bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of HCl–HF purification treatment on chemical composition and structure of humic acids
Authors: Sánchez‐ Monedero M. A. , Roig A. , Cegarra J. , Bernal M. P. , Paredes C. 
Published: March 2003

SummarySample preparation for the study of humic acids involves a purification treatment to remove both mineral and organic components extracted along with the humic substances. The effects of HCl–HF purification on the chemical composition and structure of humic acids were studied in samples from eight different composts. Only small increases in the concentrations of C, N and H and a decrease in O were found in purified humic acids when compared with the unpurified materials, no more than 10% of average concentration. Total and phenolic acidity increased in the purified materials, whereas carboxylic and carbonyl acidity showed no statistically significant differences as a result of the purification. Gel permeation chromatography showed that only minor changes occurred in molecular size distribution of the humic acids, and the infrared spectra showed no appreciable differences between the purified humic acids and the untreated materials. We conclude that the HCl–HF treatment successfully reduced the ash contents of the humic acids without modifying their chemical composition and structure significantly.
Changes in soil chemistry and aggregate stability induced by fertilizer applications, burning and trash retention on a long‐term sugarcane experiment in South Africa
Authors: Graham M. H. , Haynes R. J. , Meyer J. H. 
Published: March 2003

SummaryThroughout the world there is a trend towards retaining crop residues rather than burning them. For this reason, changes in soil chemistry and aggregation in a Vertisol induced by 59 years of burning or green cane harvesting with or without annual fertilizer applications were investigated. Crop residues were either burnt prior to harvest with the harvest residues raked off (R1), burnt prior to harvest with the harvest residues left on the soil surface (R2), or left unburnt with all the trash left on the soil surface (R3). Concentrations of organic C in the surface 10 cm of soil increased with fertilizer applications and with increasing amounts of crop residue returned in the order R1 < R2 < R3. Fertilizer applications caused an accumulation of residual P in both inorganic (Pi) and organic (Po) forms. A sequential P fractionation showed that fertilizer P accumulated in both labile and recalcitrant Pi and Po forms, and trash retention caused an accumulation of recalcitrant Po. Concentrations of K decreased in the unfertilized R1and R2treatments because K reserves were depleted. By contrast, there was an increase in the concentrations of K in the fertilized R3treatment. The soil became more acid on the fertilized and, to a lesser extent, trash retention plots. We attribute this to nitrification and subsequent nitrate leaching. Acidification resulted in a loss of exchangeable Ca and Mg, a decrease in ECEC, and an increase in the concentrations of total and monomeric Al in soil solution, in exchangeable Al3+and in the buffering reserve of non‐exchangeable Al associated with organic matter. Aggregate stability was increased by increasing crop residues but decreased by fertilizer applications. The decrease was attributed to an increase in the proportion of exchangeable cations present in monovalent form due to applications of fertilizer K and leaching of Ca and Mg. We conclude that trash retention and annual fertilizer applications have substantial long‐term effects on both organic matter status and soil pH and therefore on other soil chemical and physical properties.
Potassium bentonites reduce radiocaesium availability to plants
Authors: Vandenhove H. , Smolders E. , Cremers A. 
Published: March 2003

SummaryAfter the Chernobyl accident in 1986 the fate of radiocaesium from the fallout became of pressing concern. Specific soil amendments, as K fertilizer and specific clay minerals, promised to mitigate the worst effects. We therefore investigated the influence of bentonite and the K status of the soil on the radiocaesium equilibria in soil and on its availability to ryegrass.A sample of a sandy soil was contaminated with 134Cs and amended with K and Ca salts (0–0.97 mmol kg−1) and K bentonite (0–2%). After 4 weeks' incubation of the soil mixtures, ryegrass was grown for 18 weeks in a pot trial and harvested on seven occasions. No significant treatment effects on 134Cs activity concentrations were found at the first and second harvest. From the third harvest onwards, however, 134Cs activity concentrations in the grass were reduced up to twofold (P < 0.05) by increasing rates of K bentonite. Adsorption studies with 137Cs revealed that the radiocaesium interception potential (RIP) of the soil–bentonite mixtures (> 1% bentonite) increased about 10‐fold during plant growth. The RIP of the K bentonite after plant growth was up to 10 times larger than that of pure illite. The formation of specific Cs sorption sites is ascribed to the in situ illitization of the K bentonite. The increase in RIP during plant growth is reflected in a decrease in exchangeable K+ at 2% K bentonite of about 18%. Radiocaesium concentrations in grass could be reliably predicted from the Cs+ and K+ concentrations in the soil solution. Adding K bentonite to a soil contaminated with radiocaesium is effective in fixing Cs in the soil.
Environmental effects on swordfish and blue shark catch rates in the US North Pacific longline fishery
Authors: Bigelow Keith A. , Boggs Christofer H. , HE XI 
Published: March 2003

