bluuebunny/crossref_metadata_2025 huggingface dataset:
Distribution of benthic diatoms in U.S. rivers in relation to conductivity and ionic composition
Authors: Potapova Marina , Charles Donald F.
Published: July 2003

We quantified the relationships between diatom relative abundance and water conductivity and ionic composition, using a dataset of 3239 benthic diatom samples collected from 1109 river sites throughout the U.S.A. [U.S. Geological Survey National Water‐Quality Assessment (NAWQA) Program dataset]. This dataset provided a unique opportunity to explore the autecology of freshwater diatoms over a broad range of environmental conditions.

Conductivity ranged from 10 to 14 500 μS cm−1, but most of the rivers had moderate conductivity (interquartile range 180–618 μS cm−1). Calcium and bicarbonate were the dominant ions. Ionic composition, however, varied greatly because of the influence of natural and anthropogenic factors.

Canonical correspondence analysis (CCA) and Monte Carlo permutation tests showed that conductivity and abundances of major ions (HCO + CO, Cl−, SO, Ca2+, Mg2+, Na+, K+) all explained a statistically significant amount of the variation in assemblage composition of benthic diatoms. Concentrations of HCO + CO and Ca2+ were the most significant sources of environmental variance.

The CCA showed that the gradient of ionic composition explaining most variation in diatom assemblage structure ranged from waters dominated by Ca2+ and HCO + CO to waters with higher proportions of Na+, K+, and Cl−. The CCA also revealed that the distributions of some diatoms correlated strongly with proportions of individual cations and anions, and with the ratio of monovalent to divalent cations.

We present species indicator values (optima) for conductivity, major ions and proportions of those ions. We also identify diatom taxa characteristic of specific major‐ion chemistries. These species optima may be useful in future interpretations of diatom ecology and as indicator values in water‐quality assessment.
Spatial and temporal distribution of fish and zooplankton in a shallow lake
Authors: Romare Pia , Berg Søren , Lauridsen Torben , Jeppesen Erik
Published: July 2003

Summary 1. We performed both a large‐ and a small‐scale echo sounding study on the spatial and temporal distribution of fish (mainly roach, Rutilus rutilus and perch, Perca fluviatlis), as well as a small‐scale study of zooplankton distribution in the small, shallow and eutrophic Lake Hanebjerg in Denmark. In the small‐scale study, sampling was conducted in open water as well as in the edge zone immediately outside two different types of vegetation.

2. Fish daytime abundances differed between the northern and the southern parts of the lake and, on a small scale, small fish aggregated in the edge zones during day, preferably outside dense emergent vegetation. Copepods avoided emergent vegetation, while cladocerans showed no habitat preference. Both small fish and cladoceran numbers were found to be higher during night than day.

3. The relative abundance (number per sample) of cladocerans in the edge zone immediately outside vegetation was negatively correlated with the relative abundance of fish in that zone. There was no correlation between cladoceran and fish abundance in open water, or between the relative abundance of copepods and fish.

4. The presence of pelagic piscivores in combination with avoidance behaviour of both fish and zooplankton is a likely explanation for the observed distribution of small fish and cladocerans in Lake Hanebjerg. Both small‐ and large‐scale distribution patterns may be dependent on the type and distribution of complex structure in the lake. Even in a small lake, large‐scale patterns may affect the interpretation of small‐scale data.
Structuring of the cyanobacterial community by pelagic fish in subtropical reservoirs: experimental evidence from Australia
Authors: Hunt Richard J. , Matveev Vlad , Jones Gary J. , Warburton Kevin
Published: July 2003

1. Subtropical reservoirs of Australia are commonly subject to summer blooms of cyanobacteria. The potential for food web manipulation to control cyanobacterial blooms was investigated in Lake Maroon, south east Queensland using enclosures in which the density of the Australian gudgeon Hypseleotris spp. was manipulated.

2. Zooplankton biomass and community structure were strongly affected by fish density. A size dependent predation effect of Hypseleotris on zooplankton was observed at ambient fish densities, and the community shifted towards a dominance of copepod juveniles and nauplii. Substantial increases in the populations of Ceriodaphnia and calanoid copepods were observed at low fish densities and in the absence of fish.

3. At ambient fish densities total phytoplankton and the proportion of cyanobacteria were maintained at levels similar to those prevailing at day 0. Total phytoplankton and the proportion of cyanobacteria decreased substantially at low fish densities and in the absence of fish. Chlorophytes became dominant in the ‘no fish’ treatment and the grazing‐resistant species Oocystis and Dictyosphaerium were significantly higher than at ambient fish densities.

4. The experiment demonstrated a strong positive relationship between Hypseleotris density and cyanobacteria, and the results suggest that subtropical reservoirs may be suited to food web manipulation as a means of controlling summer cyanobacterial blooms.
Land‐use influences macroinvertebrate community response following a pulse disturbance
Authors: Collier Kevin J. , Quinn John M.
Published: July 2003

1. We tested the hypothesis that interactions between disturbance types can influence invertebrate community response and recovery in two streams draining pasture (press‐pulse disturbance) and native forest (pulse disturbance) catchments before and after a one‐in‐28‐year flood. We also sampled drift and adult insects to gain insights into the relative importance of these two postdisturbance recolonisation pathways.

2. Taxa numbers and total density declined markedly at the forested site after the flood, but there was a delayed response at the pasture site, reflecting greater initial resistance to this pulse disturbance among taxa adapted to the underlying press disturbance.

