bluuebunny/crossref_metadata_2025_split huggingface dataset:
Evaluation of a nitrogen transport and transformation model in a bare soil
Authors: Garnier P. , Néel C. , Mary B. , Lafolie F. 
Published: March 2003

SummarySimulation models are useful tools to understand the interaction between the transformation and the transport of nitrogen in the field. This study was done to calibrate, test and analyse a mechanistic, one‐dimensional model that describes the transport and transformations of nitrogen in the soil. The physical module describes transport of water, heat and solute, and the biological module simulates transformations of C and N with a restricted number of measurable organic pools. The calibration was based mainly on laboratory experiments independent of those used to evaluate the model. The evaluation procedure used field data collected on a bare loamy soil. The profiles of water content, water potential, temperature, chloride and nitrate (15N‐labelled and unlabelled) concentrations were measured from 0 to 150 cm continuously for 1 year. Simulated results were in good agreement with experimental data. However, some discrepancies were noticeable for chloride and nitrate concentrations in the deep layers. These differences were probably due to an underestimation of mass transport in the deep layers. A sensitivity analysis was carried out to determine the response to changes in some parameters in terms of mineralization, leaching and model efficiency. Mineralization is more sensitive to biological factors whereas nitrate leaching is more sensitive to initial and boundary conditions and hydraulic parameters. The experiment ran for only 1 year, which was too short a time to test biological factors.
Simulating the dynamics of glucose and NH4+ in alkaline saline soils of the former Lake Texcoco with the Detran model
Authors: Luna‐Guido M. L. , Dendooven L. 
Published: March 2003

SummaryThe turnover of organic matter determines the availability of plant nutrients in unfertilized soils, and this applies particularly to the alkaline saline soil of the former Lake Texcoco in Mexico. We investigated the effects of alkalinity and salinity on dynamics of organic material and inorganic N added to the soil. Glucose labelled with 14C was added to soil of the former Lake Texcoco drained for different lengths of time, and dynamics of 14C, C and N were investigated with the Detran model. Soil was sampled from an undrained plot and from three drained for 1, 5 and 8 years, amended with 1000 mg 14C‐labelled glucose kg−1 and 200 mg NH4+‐N kg−1, and incubated aerobically. Production of 14CO2 and CO2, dynamics of NH4+, NO2– and NO3–, and microbial biomass 14C, C and N were monitored and simulated with the Detran model. A third stable microbial biomass fraction had to be introduced in the model to simulate the dynamics of glucose, because > 90 mg 14C kg−1 soil persisted in the soil microbial biomass after 97 days. The observed priming effect was mostly due to an increased decay of soil organic matter, but an increased turnover of the microbial biomass C contributed somewhat to the phenomenon. The dynamics of NH4+ and NO3– in the NH4+‐amended soil could not be simulated unless an immobilization of NH4+ into the microbial biomass occurred in the first day of the incubation without an immediate incorporation of it into microbial organic material. The dynamics of C and a priming effect could be simulated satisfactorily, but the model had to be adjusted to simulate the dynamics of N when NH4+ was added to alkaline saline soils.
The design of porous material sensors to measure the matric potential of water in soil
Authors: Whalley W. R. , Watts C. W. , Hilhorst M. A. , Bird N. R. A. , Balendonck J. , Longstaff D. J. 
Published: March 2003