Generalized additive models (GAMs) were applied to examine the relative influence of various factors on fishery performance, defined as nominal catch‐ per‐unit‐effort (CPUE) of swordfish (Xiphias gladius) and blue shark (Prionace glauca) in the Hawaii‐based swordfish fishery. Commercial fisheries data for the analysis consisted of a 5 year (1991–1995) time series of 27 901 longline sets. Mesoscale relationships were analysed for seven physical variables (latitude, longitude, SST, SST frontal energy, temporal changes in SST (ΔSST), SST frontal energy (ΔSST frontal energy) and bathymetry), all of which may affect the availability of swordfish and blue shark to the fishery, and three variables (number of lightsticks per hook, lunar index, and wind velocity) which may relate to the effectiveness of the fishing gear. Longline CPUE data were analysed in relation to SST data on three spatiotemporal scales (18 km weekly, 1°‐weekly, 1°‐monthly). Depending on the scale of SST data, GAM analysis accounted for 39–42% and 44–45% of the variance in nominal CPUE for swordfish and blue shark, respectively. Stepwise GAM building revealed the relative importance of the variables in explaining the variance in CPUE. For swordfish, by decreasing importance, the variables ranked: (1) latitude, (2) time, (3) longitude, (4) lunar index, (5) lightsticks per hook, (6) SST, (7) ΔSST frontal energy, (8) wind velocity, (9) SST frontal energy, (10) bathymetry, and (11) ΔSST. For blue shark, the variables ranked: (1) latitude, (2) longitude, (3) time, (4) SST, (5) lightsticks per hook, (6) ΔSST, (7) ΔSST frontal energy, (8) SST frontal energy, (9) wind velocity, (10) lunar index, and (11) bathymetry. Swordfish CPUE increased with latitude to peak at 35–40°N and increased in the vicinity of temperature fronts and during the full moon. Shark CPUE also increased with latitude up to 40°N, and increased westward, but declined abruptly at SSTs colder than 16°C.As a comparison with modelling fishery performance in relation to specific environmental and fishery operational effects, fishery performance was also modelled as a function of categorical time (month) and area (2° squares) variables using a generalized linear model (GLM) approach. The variance accounted for by the GLMs was ≈ 1–3% lower than the variance explained by the GAMs. Time series of swordfish and blue shark CPUE standardized for the environmental and operational variables quantified in the GAM and for the time‐area effects in the GLM are presented. For swordfish, both nominal and standardized time series indicate a decline in CPUE, whereas the opposite trend was seen for blue shark.
An oceanographic characterization of swordfish (Xiphias gladius) longline fishing grounds in the springtime subtropical North Pacific
Authors: Seki Michael P. , Polovina Jeffrey J. , Kobayashi Donald R. , Bidigare Robert R. , Mitchum Gary T. 
Published: March 2003