3. Community composition was less stable at the pasture site where per cent abundance of taxa was highly variable prior to the flood and over the 2‐year postflood sampling period. After the flood, the pasture stream fauna was more heavily dominated by vagile taxa, including several chironomid species and hydroptilid caddisflies.

4. Taxa numbers and densities recovered to preflood levels within 5–7 months at both sites, but a range of taxa‐specific responses was observed that took up to 18 months to recover to preflood densities. Community stability at the pasture site had not returned to preflood composition by 2 years postflood.

5. Changes in drift densities of several common stream invertebrates at the pasture site reflected postflood changes in benthic densities and seasonally low drift in winter. Terrestrial invertebrates dominated drift at the pasture site for 3 months postflood whereas Ephemeroptera were most common at the native forest site.

6. Flight patterns of selected adult aquatic insects showed a strongly seasonal pattern. Abundance of adults at the pasture site in the second year following the flood increased in line with the recovery of the non‐Dipteran benthic fauna. Significant upstream flight occurred for several caddisfly species at the native forest site, and weakly directional or downstream flight was evident for most common Plecoptera and Ephemeroptera.

7. This study indicates that the magnitude and duration of responses to major pulse disturbances can depend on the presence or absence of an underlying press disturbance. This finding has implications for monitoring, and suggests that a knowledge of disturbance history beyond 2 years may be required to interpret mechanisms contributing to observed land‐use impacts.
Factors affecting ammonium uptake in streams – an inter‐biome perspective
Authors: Webster Jackson R. , Mulholland Patrick J. , Tank Jennifer L. , Valett H. Maurice , Dodds Walter K. , Peterson Bruce J. , Bowden William B. , Dahm Clifford N. , Findlay Stuart , Gregory Stanley V. , Grimm Nancy B. , Hamilton Stephen K. , Johnson Sherri L. , Martí Eugènia , Mcdowell William H. , Meyer Judy L. , Morrall Donna D. , Thomas Steven A. , Wollheim Wilfred M.
Published: July 2003

1. The Lotic Intersite Nitrogen eXperiment (LINX) was a coordinated study of the relationships between North American biomes and factors governing ammonium uptake in streams. Our objective was to relate inter‐biome variability of ammonium uptake to physical, chemical and biological processes.

2. Data were collected from 11 streams ranging from arctic to tropical and from desert to rainforest. Measurements at each site included physical, hydraulic and chemical characteristics, biological parameters, whole‐stream metabolism and ammonium uptake. Ammonium uptake was measured by injection of 15N‐ammonium and downstream measurements of 15N‐ammonium concentration.

3. We found no general, statistically significant relationships that explained the variability in ammonium uptake among sites. However, this approach does not account for the multiple mechanisms of ammonium uptake in streams. When we estimated biological demand for inorganic nitrogen based on our measurements of in‐stream metabolism, we found good correspondence between calculated nitrogen demand and measured assimilative nitrogen uptake.

4. Nitrogen uptake varied little among sites, reflecting metabolic compensation in streams in a variety of distinctly different biomes (autotrophic production is high where allochthonous inputs are relatively low and vice versa).

5. Both autotrophic and heterotrophic metabolism require nitrogen and these biotic processes dominate inorganic nitrogen retention in streams. Factors that affect the relative balance of autotrophic and heterotrophic metabolism indirectly control inorganic nitrogen uptake.
Combined stable isotope and gut contents analysis of food webs in plant‐dominated, shallow lakes
Authors: Jones J. Iwan , Waldron Susan
Published: July 2003

Summary 1. To determine feeding links between primary producers, invertebrates and fish, stable isotope analyses and gut content analyses of fish were conducted on the components of four shallow, eutrophic to hypertrophic, plant‐dominated lakes.

2. Although separation of basal resources was possible, the diets of both fish and invertebrates were broad, comprising food from different compartments (planktonic, epiphytic/benthic), as well as from different trophic levels.

3. Mixing models were used to determine the extent to which periphyton production supported higher trophic levels. Only one species of invertebrate relied upon periphyton production exclusively.

4. Fish density affected the diets of invertebrates. The response was different for planktonic and epiphytic/benthic invertebrates. The proportion of periphyton production in the diets of zooplankton appeared to increase with fish density, whilst it decreased for other invertebrates.

5. As all zooplankton samples were collected in the open water at dusk, these results are further evidence for the diurnal horizontal migration of zooplankton. Although not conclusive, they are consistent with a behavioural response by invertebrates and zooplankton in the presence of fish.
An experimental study of the effects of nutrient supply and Chaoborus predation on zooplankton communities of a shallow tropical reservoir (Lake Brobo, Côte d'Ivoire)
Authors: Pagano Marc , Koffi Maryse Aka , Cecchi Philippe , Corbin Daniel , Champalbert Gisèle , Saint‐Jean Lucien
Published: July 2003

1. Based on two mesocosm experiments and 10 in vitro predation experiments, this work aimed to evaluate the impact of nutrient supply and Chaoborus predation on the structure of the zooplankton community in a small reservoir in Côte d'Ivoire.

2. During the first mesocosm experiment (M1), P enrichment had no effect on phytoplankton biomass (chlorophyll a) but significantly increased the biomass of some herbivorous zooplankton species (Filinia sp, Ceriodaphnia affinis). During the second experiment (M2), N and P enrichment greatly increased phytoplankton biomass, rotifers and cladocerans (C. affinis, C. cornuta, Moina micrura and Diaphanosoma excisum). In both experiments, nutrient addition had a negative impact on cyclopoid copepods.

