Land Surface (land + surface)

Distribution by Scientific Domains
Distribution within Earth and Environmental Science

Kinds of Land Surface

  • earth land surface

  • Selected Abstracts

    The micro-topography of the wetlands of the Okavango Delta, Botswana

    T. Gumbricht
    Abstract The surface of the 40 000 km2 Okavango alluvial fan is remarkably smooth, and almost everywhere lies within two to three metres of a perfectly smooth theoretical surface. Deviations from this perfect surface give rise to islands in the Okavango wetlands. This micro-topography was mapped by assigning empirical elevations to remotely sensed vegetation community classes, based on the observation that vegetation is very sensitive to small, local differences in elevation. Even though empirical, the method produces fairly accurate results. The technique allows estimation of depths of inundation and therefore will be applicable even when high resolution radar altimetry becomes available. The micro-topography has arisen as a result of clastic sedimentation in distributary channels, which produces local relief of less than two metres, and more importantly as a result of chemical precipitation in island soils, which produces similar local relief. The micro-topography is, therefore, an expression of the non-random sedimentation taking place on the fan. Volume calculations of islands extracted from the micro-topography, combined with estimates of current sediment in,ux, suggest that the land surface of the wetland may only be a few tens of thousands of years old. Constant switching of water distribution, driven by local aggradation, has distributed sediment widely. Mass balance calculations suggest that over a period of c. 150 000 years all of the fan would at one time or other have been inundated, and thus subject to sedimentation. Coalescing of islands over time results in net aggradation of the fan surface. The amount of vertical aggradation on islands and in channels is restricted by the water depth. Restricted vertical relief, in turn, maximizes the distribution of water, limiting its average depth. Aggradation in the permanent swamps occurs predominantly by clastic sedimentation. Rates of aggradation here are very similar to those in the seasonal swamps, maintaining the overall gradient, possibly because of the operation of a feedback loop between the two. The limited amount of local aggradation arising from both clastic and chemical sedimentation, combined with constant changes in water distribution, has resulted in a near-perfect conical surface over the fan. In addition to providing information on sedimentary processes, the micro-topography has several useful hydrological applications. Copyright 2004 John Wiley & Sons, Ltd. [source]

    Analysing soil variation in two dimensions with the discrete wavelet transform

    R. M. Lark
    Summary Complex spatial variation in soil can be analysed by wavelets into contributions at several scales or resolutions. The first applications were to data recorded at regular intervals in one dimension, i.e. on transects. The theory extends readily to two dimensions, but the application to small sets of gridded data such as one is likely to have from a soil survey requires special adaptation. This paper describes the extension of wavelet theory to two dimensions. The adaptation of the wavelet filters near the limits of a region that was successful in one dimension proved unsuitable in two dimensions. We therefore had to pad the data out symmetrically beyond the limits to minimize edge effects. With the above modifications and Daubechies's wavelet with two vanishing moments the analysis is applied to soil thickness, slope gradient, and direct solar beam radiation at the land surface recorded at 100-m intervals on a 60 101 square grid in south-west England. The analysis revealed contributions to the variance at several scales and for different directions and correlations between the variables that were not evident in maps of the original data. In particular, it showed how the thickness of the soil increasingly matches the geological structure with increasing dilation of the wavelet, this relationship being local to the strongly aligned outcrops. The analysis reveals a similar pattern in slope gradient, and a negative correlation with soil thickness, most clearly evident at the coarser scales. The solar beam radiation integrates slope gradient and azimuth, and the analysis emphasizes the relations with topography at the various spatial scales and reveals additional effects of aspect on soil thickness. [source]

    Origin of post-Minoan caves and volcaniclastic cave fill, Thera (Santorini), Greece

    Joan M. Ramage
    The Aegean island of Thera (Santorini) was covered by tephra from its cataclysmic Late Bronze Age (ca. 3600 yr B.P.) eruption. Vertical exposures of the eruptive sequence show secondary, nonvolcanic, circular (in cross section) features composed of stratified sediment. Many are inaccessible from the floors of modern quarries and appear to be caves filled with younger sediment, but show no connection to the land surface. A filled cave was found in the wall of a modern gully outside the modern quarries, and a filled cave was found in a terrace scarp, well above the modern gully. Natural (and probably rapid) incision by gullies into the thick tephra deposit left many locations with lateral access to tephra. Inhabitants from post-Minoan to recent times excavated tephra for materials and buildings, and caves were subsequently filled by sporadic (possibly seasonal) flood events that deposited sediment. These gullies may have provided access for modern tephra removal that isolated the filled caves high on the modern quarry walls. 2003 Wiley Periodicals, Inc. [source]

    Fluid injection and surface deformation at the KTB location: modelling of expected tilt effects

    GEOFLUIDS (ELECTRONIC), Issue 1 2005
    T. JAHR
    Abstract This investigation is indented to explore the relationship between changes in pore fluid pressure and deformation of the land surface induced by a large-scale injection experiment at the KTB site. Deformation will be monitored by ASKANIA borehole tiltmeters at five locations. During the year 2003, a network of borehole tiltmeters was installed, data transmission links established and tested, and recording of tilt data started. Our first main interest was to receive data sets of all stations well before the injection experiment to start in May 2004, to be able to evaluate local site effects. Thus, the separation of injection-induced effects will be more reliable. Principal 3D numerical modelling (poro-elastic modelling and investigations, using the finite element method, FEM) of poro-elastic behaviour showed that significant tilt amplitudes can be expected during controlled fluid injection. Observed deformation will be investigated within the framework of the fluid flow behaviour and resulting deformation. Two models have been used: a coupled hydro geomechanical finite element model (abaqus) and, as a first step, also a multi-layered poro-elastic crust (poel). With the numerical model two effects can be quantified: (i) the deformation of the upper crust (tilt measurements) and (ii) the spatial distribution and the changes of material properties in the KTB area. The main aim of the project is to improve the knowledge of coupled geomechanic,hydraulic processes and to quantify important parameters. Thus, the understanding of fracture-dominated changes of the hydrogeological parameters will be enhanced, geomechanical parameter changes and the heterogeneity of the parameter field quantified. In addition, the induced stress field variation can be explained, which is believed to be mainly responsible for the increase of local seismic activity. Here, we introduce the tiltmeter array at the KTB site, the modelling for a poro-elastic crust and the preliminary FEM modelling. [source]

