JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 2 2004
John M. Laflen
ABSTRACT: The objectives of this paper are to discuss expectations for the Water Erosion Prediction Project (WEPP) accuracy, to review published studies related to WEPP goodness of fit, and to evaluate these in the context of expectations for WEPP's goodness of fit. WEPP model erosion predictions have been compared in numerous studies to observed values for soil loss and sediment delivery from cropland plots, forest roads, irrigated lands and small watersheds. A number of different techniques for evaluating WEPP have been used, including one recently developed where the ability of WEPP to accurately predict soil erosion can be compared to the accuracy of replicated plots to predict soil erosion. In one study involving 1,594 years of data from runoff plots, WEPP performed similarly to the Universal Soil Loss Erosion (USLE) technology, indicating that WEPP has met the criteria of results being "at least as good with respect to observed data and known relationships as those from the USLE," particularly when the USLE technology was developed using relationships derived from that data set, and using soil erodibility values measured on those plots using data sets from the same period of record. In many cases, WEPP performed as well as could be expected, based on comparisons with the variability in replicate data sets. One major finding has been that soil erodibility values calculated using the technology in WEPP for rainfall conditions may not be suitable for furrow irrigated conditions. WEPP was found to represent the major storms that account for high percentages of soil loss quite well,a single storm application that the USLE technology is unsuitable for,and WEPP has performed well for disturbed forests and forest roads. WEPP has been able to reflect the extremes of soil loss, being quite responsive to the wide differences in cropping, tillage, and other forms of management, one of the requirements for WEPP validation. WEPP was also found to perform well on a wide range of small watersheds, an area where USLE technology cannot be used. [source]

SOIL EROSION AND DEGRADATION BASED ON SAND PARTICLES TRANSPORT CAUSED BY WIND BLOWING

NATURAL RESOURCE MODELING, Issue 2 2010
MIHAI DUPAC
Abstract In this paper, the effect of sand particles transport caused by wind blowing and its role in the land degradation and desertification process is considered. For the modeling of the 3D landscape, a grayscale height map has been used, the vegetation has been modeled using a Lindenmayer system, and the sand particles have been modeled as a 3D mesh-free particles system. It was assumed that both the sand motion and the wind motion are incompressible continuum systems and their behavior follows the Navier,Stokes equations. To simulate the sand transport, the Navier,Stokes equations are discretized using the moving particle Semi-implicit (MPS) method. Different types of revegetation patterns (windbreakers) have been used to show some effective measures preventing soils from erosion. [source]

INTEGRATING LANDSCAPE ASSESSMENT AND HYDROLOGIC MODELING FOR LAND COVER CHANGE ANALYSIS,

JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 4 2002
Scott N. Miller
ABSTRACT: Significant land cover changes have occurred in the watersheds that contribute runoff to the upper San Pedro River in Sonora, Mexico, and southeast Arizona. These changes, observed using a series of remotely sensed images taken in the 1970s, 1980s, and 1990s, have been implicated in the alteration of the basin hydrologic response. The Cannonsville subwatershed, located in the Catskill/Delaware watershed complex that delivers water to New York City, provides a contrast in land cover change. In this region, the Cannonsville watershed condition has improved over a comparable time period. A landscape assessment tool using a geographic information system (GIS) has been developed that automates the parameterization of the Soil and Water Assessment Tool (SWAT) and KINEmatic Runoff and EROSion (KINEROS) hydrologic models. The Automated Geospatial Watershed Assessment (AGWA) tool was used to prepare parameter input files for the Upper San Pedro Basin, a subwatershed within the San Pedro undergoing significant changes, and the Cannonsville watershed using historical land cover data. Runoff and sediment yield were simulated using these models. In the Cannonsville watershed, land cover change had a beneficial impact on modeled watershed response due to the transition from agriculture to forest land cover. Simulation results for the San Pedro indicate that increasing urban and agricultural areas and the simultaneous invasion of woody plants and decline of grasslands resulted in increased annual and event runoff volumes, flashier flood response, and decreased water quality due to sediment loading. These results demonstrate the usefulness of integrating remote sensing and distributed hydrologic models through the use of GIS for assessing watershed condition and the relative impacts of land cover transitions on hydrologic response. [source]

The Machakos Case Study: Solid Outcomes, Unhelpful Hyperbole

DEVELOPMENT POLICY REVIEW, Issue 1 2006
Jules Siedenburg
This article revisits the well-known study of Machakos District, Kenya reported in the book More People, Less Erosion by Tiffen et al., which found dramatic, compelling evidence of successful endogenous adaptation to changing circumstances by rural Africans. The article seeks to elucidate discrepancies between the Machakos findings and other findings in the interest of both scientific accuracy and policy relevance. It is suggested that the Machakos study comprises hopeful data, on the one hand, and problematic calculations and assertions, on the other. After exploring problems with the study, the article suggests an alternative interpretation of the data that is arguably more pertinent to contemporary concerns with rural poverty and environmental degradation as well as more widely applicable in sub-Saharan Africa. [source]