3. Larger zooplankton, such as cladocerans or copepodites and adults of Thermocyclops sp., were significantly reduced in enclosures with Chaoborus in both mesocosm experiments, whereas there was no significant reduction of rotifers and copepod nauplii. This selective predation by Chaoborus shaped the zooplankton community and modified its size structure. In addition, a significant Chaoborus effect on chlorophyll a was shown in both experiments.

4. The preference of Chaoborus for larger prey was confirmed in the predation experiments. Cladocerans D. excisum and M. micrura were the most selected prey. Rotifer abundance was not significantly reduced in any of the 10 experiments performed.

5. In conclusion, both bottom‐up and top‐down factors may exert a structuring control on the zooplankton community. Nutrients favoured more strictly herbivorous taxa and disadvantaged the cyclopoid copepods. Chaoborus predation had a strong direct negative impact on larger crustaceans, favoured small herbivores (rotifer, nauplii) and seemed to cascade down to phytoplankton.
Hyporheic community composition in a gravel‐bed stream: influence of vertical hydrological exchange, sediment structure and physicochemistry
Authors: Olsen Dean A. , Townsend Colin R.
Published: July 2003

Summary 1. We studied the relative contributions of the magnitude and direction of vertical hydrological exchange, subsurface sediment composition and interstitial physicochemistry in determining the distribution of hyporheic invertebrates in the Kye Burn, a fourth order gravel‐bed stream in New Zealand.

2. In winter 2000 and summer 2001, we measured vertical hydrological gradient (VHG), dissolved oxygen, water temperature and water chemistry using mini‐piezometers, each installed in a different upwelling or downwelling zone. Next to every piezometer, a freeze core sample was taken to quantify the sediment, particulate organic matter and invertebrates.

3. Dissolved oxygen concentration at 25 cm was high on both occasions (>9 mg L−1) but was higher in winter than summer. Interstitial water temperature was higher in down than upwellings and was substantially higher in summer than winter. Other features of the subsurface sediments and interstitial nitrate–nitrite concentrations were similar on both occasions and in up and downwellings. Interstitial ammonium and soluble reactive phosphorous concentrations were higher in winter than summer and ammonium was higher in up than downwelling areas.

4. The proportion of fine sediment (63 μm–1 mm), sediment heterogeneity and VHG accounted for the greatest proportion of variance in invertebrate distributions in both summer and winter.

5. The hyporheos was numerically dominated by early instar leptophlebiid mayfly nymphs and asellotan isopods. Water mites were a taxonomically diverse group with 13 genera. Taxonomic diversity (Shannon–Weaver), but not taxon richness, was higher in upwelling areas, reflecting lower numerical dominance by a few taxa in these locations.

6. Sediment composition (particularly the amount of fine sediments) and vertical hydrological exchange determined the composition and distribution of the hyporheos. Patchiness in these factors is important in planning sampling regimes or field manipulations in the hyporheic zone.
Macrophytic, epipelic and epilithic primary production in a semiarid Mediterranean stream
Authors: Velasco J. , Millan A. , Vidal‐Abarca M. R. , Suarez M. L. , Guerrero C. , Ortega M.
Published: July 2003

Summary 1. Primary production by Chara vulgaris and by epipelic and epilithic algal assemblages was measured in a semiarid, Mediterranean stream (Chicamo stream, Murcia, Spain) during one annual cycle.

2. The rates of gross primary production (GPP) and community respiration (CR) were determined for each algal assemblage using oxygen change in chambers. The net daily metabolism (NDM) and the GPPd−1 : CR24 ratio were estimated by patch‐weighting the assemblage‐level metabolism values.

3. Gross primary production and CR showed significant differences between assemblages and dates. The highest rates were measured in summer and spring, while December was the only month when there were no significant differences in either parameters between assemblages. GPP was strongly correlated with respiration, but not with algal biomass.

4. Chara vulgaris showed the highest mean annual metabolic rates (GPP = 2.80 ± 0.83 gC m−2 h−1, CR = 0.76 ± 0.29 gC m−2 h−1), followed by the epilithic assemblage (GPP = 1.97 ± 0.73 gC m−2 h−1, CR = 0.41 ± 0.12 gC m−2 h−1) and epipelic algae (GPP = 1.36 ± 0.22 gC m−2 h−1, CR = 0.39 ± 0.06 gC m−2 h−1).

5. The epipelic assemblage dominated in terms of biomass (82%) and areal cover (88%), compared with the other primary producers. Epipelic algae contributed 84% of gross primary production and 86% of community respiration in the stream.

6. Mean monthly air temperature was the best single predictor of macrophyte respiration and of epipelic GPP and CR. However, ammonium concentration was the best single predictor of C. vulgaris GPP, and suspended solid concentration of epilithon GPP and CR.

7. Around 70% of the variation in both mean GPP and mean CR was explained by the mean monthly air temperature alone. A multiple regression model that included conductivity, PAR and nitrates in addition to mean monthly air temperature, explained 99.99% of the variation in mean CR.

8. Throughout the year, NDM was positive (mean value 7.03 gC m−2 day−1), while the GPP : CR24 ratio was higher than 1, confirming the net autotrophy of the system.
Predation and refugia: implications for Chaoborus abundance and species composition
Authors: Wissel B. , Yan N. D. , Ramcharan C. W.
Published: July 2003

1. Previous studies have suggested that the occurrence of larval Chaoborus in lakes may be affected by fish predation, pH, elevation, temperature, nutrient level, water transparency and interspecific competition, but so far, a detailed statistical evaluation of these findings has not been performed.