    Landscape and Coast Development of A Lowland Fjord Margin Following Deglaciation, East Greenland

    Louise Hansen
    The landscapes of western Jameson Land bordering Hall Bredning fjord comprise upper river basins, glacial landscapes, lower river basins and a near-shore zone. The upper river basins are incised into bedrock and display no cover of young sediments whilst the glacial landscapes, located closer to the coast, are dominated by Pleistocene deposits and an irregular topography with hills and ridges. The lower river basins, dissecting the glacial landscapes, are connected to the upper river basins and contain well-defined Holocene delta terraces. The near-shore zone, which includes the present coast, displays a few raised shorelines. Geomorphological observations combined with stratigraphic work and 14C dates provide a chronological framework for the development of landscape and shoreline, as presented by a four-stage reconstruction. The first stage covers the deglaciation of western Jameson Land at the Weichselian-Holocene transition after a collapse of the main fjord glacier in Hall Bredning. The sea inundated the low-lying areas on Jameson Land forming small side-entry fjord basins that possibly follow the track of older valleys. This was followed by a second stage, the paraglacial period, when large meltwater production and sediment transport resulted in a fast infilling of the side-entry fjord basins by deltas. These are now exposed in terraces in the lower river basins at 70,80 m a.s.l. During a third stage, the relaxation period, fluvial activity decreased and the land surface was increasingly occupied by a cover of tundra vegetation. A glacio-isostatic rebound resulted in a relative sea level fall and fluvial incision. During stages two and three the coast was exposed to shallow marine processes that aided the alignment of the coast. Stages one to three presumably lasted for less than 2000 years. During stage four, the stable period, lasting for several thousand years till the present, there were minor adjustments of shoreline and landscape. The four-step reconstruction describes the sedimentary response of a lowland fjord margin to dramatic changes in climate and sea level. The distribution of erosion and sedimentation during this development was mainly controlled by topography. The reconstruction of the latest environmental development of Jameson Land puts new light on Jameson Land's long and complex Quaternary stratigraphic record. The reconstruction may also be used as a model for the interpretation of deposits in similar areas elsewhere. [source]

    Dealing with Landscape Heterogeneity in Watershed Hydrology: A Review of Recent Progress toward New Hydrological Theory

    Peter A. Troch
    Predictions of hydrologic system response to natural and anthropogenic forcing are highly uncertain due to the heterogeneity of the land surface and subsurface. Landscape heterogeneity results in spatiotemporal variability of hydrological states and fluxes, scale-dependent flow and transport properties, and incomplete process understanding. Recent community activities, such as Prediction in Ungauged Basins of International Association of Hydrological Sciences, have recognized the impasse current catchment hydrology is facing and have called for a focused research agenda toward new hydrological theory at the watershed scale. This new hydrological theory should recognize the dominant control of landscape heterogeneity on hydrological processes, should explore novel ways to account for its effect at the watershed scale, and should build on an interdisciplinary understanding of how feedback mechanisms between hydrology, biogeochemistry, pedology, geomorphology, and ecology affect catchment evolution and functioning. [source]

    Connecting Atmosphere and Wetland: Energy and Water Vapour Exchange

    Peter M. Lafleur
    Wetlands are ubiquitous over the globe, comprise a vast array of ecosystem types and are of great ecological and social importance. Their functioning is intimately tied to the atmosphere by the energy and mass exchanges that take place across the wetland,atmosphere boundary. This article examines recent research into these exchanges, with an emphasis on the water vapour exchange. Although broad classes of wetland type, such as fen, bog and marsh, can be defined using ecological or hydrologic metrics, distinct difference in energy exchanges between the classes cannot be found. This arises because there are many factors that control the energy exchanges and interplay of these factors is unique to every wetland ecosystem. Wetlands are more similar in their radiation balances than in the partitioning of this energy into conductive and turbulent heat fluxes. This is especially true of evapotranspiration (ET) rates, which vary considerably among and within wetland classes. A global survey of wetland ET studies shows that location has little to do with ET rates and that variation in rates is largely determined by local climate and wetland characteristics. Recent modelling studies suggest that although wetlands occupy a small portion of the global land surface, their water and energy exchanges may be important in regional and global climates. Although the number of studies of wetland,atmosphere interactions has increased in recent years more research is needed. Five key areas of study are identified: (i) the importance of moss covers, (ii) lack of study in tropical systems, (iii) inclusion of wetlands in global climate models, (iv) importance of microforms in wetlands and their scaling to the whole ecosystem, and (v) the paucity of annual ET measurements. [source]

