bluuebunny/crossref_metadata_2025 huggingface dataset:
Interaction between stream temperature, streamflow, and groundwater exchanges in alpine streams
Authors: Constantz Jim
Published: February 2004

Four alpine streams were monitored to continuously collect stream temperature and streamflow for periods ranging from a week to a year. In a small stream in the Colorado Rockies, diurnal variations in both stream temperature and streamflow were significantly greater in losing reaches than in gaining reaches, with minimum streamflow losses occurring early in the day and maximum losses occurring early in the evening. Using measured stream temperature changes, diurnal streambed infiltration rates were predicted to increase as much as 35% during the day (based on a heat and water transport groundwater model), while the measured increase in streamflow loss was 40%. For two large streams in the Sierra Nevada Mountains, annual stream temperature variations ranged from 0° to 25°C. In summer months, diurnal stream temperature variations were 30–40% of annual stream temperature variations, owing to reduced streamflows and increased atmospheric heating. Previous reports document that one Sierra stream site generally gains groundwater during low flows, while the second Sierra stream site may lose water during low flows. For August the diurnal streamflow variation was 11% at the gaining stream site and 30% at the losing stream site. On the basis of measured diurnal stream temperature variations, streambed infiltration rates were predicted to vary diurnally as much as 20% at the losing stream site. Analysis of results suggests that evapotranspiration losses determined diurnal streamflow variations in the gaining reaches, while in the losing reaches, evapotranspiration losses were compounded by diurnal variations in streambed infiltration. Diurnal variations in stream temperature were reduced in the gaining reaches as a result of discharging groundwater of relatively constant temperature. For the Sierra sites, comparison of results with those from a small tributary demonstrated that stream temperature patterns were useful in delineating discharges of bank storage following dam releases. Direct coupling may have occurred between streamflow and stream temperature for losing stream reaches, such that reduced streamflows facilitated increased afternoon stream temperatures and increased afternoon stream temperatures induced increased streambed losses, leading to even greater increases in both stream temperature and streamflow losses.
An analysis of complex reaction networks in groundwater modeling
Authors: Chilakapati Ashok , Ginn Timothy , Szecsody James
Published: February 2004

The complex chemistry describing the biogeochemical dynamics in the natural subsurface environments gives rise to heterogeneous reaction networks, the individual segments of which can feature a wide range of timescales. This paper presents a formulation of the mass balance equations for the batch chemistry and the transport of groundwater contaminants participating in such arbitrarily complex networks of reactions. We formulate the batch problem as an initial‐value differential algebraic equation (DAE) system and compute its “index” so that the ease of solvability of the system is determined. We show that when the equilibrium reactions obey the law of mass action, the index of this initial‐value DAE system is always unity (thus solvable with well‐developed techniques) and that the system can be decoupled into a set of linearly implicit ordinary differential equations and a set of explicit algebraic equations. The formulations for the transport of these reaction networks can take advantage of their solvability properties under batch conditions. To avoid the error associated with time splitting fast reactions from transport, we present a split‐kinetics approach where the fast equilibrium reactions are combined with transport equations while only the slower kinetic reactions are time split. These results are used to formulate and solve a simplified reaction network for the biogeochemical transformation of Co(II) ethylenediaminetetraacetic acid (EDTA) in the presence of iron‐coated sediments.
Temporal patterns of nitrogen leakage from mid‐Appalachian forested watersheds: Role of insect defoliation
Authors: Eshleman Keith N. , Morgan Raymond P. , Webb James R. , Deviney Frank A. , Galloway James N.
Published: February 2004

Fluxes of dissolved nitrogen (N) as nitrate from forested watersheds in the mid‐Appalachian region have important water quality ramifications for small acid‐sensitive streams and for downstream receiving waters such as the Chesapeake Bay. Previous studies of N leakage have suggested that annual dissolved N fluxes from small watersheds can vary by several orders of magnitude and may be increasing as second‐growth forests gradually become N saturated from the accrual of atmospheric N loadings. In this study, we examined the temporal (intra‐annual and interannual) variability in dissolved nitrate fluxes from five small (area < 15 km2) forested watersheds in the mid‐Appalachian region from 1988 to 1995. At all sites, nitrate concentrations were observed to increase dramatically during storm flow events, with nitric acid contributing significantly to depressions in pH and acid‐neutralizing capacity; annual nitrate fluxes were dominated by high‐discharge periods. Interannually, the fluxes at each site varied by 1–2 orders of magnitude, but the patterns of N leakage displayed considerable synchrony with outbreaks of gypsy moth caterpillar defoliation that began in the late 1980s and early 1990s in this region. N leakage from forested watersheds apparently lagged the initial defoliation by several months to perhaps a year or more. Defoliation outbreaks by the gypsy moth caterpillar (or other herbivorous pests) thus provide an alternative explanation of N leakage from forest ecosystems. Poorly documented insect defoliations, rather than premature N saturation of intact forest ecosystems, need to be considered as a possible explanation of N leakage from forested watersheds in the mid‐Appalachian region and elsewhere.
Influence of image resolution and thresholding on the apparent mass fractal characteristics of preferential flow patterns in field soils
Authors: Baveye Philippe , Boast Charles W. , Ogawa Susumu , Parlange Jean‐Yves , Steenhuis Tammo
Published: February 2004

