bluuebunny/crossref_metadata_2025 huggingface dataset:
Long‐Term Precipitation Database, Reynolds Creek Experimental Watershed, Idaho, United States
Authors: Hanson C. L.
Published: February 2004

An extensive precipitation database has been developed over the past 35 years with the first records starting in January 1962 and going through September 1996 from the Reynolds Creek Experimental Watershed located near the north end of the Owyhee Mountains in southwest Idaho. Precipitation ranges from 236 mm on the lowest elevations at the north end of the watershed to 1123 mm at the southwest corner of the watershed. There are continuous 35 year records available for 12 sites, 20–32 year records available for 8 sites, 10–19 year records available for 25 sites, and 4–9 year records for 8 sites for a total of 53 sites. All of these data have been stored as breakpoint and hourly records in the U.S. Department of Agriculture, Agricultural Research Service, Northwest Watershed Research Center database. These breakpoint and hourly data are available from the anonymous ftp site: ftp.nwrc.ars.usda.gov.
Long‐Term Soil Water Content Database, Reynolds Creek Experimental Watershed, Idaho, United States
Authors: Seyfried M. S. , Murdock M. D. , Hanson C. L. , Flerchinger G. N. , Van Vactor S.
Published: February 2004

We describe long‐term soil water data collected at the Reynolds Creek Experimental Watershed (RCEW). Data were collected for 10–25 years at 18 sites representing different climatic regimes and soils in the RCEW. Soil profile data are also available. High correlation between neutron probe and lysimeter measurements are the basis for assessing the accuracy of neutron probe–measured changes in soil water content. These data are available to the public via the U.S. Department of Agriculture, Agricultural Research Service, Northwest Watershed Research Center anonymous ftp site ftp.nwrc.ars.usda.gov.
Long‐Term Lysimeter Database, Reynolds Creek Experimental Watershed, Idaho, United States
Authors: Seyfried M. S. , Hanson C. L. , Murdock M. D. , Van Vactor S.
Published: February 2004

We describe long‐term lysimeter data collected at the Reynolds Creek Experimental Watershed. The length of record is >15 years for lysimeters at two sites representing different soil and climatic conditions. These data describe changes in soil water during the snow‐free season. In addition to measuring changes in total soil water, soil water content profiles and soil temperature profiles were measured within or adjacent to the lysimeters and are reported in accompanying reports. These data are available to the public via the U.S. Department of Agriculture, Agricultural Research Service, Northwest Watershed Research Center anonymous ftp site ftp.nwrc.ars.usda.gov.
Role of organic nitrogen in the nitrogen cycle of a high‐elevation catchment, Colorado Front Range
Authors: Williams Mark W. , Hood Eran , Caine Nel
Published: February 2004

Here we report on 3 years (1996–1998) of measurements of organic and inorganic nitrogen (N) fluxes to and from Green Lakes Valley, a high‐elevation ecosystem in the Colorado Front Range of the Rocky Mountains. Nitrate‐N (NO3−N) was the dominant form of N in both precipitation and stream water. Annual precipitation contained 52% NO3−N, 32% ammonium‐N (NH4−N), 9% dissolved organic N (DON), and 7% particulate organic N (PON). Annual export of N in streamflow was composed of 70% NO3−N, 4% NH4−N, 14% DON, and 12% PON. Thus the percentage of organic N increased from 16% of total N in precipitation to 26% of total N in streamflow. Subtracting inputs from outputs, Green Lakes Valley always shows net retention of inorganic N. The only form of N that showed net export was DON. DON export was low (0.18 to −0.13 kg ha−1 yr−1), with net export recorded in 2 years and basin retention recorded in 1 year. There was a seasonal pattern in the concentrations of inorganic N (NO3−N+NH4−N) and organic N (DON+PON). Concentrations of inorganic N were ∼15–25 μmol L−11 during base flow, increased to ∼30 μmol L−1 on the rising limb of the hydrograph during snowmelt runoff, then decreased to ∼5 μ L−1 on the recession limb of late summer, with a return to base flow values in the autumn. In contrast, organic N was 7–15 μ L−1 during base flow and decreased to near or below detection limits on the rising limb of the hydrograph, with a gradual but consistent increase on the recession limb and on into the autumn. The amount of N in dissolved organic matter changed over time, with the dissolved organic carbon (DOC):DON ratio decreasing from ∼45 on the rising limb of the hydrograph to <20 in the autumn. Spatially, there was a striking difference in the ratios of NO3−N and DON between talus and tundra areas. Nitrate concentrations in surface water draining talus areas were always greater than DON. In contrast, DON concentrations in surface water draining tundra areas were always greater than NO3−N. Concentrations of DON were not significantly correlated with DOC (R2 = 0.04, p > 0.05), indicating that controls on DON export may be different than controls on DOC export. Our results suggest that the ratio of the annual mass flux of inorganic N to organic N in stream waters may provide a novel index to evaluate the N status of terrestrial ecosystems from various biomes.
Downstream fining in a rapidly aggrading gravel bed river
Authors: Gomez Basil , Rosser Brenda J. , Peacock David H. , Hicks D. Murray , Palmer Julie A.
Published: February 2004

