Local High Points Research Articles

Numerical and Experimental Study on the Process of Filling Water in Pressurized Water Pipeline

As an important working condition in water conveyance projects, the water filling process of pipelines is a complex hydraulic transition process involving water–air two-phase flow with sharp pressure changes that can easily cause pipeline damage. In light of the complex water–air two-phase flow during pipeline water filling, this study explores the water filling process of right-angle elbow pressure pipelines using CFD numerical simulations and physical model experiments, analyzing changes in water phase volume fraction, water-gas two-phase flow patterns, and hydraulic parameters in the pipeline under low flow rate conditions of 0.6 m/s and high flow rate conditions of 1.5 m/s. Results show that under low flow rate conditions, there is more local trapped gas at the top of the pipeline, causing negative pressure at local high points in the pipeline and forming a vacuum. Under high velocity conditions, water-gas two-phase flow changes more frequently in the pipeline, with a large number of bubbles collapsing at the top, resulting in large fluctuations in pipeline pressure. Finally, through physical experiments, the main flow patterns during water filling in right-angle elbows are verified and analyzed. These results have certain reference significance for formulating safe and efficient water filling velocity schemes for pressurized pipelines.

Effects of microforms on the evaporation of peat‐bryophyte‐litter column in a montane peatland in Canadian Rocky Mountain

AbstractPeatland microtopography contains hummocks (local high points) and hollows (local low points). Little is known about how the evaporation of peat (P), peat‐bryophyte (BP), peat‐litter (LP) and peat‐bryophyte‐litter (LBP) columns varies with peatland microforms. That is, whether there are fine‐scale variations in peatland evaporation, and if they are critical when being upscaled to the entire peatland ecosystem is yet to be answered. This study found that evaporation was significantly affected by cover type (P, BP, LP or LBP) and the interaction effect of the cover type and microform, based on the field evaporation experiments in a montane peatland in the Canadian Rocky Mountains, during the growing season of 2021. Mean daily evaporation of P‐Hummock and P‐Hollow is 14.16 and 11.76 g day−1, respectively; BP‐Hummock and BP‐Hollow is 9.57 and 14.38 g day−1, respectively; LBP‐Hummock and LBP‐Hollow is 9.44 and 9.91 g day−1, respectively; and evaporation of LP‐Hummock and LP‐Hollow is 5.68 and 7.64 g day−1, respectively. Peatland microform indirectly affected evaporation through interactions with cover type, modifying the vertical profile of soil temperature and changing key environmental drivers of evaporation. Moreover, the ability of two widely used models in modelling the spatial variation of peatland evaporation was also tested. It was found that Penman–Monteith (P–M) model and the bryophyte layer model in the Atmosphere‐Plant Exchange Simulator (APES) were able to yield satisfactory results based on field measurements of soil temperature and soil moisture. This study supports developing more practical evaluation tools on the hydrological state of peatland ecosystems.

How to avoid gas clogging in groundwater heat pump systems: a case study from the Lena terrasse system in Melhus, Norway

Vacuum pressures are unfavorable in water pipes since they pose a risk to degassing dissolved gases from the water and air in-leakage. If the water flow rate through the pipeline is too low, gas bubbles will rise to local high points and create stagnant gas pockets. Gas pockets may clog both directly by obstructing the flow cross-section and indirectly by disturbing chemical equilibria. Gas clogging in the Lena terrasse groundwater heat pump system (GWHP) in Melhus, Norway, has been investigated by pressure, temperature, groundwater flow rate, and pump power consumption monitoring data. The GWHP extracts groundwater through a production well, leads it to a heat exchanger at the terrain level, and then re-injects the water through an injection well. It thus operates as a siphon which is prone to vacuum pressures. Analytical tools adapted from hydraulic engineering have been used to identify vacuum pressures and insufficient pipe flow rates to remove gas pockets in the Lena terrasse GWHP. Monitoring data shows that incrustation induced pressure build-up in the injection well filter does not impact the pump production capacity. This indicates gravity driven waterfall flow from the heat exchanger to the injection well, caused by stagnant gas pockets. It is recommended to install a backpressure valve at the end of the injection pipe or multiple narrow injection pipes inside the injection well, and air release valves at the local high points, to ensure the system is kept pressurized and water-filled. The extra required pumping head will approximately equal the overpressure criterion (e.g., 0.5 bar) set at the pressure minimum in the groundwater circuit, which introduces quite modest extra pumping costs per year.

