bluuebunny/crossref_metadata_2025_split huggingface dataset:
A simple equation to describe sorption of anions by goethite
Authors: Barrow N. J. 
Published: March 2003

SummaryA simple equation to describe sorption of anions by goethite would be useful as a means of characterizing batches of goethite and in studies of plant uptake of anions from the sorbed form. A suitable relationship between solution concentration (c) of phosphate or citrate and their sorption (S) by goethite at a constant pH or at different pH values is
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where b is a parameter, SMax is the maximum sorption, and a is a parameter at constant pH. In the middle range of sorption (from about 30% to about 70% of maximum sorption) this equation approximated to a Tempkin equation, but the full equation is more useful as it applied over the whole sorption range. The values of a varied with pH. This variation could be explained by changes in the electric potential of the adsorbing surfaces and in the degree of dissociation of the anions. The parameter a could therefore be replaced by a function of pH. The effects were consistent with formation of bidentate phosphate complexes and tridentate citrate complexes with the goethite surface.
A comparison of models for characterizing the distribution of radionuclides with depth in soils
Authors: Smith J. T. , Elder D. G. 
Published: March 2003

SummaryIt is common practice to fit mathematical models to radionuclide activity–depth profiles in soils in order to quantify rates of vertical migration through the soil profile. We have fitted six such models to 21 different activity–depth profiles of radiocaesium (137Cs) derived from Chernobyl and determined relations between the models and the values of their parameters. The advection and dispersion parameters obtained using four solutions to the advection–dispersion equation (each based on different initial and boundary conditions or different simplifications) are in good agreement. We further develop a relation between parameter values obtained using the advection–dispersion models and those determined by a simpler exponential function of the form Aexp(–Bt) where t is the time and A and B are parameters to be estimated. One of the advection–dispersion models proved to be significantly better than the others in terms of goodness‐of‐fit, versatility and ease of use. A simple model, using calculations based on measured characteristics of the activity–depth profile, was shown to accord well with parameters derived from more complex models based on statistical curve fitting. We have also evaluated the ‘residence time’ or ‘compartmental’ model approach to characterizing radionuclide activity–depth profiles. We relate such models to a numerical solution of a simple advection equation, and we show that apparent dispersion in compartmental models is an artefact of numerical dispersion, which can be quantified by the Courant condition. For activity profiles that have a significant advection component, using solutions to the advection–dispersion equation, we have observed a strong positive correlation between advection and dispersion in the profile.
Evaluating soil salinity status from bulk electrical conductivity and permittivity
Authors: Malicki M. A. , Walczak R. T. 
Published: March 2003

SummaryIn the range of volumetric water content, θ, from about 0.12 cm3 cm–3 to saturation the relation between bulk electrical conductivity, Cb, and bulk electrical permittivity, ε, of mineral soils was observed to be linear. The partial derivative ∂Cb/∂ε appeared independent of the moisture content and directly proportional to soil salinity. We found that the variable Xs = ∂Cb/∂ε determined from in situ measurements of Cb(θ > 0.2) and ε(θ > 0.2) can be considered as an index of soil salinity, and we call it the ‘salinity index’. Knowing the index and sand content for a given soil we could calculate the electrical conductivity of the soil water, Cw, which is a widely accepted measure of soil salinity. The two variables from which the salinity index can be calculated, i.e. Cb and ε, can be read simultaneously from the same sensor by time‐domain reflectometry.Quantities and symbolsa constant /dS m–1b constantc constant /dS m–1C
b electrical conductivity of bulk soil /dS m–1C
b′ constant equal to 0.08 dS m–1C
s electrical conductivity of a solution used to moisten soil samples /dS m–1C
w electrical conductivity of soil water defined as the soil salinity /dS m–1C
wref reference salinity (that truly existing) resulting from the procedure of moistening samples, expressed as Cs + Cr/dS m–1C
r baseline value of Cs due to residual soluble salts present in the soil /dS m–1d constantD dry soil bulk density /g cm–3l sloper ratioS sand content /% by weightt time /sX
s salinity index /dS m–1X
si initial salinity index when distilled water is used to moisten soil samples /dS m–1Y a moisture‐independent salinity‐dependent variable /dS m–1z coordinate along direction of flow of the soil solutionε′ constant equal to 6.2ε relative bulk electrical permittivity (dielectric constant) of the soilθ volumetric water content determined thermogravimetrically using oven‐drying /cm3 cm–3
Changes to hardsetting properties of soil by addition of metal hydroxides
Authors: Breuer J. , Schwertmann U. 
Published: March 2003