    Severe Deep Moist Convective Storms: Forecasting and Mitigation

    David L. Arnold
    Small-scale (2,20 km) circulations, termed ,severe deep moist convective storms', account for a disproportionate share of the world's insured weather-related losses. Spatial frequency maximums of severe convective events occur in South Africa, India, Mexico, the Caucasus, and Great Plains/Prairies region of North America, where the maximum tornado frequency occurs east of the Rocky Mountains. Interest in forecasting severe deep moist convective systems, especially those that produce tornadoes, dates to 1884 when tornado alerts were first provided in the central United States. Modern thunderstorm and tornado forecasting relies on technology and theory, but in the post-World War II era interest in forecasting has also been driven by public pressure. The forecasting process begins with a diagnostic analysis, in which the forecaster considers the potential of the atmospheric environment to produce severe convective storms (which requires knowledge of the evolving kinematic and thermodynamic fields, and the character of the land surface over which the storms will pass), and the likely character of the storms that may develop. Improvements in forecasting will likely depend on technological advancements, such as the development of phased-array radar systems and finer resolution numerical weather prediction models. Once initiated, the evolution of deep convective storms is monitored by satellite and radar. Mitigation of the hazards posed by severe deep moist convective storms is a three-step process, involving preparedness, response, and recovery. Preparedness implies that risks have been identified and organizations and individuals are familiar with a response plan. Response necessitates that potential events are identified before they occur and the developing threat is communicated to the public. Recovery is a function of the awareness of local, regional, and even national governments to the character and magnitude of potential events in specific locations, and whether or not long-term operational plans are in place at the time of disasters. [source]

    Palaeoenvironmental context of the Late-glacial woolly mammoth (Mammuthus primigenius) discoveries at Condover, Shropshire, UK

    GEOLOGICAL JOURNAL, Issue 4 2009
    J. R. M. Allen
    Abstract In 1986/1987 the remains of several mammoths, Mammuthus primigenius (Blumenbach), were discovered on the spoil heap of an actively working gravel pit at Condover, Shropshire, England. The discovery of the remains posed two questions that could be addressed by analyses of biological proxies. First, as none of the bones was found in situ it was necessary to confirm the stratum in which the remains occurred. Second, what was the environment in which these animals lived and died? A range of biological indicators was used to address these questions, including pollen, spore and algal, plant macrofossil, invertebrate, anuran and biological mineral analyses. Multivariate statistical analyses of palynological and Pediastrum data, along with evidence from the Coleopteran assemblages, support the attribution of the mammoth bones to a unit of dark grey clayey sandy silt, although they may have lived at the time of the overlying green detritus mud. The palaeobiological data supports the correlation of these sediments to the Devensian Late-glacial. The mammoths entered this basin at the start of the Late-glacial Interstadial (Greenland Interstadial 1e) (ca. 14,830,3930 cal. year BP; 12,300,,110 14C year BP) and became mired in soft cohesive sediments. Palaeotemperature reconstructions, based on the Coleopteran assemblages, from the time when the mammoths actually became mired, show that the climate was temperate with mean July temperatures between 15 and 19C and mean January temperatures between ,13 and +6C. Biological indicators from the sediments encasing the mammoths indicate that the landscape surrounding the basin was treeless and dry, contrasting with rich vegetation within the basin itself that had possibly attracted the mammoths to the site. Evidence of sedimentary disturbance suggests that the mammoths caused large-scale bioturbation of the deposits making palaeoenvironmental interpretations difficult. Fossils of terrestrial blowflies, carcass and dung beetles show that some of the decaying corpses must have lain exposed on the land surface for sufficient time for the soft parts to have rotted away and skin and bones to have become desiccated before many of them sank into the dark grey clayey sandy silt. Copyright 2009 John Wiley & Sons, Ltd. [source]

    Decline in a dominant invertebrate species contributes to altered carbon cycling in a low-diversity soil ecosystem

    Abstract Low-diversity ecosystems cover large portions of the Earth's land surface, yet studies of climate change on ecosystem functioning typically focus on temperate ecosystems, where diversity is high and the effects of individual species on ecosystem functioning are difficult to determine. We show that a climate-induced decline of an invertebrate species in a low-diversity ecosystem could contribute to significant changes in carbon (C) cycling. Recent climate variability in the McMurdo Dry Valleys of Antarctica is associated with changes in hydrology, biological productivity, and community composition of terrestrial and aquatic ecosystems. One of the greatest changes documented in the dry valleys is a 65% decrease in the abundance of the dominant soil invertebrate (Scottnema lindsayae, Nematoda) between 1993 and 2005, illustrating sensitivity of biota in this ecosystem to small changes in temperature. Globally, such declines are expected to have significant influences over ecosystem processes such as C cycling. To determine the implications of this climate-induced decline in nematode abundance on soil C cycling we followed the fate of a 13C tracer added to soils in Taylor Valley, Antarctica. Carbon assimilation by the dry valley nematode community contributed significantly to soil C cycling (2,7% of the heterotrophic C flux). Thus, the influence of a climate-induced decline in abundance of a dominant species may have a significant effect on ecosystem functioning in a low-diversity ecosystem. [source]