Submerged Wall Instead of a Penstock Shutoff Valve—Alternative Protection as Part of a Refurbishment

Hydropower is an important source of renewable energy. Due to ageing infrastructure, more and more existing hydropower plants have to be refurbished and modernised. This includes a complete review of the design parameters as well as the change of specific parts. Investments should be targeted to improve the overall performance of hydropower plants and ensure a long lasting life extension. This paper presents the concept of the submerged wall as a local high point in the headrace tunnel, which can—in combination with the intake gates—replace existing penstock shutoff valves. Such a replacement was conducted for the hydropower plant Schneiderau in Austria, which also allowed us to prove the concept based on measurements including a simulated break of the penstock. The presented solution can help to reduce investment costs and also minimise maintenance efforts and therefore is an attractive option for classic penstock shutoff valves for comparable projects.

Evaluation of Lithology Variations in Layered Red Beds with Depth: An Example of the Yellow River Guxian Dam, NW China

Abstract Lithology variations, which are recognized as rock type differences, significantly affect the physical properties of rock masses in red beds. In this paper, we introduce a statistical method for quantitatively evaluating the degree of lithology variations in layered red beds with depth. The core of this method is to use borehole logs as random variables for statistical analysis to calculate the percentage of a specified lithology at a given elevation, which involves seven steps of attitude calculation, reference point selection, distance calculation, elevation modification, data discretization, data statistics, and curve plotting. The Yellow River Guxian Dam is chosen as a field case study. We classify rock types of feldspar sandstone, fine sandstone, and conglomerate into hard rocks and that rock types of calcareous siltstone, argillaceous siltstone, and mudstone into soft rocks. Borehole logs recorded during the geological investigation are used to plot the percentage curve of hard rocks. We find that the degree of lithology variations for each lithology group differs greatly, the general behaviors of lithology variations on two sides of the Guxian Dam riverbed are quite similar but still with some differences, and that some thick lithology groups can be finely divided into several subgroups. On the basis of the hard rock percentage curve, we introduce a lithology variation index to quantitatively characterize the degree of lithology variations, which can be used as an important index to supplement the traditional methods when performing rock mass classifications in red beds. We also plot the trilithology percentage curve of sandstone, calcareous siltstone, and argillaceous siltstone, which serves for the determination of physical parameters of the dam foundation rock mass, the identification of the potential shear sliding surface, and the search for an impervious grouting bottom. Moreover, we find that the crest and trough, which are local high and low points in the hard rock percentage curve, can be used to show some characteristics of shear zones. The locations of shear zones are well represented in the form of troughs and that the development of shear zones has a good linear relationship with the hard rock percentage of the corresponding crest. The method proposed in this paper can be promoted and applied in similar projects or studies.

Co-culture fermentation on the production of bacterial cellulose nanocomposite produced by Komagataeibacter hansenii

Bacterial cellulose (BC11Uncommon abbreviation used: BC – Bacterial Cellulose) is a biomaterial produced by various strains of microorganisms. BC has improved strength and unique structural properties as compared to plant cellulose, thus has many usages in the food and pharmaceutical industries. In our previous study, a novel co-culture agitated fermentation of Komagataeibacter hansenii, a BC producer, with Aureobasidium pullulans, a producer of pullulan polysaccharide, had been demonstrated where the BC produced exhibited improved mechanical properties. Therefore, this study is undertaken to analyze BC production under different medium composition using response surface methodology (RSM) in shake-flasks and benchtop bioreactors. A verified local high point provided 22.4% higher BC production and 4.5- to 6- folds higher elastic moduli in shake-flasks and bioreactors compared to the baseline media. Overall, the study had revealed the potential of the co-culturing method to enhance BC production while maintaining the desired mechanical properties of BC produced in shake-flasks and larger scale bioreactors.