Downstream changes in particle size that occur in the Waipaoa River, a 104‐km‐long gravel bed river in which rapid aggradation in the historic (post‐1800) period was triggered by the conversion of native forest to pasture, are summarized in this paper. The textural data presented are unique for a field situation, not only because of the spatial resolution and extent of the sampling program but also because they provide information about the pattern of fining at different points in time. They are supported by equally comprehensive topographic survey data from which local rates of aggradation can be derived. Despite variability induced by lateral sediment inputs, there is an essentially continuous pattern of fining along the entire length of the river. Fining occurs in both the fine and coarse size fractions of the bed material. The highest rates of fining occur in the larger percentiles of the subsurface bed material and in the surface bed material. Downstream fining in the Waipaoa River appears to be a response to changes in flow hydraulics that are regulated by the concave configuration of the long profile. The fining gradient developed rapidly (in <45 years). It does not appear to be influenced by the rate of aggradation (nor the overall rate of sediment supply to the channel system), because, in the short term, aggradation has a negligible impact on the inherited form of the long profile.
Confidence intervals for expected moments algorithm flood quantile estimates
Authors: Cohn Timothy A. , Lane William L. , Stedinger Jery R.
Published: February 2004

Historical and paleoflood information can substantially improve flood frequency estimates if appropriate statistical procedures are properly applied. However, the Federal guidelines for flood frequency analysis, set forth in Bulletin 17B, rely on an inefficient “weighting” procedure that fails to take advantage of historical and paleoflood information. This has led researchers to propose several more efficient alternatives including the Expected Moments Algorithm (EMA), which is attractive because it retains Bulletin 17B's statistical structure (method of moments with the Log Pearson Type 3 distribution) and thus can be easily integrated into flood analyses employing the rest of the Bulletin 17B approach. The practical utility of EMA, however, has been limited because no closed‐form method has been available for quantifying the uncertainty of EMA‐based flood quantile estimates. This paper addresses that concern by providing analytical expressions for the asymptotic variance of EMA flood‐quantile estimators and confidence intervals for flood quantile estimates. Monte Carlo simulations demonstrate the properties of such confidence intervals for sites where a 25‐ to 100‐year streamgage record is augmented by 50 to 150 years of historical information. The experiments show that the confidence intervals, though not exact, should be acceptable for most purposes.
Are models predicting a realistic picture of vertical total electron content?
Authors: Coïsson P. , Radicella S. M. , Leitinger R. , Ciraolo L.
Published: February 2004

The present work analyzes results coming from global maps of ionospheric total electron content (TEC) obtained from observations and from different empirical models like the International Reference Ionosphere (IRI), the model family developed at Trieste and Graz (NeQuick, COSTprof, and NeUoG‐plas), and the GPS operational model (formulation by J. A. Klobuchar). Since they still appear in the context of assessment studies we have also included “old” models like the Bent model. The attention is focused on situations which occurred in the present period of high solar activity, pointing out features like the equatorial anomaly and polar regions, which are crucial test regions for ionospheric TEC models. Experimental estimates of slant TEC from International GPS Service (IGS) stations have been compared particularly with the predictions of the NeQuick and GPS models. A very simple picture of the ionosphere like the one given by the GPS operational model appears to be insufficient to reproduce the global complex behavior of the ionosphere, as it is needed for assessment studies or for modern operational real‐time corrections of transionospheric propagation errors. The IRI estimates of TEC still present serious problems, essentially owing to the topside under high solar activity conditions, and the model cannot be integrated to heights above 2000 km. With processing resources suitable for real‐time operation, it seems that the NeQuick model can give a more widely reliable picture of the TEC estimated from GPS measurements. Computing times for this model are considerably smaller than for more complex models like NeUoG‐plas.
Geographic distribution of major crops across the world
Authors: Leff Billie , Ramankutty Navin , Foley Jonathan A.
Published: January 2004

Humans have transformed the surface of the planet through agricultural activities, and today, ∼12% of the land surface is used for cultivation and another 22% is used for pastures and rangelands. In this paper, we have synthesized satellite‐derived land cover data and agricultural census data to produce global data sets of the distribution of 18 major crops across the world. The resulting data are representative of the early 1990s, have a spatial resolution of 5 min. (∼10 km), and describe the fraction of a grid cell occupied by each of the 18 crops. The global crop data are consistent with our knowledge of agricultural geography, and compares favorably to another existing data set that partially overlaps with our product. We have also analyzed how different crops are grown in combination to form major crop belts throughout the world. Further, we analyzed the patterns of crop diversification across the world. While these data are not sufficiently accurate at local scales, they can be used to analyze crop geography in a regional‐to‐global context. They can also be used to understand the global patterns of farming systems, in analyses of food security, and within global ecosystem and climate models to understand the environmental consequences of cultivation.
S‐wave energy estimation of small‐earthquakes in the western Nagano region, Japan
Authors: Matsuzawa Takanori , Takeo Minoru , Ide Satoshi , Iio Yoshihisa , Ito Hisao , Imanishi Kazutoshi , Horiuchi Shigeki
Published: February 2004