SummaryIn recent years the use of porous material sensors for matric potential, which were originally intended for soil drier than −100 kPa, has been extended to wet soils. In these wetter soils, unpredictable behaviour of the sensors has been reported. We have studied the design of porous material sensors of matric potential in soil and propose a hypothesis to explain this unpredictability, and suggest recommendations for a design of sensor which will behave more reliably. The development of an experimental porous material sensor of matric potential based on this design is described. It operates between 0 and −60 kPa, and both the drying and wetting moisture characteristics were measured. In this sensor the porous material was a ceramic and its water content was measured with a dielectric water content sensor. We tested a simple closed‐form hysteresis model to convert the measured water content of the porous material into matric potential under laboratory conditions. This was shown to give better results than using a calibration based on the drying moisture characteristic curve, where the predicted matric potentials were too small. The use of the experimental sensors in the field environment is described. Both types of sensor were installed using the same procedure. As far as we are aware the experimental sensor described in this paper is the first porous material sensor of matric potential that can be installed in the same way as a conventional tensiometer. Both conventional tensiometers and the experimental porous material sensors gave similar estimates of matric potential.
Fate of anthracene in contaminated soil: transport and biochemical transformation under unsaturated flow conditions
Authors: Weigand H. , Totsche K. U. , Kögel‐Knabner I. , Annweiler E. , Richnow H. H. , Michaelis W. 
Published: March 2003

SummaryTo obtain reliable estimates for the loss of polycyclic aromatic hydrocarbons (PAHs) from contaminated soils, one has to distinguish between (i) losses due to release and solute transport and (ii) losses resulting from degradation. We studied the interplay of these processes in a column experiment representing a typical soil contamination scenario: in the upper part of the column was a contaminated layer, spiked with 9‐13C‐labelled anthracene, and beneath it uncontaminated pristine soil. The experimental course comprised a steady‐state flow phase (constant irrigation for 4 months) followed by several periods during which flow was halted. The effects of varied residence time on anthracene biodegradation and on anthracene mass transfer were investigated. We monitored labelled anthracene and its transformation products, dissolved organic carbon, electric conductivity (EC), pH, and inorganic carbonate content in the column effluent, and the CO2 evolved.Under steady‐state flow, pH, dissolved organic C, and EC approached steady states after 350 pore volumes. Concentrations of anthracene in the effluent, however, increased continuously and levelled off after 800 pore volumes. This marked retardation reflects the great affinity of anthracene to soil organic matter. The response to interruptions in the flow revealed that mass is transferred without equilibrium between solid and liquid phase for both anthracene and dissolved organic C. Thus, residence time is one factor controlling the concentration of anthracene in the effluent and therefore the export of contaminant to the aquifer. In the course of the experiment several labelled anthracene degradation products appeared in the effluent. At least three of them were identified as transformation products showing a dramatic increase in mobility relative to the parent compound. A third of the overall anthracene loss from the column was due to solute transport, and biodegradation was responsible for the remaining two thirds. The incomplete degradation of anthracene leads to the formation of highly mobile transformation products and thus promotes the export of carbon, derived from the contaminant.
Physicochemical factors controlling the release of dissolved organic carbon from columns of forest subsoils
Authors: Münch J.‐M. , Totsche K. U. , Kaiser K. 
Published: March 2003

SummaryRetention of dissolved organic carbon in soil depends on the chemical and physical environment. We studied the release of organic carbon from three carbonate‐free forest subsoil materials (Bs1, Bs2, Bg) in unsaturated column experiments as influenced by (i) variations of the flow regime and (ii) varied chemical properties of the irrigation solution. We investigated the effect of flow initiation, constant irrigation, interruptions to flow, and variation in the effective pore water velocity on the release of organic C. The influence of ionic strength and cation valence in the irrigation solution was studied by stepped pulses of NaCl and CaCl2. The release of C from all materials was characterized by an initial large output and a decline to constant concentrations under long‐term irrigation. Interrupting the flow increased its release when flow was resumed. The release from the Bs1 material was not related to the duration of the interruption. The Bs2 material, in contrast, released organic carbon in a way that was successfully described by a kinetic first‐order model. Increased pore water velocity decreased the concentrations of C in the effluent from it. The pH of the irrigation solution had negligible effects on the mobilization of C. Increased ionic strength reduced the release, whereas rinsing with distilled water increased the concentrations of C in the effluent. The response of dissolved C to pulses of weak solutions, however, was sensitive to the type of cation in the previous step with strong solutions. The results suggest that the release of organic matter in the soils depends on its colloidal properties.
Distribution and fractionation of heavy metals in pairs of arable and afforested soils in Denmark
Authors: Andersen M. K. , Raulund Rasmussen K. , Hansen H. C.B. , Strobel B. W. 
Published: March 2003