    Large annual net ecosystem CO2 uptake of a Mojave Desert ecosystem

    Abstract The net ecosystem CO2 exchange (NEE) between a Mojave Desert ecosystem and the atmosphere was measured over the course of 2 years at the Mojave Global Change Facility (MGCF, Nevada, USA) using the eddy covariance method. The investigated desert ecosystem was a sink for CO2, taking up 10267 and 11070 g C m,2 during 2005 and 2006, respectively. A comprehensive uncertainty analysis showed that most of the uncertainty of the inferred sink strength was due to the need to account for the effects of air density fluctuations on CO2 densities measured with an open-path infrared gas analyser. In order to keep this uncertainty within acceptable bounds, highest standards with regard to maintenance of instrumentation and flux measurement postprocessing have to be met. Most of the variability in half-hourly NEE was explained by the amount of incident photosynthetically active radiation (PAR). On a seasonal scale, PAR and soil water content were the most important determinants of NEE. Precipitation events resulted in an initial pulse of CO2 to the atmosphere, temporarily reducing NEE or even causing it to switch sign. During summer, when soil moisture was low, a lag of 3,4 days was observed before the correlation between NEE and precipitation switched from positive to negative, as opposed to conditions of high soil water availability in spring, when this transition occurred within the same day the rain took place. Our results indicate that desert ecosystem CO2 exchange may be playing a much larger role in global carbon cycling and in modulating atmospheric CO2 levels than previously assumed , especially since arid and semiarid biomes make up >30% of Earth's land surface. [source]

    Pristine New Zealand forest soil is a strong methane sink

    Sally J. Price
    Abstract Methanotrophic bacteria oxidize methane (CH4) in forest soils that cover ,30% of Earth's land surface. The first measurements for a pristine Southern Hemisphere forest are reported here. Soil CH4 oxidation rate averaged 10.50.6 kg CH4 ha,1 yr,1, with the greatest rates in dry warm soil (up to 17 kg CH4 ha,1 yr,1). Methanotrophic activity was concentrated beneath the organic horizon at 50,100 mm depth. Water content was the principal regulator of (r2=0.88) from the most common value of field capacity to less than half of this when the soil was driest. Multiple linear regression analysis showed that soil temperature was not very influential. However, inverse co-variability confounded the separation of soil water and temperature effects in situ. Fick's law explained the role of water content in regulating gas diffusion and substrate supply to the methanotrophs and the importance of pore size distribution and tortuosity. This analysis also showed that the chambers used in the study did not affect the oxidation rate measurements. The soil was always a net sink for atmospheric CH4 and no net CH4 (or nitrous oxide, N2O) emissions were measured over the 17-month long study. For New Zealand, national-scale extrapolation of our data suggested the potential to offset 13% of CH4 emissions from ca. 90 M ruminant animals. Our average was about 6.5 times higher than rates reported for most Northern Hemisphere forest soils. This very high was attributed to the lack of anthropogenic disturbance for at least 3000,5000 years and the low rate of atmospheric nitrogen deposition. Our truly baseline data could represent a valid preagricultural, preindustrial estimate of the soil sink for temperate latitudes. [source]

    Importance of Unsaturated Zone Flow for Simulating Recharge in a Humid Climate

    GROUND WATER, Issue 4 2008
    Randall J. Hunt
    Transient recharge to the water table is often not well understood or quantified. Two approaches for simulating transient recharge in a ground water flow model were investigated using the Trout Lake watershed in north-central Wisconsin: (1) a traditional approach of adding recharge directly to the water table and (2) routing the same volume of water through an unsaturated zone column to the water table. Areas with thin (less than 1 m) unsaturated zones showed little difference in timing of recharge between the two approaches; when water was routed through the unsaturated zone, however, less recharge was delivered to the water table and more discharge occurred to the surface because recharge direction and magnitude changed when the water table rose to the land surface. Areas with a thick (15 to 26 m) unsaturated zone were characterized by multimonth lags between infiltration and recharge, and, in some cases, wetting fronts from precipitation events during the fall overtook and mixed with infiltration from the previous spring snowmelt. Thus, in thicker unsaturated zones, the volume of water infiltrated was properly simulated using the traditional approach, but the timing was different from simulations that included unsaturated zone flow. Routing of rejected recharge and ground water discharge at land surface to surface water features also provided a better simulation of the observed flow regime in a stream at the basin outlet. These results demonstrate that consideration of flow through the unsaturated zone may be important when simulating transient ground water flow in humid climates with shallow water tables. [source]

    Artificial Recharge Through a Thick, Heterogeneous Unsaturated Zone

    GROUND WATER, Issue 3 2008
    John A. Izbicki
    Thick, heterogeneous unsaturated zones away from large streams in desert areas have not previously been considered suitable for artificial recharge from ponds. To test the potential for recharge in these settings, 1.3 106 m3 of water was infiltrated through a 0.36-ha pond along Oro Grande Wash near Victorville, California, between October 2002 and January 2006. The pond overlies a regional pumping depression 117 m below land surface and is located where thickness and permeability of unsaturated deposits allowed infiltration and saturated alluvial deposits were sufficiently permeable to allow recovery of water. Because large changes in water levels caused by nearby pumping would obscure arrival of water at the water table, downward movement of water was measured using sensors in the unsaturated zone. The downward rate of water movement was initially as high as 6 m/d and decreased with depth to 0.07 m/d; the initial time to reach the water table was 3 years. After the unsaturated zone was wetted, water reached the water table in 1 year. Soluble salts and nitrate moved readily with the infiltrated water, whereas arsenic and chromium were less mobile. Numerical simulations done using the computer program TOUGH2 duplicated the downward rate of water movement, accumulation of water on perched zones, and its arrival at the water table. Assuming 10 106 m3 of recharge annually for 20 years, a regional ground water flow model predicted water level rises of 30 m beneath the ponds, and rises exceeding 3 m in most wells serving the nearby urban area. [source]

