bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of clay content and silt—clay fabric on stability of artificial aggregates
Authors: ATTOU F. , BRUAND A. , LE BISSONNAIS Y. 
Published: March 2003

SummaryThe influence of clay content and silt–clay fabric on aggregate stability was investigated. Two silt—clay fabrics were produced in the laboratory by mixing silt particles with a clay phase: (i) a loose packing of the silt particles with clay aggregates, and (ii) a close packing of the silt particles with the dispersed clay phase, the latter coating and bridging the silt particles. Porosity and pore size distribution were measured, and the silt—clay fabric was described using scanning electron microscopy. The aggregate stability was measured under three treatments corresponding to different wetting conditions and energy levels: fast wetting, mechanical breakdown and slow wetting. Our results show that aggregate stability is related to both clay content and silt—clay fabric. Comparison of fragment size distributions and their mean weight diameter amongst the three treatments enabled identification of mechanisms responsible for the variation of aggregate breakdown. The compression of trapped air was the predominant breakdown mechanism for both fast and slow wetting and was related mainly to porosity characteristics. For the mechanical breakdown, the degree of disintegration depended on the cohesion of the silt–clay fabric, which is related to the continuity of the solid phase.
Bromide and herbicide transport under steady‐state and transient flow conditions
Authors: Meyer‐Windel S. , Lennartz B. , Widmoser P. 
Published: March 2003

SummaryThe dynamics of water flow in soils influences the transport behaviour of solutes. Transport of bromide and herbicides through undisturbed soil columns was investigated under conditions of unsaturated steady‐state and transient water flow. Effective transport parameters were obtained from fitting the convection–dispersion equation to curves of concentration against cumulative drainage, and these enabled us to interpret the observed behaviour. Under both steady‐state and transient flow bromide and herbicides were transported through similar parts of the pore volume of a homogeneous single grain soil (Bv horizon). However, in aggregated Ah and Ap horizons preferential transport occurred during transient flow but not during steady‐state flow. For preferential flow the mean transport volume seemed to depend on the prevailing pore system and the fraction of preferentially flowing water. Solute leaching was more efficient under steady‐state than under transient flow for bromide in all soils and for herbicides in the Bv horizon. However, when transient flow caused preferential transport, herbicide loss was greater under transient flow than during steady‐state flow. Under preferential flow conditions a three‐step herbicide concentration development recurred in successive drainage events. This behaviour was not observed for the non‐reactive tracer. It seemed to be caused by sorption. A steady‐state model with cumulative drainage as independent variable instead of time can predict the transport of non‐reactive and adsorbed solutes in homogeneous soils without features of preferential flow. Otherwise constant effective input parameters cannot be assessed a priori.
Efficacy of perforating the soil to capture and store rain during fallow in dry regions
Authors: Cattle S. R. 
Published: March 2003

SummaryPerforating topsoil of poor conductivity with artificial macropores can often improve the capture and storage of rain in dryland cropping. However, several features can render it of little merit. These include the inability of artificial macropores effectively to harvest coalescing water on the soil surface, and the increased evaporation caused by the greater surface area of subsoil exposed to the atmosphere in such pores. To ascertain the extent of these effects I used a sprinkling infiltrometer to determine the time‐to‐ponding of small areas of perforated and unperforated soil subjected to different intensities of ‘rain’, and determined the rate of evaporation on perforated and unperforated microlysimeters. On average the perforated plots tended to take longer to pond than the unperforated ones, but the water‐harvesting efficacy of individual artificial macropores was highly variable, depending on their position in the microlandscape, the degree of connectivity with subsoil pores, the rate at which the water was applied, and the antecedent water content of the topsoil. The microlysimeter experiments revealed consistently greater evaporation from the perforated samples, with average daily differences between the treatments ranging from 2 to 26%. Antecedent soil water content and air temperature and windspeed affected the amounts of evaporation from both treatments. The ultimate efficacy of perforation for capturing water will vary spatially and temporally according to the extent to which the properties of the soil and environment impact on the behaviour of the penetrating water.
Calculation of nitrogen mineralization and leaching in fallow soil using a simple dynamic model
Authors: Mary B. , Beaudoin N. , Justes E. , Machet J. M. 
Published: March 2003