AbstractDuring January–May, surface manifestation of multiple, individual basin‐scale fronts accentuate the central North Pacific Subtropical Frontal Zone (STFZ) system. The most prominent of these fronts are climatologically located at 32°−34°N and at 28°−30°N latitudes [herein nominally referred to as the ‘Subtropical Front’ (STF) and the ‘South Subtropical Front’ (SSTF), respectively], although considerable interannual variability in both position and intensity is observed. This seasonally dynamic system is also the region typically targeted by the Hawaii‐based swordfish (Xiphias gladius) longline fishing fleet, where the presence, position, and strength of the convergent fronts are believed to play a key role with regard to the catch and catch rates of swordfish. Information furnished by a recent series of meridional hydrographic surveys and concurrent satellite remote sensing data elucidate structural patterns and coupling of the physics and biology associated with these fronts. This enables a re‐characterization of the spring North Pacific STFZ and offers new insight into the seasonal variability of the phytoplankton dynamics in the subtropical North Pacific.On synoptic time scales, geographical positioning of the fronts may be systematically identified through surface outcropping of diagnostic thermohaline isopleths and therefore readily discerned from both shipboard surveys and by spaceborne sensors. The STF during spring can be characterized by the surface expression of the 34.8 isohaline and the 17°C isotherm within the frontal gradient. Biologically, the STF marks the transition from low chloropigment (chlorophyll + phaeopigments), nutrient‐depleted surface waters to the south to a more productive regime to the north. To the south, the 20°C and 35.0 surface isotherm and isohaline, respectively, are characteristically embedded in the thermohaline gradients associated with the SSTF. A sharp increase in depth‐integrated chloropigment is also observed at the SSTF and is ascribed to an increase in the concentration and thickness of the subsurface chloropigment maximum (SCM) prompted by the shoaling of the nutricline with the thermocline structure into the euphotic zone.
Can a community of small‐bodied grazers control phytoplankton in rivers?
Authors: Gosselain V. , Viroux L. , Descy J. ‐P. 
Published: March 2003

1. Phytoplankton, zooplankton and grazing were monitored throughout the growing season for three years (1994–96) in the Belgian section of the River Meuse.2. A size structure analysis of the algal community shows that there was a summer shift toward larger algal units, following a decline in phytoplankton biomass. These changes occurred after an increase in zooplankton biomass and diversity.3. Daily filtration rates of grazers ranged from 1 to 113% day–1 and maxima were observed during the summer period. Higher rates tended to correspond with peaks of rotifer biomass. A decline in total phytoplankton biomass within two weeks followed the increase in zooplankton biomass and filtration rate. A rapid biomass recovery was then observed, along with a shift of the algal community toward larger units. When grazing activity was not sustained, due to zooplankton fluctuations, the change in phytoplankton size structure was less marked.4. We suggest that the composition of the phytoplankton community of large rivers may at times be controlled by grazers. However, such biotic interactions can take place only when physical constraints are reduced, i.e. when discharge is low, and when increased transfer time, high temperature and availability of grazeable algae allow high zooplankton biomass.
Measurements of phosphorus uptake by macrophytes and epiphytes from the LaPlatte River (VT) using 32P in stream microcosms
Authors: Pelton Deborah K. , Levine Suzanne N. , Braner Moshe 
Published: March 2003

1. Phosphorus (P) uptake by macrophytes and epiphytes from the LaPlatte River (VT) was examined in the laboratory by adding 32PO4‐P to recirculating stream microcosms.2. Water, plugs of sediment and plants were removed from the river and placed into the microcosms. 32PO4‐P was then added either to the water or the sediment, and its incorporation into plants and epiphytes was monitored over 3 days. Uptake was examined at both ambient (5 μg L–1) and increased (50 μg L–1) soluble reactive phosphorus (SRP) concentrations. A computer program was developed to fit curves to the radiotracer data and calculate rate constants for the simultaneous transfer of 32P among compartments.3. Both macrophytes and epiphytes removed P from the water, but epiphyte uptake of P was more rapid. Phosphate enrichment stimulated P uptake by both macrophytes and epiphytes. Macrophytes also obtained P from the sediment. The relative contribution of P to macrophytes from the water vs. that from the sediment appeared to vary with SRP in the overlying water. Accurate estimates of rates of P uptake from sediments by macrophytes were difficult to obtain however, due to very low and highly variable unit rate constants for P uptake and uncertainty about the magnitude of the phosphate pool available for uptake.4. SRP concentrations were greater in the overlying water than in the sediment pore water of stream microcosms in the present study. Numerous reports in the literature have suggested that this condition favours uptake by macrophyte stems and leaves rather than by roots.5. Phosphate uptake from the water by macrophytes in shallow streams may be more common than for macrophytes in lakes.
Spatial scale and the aggregation of stream macroinvertebrates associated with leaf packs
Authors: Murphy John F. , Giller Paul S. , Horan Margaret A. 
Published: March 2003