We estimate the S‐wave energy radiated by nine small earthquakes (MW 1.2–2.4) that occurred in the western Nagano region, Japan. First, we obtain the S‐wave energy radiated by 156 earthquakes (MW 0.8–2.6) below 60 Hz in the frequency domain. We separate the radiated energy spectra and the site amplification functions using a least squares inversion method including corrections for the S‐wave radiation pattern at the source and the attenuation along the path. Then, we assume an ω2‐model to determine the corner frequencies for the nine earthquakes by using an empirical Green's function (EGF) method to remove the site and attenuation effects. Using the obtained corner frequencies, we then calculate radiated energy using these source models above 60 Hz. Our result indicates that the ratio of the seismic moment and S‐wave energy is between 8 × 10−6 and 7 × 10−5.
On the role of the NAO in the recent northeastern Atlantic Arctic warming
Authors: Rogers Jeffrey C. , Wang Sheng‐Hung , Bromwich David H.
Published: January 2004

Studies such as those by Zhang et al. [1998] and Peterson et al. [2003] suggest that the northeastern Atlantic Arctic warmed in the early 1990s and that regional sea level pressure (SLP) variations and the NAO may be responsible. Sea surface temperature changes in Fram Strait and the Barents Sea depend, respectively, on SLP variations over the Barents Sea and Norwegian Sea. Since winter 1972, SLP over the Barents and Norwegian Seas has been unusually low during NAO+ winters. Little pressure field change occurred during NAO‐ winters or around the Denmark Strait, the normal location of the Icelandic Low. Simultaneously, the NAO+ mode became highly persistent on a month‐to‐month basis throughout the NAO+ winters and ultimately throughout all seasons during a multiyear episode in which the Arctic reached peak warming. A similar NAO+ persistence episode is shown to have occurred from 1920–1925, during another notable Arctic warming event.
Arctic decadal variability: An auto‐oscillatory system of heat and fresh water exchange
Authors: Dukhovskoy Dmitry S. , Johnson Mark A. , Proshutinsky Andrey
Published: February 2004

This paper presents a mechanism of decadal variability in the Artic Ocean–GIN Sea (Greenland, Iceland and Norwegian Seas) atmosphere‐ice‐ocean system. We hypothesize that Arctic variability is regulated by heat and freshwater exchange between the Arctic Ocean and the GIN Sea. The interaction between basins is weak during anticyclonic circulation regimes (low AO/NAO) and strong during cyclonic circulation regimes (high AO/NAO). Regime shifts are controlled by the system itself through oceanic and atmospheric gradients (dynamic height and surface air temperature) that increase during the anticyclonic regime and decrease during the cyclonic regime. This conceptual mechanism for Arctic decadal variability has been reproduced in a model experiment. Both model results and observational data support the suggested mechanism.
Electromagnetic ion cyclotron waves in the subsolar region under normal dynamic pressure: Wind observations and theory
Authors: Farrugia C. J. , Gnavi G. , Gratton F. T. , Matsui H. , Torbert R. B. , Lepping R. P. , Oieroset M. , Lin R. P.
Published: February 2004

We analyze observations on electromagnetic ion cyclotron waves (EICWs) in the plasma depletion layer (PDL) made by Wind on three inbound passes of the magnetosheath near the stagnation streamline and model the observations using recent theory [Gnavi et al., 2000]. While one pass was under substantially high solar wind dynamic pressure Pdyn (∼6.4 nPa), two passes were under typical Pdyn at 1 AU (∼2.2 nPa), which allows us to extend the study of EICWs into this lower pressure regime. Two passes were under steady, and one under time varying, conditions. We subdivide the PDL into inner, middle, and outer regions and compute in each the power spectral density (PSD) of the magnetic fluctuations transverse to the background field, using high‐resolution (∼11 samples/s) data from the Magnetic Field Investigation (MFI). The theory solves the kinetic dispersion relation in a plasma composed of electrons, protons, and α particles, each species modeled by bi‐Maxwellian distribution functions. Results and trends indicated by the theory are found to be in qualitative agreement with the data. The observations show (1) at the inner PDL position the spectral PSD weakens as Pdyn decreases, and (2) the frequency range of emission shifts downward with diminishing Pdyn. Comparing observations with the classification of spectral types in the PDL under compressed conditions proposed by Anderson et al. [1994], we find a preponderance of so‐called low and continuous spectra and only marginally bifurcated spectra with activity peaks below and above the alpha‐resonance frequency. In general, as a consequence of smaller Pdyn, near the magnetopause our temperature anisotropies Ap are at the lower end of values characterizing bifurcated spectra in AMPTE/CCE.
Magnetic properties of the Old Crow tephra: Identification of a complex iron titanium oxide mineralogy
Authors: Lagroix France , Banerjee Subir K. , Jackson Mike J.
Published: January 2004