SummaryAfforestation of sandy arable soils in northern Europe is likely to lead to an increase in the soil's acidity and changes in the behaviour of the organic matter, and this might affect the ability of the soil to retain heavy metals. It is important to assess the impact of such a change in the land use on the solubility of the heavy metals and to assess the risk of leaching to surface‐ and groundwater and the possible entrapment of heavy metals in the tree canopy. The impact of afforestation was assessed by excavating soil profiles in adjacent 34‐year‐old Norway spruce stands and arable plots at four different sites. We found that after 34 years the pH had decreased and cations were depleted in the topsoil under forest. The aqua regia‐extractable heavy metals were determined, and the heavy metal binding within the soil was assessed using a modified version of the BCR (Community Bureau of Reference) sequential extraction procedure. Higher contents of heavy metal were found in the arable plots in the loamy sand soils. Cadmium was found only in the most mobile fractions. The content of Pb in the subsoil was strongly correlated with the clay content, but not in the topsoil, which suggested that Pb had been added to the topsoil. We found strong correlations between the clay content and the Cu, Ni and Zn in the residual fraction, leading us to conclude that much of the Cu, Ni and Zn is of geological origin. No significant differences in the heavy metal fractionation between forest and arable soil were found, presumably because 34 years of different land use is not long enough to produce such differences.
Microaggregates in agricultural soils and their size distribution determined by X‐ray attenuation
Authors: Leifeld J. , Kögel‐Knabner I. 
Published: March 2003

SummaryUnderstanding mechanisms of microaggregate formation in soils requires knowledge of their exact size distribution. With this in mind, we have used X‐ray attenuation to determine the size distributions of microaggregates and primary particles in the range 0.2–63 μm, with a resolution of 100 size increments. Ten arable and grassland soils with organic C contents ranging from 14.7 to 37.7 g kg−1 were analysed. They were subjected to ultrasound at 52 J ml−1 which destroyed most aggregates > 63 μm to give microaggregates in the size range 1–63 μm. The size distribution of microaggregates differed significantly from that of primary particles and was largely independent of their organic C content. Microaggregates were most abundant in 19 of the 100 size increments, contributing to 92% of the major peaks of the size distribution. These preferred increments differed from those of primary particles, but the order for the two was similar. Further analysis of the size distribution revealed a larger mean weight diameter of microaggregates, depending on the size distribution of primary particles. The results suggest a major effect of the size distribution of primary particles on microaggregation, whereas land use seems to have a negligible effect. The proportion of mechanically dispersible clay decreased with increasing C content and indicates structural stability at the microscale.
Present state and perspectives for the southern Brazil shelf demersal fisheries
Authors: HAIMOVICI M. 
Published: March 2003

AbstractThe demersal fish stocks in southern Brazil were assessed from landings and catchper‐unit effort data trends between 1975 and 1994, available information on the life history patterns, and population dynamics of the most important species. The fishing gears, mostly otter and pair bottom trawls in the 1970s, diversified towards double‐rig trawls for fish and shrimp and bottom gill nets in the mid 1980s, and bottom longlines in the upper slope in the early 1990s. There were also some less successful attempts with traps for fish and crabs. The demersal fisheries are more intensive in winter when migratory species move northward, associated with the seasonal displacement of the western boundary of the Subtropical Convergence. Landings between 1975 and 1994 were mostly of sciaenid fishes (>70%) and elasmobranchs (10%) and oscillated around 59 000 t. There was not a decrease in total landings but a shift from more to less exploited stocks. Since 1989, 4% of the landings came from depleted stocks of Pagrus pagrus (L.), Netuma barba (Lacépède), Pogonias cromis (L.) and Rhinobatos horkelli (Muller & Henle); 37% from overexploited stocks: Micropogonias furnieri (Desmarest), Paralichthys patagonicus Jordan, Squatina guggenheim Marini, and Galeorhinus galeus (L.); 24% from heavily exploited stocks of Umbrina canosai Berg, and Macrodon ancylodon (Bloch & Schneider); and 35% of Cynoscion guatucupa (Cuvier) and small stocks with unclear status. The demersal fisheries are virtually unmanaged and future landings are expected to decrease if fishing pressure remains high. Effective management will require the participation of all three countries in the region because most of the stocks fished in southern Brazil are shared with Uruguay and Argentina.
Effect of habitat type on growth and diet of brown trout, Salmo trutta L., in stream enclosures
Authors: GREENBERG L. A. , DAHL J. 
Published: March 2003