2. The aim of this study was to apply regression and ordination techniques to a large data set of 56 lakes in order to test which variables related to lake morphology, water chemistry, and fish predation determine (1) the abundance of individual Chaoborus species and (2) their species composition.

3. Individual Chaoborus species were influenced by very different sets of environmental factors. Nutrient levels positively affected the largest species, Chaoborus americanus, which was restricted to fishless lakes. Abundance of the smallest and most transparent species, C. punctipennis, seemed to be controlled more by the larger Chaoborus species than by fish. Larger chaoborids required low water clarity in order to co‐exist with fish, probably to increase refuge availability. Generally, small lakes (for C. flavicans/C. trivittatus) and shallow lakes (for C. punctipennis) supported higher abundances of Chaoborus.
Nutritional quality of leaf detritus altered by elevated atmospheric CO2: effects on development of mosquito larvae
Authors: Tuchman Nancy C. , Wahtera Kirk A. , Wetzel Robert G. , Russo Nicole M. , Kilbane Grace M. , Sasso Lisa M. , Teeri James A.
Published: July 2003

1. Populus tremuloides leaf litter was produced under elevated (ELEV = 720 ppm) and ambient (AMB = 360 ppm) atmospheric CO2 conditions. Leaf chemical quality was significantly altered by CO2 enrichment. ELEV leaves had significantly higher concentrations of phenolic compounds and lignins, and higher C : N ratios than AMB.

2. Leaf litter was incubated in a headwater stream for 14 days to become colonised by microorganisms; aquatic bacterial productivity was significantly lower on ELEV than on AMB leaf litter. Colonised leaves were fed to four species of detritivorous mosquito larvae to assess their survivorship and development rates.

3. Larval mortality was 2.2 times higher for Aedes albopictus fed ELEV litter when compared with AMB. Although mortality of A. triseriatus, A. aegypti and Armigeres subalbatus was not affected by treatment, larval development rate was delayed by 78, 25 and 27%, respectively, when fed ELEV litter.

4. Increased mosquito mortality and/or delayed larval development rates are more likely to have negative implications for food web structure and productivity in ecosystems where immature stages of mosquitoes are an important food source of predators.
Comment on: ‘The 3D shear experiment over the Natih field in Oman: the effects of fracture‐filling fluids on shear propagation’ by C.M. van der Kolk, W.S. Guest and J.H.H.M. Potters
Authors: Hudson J.A. , Crampin Stuart
Published: July 2003

We find errors in theory and application in the paper by van der Kolket al. (Geophysical Prospecting49, 179–197 (2001)) that invalidate their arguments for the cause of the reduction in the velocity of the vertically propagating slower split shear‐wave in the gas cap over the Natih field in Oman. We suggest that existing theories are adequate and can explain the anomaly.
Towards non‐linear inversion for characterization of time‐lapse phenomena through numerical modelling
Authors: Abubakar A. , Van Den Berg P.M. , Fokkema J.T.
Published: July 2003

We compare two geophysical survey measurements of the same type made at different times in order to characterize the change in the geological medium during the elapsed time. The aim of this study is to develop a strategy using a full non‐linear inversion algorithm as the interpretation tool. In this way, not only the location and the form of the changes are recovered, but also the changes in the material parameters of the geological medium can be estimated. In order to solve this fully non‐linear problem, the so‐called ‘multiplicative regularized contrast source inversion’ (MR‐CSI) method is employed. The unique property of this iterative method is that it does not solve the forward problem at each iterative step. This makes it possible to use the non‐linear inversion algorithm for large‐scale computation problems. The numerical results show that by taking into account the non‐linear nature of the problem, interpretation of the time‐lapse data can be significantly improved, compared with that obtained using linear inversion.
Seismic velocity analysis in the scattering‐angle/azimuth domain
Authors: Brandsberg‐Dahl S. , Ursin B. , De Hoop M.V.
Published: July 2003

Migration velocity analysis is carried out by analysing the residual moveout and amplitude variations in common image point gathers (CIGs) parametrized by scattering angle and azimuth. The misfit criterion in the analysis is of the differential‐semblance type. By using angles to parametrize the imaging we are able to handle and exploit data with multiple arrivals, although artefacts may occur in the CIGs and need to be suppressed.

The CIGs are generated by angle migration, an approach based on the generalized Radon transform (GRT) inversion, and they provide multiple images of reflectors in the subsurface for a range of scattering angles and azimuths. Within the differential semblance applied to these CIGs, we compensate for amplitude versus angle (AVA) effects. Thus, using a correct background velocity model, the CIGs should have no residual moveout nor amplitude variation with angles, and the differential semblance should vanish. If the velocity model is incorrect, however, the events in the CIGs will appear at different depths for different angles and the amplitude along the events will be non‐uniform. A standard, gradient‐based optimization scheme is employed to develop a velocity updating procedure. The model update is formed by backprojecting the differential semblance misfits through ray perturbation kernels, within a GRT inverse. The GRT inverse acts on the data, subject to a shift in accordance with ray perturbation theory.