Optimization of modular data center air conditioning system

In high-density data center, energy consumption is increasing dramatically. For reducing the energy consumption, CFD software, Fluent 15.0, is used to simulate the flow and temperature field distribution with [Formula: see text] turbulence model and fluid–solid coupling method. Fans on the back of racks are simplified as walls with a certain pressure jump. Severs are treated as solid heat sources and porous media. Simulation results reveal that the temperature distribution on the back of racks is not uniform when air conditioners are arranged face-to-face, and local high temperature points emerge near the side wall of air conditioners. Factors affecting cooling efficiency, such as location of air conditioners, speed of inlets, distance of racks, etc., need to be improved. Geometric model is optimized by using a diagonal rack arrangement and drilling holes on the side wall. Based on this, four different cases with various hot aisle distance are proposed. Single and double modular data center are both simulated. Results of new model are better than those of baseline model.

Sedimentary characteristics of microbialites influenced by volcanic eruption: a case study from the Lower Cretaceous Shipu Group in Zhejiang Province, East China

This study describes a sequence of microbialites and volcanics of the Lower Cretaceous Shipu Group, an example of microbialites influenced by volcanic activity. It is located at Shipu town in eastern Zhejiang Province on the coast of southeastern China. Based on macroscopic outcrop observations, microscopic examination of thin sections, electron probe microanalysis (EPMA), field emission scanning electron microscopy (FESEM) imaging analysis, and energy dispersive X-ray spectrometry (EDS) analysis, nine microbialite–tuffite assemblages have been recognized in the section. Their thickness increased gradually upwards as volcanism decreased. There are ooids, bioclastic grains, intraclasts and tuffaceous grains in the grain shoal with local dolomitization. Above the grain shoal, microbial reefs develop either individually or conjoining with adjacent ones, and consist of stromatolites and serpulid tubes with common recrystallization. Tubes of serpulids are calcified and the tube wall is micrite. The tube and intertube parts are filled by sparry calcite. Colonial serpulids are surrounded by microbes to form stromatolites. Black layers of stromatolites contain many calcite crystals with fan-shaped growth pattern and preserved organic matter. Microbes are so well preserved in crystal lattices that the original microstructure of the microbes can be clearly observed by FESEM imaging analysis. Microbial reefs develop at a local high point near or above fair-weather wave-base where waves removed fine volcanic ashes. Interreef deposits are coarse tuffite due to physical differentiation. Volcanic activity could provide rich nutrition for microbes, but too much fine volcanic ash inhibits microbial growth. As a result, a moderate supply of volcanic ash favors the development of microbialites.

Microtopography is a fundamental organizing structure of vegetation and soil chemistry in black ash wetlands

Abstract. All wetland ecosystems are controlled by water table and soil saturation dynamics, so any local-scale deviation in soil elevation and thus water table position represents variability in this primary control. Wetland microtopography is the structured variability in soil elevation and is typically categorized into a binary classification of local high points (hummocks) and local low points (hollows). Although the influence of microtopography on vegetation composition and biogeochemical processes in wetlands has received attention around the globe, its role in forested wetlands is still less understood. We studied relationships among microtopography and understory vegetation communities, tree biomass, and soil chemistry in 10 black ash (Fraxinus nigra Marshall) wetlands in northern Minnesota, USA. To do so, we combined a 1 cm resolution surface elevation model generated from terrestrial laser scanning (TLS) with colocated water table, vegetation, and soil measurements. We observed that microtopography was an important structural element across sites, where hummocks were loci of greater species richness; greater midstory and canopy basal area; and higher soil concentrations of chloride, phosphorus, and base cations. In contrast, hollows were associated with higher soil nitrate and sulfate concentrations. We also found that the effect of microtopography on vegetation and soils was greater at wetter sites than at drier sites, suggesting that the distance-to-mean water table is a primary determinant of wetland biogeochemistry. These findings highlight clear controls of microtopography on vegetation and soil distributions while also supporting the notion that microtopography arises from feedbacks that concentrate biomass, soil nutrients, and productivity on microsite highs, especially in otherwise wet conditions. We therefore conclude that microtopography is a fundamental organizing structure in black ash wetlands.

