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Field Measurements (field + measurement)
Kinds of Field Measurements Selected AbstractsA Sampling Approach for Evaluating Particle Loss During Continuous Field Measurement of Particulate MatterPARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 2 2005Christopher A. Noble Abstract A method for evaluating sample bias in field measurements is presented. Experiments were performed in the field and laboratory to quantify the bias as a function of particle size for the scanning mobility particle sizer and the aerodynamic particle sizer. Sources of bias and sample loss considered in this work were sampling line loss, instrumental differences and inlet efficiencies. Measurement of the bias and sample loss allow for correction of the data acquired in the field, so as to obtain more representative samples of atmospheric concentrations. Substantial losses of fine and ultrafine particle count were observed, with sampling line losses ranging from 10,50,%, dependent on particle size. Only minor line losses were observed for coarse particles (approximately 5,%) because the sampling line was oriented vertically. Please note: corrected DOI, in print wrong DOI (10.1002/ppsc.200400939) [source] Morphodynamics of the exit of a cutoff meander: experimental findings from field and laboratory studies,EARTH SURFACE PROCESSES AND LANDFORMS, Issue 3 2010J. Le Coz Abstract The morphological evolution of the entrances and exits of abandoned river channels governs their hydrological connectivity. The study focusses on flow and sediment dynamics in the exit of a cutoff meander where the downstream entrance is still connected to the main channel, but the upstream entrance is closed. Two similar field and laboratory cases were investigated using innovative velocimetry techniques (acoustic Doppler profiling, image analysis). Laboratory experiments were conducted with a mobile-bed physical model of the Morava River (Slovakia). Field measurements were performed in the exit of the Port-Galland cutoff meander, Ain River (France). Both cases yielded consistent and complementary results from which a generic scheme for flow patterns and morphological evolution was derived. A simple analogy with flows in rectangular side cavities was used to explain the recirculating flow patterns which developed in the exit. A decelerating inflow deposits bedload in the downstream part of the cavity, while the upstream part is eroded by an accelerating outflow, leading to the retreat of the upstream bank. In the field, strong secondary currents were observed, especially in the inflow, which may enhance the scouring of the downstream corner of the cavity. Also, fine sediment deposits constituted a silt layer in a transitional zone, located between the mouth of the abandoned channel and the oxbow-lake within the cutoff meander. Attempts at morphological prediction should consider not only the flow and sediment conditions in the cavity, but also the dynamics of the main channel. Copyright © 2010 John Wiley & Sons, Ltd [source] Suspended sediment transport in a small Mediterranean agricultural catchmentEARTH SURFACE PROCESSES AND LANDFORMS, Issue 7 2009Joan Estrany Abstract The aim of this study is to analyze suspended sediment transport in a Mediterranean agricultural catchment under traditional soil and water conservation practices. Field measurements were conducted in Can Revull, a small ephemeral catchment (1.03 km2) on the island of Mallorca. This study uses continuous turbidity records to analyse suspended sediment transport regimes, construct and interpret multiple regression models of total suspended sediment concentration (SSC) and of SSC related to stormflow discharge, and assess the sediment loads and yields of three hydrological years (2004,2005 to 2006,2007). An annual average SSC of 17.3 mg l,1, with a maximum of 2270 mg l,1, was recorded in the middle of the winter period when rainfall intensities are high and headwater slopes are ploughed and thus bare. Strong seasonal contrasts of baseflow dynamics associated with different degrees of dilution provide a large scatter in SSC and in the derived rating curves, reflecting that other factors control the supply of suspended sediment. Multiple regression models identify rainfall intensity as the most significant variable in sediment supply. However, under baseflow conditions, physical and biological processes generate sediment in the channel that is subsequently removed during high flow. In contrast, when baseflow is not present, rainfall intensity is the only process that supplies sediment to the channel, mostly from hillslopes. Considering the study period as average in terms of total annual rainfall and intensities, suspended sediment yields were an order of magnitude lower than those obtained in other Mediterranean catchments, a factor that can be related to the historical use of soil conservation practices. Copyright © 2009 John Wiley & Sons, Ltd. [source] Vegetation and topographic controls on sediment deposition and storage on gully beds in a degraded mountain areaEARTH SURFACE PROCESSES AND LANDFORMS, Issue 6 2009Armando Molina Abstract Active gully systems developed on highly weathered or loose parent material are an important source of runoff and sediment production in degraded areas. However, a decrease of land pressure may lead to a return of a partial vegetation cover, whereby gully beds are preferred recolonization spots. Although the current knowledge on the role of vegetation on reducing sediment production on slopes is well developed, few studies exist on the significance of restoring sediment transport pathways on the total sediment budget of degraded mountainous catchments. This study in the Ecuadorian Andes evaluates the potential of vegetation to stabilize active gully systems by trapping and retaining eroded sediment in the gully bed, and analyses the significance of vegetation restoration in the gully bed in reducing sediment export from degraded catchments. Field measurements on 138 gully segments located in 13 ephemeral steep gullies with different ground vegetation cover indicate that gully bed vegetation is the most important factor in promoting short-term (1,15 years) sediment deposition and gully stabilization. In well-vegetated gully systems ( , 30% of ground vegetation cover), 0.035 m3 m,1 of sediment is deposited yearly in the gully bed. Almost 50 per cent of the observed variance in sediment deposition volumes can be explained by the mean ground vegetation cover of the gully bed. The presence of vegetation in gully beds gives rise to the formation of vegetated buffer zones, which enhance short-term sediment trapping even in active gully systems in mountainous environments. Vegetation buffer zones are shown to modify the connectivity of sediment fluxes, as they reduce the transport efficiency of gully systems. First calculations on data on sediment deposition patterns in our study area show that gully bed deposition in response to gully bed revegetation can represent more than 25 per cent of the volume of sediment generated