The mineralogy and grain‐size distribution of the Fe‐Ti oxide population of the Old Crow tephra bed, outcropping at the Halfway House loess deposit in central Alaska, are characterized through multiple low‐ and high‐temperature magnetization experiments. The characterization is facilitated by heavy liquid separation of the bulk sample into a low‐density (<2850 kg/m3, LD) and high‐density (≥2850 kg/m3, HD) fraction. Three phases of the magnetite‐ulvöspinel solid solution series, Fe3−xTixO4, x = 0, 0.1, and 0.3 are identified along with one phase of the ilmenite‐hematite solid solution series, Fe2−yTiyO3, y = 0.83. All four phases are present in both density separates, where coarser grains dominate the HD sample and finer more oxidized grains dominate in the LD sample. Low‐temperature frequency dependence and field dependence of both the in‐phase and quadrature components of magnetic susceptibility are found particularly useful in identifying the magnetic ordering temperature of titanohematite phases with y > 0.8 and may play an equally important role as magnetic indicator of titanomagnetite. Furthermore, we demonstrate the ability of low‐temperature magnetism to locate a 1 mm thick tephra bed dispersed in loess over 10 cm depth, through the identification of very low concentrations of a titanohematite phase with y = 0.9. The potential for advancing regional correlation of sedimentary deposits through the identification of Fe‐Ti oxides common to tephra beds by low‐temperature magnetism is illustrated in this study.
Impact of salinity on the 1997 Indian Ocean dipole event in a numerical experiment
Authors: Masson Sébastien , Boulanger Jean‐Philippe , Menkes Christophe , Delecluse Pascale , Yamagata Toshio
Published: February 2004

The role of salinity during the onset and growth of the 1997 Indian Ocean Dipole Mode event is explored with an ocean general circulation model thoroughly validated to observations. In fall 1997, anomalous easterlies drive an Indian Ocean equatorial circulation similar to that regularly observed in the Pacific Ocean: a South Equatorial Current (SEC) near the equator, an Equatorial Under Current (EUC) subsurface, and intense upwelling in the eastern part of the basin. The SEC transports westward the eastern Indian Ocean fresh pool creating, along the equator, a shallow salinity stratification favoring the creation of a barrier layer. In our experiment, the shallow top of the thermocline limits the barrier layer thickness to about 10 m; nevertheless, salinity has a significant impact on sea surface temperature (SST). Indeed, the shallow salinity stratification along the equator traps the wind forcing in a thin surface mixed‐layer. The reduction of wind momentum penetration decreases the deceleration of the EUC, and the greater amplitude of wind momentum input in surface layers strengthens the SEC. This intensification of the equatorial zonal circulation increases the Sumatra upwelling and its associated meridional circulation. This strengthening of the whole equatorial circulation shifts upward the thermohaline structure and reinforces the cold SST anomaly off Sumatra by about 20%. Overall, the effect of salinity on the 1997 Indian Ocean Dipole is to reinforce the oceanic anomalies favoring a strengthening of the air‐sea interactions.
Differences between surface and column atmospheric CO2 and implications for carbon cycle research
Authors: Olsen Seth C. , Randerson James T.
Published: January 2004

We used a three‐dimensional atmospheric transport model to investigate several aspects of column CO2 that are important for the design of new satellite‐based observation systems and for the interpretation of observations collected by Sun‐viewing spectrometers. These aspects included the amplitude of the diurnal cycle and how it is related to surface fluxes, the amplitude and phase of the seasonal cycle, and the magnitude of the north‐south hemispheric gradient. In our simulation, we found that column CO2 had less variability than surface CO2 on all scales. The annual mean column CO2 north‐south gradient and seasonal cycle amplitude were approximately one half of their surface counterparts and the column CO2 diurnal amplitude rarely exceeded 1 ppm. A 1 Gt C yr−1 Northern Hemisphere carbon sink decreased the north‐south column CO2 gradient by ∼0.4 ppm.
Paleorecharge by the Niger River (Mali) Deduced from groundwater geochemistry
Authors: Fontes Jean‐Charles , Andrews John N. , Edmunds W. Michael , Guerre Alain , Travi Yves
Published: February 2004

Stable isotopes, major elements, trace elements, and noble gases in groundwater from northern Mali permit a reconstruction of the paleohydrology of the Sahelian and sub‐Saharan regions of west Africa. Major floods of the Niger River during the more humid episodes of the Holocene, probably associated with northward migration of the interior river delta (flood zone), were responsible for groundwater recharge. A marine aerosol input, somewhat modified by rock‐water interaction, dominates the groundwater chemistry. Stable isotope compositions distinguish the Saharan zone groundwater from waters recharged in the Sahelian zone south of the Azaouad ridge. Carbon 14 dating shows that whereas the latter are modem, the Saharan zone was recharged in the Early to Middle Holocene. Noble gas contents suggest that recharge north of Azaouad occurred under cooler climatic conditions than presently prevail.
Light stable isotope systematics of large‐scale hydrologic regimes in California and Nevada
Authors: Ingraham Neil L. , Taylor Bruce E.
Published: February 2004