Controlling factors of remaining oil distribution after water flooding and enhanced oil recovery methods for fracture-cavity carbonate reservoirs in Tahe Oilfield

Abstract Based on comprehensive analysis of core, well logging, seismic and production data, the multi-scale reservoir space, reservoir types, spatial shape and distribution of fractures and caves, and the configuration relationship with production wells in fracture-cavity carbonate reservoirs were studied systematically, the influence of them on the distribution of residual oil was analyzed, and the main controlling factors mode of residual oil distribution after water flooding was established. Enhanced oil recovery methods were studied considering the development practice of Tahe oilfield. Research shows that the main controlling factors of residual oil distribution after water flooding in fracture-cavity carbonate reservoirs can be classified into four categories: local high point, insufficient well control, flow channel shielding and weak hydrodynamic. It is a systematic project to improve oil recovery in fracture-cavity carbonate reservoirs. In the stage of natural depletion, production should be well regulated to prevent bottom water channeling. In the early stage of waterflooding, injection-production relationship should be constructed according to reservoir type, connectivity and spatial location to enhance control and producing degree of waterflooding and minimize remaining oil. In the middle and late stage, according to the main controlling factors and distribution characteristics of remaining oil after water flooding, remaining oil should be tapped precisely by making use of gravity differentiation and capillary force imbibition, enhancing well control, disturbing the flow field and so on. Meanwhile, backup technologies of reservoir stimulation, new injection media, intelligent optimization etc. should be developed, smooth shift from water injection to gas injection should be ensured to maximize oil recovery.

Quantifying wetland microtopography with terrestrial laser scanning

Wetlands hold the highest density of belowground carbon stocks on earth, provide myriad biogeochemical and habitat functions, and are at increasing risk of degradation due to climate and land use change. Microtopographic variation is a common and functionally important feature of wetlands but is challenging to quantify, constraining estimates of the processes and functions (e.g., habitat diversity, carbon storage) that it regulates. We introduce a novel method of quantifying fine-scale microtopographic structure with Terrestrial Laser Scanning using 10 black ash (Fraxinus nigra) wetlands in northern Minnesota, USA as test cases. Our method reconstructs surface models with fine detail on the order of 1 cm. Our independent validation verifies the surface models capture hummock (local high points) and hollow (local low points) features with high precision (RMSE = 3.67 cm) and low bias (1.26 cm). A sensitivity analysis of surface model resolution showed a doubling of model error between 1 cm and 50 cm resolutions, suggesting high-resolution reconstructions most precisely capture surface variation. We also compared five classification methods at resolutions ranging from 1 cm to 1 m and determined that maximum likelihood classification at 25 cm resolution most accurately (78.7%) identifies hummock and hollow features, but a simple thresholding of surface model elevation and slope was ideal for hummock feature delineation, retaining over 91% of hummock areas. Finally, we test and validate a novel microtopographic delineation method (TopoSeg) that accurately (Bias = 0.2–11.9%, RMSE = 19.6–24.1%) estimates the height, area, volume, and perimeter of individual hummock features. For the first time, we introduce an accurate and automated approach for quantifying fine-scale microtopography through high resolution surface models, feature classification, and feature delineation, enabling geospatial statistics that can explain spatial heterogeneity of habitat structure, soil processes, and carbon storage in wetland systems.