within the catchment. Our findings indicate that relatively small changes in landscape connectivity have the potential to create strong (positive) feedback loops between erosion and vegetation dynamics. Copyright © 2009 John Wiley & Sons, Ltd. [source] Effects of wet meadow riparian vegetation on streambank erosion.EARTH SURFACE PROCESSES AND LANDFORMS, Issue 7 2002Abstract We measured the effect of wet meadow vegetation on the bank strength and failure mechanics of a meandering montane meadow stream, the South Fork of the Kern River at Monache Meadow, in California's Sierra Nevada. Streambanks colonized by ,wet' graminoid meadow vegetation were on average five times stronger than those colonized by ,dry' xeric meadow and scrub vegetation. Our measurements show that strength is correlated with vegetation density indicators, including stem counts, standing biomass per unit area, and the ratio of root mass to soil mass. Rushes appear better than sedges at stabilizing coarse bar surfaces, while sedges are far more effective at stabilizing actively eroding cut banks. Wet meadow floodplain vegetation creates a composite cut bank configuration (a cohesive layer overlying cohesionless materials) that erodes via cantilever failure. Field measurements and a geotechnical model of cantilever stability show that by increasing bank strength, wet meadow vegetation increases the thickness, width, and cohesiveness of a bank cantilever, which, in turn, increases the amount of time required to undermine, detach, and remove bank failure blocks. At Monache Meadow, it takes approximately four years to produce and remove a 1 m wide wet meadow bank block. Wet meadow vegetation limits bank migration rates by increasing bank strength, altering bank failure modes, and reducing bank failure frequency. Copyright © 2002 John Wiley & Sons, Ltd. [source] How a mega-grazer copes with the dry season: food and nutrient intake rates by white rhinoceros in the wildFUNCTIONAL ECOLOGY, Issue 2 2006A. M. SHRADER Summary 1Few studies have investigated how free-ranging wild herbivores adjust their food intake rate and nutrient gains during the dry season. Our study focused on the largest extant grazer, the white rhinoceros (Ceratotherium simum Burchell 1817). Field measurements were made on changes in bite mass, bite rate and nutrient concentrations of food eaten during the dry season. 2As the dry season progressed, the quality and availability of food resources declined. During this time white rhinos foraged mainly in high-quality short and woodland grasslands. Late in the dry season they also used flushes of green grass in previously burnt Themeda grasslands. 3Bite mass increased linearly with increasing sward height, while bite rate declined. Intake rate was determined primarily by bite mass and thus tended to increase linearly with sward height. Maximum bite mass and intake rate was obtained in swards >20 cm. 4White rhinos did not compensate for seasonal declines in food quality by adjusting their food intake rate or diet breadth. We suggest that white rhinos mobilize fat reserves to help meet their nutritional needs during the dry season. [source] Hydrologic responses to earthquakes and a general metricGEOFLUIDS (ELECTRONIC), Issue 1-2 2010CHI-YUEN WANG Geofluids (2010) 10, 206,216 Abstract Hydrologic responses to earthquakes, including liquefaction, changes in stream and spring discharge, changes in the properties of groundwater such as geochemistry, temperature and turbidity, changes in the water level in wells, and the eruption of mud volcanoes, have been documented for thousands of years. Except for some water-level changes in the near field which can be explained by poroelastic responses to static stress changes, most hydrologic responses, both within and beyond the near field, can only be explained by the dynamic responses associated with seismic waves. For these responses, the seismic energy density e may be used as a general metric to relate and compare the various hydrologic responses. We show that liquefaction, eruption of mud volcanoes and increases in streamflow are bounded by e , 10,1 J m,3; temperature changes in hot springs are bounded by e , 10,2 J m,3; most sustained groundwater changes are bounded by e , 10,3 J m,3; geysers and triggered seismicity may respond to seismic energy density as small as 10,3 and 10,4 J m,3, respectively. Comparing the threshold energy densities with published laboratory measurements, we show that undrained consolidation induced by dynamic stresses can explain liquefaction only in the near field, but not beyond the near field. We propose that in the intermediate field and far field, most responses are triggered by changes in permeability that in turn are a response to the cyclic deformation and oscillatory fluid flow. Published laboratory measurements confirm that changes in flow and time-varying stresses can change permeability, inducing both increases and decreases. Field measurements in wells also indicate that permeability can be changed by earthquakes in the intermediate field and far field. Further work, in particular field monitoring and measurements, are needed to assess the generality of permeability changes in explaining far-field hydrologic responses to earthquakes. [source] Amazon drought and its implications for forest flammability and tree growth: a basin-wide analysisGLOBAL CHANGE BIOLOGY, Issue 5 2004Daniel Nepstad Abstract Severe drought in moist tropical forests provokes large carbon emissions by increasing forest flammability and tree mortality, and by suppressing tree growth. The frequency and severity of drought in the tropics may increase through stronger El Niño Southern Oscillation (ENSO) episodes, global warming, and rainfall inhibition by land use change. However, little is known about the spatial and temporal patterns of drought in moist tropical forests, and the complex relationships between patterns of drought and forest fire regimes, tree mortality, and productivity. We present a simple geographic information system soil water balance model, called RisQue (Risco de Queimada , Fire Risk) for the Amazon basin that we use to conduct an analysis of these patterns for 1996,2001. RisQue features a map of maximum plant-available soil water (PAWmax) developed using 1565 soil texture profiles and empirical relationships between soil texture and critical soil water parameters. PAW is depleted by monthly evapotranspiration (ET) fields estimated using the Penman,Monteith equation and satellite-derived radiation inputs and recharged by monthly rain fields estimated from 266 meteorological stations. Modeled PAW to 10 m depth (PAW10 m) was similar to field measurements made in two Amazon forests. During the severe drought of 2001, PAW10 m fell to below 25% of PAWmax in 31% of the region's forests and fell below 50% PAWmax in half of the forests. Field measurements and experimental forest fires indicate that soil moisture depletion below 25% PAWmax corresponds to a reduction in leaf area index of approximately 25%, increasing forest flammability. Hence, approximately one-third of Amazon