Climate-driven decrease in erosion in extant Mediterranean badlands

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 11 2010
Michèle L. Clarke
Abstract Badland areas provide some of the highest erosion rates globally. Most studies of erosion have insufficient lengths of record to interrogate the impacts of decadal-scale changes in precipitation on rates of badland erosion in regions such as the Mediterranean, which are known to be sensitive to land degradation and desertification. Erosion measurements, derived from field monitoring using erosion pins, in southern Italy during the period 1974,2004 are used to explore the impacts of changing precipitation patterns on badland erosion. Erosion on badland inter-rill areas is strongly correlated with cumulative rainfall over each monitoring period. Annual precipitation has a substantial dynamic range, but both annual and winter (December, January, February) rainfall amounts in southern Italy show a steady decrease over the period 1970,2000. The persistence of positive values of the winter North Atlantic Oscillation index in the period 1980,2000 is correlated with a reduction in the winter rainfall amounts. Future climate scenarios show a reduction in annual rainfall across the western and central Mediterranean which is likely to result in a further reduction in erosion rates in existing badlands. Copyright © 2010 John Wiley & Sons, Ltd. [source]

SCALES: a large-scale assessment model of soil erosion hazard in Basse-Normandie (northern-western France)

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 8 2010
P. Le Gouée
Abstract The cartography of erosion risk is mainly based on the development of models, which evaluate in a qualitative and quantitative manner the physical reproduction of the erosion processes (CORINE, EHU, INRA). These models are mainly semi-quantitative but can be physically based and spatially distributed (the Pan-European Soil Erosion Risk Assessment, PESERA). They are characterized by their simplicity and their applicability potential at large temporal and spatial scales. In developing our model SCALES (Spatialisation d'éChelle fine de l'ALéa Erosion des Sols/large-scale assessment and mapping model of soil erosion hazard), we had in mind several objectives: (1) to map soil erosion at a regional scale with the guarantee of a large accuracy on the local level, (2) to envisage an applicability of the model in European oceanic areas, (3) to focus the erosion hazard estimation on the level of source areas (on-site erosion), which are the agricultural parcels, (4) to take into account the weight of the temporality of agricultural practices (land-use concept). Because of these objectives, the nature of variables, which characterize the erosion factors and because of its structure, SCALES differs from other models. Tested in Basse-Normandie (Calvados 5500,km2) SCALES reveals a strong predisposition of the study area to the soil erosion which should require to be expressed in a wet year. Apart from an internal validation, we tried an intermediate one by comparing our results with those from INRA and PESERA. It appeared that these models under estimate medium erosion levels and differ in the spatial localization of areas with the highest erosion risks. SCALES underlines here the limitations in the use of pedo-transfer functions and the interpolation of input data with a low resolution. One must not forget however that these models are mainly focused on an interregional comparative approach. Therefore the comparison of SCALES data with those of the INRA and PESERA models cannot result on a convincing validation of our model. For the moment the validation is based on the opinion of local experts, who agree with the qualitative indications delivered by our cartography. An external validation of SCALES is foreseen, which will be based on a thorough inventory of erosion signals in areas with different hazard levels. Copyright © 2010 John Wiley & Sons, Ltd. [source]

Prescribed-fire effects on rill and interrill runoff and erosion in a mountainous sagebrush landscape ,

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 2 2009
Frederick B. Pierson
Abstract Changing fire regimes and prescribed-fire use in invasive species management on rangelands require improved understanding of fire effects on runoff and erosion from steeply sloping sagebrush-steppe. Small (0·5 m2) and large (32·5 m2) plot rainfall simulations (85 mm h,1, 1 h) and concentrated flow methodologies were employed immediately following burning and 1 and 2 years post-fire to investigate infiltration, runoff and erosion from interrill (rainsplash, sheetwash) and rill (concentrated flow) processes on unburned and burned areas of a steeply sloped sagebrush site on coarse-textured soils. Soil water repellency and vegetation were assessed to infer relationships in soil and vegetation factors that influence runoff and erosion. Runoff and erosion from rainfall simulations and concentrated flow experiments increased immediately following burning. Runoff returned to near pre-burn levels and sediment yield was greatly reduced with ground cover recovery to 40 per cent 1 year post-fire. Erosion remained above pre-burn levels on large rainfall simulation and concentrated flow plots until ground cover reached 60 per cent two growing seasons post-fire. The greatest impact of the fire was the threefold reduction of ground cover. Removal of vegetation and ground cover and the influence of pre-existing strong soil-water repellency increased the spatial continuity of overland flow, reduced runoff and sediment filtering effects of vegetation and ground cover, and facilitated increased velocity and transport capacity of overland flow. Small plot rainfall simulations suggest ground cover recovery to 40 per cent probably protected the site from low-return-interval storms, large plot rainfall and concentrated flow experiments indicate the site remained susceptible to elevated erosion rates during high-intensity or long duration events until ground cover levels reached 60 per cent. The data demonstrate that the persistence of fire effects on steeply-sloped, sandy sagebrush sites depends on the time period required for ground cover to recover to near 60 per cent and on the strength and persistence of ,background' or fire-induced soil water repellency. Published in 2009 by John Wiley & Sons, Ltd. [source]