    Application of Superposition with Nonlinear Head-Dependent Fluxes

    GROUND WATER, Issue 2 2008
    Timothy Durbin
    While superposition is commonly used to address linear ground water problems, it can also be used to address certain nonlinear problems. In particular, it can be used to address problems with nonlinear head-dependent fluxes, where the problem can be separated conveniently into steady-state and transient-state components. Superposition can be used to simulate the transient-state head changes independently from the steady-state heads. The problems addressable by superposition include phreatophyte discharges, stream-aquifer interactions, spring discharges, and drain discharges. Each of these represents a nonlinear head-dependent flux, where the flux depends on the elevation of the land surface or some other feature. Superposition is applied by referencing elevations to the local steady-state water table and by imposing the negative of the steady-state flux on the transient-state problem. [source]

    A Modular Injection System, Multilevel Sampler, and Manifold for Tracer Tests

    GROUND WATER, Issue 6 2003
    Brian J. Mailloux
    Ground water injection and sampling systems were developed for bacterial transport experiments in both homogenous and heterogeneous unconsolidated, surficial aquifers. Two types of injection systems, a large single tank and a dynamic mixing tank, were designed to deliver more than 800 L of amended ground water to the aquifer over 12 hours, without altering the ground water temperature, pH, Eh, or dissolved gas composition. Two types of multilevel samplers (MLSs) were designed and installed. Permanent MLSs performed well for the homogenous surficial aquifer, but their installation procedure promoted vertical mixing, which could obfuscate experimental data obtained from vertically stratified, heterogeneous aquifers. A novel, removable MLS was designed to fit in 2- and 4-inch wells. Expandable O-rings between each sampling port hydraulically isolated each port for sample collection when a nut was tightened at the land surface. A low-cost vacuum manifold system designed to work with both MLS designs used 50 mL centrifuge tubes to efficiently sample 12 MLS ports with one peristaltic pump head. The integrated system was developed and used during four field campaigns over a period of three years. During each campaign, more than 3000 ground water samples were collected in less than one week. This system should prove particularly useful for ground water tracer, injection, and push-pull experiments that require high-frequency and/or high-density sampling. [source]

    A Statistical Estimator of the Spatial Distribution of the Water-Table Altitude

    GROUND WATER, Issue 1 2003
    Nicasio Seplveda
    An algorithm was designed to statistically estimate the areal distribution of water-table altitude. The altitude of the water table was bounded below by the minimum water-table surface and above by the land surface. Using lake elevations and stream stages, and interpolating between lakes and streams, the minimum water-table surface was generated. A multiple linear regression among the minimum water-table altitude, the difference between land-surface and minimum water-table altitudes, and the water-level measurements from surficial aquifer system wells resulted in a consistently high correlation for all groups of physiographic regions in Florida. A simple linear regression between land-surface and water-level measurements resulted in a root-mean-square residual of 4.23 m, with residuals ranging from , 8.78 to 41.54 m. A simple linear regression between the minimum water table and the water-level measurements resulted in a root-mean-square residual of 1.45 m, with residuals ranging from ,7.39 to 4.10 m. The application of the multiple linear regression presented herein resulted in a root-mean-square residual of 1.05 m, with residuals ranging from , 5.24 to 5.63 m. Results from complete and partial F tests rejected the hypothesis of eliminating any of the regressors in the multiple linear regression presented in this study. [source]

    Chemical and Bacterial Quality of Aeration-Type Waste Water Treatment System Discharge

    Samuel V Panno
    On-site waste water treatment systems are a potential source of chemical and bacterial contamination to ground water in areas with highly susceptible aquifers such as the sinkhole plain of southwestern Illinois. Ground water from wells, cave streams, and water that discharges from the numerous springs in this area is typically contaminated with nitrate and enteric bacteria and thus may pose a health hazard to those who come into contact with it. In order to determine if the most popular type of on-site waste water treatment systems in the study area was a potential source, samples of effluents discharged at the land surface from 23 domestic aeration-type on-site waste water treatment systems were collected to characterize their water quality and bacterial contents. Most of the effluents contained relatively large concentrations of sodium (Na+), chloride (Cl,), nutrients (nitrogen [N], phosphate [PO43,], and potassium [K+]), and enteric bacteria. Ion concentration ranges (in mg/L) were Na+ (46 to 416), Cl, (21 to 618), N (4.7 to 67), PO4 -P (1.4 to 48), and K+ (6.0 to 257). The sources of elevated Na+ and Cl, were human waste and NaCl used in the water softening systems of the houses. Ammonium was usually the dominant inorganic N species, indicating incomplete oxidation of the waste water. Discharge of Na+, Cl,, and nutrients could also have negative impacts on ground water and surface water quality, subsurface and surface aquatic ecosystems, and vegetation. Our characterization of effluent from these waste water treatment systems revealed their generally poor quality and the likelihood that they can contaminate ground water in areas with highly vulnerable aquifers. [source]

    Thermal influence of urban groundwater recharge from stormwater infiltration basins

    Arnaud Foulquier
    Abstract Groundwater warming below cities has become a major environmental issue; but the effect of distinct local anthropogenic sources of heat on urban groundwater temperature distributions is still poorly documented. Our study addressed the local effect of stormwater infiltration on the thermal regime of urban groundwater by examining differences in water temperature beneath stormwater infiltration basins (SIB) and reference sites fed exclusively by direct infiltration of rainwater at the land surface. Stormwater infiltration dramatically increased the thermal amplitude of groundwater at event and season scales. Temperature variation at the scale of rainfall events reached 3 C and was controlled by the interaction between runoff amount and difference in temperature between stormwater and groundwater. The annual amplitude of groundwater temperature was on average nine times higher below SIB (range: 09,86 C) than at reference sites (range: 0,12 C) and increased with catchment area of SIB. Elevated summer temperature of infiltrating stormwater (up to 21 C) decreased oxygen solubility and stimulated microbial respiration in the soil and vadose zone, thereby lowering dissolved oxygen (DO) concentration in groundwater. The net effect of infiltration on average groundwater temperature depended upon the seasonal distribution of rainfall: groundwater below large SIB warmed up (+04 C) when rainfall occurred predominantly during warm seasons. The thermal effect of stormwater infiltration strongly attenuated with increasing depth below the groundwater table indicating advective heat transport was restricted to the uppermost layers of groundwater. Moreover, excessive groundwater temperature variation at event and season scales can be attenuated by reducing the size of catchment areas drained by SIB and by promoting source control drainage systems. Copyright 2009 John Wiley & Sons, Ltd. [source]