Surface waters, shallow groundwaters, and precipitation samples were collected along three traverses, which begin at the California coast and are oriented in an east–west manner, roughly parallel to the atmospheric flow path of meteoric water. The hydrogen isotope compositions from short‐term precipitation records varied as much as 40‰ at one location and were not representative of the average annual isotopic composition of precipitation. The hydrogen isotope ratios of surface waters and shallow groundwaters distinguish segments with isotopic variations that correlate with measured vertical fluxes of meteoric water. One coastal segment appears to closely approximate an open system in which precipitation dominates over evapotranspiration. Most segments are described by rather regular variations in δD: 3–45‰ per 100 km, which represent different degrees of closure of the hydrologic system caused by variable partitioning of precipitation between runoff and evapotranspiration. All partially closed systems imply terrestrial recycling of water. A simple model estimates this amount to be about 20% across northern and central California. Three segments, representing the Great Basin, show virtually no geographic variation and appear to represent isotopically closed systems.
Approaches to groundwater quality protection in the western United States
Authors: MacDonnell Lawrence J. , Guy David J.
Published: February 2004

Groundwater sources supply about 38% of all water uses in the 19 western states. Most attention has focused on withdrawals from these sources but, in recent years, concerns have been raised about the quality of groundwater. At the federal level, several laws address aspects of groundwater quality but protection of this resource has been left primarily to the states. Western state groundwater quality protection programs were comprehensively surveyed relating to six aspects: assessment of existing groundwater quality, levels of protection established, controls placed on sources of contamination, use of special management areas, coordination among the involved agencies, and program enforcement. The survey revealed several promising approaches in each of these areas in the western states which are set forth in the paper. Most of these approaches have been established in recent years, reflecting the greatly increased state attention to groundwater quality protection. It is too early to evaluate the effectiveness of particular approaches. In general the western states are taking a more active role in groundwater quality protection, and several states recently have established comprehensive programs for this purpose. Others, however, are still considering approaches to protection of groundwater quality and may find the discussion in this paper of some use.
Steady fluid flow and travel times in partially saturated fractures using a discrete air‐water interface
Authors: Rasmussen Todd C.
Published: February 2004

Fracture flow under conditions of partial fluid saturation is studied where a portion of the fracture is filled with water and the remaining portion is filled with air. A discrete air‐water interface is used to separate the saturated from the drained regions within the fracture. A laboratory flow experiment is presented which demonstrates the interface concept. The steady state air‐water interface position is observed by maintaining a circular water source at constant positive pressure head between two vertical glass plates. An analytic solution to the flow problem is compared to the observed interface position and to simulated results which assume that a constant capillary pressure head can be assigned along the interface. Simulations performed for a hypothetical vertical fracture indicate zones of positive and negative pressure head in the saturated zone as well as an air‐filled zone. For the hypothetical fracture examined, fluid travel times are not substantially changed as fracture saturation decreases. This result may not hold generally for all fractures.
A stochastic model of reactive solute transport with time‐varying velocity in a heterogeneous aquifer
Authors: Kabala Z. J. , Sposito Garrison
Published: February 2004

The cumulant expansion method, used previously by Sposito and Barry (1987) to derive an ensemble average transport equation for a tracer moving in a heterogeneous aquifer, is generalized to the case of a reactive solute that can adsorb linearly and undergo first‐order decay. In the process we also generalize the Van Kampen (1987) result for the cumulant expansion of a multiplicative stochastic differential equation containing a time‐dependent sure matrix. The resulting partial differential equation exhibits terms with field‐scale coefficients that are analogous to those in the corresponding nonstochastic local‐scale transport equation. There are also new terms in the third‐ and fourth‐order spatial derivatives of the ensemble average concentration. It is demonstrated that the effective solute velocity for the aqueous concentration, not that for the total concentration (aqueous plus sorbed), is relevant for a field‐scale description of solute transport. The field‐scale effective solute velocity, dispersion coefficient, retardation factor, and first‐order decay parameters, unlike their local‐scale counterparts, are time‐dependent because of autocorrelations and cross correlations among the random local solute velocity, retardation factor, and first‐order decay constant. It is shown also that negative cross correlations between the random tracer solute velocity and the inverse of the local retardation factor may produce both enhanced dispersion and a temporal growth in the field‐scale retardation factor. These effects are possible in any heterogeneous aquifer for which a stochastic description of aquifer spatial variability is appropriate.
Mass arrival of reactive solute in single fractures
Authors: Cvetkovic Vladimir D.
Published: February 2004