forests became susceptible to fire during the 2001 ENSO period. Field measurements also suggest that the ENSO drought of 2001 reduced carbon storage by approximately 0.2 Pg relative to years without severe soil moisture deficits. RisQue is sensitive to spin-up time, rooting depth, and errors in ET estimates. Improvements in our ability to accurately model soil moisture content of Amazon forests will depend upon better understanding of forest rooting depths, which can extend to beyond 15 m. RisQue provides a tool for early detection of forest fire risk. [source] Predicting and quantifying the structure of tropical dry forests in South Florida and the Neotropics using spaceborne imageryGLOBAL ECOLOGY, Issue 3 2006Thomas W. Gillespie ABSTRACT Aim, This research examines environmental theories and remote sensing methods that have been hypothesized to be associated with tropical dry forest structure. Location, Tropical dry forests of South Florida and the Neotropics. Methods, Field measurements of stand density, basal area and tree height were collected from 22 stands in South Florida and 30 stands in the Neotropics. In South Florida, field measurements were compared to climatic (temperature, precipitation, hurricane disturbance) and edaphic (rockiness, soil depth) variables, spectral indices (NDVI, IRI, MIRI) from Landsat 7 ETM+, and estimates of tree height from the Shuttle Radar Topography Mission (SRTM) and the National Elevation Dataset (NED). Environmental variables associated with tropical dry forest structure in South Florida were compared to tropical dry forest in other Neotropical sites. Results, There were significant correlations among temperature and precipitation, and stand density and tree height in South Florida. There were significant correlations between (i) stand density and mean NDVI and standard deviation of NDVI, (ii) MIRI and stand density, basal area and mean tree height, and (iii) estimates of tree height from SRTM with maximum tree height. In the Neotropics, there were no relationships between temperature or precipitation and tropical dry forest structure, however, Neotropical sites that experience hurricane disturbance had significantly shorter tree heights and higher stand densities. Main conclusions, It is possible to predict and quantify the forest structure characteristics of tropical dry forests using climatic data, Landsat 7 ETM+ imagery and SRTM data in South Florida. However, results based on climatic data are region-specific and not necessarily transferable between tropical dry forests at a continental spatial scale. Spectral indices from Landsat 7 ETM+ can be used to quantify forest structure characteristics, but SRTM data are currently not transferable to other regions. Hurricane disturbance has a significant impact on forest structure in the Neotropics. [source] 3D float tracking: in situ floodplain roughness estimationHYDROLOGICAL PROCESSES, Issue 2 2009Menno Straatsma Abstract This paper presents a novel technique to quantify in situ hydrodynamic roughness of submerged floodplain vegetation: 3D float tracking. This method uses a custom-built floating tripod that is released on the inundated floodplain and tracked from shore by a robotic total station. Simultaneously, an acoustic Doppler current profiler (ADCP) collects flow velocity profiles and water depth data. Roughness values are derived from two methods based on (1) run-averaged values of water depth, slope and flow velocity to compute the roughness based on the Chézy equation, assuming uniform flow, (2) the equation for one-dimensional free surface flow in a moving window. A sensitivity analysis using synthetic data proved that the median value of the roughness, derived using method 2, is independent of (1) the noise in water levels, up to 9 mm, (2) bottom surface slope, and (3) topographic undulations. The window size should be at least 40 m for a typical lowland river setup. Field measurements were carried out on two floodplain sections with an average vegetation height of 0·030 (Arnhem) and 0·043 m (Dreumel). Method 1 resulted in a Nikuradse roughness length of 0·08 m for both locations. Method 2 gave 0·12 m for Arnhem and 0·19 m for Dreumel. In Arnhem, a spatial pattern of roughness values was present, which might be related to fractional vegetation cover or vegetation density during the flood peak. 3D float tracking proved a flexible and detailed method for roughness determination in the absence of waves, and provided an unrestricted view from shore. Copyright © 2008 John Wiley & Sons, Ltd. [source] Comparing the hydrology of grassed and cultivated catchments in the semi-arid Canadian prairiesHYDROLOGICAL PROCESSES, Issue 3 2003G. van der Kamp Abstract At the St Denis National Wildlife Area in the prairie region of southern Saskatchewan, Canada, water levels in wetlands have been monitored since 1968. In 1980 and 1983 a total of about one-third of the 4 km2 area was converted from cultivation to an undisturbed cover of brome grass. A few years after this conversion all the wetlands within the area of grass dried out; they have remained dry since, whereas wetlands in adjacent cultivated lands have held water as before. Field measurements show that introduction of undisturbed grass reduces water input to the wetlands mainly through a combination of efficient snow trapping and enhanced infiltration into frozen soil. In winter, the tall brome grass traps most of the snowfall, whereas in the cultivated fields more wind transport of snow occurs, especially for short stubble and fallow fields. Single-ring infiltration tests were conducted during snowmelt, while the soil was still frozen, and again in summer. The infiltrability of the frozen soil in the grassland is high enough to absorb most or all of the snowmelt, whereas in the cultivated fields the infiltration into the frozen soil is limited and significant runoff occurs. In summer, the infiltrability increases for the cultivated fields, but the grassland retains a much higher infiltrability than the cultivated land. The development of enhanced infiltrability takes several years after the conversion from cultivation to grass, and is likely due to the gradual development of macropores, such as root holes, desiccation cracks, and animal burrows. Copyright ©2002 Crown in the right of Canada. Published by John Wiley & Sons, Ltd. [source] A simple finite element model for vibration analyses induced by moving vehiclesINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 12 2006Shen-Haw Ju Abstract This study developed a simple finite element method combining the moving wheel element, spring,damper element, lumped mass and rigid link effect to simulate complicated vehicles. The advantages of this vehicle model are (1) the dynamic matrix equation is symmetric, (2) the theory and formulations are very simple and can be added to a standard dynamic finite element codes easily and (3) very complicated vehicle models can be assembled using the proposed elements as simple as the traditional finite element method. The Fryba's solution of a simply supported beam subjected to a