Preferential flow is ubiquitous in field soils, where it has important practical implications for water and contaminant transport. Dyes are frequently used to visualize preferential flow pathways. The fact that stain patterns in pictures of soil profiles often exhibit convoluted geometries, reminiscent of fractals, has encouraged a number of authors to use the principles of fractal geometry to describe stain patterns. This description typically involves two numbers, a mass and a surface fractal dimension. The evaluation of either one via image analysis requires numerous subjective choices to be made, including choices regarding image resolution, the definition adopted for the “fractal” dimension, and the thresholding algorithm used to generate binary images. The present article analyzes in detail the influence of these various choices on the mass fractal dimension of stained preferential flow patterns. A theoretical framework in which to envisage these choices is developed, using the classical quadratic von Koch island as an example. This framework is then applied to a set of pictures of an actual stain pattern in an orchard soil. The results suggest that the (apparent) mass fractal dimension of the stain pattern varies between 1.56 and 1.88, depending on choices made at different stages in the evaluation of the fractal dimension. In each case considered, the dimension, determined by a straight line fit in a log‐log plot, has extremely high statistical significance, with R > 0.999. Of the various parameters subject to choice, image resolution seems to have the most pronounced influence on the value of the fractal dimension, which increases markedly at higher resolution (smaller‐pixel size). By analogy with the case of the quadratic von Koch island, this dependence on image resolution, as well as the fact that the surface area of the stain pattern does not decrease with pixel size, suggests that the stain pattern is not a mass fractal; that is, there is no reason to believe that its various dimensions differ from 2. The approach adopted in the present article could be useful whenever fractal dimensions are evaluated via image analysis.
Effect of groundwater springs on NO3− concentrations during summer in Catskill Mountain streams
Authors: Burns Douglas A. , Murdoch Peter S. , Lawrence Gregory B. , Michel Robert L.
Published: February 2004

Groundwater and stream water data collected at three headwater catchments in the Neversink River watershed indicate that base flow is sustained by groundwater from two sources: a shallow flow system within the till and soil and a deep flow system within bedrock fractures and bedding planes that discharges as perennial springs. Data from eight wells finished near the till/bedrock interface indicate that saturated conditions are not maintained in the shallow flow system during most summers. In contrast, the discharge of a perennial spring remained constant during two summer rainstorms, providing evidence that the deep flow system is disconnected from the shallow flow system in summer. Discharge from perennial springs was the principal source of streamflow in a headwater reach during low flow. Mean NO3− concentrations were 20–25 μmol L−1 in five perennial springs during the summer but only 5–10 μmol L−1 in shallow groundwater. Thus the deep flow system does not reflect typical NO3− concentrations in the soil during summer. A hydrologic budget at a headwater drainage reveals that March and late fall are the principal groundwater recharge periods. Residence time modeling based on analyses of 18O and 35S indicates that groundwater in the deep flow system is 6–22 months old. These data indicate that summer base flow largely originates from previous dormant seasons when available soil NO3− is greater. In these Catskill watersheds, high base flow concentrations of NO3− during summer do not provide sufficient evidence that the atmospheric N deposition rate exceeds the demand of terrestrial vegetation.
Detection of aquifer system compaction and land subsidence using interferometric synthetic aperture radar, Antelope Valley, Mojave Desert, California
Authors: Galloway D. L. , Hudnut K. W. , Ingebritsen S. E. , Phillips S. P. , Peltzer G. , Rogez F. , Rosen P. A.
Published: February 2004

Interferometric synthetic aperture radar (InSAR) has great potential to detect and quantify land subsidence caused by aquifer system compaction. InSAR maps with high spatial detail and resolution of range displacement (±10 mm in change of land surface elevation) were developed for a groundwater basin (∼103 km2) in Antelope Valley, California, using radar data collected from the ERS‐1 satellite. These data allow comprehensive comparison between recent (1993–1995) subsidence patterns and those detected historically (1926–1992) by more traditional methods. The changed subsidence patterns are generally compatible with recent shifts in land and water use. The InSAR‐detected patterns are generally consistent with predictions based on a coupled model of groundwater flow and aquifer system compaction. The minor inconsistencies may reflect our imperfect knowledge of the distribution and properties of compressible sediments. When used in conjunction with coincident measurements of groundwater levels and other geologic information, InSAR data may be useful for constraining parameter estimates in simulations of aquifer system compaction.
The fundamental principles of cost‐benefit analysis
Authors: Griffin Ronald C.
Published: February 2004