The performance of our algorithm is demonstrated with two synthetic data examples using isotropic elastic models. The first one allows velocity variation with depth only. In the second one, we reconstruct a low‐velocity lens in the model that gives rise to multipathing. The velocity model parametrization is based upon the eigentensor decomposition of the stiffness tensor and makes use of B‐splines.
CDP mapping in tilted transversely isotropic (TTI) media. Part I: Method and effectiveness
Authors: Qin Yilong , Zhang Zhongjie , Li Shoulin
Published: July 2003

Transverse isotropy with a tilted axis of symmetry (TTI) causes image distortion if isotropic models are assumed during data processing. A simple anisotropic migration approach needs long computational times and is sensitive to the signal‐to‐noise ratio. This paper presents an efficient, general approach to common‐depth‐point (CDP) mapping to image the subsurface in TTI media from qP‐wave seismic data by adding anisotropic and dip parameters to the velocity model. The method consists of three steps: (i) calculating traveltimes and positions of the CDP points; (ii) determining CDP trajectories; (iii) CDP imaging. A crucial step is the rapid computation of traveltimes and raypaths in the TTI media, which is achieved by the Fermat method, specially adapted for anisotropic layered media. The algorithm can image the subsurface of a given model quickly and accurately, and is suitable for application to a bending reflector. The effectiveness of the method is demonstrated by comparing the raypaths, the traveltimes and the results of CDP mapping, when assuming isotropic media, transversely isotropic media with a vertical axis of symmetry (TIV), and TTI media.
CDP mapping in tilted transversely isotropic (TTI) media. Part II: Velocity analysis by combining CDP mapping with a genetic algorithm
Authors: Qin Yilong , Zhang Zhongjie , Xu Shenhui
Published: July 2003

This paper presents a method for velocity analysis in tilted transversely isotropic (TTI) media by combining CDP mapping with a genetic algorithm. CDP mapping is a velocity analysis method for determining anisotropic velocity but has difficulties due to the following factors: (i) it involves a non‐linear and multimodal objective function; (ii) it is prohibitively expensive in the evaluation of candidate solutions, which often involves the calculation of images in the depth domain; (iii) there is often a very large parameter space. Recognizing the global and multimodal nature of the problem, a genetic algorithm is employed to search for the optimal velocity model. The efficiency of the method contributes to two critical processes: rapid model evaluation, achieved by generating CDP mapping only in the neighbourhood of specific reflectors, and fast computation, based on Fermat's principle, of the CDP points and traveltimes in TTI media. The method produces subsurface structure images in the depth domain, and can also solve for Thomsen's anisotropic parameters (ɛ and δ), the vertical velocity and the dip of the symmetry axis in the model space, simultaneously.
Decorrugation and removal of directional trends of magnetic fields by the wavelet transform: application to archaeological areas
Authors: Fedi Maurizio , Florio Giovanni
Published: July 2003

The problem of removing directional trends frequently occurs in the processing of magnetic data and also in the subsequent steps of data interpretation. The so‐called corrugations are typical directional trends occurring in levelled data, which may be removed in several ways. Classical techniques are based on high‐pass filtering of the data and successively filtering these transformed data with directional cosine filters. Other linear features are due to real sources, such as pipelines in shallow surveys or dike swarms in regional surveys. They should, nevertheless, be considered as noise, due to the fact that their effect is strong and tends to hide the field features related to structures of more interest. We deal with both kinds of problem, presenting the results of a study in an archaeological area of southern Italy. Decorrugation of magnetic field anomalies is performed using a method based on the excellent space–frequency localization properties of wavelet bases, allowing a very sharp filtering of the field along a selected direction. We compare this technique with the classical one in a synthetic case and find that the wavelet decorrugation is simpler and produces low distortion maps. Besides the field decorrugation, the wavelet approach was also shown to be useful in the subsequent enhancement of the measured field. In fact, we show that the wavelet analysis offers a unique framework where various filtering problems (directional, isotropic, global or local as well) may be easily solved. As regards the archaeological case, strong noisy effects from elongated sources (pipelines) were successfully removed in a sharp and local way.
3D F–K and finite‐difference dip moveout in cross‐spreads
Authors: Masjukov Andrey V.
Published: July 2003

A 3D F–K dip‐moveout (DMO) is developed, which is applicable to data acquired in an elementary single‐fold cross‐spread. The key idea is that a 3D log‐stretch transform and the inherent regularity of the cross‐spread geometry make it possible to transform 3D Fourier DMO. The derived theory generalizes the 2D Fourier shot‐gather DMO in the log‐stretch domain; 2D turns out to be a special case. Similarly to 2D, the cross‐spread DMO becomes convolutional after multidimensional logarithmic stretch. The proposed method works for orthogonal and slanted acquisition geometries; the cross‐spread DMO relationships are found to be independent of the intersection angle of the shot and receiver lines. In contrast to integral (Kirchhoff‐style) methods, the cross‐spread F–K DMO does not degrade from the inevitable irregularity in 3D sampling of offsets in a CMP gather. The newly derived F–K DMO operator can be approximated by finite‐difference (FD) schemes; the low‐order FD cross‐spread DMO equation is shown to be the 3D extension of the Bolondi and Rocca offset continuation. It is shown that F–K and low‐order FD operators are effective in a synthetic case.
Using DC resistivity tomography to detect and characterize mountain permafrost
Authors: Hauck Christian , Vonder Mühll Daniel , Maurer Hansruedi
Published: July 2003