moving two-axle system was analysed to validate this finite element model. For a number of numerical simulations, the two solutions are almost identical, which means that the proposed finite element model of moving vehicles is considerably accurate. Field measurements were also used to validate this vehicle model through a very complicated finite element analysis, which indicates that the current moving vehicle model can be used to simulate complex problem with acceptable accuracy. Copyright © 2006 John Wiley & Sons, Ltd. [source] Water management tasks in the summer polders of the Nemunas lowland,IRRIGATION AND DRAINAGE, Issue 2 2006Antanas Lukianas plaine d'inondation; polders d'été; gestion des eaux Abstract Surplus water during floods as well as the low level of the soil surface determine the complicated ecological, economic and demographic conditions in the Nemunas delta. Subsequently, it leads to different types and intensity of use of farmland as well as different methods of water regime regulation: summer or winter type polders. The building of 17 summer polders in the 32,500,ha floodplain area was a compromise, seeking to improve farming conditions and maintain the stability of the flood regime and ecology in the delta. Field measurements and mathematical modelling were carried out. As study results have shown, grass yield losses due to flooding depend on the distribution of water levels and flood duration in the summer polders. Relative damage to agriculture is insignificant and makes up only 10,15% of the total amount of flood damage in the Nemunas lowland. The field measurements and hydraulic and mathematical modelling of flow and sediment regime as well as study of flooding and changed farming conditions also show that it is possible to reduce the height of floods and economic and ecological damage. Rearrangement of the system of protective dikes, regulation of the main river canal and water/sedimentation regime with the help of pumping stations, decrease of pollutant migration into the Curonian Lagoon and Baltic Sea, and recreation of natural meadows are important in that case. Copyright © 2006 John Wiley & Sons, Ltd. Des eaux excédentaires en période de crues et un faible niveau du sol déterminent les conditions écologiques, économiques et démographiques complexes du delta du fleuve Nemunas. En particulier, des types et intensités différentes dans l'utilisation des terres arables, ainsi que des méthodes différentes de régulation du régime des eaux: polders d'été ou d'hiver. La construction de 17 polders d'été sur 32 500,ha de plaine d'inondation a été une solution de compromis pour améliorer l'agriculture et maintenir la stabilité du régime des crues et de l'écologie du delta. Des mesures de terrain et des modèles mathématique ont été réalisés. D'après les résultats des études, les pertes de récolte d'herbe dûes aux crues dépendent de la distribution des niveaux d'eau et de la durée de la crue dans les polders d'été. L'impact négatif sur l'agriculture est négligeable et ne représente que 10 à 15% des dommages totaux dus aux crues dans le delta du fleuve Nemunas. Les mesures de terrain et la modélisation hydraulique et mathématique de l'écoulement et de la sédimentation, ainsi que l'analyse des crues et des modifications de production agricole, prouvent également qu'il est possible de réduire la hauteur des crues et de diminuer ainsi les dommages économiques et écologiques. Dans ce cas, il convient de réorganiser le système des digues de protection, de réguler le chenal principal du fleuve et le régime de sédimentation des eaux à l'aide de stations de pompage, de réduire les déversements polluants dans la lagune Curonian et la mer Baltique, et de régénérer des pâturages naturels. Copyright © 2006 John Wiley & Sons, Ltd. [source] Field hearing measurements of the Atlantic sharpnose shark Rhizoprionodon terraenovaeJOURNAL OF FISH BIOLOGY, Issue 10 2009B. M. Casper Field measurements of hearing thresholds were obtained from the Atlantic sharpnose shark Rhizoprionodon terraenovae using the auditory evoked potential method (AEP). The fish had most sensitive hearing at 20 Hz, the lowest frequency tested, with decreasing sensitivity at higher frequencies. Hearing thresholds were lower than AEP thresholds previously measured for the nurse shark Ginglymostoma cirratum and yellow stingray Urobatis jamaicensis at frequencies <200 Hz, and similar at 200 Hz and above. Rhizoprionodon terraenovae represents the closest comparison in terms of pelagic lifestyle to the sharks which have been observed in acoustic field attraction experiments. The sound pressure levels that would be equivalent to the particle acceleration thresholds of R. terraenovae were much higher than the sound levels which attracted closely related sharks suggesting a discrepancy between the hearing threshold experiments and the field attraction experiments. [source] Field measurements of the water content in the top soil using a new capacitance sensor with a flat sensitive volumeJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 2 2005Bernhard Ruth Abstract Water content directly near the soil surface plays an essential role for degradation of natural organic material and agrochemicals by soil microbes. Furthermore, the water losses by evaporation depend sensitively on the top-soil water content. Rain, irrigation, evaporation, and the water flow between the soil horizons together with the natural inhomogeneity of soils cause a high spatial gradient and a pronounced time dependence of the water content in the top soil. To understand processes in top soil such as redox gradients, the knowledge on ecological conditions in the top soil, which is subject to rapid changes, is essential. In order to meet the requirements for such field measurements, a capacitance sensor with a depth resolution of 1,cm and an active area of 7.5,cm × 14,cm was constructed and operated by a special electronic circuit. Field measurements using these sensors at 1,cm depth showed the high dynamics when measurements were carried out every 10,min. As simultaneous measurements of the soil temperature at 1,cm depth exhibit large temperature variations during the day, its influence on the measurements must be compensated for. As the data, measured during drying periods, allow the assessment of the temperature coefficient, the water content at a reference temperature can be calculated. The course of the water content reflects precipitation events and quantifies the drying of the soil, providing these parameters for process evaluation. Furthermore, the diurnal variation exhibits the drying during the day and the possible rewetting from deeper horizons during the night. Freilandmessungen des Wassergehalts im Oberboden mit einem neuen Kapazitätssensor mit flachem sensitiven Volumen Der Wassergehalt direkt an der Bodenoberfläche spielt für den mikrobiellen Abbau natürlicher organischer Substanz und von Agrochemikalien eine bedeutende Rolle. Darüber hinaus hängen die Wasserverluste durch Evaporation empfindlich vom Wassergehalt an der Bodenoberfläche ab. Regen, Bewässerung, Evaporation