Cost‐benefit analysis is reducible to several major principles that collectively describe the assumption base, objectives, analytical tasks, and merits of this important project assessment methodology. Here, these principles are identified and described using basic economic terms and concepts. The deficiencies of cost‐benefit analysis also emerge from these principles, and these issues are also observed in this article. Further discussion investigates high‐profile issues in the economic assessment of environmental affects and the economic effects on sectors linked to water‐project‐impacted sectors.
Robust solution of Richards' equation for nonuniform porous media
Authors: Miller Cass T. , Williams Glenn A. , Kelley C. T. , Tocci Michael D.
Published: February 2004

Capillary pressure–saturation‐relative permeability relations described using the van Genuchten [1980] and Mualem [1976] models for nonuniform porous media lead to numerical convergence difficulties when used with Richards' equation for certain auxiliary conditions. These difficulties arise because of discontinuities in the derivative of specific moisture capacity and relative permeability as a function of capillary pressure. Convergence difficulties are illustrated using standard numerical approaches to simulate such problems. We investigate constitutive relations, interblock permeability, nonlinear algebraic system approximation methods, and two time integration approaches. An integral permeability approach approximated by Hermite polynomials is recommended and shown to be robust and economical for a set of test problems, which correspond to sand, loam, and clay loam media.
A proposed stepwise regression method for model structure identification
Authors: Sun Ne‐Zheng , Yang Shu‐li , Yeh William W‐G.
Published: February 2004

This paper proposes a new methodology for constructing groundwater models. The proposed methodology, which determines simultaneously both model structure and model parameters, is based on the following ideas: (1) When solving the inverse problem, different model structures always produce different model parameters; (2) since the number of possible model structures of an aquifer is infinite, the number of possible representative parameters is also infinite; (3) to obtain a set of appropriate representative model parameters, we must have an appropriate model structure; and (4) an appropriate model structure should be determined not only by observation data and prior information but also by the accuracy requirements of model applications. In this proposed methodology we start with a homogeneous model structure and, step by step, gradually increase the complexity of the model structure. At each level of complexity we calculate not only the fitting residual of parameter identification but also the error of model structure to determine if a more complex model structure is needed. The model structure error of using one model structure to replace another model structure is defined by a maximum‐minimum (max‐min) problem that is based on the distance between the two models and is measured in parameter, observation, and prediction (or decision) spaces. This proposed methodology is used to solve a hypothetical remediation design problem in which the true hydraulic conductivity is a random field with a certain trend. We have found that for the example problem, virtually identical pumping policy is obtained when a five‐zone model with an optimized zonation pattern is used to represent the nonstationary random field. We have also found that observation errors have minimum impact on management solution in comparison with structure errors. To calculate the model structure error for this example, the inverse solution is coupled with a management problem. We have also developed an effective iteration method to handle nonlinear water quality constraints.
On the connectivity of three‐dimensional fault networks
Authors: Bour Olivier , Davy Philippe
Published: February 2004

Natural fault networks involve a very broad range of fault lengths, modeled in general by a power law length distribution, n (l) ∼ αl−a. Such a scaling law does not allow to define any a priori pertinent scale of observation for hydraulic field experiments in fractured media. To investigate the relative effects of faults depending on their length, we undertake in the spirit of percolation theory a theoretical and numerical study of the connectivity of three‐dimensional fault networks following power law length distributions. We first establish the correct analytical expression of a percolation parameter p, which describes the connectivity of the system. The parameter p is found to be dependent on the third moment of the length distribution for fault planes. It allows us to identify different regimes of connectivity depending on a, the exponent of the fault length distribution. The geometrical properties of the infinite cluster, which partly control transport properties, are also established at the percolation threshold. For natural fault networks, our theoretical analysis suggests that faults larger than a critical length scale may form a well‐connected network, while smaller faults may be not connected on average. This result, which implies an increase of the connectivity with scale, is consistent with scaling effects observed on permeability measurements.
Noble gases as natural tracers of water circulation in the Paris Basin: 1. Measurements and discussion of their origin and mechanisms of vertical transport in the basin
Authors: Castro Maria Clara , Jambon Albert , de Marsily Ghislain , Schlosser Peter
Published: February 2004