Automated summit spot height generation for modern topographic mapping

Abstract. Spot elevations published on historical U.S. Geological Survey (USGS) topographic maps were established as needed to enhance information imparted by the quadrangle’s contours. In addition to a number of other features like road intersections, section corners, lakes and water wells, labels were routinely placed on mountain peaks, local high points, passes and saddles. While some elevations were established through field survey triangulation, many were “dropped” during photogrammetric stereocompilation. The average accuracy, which varied with method, terrain, and map vintage, was on the order of ± 10 feet. Today, inexpensive consumer devices deliver comparable accuracy using the Global Positioning System (GPS). Professional equipment can achieve even better accuracies. These methods have replaced the field- and funding-intensive traditional triangulation methods in the geographic sciences. However, since GPS measurements require visiting the feature location, a national dataset containing high-accuracy spot elevations has not yet been created. Consequently, modern US Topo maps are devoid of mountain peak or other spot elevations. Additionally, no government agency is currently mandated to create one. Still, US Topo map users continue to demand the display of spot heights, particularly mountain peak elevations. As lidar data are collected through the 3D Elevation Program (3DEP), the source for higher accuracy spot heights increases. Therefore, a pilot study was conducted to evaluate the feasibility of automatically generating elevation values at summits named in the Board on Geographic Name’s Geographic Names Information System (GNIS), using 3DEP data. As the 3DEP incorporates more lidar data, these values should become increasingly more accurate. The first step in the automation process involved “snapping” GNIS summits to the highest and most accurate nearby point (pixel) in the 3DEP one-third arc second seamless dataset (1/3 a-s). Development of this step was completed in a prior study and will be reported elsewhere. In Step 2, a process similar to Step 1 was implemented to identify the highest pixel in the 3DEP one-meter dataset (1-m) from an area defined by a one-pixel buffer around the snapped point pixel. After finding the highest pixel in the 1-m dataset, the same process for Step 2 was repeated on the lidar point cloud dataset (LPC). In the latter case, the highest lidar point within the buffered area was chosen where there were more than one, which was the case in most instances. In the case that the next higher resolution data were unavailable, the summit spot elevation was set to the value obtained from the lower resolution layer. Hence, if 1-m data were unavailable, but LPC data did exist, the program in its current state was unable use the higher resolution data. This is due to the fact that the 1-m data are employed to drive the software to a more precise location of the summit. Without that intermediate step the method fails to identify the correct LPC point. Work in progress is aimed at overcoming this disadvantage, which is particularly important until the time when the 1-m dataset is populated for the entire nation. The National Geospatial Program estimates the completion of lidar acquisition by 2023. Processing from acquisition to update of the 1-m dataset, including quality assessment and revisions, currently requires between two and three years. Resulting elevation values are compared to those published by Peakbagger.com and TOPOZONE.com. Preliminary results from 40 summits indicate that values derived from lidar are generally higher, whereas those populated from the 1/3 arc-second are generally lower. A thorough understanding of these relationships will require the evaluation of more points.

Catalytic Removal of NOx by Cerium-modified Zirconium Composite Oxide

Diesel engines have been widely used due to their high thermal efficiency, good environmental adaptability, wide power adjustment range, convenient maintenance and long service life. However, the application of diesel engines is also facing a serious problem; that is, the emission of nitrogen oxides and particulate matter is serious. For marine diesel engine emission requirements, MARPOL Convention Annex VI imposes strict restrictions on the emission of atmospheric pollutants. The limit emission of nitrogen oxides in the Tier III emission standards mandated by IMO is 3.4 g/kWh. Therefore, in order to meet the requirements of international conventions and countries and regions, it is necessary to control the emissions of diesel engines. The NOx in the exhaust gas is mostly a thermal type of nitrogen oxide which is produced under high temperature and high pressure conditions formed during compression and combustion strokes. The diesel engine relies on the compression energy of the mixture to ignite, and the good injection atomization effect is not achieved. The distribution of the detonation point is not uniform, and local high temperature points are generated in some areas, which increases the NOx formation. The main means of reducing NOx emissions are organic internal control and post-treatment. However, the use of internal control technology to reduce the internal temperature of the machine will deteriorate the fuel combustion conditions, so that the fuel cannot be completely burned, and the emissions of incomplete combustion products such as PM and CO increase. It is difficult to achieve NOx reduction by simply relying on the internal control technology, so it is necessary to use post-processing technology. The combined use of different emission reduction technologies is also a hot topic in emissions control research. The post-treatment methods for NOx emission reduction include direct catalytic decomposition, selective non-catalytic reduction, selective catalytic reduction, lean-burn adsorption catalytic reduction, and low-temperature plasma assisted technology. The current research and application schemes in the industry are SCR selectivity. Catalytic reduction and LNT lean combustion adsorption reduction. In this paper, the partial replacement of Ce by La is carried out to modify the Ce/Zr composite oxide. The mass fraction of La2O3 in the prepared La/Ce/Zr composite oxide was 5%, and the physicochemical properties of La/Ce/Zr composite oxide powder were analyzed by ICP, OSC, SEM and TPR techniques. The experiment found that: 1) La can refine the grain and inhibit the grain growth, so that the powder obtains a higher specific surface area and a smaller particle size distribution. 2) The addition of La reduces the sintering of cerium-zirconium and improves the heat aging resistance of the catalyst under the inhibition of high temperature. 3) After doping La, it enhances the migration of surface lattice oxygen and enhances the oxygen storage capacity; the addition of La enhances the NO adsorption capacity of cerium-zirconium and improves the catalytic activity of the catalyst. The light-off temperature and the highest activity temperature of PM decrease, and the reduction rate of No is 19.2%.

