bluuebunny/crossref_metadata_2025_split huggingface dataset:
Iron reduction and changes in cation exchange capacity in intermittently waterlogged soil
Authors: Favre F. , Tessier D. , Abdelmoula M. , Génin J. M. , Gates W. P. , Boivin P. 
Published: March 2003

SummaryThe long‐term effects of intermittent flooding on soil properties were studied in field experiments on a Vertisol cropped with rice in Senegal. The dominant clay minerals were smectite and kaolinite. When the soil was reduced after flooding, its cation exchange capacity (CEC) increased to twice that of its oxidized, unflooded state. Mössbauer spectroscopy showed an increase in smectite structural FeII upon reduction, which explained a part of the increase in CEC. The rest of the increase was attributed to the removal of iron oxyhydroxide coatings by reductive dissolution. The reduction and dissolution of oxides under the field conditions were substantiated by analysis of the surfaces of vermiculites buried in the Ap horizons of the cropped and the non‐cropped soils. The redox‐induced CEC changes were found to be reversible after 22 cycles of rice cropping. Nevertheless, the structural Fe and free Fe contents of the rice field Ap horizon were less than those of soil in uncropped neighbouring land, suggesting that inundation induced weathering and eluviation of the minerals. The observed changes in CEC and related redox reactions may substantially modify proton, anion and cation balances in intermittently flooded soils.
Quantification of pore structure and gas diffusion as a function of scale
Authors: Vogel H.‐J. , Cousin I. , Roth K. 
Published: March 2003

SummaryThe quantification of the spatial heterogeneity of soil structure is one of the main difficulties to overcome for an adequate understanding of soil processes. There are different competing concepts for the type of heterogeneity, including macroscopic homogeneity, discrete hierarchy or fractal. With respect to these different concepts we investigate the structure of the pore space in one single sample (4 × 103 mm3) by analysing basic geometric quantities of the pores > 0.3 mm within gradually increasing subsamples. To demonstrate the relation between geometrical and functional properties we simulate gas diffusion within the three‐dimensional pore space of the different subsamples. An efficient tool to determine the geometric quantities is presented. As a result, no representative elementary volume (REV) is found in terms of pore‐volume density which increases with sample size. The same is true for the simulated gas diffusion coefficient. This effect is explained by two different types of pores, i.e. big root channels and smaller pores, having different levels of organization. We discuss the different concepts of structural organization which may be appropriate models for the structure investigated. We argue that the discrete hierarchical approach is the most profitable in practice.
Pressure plate studies to determine how moisture affects access of bacterial‐feeding nematodes to food in soil
Authors: Yeates G.W. , Dando J. L. , Shepherd T. G. 
Published: March 2003

SummaryNematode activity in the soil depends on the presence of free water. We conducted pressure plate experiments to understand better how soil matric potential and structural degradation affect the population growth of three bacterial‐feeding nematodes (Cephalobus,Pristionchus,Rhabditis). We took undisturbed cores from six soils (sand, silt loam and silty clay loam with four management regimes), and removed all fauna from them. Ten or 30 nematodes were added, and pressures corresponding to soil matric potentials of −10, −33, −50, −100 or −1500 kPa were applied for 35 days. The nematodes were then counted. Significant reproduction of all bacterial‐feeding nematodes occurred when the diameters of water‐filled pores were approximately 1 μm. This confirms observations using repacked soils and field manipulations. Only forPristionchusdid declining populations match the reduction in total soil porosity related to intensification of land use on the silty clay loam. We had not expectedCephalobusto have the fastest increase in population of the three nematodes in intact soil cores, and our evidence questions the relative importance given to the three nematode families in soil processes. The differing rates of population increase of the three nematodes in the various soils reflect both habitable pore space and trophic interactions. This suggests that the very diversity of nematode assemblages is crucial in the resilience of biological soil processes. That water‐filled pores as small as 1 μm provide suitable spaces for sizeable populations of bacterial‐feeding nematodes accords with the observed migration of infective juveniles of trichostrongylid nematodes and mermithids in water films on herbage. Our results imply that assessment of the role of nematodes in soil processes may be a key to the understanding of biological interactions in water films, and the selection pressures on nematode morphology.
The relationship between copper accumulated in vineyard calcareous soils and soil organic matter and iron
Authors: Parat C. , Chaussod R. , Lévêque J. , Dousset S. , Andreux F. 
Published: March 2003

SummaryThe intensive use for over 100 years of copper sulphate (Bordeaux mixture) to fight mildew in vineyards has led to a substantial accumulation of copper (Cu) in surface soils. To assess the effects of such large concentrations, the surface soils of 10 Burgundy vineyards were sampled and analysed for total organic matter (carbon and nitrogen) and metal (copper and iron) contents. Physical (i.e. size fractionation) and chemical (sequential extraction) methods were used to determine the distribution of these elements. The most Cu‐contaminated plots showed the largest accumulation of organic carbon and Cu in the coarse sand and fine sand fractions. Copper was strongly correlated with organic carbon and organic nitrogen in the coarse sand fraction and with organic nitrogen in the fine sand fraction. Copper was also highly correlated with both Fe and organic nitrogen in the clay fraction but not significantly with organic carbon. The sequential extraction showed that Cu was bound mainly to the Fe oxides. However, in the most Cu‐contaminated plots, a part of added Cu was bound to organic matter. This study suggests that Cu protected indirectly the organic matter present in the coarse fractions against biodegradation, and therefore modified the distribution of organic carbon among the particle‐size fractions. Iron appeared as the main factor responsible for Cu accumulation in the clay fraction, mainly through inclusion of Cu in Fe oxyhydroxides and possibly in clay–humus complexes.
An adjoint data assimilation approach to diagnosis of physical and biological controls on Pseudocalanus spp. in the Gulf of Maine–Georges Bank region
Authors: MCGILLICUDDY D. J. , LYNCH D. R. , MOORE A. M. , GENTLEMAN W. C. , DAVIS C. S. , MEISE C. J. 
Published: March 2003