The concentrations and isotopic compositions of helium, neon, and argon were measured in 29 water samples collected from five superposed aquifers in the Paris Basin (Ypresian, Albian, Neocomian, Dogger, and Trias). In all these groundwater flow systems the data showed excesses of 3He, 4He, and 40Ar above the solubility equilibrium with the atmosphere (air saturated water (ASW)), as well as vertical concentration gradients of these isotopes throughout the basin. The water of the Dogger and the Trias formations also had a 21Ne excess above ASW values. The mean rate of radiogenic and nucleogenic isotope production in the entire sedimentary sequence of the basin cannot produce the measured quantities of 3He, 4He, 21Ne, and 40Ar, if reasonable water residence times are considered. The total calculated production is estimated to represent less than about 13% of the measured values for all isotopes. The greater part (>87%) of the radiogenic and nucleogenic noble gas isotopes is thus believed to originate from the bedrock, and the isotopes are transported vertically through the entire basin. Three mechanisms of transport are considered: advection, dispersion, and molecular diffusion. For the Trias the radiogenic/nucleogenic production ratios of 4He/40Ar and 21Ne/40Ar are close to the mean production rate in the crust (4 ± 3 and 0.96 × 10−7, respectively). For the overlying Dogger, however, these ratios are much higher (4He/40Ar: 10 to 70; 21Ne/40Ar: 8 × 10−7 to 23 × 10−7). We suggest that differences in the vertical diffusive flux of 4He, 21Ne, and 40Ar are the reason for the high isotope ratios observed in the Dogger. In the vertical direction, 4He is transported mostly by diffusion, whereas 40Ar is transported mostly by advection. Neon 21 represents an intermediate situation. The distribution of 3He, 4He,21Ne, and 40Ar throughout the basin can be explained by the existence of only two sources: an atmospheric component contributed by recharge water and a radiogenic/nucleogenic component originating mainly in the bedrock. This concept is supported by two‐dimensional cross‐section modeling of the water flow in the Paris Basin and the advective, dispersive, and diffusive transport of these noble gases in its multiaquifer system presented in part 2 of this study.
Noble gases as natural tracers of water circulation in the Paris Basin: 2. Calibration of a groundwater flow model using noble gas isotope data
Authors: Castro Maria Clara , Goblet Patrick , Ledoux Emmanuel , Violette Sophie , de Marsily Ghislain
Published: February 2004

Using the rare gas concentrations in the aquifers of the Paris Basin (see part 1 of this series), a numerical model of a two‐dimensional cross section of the entire Paris Basin was built to simulate groundwater flow and the transport of 3He, 4He, and 40Ar isotopes. The model included seven aquifers separated by seven aquitards in a steady state flow regime. Transport of the gases is by advection, diffusion, and dispersion in steady or transient states. The 4He transport was simulated first and made it possible to calibrate both the crustal flux of this isotope and the average permeability of each aquifer, which were then favorably compared with measured values. These values present a high variability from aquifer to aquifer, between 8.5 × 10−7 and 3.5 × 10−4 m s−1. The water velocities and average residence times were also estimated. Average turnover times for the different aquifers are highly variable, ranging from 8700 years for the shallowest one (Ypresian) to 30 Myr for the deepest one (Trias). The calibrated model was also able to correctly represent the distribution of 3He and 40Ar in the basin. Diffusion proved to be an important mechanism for vertical transfer through the aquitards of the helium isotopes, as opposed to 40Ar, which is transported mainly by advection. On the basis of the (4He/40Ar) radiogenic ratio a constant value of 10−l1 m s−1 was attributed to the permeability of all the aquitards. A sensitivity study showed that the permeability of the aquitards situated in the lower part of the basin (Lias and aquitards in the Triassic and Dogger) could not be higher than 10−11 m s−1 given the observed distribution of the radiogenic 4He/40Ar ratio, but a lower limit could not be defined. The crustal fluxes of 3He, 4He, and 40Ar in the basin were estimated at 4.33 × 10−13 mol m−2 yr−1, 4. × 10−6 mol m−2 yr−1 and 2.52 × 10−7 mol m−2 yr−1, respectively. The simulation of the 3He and 4He transport showed that theR/Ra ratio (value of the measured R = 3He/4He ratio normalized to the atmospheric ratio Ra) entering at the base of the Trias from the bedrock remained constant while crossing the basin except in the zones close to the recharge areas where it is influenced by the atmospheric component. This constancy is due to the low radiogenic/nucleogenic production rate of these isotopes inside the basin, as compared to the crustal flux.
Laboratory experiments on heat‐driven two‐phase flows in natural and artificial rock fractures
Authors: Kneafsey Timothy J. , Pruess Karsten
Published: February 2004

Water flow in partially saturated fractures under thermal drive may lead to fast flow along preferential localized pathways and heat pipe conditions. At the potential high‐level nuclear waste repository at Yucca Mountain, water flowing in fast pathways may ultimately contact waste packages and transport radionuclides to the accessible environment. Sixteen experiments were conducted to visualize heat‐driven liquid flow in fracture models that included (1) assemblies of roughened glass plates, (2) epoxy replicas of rock fractures, and (3) a fractured specimen of Topopah Spring tuff. Continuous rivulet flow was observed for high liquid flow rates, intermittent rivulet flow and drop flow for intermediate flow rates, and film flow for lower flow rates and wide apertures. Heat pipe conditions (vapor‐liquid counterflow with phase change) were identified in five of the seven experiments in which spatially resolved thermal monitoring was performed but not when vapor‐liquid counterflow was hindered by very narrow apertures and when an inadequate working fluid volume was used.
Rill erosion and morphological evolution: A simulation model
Authors: Lei Tingwu , Nearing Mark A. , Haghighi Kamyar , Bralts Vincent F.
Published: February 2004