SummarySimple models describing nitrogen processes are required both to estimate nitrogen mineralization in field conditions and to predict nitrate leaching at large scales. We have evaluated such a model called LIXIM, which allows calculation of nitrogen mineralization and leaching from bare soils, assuming that these are the dominant processes affecting N in bare soil. LIXIM is a layered, functional model, with a 1‐day time step. Input data consist of frequent measurements of water and mineral N contents in soil cores, standard meteorological data and simple soil characteristics. The nitrate transport is simulated using the ‘mixing‐cells’ approach. The variations in N mineralization with temperature and moisture are accounted for, providing calculation of the ‘normalized time’. An optimization routine is used to estimate the actual evaporation and the N mineralization rates that provide the best fit between observed and simulated values of water and nitrate contents in all measured soil layers.The model was evaluated in two field experiments (on loamy and chalky soils) including treatments, lasting 9–20 months. The water and nitrate contents in soil were satisfactorily simulated in both sites, and all treatments, including a 15N tracer experiment performed in the loamy soil. In the chalky soil, the calculated water balance agreed well with drainage results obtained in lysimeters and independent estimates of evaporation. At both sites, N mineralization was reduced by the incorporation of crop residues (wheat or oilseed rape straw); the amounts of nitrogen immobilized varied between 20 and 35 kg N ha−1. In the treatments without crop residues, the mineralization rate followed first‐order kinetics (against normalized time) in the loamy soil, and zero‐order kinetics in the chalky soil. In the latter soil, the mineralization kinetics calculated in situ were close to the kinetics measured in laboratory conditions when both were expressed against normalized time.
Interactions of allophane with humic acid and cations
Authors: Yuan G. , Theng B. K. G. , Parfitt R. L. , Percival H. J. 
Published: March 2003

SummaryAllophanic soils are known to accumulate organic matter, but the underlying mechanism is not well understood. Here we have investigated the sorption of humic acid (HA) by an allophanic clay in the presence of varied concentrations of either CaCl2 or NaCl as background electrolytes. Both the HA and the clay were separated from New Zealand soils. Much more HA was sorbed in CaCl2 than in NaCl of the same ionic strength. Apparently Ca2+ ions were more effective than Na+ ions in screening the negative charge on HA. In CaCl2 the HA molecule might also assume a more compact configuration than in NaCl. In the presence of CaCl2 sorption increased, reached a maximum, and then declined as the concentration of HA in solution was increased. This behaviour was not observed in NaCl where sorption showed a gradual and steady increase with HA concentration. We propose that ligand exchange occurs between the surface hydroxyl groups of allophane and the carboxylate groups of HA. As a result, the allophane–HA complex acquires negative charges, requiring the co‐sorption of extraneous cations (Ca2+ or Na+) for charge balance. The Ca2+ co‐sorbed can attract more HA to the complex possibly by a cation‐bridging mechanism, giving rise to a maximum in sorption. The decline in sorption beyond the maximum may be ascribed to a decrease in the concentration of free Ca2+ ions through binding to HA molecules in solution. The increase in supernatant pH may be attributed to a ligand exchange reaction between the surface hydroxyls of allophane and the carboxylate groups of HA, and proton binding to the allophane–HA complex.
A mathematical model of root uptake of cations incorporating root turnover, distribution within the plant, and recycling of absorbed species
Authors: Darrah P. R. , Staunton S. 
Published: March 2003

SummaryUnderstanding the movement of cations in soil, particularly trace metals, is required in many applications such as phytoremediation and pollution control. A dynamic mechanistic model has been developed to describe the long‐term root uptake of a surface‐applied, strongly adsorbed, pollutant metal cation, such as radiocaesium, from soil. It consists of two submodels. The first calculates uptake per unit root length at a local scale over a root's lifetime, for various initial conditions. The second calculates cumulative uptake at a whole‐plant scale for the entire rooting depth as a function of time. The model takes into account the renewal of roots which are considered to have a limited lifetime. Root density may be a function of soil depth and a proportion of roots need not contribute to uptake. Recycling from decaying, or grazed, roots and shoots is considered.Simulations show that removal of cations from soil is exaggerated unless some recycling by roots or shoots is considered or the entire root length does not contribute to uptake. Because of root turnover, uptake is not rapidly limited by diffusive flux of the cation from the bulk soil solution to the solution–root interface. Uptake is very sensitive to root architecture and plant physiology.
Single‐ and dual‐porosity modelling of multiple tracer transport through soil columns: effects of initial moisture and mode of application
Authors: Kätterer T. , Schmied B. , Abbaspour K. C. , Schulin R. 
Published: March 2003