Influence of velocity head on filling transients in a branched pipeline

PurposeThe velocity head is usually neglected in the energy equation for a pipeline junction when one-dimensional (1D) hydraulic transient flow is solved by method of characteristics. The purpose of this paper is to investigate the effect of velocity head on filling transients in a branched pipeline by an energy equation considering velocity head.Design/methodology/approachAn interface tracking method is used to locate the air–water interface during pipeline filling. The pressured pipe flow is solved by a method of characteristics. A discrete gas cavity model is included to permit the occurrence of column separation. A universal energy equation is built by considering the velocity head. The numerical method is provisionally verified in a series pipeline and the numerical results and experimental data accord well with each other.FindingsThe numerical results show that some differences in filling velocity and piezometric head occur in the branched pipeline. These differences arise because the velocity head in the energy equation can become an important contributor to the hydraulic response of the system. It is also confirmed that a local high point in the profile is apt to experience column separation during rapid filling. Significantly, the magnitude of overpressure and cavity volume induced by filling transients at the local high point is predicted to increase with the velocity in the pipes.Originality/valueThe velocity head in the energy equation for a pipeline junction could play an important role in the prediction of filling velocity, piezometric head and column separation phenomenon, which should be given more attention in 1D hydraulic transient analysis.

Assessment of the potential of a range of microhabitats for use as seed production areas in moderately degraded rangelands in semiarid Australia

Previous studies in mulga country with hard-setting red earth soils in north-west New South Wales, Australia, have demonstrated that small fenced seed production areas on local high points can contribute to regeneration of native perennial vegetation, and increases in the soil seedbank, on surrounding slopes. In this study the potential of seven microhabitats in this environment, each replicated twice, for use as seed production areas was assessed indirectly by a study of their functional characteristics and vegetation dynamics. Indices of landscape function (stability, infiltration and nutrient cycling) were determined for each of the 14 sites at the time of fencing and at the end of the study, over 2 years later, by determining the extent and surface characteristics of 53 surface types (in total) along three parallel transects within each site. Variation in establishment and survival of ground storey species among surface types was examined by co-ordination of all plants within belts centred on the line transects. At the start of the study landscape function indices for the ‘rocky ridge with rock outcrop’ microhabitat were not significantly higher than all, or some, other microhabitats. By the end of the study two of the three indices for this microhabitat were significantly higher than for all other microhabitats. This microhabitat also favoured the establishment and survival of the pastorally preferred species Monachather paradoxus Steud and Thyridolepis mitchelliana (Nees) S.T. Blake but did not favour establishment and survival of the pastorally unpreferred species Aristida jerichoensis (Domin) Henrad and Austrostipa variabilis (Hughes) S.W.L. Jacobs and J. Everett. This microhabitat was characterised by extensive areas of ‘water catchment’ surface types associated with in-situ rock outcrop, which facilitated the observed vegetation dynamics. This ‘rocky ridge with rock outcrop’ microhabitat occurs on local high points in the landscape and is readily recognised. It is therefore ideally suited for use as fenced seed production areas to assist rangeland regeneration.

Relationship between saddle pressure measurements and clinical signs of saddle soreness at the withers

Similar to human decubitus ulcers, local high pressure points from ill-fitting saddles induce perfusion disturbances of different degrees resulting in tissue hypoxia and alteration in sweat production. To relate the different clinical manifestations of saddle sores to the magnitude of saddle pressures at the location of the withers. Sixteen horses with dry spots after exercise (Group A) and 7 cases presented with acute clinical signs of saddle pressure in the withers area (Group B) were compared with a control group of 16 sound horses with well fitting saddles (Group C). All horses underwent a saddle pressure measurement at walk, trot and canter. Mean and maximal pressures in the area of interest were compared between groups within each gait. Mean pressures differed significantly between groups in all 3 gaits. Maximal pressure differed between groups at trot; at walk and canter, however, the only significant difference was between Group C and Groups A and B, respectively, (P > 0.05). Mean and maximal pressures at walk in Group A were 15.3 and 30.6 kPa, in Group B 24.0 and 38.9 kPa and in Group C 7.8 and 13.4 kPa, respectively; at trot in Group A 18.1 and 43.4 kPa, in Group B 29.7 and 53.3 kPa and in Group C 9.8 and 21.0 kPa, respectively; and at canter in Group A 21.4 and 48.9 kPa, in Group B 28.6 and 56.0 kPa and in Group C 10.9 and 24.7 kPa, respectively. The study shows that there is a distinguishable difference between the 3 groups regarding the mean pressure value, in all gaits.