SummaryHardsetting of soil comprises two contrasting, unfavourable physical conditions at different water contents, namely extreme hardness when dry and complete slaking when wet. This behaviour was changed by adding small amounts of ferrihydrite and aluminium hydroxide to the soil. The aggregation and its stability in the wet state increased, whereas the tensile strength of the dry soils decreased. Both resulted mainly by making the fine particles less mobile by aggregation. In some cases adding large amounts of Al hydroxide caused a resuspension of soil particles by reversing the charge, resulting in instability when wet and high stability when dry. We postulate that aggregation results from the interaction between negatively charged siliceous surfaces and positively charged oxides. In addition we think that newly formed Si–O–Fe bonds play a role in binding particles together as a result of a positive relation between the amount of ferrihydrite added and the oxalate‐soluble Si. We conclude that hardsetting resulting from weak structure is caused by lack of aggregating agents such as metal hydroxides.
Incipient podzolization and weathering caused by complexation in a forest Cambisol on loess as revealed by a soil solution study
Authors: Brahy V. , Titeux H. , Delvaux B. 
Published: March 2003

SummarySurface podzolization has so far been diagnosed from morphological observations, selective extraction and mineralogical investigations. We studied this process in two Cambisol profiles developed in loess, one with a fibrimor humus and the other with a dysmoder humus, by characterizing the chemical composition and the complexing properties of the soil solution. The solutions were sampled bimonthly for 3 years at four depths (4, 8, 13, 25 cm) using both zero‐tension and low‐tension capillary‐wick lysimeters. The leachates from the Ah horizon of the soil with fibrimor contained less nitrate, sulphate and calcium than those from the one with a dysmoder because there was less bioturbation and mineralization in it. Both the complexation capacity and the density of ligand binding sites were larger in the soil solutions of the Ah (4 cm) and AB (8 cm) horizons of the soil with the fibrimor. In this soil, the complexing properties of the liquid phase induced a depletion of inorganic monomeric aluminium. In this environment, the hydroxy interlayered 2:1 clay minerals lose their Al‐interlayers and transform into vermiculite and smectite, which in turn weather, producing large amounts of magnesium in the soil solution. This was found to be a major characteristic of weathering by complexation and incipient podzolization in the Cambisol with the fibrimor. In this process, nitric acid probably contributes to mineral dissolution.
Effect of suspended soil material and pig slurry on the facilitated transport of pesticides, phosphate and bromide in sandy soil
Authors: Hesketh N. , Brookes P. C. , Addiscott T. M. 
Published: March 2003