und die Wasserbewegung zwischen den Bodenhorizonten, sowie die natürliche Inhomogenität des Bodens verursachen einen großen Gradienten und eine ausgeprägte Zeitabhängigkeit des Wassergehalts und entsprechender Stofftransformationsprozesse im Oberboden. Für das Verständnis der Prozesse im Oberboden, wie z.,B. der Redox-Gradienten, ist die Kenntnis der ökologischen Bedingungen in dem sich schnell verändernden Oberboden unerlässlich. Um die Anforderungen für solche Feldmessungen zu erfüllen, wurde ein Kapazitätssensor mit einer Tiefenauflösung von 1,cm und einer aktiven Fläche von 7.5,cm × 14,cm konstruiert und mit einem speziellen elektronischen Schaltkreis betrieben. Feldmessungen in der Tiefe von 1,cm zeigen eine große Dynamik, wenn alle 10 min ein neuer Messwert erfasst wird. Da simultane Messungen der Bodentemperatur in 1,cm Tiefe hohe Variationen zeigen, muss deren Einfluss auf die Messung kompensiert werden. Da die Messungen während der Trockenperioden die Abschätzung des Temperaturkoeffizienten erlauben, kann der Wassergehalt bei einer Referenztemperatur errechnet werden. Die Messergebnisse korrespondieren mit Regenereignissen und erfassen die Austrocknung des Bodens, so dass damit Parameter für die Prozessberechnung zur Verfügung gestellt werden. Der Tagesgang zeigt Austrocknung während des Tages und die mögliche Wiederbefeuchtung aus tieferen Horizonten während der Nacht. [source] Quantification of dead-ice melting in ice-cored moraines at the high-Arctic glacier Holmströmbreen, SvalbardBOREAS, Issue 2 2008ANDERS SCHOMACKER An extensive dead-ice area has developed at the stagnant snout of the Holmströmbreen glacier, Svalbard, following its last advance during the Little Ice Age (LIA). The most common landform is ice-cored slopes hosting sediment gravity flows. Dead-ice melting is described and quantified through field studies and analyses of high-resolution, multi-temporal aerial photographs and QuickBird 2 satellite imagery. Field measurements of backwasting of ice-cored slopes indicate melting rates of 9.2 cm/day. Downwasting rates reveal a dead-ice surface lowering of 0.9 m/yr from 1984 to 2004. The volume of melted dead-ice in the marginal zone since the LIA is estimated at 2.72 km3. Most prominently, dead-ice melting causes the growth of an ice-walled lake with an area increasing near-exponentially over the last 40 years. Despite the high-Arctic setting, dead-ice melting progresses with similar rates as in humid sub-polar climates, stressing that melt rates are governed by processes and topography rather than climate. We suggest that the permafrost and lack of glacier karst prevent meltwater percolation, thus maintaining a liquefied debris-cover where new dead-ice is continuously exposed to melting. As long as backwasting and mass movement processes prevent build-up of an insulating debris-cover, the de-icing continues despite the continuous permafrost. [source] Strain field measurements of rubber by image analysis and design criteria for laminated rubber bearings (LRB)EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 4 2004Chamindalal Sujeewa Lewangamage Abstract Although seismic isolation rubber bearings in bridges and buildings have proven to be a very effective passive method for reducing earthquake-induced forces, a detailed mechanical modeling of the rubber that is used in bearings under large strains has not been established. Therefore, a 3D model of failure behavior and the design criteria for the safety evaluation of seismic isolation bearings have not yet been developed. This paper presents: (1) correlation-based template-matching algorithms to measure large strain fields of continua; (2) a failure criterion for rubber; and (3) the design criteria for the safety evaluation of laminated algorithms, data-validation algorithms were developed and implemented to eliminate possible unrealistic displacement vectors present in the measured displacement field. The algorithms were successfully employed in the strain field measurement of LRB and rubber materials that are subjected to failure. The measured local strains for rubber material at failure were used to develop a failure criterion for rubber. The validity of the proposed criterion was evaluated by applying it to the LRB; the criterion was introduced into a 3D finite element model of LRB, compared with the experimental results of bearings failure, and verified. Finally, design criteria are proposed for LRB for the safety evaluation. Copyright © 2003 John Wiley & Sons, Ltd. [source] Predicting pasture root density from soil spectral reflectance: field measurementEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 1 2010B. H. KUSUMO This paper reports the development and evaluation of a field technique for in situ measurement of root density using a portable spectroradiometer. The technique was evaluated at two sites in permanent pasture on contrasting soils (an Allophanic and a Fluvial Recent soil) in the Manawatu region, New Zealand. Using a modified soil probe, reflectance spectra (350,2500 nm) were acquired from horizontal surfaces at three depths (15, 30 and 60 mm) of an 80-mm diameter soil core, totalling 108 samples for both soils. After scanning, 3-mm soil slices were taken at each depth for root density measurement and soil carbon (C) and nitrogen (N) analysis. The two soils exhibited a wide range of root densities from 1.53 to 37.03 mg dry root g,1 soil. The average root density in the Fluvial soil (13.21 mg g,1) was twice that in the Allophanic soil (6.88 mg g,1). Calibration models, developed using partial least squares regression (PLSR) of the first derivative spectra and reference data, were able to predict root density on unknown samples using a leave-one-out cross-validation procedure. The root density predictions were more accurate when the samples from the two soil types were separated (rather than grouped) to give sub-populations (n = 54) of spectral data with more similar attributes. A better prediction of root density was achieved in the Allophanic soil (r2 = 0.83, ratio prediction to deviation (RPD ) = 2.44, root mean square error of cross-validation (RMSECV ) = 1.96 mg g ,1) than in the Fluvial soil (r2 = 0.75, RPD = 1.98, RMSECV = 5.11 mg g ,1). It is concluded that pasture root density can be predicted from soil reflectance spectra acquired from field soil cores. Improved PLSR models for predicting field root density can be produced by selecting calibration data from field data sources with similar spectral attributes to the validation set. Root density and soil C content can be predicted independently, which could be particularly useful in studies examining potential rates of soil organic matter change. [source] Selenium effects: A weight-of-evidence approachINTEGRATED ENVIRONMENTAL ASSESSMENT AND MANAGEMENT, Issue 1 2007Blair G McDonald Abstract Selenium is increasingly an issue for a wide range of mining, industrial, and agricultural operations. Appropriate methods for evaluating the impacts of selenium in aquatic ecosystems are vigorously debated in the literature. Two common approaches include the use