Editorial: joint meeting of the 5th International Conference on Aeolian Research and the Global Change and Terrestrial Ecosystems,Soil Erosion Network,

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 11 2003
Ted M. Zobeck
No abstract is available for this article. [source]

Extreme events controlling erosion and sediment transport in a semi-arid sub-andean valley

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 13 2002
R. Coppus
Abstract The importance of extreme events in controlling erosion and sediment transport in semi-arid areas has long been appreciated but in practice being by definition rare and episodic they are difficult to study. When they are observed this is frequently in catchments for which little data are available. Another difficulty is that even when catchments are being monitored the instruments that record discharge, sediment load and hillslope sediment fluxes perform inaccurately or unpredictably during extreme weather conditions. This paper describes slope and channel processes that were actually observed by the authors during a (at least) 1 : 30 year 30 minute event with a rainfall intensity of 240 mm h,1 in a second-order tributary of the Rio Camacho near Tarija in southern Bolivia. During the event, it could be observed how different tributary streams and slope sections contributed sediments and flow to the main channel. Evidence for these contributions did not survive the event, which has implications for both modelling and monitoring. Before the onset of the event open erosion plots were functioning on the slopes where rainfall and runoff were being measured. Rainfall experiments were used to obtain infiltration rates. The storm began with a moderate intensity of about 5 cm per hour but increased after 5 minutes to 30 cm per hour and continued for 30 minutes. At this time, the rainfall intensity greatly exceeded the infiltration capacity and water started draining the steep slopes. The ephemeral channel rapidly filled up with runoff. Erosion by hailstones was considerable. Provisionally, the discharge during peak runoff was estimated at 43·7 m3 s,1 (Manning equation). On the basis of sediment loads carried by previous storms, (average concentration of 21 g l,1) the total suspended load discharge during the storm would have been 15 ton ha,1. Within the ephemeral channel, 10 to 50 cm thick layers of coarse sediments were deposited. The collectors of the open erosion plots could not handle the large amounts of runoff and sediment and were completely filled to overflowing. Comparing these data with soil losses during less intense storms it can be concluded that extreme events largely contribute to erosion and sediment transport and that the majority of the rainstorms play only a minor role. The results also show how limited the values of rainfall experiments are in understanding geomorphic events. This makes modelling of erosion and soil losses a difficult and hazardous task. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Fate of microbial residues in sandy soils of the South African Highveld as influenced by prolonged arable cropping

EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 1 2002
W. Amelung
Summary Long-term cultivation of former grassland soils results in a significant decline of both living and dead microbial biomass. We evaluated the effect of duration of cropping on the preservation of fungal and bacterial residues in the coarse-textured soils of the South African Highveld. Composite samples were taken from the top 20 cm of soils (Plinthustalfs) that have been cropped for periods varying from 0 to 98 years in each of three different agro-ecosystems in the Free State Province. Amino sugars were determined as markers for the microbial residues in bulk soil and its particle-size fractions. Long-term cultivation reduced N in the soil by 55% and the contents of amino sugars by 60%. Loss rates of amino sugars followed bi-exponential functions, suggesting that they comprised both labile and stable fractions. With increased duration of cropping the amino sugars attached to silt dissipated faster than those associated with the clay. This dissipation was in part because silt was preferentially lost through erosion, while clay particles (and their associated microbial residues) remained. Erosion was not solely responsible for the reduction in amino sugar concentrations, however. Bacterial amino sugars were lost in preference to fungal ones as a result of cultivation, and this effect was evident in both silt- and clay-sized separates. This shift from fungal to bacterial residues was most pronounced within the first 20 years after converting the native grassland to arable cropland, but continued after 98 years of cultivation. [source]

Paleoindian environmental change and landscape response in Barger Gulch, Middle Park, Colorado

GEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 6 2005
James H. Mayer
Middle Park, a high-altitude basin in the Southern Rocky Mountains of north-central Colorado, contains at least 59 known Paleoindian localities. At Barger Gulch Locality B, an extensive Folsom assemblage (,10,500 14C yr B.P.) occurs within a buried soil. Radiocarbon ages of charcoal and soil organic matter, as well as stratigraphic positions of artifacts, indicate the soil is a composite of a truncated, latest-Pleistocene soil and a younger mollic epipedon formed between ,6000 and 5200 14C yr B.P. and partially welded onto the older soil following erosion and truncation. Radiocarbon ages from an alluvial terrace adjacent to the excavation area indicate that erosion followed by aggradation occurred between ,10,200 and 9700 14C yr B.P., and that the erosion is likely related to truncation of the latest-Pleistocene soil. Erosion along the main axis of Barger Gulch occurring between ,10,000 and 9700 14C yr B.P. was followed by rapid aggradation between ,9700 and 9550 14C yr B.P., which, along with the erosion at Locality B, coincides with the abrupt onset of monsoonal precipitation following cooling in the region ,11,000,10,000 14C yr B.P. during the Younger Dryas oscillation. Buried soils dated between ,9500 and 8000 14C yr B.P. indicate relative landscape stability and soil formation throughout Middle Park. Morphological characteristics displayed by early Holocene soils suggest pedogenesis under parkland vegetation in areas currently characterized by sagebrush steppe. The expansion of forest cover into lower elevations during the early Holocene may have resulted in lower productivity in regards to mammalian fauna, and may partly explain the abundance of early Paleoindian sites (,11,000,10,000 14C yr B.P., 76%) relative to late Paleoindian sites (,10,000,8000 14C yr B.P., 24%) documented in Middle Park. © 2005 Wiley Periodicals, Inc. [source]

Erosion and Nutrient Loss on Sloping Land under Intense Cultivation in Southern Vietnam

GEOGRAPHICAL RESEARCH, Issue 1 2008
NGUYEN VAN DE
Abstract To help improve the well-being of the local people, a joint Vietnamese-UK team set out to establish a way of estimating soil and nutrient losses under different land management scenarios, using field data extrapolated through remote sensing and GIS, to obtain catchment-wide estimates of the impact of land cover change. Immigration from remote provinces to the Dong Phu District of Binh Phuóc Province, about 120 km north of Ho Chi Minh City, has led to disruption of soil surface stability on easily eroded clayey sandstones, creating rapid nutrient depletion that affects crop yields and siltation in the channel of the Rach Rat river downstream. The poor farmers of the areas see crop yields drop dramatically after two or three years of cultivation due to the fertility decline. Soil loss varies dramatically between wet season and dry season and with ground cover. Erosion bridge measurements showed a mean loss of 85.2 t ha,1 y,1 under cassava saplings with cashew nuts, 43.3 t ha,1 y,1 on uncultivated land and 41.7 t ha,1 y,1 under mature cassava. The rates of erosion were higher than those reported in many other parts of Vietnam, reflecting the high erodibility of the friable sandy soils on the steep side-slopes of the Rach Rat catchment. However, although the actual measurements provide better soil loss data than estimates based on the parameters of soil loss equations, a large number of measurement sites is needed to provide adequate coverage of the crop and slope combinations in this dissected terrain for good prediction using GIS and remote sensing. [source]

Local Knowledge and Economic Realities Affecting Soil Erosion in the Rach Rat Catchment, Vietnam

GEOGRAPHICAL RESEARCH, Issue 1 2008
DAO KIM NGUYEN THUY BINH
Abstract Several parts of Binh Phuóc Province, southern Vietnam, suffer from degraded soils and vegetation as a result of both natural erosion of weak mud rocks and sandstones and intensive human activity, especially through land clearing for agriculture on unstable slopes, deforestation, and abandonment of poor farmland. The underlying cause of this land degradation has been the farming habits of migrants of varying ethnic groups who have settled in the area since 1980. The indigenous farming knowledge of these people and the role of that knowledge in soil erosion were examined by a series of household surveys. They enabled farming practices to be related to ground cover established from a 2002 Landsat 7 ETM (Enhanced Thematic Mapper), and erosion data from a series of erosion bridge measurements. A GIS (Geographical Information System) approach was piloted as a means of identifying areas vulnerable to erosion. This could then be combined with the understanding of farming practices to reveal the relative roles of farmer behaviour, crop cover, and slope and soil characteristics in the erosion process. Land use, local people's knowledge and economic realities are the main factors, as well as natural conditions, that drive this land degradation. [source]

Modelling Soil Erosion by Grazing: Recent Developments and New Approaches

GEOGRAPHICAL RESEARCH, Issue 1 2007
JOHN B. THORNES
Abstract Grazing is still widely held responsible for land degradation. The interaction between grazing and erosion is still rather poorly understood. As a consequence, counter-measures and associated management techniques have been slow to develop in southern Europe compared with Australia. Developments in ecological and economic-ecological modelling have improved our understanding of the processes and enhanced management capacity. Some of these developments are reviewed and two applications are described. One is a model for semi-extensive grazing in dry Mediterranean mountain conditions in which the shepherds, on random paths, seek to optimise resources use for economic benefit. The other is a spatial optimisation of vegetation canopy to minimise erosion rates. [source]