Transport of reactive solute in individual fractures is investigated. Solute advection is coupled with matrix diffusion that is assumed perpendicular to the fracture plane. Fluid advection in the fracture is viewed as intersecting flow paths, whereby the advection velocity of a solute particle varies along individual streamlines. Solute mass arrival at a fixed position averaged in the direction perpendicular to the mean flow is examined. The dispersion in the solute breakthrough arises because of the different advection travel times and varying mass flux along individual streamlines. The fracture is conceptualized as a two‐dimensional porous medium with a statistically anisotropic, spatially varying transmissivity with a given correlation structure; the assumed anisotropy condition is consistent with elongated, channel‐like flow paths that have been observed in single fractures. Approximate expressions for the first two moments of solute travel time are used to illustrate the sensitivity to different correlation models for the fracture transmissivity. In particular, the finite correlation scale model, the self‐similar (fGn) model, and the channel model are considered. The expected cumulative mass arrival is more sensitive to the assumed correlation model for lower rates of matrix diffusion. The derived expression for the mass arrival can also be used for analyzing the effect of nonequilibrium sorption‐desorption reactions in single fractures.
Boundary element solution for stochastic groundwater flow: Random boundary condition and recharge
Authors: Cheng A. H.‐D. , Lafe O. E.
Published: February 2004

This paper presents an integral equation technique for solving stochastic boundary value problems in groundwater flow. The aquifer considered has deterministic hydraulic conductivity but is subject to random boundary condition and domain recharge. Using the distribution of fictitious sources and dipoles, stochastic integral equations for the mean and covariance of head and flux are derived. An iterative boundary element technique is applied for numerical solution. Two one‐dimensional examples are examined and compared with exact solution. A two‐dimensional problem is then presented.
Kinetics of chemical weathering in b horizon spodosol fraction
Authors: Asolekar S. R. , Valentine R. L. , Schnoor J. L.
Published: February 2004

Studies on a B horizon soil from Maine have been conducted to determine the weathering rate dependence on hydrogen ion concentration in soil solution. Effects of soil concentration and solution chemistry on chemical weathering rate were also investigated. Studies were conducted using a laboratory pH‐stat semicontinuous reactor at pH 2.7 and 3.5 for two concentrations of B horizon soil. Homogenized B horizon soil in the size range 63–125 μm was washed in deionized water and acetone and used without further treatment. Results obtained from titrations of 10, 30, and 100 g/L of soil at a constant pH of 2.7 suggest that the weathering rate, expressed in μeq H+/hr/g soil, does not depend on the soil concentration in the pH‐stat reactor. In order to test the effect of solute concentration on weathering rate, experiments were performed at two different concentrations of accumulated solutes. Weathering rates were the same at the two solute concentrations, indicating that significant back reactions were not likely occurring. The weathering rate at pH 2.7 was estimated in the range 0.53–0.93 μeq H+/hr/g soil, at pH 3.0 as 0.52 μeq H+/hr/g soil, at pH 3.5 as 0.36 μeq H+/hr/g soil, and at pH 4.0 as 0.04 μeq H+/hr/g soil. Assuming a weathering rate proportional to {H+}m, the fractional order m was determined to be approximately 0.8. Results were consistent with a surface‐reaction‐controlled dissolution mechanism.
National estimates of the recreational value of streamflow
Authors: Hansen LeRoy T. , Hallam Arne
Published: February 2004

This paper presents one practical method of valuing the recreational fishing benefits generated by a unit of water as it moves downstream. A cross‐sectional analysis is employed to estimate the change in individuals' fishing behavior due to a change in availability of fishery resources. A proxy for the availability of stream fishery resources is derived from the link between changes in streamflow consumption to changes in the quality of fishing downstream. The results show that marginal increases in streamflow can generate recreational benefits that exceed the marginal value of water in agriculture in some regions of the country.
Estimation of regional evaporation for a tallgrass prairie from measurements of properties of the atmospheric boundary layer
Authors: Munley William G. , Hipps Lawrence E.
Published: February 2004

Regional scale latent heat flux (LE) was estimated from rawinsonde soundings of the planetary boundary layer (PBL) over the Konza tailgrass prairie in July 1986. Two approaches were used to calculate LE: similarity theory and an algebraic solution of a conservation equation for water vapor in the PBL. Nine of the soundings were complete. However, the latter five soundings only recovered data for every sixth possible level. The results were compared with estimates made by an array of nine Bowen Ratio surface stations. Similarity theory, using vertically averaged values, produced estimates that were reasonably close to the surface values. However, the use of values at the top of the PBL resulted in large overestimation of the evaporation fluxes. When complete soundings were available, the conservation equation yielded estimates which agreed very well with surface values. The agreement was reduced for incomplete soundings. This is likely related to the sensitivity of the equation to uncertainties in the height of the inversion. Overall, the conservation equation produced estimates in closest agreement with the surface stations. The results suggest that adequate vertical resolution of measured profiles is important for proper estimation of regional surface fluxes.
Effect of interfacial forces on two‐phase capillary pressure—saturation relationships
Authors: Demond Avery H. , Roberts Paul V.
Published: February 2004