Direct‐current (DC) resistivity tomography has been applied to different mountain permafrost regions. Despite problems with the very high resistivities of the frozen material, plausible results were obtained. Inversions with synthetic data revealed that an appropriate choice of regularization constraints was important, and that a joint analysis of several tomograms computed with different constraints was required to judge the reliability of individual features. The theoretical results were verified with three field experiments conducted in the Swiss and the Italian Alps. At the first site, near Zermatt, Switzerland, the location and the approximate lateral and vertical extent of an ice core within a moraine could be delineated. On the Murtel rock glacier, eastern Swiss Alps, a steeply dipping boundary at its frontal part was observed, and extremely high resistivities of several MΩ indicated a high ice content. The base of the rock glacier remained unresolved by the DC resistivity measurements, but it could be constrained with transient EM soundings. On another rock glacier near the Stelvio Pass, eastern Italian Alps, DC resistivity tomography allowed delineation of the rock glacier base, and the only moderately high resistivities within the rock glacier body indicated that the ice content must be lower compared with the Murtel rock glacier.
Phase behaviour of P‐SV converted waves recorded at the sea‐bed
Authors: Dai Hengchang
Published: July 2003

Shear waves recorded at or near the sea‐bed, i.e. a water–sediment interface, may suffer from unwanted phase change, which is detrimental to velocity analysis and processing and degrades the quality of the final stacked or migrated image. In this study, this phenomenon is analysed for P‐SV converted waves recorded at the sea‐bed. Theoretical analysis shows that phase change does not occur if the converted shear waves always maintain raypaths that lie within the critical angle, provided the subsurface layering is horizontal. A phase change that is asymmetric with offset can readily be explained as being due to dipping layers at targets or the dipping sea‐bed. This analysis is extended to multiple layers and anisotropic media and shows that the same conclusions hold. The analysis performed on two sets of ocean‐bottom‐cable seismic data shows that the majority of observations show little evidence of phase change, and occasionally display the asymmetric phase change with offset. This finding underlines the robustness of converted shear waves for imaging the horizontal subsurfaces and sea‐bed as all of the offset information may be used.
Evidence for post‐transcriptional regulation of interleukin‐5 by dexamethasone
Authors: Staples Karl J. , Bergmann Martin W. , Barnes Peter J. , Newton Robert
Published: July 2003

Interleukin‐5 (IL‐5) is a T helper type 2 cytokine, which is implicated in the pathogenesis of eosinophilic diseases such as asthma. Both peripheral blood mononuclear cells (PBMC) and primary human T cells display similar patterns of IL‐5 expression when stimulated with both phorbol‐12‐myristate 13‐acetate and phytohaemagglutinin. The expression of IL‐5 stimulated by these agents was shown to require de novo transcription and translation. However, although dexamethasone was a potent inhibitor of both IL‐5 release and messenger RNA accumulation from PBMC and T cells, dexamethasone had no effect on the luciferase activity of a reporter construct under the control of an IL‐5 promoter region transiently transfected into primary human T cells. Furthermore, dexamethasone appeared to decrease the stability of IL‐5 messenger RNA and this effect was dependent upon de novo transcription. Taken together, the results presented here suggest that, whilst transcriptional processes predominantly regulate IL‐5 release, the mechanism by which dexamethasone inhibits IL‐5 is post‐transcriptional.
Role of chemokine ligand 2 in the protective response to early murine pulmonary tuberculosis
Authors: Kipnis Andre , Basaraba Randall J. , Orme Ian M. , Cooper Andrea M.
Published: July 2003

Chemokines play an important role in the development of immunity to tuberculosis. Chemokine ligand 2 (CCL2, JE, monocyte chemoattractant protein‐1) is thought to be primarily responsible for recruiting monocytes, dendritic cells, natural killer cells and activated T cells, all of which play critical roles in the effective control of tuberculosis infection in mice. We show here that in mice in which the CCL2 gene was disrupted, low‐dose aerosol infection with Mycobacterium tuberculosis resulted in fewer macrophages entering the lungs, but only a minor and transient increase in bacterial load in the lungs; these mice were still able to establish a state of chronic disease. Such animals showed similar numbers of activated T cells as wild‐type mice, as determined by their expression of the CD44hi CD62lo phenotype, but a transient reduction in cells secreting interferon‐γ. These data indicate that the primary deficiency in mice unable to produce CCL2 is a transient failure to focus antigen‐specific T lymphocytes into the infected lung, whereas other elements of the acquired host response are compensated for by different ligands interacting with the chemokine receptor CCR2.
Rat C‐reactive protein activates the autologous complement system
Authors: Padilla Niubel Diaz , Bleeker Wim K. , Lubbers Yvonne , Rigter Gemma M. M. , Van Mierlo Gerard J. , Daha Mohamed R. , Hack C. Erik
Published: July 2003

Activation of complement is a biological function of human C‐reactive protein (hCRP), whereas rat CRP (rCRP) has been claimed to be unable to activate complement. As important biological functions of proteins are probably conserved among species, we re‐evaluated, using various ligands, the capability of rCRP to activate complement. The activation of complement by hCRP and rCRP was investigated in solid‐ and fluid‐phase systems. In the solid‐phase system, purified CRP was fixed to enzyme‐linked immunosorbent assay (ELISA) plates and incubated with human or rat recalcified plasma. Dose‐dependent binding of human and rat C3 and C4 was observed to human and rat CRP, respectively. In the fluid‐phase system, recalcified rat plasma, which contains about 500 mg/l of CRP, or human plasma supplemented with hCRP, were incubated with lyso‐phosphatidylcholine. A dose‐dependent activation of complement was observed upon incubation with this ligand, as reflected by the generation of activated C4 as well as of CRP–complement complexes. This activation was, in both cases, inhibited by preincubation of plasma with p‐aminophosphorylcholine, a specific inhibitor of the interaction of CRP with its ligands, or by chelation of calcium ions. We conclude that rat CRP, similarly to human CRP, can activate autologous complement. These results support the notion that opsonization of ligands with complement is an important biological function of CRP.
Allergen‐induced fluctuation in CC chemokine receptor 3 expression on bone marrow CD34+ cells from asthmatic subjects: significance for mobilization of haemopoietic progenitor cells in allergic inflammation
Authors: Sehmi Roma , Dorman Sandra , Baatjes Adrian , Watson Rick , Foley Ronan , Ying Sun , Robinson Douglas S. , Kay A. Barry , O'Byrne Paul M. , Denburg Judah A.
Published: July 2003