    Performance assessment of a GCM land surface scheme using a fine-scale calibrated hydrological model: an evaluation of MOSES for the Nile Basin

    Mohamed Ezzat Elshamy
    Abstract Land surface schemes (LSSs) represent the interface between land surface and the atmosphere in general circulation models (GCMs). Errors in LSS-simulated heat and moisture fluxes can result from inadequate representation of hydrological features and the derivation of effective surface parameters for large heterogeneous GCM gridboxes from small-scale observations. Previous assessments of LSS performance have generally compared simulated heat and moisture fluxes to observations over a defined experimental domain for a limited period. A different approach has been evaluated in this study, which uses a fine-resolution calibrated hydrological model of the study basin to provide a quasi-observed runoff series for direct comparison with simulated runoff from a selected LSS at GCM scale. The approach is tested on two GCM gridboxes covering two contrasting regions within the Nile Basin. Performance is mixed; output from the LSS is generally compatible with that of the fine-resolution model for one gridbox while it cannot reproduce the runoff dynamics for the other. The results also demonstrate the high sensitivity of runoff and evapotranspiration to radiation and precipitation inputs and show the importance of subtle issues such as temporal disaggregation of climatic inputs. We conclude that the use of a fine-resolution calibrated model to evaluate a LSS has several advantages, can be generalized to other areas to improve the performance of global models and provides useful data that can be used to constrain LSS parameterizations. Copyright 2009 John Wiley & Sons, Ltd. [source]

    Boundary and border considerations in hydrology

    Ming-ko Woo
    Abstract This paper examines several issues related to hydrological boundaries and their border zones. In a two-dimensional space, a boundary is a line that separates two domains possessing different hydrological properties or dominated by different hydrological processes, and a border is an area that experiences an edge effect owing to transitions or mixing of processes. Hydrological boundaries may be static, such as drainage divides, or dynamic, such as the edges of a seasonal snow cover. They may be open or closed to the transfer of matter and energy, although most boundaries tend to be perforated, permitting different rates of movement across different segments. Borders may be narrow or the edge effect can affect large areas, as happens to the sensible heat flux over a highly fragmented melting snowfield. The introduction of artificial boundaries, notably the grid patterns of remote sensing pixels, digital elevation models and land surface schemes, gives rise to problems of mismatch with the natural hydrological boundaries. Incorrect demarcation, omission and generalization of boundaries can produce errors that are hard to rectify. Serious biases are involved when point observations are used to calibrate parameters or to validate model outputs integrated over a bounded area. Examples are drawn mainly from cold climate hydrology to illustrate the boundary issues but the questions transcend disciplinary areas. The intent of this presentation is to stimulate discussions that could be a prelude to finding solutions to many boundary problems which have thus far eluded hydrological investigations. Copyright 2004 John Wiley & Sons, Ltd. [source]

    Aircraft observations of the atmospheric boundary layer over a heterogeneous surface in eastern Siberia

    T. Hiyama
    Abstract This paper outlines specifications and gives preliminary results of aircraft observations made during the Intensive Observation Period in 2000 (IOP2000) over the Yakutsk area of eastern Siberia. The observations were part of the GAME-Siberia project. Spatial and seasonal variation in the fluxes of sensible heat, latent heat, and carbon dioxide were determined using a Russian aircraft equipped with turbulence sensors. Two flight paths covered 12 32 km2 grids over heterogeneous forest and grass surfaces on the left- and right-hand banks of the Lena River. The spatial flux distributions were consistent with the underlying vegetation cover. A video camera recorded aerial images of the land, while a spectrometer observed the spectral reflectance of the land surface. These data helped describe the relationship between the atmosphere and the land surface. The vertical structure of the atmospheric boundary layer (ABL) was also observed on long flight paths between the left and right banks of the Lena River. Thermally induced internal boundary layers (TIBLs) developed in the ABL under different thermal and dynamic conditions near the Lena River. The horizontal and vertical distributions of sensible and latent heats in the ABL were consistent with the generation of cumulus, which appeared over the forested area, but not over the Lena River lowland. Copyright 2003 John Wiley & Sons, Ltd. [source]