Depositional environment and sequence architecture of the Silurian Coralliferous Group, Southern Pembrokeshire, UK

GEOLOGICAL JOURNAL, Issue 3 2002
Robert D. Hillier
Abstract The Lower Silurian siliciclastic Coralliferous Group is shown to have been deposited in an intra-shelf position 10,15,km south of the palaeogeographic shelf-break of the Welsh Basin. After a phase of thermal subsidence related to the development of the predominantly Llandovery Skomer Volcanic Group, the shelf basin was transgressed. This transgression was punctuated by an episode of tectonic uplift in southern Pembrokeshire, resulting in subaerial exposure of the shelf and a significant basinward shift in sedimentary environments. Erosion and sediment bypass ensued, with coarse-grained low-sinuosity fluvial channels transporting sediment to the northerly Welsh Basin, where significant submarine fans developed. During the early Telychian, renewed transgression took place, with lowstand gravels being ravined and reworked into parasequences of the transgressive systems tract. These thin, coarse-grained parasequences record deposition within high-energy wave-dominated shoreface/inner shelf environments. Further coastal onlap resulted in the closing down of significant coarse-grained sediment supply, with the remaining Coralliferous Group being dominated by wave-influenced silts, mud-shales and thin sandstones comprising the highstand systems tract. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Comparative assessment of two distributed watershed models with application to a small watershed

HYDROLOGICAL PROCESSES, Issue 11 2006
Latif Kalin
Abstract Distributed watershed models are beneficial tools for the assessment of management practices on runoff and water-induced erosion. This paper evaluates, by application to an experimental watershed, two promising distributed watershed-scale sediment models in detail: the Kinematic Runoff and Erosion (KINEROS-2) model and the Gridded Surface Subsurface Hydrologic Analysis (GSSHA) model. The physics behind each model are to some extent similar, though they have different watershed conceptualizations. KINEROS-2 was calibrated using three rainfall events and validated over four separate rainfall events. Parameters estimated by this calibration process were adapted to GSSHA. With these parameters, GSSHA generated larger and retarded flow hydrographs. A 30% reduction in both plane and channel roughness in GSSHA along with the assumption of Green-Ampt conductivity KG-A = Ks, where Ks is the saturated conductivity, resulted in almost identical hydrographs. Sediment parameters not common in both models were calibrated independently of KINEROS-2. A comparative discussion of simulation results is presented. Even though GSSHA's flow component slightly overperformed KINEROS-2, the latter outperformed GSSHA in simulations for sediment transport. In spite of the fact that KINEROS-2 is not geared toward continuous-time simulations, simulations performed with both models over a 1 month period generated comparable results. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Peeling Back the Layers: Controlled Erosion and Triggered Disassembly of Multilayered Polyelectrolyte Thin Films,

ADVANCED MATERIALS, Issue 23 2007
M. Lynn
Abstract Methods for the layer-by-layer deposition of oppositely charged polymers on surfaces can be used to assemble thin multilayered films using a broad range of natural, synthetic, and biologically relevant materials. These methods also permit precise, nanometer-scale control over the compositions and internal structures of multicomponent assemblies. Provided that the individual components of these materials are selected or designed appropriately, these methods provide tantalizing new opportunities to design thin films and coatings that provide spatial, temporal, or active control over the release of one or several different agents from surfaces. The last two years have seen a significant increase in reports describing the development of new chemical, physical, and biomolecular approaches to the controlled erosion, triggered disassembly, or general deconstruction of multilayered polymer films. In this Progress Report, we highlight recent work from our laboratory and several other groups toward the design of ultrathin multilayered assemblies that i),permit broad, tunable, and sophisticated control over film erosion, and ii),provide new opportunities for the localized release of macromolecular therapeutics, such as DNA and proteins, from surfaces. [source]

The progression of tooth erosion in a cohort of adolescents of mixed ethnicity

INTERNATIONAL JOURNAL OF PAEDIATRIC DENTISTRY, Issue 5 2003
C. R. Dugmore
Summary. Objectives. To establish the prevalence of tooth erosion in a sample of 12-year-old children and to monitor changes over the subsequent 2 years. Methods. A random sample of 1753 children aged 12 years was drawn from all 62 state maintained schools in Leicestershire. A total of 1308 were re-examined 2 years later. Erosion was recorded on incisors and first molars using an erosion index based upon that from the Children's Dental Health in the United Kingdom 1993 survey. A score was also allocated to each subject according to the most advanced lesion in the mouth. Results. Erosion was present in 56·3% of subjects at age 12 and 64·1% at age 14. Deep enamel or dentine was eroded in 4·9% and 13·1% of subjects, respectively, at the same ages. One hundred and sixty-one (12·3%) children who were erosion-free at 12 years of age developed erosion over the subsequent 2 years. Boys had more erosion than girls, as did white compared to Asian children. Associations were found between erosion experience and social deprivation. Conclusion. New erosive lesions developed in 12·3% of the subjects between the ages of 12 and 14 years. New or more advanced lesions were seen in 27% of the children over the 2 years of the study. Males, white children and social deprivation were significantly associated with erosion experience. [source]