AbstractThe effect of habitat on the growth and diet of brown trout, Salmo trutta L., stocked at the same densities in nine stream enclosures, comprising three habitat types of different quality, were tested. The habitats, which were created based on microhabitat preference data, were a shallow water habitat lacking cobbles (habitat 1), a deeper, mixed cobble‐bottomed (128‐384 mm diameter) habitat (habitat 2) and a large cobble‐bottomed (256‐384 mm) habitat of intermediate depth (habitat 3). Brown trout were found to have greater increases in total biomass in habitats 2 and 3 than in habitat 1. The pattern for length did not follow that of biomass as trout had greater increases in total length in habitat 2 than in the other two habitats. Biomass of food in trout diets reflected habitat‐specific fish biomass changes, with a greater total biomass of prey as well a greater biomass of the leech, Erpobdella, in habitats 2 and 3 than in habitat 1. There were no habitat‐specific differences in the biomass of benthic or drifting invertebrates in the enclosures, with the exception of a tendency for an effect of habitat on the biomass of Erpobdella. Although there may have been habitat‐specific differences in food resources that were not detected, it is believed that the higher biomass growth in habitats 2 and 3 may have reflected differences in cover afforded by the deeper water and coarser substrates and/or improved foraging opportunities facilitated by the larger volumes of water in the deeper habitats in which the trout could search for prey.
Fisheries management based on ecosystem dynamics and feedback control
Authors: Matsuda Hiroyuki , Katsukawa Toshio 
Published: March 2003

AbstractRecently, ecosystem management has become popular for forestry, agriculture and fisheries management. Carrying capacity and maximum sustainable yield for a particular species definitely depend on population sizes of other species in the same ecosystem. Natural stock fluctuations of sardine, anchovy and chub mackerel are well known examples of large, natural fluctuations. There is a negative correlation among their fluctuations. In accordance with the cyclic advantage hypothesis for replacement of pelagic fish species (Matsuda et al., 1992), we can predict the next dominant species, despite an uncertainty in the year of the next replacement. We recommend that commercial fisheries should switch their target to the next dominant species before the stock of the present dominant species collapses. Whilst total allowable catch (TAC) of the present dominant species can be as large as we can consume, TAC after the species collapses should be much smaller than the present catch level.
Biomass and taxonomic composition of micronekton in the western tropical–subtropical Pacific
Authors: Hidaka Kiyotaka , Kawaguchi Kouichi , Tanabe Toshiyuki , Takahashi Mio , Kubodera Tsunemi 
Published: March 2003

AbstractThe biomass distribution, community structure and species composition of the dominant micronektonic animals were determined in the western tropical Pacific, using day/night sampling from upper 200 m depth with a commercial midwater otter trawl in fall‐winter of 1994, 1995 and 1997. Night‐time micronekton biomass was significantly higher than daytime biomass except for a few cases. All the night‐time catches had similar taxonomic composition, dominated by myctophid fishes, small squids, shrimps and euphausiids. Night‐time micronekton biomass in the upper 200 m was assumed to be higher in the North Equatorial Counter Current than in the North Equatorial Current, reflecting the zooplankton biomass distribution which micronektons feed on at night. A total of 42 species of myctophid fishes, 34 species of squids, 27 species of shrimps and six species of euphausiids were collected. Community types of each dominant taxonomic group were classified by cluster analysis based on the species composition. A station located north of the subtropical convergence zone was distinct from other tropical stations south of the convergence zone, having significantly different species composition in three of the four dominant taxonomic groups (myctophids, squids and shrimps). The interaction between the larvae of commercially important fishes and micronektonic animals is discussed.
Relationships between zooplankton community structure and phytoplankton in two lime‐treated eutrophic hardwater lakes
Authors: Ghadouani Anas , Alloul Bernadette Pinel , Zhang Ying , Prepas And Ellie E. 
Published: March 2003