    Hydrological regime analysis of the Selenge River basin, Mongolia

    X. Ma
    Abstract Arid and semi-arid regions are very vulnerable to environmental changes. Climate change studies indicate that the environment in such areas will steadily deteriorate with global warming; inland lakes will shrink and desert areas will expand. Mongolia is a landlocked country in north-central Asia that contains a unique ecological system consisting of taiga, steppe, and desert from north to south. The Selenge River basin (280 000 km2) in northern Mongolia is a semi-arid region underlain by permafrost, between latitudes 46 and 52N, and longitudes 96 and 109E. The issue of sustainable development of the basin is very important owing to its limited natural resources, including fresh water, forest, and rangeland. To examine the water cycle processes in the basin, a hydrological analysis was carried out using a simple scheme for the interaction between the land surface and atmosphere (big-leaf model) coupled to a hydrological model for the period 1988,92 to estimate the hydrological regime of the basin. Annual precipitation in this period averaged 298 mm, ranging from 212 to 352 mm at a 1 1 resolution based on data from 10 gauges, and the estimated annual evapotranspiration averaged 241 mm, ranging between 153 and 300 mm. This indicates that evapotranspiration accounts for the overwhelming majority of the annual precipitation, averaging 81% and ranging between 64 and 96%. The annual potential evapotranspiration in the basin averaged 2009 mm; the ratio of evapotranspiration (actual to potential evapotranspiration) was 012 and the wetness index (annual precipitation to potential evapotranspiration) was 015. Copyright 2003 John Wiley & Sons, Ltd. [source]

    Europe's 2003 heat wave: a satellite view of impacts and land,atmosphere feedbacks

    Benjamin F. Zaitchik
    Abstract A combination of satellite imagery, meteorological station data, and the NCEP/NCAR reanalysis has been used to explore the spatial and temporal evolution of the 2003 heat wave in France, with focus on understanding the impacts and feedbacks at the land surface. Vegetation was severely affected across the study area, especially in a swath across central France that corresponds to the Western European Broadleaf (WEB) Forests ecological zone. The remotely sensed surface temperature anomaly was also greatest in this zone, peaking at +15.4 C in August. On a finer spatial scale, both the vegetation and surface temperature anomalies were greater for crops and pastures than for forested lands. The heat wave was also associated with an anomalous surface forcing of air temperature. Relative to other years in record, satellite-derived estimates of surface-sensible heat flux indicate an enhancement of 48,61% (24.0,30.5 W m,2) in WEB during the August heat wave maximum. Longwave radiative heating of the planetary boundary layer (PBL) was enhanced by 10.5 W m,2 in WEB for the same period. The magnitude and spatial structure of this local heating is consistent with models of the late twenty-first century climate in France, which predict a transitional climate zone that will become increasingly affected by summertime drought. Models of future climate also suggest that a soil-moisture feedback on the surface energy balance might exacerbate summertime drought, and these proposed feedback mechanisms were tested using satellite-derived heat budgets. Copyright 2006 Royal Meteorological Society. [source]

    An improved method of constructing a database of monthly climate observations and associated high-resolution grids

    Timothy D. Mitchell
    Abstract A database of monthly climate observations from meteorological stations is constructed. The database includes six climate elements and extends over the global land surface. The database is checked for inhomogeneities in the station records using an automated method that refines previous methods by using incomplete and partially overlapping records and by detecting inhomogeneities with opposite signs in different seasons. The method includes the development of reference series using neighbouring stations. Information from different sources about a single station may be combined, even without an overlapping period, using a reference series. Thus, a longer station record may be obtained and fragmentation of records reduced. The reference series also enables 1961,90 normals to be calculated for a larger proportion of stations. The station anomalies are interpolated onto a 0.5 grid covering the global land surface (excluding Antarctica) and combined with a published normal from 1961,90. Thus, climate grids are constructed for nine climate variables (temperature, diurnal temperature range, daily minimum and maximum temperatures, precipitation, wet-day frequency, frost-day frequency, vapour pressure, and cloud cover) for the period 1901,2002. This dataset is known as CRU TS 2.1 and is publicly available ( Copyright 2005 Royal Meteorological Society [source]

    The evolution of, and revolution in, land surface schemes designed for climate models

    A. J. Pitman
    Abstract The land surface is a key component of climate models. It controls the partitioning of available energy at the surface between sensible and latent heat, and it controls the partitioning of available water between evaporation and runoff. The land surface is also the location of the terrestrial carbon sink. Evidence is increasing that the influence of the land surface is significant on climate and that changes in the land surface can influence regional- to global-scale climate on time scales from days to millennia. Further, there is now a suggestion that the terrestrial carbon sink may decrease as global temperatures increase as a consequence of rising CO2 levels. This paper provides the theoretical background that explains why the land surface should play a central role in climate. It also provides evidence, sourced from climate model experiments, that the land surface is of central importance. This paper then reviews the development of land surface models designed for climate models from the early, very simple models through to recent efforts, which include a coupling of biophysical processes to represent carbon exchange. It is pointed out that significant problems remain to be addressed, including the difficulties in parameterizing hydrological processes, root processes, sub-grid-scale heterogeneity and biogeochemical cycles. It is argued that continued development of land surface models requires more multidisciplinary efforts by scientists with a wide range of skills. However, it is also argued that the framework is now in place within the international community to build and maintain the latest generation of land surface models. Further, there should be considerable optimism that consolidating the recent rapid advances in land surface modelling will enhance our capability to simulate the impacts of land-cover change and the impacts of increasing CO2 on the global and regional environment. Copyright 2003 Royal Meteorological Society [source]

    The impact of land-cover modification on the June meteorology of China since 1700, simulated using a regional climate model