1. An experimental field study examined the aggregation of stream macroinvertebrates associated with leaf packs over different spatial scales (several metres–km) (extent), at different patch sizes (grain) and temporal scales (2 and 4 weeks).2. Standardized leaf packs were constructed and set in eighteen blocks of nine equally spaced packs in glide areas over a 2 km stretch of a wooded stream. The distribution of macroinvertebrates colonizing the artificial leaf packs was investigated to examine the extent of both intraspecific and interspecific aggregation across leaf packs.3. All major colonizing taxa were intraspecifically aggregated across the leaf packs. Aggregation decreased with increasing patch size (grain) (from pack to block), and also decreased with decreasing spatial extent (from 2 km stretch to within‐block scale) with patch size held constant. Interspecific associations among all major taxa were not common on most occasions at the short temporal scale, although the proportion of significant associations tended to increase somewhat over time and with spatial scale, but did not exceed 42% of all possible associations. The vast majority of significant associations were positive rather than negative.4. The influence of heterogeneity in a number of environmental variables measured for each leaf pack (accumulated detritus and sediment, leaf mass, flow and depth) on the distribution of invertebrates was considered, but this could only partially explain the variation in macroinvertebrate abundance across leaf packs.5. The roles of intrinsic aggregation and stochastic processes were examined as alternative explanations for the distribution patterns observed. It is apparent from this study that intrinsic aggregation, in concert with resource partitioning, influences the community structure of stream macroinvertebrates associated with leaf packs. These findings may also have implications for the distribution of taxa in the benthos as a whole.
Patterns in the epilithic community of a lake littoral
Authors: Harrison Simon S. C. , Hildrew And Alan G. 
Published: March 2003

1. The algae and sedentary macroinvertebrates on the upper surface of stones from the littoral of Crosemere were investigated over 13 months. This lake is one of a series of eutrophic meres of glacial origin in the English Midlands.2. Stones were taken from shallow and deep areas in the littoral and from areas shaded by bankside trees and those away from trees. This gave four habitat types: open/shallow; open/deep; shade/shallow; shade/deep. Epilithic algae and sedentary macroinvertebrates from the upper surfaces of the stones were quantified monthly for each habitat type.3. Chlorophyll a and ash‐free dry mass both showed a strong seasonal pattern common to all habitat types, with a spring peak declining to a summer minimum, followed by a small autumn recovery, and a winter minimum.4. In terms of percentage cover, Cladophora glomerata showed a markedly different pattern. There were strong differences between habitat types, with shaded stones from the shallows, in particular, having very sparse Cladophora cover. In the open, Cladophora cover was high in summer and low at other times.5. The invertebrate community was dominated by retreat‐dwelling larvae of the psychomyiid caddis, Tinodes waeneri, and four species of chironomids with tube‐building larvae, Cricotopus sylvestris, Microtendipes pedellus, Glyptotendipes pallens and Endochironomus albipennis. For Tinodes, Cricotopus and Microtendipes, peaks of density occurred chiefly beneath trees in spring and summer.6. The seasonal pattern of algal abundance showed little relationship with that of invertebrate biomass. The ratio of chlorophyll a to ash‐free dry mass also declined in summer, despite the higher invertebrate biomass. This indicated that grazing was not the dominant factor diminishing algal abundance seasonally. It seems likely that algae were limited chiefly by physical factors, such as light and temperature, and by nutrients, particularly nitrates, which decline in summer in the epilimnion of the lake.7. Grazing may have contributed to spatial patchiness of algae in summer, however, particularly that of Cladophora. The scarcity of Cladophora on shallow, shaded stones coincided with a high abundance of Tinodes on these stones in early summer. Riparian trees could thus have affected epilithic algae, not only by shading but also indirectly through the supply of grazers.
Influence of submerged macrophytes on sediment composition and near‐bed flow in lowland streams
Authors: Sand‐jensen Kaj 
Published: March 2003