SummaryWe investigated the effect of initial moisture contents and mode of application on the displacement of multiple conservative tracers through undisturbed columns of a Humic Gleysol. Bromide was applied at the soil surface and chloride was injected at 5 cm depth. The columns were irrigated with deuterium‐enriched water. A dual‐porosity model and two single‐porosity models were calibrated separately to Br– and Cl– elution curves in the two columns.Elution curves were almost identical for Br– and Cl– under initially wet conditions, whereas the displacement of Br– was faster than that of Cl– in the initially dry column, indicating rapid transport with preferential flow. Only the dual‐porosity model described the long‐tailing breakthrough of Cl– in the initially dry column adequately. The parameter values giving acceptable fits for ‘Br dry’ were not compatible with the description of the three other elution curves, which could be adequately modelled with a single set of parameter values.The estimated set of common parameters was validated by comparing with the elution curves of deuterium water, nitrate and sulphate, as well as with resident tracer concentrations at four depths. The results showed that solutes can be displaced much faster when applied at the surface of initially dry soil than when applied to wet soil or when resident in the soil matrix. The simulation results suggest that solute transport under initially dry conditions was governed by preferential flow of infiltration water through macropores by‐passing the matrix due to shrinkage cracks and water repellence of matrix surfaces.
Three‐dimensional trajectories of 60Co‐labelled earthworms in artificial cores of soil
Authors: Capowiez Y. , Renault P. , Belzunces L. 
Published: March 2003

SummaryInformation on earthworm burrowing behaviour is scarce and therefore the evolution of the macroporosity related to earthworm activities is still poorly known. We have designed a new apparatus, ‘Colonne Gamma’, to follow the three‐dimensional trajectories of radio‐labelled earthworms in artificial cores of soil. Earthworms are radio‐labelled by injecting into their coelomic cavity a small source of 60Co (volume 0.1 mm3, intensity 13.5 μCi). The emission of gamma rays is recorded by three detectors carried by a disc that oscillates vertically around the soil core where the earthworm is introduced. We have also developed a deterministic model to estimate the positions of the 60Co source from the number of gamma rays received by each detector during an oscillation. Numerical experiments showed that the uncertainties of estimates were less than 3 mm for each coordinate. To validate the results, we tracked the trajectory (one position every 4 minutes) of a radio‐labelled earthworm for 1 week and compared it with the skeleton of the macroporosity obtained by computer assisted tomography of the same soil core. There was a general qualitative agreement between the trajectory and the skeleton. Moreover, based on the precise study of the successive positions of the earthworm we could distinguish two different kinds of activities in the trajectory: displacement and digging events. The ‘Colonne Gamma’ apparatus therefore has great potential for studies of the ecology and the behaviour of earthworms.
Fate of microbial residues in sandy soils of the South African Highveld as influenced by prolonged arable cropping
Authors: Amelung W. , Lobe I. , Du Preez C. C. 
Published: March 2003