of tissue residue guidelines and reproductive toxicity testing using field-collected fish; however, each approach on its own does not provide sufficient evidence that wild fish populations are in fact impaired. The limitations of each method are discussed, and recommendations to improve the relevance of each line of evidence are provided. A 3rd line of evidence, field measurement of fish population dynamics, is proposed and also discussed. A framework, consistent with an ecological risk assessment methodology, for the design, application, and interpretation of selenium weight-of-evidence investigations is proposed. [source] Estimates of environmental effects and genetic parameters for body measurements and weight in Brahman cattle raised in MexicoJOURNAL OF ANIMAL BREEDING AND GENETICS, Issue 4 2002C. D. U. Magnabosco Summary A Derivative Free Restricted Maximum Likelihood (DFREML) algorithm was used with single trait and two traits animal models to estimate the variance and covariance components and thus, heritabilities and phenotypic, genetic and environmental correlations among nine different body measurements and weights of Brahman cattle raised in Mexico. The following measurements were considered: hip width, pin width, hip-pin width, anterior height, posterior height, body length, thorax perimeter, scrotal circumference and weight. The analysis was based on a total of 1018 animals, born between 1992 and 1995, from 17 herds in the Mexican States of Chiapas, San Luis Potosi, Tabasco, Tamaulipas and Veracruz. The model included the following fixed effects: herd, year-season of birth, sex, age of the animal and feed management. The only random effect was the direct additive genetic contribution of each animal. All fixed effects in the model were significant for all traits (p < 0.05). Estimated heritabilities for the traits were: hip width 0.57, pin width 0.32, hip-pin width 0.41, anterior height 0.56, posterior height 0.54, body length 0.32, thorax perimeter 0.49, scrotal circumference 0.02 and weight 0.66. The magnitude of the heritabilities was medium to high, with the exception of scrotal circumference. The genetic correlations among all body measurements were consistently positive and high, ranging from 0.64 to 1.00. Although other measures showed higher genetic correlations with weight, thorax perimeter combines a high value (0.70) with ease and repeatability, making it a useful field measurement to estimate body weight when scales are not available. Resumen Estimados de efectos ambientales y parámetros genéticos para medidas corporales y peso vivo en ganado brahman criado en méjico Fue usado un algoritmo de Máxima Verosimilitud Restricta Libre de Derivadas (DFREML) con modelos animales para una y dos características para estimar componentes de (co)varianzas, heredabilidades y correlaciones fenotípicas, genéticas y ambientales entre nueve diferentes medidas corporales y peso vivo de ganado Brahman criado en México. Fueron considerados los siguientes rasgos: ancho anterior de la grupa, ancho posterior de la grupa, largo de la grupa, altura a la cruz, altura a la grupa, largo del cuerpo, perímetro toráxico, perímetro escrotal y peso vivo. Se usaron datos de 1018 animales, nacidos entre 1992 y 1995, procedentes de 17 rebaños de los Estados mejicanos de Chiapas, San Luis Potosí, Tabasco, Tamaulipas y Veracruz. El modelo matemático incluyó los siguientes efectos fijos: rebaño, año-época de nacimiento, sexo, clase de edad del animal y manejo alimentar. Se consideró el efecto aditivo directo de cada animal como el único efecto aleatorio. Todos los efectos fijos del modelo fueron significativos para todas las características (P < 0.05). Las heredabilidades estimadas fueron: ancho anterior de la grupa 0.57, ancho posterior de la grupa 0.32, largo de la grupa 0.41, altura a la cruz 0.56, altura a la grupa 0.54, largo del cuerpo 0.32, perímetro toráxico 0.49, perímetro escrotal 0.02 y peso vivo 0.66. Las magnitudes de las heredabilidades fueron de medias a altas, con excepción del perímetro escrotal. Las correlaciones genéticas entre todas las medidas corporales fueron consistentemente positivas y altas, variando de 0.64 a 1.00. Aunque otras medidas corporales mostraron altas correlaciones genéticas con el peso vivo, el perímetro toráxico combina un alto valor de esa correlación (0.70) con facilidad de medición y alta repetibilidad, haciendo de esta una medida útil, para estimar el peso vivo, en condiciones de campo donde no se dispone de balanza. [source] Lead in soil by field-portable x-ray fluorescence spectrometry,an examination of paired In Situ and laboratory ICP-AES resultsREMEDIATION, Issue 3 2008David A. Binstock A major aspect of lead hazard control is the evaluation of soil lead hazards around housing coated with lead-based paint. The use of field-portable X-ray fluorescence (FPXRF) to do detailed surveying, with limited laboratory confirmation, can provide lead measurements in soil (especially for planning abatement activities) in a far more cost-efficient and timely manner than laboratory analysis. To date, one obstacle to the acceptance of FPXRF as an approved method of measuring lead in soil has been a lack of correspondence between field and laboratory results. In order to minimize the differences between field and laboratory results, RTI International (RTI) has developed a new protocol for field drying and sieving soil samples for field measurement by FPXRF. To evaluate this new protocol, composite samples were collected in the field following both U.S. Department of Housing and Urban Development (HUD) guidelines and ASTM International (ASTM) protocols, measured after drying by FPXRF, and returned to the laboratory for confirmatory inductively coupled plasma atomic emission spectroscopy (ICP-AES) analysis. Evaluation of study data from several diverse sites revealed no statistical difference between paired FPXRF and ICP-AES measurements using the new method. © 2008 Wiley Periodicals, Inc. [source] Mercury and halides emissions from 200 MW pulverized coal combustion boilerASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2010Hui Wu Abstract Mercury emission from coal-fired power plants is the major industrial source of mercury pollution in China. For a better understanding about the coal combustion Hg emission in China, a field measurement was conducted on a 200 MW pulverized coal fired boiler. Halides being proved to be mercury transformation participators, the U.S. EPA (Environmental Protection Agency) recommended Ontario Hydro method (OHM) and EPA Method 26A were adopted to determine the speciation of Hg and halides in postcombustion flue gases, respectively. Results indicated that, as the flue gas cooling down, the percentage of oxidized mercury in total gas phase mercury (Hg2+(g)/HgT(G)) increased from 41% to about 74% across the electrostatic precipitator (ESP) outlet. Oxidized mercury (Hg2+(g)) was more apt to be absorbed onto the fly ash. The main halides measured in flue gas were HF and HCl, while the concentrations of Cl2 and HBr were extremely low and no Br2 was detected in flue gas. Analysis indicated that acid flue gas components, such as HCl, HF, SO2 and NO, showed a certain extent of promotion on Hg oxidation. The measured mercury emission factor (EMF) in this test was 5.63 g/1012J (13.1 lb/1012Btu). Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Measurements of mean longitudinal magnetic fields in the Of?p stars HD 108 and HD 191612,ASTRONOMISCHE NACHRICHTEN, Issue 8 2010S. Hubrig Abstract Using polarimetric spectra obtained with the SOFIN spectrograph installed at the Nordic Optical Telescope, we detect a longitudinal magnetic field ,Bz, = ,168±35 G in the Of?p star HD 108. This result is in agreement with the longitudinal magnetic field measurement of the order of ,150 G recently reported by the MiMeS team. The measurement of the longitudinal magnetic field in the Of?p star HD 191612 results in ,Bz, = +450±153 G. The only previously published magnetic field measurement for this star showed a negative longitudinal magnetic field ,Bz, = ,220±38 G, indicating a change of polarity over ,100 days. Further, we report the detection of distinct Zeeman features in the narrow Ca II and Na I doublet lines for both Of?p stars, hinting at the possible presence of material around these stars. The origin of these features is not yet clear and more work is needed to investigate how magnetic fields interact with stellar wind dynamics (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Prüfung von Spannbetonbauteilen mit magnetischen MethodenBETON- UND STAHLBETONBAU, Issue 3 2010Gottfried Sawade Dr. Bauwerksüberwachung; Bewehrung; Brückenbau; Spannbeton Abstract Die Methoden der magnetischen Streufeldmessung und der magnetischen Restfeldmessung eignen sich gut zur zerstörungsfreien Detektion von Spanndrahtbrüchen in Spannbetonbauteilen. Unter Verwendung eines Jochmagneten mit integrierten Magnetfeldsensoren werden die Bauteile mit mehreren Messfahrten bei verschiedenen Magnetisierungsfeldstärken abgescannt. Die Auswertung basiert auf dem Vergleich von Messungen nach verschiedenen Vormagnetisierungen sowie der Bestimmung der Korrelation mit idealisierten Bügel- und Bruchsignalen. Die Nachweisgrenze des Verfahrens wird fallabhängig diskutiert. Die Anwendung in der Prüfpraxis wird an drei Beispielen illustriert. Inspection of Prestressed Concrete Structural Members with Magnetic Methods The methods of magnetic stray field measurement and of magnetic remanence measurment are well suited for nondestructive detection of ruptures in prestressing wires of concrete structural members. Using a yoke magnet with integrated magnetic field sensors, the members are scanned several times with varying magnetization field strength. The signal analysis is based on the comparison of measurements after different premagnetizations as well as on the determination of the correlation with idealized rebar and crack signals. The limits of detection are discussed on a case-by-case basis. The application in inspection practice is illustrated with three examples. [source] Optical remote mapping of rivers at sub-meter resolutions and watershed extentsEARTH SURFACE PROCESSES AND LANDFORMS, Issue 1 2008W. Andrew Marcus Abstract At watershed extents, our understanding of river form, process and function is largely based on locally intensive mapping of river reaches, or on spatially extensive but low density data scattered throughout a watershed (e.g. cross sections). The net effect has been to characterize streams as discontinuous systems. Recent advances in optical remote sensing of rivers indicate that it should now be possible to generate accurate and continuous maps of in-stream habitats, depths, algae, wood, stream power and other features at sub-meter resolutions across entire watersheds so long as the water is clear and the aerial view is unobstructed. Such maps would transform river science and management by providing improved data, better models and explanation, and enhanced applications. Obstacles to achieving this vision include variations in optics associated with shadows, water clarity, variable substrates and target,sun angle geometry. Logistical obstacles are primarily due to the reliance of existing ground validation procedures on time-of-flight field measurements, which are impossible to accomplish at watershed extents, particularly in large and difficult to access river basins. Philosophical issues must also be addressed that relate to the expectations around accuracy assessment, the need for and utility of physically based models to evaluate remote sensing results and the ethics of revealing information about river resources at fine spatial resolutions. Despite these obstacles and issues, catchment extent remote river mapping is now feasible, as is demonstrated by a proof-of-concept example for the Nueces River, Texas, and examples of how different image types (radar, lidar, thermal) could be merged with optical imagery. The greatest obstacle to development and implementation of more remote sensing, catchment scale ,river observatories' is the absence of broadly based funding initiatives to support collaborative research by multiple investigators in different river settings. Copyright © 2007 John Wiley & Sons, Ltd. [source] Investigating the transport dynamics and the properties of bedload material with a hydro-acoustic measuring systemEARTH SURFACE PROCESSES AND LANDFORMS, Issue 1 2008Andreas Krein Abstract This article deals with the following two questions. Are acoustic measurements in running waters appropriate for a highly resolved investigation of the bedload transport? Which characterizations of the bedload regarding mass and shape are possible via the acoustic signals? The signals were recorded by means of data recorders (Tascam Inc. DAP1 Portable Data Recorder) and hydrophones (International Transducer Corp. ITC-4001 A). The ITC-4001 is a shallow water omnidirectional transducer containing a flexural disc transducer utilizing Channelite-5400 ceramics mounted in a rugged corrosion-resistant housing. These hydrophones were screwed onto the bottom side of stainless steel plates, serving as a contact surface for the bedload in motion above them. After more than 100 series of tests in the laboratory, which indicated the basic relations between the dimension, shape and weight of the bedload and the resulting signal, field tests of the measuring system were conducted. By artificially produced flood waves in the small brooks Riverisbach, Olewiger Bach and by a winter flood wave in the River Moselle, it is possible to elaborate similar structures of the signal course of the bedload movement. The highest transport rates can be observed at the beginning of the increasing limbs and behind the peaks of the waves. At the beginning of the waves, the increasing transport power of the water and the loose material can be considered as the cause for this result. The high stream velocity behind the wave peaks explains the increase in the bedload transport so that material from the channel beds is unfastened and will be mobilized. The characterization of the bedload regarding the shape and mass is still limited regarding