SummaryThe colloid‐facilitated transport of pesticides and other pollutants to groundwaters is a source of concern to authorities in the European Union and other countries. It has been suggested that colloids are good sorbents for pesticides and other pollutants, and it is now suspected that the spreading of animal manures increases the potential for colloid‐facilitated transport. In experiments in lysimeters of sandy soil to which phosphate, triallate, chlordane and bromide were applied to the surface, the first concentration peaks of the other chemicals always appeared before that of bromide, suggesting that their transport was facilitated by colloidal or suspended soil material. Chlordane was transported only when sorbed on suspended soil material and was associated most closely with the coarsest of suspended material (> 1.2 μm), possibly because it contained the most organic matter. Phosphate was also associated with this class but probably because of the clay it contained. Applying pig slurry to the soil significantly increased the loss of triallate from the lysimeters but not that of chlordane, probably because the latter was held strongly by the soil's organic matter. The loss of triallate was not associated with that of any of the size classes of suspended soil material, which may imply that it was transported in association with dissolved or colloidal organic matter. Neither the pig slurry nor an equivalent amount of inorganic phosphate significantly increased the loss of phosphate. The amounts of triallate and chlordane applied were 100 times the standard agricultural applications, but the largest concentration of chlordane measured was still less than the European Union limit of 0.1 μg l−1. That of triallate was greater than the limit but would almost certainly have been less than it with the standard application. The greatest cumulative losses of phosphate, triallate and chlordane were, respectively, 1%, 0.003% and 0.00002% of the amounts applied. All the results suggest there is only a very small pollution risk to groundwaters from the pesticides and phosphate.
Application of cellular and immunological biosensor techniques to assess herbicide toxicity in soils
Authors: Strachan G. , Capel S. , Maciel H. , Porter A.J.R. , Paton G. I. 
Published: March 2003

SummaryThere is growing concern about the fate and toxicity of herbicides to non‐target receptors and an increasing need to measure these analytes sensitively. The responses of cellular and immunological biosensors to four commonly used herbicides (atrazine, diuron, mecoprop and paraquat) were investigated. In combination, these sensors assess toxicity and quantify concentrations of herbicides present in extracts from soil. The bioluminescence response of the lux‐marked bacterial biosensor Escherichia coli HB101 was determined in aqueous extracts from soil to indicate toxicity. Smaller concentrations caused a toxic response for all four herbicides recovered from the Insch series than for those recovered from spiked water samples, but this was not a result of biodegradation of herbicides in the soil. This suggests that intrinsic soil factors may be altering the bioavailable fraction of herbicides, making them more toxic than equivalent concentrations in water.Herbicide concentrations were determined using immunological biosensors consisting of stabilized recombinant single chain antibodies (stAbs) specific for the four different groups of herbicides. These stAb fragments retain functionality in organic solvents such as methanol commonly used in soil extraction. Anti‐atrazine, mecoprop, diuron and paraquat stAbs were successfully used to identify and quantify herbicides present in aqueous and methanol extracts from soil. The amounts recovered from immunoassay analysis were compared with chemical analysis using high performance liquid chromatography, and the two methods correlated. These stAb fragments might provide a more rapid and sensitive means of quantifying trace amounts of herbicides and their metabolites in aqueous and methanol extracts from soil.
Rate, kinetic energy and momentum of preferential flow estimated from in situ water content measurements
Authors: Germann P. F. , Jäggi E. , Niggli T. 
Published: March 2003

SummaryPreferential flow needs self‐dependent fluid mechanical characterization and quantification. A theoretical and experimental approach is presented to describe preferential flow with the three variables volume of flowing water and its kinetic energy and momentum. Two soils were irrigated at rates of 50, 75 and 100 mm hour−1 at one site and three times at 100 mm hour−1 at a second site. The variations of soil water content caused by irrigation were measured at five depths with horizontally installed TDR wave guides at 300‐s intervals. The volume flux densities were calculated from the water balances. The computation of momentum and kinetic energy of preferential flow was based on the velocities of the wetting fronts and the amplitudes of the variations of soil water. Kinetic energy per unit volume of flow in the soil exceeds the one of irrigation by factors between 100 and 1000, which indicates concentration of flow. However, kinetic energy per unit volume of flow in the soil is less by factors of 106 to 108 than the capillary potential of soil water. Kinetic energy per unit volume of flow seems a reasonable variable for discriminating between preferential and ordinary flow at a threshold of 2 × 10−6 Pa.
Cadmium leaching from some New Zealand pasture soils
Authors: Gray C. W. , McLaren R. G. , Roberts A. H. C. 
Published: March 2003