There is increasing evidence that primitive progenitors migrate from the bone marrow (BM) via the peripheral circulation to tissue sites where they undergo in situ differentiation to provide a continued source of effector cells, such as eosinophils, during an allergic inflammatory response. To study mechanisms of progenitor cell mobilization in allergic reactions, we investigated fluctuations in the expression of the eotaxin receptor, CC chemokine receptor 3 (CCR3), on CD34+ cells from stable asthmatics following allergen (i.e. antigen) challenge. BM aspirates were taken from seven early responder (ER) and 10 dual responder (DR) asthmatics who, following antigen challenge developed only an early bronchoconstrictor response and an early and late‐ bronchoconstrictor response, respectively. Expression of CCR3 was detected on primitive (CD34+ cells) and eosinophil‐lineage committed progenitors (CD34+ interleukin‐5 receptor alpha‐subunit+ cells) by flow cytometry and confirmed by co‐localization of CCR3 messenger RNA to CD34 immunopositive cells using in situ hybridization. When preantigen levels were compared to 24‐hr postantigen levels, significant increases in BM CD34+ CCR3+ cells were detected in DR, who also developed a significant sputum and blood eosinophilia and increased methacholine airway responsiveness. In contrast, a significant attenuation of BM CD34+ CCR3+ cells was observed in ER. In a dose‐dependent manner eotaxin, but not interleukin (IL)‐5, stimulated CD34+ progenitor cell migration in vitro. This migrational response to eotaxin was abrogated by anti‐CCR3 monoclonal antibody and primed by preincubation with IL‐5. We propose that fluctuations in CCR3 expression on human BM CD34+ cells may facilitate chemokine‐mediated progenitor cell mobilization to the peripheral circulation and the resultant development of pulmonary eosinophilia, a cardinal feature of asthma.
CD8+ immunoregulatory cells in the graft‐versus‐host reaction: CD8 T cells activate dendritic cells to secrete interleukin‐12/interleukin‐18 and induce T helper 1 autoantibody
Authors: Noble Alistair , Leggat Jamie A. , Inderberg Else M.
Published: July 2003

Initiation of cell‐mediated immunity or autoimmunity requires secretion of interleukin (IL)‐12 from dendritic cells (DC), which drives the generation of T helper 1 (Th1) effector cells in synergy with IL‐18. Induction of IL‐12 can be triggered by microbial stimuli but also requires signals from activated T cells. We investigated interactions between alloreactive CD4 and CD8 T cells in mixed lymphocyte reactions (MLR) in vitro and in the graft‐versus‐host reaction (GVHR) in vivo. In a parent‐into‐F1 model of GVHR, donor CD8 cells were found to suppress the hyper‐immunoglobulin E (IgE) syndrome, anti‐DNA immunoglobulin G1 (IgG1) autoantibodies and donor CD4‐cell expansion, but were essential for Th1‐dependent immunoglobulin G2a (IgG2a) autoantibody production and release of serum IL‐12 p40. In vitro, addition of alloreactive CD8 cells to CD4 cells and mature DC enhanced Th1 development. CD4 and CD8 T cells induced IL‐18 from DC and primed for IL‐12 p70 secretion via interferon‐γ (IFN‐γ) or tumour necrosis factor‐α (TNF‐α). However CD8 T cells, but not CD4 cells, released IFN‐γ/TNF‐α after primary stimulation. The data suggest that rapid release of inflammatory cytokines from central memory‐type CD8 cells early in immunity is critical for induction of Th1 cells via DC activation and IL‐12 production. This pathway could provide a means for amplification of cell‐mediated autoimmunity in the absence of microbial stimuli.
Host response of platelet‐activating factor receptor‐deficient mice during pulmonary tuberculosis
Authors: Weijer Sebastiaan , Leemans Jaklien C. , Florquin Sandrine , Shimizu Takao , Ishii Satoshi , Van Der Poll Tom
Published: July 2003

Platelet‐activating factor (PAF) is a phospholipid with potent, diverse actions, which has been implicated as an important mediator in host defence against several intracellular pathogens. To determine the role of PAF in host defence in pulmonary tuberculosis, PAF receptor‐deficient (PAFR−/−) and wild‐type (PAFR+/+) mice were infected intranasally with a virulent strain of Mycobacterium tuberculosis. Mycobacterial outgrowth in lungs and liver did not differ significantly between PAFR−/− and PAFR+/+ mice at 2 or 6 weeks postinfection. After 28 weeks, 86% of PAFR−/− mice and 79% of PAFR+/+ mice had died (non‐significant). In addition, both mouse strains were indistinguishable with respect to histopathology, the recruitment and activation of lymphocytes, and cytokine concentrations in the lung. These data suggest that PAF is not involved in the protective immune response to tuberculosis.
Inhibition of B‐cell death does not restore T‐cell‐dependent immune responses in CD40‐deficient mice
Authors: Merino Jesús , Díez Miguel A. , Muñiz María , Buelta Luis , Núñez Gabriel , López‐Hoyos Marcos , Merino Ramón
Published: July 2003