the field measurements and could be solved only for homogeneous grain sizes and single stones under laboratory conditions. Copyright © 2007 John Wiley & Sons, Ltd. [source] Use of terrain variables for mapping gully erosion susceptibility in LebanonEARTH SURFACE PROCESSES AND LANDFORMS, Issue 12 2007Rania Bou Kheir Abstract This paper predicts the geographic distribution and size of gullies across central Lebanon using a geographic information system (GIS) and terrain analysis. Eleven primary (elevation; upslope contributing area; aspect; slope; plan, profile and tangential curvature; flow direction; flow width; flow path length; rate of change of specific catchment area along the direction of flow) and three secondary (steady-state; quasi-dynamic topographic wetness; sediment transport capacity) topographic variables were generated and used along with digital data collected from other sources (soil, geology) to statistically explain gully erosion field measurements. Three tree-based regression models were developed using (1) all variables, (2) primary topographic variables only and (3) different pairs of variables. The best regression tree model combined the steady-state topographic wetness and sediment transport capacity indices and explained 80% of the variability in field gully measurements. This model proved to be simple, quick, realistic and practical, and it can be applied to other areas of the Mediterranean region with similar environmental conditions, thereby providing a tool to help with the implementation of plans for soil conservation and sustainable management. Copyright © 2007 John Wiley & Sons, Ltd. [source] Consequences of hyperconcentrated flow for process-based soil erosion modelling on the Chinese Loess PlateauEARTH SURFACE PROCESSES AND LANDFORMS, Issue 9 2006Rudi Hessel Abstract High sediment concentrations in runoff are a characteristic feature of the Chinese Loess Plateau, and are probably caused by factors such as the occurrence of erodible materials on steep slopes, the characteristics of the loess and the harsh climate that results in low plant cover. When sediment concentration increases, fluid density increases, viscosity increases and settling velocity decreases. These effects become increasingly important with increasing concentration and can result in flow behaviour that is quite different from that of clear water flow. Although the net effect of these changes on the flow is not always apparent, erosion models that deal with high sediment concentrations should consider such effects and could include corrections for some of these effects. A case study in a small catchment on the Loess Plateau indicated that sediment concentrations were considerable, and literature data suggested that for such sediment concentrations, corrections for settling velocity, fluid density and viscosity are needed. Furthermore, a number of corrections are necessary to be able to compare field measurements with results of soil erosion models: sediment volume should be subtracted from runoff volume and a density correction is needed to use data from a pressure transducer. For flumes that were used to measure discharge from smaller areas inside the catchment, the measured water level should be corrected by subtracting the sediment level in the flume from the water level, while the sediment volume should also be subtracted from the discharge. Finally, measured concentration should be corrected to give concentration expressed as grams per litre of clear water, since soil erosion models express sediment concentration in this way. Copyright © 2006 John Wiley & Sons, Ltd. [source] Particle clusters in gravel-bed rivers: an experimental morphological approach to bed material transport and stability conceptsEARTH SURFACE PROCESSES AND LANDFORMS, Issue 11 2005Lea Wittenberg Abstract Structured gravel river beds clearly exert a major influence on bed stability. Indexing structural stability by field measurements of bed strength neglects the processes operating to entrain and transport bed material in different parts of each structure. This study takes a morphological approach to interpreting the critical processes, using particle tracing to determine the movement of individual cluster particles over a range of flood event magnitudes and durations. The experiment was carried out on the River South Tyne, UK; it uses flow hydrographs measured nearby and also benefits from previous studies of historical development, channel morphology and sediment transport at the same site. More than 30 clusters were monitored over a seven-month period during which clusters occupied 7,16 per cent of the bed. Threshold flows delimiting three apparently contrasting bed sediment process regimes for cluster particles are tentatively set at 100 m3 s,1 and 183 m3 s,1; durations of flow at these levels are critical for cluster development, rather than flow peak values. Wake particles are transported most easily. Flow straightening in the wandering channel planform reduces the stability of clusters, since mechanical strength is markedly reduced by this change of direction. The overall area covered by clusters between significant transport events varies little, implying a dynamic equilibrium condition. Copyright © 2005 John Wiley & Sons, Ltd. [source] Ericaceous shrubs on abandoned block-cut peatlands: implications for soil water availability and Sphagnum restorationECOHYDROLOGY, Issue 4 2009Kegan K Farrick Abstract Following harvesting by manual block-cut methods and subsequent abandonment, Cacouna bog has undergone a natural vegetation succession, with ericaceous shrubs covering more than 90% of the surface. The abundance of shrubs plays a major role in the soil water flux and availability at the site, impacting Sphagnum regeneration. From June 1 to August 22, 2007, field measurements indicate that transpiration represented the largest water loss from the shrubs at 1·7 mm day,1, comprising 142 mm (42%) of rainfall, compared to 93 mm of evaporation (28%) from bare soil. The rainfall interception from the canopy (62 mm) and litter (15 mm) accounted for 23% of seasonal rainfall. Thus after transpiration and interception losses are accounted for, only 115 mm of the 334 mm of rain (34%) remained available for other processes (recharge/soil evaporation). In the field, the litter layer prevented 17 mm from being lost over the summer as it reduced evaporation by 18%. Laboratory experiments using intact soil monoliths with and without shrubs and litter indicate that at depths below 10 cm the water content from the shrub monoliths decreased 27% versus 20% in the bare peat monoliths because of root water uptake. As a management prescription, raising the water table within 20 cm of the surface would provide water to the most active root uptake zones, reducing the need for extraction from the upper 10 cm of the peat. At this level sufficient water can be supplied to the surface through capillary rise, providing adequate water for the reestablishment/survival of Sphagnum. Copyright © 2009 John Wiley & Sons, Ltd. [source] | |||||||||||||||||||||||||||||||