A mathematical model is advanced to simulate dynamically and spatially varied shallow water flow and soil detachment, transport, and deposition in rills. The model mimics the dynamic process of rill evolution, including variable rates of sediment redistribution along the bed and changes in local bed morphology. The sediment source term in the model uses a point scale, probabilistic relationship based on turbulent flow mechanics and a recently developed sediment transport relationship for rills based on stream power. The interdependent feedback loops between channel bed morphology, local flow hydraulics, and local scour and deposition, within the framework of the full hydrodynamic equations with inertial terms, constitute a mathematical model with the capacity to represent spatial variability and temporal evolution of the rill. Finite elements were applied to numerically solve the hydrodynamic and sediment continuity equations. A series of laboratory flume experiments were performed to evaluate the model. Initial bed slopes were 3, 5, and 7% with step increases of water inflow rates of 7.6, 11.4, and 15.2 L min−1. The soil material used in the flume was a kaolinitic, sandy‐clay loam. The rill model equations were solved for increasingly complex cases of spatial and temporal variabilities. The model followed measured patterns of morphological changes as the rill evolved, which suggests that the feedback loops in the model between erosion, bed morphological changes, and hydraulics were adequate to capture the essence of rill evolution.
Robust estimation of hydrogeologic model parameters
Authors: Finsterle Stefan , Najita Julie
Published: February 2004

Inverse modeling has become a standard technique for estimating hydrogeologic parameters. These parameters are usually inferred by minimizing the sum of the squared differences between the observed system state and the one calculated by a mathematical model. The robustness of the least squares criterion, however, has to be questioned because of the tendency of outliers in the measurements to strongly influence the outcome of the inversion. We have examined alternative approaches to the standard least squares formulation. The robustness of these estimators has been tested by means of Monte Carlo simulations of a synthetic experiment, in which both non‐Gaussian random errors and systematic modeling errors have been introduced. The approach was then applied to data from an actual gas‐pressure‐pulse‐decay experiment. The study demonstrates that robust estimators have the potential to reduce estimation bias in the presence of noisy data and minor systematic errors, which may be a significant advantage over the standard least squares method.
Modeling the transport and reaction of trace metals in water‐saturated soils and sediments
Authors: Smith S. Lan , Jaffé Peter R.
Published: February 2004

A model has been formulated of the equilibrium speciation, kinetic reaction, and transport of trace metals in the presence of biodegradation of organic substrates in saturated porous media. Kinetics of various processes (biodegradation, chemical reactions, and precipitation and dissolution of minerals) together with transport processes (advection, bioturbation, and diffusive/dispersive mixing) are quantified in a set of coupled mass balance equations (for the organic substrate, electron acceptors, reduced species, and trace metals). These steady state, one‐dimensional equations are discretized using a second‐order‐accurate finite difference approximation. A pE is estimated at each node in the domain on the basis the concentrations calculated and the half reaction for the dominant terminal electron acceptor at that location. The dynamic model is coupled iteratively to a modified version of the U.S. Environmental Protection Agency's MINTEQA2, which calculates equilibrium chemical speciation (including aqueous speciation, adsorption, and precipitation of minerals) at each node of the domain. The primary dependent variables are the total dissolved concentrations of the aqueous species together with the solid concentrations of the minerals. To demonstrate that this formulation can simulate biodegradation using reaction rates consistent with published values, simulations are compared to data from the sediment pore waters of a small lake. Simulations are presented of the transport and reaction of arsenic in lake sediments to illustrate how this model can be used to evaluate trends in trace metal mobility as affected by various water quality parameters through their influence on the biogeochemistry of natural systems.
Feasible optimality implies Hack's Law
Authors: Rigon Riccardo , Rodriguez‐Iturbe Ignacio , Rinaldo Andrea
Published: February 2004

We analyze the elongation (the scaling properties of drainage area with mainstream length) in optimal channel networks (OCNs) obtained through different algorithms searching for the minimum of a functional computing the total energy dissipation of the drainage system. The algorithms have different capabilities to overcome the imprinting of initial and boundary conditions, and thus they have different chances of attaining the global optimum. We find that suboptimal shapes, i.e., dynamically accessible states characterized by locally stationary total potential energy, show the robust type of elongation that is consistently observed in nature. This suggestive and directly measurable property is not found in the so‐called ground state, i.e., the global minimum, whose features, including elongation, are known exactly. The global minimum is shown to be too regular and symmetric to be dynamically accessible in nature, owing to features and constraints of erosional processes. Thus Hack's law is seen as a signature of feasible optimality thus yielding further support to the suggestion that optimality of the system as a whole explains the dynamic origin of fractal forms in nature.
Modeling water table fluctuations by means of a stochastic differential equation
Authors: Bierkens Marc F. P.
Published: February 2004