A comparison of Greenland ice-sheet volume changes derived from altimetry measurements

AbstractWe compare rates of surface-elevation change on the Greenland ice sheet derived from European Remote-sensing Satellite-2 (ERS-2) radar-altimeter data with those obtained from laser-altimeter data collected over nearly the same time periods. Radar-altimeter data show more rapid thickening (9 ± 1 cm a−1 above 1500 m elevation in the north, and 3 ± 1 cm a−1 above 2000 m in the south) than the laser estimates, possibly caused by a lifting of the radar-reflection horizon associated with changes in the snowpack, such as those caused by progressively increased surface melting, as summer temperatures rise. Over all the ice sheet above 2000 m, this results in an ERS-derived volume balance ∼75 ± 15 km3 a−1 more positive than that from laser data. This bias between laser and radar estimates of elevation change varies spatially and temporally, so cannot at present be corrected without independent surveys such as those presented here. At lower elevations, comparison of detailed repeat laser surveys over Jakobshavn Isbræ with ERS results over the same time interval shows substantial ERS underestimation of ice-thinning rates. This results partly from missing data because of ‘bad’ radar waveforms over the very rough surface topography, and partly from the tendency for large radar footprints to sample preferentially local high points in the topography, thus missing regions of most rapid thinning along glacier depressions.

Habitat use and movement patterns in the graceful crag lizard, Pseudocordylus capensis

We characterized the habitat use and movement patterns of adult male, adult female and juvenile Pseudocordylus capensis, a diurnal, rock-dwelling, insectivorous lizard. Rock use was vertically stratified: males spent most of their time at local high points, females at mid-level on the rocks, and juveniles were typically in the lower regions. Movement patterns varied with demographic class as well: juveniles moved more frequently and spent a greater proportion of their time in motion than did adults, and the number of moves of different durations varied among the classes. Finally, juveniles scanned their surroundings and appeared to feed more frequently than adults.

Habitat use and movement patterns in the graceful crag lizard, Pseudocordylus capensis

We characterized the habitat use and movement patterns of adult male, adult female and juvenile Pseudocordylus capensis, a diurnal, rock-dwelling, insectivorous lizard. Rock use was vertically stratified: males spent most of their time at local high points, females at mid-level on the rocks, and juveniles were typically in the lower regions. Movement patterns varied with demographic class as well: juveniles moved more frequently and spent a greater proportion of their time in motion than did adults, and the number of moves of different durations varied among the classes. Finally, juveniles scanned their surroundings and appeared to feed more frequently than adults.

Hillslope nutrient flux during near-stream vegetation removal

At the Coweeta Hydrologie Laboratory in the southern Appalachians of western North Carolina, a near-stream vegetation manipulation experiment is being conducted to determine the effect of removal of streamside Rhododendron maximum L. on the export of hillslope nutrients (K, Na, Ca, Mg, N, P, S) and organic matter. Experimental hillslope transects that span topographical flowpaths from a local highpoint to the stream have been instrumented with lysimeters and TDR rods at two depths, as well as with streambed and streambank piezometers. We present a review of studies of nutrient flux in the riparian zone of forested watersheds. In the southern Appalachians, we hypothesize that R. maximum is a keystone species at the interface between terrestrial and aquatic systems, with extensive near-stream thickets having a possible impact on carbon and nutrient transport into streams. We present the conceptual basis and initial implementation of a model-based experimental design to test the effect of R. maximum removal on hillslope nutrient and organic matter export in upland watersheds. The model is terrain-based and will be used to extrapolate elemental flux measurements both spatially from the hillslope to watershed scale and temporally for various climate regimes. The model consists of three modules: (1) objective terrain analysis (TAPES-C); (2) a dynamic interception canopy module; (3) a hillslope hydrology module (IHDM4) with a 2-D Richard's equation of subsurface moisture dynamics. Calibration and validation of the model will occur at two scales: at the hillslope scale, using well, lysimeter, and TDR data; at the watershed scale, using streamflow measurements across a variety of storm types. We show watershed terrain analysis for the experimental watershed (WS56) and discuss use of the model for understanding effects of watershed management of riparian zone processes.