    H. Wang
    Abstract A series of simulations was conducted using a regional climate model with a domain covering mainland China. Simulations were conducted for a single June using estimated land cover for 1700, 1750, 1800, 1850, 1900, 1950, 1970 and 1990. The conversion of land cover between these periods was extensive over mainland China, where large areas were altered from natural forests to either grass or crops, or from natural grasslands to crops. These land-cover modifications affect various characteristics of the land surface, which lead to changes in the way available energy and water are partitioned. Over areas where land cover was modified, substantial changes are simulated. The conversion from forests to grasses or crops leads to warming and to reductions in root zone soil moisture and latent heat fluxes. Regionally, the conversion from forest to grasses and crops leads to significant warming over large areas of China, but there is an area of cooling present that is coincident with the main location of a land-use change from short grass to crops. The changes in temperature propagate to about 1500 m above the surface and affect specific humidity throughout this part of the atmosphere. An analysis of daily average results shows a consistent impact of land-cover modification on temperature, latent heat flux and soil moisture. Therefore, we find large and consistent impacts over China resulting from historical land-cover modification that are sufficiently important to the regional-scale climate to warrant inclusion in future modelling efforts. Our results suggest that efforts to attribute warming patterns over China to any particular cause need to take into account the conversion of the land cover that has taken place over China over the last 300 years. Copyright 2003 Royal Meteorological Society [source]

    Detailed measurements of thickness and grain size of a widespread onshore tsunami deposit in Phang-nga Province, southwestern Thailand

    ISLAND ARC, Issue 3 2010
    Shigehiro Fujino
    Abstract Measurements of thickness and grain size along flow-parallel transects across onshore deposits of the 2004 Indian Ocean tsunami revealed macroscopic horizontal variations and provided new insights into tsunami sedimentation. The tsunami caused severe erosion of beaches, river mouths, and the shallow seafloor along the coast of southwestern Thailand and supplied sufficient sediment to deposit a kilometer-wide blanket of sand on the land surface. The tsunami deposits generally fine landward with some fluctuations caused by local entrainment and settlement of sediments. Sediments of medium and fine sand are restricted to a few hundreds of meters inland from their source, whereas finer grained sediments were suspended longer and deposited 1 km or more inland. Although the thickness of the tsunami deposits is strongly influenced by local topography, they generally thin landward. In areas of low-relief topography, the rate of landward thinning is exponential and reflects the dominance of sediment supply to nearshore areas over that to areas farther inland. [source]

    Surrogacy and persistence in reserve selection: landscape prioritization for multiple taxa in Britain

    Aldina M. A. Franco
    Summary 1A principal goal of protected-area networks is to maintain viable populations of as many species as possible, particularly those that are vulnerable to environmental change outside reserves. Ideally, one wants to be able to protect all biodiversity when selecting priority areas for conservation. 2Using the area-prioritization algorithm ZONATION, we identified the locations where UK Biodiversity Action Plan (BAP) species of mammals, birds, herptiles, butterflies and plants occur in concentrated populations with high connectivity. Both these features are likely to be correlated with population persistence. The analyses were successful in maintaining a high proportion of the connectivity of narrow-range species, and large total amounts of the connectivity of wider-range species over 10% of the land surface of Great Britain. 3Biodiversity Action Plan (BAP , high priority) species of one taxonomic group were not particularly good surrogates (indicators) for BAP species of other taxonomic groups. Hence, maintaining population concentrations of one taxonomic group did not guarantee doing likewise for other taxa. 4Species with narrow geographic ranges were most effective at predicting conservation success for other species, probably because they represent the range of environmental conditions required by other species. 5Synthesis and applications. This study identifies landscape-scale priority areas for conservation of priority species from several taxonomic groups, using the Zonation software. ,Indicator groups' were only partially successful as predictors of priority areas for other taxonomic groups, and therefore, the identification of priority areas for biodiversity conservation should include information from all taxonomic groups available. Larger areas should be protected to account for species not included in the analyses. Conservation solutions based on data for many different species, and particularly those species with narrowly defined ranges, appear to be most effective at protecting other rare taxa. [source]

    Correlates of biological soil crust abundance across a continuum of spatial scales: support for a hierarchical conceptual model

    Summary 1Desertification negatively impacts a large proportion of the global human population and > 30% of the terrestrial land surface. Better methods are needed to detect areas that are at risk of desertification and to ameliorate desertified areas. Biological soil crusts are an important soil lichen-moss-microbial community that can be used toward these goals, as (i) bioindicators of desertification damage and (ii) promoters of soil stability and fertility. 2We identified environmental factors that correlate with soil crust occurrence on the landscape and might be manipulated to assist recovery of soil crusts in degraded areas. We conducted three studies on the Colorado Plateau, USA, to investigate the hypotheses that soil fertility [particularly phosphorus (P), manganese (Mn) and zinc (Zn)] and/or moisture limit soil crust lichens and mosses at four spatial scales. 3In support of the soil fertility hypothesis, we found that lichen,moss crusts were positively correlated with several nutrients [Mn, Zn, potassium (K) and magnesium (Mg) were most consistent] at three of four spatial scales ranging from 35 cm2 in area to c. 800 km2. In contrast, P was negatively correlated with lichen,moss crusts at three scales. 4Community composition varied with micro-aspect on ridges in the soil crust. Three micro-aspects [north-north-west (NNW), east-north-east (ENE) and TOP] supported greater lichen and moss cover than the warmer, windward and more xeric micro-aspects [west-south-west (WSW) and south-south-east (SSE)]. This pattern was poorly related to soil fertility; rather, it was consistent with the moisture limitation hypothesis. 5Synthesis and application. Use of crusts as desertification bioindicators requires knowledge of a site's potential for crust cover in the absence of desertification. We present a multi-scale model of crust potential as a function of site properties. Future quantitative studies can use this model to guide sampling efforts. Also, our results suggest new directions in restoration research: enhancement of moisture residence time and fertilization with key nutrients (Mn, Zn, K and Mg). Re-establishment of soil crusts in desertified lands will help regain lost soil stability and fertility, and facilitate plant re-establishment. [source]