The combined system of soil‐water and shallow groundwater is modeled with simple mass balance equations assuming equilibrium soil moisture conditions. This results in an ordinary but nonlinear differential equation of water table depth at a single location. If errors in model inputs, errors due to model assumptions and parameter uncertainty are lumped and modeled as a wide band noise process, a stochastic differential equation (SDE) results. A solution for the stationary probability density function is given through use of the Fokker‐Planck equation. For the nonstationary case, where the model inputs are given as daily time series, sample functions of water table depth, soil saturation, and drainage discharge can be simulated by numerically solving the SDE. These sample functions can be used for designing drainage systems and to perform risk analyses. The parameters and noise statistics of the SDE are calibrated on time series of water table depths by embedding the SDE in a Kaiman filter algorithm and using the filter innovations in a filter‐type maximum likelihood criterion. The stochastic model is calibrated and validated at two locations: a peat soil with a very shallow water table and a loamy sand soil with a moderately shallow water table. It is shown in both cases that sample functions simulated with the SDE are able to reproduce a wide range of statistics of water table depth. Despite its unrealistic assumption of constant inputs, the stationary solution derived from the Fokker‐Planck equation gives good results for the peat soil, most likely because the characteristic response time of the water table is very small.
Controls on gully formation following forest clearing in a humid temperate environment
Authors: Prosser Ian P. , Soufi Majid
Published: February 2004

We have constructed a chronology of gully initiation, forest clearing, and rainfall events for gullies eroded into pine plantations near Bombala, southeastern Australia, over the last 15 years. The chronology suggests that daily rainfall of 80–100 mm, which has a recurrence interval of 1.4–2 years, can initiate gully erosion on areas cleared of native forest within the previous year. Massive gully erosion was experienced from a daily rainfall of 200 mm with a recurrence of 10–15 years. Resistance to channel initiation effectively recovers within a year of disturbance, allowing only a limited opportunity for erosion. Analysis of the spatial pattern of gully erosion, using a digital elevation model, shows that gullies were initiated across all landscape positions. In contrast to previous studies, there is no clear topographic threshold that limits the extent of the gully network. We infer that the weak topographic threshold results from low resistance to scour, allowing local flow convergence to dominate over topographic accumulation of flow. Although resistance to scour is low relative to previous studies, a process threshold for gully initiation is still a useful simplification of the erosion processes. For the soils that we studied, the threshold for gully erosion relates to intense scour exposing erodible subsoils.
Mapping snow distribution in the Alaskan Arctic using aerial photography and topographic relationships
Authors: König Max , Sturm Matthew
Published: February 2004

A method is presented for mapping the end‐of‐winter snow distribution in the Arctic using vertical aerial photographs taken during the melt. The photos show a limited number of distinctive snowmelt patterns that arise reliably year after year. Data and results from an energy balance melt model indicate that the patterns are not caused by differential melt but instead represent areas of distinctive end‐of‐winter snow depth. A map of these snowmelt patterns is thus a map of the end‐of‐winter snow distribution. Because wind transport of snow is common, the patterns are closely related to the topography. Rules based on this pattern‐topography relationship are developed and used to map the snow cover directly from topographic maps for three areas covering ∼220 km2 of the Kuparuk Basin in northern Alaska. Analysis of the snow maps suggests that about 75% of the area was mapped correctly. Applicability, reliability, and limitations of this mapping approach are discussed.
Radiometric and equivalent isothermal surface temperatures
Authors: Crago Richard D.
Published: February 2004

The analytical solution for the heat flux from an anisothermal canopy developed from K theory by Brutsaert and Sugita [1996] (hereinafter referred to as B&S) has been extended to provide a parameterization of the difference between the radiometric and the equivalent isothermal surface temperature. The latter is the isothermal temperature at which a canopy would give the correct sensible heat flux if the sensible heat roughness length z0h was given its theoretical, isothermal value derived by B&S. A parameterization of the canopy temperature seen by a radiometer is developed which incorporates the same foliage temperature profile as that used by B&S. From this the weighting fraction (i.e., the fraction of canopy top versus canopy bottom temperature “seen” by the radiometer) can be derived, as can an equation for the view zenith angle at which the radiometric and equivalent isothermal surface temperatures are the same. Field data indicate that multiangle radiometric surface temperatures alone cannot determine the three unknowns describing the foliage temperature profile. Several strategies to overcome this problem are outlined. The parameterization may eventually help to interpret remotely sensed infrared surface temperatures and to improve estimates of sensible heat flux and evapotranspiration, but comprehensive field testing is still needed.
A note on conservative transport in anisotropic, heterogeneous porous media in the presence of small‐amplitude transients
Authors: Naff R. L.
Published: February 2004

The late‐time macrodispersion coefficients are obtained for the case of flow in the presence of a small‐scale deterministic transient in a three‐dimensional anisotropic, heterogeneous medium. The transient is assumed to affect only the velocity component transverse to the mean flow direction and to take the form of a periodic function. For the case of a highly stratified medium, these late‐time macrodispersion coefficients behave largely as the standard coefficients used in the transport equation. Only in the event that the medium is isotropic is it probable that significant deviations from the standard coefficients would occur.
Long‐term evaluation of trabeculectomy in primary open angle glaucoma and chronic primary angle closure glaucoma in an Asian population
Authors: Sihota Ramanjit , Gupta Viney , Agarwal Harish C
Published: February 2004

Purpose: A retrospective cohort study was undertaken to evaluate and compare the long‐term results of trabeculectomy in primary open angle glaucoma (POAG) and chronic primary angle closure glaucoma (CPACG) in an Asian population.