SummaryCadmium (Cd) inputs and losses from agricultural soils are of great importance because of the potential adverse effects Cd can pose to food quality, soil health and the environment in general. One important pathway for Cd losses from soil systems is by leaching. We investigated loss of Cd from a range of contrasting New Zealand pasture soils that had received Cd predominantly from repeated applications of phosphate fertilizer. Annual leaching losses of Cd ranged between 0.27 and 0.86 g ha–l, which are less than most losses recorded elsewhere. These losses equate to between 5 and 15% of the Cd added to soil through a typical annual application of single superphosphate, which in New Zealand contains on average 280 mg Cd kg−1 P. It appears that Cd added to soil from phosphate fertilizer is fairly immobile and Cd tends to accumulate in the topsoil. The pH of the leachate and the total volume of drainage to some extent control the amount of Cd leached. Additional factors, such as the soil sorption capacity, are also important in controlling Cd movement in these pasture soils. The prediction of the amount of Cd leached using the measured concentrations of Cd in the soil solution and rainfall data resulted in an overestimation of Cd losses. Cadmium concentrations in drainage water are substantially less than the current maximum acceptable value of 3 µg l−1 for drinking water in New Zealand set by the Ministry of Health.
Ecophysiological diversity of alpine populations of Gammarus lacustris in relation to environmental calcium
Authors: Meyran J. ‐C. 
Published: March 2003

1. The contribution of environmental calcium to ecophysiological diversity among populations of Gammarus lacustris was investigated by comparing five alpine lakes in France.2. Calcium concentrations in the water varied with substratum lithology, ranging from 6 mg L–1 in lakes on crystalline (igneous) rocks to 32.7 mg L–1 in lakes on limestone, and up to 248 mg L–1 in a lake with a gypsum environment.3. The duration of the moult cycle and mortality rate were compared between populations by means of field and in situ laboratory and translocation experiments on adult males. Animals from water with low calcium concentrations showed a significantly longer moult cycle and higher mortality rate than those from water with high calcium concentrations. A significant increase in the duration of the moult cycle was observed in animals translocated to water of lower calcium concentration and vice versa.4. These results suggest the existence of different physiological races of G. lacustris with an ecophysiological plasticity of calcium metabolism narrower than that of river‐dwelling gammarids such as G. fossarum. This may be a consequence of geographic isolation among lacustrine populations together with the relatively stable environmental parameters in lakes.
Seasonal changes in planktonic bacterial assemblages of two Ohio streams
Authors: Leff Laura G. , Leff Adam A. , Lemke Michael J. 
Published: March 2003

1. Monthly water samples were collected from two Ohio streams (Bixon and Mahoning) for 14 months to assess the extent of seasonal changes in the bacterial assemblage and in a population within the assemblage. At the assemblage level, abundances of total bacteria and colony forming units (CFUs) were measured. Populations of Burkholderia (Pseudomonas) cepacia were quantified by colony hybridization using a species‐specific rDNA probe.2. Total bacterial numbers were highest in early winter and were lowest during summer and when the streams were covered with ice. Changes in the number of CFUs were more variable than changes in total number, but did not exhibit a clear seasonal pattern.3. B. cepacia was not detected during summer, but up to 8000 ml–1 were present in November. Seasonal changes in assemblage‐level measurements were dissimilar to population‐level changes in B. cepacia abundance.4. The temporal changes observed in this study suggest that populations of stream bacteria, such as B. cepacia, exhibit seasonal blooms that are undetected by assemblage level measurements.
An application of the plaster dissolution method for quantifying water velocity in the shallow hyporheic zone of an Appalachian stream system
Authors: Angradi Ted , Hood Robert 
Published: March 2003