Signalling through CD40 is essential for the development of immunoglobulin G (IgG) antibody responses, germinal centres and B‐cell memory against T‐dependent antigens. In addition, engagement of CD40 in B cells promotes cell survival by inducing the expression of anti‐apoptotic members of the bcl‐2 family of cell‐death regulators. In the present study we analysed whether T‐dependent immune responses can be developed in mice deficient in CD40 if the anti‐apoptotic activity mediated by the engagement of CD40 in B cells is compensated by the constitutive over‐expression of anti‐apoptotic genes of the bcl‐2 family. We showed that the over‐expression of either hbcl‐2 or hbcl‐xL transgenes in B cells is not sufficient to restore IgG antibody responses and germinal centre formation in CD40‐deficient mice. These results indicate that CD40 functions, other than those mediated through survival, are required for the establishment of T‐dependent B‐cell responses.
αβ T‐cell development is not affected by inversion of TCRβ gene enhancer sequences: polar enhancement of gene expression regardless of enhancer orientation
Authors: Huang Fang , Cabaud Olivier , Verthuy Christophe , Hueber Anne‐Odile , Ferrier Pierre
Published: July 2003

V(D)J recombination and expression of the T‐cell receptor β (TCRβ) gene are required for the development of the αβ T lymphocyte lineage. These processes depend on a transcriptional enhancer (Eβ) which acts preferentially on adjacent upstream sequences, and has little impact on the 5′ distal and 3′ proximal regions of the TCRβ locus. Using knock‐in mice, we show that αβ T‐cell differentiation and TCRβ gene recombination and expression are not sensitive to the orientation of Eβ sequences. We discuss the implication of these results regarding the mode of enhancer function at this locus during T lymphocyte development.
The membrane attack complex of complement contributes to plasmin‐induced synthesis of platelet‐activating factor by endothelial cells and neutrophils
Authors: Lupia Enrico , Del Sorbo Lorenzo , Bergerone Serena , Emanuelli Giorgio , Camussi Giovanni , Montrucchio Giuseppe
Published: July 2003

Thrombolytic agents, used to restore blood flow to ischaemic tissues, activate several enzymatic systems with pro‐inflammatory effects, thus potentially contributing to the pathogenesis of ischaemia–reperfusion injury. Platelet‐activating factor (PAF), a phospholipid mediator of inflammation, has been implicated in the pathogenesis of this process. We previously showed that the infusion of streptokinase (SK) induces the intravascular release of PAF in patients with acute myocardial infarction (AMI), and that cultured human endothelial cells (EC) synthesized PAF in response to SK and plasmin (PLN). In the present study, we investigated the role of the membrane attack complex (MAC) of complement in the PLN‐induced synthesis of PAF. In vivo, we showed a correlation between the levels of soluble terminal complement components (sC5b‐9) and the concentrations of PAF detected in blood of patients with AMI infused with SK. In vitro both EC and polymorphonuclear neutrophils (PMN), incubated in the presence of PLN and normal human serum, showed an intense staining for the MAC neoepitope, while no staining was detected when they were incubated with PLN in the presence of heat‐inactivated normal human serum. Moreover, the insertion of MAC on EC and PMN plasmamembrane elicited the synthesis of PAF. In conclusion, our results elucidate the mechanisms involved in PAF production during the activation of the fibrinolytic system, showing a role for complement products in this setting. The release of PAF may increase the inflammatory response, thus limiting the beneficial effects of thrombolytic therapy. Moreover, it may have a pathogenic role in other pathological conditions, such as transplant rejection, tumoral angiogenesis, and septic shock, where fibrinolysis is activated.
Murine lymph node‐derived stromal cells effectively support survival but induce no activation/proliferation of peripheral resting T cells in vitro
Authors: Zhou Yan‐wen , Aritake Sayoko , Tri Endharti Agustina , Wu Jianghong , Hayakawa Akemi , Nakashima Izumi , Suzuki Haruhiko
Published: July 2003

Little is known about the homeostatic mechanisms by which the levels of peripheral lymphocytes are maintained. The survival of naïve T cells in vivo must be maintained by some factors that have not been characterized in an in vitro culture system. In this study, we established a culture system of stromal cells derived from murine lymph nodes and investigated the action of the stromal cells in supporting the survival of resting T cells in vitro. Most of the T cells cocultured with the stromal cells did not die, and the supernatant of cultured stromal cells increase the viability of T cells. This T‐cell survival‐supporting activity was maintained for more than 7 days. Although interleukin (IL)‐4, IL‐6, IL‐7, and interferon‐β also rescued peripheral T cells from spontaneous cell death, medium‐soluble and heat‐sensitive factor(s) derived from the stromal cells supported the survival of T cells more effectively and for a longer time than did these cytokines. T cells maintained in the culture system with the stromal cells appeared to remain in a resting G0/G1 state and did not show remarkable DNA synthesis. From these results, it is presumed that some soluble factor(s) other than the tested cytokines that have been identified as supporting T‐cell survival are produced from lymph node stromal cells. These factor(s) play an important role in maintenance of resting T cells.