIDAR and historical aerial photography

The methodology and errors involved in determining the meander migration rates and amount of sediment produced by river bank and cliff erosion over five decades along a 16- and 28-km reach of the Waipaoa River, New Zealand, are described. The reach average meander migration rates (0.22 and 0.12 m a –1, respectively) are low by international standards for rivers of comparable size, suggesting considerable stability of the river planform. The contribution of sediment from bank and cliff erosion (74.3 and 23.3 kt a –1, respectively) to suspended sediment load is also low (< 2%) because this river has a high specific load dominated by mass movement erosion sources in tributary watersheds. Cliff erosion is the dominant process accounting for 69–88% of sediment delivered from channel side processes. The average channel migration rates due to cliff erosion are broadly comparable with long-term rates of valley widening over the past 18 ka BP, suggesting there has been no appreciable change in rates of cliff erosion over this time. Bank and cliff erosion processes were likely relatively more important as a source of sediment before widespread land-use conversions from native forest cover to grasslands.

A quantitative method for determining medial migration of the humeral head after shoulder arthroplasty: preliminary results in assessing glenoid wear at a minimum of two years after hemiarthroplasty with concentric glenoid reaming

Glenoid erosion and medial migration of the humeral head prosthesis have been observed after most types of shoulder arthroplasty. A method of measuring the change in humeral head position with time after shoulder prosthetic arthroplasty was applied it to 14 shoulders that underwent humeral hemiarthroplasty with concentric glenoid reaming. We hypothesized that the measurement technique would be reproducible and that the rate of wear would be small in the series of shoulders studied. Standardized anteroposterior and axillary radiographs were obtained after surgery. Two examiners measured the position of the humeral head center in relation to scapular reference coordinates for the anteroposterior and axillary projections and plotted these values against time after surgery. The change in position was characterized as the slope of this plot. Shoulders were included if there were at least 3 sets of postoperative films, the last being at least 2 years after surgery. The slopes measured by the 2 examiners agreed within 0.5 mm/y for the anteroposterior and the axillary projections. For the series of shoulder arthroplasties, the rate of movement of the head center toward the scapula was less than 0.4 mm/y for either examiner in either projection. Medial migration is a concern after any type of shoulder arthroplasty, whether a hemiarthroplasty, a biological interpositional arthroplasty, or a total shoulder arthroplasty. Quantifying the rate of medial migration over time after shoulder arthroplasty is an important element of clinical follow-up. This is an inexpensive, practical, and reproducible method that can be used to determine the rate of medial migration of the humeral head on plain radiographs after shoulder arthroplasty. The average rate of medial migration in the shoulders in this study was small.

Synergic stimulation of laminin and epidermal growth factor facilitates the myoblast growth through promoting migration

The dynamic behaviors of human skeletal muscle myoblasts were investigated in the culture on a laminin-coated surface in the presence of 100 ng/ml epidermal growth factor (EGF) in medium. The coexistence of laminin and EGF caused the enhancement of myoblast migration, giving an average migration rate of 62.0 microm/h, which was 2.7 times that on a plain surface. This encouraged migration could be a driving force to separate the dividing cells from each other, accompanied by shortened disjunction time of daughter cells to complete cytokinesis. In addition, the synergic effect of laminin and EGF led to the promotion of myoblast growth with keeping a relatively high fraction of proliferative cells during the culture for 150 h, which is considered to arise from the reduced frequency of cell-cell contacts during cytokinesis and thereby suppressing the process towards myotube formation after cell division.