SummaryLong‐term cultivation of former grassland soils results in a significant decline of both living and dead microbial biomass. We evaluated the effect of duration of cropping on the preservation of fungal and bacterial residues in the coarse‐textured soils of the South African Highveld. Composite samples were taken from the top 20 cm of soils (Plinthustalfs) that have been cropped for periods varying from 0 to 98 years in each of three different agro‐ecosystems in the Free State Province. Amino sugars were determined as markers for the microbial residues in bulk soil and its particle‐size fractions. Long‐term cultivation reduced N in the soil by 55% and the contents of amino sugars by 60%. Loss rates of amino sugars followed bi‐exponential functions, suggesting that they comprised both labile and stable fractions. With increased duration of cropping the amino sugars attached to silt dissipated faster than those associated with the clay. This dissipation was in part because silt was preferentially lost through erosion, while clay particles (and their associated microbial residues) remained. Erosion was not solely responsible for the reduction in amino sugar concentrations, however. Bacterial amino sugars were lost in preference to fungal ones as a result of cultivation, and this effect was evident in both silt‐ and clay‐sized separates. This shift from fungal to bacterial residues was most pronounced within the first 20 years after converting the native grassland to arable cropland, but continued after 98 years of cultivation.
Genetic population structure of goldsinny wrasse, Ctenolabrus rupestris (L.), in Norway: implications for future management of parasite cleaners in the salmon farming industry
Authors: SUNDT R. C. , JØRSTAD K. E. 
Published: March 2003

AbstractThe application of goldsinny wrasse, Ctenolabrus rupestris (L.), as parasite cleaners in the salmon farming industry has led to transport of live wrasse between regions in Norway. Owing to the operation of salmon farms, some of the transferred wrasse escape from the salmon net pens and can therefore mix and potentially interbreed with the local populations. The genetic effects of such interbreeding are unknown and information about the genetic population structure of this species in Norwegian inshore waters is needed to evaluate the potential effects. A genetic study based on polymorphic tissue enzymes was therefore carried out. Four of the 35 protein coding loci screened were polymorphic at the 99% level, and only two at the 95% level. The allele frequencies of the IDDH‐1*; PGM‐1*; GPI‐1* and GPI‐2* loci were compared in wrasse samples (1442 specimens) collected at 12 localities. Significant differences were found for PGM‐1* among the samples collected at two inner fjord localities. Significant differences at the IDDH‐1*, PGM‐1* and GPI‐2* loci were found when data from a sample of transferred wrasse caught in southern Norway were compared with local wrasse in the recipient areas.
The 1882 tilefish kill — a cold event in shelf waters off the north‐eastern United States?
Authors: MARSH ROBERT , PETRIE BRIAN , WEIDMAN CHRISTOPHER R. , DICKSON ROBERT R. , LODER JOHN W. , HANNAH CHARLES G. , FRANK KENNETH , DRINKWATER KEN 
Published: March 2003

A mass mortality of `warm‐water' tilefish in the Middle Atlantic Bight between April and August of 1882 suggests an episode of extreme cold in the shelf waters off the north‐eastern United States. This cooling is hypothesized to be a consequence of enhanced equatorwards transport of cold water in the Labrador Current, coincident with a minimum in the North Atlantic Oscillation (NAO) index during the early 1880s.Although there is little direct evidence for this historical event, an analogue for the 1880s cooling is found in the 1960s, at the most recent NAO‐index minimum. Post‐1945 observations in the Middle Atlantic Bight / Gulf of Maine region reveal changes in winter baroclinic circulation between cool and warm decades, with greater equatorward penetration of south‐westwards flow along the shelf‐edge during the cool 1960s. Over the period 1934–77, the NAO is found to account for 17% of the interannual variance in Labrador Current transport around the Grand Banks.Proxy evidence for the cold episode of the early 1880s is sought. Records of bottom temperature in the Middle Atlantic Bight region are reconstructed using stable oxygen isotopic analysis on the annual bands of shells of a bivalve mollusc (Arctica islandica) and an empirical model of covariability with local air temperature. The result is confirmation of the presence of anomalously cold water during the early 1880s.
A spatial model of population dynamics of the early life stages of Japanese sardine, Sardinops melanostictus, off the Pacific coast of Japan
Authors: Suda Maki , Kishida Tatsu 
Published: March 2003