Economic Impacts of Technology, Population Growth And Soil Erosion At Watershed Level: The Case Of the Ginchi in Ethiopia

JOURNAL OF AGRICULTURAL ECONOMICS, Issue 3 2004
B.N. Okumu
A dynamic bio-economic model is used to show that, without technological and policy intervention, soil loss levels, income and nutrition could not be substantially or sustainably improved in a highland area of Ethiopia. Although cash incomes could rise by more than 40% over a twelve-year planning period, average per ha soil losses could be as high as 31 tonnes per ha. With the adoption of an integrated package of new technologies, however, results show the possibility of an average two-and-a-half-fold increase in cash incomes and a 28% decline in aggregate erosion levels even with a population growth rate of 2.3%. Moreover, a minimum daily calorie intake of 2000 per adult equivalent could be met from on-farm production with no significant increases in erosion. However, higher rates of growth in nutritional requirements and population introduce significant strains on the watershed system. From a policy perspective, there is a need for a more secure land tenure policy than currently prevailing to facilitate uptake of the new technology package, and a shift from the current livestock management strategy to one that encourages livestock keeping as a commercial enterprise. It would also imply a shift to a more site-specific approach to land management. [source]

Effects of ethyl benzoate on performance, morphology, and erosion of PLGA implants formed in situ

ADVANCES IN POLYMER TECHNOLOGY, Issue 1 2008
R. Astaneh
Abstract An in situ forming implant (ISFI) is a novel drug delivery system used for protein and peptide delivery, especially for cancer treatment. An ISFI based on 33% (w/w) poly(D,L -lactide- co -glycolide)(PLGA; 50:50)/3% (w/w) leuprolide acetate (LA)/64% (w/w) N -methyl-2-pyrrolidone (NMP) was prepared for this study. After injection of the final formulation, which is a viscous liquid to an aqueous medium, it deforms to become a semisolid or solid matrix. The performance of this matrix was investigated on the basis of peptide release from it. Erosion and morphology of ISFI were also studied. The effects of adding 12.8% (w/w) ethyl benzoate (EB) as a rate-modifying agent on performance, erosion, and morphology of ISFI were assessed. The implant containing EB showed very low burst release (5.53% ± 0.82%) and the morphology turns to closed pore-like structures. After adding EB, the morphology turns to closed pore-like structures. This type of morphology has very close relation to the performance of the implant as well. Finally, the effect of EB on performance, erosion, and morphology is explained by means of solvent,nonsolvent affinity, water permeation, and the rate of phase inversion. © 2008 Wiley Periodicals, Inc. Adv Polym Techn 27:17,26, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20114 [source]

Egypt: Nile Delta Soil Erosion

AFRICA RESEARCH BULLETIN: ECONOMIC, FINANCIAL AND TECHNICAL SERIES, Issue 3 2010
Article first published online: 4 MAY 2010
No abstract is available for this article. [source]

Interactive controls of herbivory and fluvial dynamics on landscape vegetation patterns on the Tanana River floodplain, interior Alaska

JOURNAL OF BIOGEOGRAPHY, Issue 9 2007
Lem G. Butler
Abstract Aim, We examined the interactive effects of mammalian herbivory and fluvial dynamics on vegetation dynamics and composition along the Tanana River in interior Alaska. Location, Model parameters were obtained from field studies along the Tanana River, Alaska between Fairbanks (64°50.50, N, 147°43.30, W) and Manley Hot Springs (65°0.0, N, 150°36.0, W). Methods, We used a spatially explicit model of landscape dynamics (ALFRESCO) to simulate vegetation changes on a 1-year time-step. The model was run for 250 years and was replicated 100 times. Results, Increases in herbivory decreased the proportion of early successional vegetation and increased the proportion of late successional vegetation on the simulated landscape. Erosion and accretion worked as antagonists to herbivory, increasing the amount of early successional vegetation and decreasing the amount of late successional vegetation. However, the interactive effects of herbivory and erosion/accretion were especially important in determining system response, particularly in early seral vegetation types. High erosion rates, when coupled with low herbivory, greatly increased the proportion of willow on the landscape. When coupled with high herbivory, however, they greatly increased the proportion of alder on the landscape. At low levels of herbivory, alder abundance peaked at intermediate levels of erosion/accretion. Main conclusions, Neither erosion/accretion nor herbivory produced consistent landscape patterns that could be predicted independently of the other. These findings underscore the importance of the interactive effects of biotic and abiotic disturbances in shaping large-scale landscape vegetation patterns in boreal floodplain ecosystems , systems traditionally thought to be driven primarily by abiotic disturbance alone. [source]