1. North Halfmoon Lake and Lofty Lake (Alberta, Canada) were chosen for whole‐lake liming experiments as a new restoration technology to enhance calcite precipitation and reduce eutrophication. During a 3‐year study (1991–93) the relationships between zooplankton and phytoplankton were assessed, together with the effects of lime additions.2. Zooplankton communities were numerically dominated by rotifers, while the major contribution to biomass was due to large filter‐feeding Daphnia during the first half of the summer season. In Lofty Lake, cladocerans made up to 93% of biomass, whereas in North Halfmoon Lake both cladocerans and calanoids were strongly represented.3. Total zooplankton and cladoceran biomasses were inversely correlated with chlorophyll a (chl a). The same relationship was found between large Daphnia (≥ 1 mm) and chl a. These relationships suggest that the decline in Daphnia may have been caused by an increase in cyanobacteria biomass during bloom events.4. There were minor changes in rotifer populations after liming; however, these changes have been caused by natural year‐to‐year variation rather than liming. In general, cladocerans showed an increase in body size and population biomass when pre and post‐treatment data were compared by means of ANCOVA. Statistical analysis showed that there were more cladocerans per unit of chl a after liming; however, further research is needed to relate these patterns unambiguously to the application of lime as a restoration technology.
Fatty acid biomarkers show dietary differences between dominant chironomid taxa in Lake Erken
Authors: Goedkoop  , Sonesten  , Markensten  , Ahlgren  
Published: March 2003

1. In this field study, diatom‐specific and bacteria‐specific fatty acids were used as biomarkers to evaluate the differences in diet betweenChironomus plumosus (a spring‐emerging cohort) andC. anthracinus(an autumn‐emerging cohort), andProcladiusspp. Furthermore, total lipid content ofChironomuslarvae was analysed.2. Individual dry mass of the spring cohort ofC. plumosusrapidly increased during spring and early summer. Surprisingly, the autumn‐emerging cohort showed remarkably little growth over the same time interval. The individual dry mass ofC. anthracinusinitially declined in early spring, but then increased during April and May.3. Accumulation of the diatom‐specific fatty acid palmitoleic acid (16 : 1ω7) during spring was much higher inC. plumosus(> 3‐fold increase) than inC. anthracinus(1.5‐fold). Conversely, the bacterial indicatingisoform of septadecanoic acid (17 : 0i) was higher inC. anthracinusthan in the spring‐emerging cohort ofC. plumosus. This shows thatC. plumosusassimilates energy from the spring diatom bloom to a greater degree, whereasC. anthracinusfeeds more exclusively on detritus in the sediment.4. Concentrations of 17 : 0iinProcladiuslarvae were 0.54 ± 0.13 mg g–1, i.e. consistently higher than for bothChironomustaxa, indicating that this predator gains a relatively high fraction of its energy through detrital pathways (from bacteria).5. These results show that fatty acid biomarkers can be an appropriate tool to detect differences in larval diet between coexisting chironomid species, between two closely relatedChironomusspecies and between different cohorts.6. The different feeding modes of bothChironomusspecies may be important for among‐lake distribution patterns, with filter‐feedingC. plumosusbeing dominant in relatively shallow lakes and deposit‐feedingC. anthracinusmore common in deeper lakes with stable stratifications. This conjecture was supported by a compilation of data from Lake Mälaren.