Methods: Yearly diurnal measurements of intraocular pressure (IOP), best‐corrected visual acuity, optic disc and visual field records of patients having primary adult glaucomas who had undergone trabeculectomy, without anti­mitotic agents, with a minimum of 5 years follow up were evaluated. Only one eye of each patient was studied. The success rates for IOP control in POAG and CPACG were statistically analysed.

Results: Sixty‐four eyes of 64 patients were studied. The overall probability of success of trabeculectomy in controlling IOP to ≤21 mmHg with or without additional topical antiglaucoma medication was 0.94 and 0.88 at 5 and 10 years, respectively. There was no statistically significant difference in the qualified and absolute success rates for IOP control between POAG and CPACG eyes (log rank test P= 0.6, 0.88, respectively). Twelve of 38 CPACG eyes had a two‐line decrease in visual acuity as compared to four of 26 POAG eyes (P = 0.17). Progression or development of a cataract was the most common cause of visual decline.

Conclusions: Trabeculectomy without antimetabolite use appears to be efficacious in lowering IOP and in visual field preservation over a period of 10 years in both POAG and CPACG. Development/progression of cataract especially in eyes with chronic angle closure glaucoma after trabeculectomy must be considered an important issue.
Evaluation of contact versus non‐contact diode laser cyclophotocoagulation for refractory glaucomas using similar energy settings
Authors: Agarwal Harish C , Gupta Viney , Sihota Ramanjit
Published: February 2004

Purpose: To compare the efficacy of contact and non‐contact techniques of diode transscleral cyclophotocoagulation (TSCPC) in patients with refractory glaucoma in a prospective randomized manner.

Methods: Sixty eyes with refractory glaucoma were randomly treated with either the contact or non‐contact technique of diode TSCPC and followed up for a minimum of 12 months. A standard protocol of 1500 mW for 2 s per spot, with 40 spots over the entire 360° circumference was followed for all eyes in both groups.

Results: The reduction of mean baseline intraocular pressure (IOP) from 44.5 ± 7.4 mmHg to 14.8 ± 1.8 mmHg with the contact mode was not significantly different from that in the non‐contact mode of 41.9 ± 8.8 mmHg reduced to 14.5 ± 1.5 mmHg (P = 0.34). The probability of IOP survival (<22 mmHg) at 1 year using the Kaplan−Meier plot was better using the contact mode, although the results did not achieve statistical significance. However, the average repeat treatments per eye with the non‐contact mode (1.6 ± 0.7) was significantly higher than with the contact method (1.2 ± 0.6; P < 0.05).

Conclusion: Using an energy setting of 3 J per spot, both the contact and non‐contact methods of laser delivery were found to be equally effective in lowering IOP in eyes with refractory glaucoma.
Management of isolated orbital floor blow‐out fractures: a survey of Australian and New Zealand oral and maxillofacial surgeons
Authors: Lynham Anthony J , Chapman Patrick J , Monsour Frank NT , Snape Leslie , Courtney David J , Heggie Andrew A , Jones Robert H , McKellar Geoffrey M
Published: February 2004

Background: This is the first report of involvement of Australian and New Zealand oral and maxillofacial surgeons in the management of isolated orbital floor blow‐out fractures and was conducted to obtain comparisons with the results from a recent similar survey of British oral and maxillofacial surgeons.

Methods: A questionnaire survey was sent to all 113 practising members of the Australian and New Zealand Association of Oral and Maxillofacial Surgeons in April 2002 with a second mailout 1 month later.

Results: Sixty‐nine per cent of the respondents were referred isolated orbital floor blow‐out fractures for manage­ment, and just over half of these respondents estimated that 50% or more of the cases went to surgery. The materials most commonly used in orbital floor reconstruction were resorbable membrane for small defects and autologous bone for large defects.

Conclusion: As in Britain, management of isolated orbital floor blow‐out fractures comprises part of the surgical spectrum for many oral and maxillofacial surgeons in Australia and New Zealand. The management protocol was observed to be very similar between the two groups.
Pattern of orbital exenteration in a tertiary eye care centre in India
Authors: Pushker Neelam , Kashyap Seema , Balasubramanya Ramamurthy , Bajaj Mandeep S , Sen Seema , Betharia Subhash M , Ghose Supriyo
Published: February 2004

Purpose: This study aimed to determine the clinical indications for orbital exenteration, profile of these patients and clinicopathological correlations, and to compare these results with previous published data.

Methods: A retrospective analysis was conducted of exenterations performed in adults at a tertiary eye care centre in India over a period of 10 years (January 1990 to December 2000). Patient records were reviewed to obtain demographic data, presenting symptoms and their duration, laterality, and clinical and histopathological diagnosis.