Osteoblast Function Is Compromised at Sites of Focal Bone Erosion in Inflammatory Arthritis,,

JOURNAL OF BONE AND MINERAL RESEARCH, Issue 9 2009
Nicole C Walsh PhD
Abstract In rheumatoid arthritis (RA), synovial inflammation results in focal erosion of articular bone. Despite treatment attenuating inflammation, repair of erosions with adequate formation of new bone is uncommon in RA, suggesting that bone formation may be compromised at these sites. Dynamic bone histomorphometry was used in a murine model of RA to determine the impact of inflammation on osteoblast function within eroded arthritic bone. Bone formation rates at bone surfaces adjacent to inflammation were similar to those observed in nonarthritic bone; therefore, osteoblast activity is unlikely to compensate for the increased bone resorption at these sites. Within arthritic bone, the extent of actively mineralizing surface was reduced at bone surfaces adjacent to inflammation compared with bone surfaces adjacent to normal marrow. Consistent with the reduction in mineralized bone formation, there was a notable paucity of cells expressing the mid- to late stage osteoblast lineage marker alkaline phosphatase, despite a clear presence of cells expressing the early osteoblast lineage marker Runx2. In addition, several members of the Dickkopf and secreted Frizzled-related protein families of Wnt signaling antagonists were upregulated in arthritic synovial tissues, suggesting that inhibition of Wnt signaling could be one mechanism contributing to impaired osteoblast function within arthritic bone. Together, these data indicate that the presence of inflammation within arthritic bone impairs osteoblast capacity to form adequate mineralized bone, thus contributing to the net loss of bone and failure of bone repair at sites of focal bone erosion in RA. [source]

SOIL EROSION AND SEDIMENT YIELD PREDICTION ACCURACY USING WEPP,

Identification of sediment source and sink areas in a Himalayan watershed using GIS and remote sensing

LAND DEGRADATION AND DEVELOPMENT, Issue 6 2009
M. K. Jain
Abstract Erosion is a natural geomorphic process occurring continually over the Earth's surface and it largely depends on topography, vegetation, soil and climatic variables, and therefore, exhibits pronounced spatial variability due to catchment heterogeneity and climatic variation. This problem can be circumvented by discretizing the catchment into approximately homogeneous sub-areas using GIS. In this study, the remote sensing and GIS techniques (through Imagine®8.6 and ArcGIS®9.1 software) were used for derivation of spatial information, catchment discretization, data processing etc. for the Himalayan Chaukhutia watershed (India). Various thematic layers for different factors of USLE were generated and overlaid to compute spatially distributed gross soil erosion maps for the watershed using 18-year rainfall data. The concept of transport limited accumulation was formulated and used in ArcGIS® for generating the transport capacity maps. Using these maps, the gross soil erosion was routed to the catchment outlet using hydrological drainage paths, for derivation of transport capacity limited sediment outflow maps. These maps depict the amount of sediment rate from a particular grid in spatial domain and the pixel value of the outlet grid indicates the sediment yield at the outlet of the watershed. Up on testing, the proposed method simulated the annual sediment yield with less than ±40% error. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Reducing water erosion in a gypsic soil by combined use of organic amendment and shrub revegetation

LAND DEGRADATION AND DEVELOPMENT, Issue 4 2005
M. J. Marqués
Abstract Degraded gypsic soils in the centre of Spain can be rehabilitated with organic amendment and shrub revegetation. Erosion has been measured on plots of 2×0·5,m2 under simulated rainfall of 70,mm,h,1 and a kinetic energy of 18,J,mm,1,m,2. Samples of water runoff and sediments were studied in the summer of the years 2002 and 2003. The presence of shrub Atriplex halimus (Chenonodiaceae) significantly reduces runoff from 16·9 to 6·7,ml,m,2,min,1 and sediments from 0·16 to 0·02,g,m,2,min,1. When sewage sludge is applied the differences among plots with and without bushes disappear. Although both treatments independently applied are efficient as erosion control measures, the combined use of revegetation and organic amendment allows a reduced dose of sewage sludge with the same effect on erosion. A low dose of sludge is desirable in view of the accumulation of toxic chemicals. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Soil degradation by erosion