Quantitative descriptions of two‐phase flow in the subsurface require knowledge of the capillary pressure‐saturation relationships. The effect of interfacial forces on the drainage capillary pressure‐saturation relationship for organic liquid‐water systems is usually expressed by the ratio of the liquid‐liquid interfacial tensions as given by Leverett's (1941) function. To assess the appropriateness of this approach for primary drainage of organic liquid‐water systems typical of hazardous waste sites and to evaluate its extendability to spontaneous imbibition, measurements were made of these relationships for various immiscible liquid systems in unconsolidated sand. The results showed increasing deviations with decreasing interfacial forces between the measured values and those predicted by a ratio of interfacial tensions. To improve the predictive capability of Leverett's function, forms including the intrinsic contact angle and roughness were examined. Scaling of the capillary pressure relationships was best achieved by including a correction for both interface curvature and roughness. These corrections became significant for drainage for contact angles larger than 35°–55°, and for imbibition for contact angles larger than 15°–25°. None of the forms of Leverett's function examined predicted the increased residual saturation with decreasing interfacial forces observed in this study. Consequently, their ability to scale the measured data was predicated on posing the saturation of the wetting phase in terms of the variable effective saturation.
A method to assess lake responsiveness to future acid inputs using recent synoptic water column chemistry
Authors: Young Thomas C.
Published: February 2004

Two indices are presented for assessing the expected responsiveness of lakes to changes in external acid inputs. The first is the ratio of the sum of acidic anion to sum of base cation equivalents (CA/CB), which is a familiar index of lake response to past inputs; the second quantity is buffer intensity (β = −dCA/dpH), which serves as an index of lake pH sensitivity to changes in current inputs. Because the indices account for both capacity and intensity of pH buffering, the approach provides greater information on lake responsiveness to acidification than the more customary value, acid neutralizing capacity. The approach is applied to water quality data from the Environmental Protection Agency's Eastern Lake Survey and preliminary paleolimnological data from the PIRLA project (paleolimnological investigation of recent lake acidification). These applications suggest that the approach may yield a useful tool with which to evaluate existing data from sites considered for monitoring the effects of changing acid inputs on lake systems.
Analytical modeling of aquifer decontamination by pumping when transport is affected by rate‐limited sorption
Authors: Goltz Mark N. , Oxley Mark E.
Published: February 2004

Aquifer cleanup efforts at contaminated sites frequently involve operation of a system of extraction wells. It has been found that contaminant load discharged by extraction wells typically declines with time, asymptotically approaching a residual level. Such behavior could be due to rate‐limited desorption of an organic contaminant from aquifer solids. An analytical model is presented which accounts for rate‐limited desorption of an organic solute during cleanup of a contaminated site. Model equations are presented which describe transport of a sorbing contaminant in a converging radial flow field, with sorption described by (1) equilibrium, (2) first‐order rate, and (3) Fickian diffusion expressions. The model equations are solved in the Laplace domain and numerically inverted to simulate contaminant concentrations at an extraction well. A Laplace domain solution for the total contaminant mass remaining in the aquifer is also derived. It is shown that rate‐limited sorption can have a significant impact upon aquifer remediation. Approximate equivalence among the various rate‐limited models is also demonstrated.
Application of a multiprocess nonequilibrium sorption model to solute transport in a stratified porous medium
Authors: Brusseau Mark L.
Published: February 2004

The purpose of this work was to investigate the capability of a model, which explicitly accounts for multiple sources of nonequilibrium, to predict the transport of nonequilibrium sorption‐constrained solute in a stratified porous medium. Microaquifer experiments reported in the literature served as the source of the data that were analyzed. The best available information was used to identify values for all model input parameters, allowing the multiprocess nonequilibrium (MPNE) model to be used in a predictive mode. The prediction produced by the MPNE model provided a good description of the breakthrough curve obtained at a given velocity. A breakthrough curve obtained at a slower velocity could be simulated when the apparent velocity dependence of the physical nonequilibrium parameters was taken into account. Based on the reported results, the MPNE model would seem to provide a valid representation of sorption dynamics and solute transport for stratified systems influenced by sorption capacity heterogeneity and multiple sources of nonequilibrium. The relative and combined impact of interlayer mass transfer, chemical nonequilibrium, and sorption capacity heterogeneity on the transport of a sorbing solute was elucidated.
Precipitation chemistry in and ionic loading to an Alpine Basin, Sierra Nevada
Authors: Williams Mark W. , Melack John M.
Published: February 2004

Wet deposition of solutes to an alpine catchment in the southern Sierra Nevada was measured from October 1984 through March 1988. Rainfall had a volume‐weighted pH of 4.9, and snowfall had a volume‐weighted pH of 5.3. Acetic and formic acids were important components of all wet deposition, contributing 25–30% of the measured anions in snowfall and, through analysis of charge balance deficits, the same percentage in rainfall. The NO3− to SO42− equivalent ratio for all wet deposition was 1.16. Ammonium concentration was tenfold greater than H+ in rainfall; ammonium nitrate and ammonium sulfate appear to be the principal nitrate and sulfate containing aerosols in wet deposition. Snowmelt runoff (1985 and 1986) or snowpack runoff plus rainfall during the period of snowpack runoff (1987) supplied 90% of the annual solute flux from wet deposition to the catchment. The amount of snow water equivalence (mm m−2) and H+, SO42−, and Cl− (eq m−2) in cumulative snowfall measured on snowboards was similar to the accumulated deposition of these parameters measured in snowpils at midwinter and during maximum snow accumulation periods, while about 20% of the NO3− in snowfall was not stored in the winter snowpack. Dry deposition was therefore not an important contributor of H+, NO3−, and SO42− to the winter snowpack. The source of the ions in snowfall was air masses that originated over the Pacific Ocean, while low Cl− and Na+ relative to NO3− and NH4+ in rainfall indicate that local urban and agricultural areas were the major source of the ions in rainfall.
Numerical approximations of darcian flow through unsaturated soil
Authors: Warrick A. W.
Published: February 2004