1. Submerged macrophytes have important physical and structural effects on lowland streams. This study investigated the ability of submerged macrophytes to modify the near‐bed flow and to retain mineral and organic particles in patches of four common macrophytes in shallow Danish streams during mid‐summer.2. In dense patches of Callitriche cophocarpa and Elodea canadensis, where near‐bed velocity was reduced, the sediment surface was markedly raised and enriched with fine particles. In dense patches of Ranunculus peltatus, fine sediments were deposited among rooted shoots in the upstream part of the patches, while erosion and coarse sediments prevailed in the downstream part of the patches because of the strong vortices that formed at the rear and moved up under the trailing canopy. The open canopy of Sparganium emersum, with its streamlined leaves, had little effect on flow and sediment.3. Patterns of sediment deposition and composition were closely related to the morphology and canopy structure of plant species and the presence of low velocity above the sediment among the rooted shoots. The mineral particles retained probably originate from bed‐load, and the enrichment with finer particles within the patches probably results mainly from size‐selective processes during erosion and transport of particles rather than during deposition. The mixed sediment composition within patches suggests that the flow‐resistant shoots generate an environment conducive to deposition of all transported particles.4. Fine sediments within macrophyte beds contained high concentrations of organic matter, carbon, nitrogen and phosphorus. The wide scatter in the relationships between mineral grain size and the content of organic matter and nutrients reflects the spatial and temporal complexity of erosion, transport and sedimentation of mineral and organic particles.5. Enrichment of sediment within macrophyte beds relative to the surrounding substratum ranged from 780 g organic matter m–2, 30 g N m–2 and 25 g P m–2 for the flow‐resistant dense canopies af Callitriche cophocarpa to 150 g organic matter m–2, 6.6 g N m–2 and 3.4 g P m–2 for the open canopies of Sparganium emersum. Retention of nutrient‐rich particles within the macrophyte beds is probably of limited importance for plant growth in most lowland European streams, because macrophyte growth is rarely nutrient limited.
Microflow regimes and the distribution of macroinvertebrates around stream boulders
Authors: Bouckaert Frederick W. , Davis And Jenny 
Published: March 2003

1. An acoustic doppler velocimeter (ADV) was used to collect velocity data in three dimensions in front of and in the wakes of selected boulders in a riffle, where macroinvertebrates were also sampled.2. Shear stress was calculated from the covariance of downstream and vertical velocity fluctuations.3. Velocities, shear stress and turbulence measured at three points above the bed in the front and wake regions of riffle boulders were consistent with predicted patterns of flow around isolated roughness elements. There was a significant difference in mean velocities, but not near‐bed velocities between front and wake regions. At 5 mm above the bed, velocities in both front and wake regions were greatly reduced, relative to the mean velocity (at 0.4 × total depth). Flows at the bed were directed upstream as part of the vortex formed at the front of the boulder and as part of the recirculation occurring in the wake.4. Shear stress was highest in the vertical plane in the wake of the boulders. Turbulence intensity and turbulent kinetic energy were greatest in the wake region, in both the down‐stream and cross‐stream directions. However, these results were not statistically significant. Large standard errors associated with measurements within wakes indicated that wake flows are highly variable. Further research is needed to determine the most appropriate methods of analysing differences associated with such variable flow regimes.5. The benthic macroinvertebrate fauna was significantly richer and more abundant in the wakes than at the front of boulders. Classification and ordination revealed the presence of distinct front and wake benthic communities. These differences could not be attributed to velocity differences within the benthic microhabitat, because near‐bed velocities were greatly reduced in both the front and wake regions. The fauna may be responding to the highly variable turbulent regime of the wake and associated effects, such as increased deposition of particulate organic matter and exchange of dissolved gases.6. Despite the complex flow patterns inherent in natural streamflow, a large roughness element (boulder) appears to predominate in determining microflows within in its immediate surroundings. The design of some benthic sampling programs (e.g. for biomonitoring) may need to incorporate hydraulic microhabitat considerations.7. The fine‐scale field measurements obtained with the ADV indicate that experimental determination of the role of turbulence in the ecology of stream benthos is now both possible and desirable.