AbstractWe constructed a numerical model reproducing the transport, survival and individual growth of the early life stages of Japanese sardine, Sardinops melanostictus, off the Pacific coast of Japan during 1978–93. The causes of early life stage mortality, including the influence of the effects of the spatial relationship between the spawning grounds and the Kuroshio on the mortality rate, were investigated. Survival and transport from egg stage to 60 days after spawning were modelled daily in a 1 × 1 degree mesh cell and individual growth in the period was modelled in each region (Kuroshio, Inshore, Offshore and Transition regions). Individual growth and survival from 60 to 180 days after spawning were modelled daily in the Transition region. Environmental data were taken from outside the model system. Our simulation indicates that survival variability in the larval stage (5–25 mm in standard length) is the key factor in determining the year‐class strength. The simulation revealed that strong year classes occurred with good survival in the spawning ground and whilst entrained in the Kuroshio current being transported to the main feeding grounds in the Transition region. The simulation also indicated that survival rates in 1988–93 were low in the Inshore, Kuroshio and Offshore regions, which depressed the year‐class strength during that period.
Can ingested cyanobacteria be harmful to the signal crayfish (Pacifastacus leniusculus)?
Authors: Lirås Vibeke , Lindberg Magdalena , Nyström Per , Annadotter Heléne , Lawton Linda A. , Graf Brigitte 
Published: March 2003

1. A sample of adult signal crayfish were taken from a pond with a hepatotoxic bloom of the benthic cyanobacterium Oscillatoria sancta. Cyanobacteria were found in the stomachs of thirty‐one out of thirty‐two crayfish examined.2. To examine the effect of hepatotoxic cyanobacteria on crayfish a 14‐day feeding trial was carried out with thirty‐six animals. There were three treatments: (i) hepatotoxic and (ii) non‐toxic Planktothrix agardhii; and (iii) crayfish pellets as a control.3. High‐performance liquid chromatography (HPLC) showed that microcystins (the toxins of P. agardhii) had accumulated in the hepatopancreas of 50% of the animals in the toxic treatment.4. The cyanobacteria did not appear to have any negative impact on the crayfish. All crayfish survived, remained motile and ate throughout the experiment.5. During the experiment blood samples were taken and the total number of haemocytes counted. At the end of the experiment glucose concentration and relative wet weight of the hepatopancreas were measured. No differences between crayfish fed on toxic and non‐toxic P. agardhii and the controls were found.6. The fact that microcystin accumulates in the crayfish hepatopancreas indicates that the toxin may be transferred further up the food chain.
The nutritional value of organic detrital aggregate in the diet of fathead minnows
Authors: Lemke Michael J. , Bowen Stephen H. 
Published: March 2003

1. The nutritional value of detrital aggregate, which refers to the mixture of plant debris (i.e. organic detritus) and microorganisms, in the diets of fathead minnows (Pimephales promelas Rafinesque) was assessed in experiments using surface benthic samples from three sites in Clear Lake (Houghton County, Michigan, U.S.A.).2. In the first experiment, fish were fed small (<250 μm) and large (250–1000 μm) particle detritus from one profundal and two littoral sites. Fish in all treatments lost weight. However, fish fed detritus from the littoral erosional site, where wild fish forage intensively, had significantly lower weight loss.3. In the second experiment, fish were fed various quantities of Artemia with or without ad libitum erosional site detritus. Growth was proportional to the mass of Artemia consumed, yet minnows showed increased growth with the detritus supplement at low invertebrate rations.4. This study shows that detrital aggregate produced by decompositional processes at the erosional site could be nutritionally valuable to minnows. It appears that a feeding strategy of consuming detritus with a higher nutritional quality (i.e. detrital aggregate) as a dietary supplement benefits fishes in temperate as well as tropical systems.
Predicting the spring algal biomass in Lough Neagh using time series analysis
Authors: Stronge K. M. , Smith R. V. , Lennox S. D. 
Published: March 2003

1. Lough Neagh is a large eutrophic lake covering 387 km2 with a mean depth of 8.9 m. It is an important natural resource, being the largest single source of potable water for Belfast, Northern Ireland.2. This report examines the causes of the year‐to‐year variation in the April–June (spring) algal biomass, measured as chlorophyll a, for the period 1974–92.3. The spring chlorophyll a declined following the introduction of a phosphorus (P) reduction programme at major sewage treatment works in 1981. However, since 1990 the chlorophyll a concentrations in the spring have increased.4. Time series methodology was employed to develop a model which explained 76% of the annual variation in spring chlorophyll a concentrations.5. The independent variables used in the multiple regression model were the previous year’s spring chlorophyll a concentration, soluble reactive P inputs for April–June and the particulate P concentration in the Lough during the previous summer.