The choice of appropriate intrablock approximations for the unsaturated hydraulic conductivity is a critical step for the numerical solution of Richards equation. Forms commonly used include arithmetic, geometric and harmonic averaging. The choice is most often based on convenience and custom. This study presents a framework for comparing any scheme for weighting the unsaturated hydraulic conductivity against the correct Darcian flow across a block for steady conditions. Such comparisons are carried out for a number of commonly used averages, and errors are shown to be alarmingly high in some cases. A scheme for approximately matching the correct Darcian flux is illustrated by two infiltration examples. In the first, the arithmetic and weighted schemes are superior to the geometric average when compared to a quasi‐analytical solution. For the second example, the weighted solution is slightly better than either the arithmetic or geometric averaging schemes. These examples also illustrate that an acceptable mass balance should not be used as a sole criterion for success as it can probably be attained with most schemes. The conclusions are believed relevant for algorithms which are pressure head based, water content based or other choices and for multidimensional as well as one‐dimensional flow problems.
Prediction of tracer plume migration in disordered porous media by the method of conditional probabilities
Authors: Rubin Yoram
Published: February 2004

The purpose of this study is to develop a method for predicting the spatial moments and concentration of a tracer plume conditional to locally measured data. We set this study in a probabilistic frame due to the inherent inability to characterize deterministically the flow domain. Our starting point is the Dagan (1984) conceptual model which relates the concentration to the translation of tagged elements of solute mass. Then, using Darcy's law and the flow equations, we describe that translation using a random function model for the velocity. Comparison with numerical simulations shows this model to be favorable for variances of the log conductivity as large as 2.56 (Dykstra‐Parsons coefficient of 0.8). It is shown how this random function model is correlated with the hydraulic head and conductivity fields, and furthermore, how it can be made conditional to measured data. It is concluded that conditioning improves predictions of the spatial moments of the tracer plume by making a more comprehensive use of available data and has a potential for a large range of applications.
Numerical calculation of equivalent grid block permeability tensors for heterogeneous porous media
Authors: Durlofsky Louis J.
Published: February 2004

A numerical procedure for the determination of equivalent grid block permeability tensors for heterogeneous porous media is presented. The method entails solution of the fine scale pressure equation subject to periodic boundary conditions to yield, upon appropriate averaging of the fine scale velocity field, the coarse scale or equivalent grid block permeability. When the region over which this coarse scale permeability is computed constitutes a representative elementary volume (REV), the resulting equivalent permeability may be interpreted as the effective permeability of the region. Solution of the pressure equation on the fine scale is accomplished through the application of an accurate triangle‐based finite element numerical procedure, which allows for the modeling of geometrically complex features. The specification of periodic boundary conditions is shown to yield symmetric, positive definite equivalent permeability tensors in all cases. The method is verified through application to a periodic model problem and is then applied to the scale up of areal and cross sections with fractally generated permeability fields. The applicability and limitations of the method for these more general heterogeneity fields are discussed.
One‐dimensional subsurface transport of a nonaqueous phase liquid containing sparingly water soluble organics: A front‐tracking model
Authors: Ryan Patrick A. , Cohen Yoram
Published: February 2004

A one‐dimensional multiphase mass transport model for the migration of a nonaqueous phase liquid (NAPL) containing sparingly water soluble organics in the unsaturated soil zone is described. The multiphase NAFL transport (MUNT) model consists of a two‐phase immiscible flow model linked to a four‐phase chemical transport model. The immiscible flow model incorporates a front‐tracking algorithm to determine the front of the invading NAPL as a function of penetration time. The NAPL penetration toward ground water is shown to be a function of four diniensionless groups: NAPL capillary number, the ratio of the NAPL Reynolds number to the NAPL Froude number, and the ratio of the defending phase to NAPL phase densities and viscosities. Simulations for the migration of organic chemicals show that their concentration in the air and aqueous phases past the front can be significant.
Changing responses in hydrology: Assessing the uncertainty in physically based model predictions
Authors: Binley A. M. , Beven K. J. , Calver A. , Watts L. G.
Published: February 2004

Due to the large number of model parameters requiring calibration and their inherent uncertainty, the practical application of physically based hydrologic models is not a straightforward task and yet has received inadequate attention in the literature. This work investigates the determination and usefulness of a measure of predictive uncertainty in a particular distributed physically based model, using the methods of Rosenblueth (1975) and Monte Carlo simulation, in an application to an upland catchment in Wales. An examination of the role of predictive uncertainty in assessing the hydrological effect of land use change is also made. The results of the study suggest that, even following parameter constraint through calibration, the predictive uncertainty may be high and can be sensitive to the effects of land use change.