LAND DEGRADATION AND DEVELOPMENT, Issue 6 2001
R. Lal
Abstract Soil degradation by accelerated erosion is a serious problem and will remain so during the 21st century, especially in developing countries of the tropics and subtropics. Yet, its extent, severity, and economic and environmental impacts are debatable. Estimates of global and regional land area affected are tentative and subjective. Results of field measurements are often technique-dependent. Considerable progress has been made in modeling soil erosion, yet field validation of these models remains to be done for principal soils and ecoregions. Similar to the land area affected, estimates of erosional impacts on crop yield, productivity and soil quality are tentative and subjective. Further, erosion-induced losses on crop yield are scale-dependent because of the compensatory beneficial effects on yields from depositional sites, and technology-dependent because of the masking effects of input such as fertilizers and irrigation. Erosion caused changes in soil carbon dynamics and non-point source water pollution are important environmental impacts. While erosion (e.g., detachment and transport) can lead to emission of trace gases into the atmosphere, deposition can bury and sequester some of the carbon. In addition to improving the database on the land area affected, there is also a need to assess erosional impacts on productivity and soil C balance at the watershed, regional, and global scale. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Cell-mediated Delivery and Targeted Erosion of Vascular Endothelial Growth Factor-Crosslinked Hydrogels

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 14 2010
Sung Hye Kim
Abstract We have previously reported a novel polymeric delivery vehicle that is assembled via interaction between heparin and the vascular endothelial growth factor (VEGF). Here, the cell-responsiveness of this hydrogel,including the delivery of VEGF in response to VEGFR-2 overexpressing PAE/KDR cells (porcine aortic endothelial cells (PAE) equipped with the transcript for the kinase insert domain receptor (KDR)), consequent erosion of the hydrogel matrix, and cellular response,are highlighted. The release of VEGF and hydrogel erosion reached 100% only in the presence of PAE/KDR. The [PEG-LMWH/VEGF] hydrogel (PEG,=,poly(ethylene glycol), LMWH,=,low molecular weight heparin) correspondingly prompted increases in VEGFR-2 phosphorylation and proliferation of PAE/KDR cells. This study proves that growth factor-crosslinked hydrogels can liberate VEGF in response to specific receptors, causing gel erosion and desired cell responses. The promise of these approaches in therapeutic applications, including targeted delivery, is suggested. [source]

Tribute chromite mining and environmental management on the northern Great Dyke of Zimbabwe

NATURAL RESOURCES FORUM, Issue 2 2002
Oliver Maponga
A combination of poor mining methods, waste storage and disposal systems, as well as the day-to-day activities associated with tribute and contract chromite mining are primarily responsible for environmental problems on the Zimbabwe Great Dyke. For instance, the unsystematic dumping of waste rocks in rivers blocks channels and results in flooding, which further sterilizes agricultural land and mineral resources. Erosion of these haphazardly located dumps causes siltation of water bodies and results in the dispersion of heavy metals in soils and watercourses. Vegetation growth on waste dumps is limited and constrained by the high pH levels from phytotoxic metals in soils, the lack of nutrients, poor moisture retention qualities of the mining waste and critical cation imbalances within dumps. This article attributes poor environmental management on the Dyke to poverty, a direct result of the nature of tribute agreements and output prices. Prices based on output targets are exploitative and undervalue labour and thus perpetuate poverty. By absolving claim holders from environmental liability, tribute agreements contribute directly to environmental problems. Thus, the incorporation of enforceable dual environmental responsibility requirements in contract mining agreements is needed to overcome this problem. This article recommends that, to break the poverty cycle, the primary cause of environmental mismanagement in the sector, miners need to be empowered through claim ownership and the enhancement of their capacity to negotiate prices with buyers of chrome. [source]

Roadfill Revegetation in Semiarid Mediterranean Environments.

RESTORATION ECOLOGY, Issue 1 2007
Hydroseeding, Part II: Topsoiling, Species Selection
Abstract Erosion is one of the main problems in roadfill restoration. Revegetation is widely used as a method to reduce erosion rates, and it is often carried out through hydroseeding. In semiarid Mediterranean conditions, this approach to revegetation often produces poor results due to climatic limitations. We evaluated whether (1) spreading topsoil and (2) hydroseeding with local rather than commercial species mixtures could improve the vegetative cover of roadfills. The study was carried out in 24 plots over a 20-month period. At the end of the study, vegetation cover was higher in topsoiled plots (38.8%) than in nontopsoiled plots (21.5%). Locally selected species produced higher vegetative cover (61.1%) than did standard commercial species (52.2%). After 20 months, the erosion index was not different among any treatment probably due to the low sensitivity of this variable. These results suggest that amendment of soils through the addition of topsoil is an important technique in roadfill revegetation in Mediterranean environments. Additionally, hydroseeding with local species will produce better vegetative cover on roadfills than does hydroseeding with available commercial species. [source]