1. A method for quantifying interstitial water velocity based on the dissolution rate of plaster of Paris standards was developed as part of a study of vertical, longitudinal (1–4 order sites) and seasonal variation in the biotic and physical characteristics of the shallow hyporheic zone (0–30 cm) of a headwater stream system in West Virginia, U.S.A.2. A calibration model was developed using a water velocity simulation tank to relate mass loss of plaster standards to water velocity and temperature. The model was then used to calculate water velocity through artificial substrata embedded in the shallow hyporheic zone of four stream reaches based on in situ mass loss of plaster standards.3. Water velocity in the hyporheic zone increased with stream order, was highest in early spring and winter during high stream base flows, and decreased with depth into the substratum. There was a strong interaction between depth and season: during periods of high stream discharge, water velocity through the upper level of the shallow hyporheic zone (0–10 cm into the substrate) increased disproportionately more than velocity at greater depths. Mean interstitial velocity in March ranged from 0 cm s–1 in the lowest level (20–30 cm) to 3.5 cm s–1 at the upper level (0–10 cm) at the first‐order site, and from 2.5 cm s–1 (20–30 cm) to 9.5 cm s–1 (0–10 cm s–1) at the fourth‐order site. Gradients in stream discharge and sediment permeability accounted for treatment effects.4. Use of calibrated data improved the ability to resolve among‐season differences in interstitial water movement over the use of uncalibrated mass loss data. For some applications of the plaster standard method, empirical calibration may not be necessary.
Aquatic insects in an estuarine environment: densities, distribution and salinity tolerance
Authors: Williams D. Dudley , Williams Nancy E. 
Published: March 2003

1. Aquatic insects were quantitatively surveyed at five sites along the tidally influenced section of a river‐dominated estuary in North Wales. Site 1 was the furthest upstream and was established as a reference site as it was never inundated by salt water. Site 5 was the furthest downstream and was inundated by all incoming tides. Numerically, insects made up 32% of the estuarine invertebrate fauna.2. Although the densities of most insect taxa decreased towards the estuary mouth, there were significant numbers present downstream for much of the year; for example, in April at site 4 (which was inundated by 81% of all high tides), a mean of 3514 chironomid larvae were recorded per m2 of estuary bed. Even at site 5, which was inundated twice daily, there were 747 larvae per m2. Among the larger aquatic insects, caddisfly and elmid beetle larvae, together with stonefly nymphs, were consistently taken at site 4 (e.g. maxima of forty‐eight caddisfly larvae m–2 in December and seventy elmids m–2 in April), although their densities were lower than upstream.3. There were seasonal shifts in the longitudinal distribution of several taxa, most notably the extension of chironomids down the estuary in April and July, and the concentration of simuliid larvae and mayfly nymphs at site 2 in July. The total freshwater benthos showed a downstream shift between September and December, which was maintained through April and into the summer. The latter was despite peak saltwater inundation (highest tides) in October, November and April. In June and July, when saltwater intrusion was lowest, the ranges of many aquatic insects had contracted to sites 1 and 2.4. Laboratory experiments showed that virtually all individuals of nineteen species of insects collected from site 1 (freshwater) survived a 4‐h immersion in 8.75‰ saltwater (25% strength seawater). Immersion in progressively more saline solutions reduced the survivorship of first the mayflies, followed by the caddisflies Glossosoma conformis and Hydropsyche instabilis. After 4 h in full strength seawater, all specimens of the stonefly Dinocras cephalotes, over half of the Perla bipunctata, and some individuals of nine species of caddisfly were alive. Four species of caddisfly (Sericostoma personatum, Odontocerum albicorne, Potamophylax cingulatus and Adicella reducta) survived a 24‐h simulated tidal cycle of immersion. With the exception of P. cingulatus, a few individuals of these caddisfly species survived immersion in full‐strength seawater for 24 h. For some individual species there was good agreement between their observed longitudinal distribution in the estuary and laboratory‐measured salinity tolerance; however, there was no significant correlation, overall, for the fauna.