Results: A total of 26 cases were identified. Patients ranged in age from 32 to 72 years (mean ± SD 58.7 ± 9.23 years). No sex predilection was observed. Classification of cases on histopathological criteria showed that exenterations were performed mostly for squamous cell carcinoma (10 cases), followed by sebaceous gland carcinoma (six cases) and basal cell carcinoma (two cases) of the eyelid. Conjunctival malignant melanoma contributed to 5 of 26 cases of exenteration. Adenoid cystic carcinoma of the lacrimal gland (one case), neurofibroma (one case) and orbital fungal infection (one case) were the other indications of exenteration. The clinicopathological correlation was 100% for squamous cell carcinoma, 100% for basal cell carcinoma, 80% for malignant melanoma and 75% for sebaceous gland carcinoma.

Conclusion: Exenteration is mainly performed as a life‐saving treatment for advanced malignant tumours with epithelial tumours being the commonest. In comparison to previous published data, the indications of surgery in India differed, as squamous cell carcinoma and sebaceous gland carcinoma were the commonest indications for exenteration.
Review of the effect of the dosing interval for inhaled corticosteroids in asthma control
Authors: Singer R. , Wood‐Baker R.
Published: February 2004

Abstract

Background: Asthma is recognized as an inflammatory disease of the airways and treatment includes anti‐inflammatory agents such as corticosteroids. Inhaled corticosteroids (ICS) are widely prescribed for long‐term prophylaxis, yet their optimal dosing interval is not clear.

Aims: To determine whether the dosing interval of ICS affects asthma control.

Methods: We performed an electronic search of the literature to identify studies on the dosing interval of ICS in asthmatic subjects. Data were extracted from suitable studies by two independent researchers and, where possible, a meta‐analysis performed.

Results: A total of 4267 titles were retrieved, of which 13 met inclusion and exclusion criteria and 11 had extractable data. There were no significant differences between outcomes for: (i) once daily vs twice daily administration (7 trials, 810 subjects), (ii) once daily vs four times daily administration (2 trials, 68 subjects) and (iii) twice daily vs four times daily administration (4 studies, 111 subjects). There was a variety of outcomes used to assess differences between dosing intervals. These included symptom scores, lung function, use of rescue medication and adverse drug effects. The number of subjects that could be included in the statistical analysis of any of such outcomes was small, much smaller than the total sample size.

Conclusions: There was no significant difference in measures of asthma control between the assessed dosing intervals of ICS. Current evidence indicates that single daily administration of ICS produces equivalent asthma control to multiple daily administration. (Intern Med J 2002; 32: 72–78)
Implication of Rho‐associated kinase in the elevation of extracellular dopamine levels and its related behaviors induced by methamphetamine in rats
Authors: Narita Minoru , Takagi Misa , Aoki Kazue , Kuzumaki Naoko , Suzuki Tsutomu
Published: February 2004

A growing body of evidence suggests that several protein kinases are involved in the expression of pharmacological actions induced by a psychostimulant methamphetamine. The present study was designed to investigate the role of the Rho/Rho‐associated kinase (ROCK)‐dependent pathway in the expression of the increase in extracellular levels of dopamine in the nucleus accumbens and its related behaviors induced by methamphetamine in rats. Methamphetamine (1 mg/kg, subcutaneously) produced a substantial increase in extracellular levels of dopamine in the nucleus accumbens, with a progressive augmentation of dopamine‐related behaviors including rearing and sniffing. Methamphetamine also induced the decrease in levels of its major metabolites, 3,4‐dihydroxyphenylacetic acid (DOPAC) and homovanilic acid (HVA). Both the increase in extracellular levels of dopamine and the induction of dopamine‐related behaviors by methamphetamine were significantly suppressed by pretreatment with an intranucleus accumbens injection of a selective ROCK inhibitor Y‐27632. In contrast, Y‐27632 had no effect on the decrease in levels of DOPAC and HVA induced by methamphetamine. Under these conditions, there were no changes in protein levels of membrane‐bound RhoA in the nucleus accumbens following methamphetamine treatment. It is of interest to note that the microinjection of Y‐27632 into the nucleus accumbens failed to suppress the increases in extracellular levels of dopamine, DOPAC, and HVA in the nucleus accumbens induced by subcutaneous injection of a prototype of µ‐opioid receptor agonist morphine (10 mg/kg). Furthermore, perfusion of a selective blocker of voltage‐dependent Na+ channels, tetrodotoxin (TTx) into the rat nucleus accumbens did not affect the increase in extracellular levels of dopamine in the rat nucleus accumbens by methamphetamine, whereas the morphine‐induced dopamine elevation was eliminated by this application of TTx. The extracellular level of dopamine in the nucleus accumbens was also increased by perfusion of a selective dopamine re‐uptake inhibitor 1‐[2‐[bis(4‐fluorophenyl)methoxy]‐4‐(3‐phenylpropyl)piperazine (GBR‐12909) in the nucleus accumbens. This effect was not affected by pretreatment with intranucleus accumbens injection of Y‐27632. These findings provide first evidence that Rho/ROCK pathway in the nucleus accumbens may contribute to the increase in extracellular levels of dopamine in the nucleus accumbens evoked by a single subcutaneous injection of methamphetamine. In contrast, this pathway is not essential for the increased level of dopamine in this region induced by morphine, providing further evidence for the different mechanisms of dopamine release by methamphetamine and morphine in rats.