The underlying scientific objective here is to determine the mechanisms that control seasonal variations in the abundance of Pseudocalanus spp. in the Georges Bank–Gulf of Maine region. It is postulated that the observed distributions result from the interaction of the population dynamics with the climatological circulation. The problem is posed mathematically as a 2‐D advection–diffusion–reaction equation for a scalar variable. Given an initial distribution of animals, we seek the population dynamics source term R(x,y) such that integration of the forward model will result in predictions3 that minimize the sum of squares of differences with observed concentrations at a later time. An adjoint data assimilation technique has been designed for these purposes.This approach has been used to invert for the population dynamics associated with the transition between bimonthly (i.e. for 2 months) climatological Pseudocalanus spp. distributions derived from MARMAP data. Vertically averaged velocity and diffusivity fields diagnosed from hydrodynamical simulations of the climatological flow are specified. Solutions converge rapidly, and the procedure reduces the cost function by an order of magnitude within 50 iterations. The resulting population dynamics vary considerably in space and time, as does the balance between local tendency, physical transport and biological source terms. Generally speaking, the patterns in population dynamics are not inconsistent with current knowledge concerning potential controls such as predation and food limitation. Analysis of the solutions indicates that the Pseudocalanus spp. population centres located in the western Gulf of Maine and on Georges Bank may be self‐sustaining, in contrast to prior studies which characterize the former as a source region for the latter.
BAROTROPIC TIDAL AND WIND‐DRIVEN LARVAL TRANSPORT IN THE VICINITY OF A BARRIER ISLAND INLET
Authors: Luettich Jr  , Hench  , Fulcher  , Werner  , Blanton  , Churchill  
Published: March 2003

Fish species such as Atlantic menhaden (Brevoortia tyrannus) must often transit relatively small barrier island inlets to move from their continental shelf spawning grounds to estuarine nurseries, where they spend their juvenile phase. Physical transport through these inlets is strongly influenced by tides, winds, local geometry and bathymetry, and can be very different from that occurring on the shelf. In March 1996, an extensive multidisciplinary field experiment was conducted to identify larval transport pathways in the vicinity of Beaufort Inlet, NC (
Blanton et al., 1999
;
Churchill et al., 1999
;
Forward et al., 1999
). One of the most interesting results from the field study was significant spatial inhomogeneity in the larval catches (
Forward et al., 1999
).This paper describes a computer modelling study of tidal and wind‐driven circulation and accompanying larval transport characteristics in the vicinity of Beaufort Inlet. Primary conclusions are as follows: (i) tidal currents are quite effective at creating net larval transport into the inlet; (ii) in the absence of wind forcing, to explain the spatial distribution of larval catches observed in the field experiment, the primary source of larvae must have been to the east of the inlet; (iii) the spring/neap cycle accounts for a variation of approximately 40% in larvae ingress; (iv) only a few wind directions enhance larvae ingress over the case of purely tidal forcing—wind blowing toward the north enhances ingress at the surface, and winds blowing toward the south and the east enhance ingress at the bottom; (v) if larvae are evenly distributed in space out‐side the inlet, then strong east wind (such as 10 m s−1) can cause larvae to move through the inlet in a way that is consistent with the larval catches in the field experiment. However, local wind records revealed that no significant eastward‐blowing winds occurred during or immediately preceding the field experiment.
Alternating dominance of postlarval sardine and anchovy caught by coastal fishery in relation to the Kuroshio meander in the Enshu‐nada Sea
Authors: Nakata Hideaki , Funakoshi Shigeo , Nakamura Motohiko 
Published: March 2003

In the mid 1970s, the fishery catch of postlarval Japanese anchovy (Engraulis japonica) in a shelf region of the Enshu‐nada Sea, off the central Pacific coast of Japan, started to decline corresponding to a rapid increase of postlarval sardine (Sardinops melanostictus). In late 1980s, sardine started to decline, and it was replaced by anchovy in the 1990s. This alternating dominance of postlarval sardine and anchovy corresponded to the alternation in egg abundance of these two species in the spawning habitat of this sea. It was also noteworthy that during the period of sardine decline, sardine spawning occurred in April–May, a delay of two months compared with spawning in the late 1970s.The implication of oceanographic changes in the spawning habitat for the alternating dominance of sardine and anchovy eggs was explored using time‐series data obtained in 1975–1998, focusing on the effect of the Kuroshio meander. Large meanders of the Kuroshio may have enhanced the onshore intrusion of the warm water into the shelf region and contributed to an increase in temperature in the spawning habitat. This might favour sardine, because its egg abundance in the shelf region was more dependent on the temperature in early spring than was that of anchovy. In addition, enhanced onshore intrusion could contribute to transport of sardine larvae from upstream spawning grounds of the Kuroshio region. On the other hand, anchovy egg abundance was more closely related to lower transparency at the shelf edge, which may indicate the prevalence and prolonged residence of the coastal water, and therefore higher food availability, frequently accompanying non‐meandering Kuroshio.The expansion/shrinkage of the spawning habitat of sardine and anchovy in the shelf region, apparently responding to the change in the Kuroshio, possibly makes the alternation in dominance of postlarval sardine and anchovy most prominent in the Enshu‐nada Sea, in combination with changes in the abundance of spawning adults, which occurred almost simultaneously in the overall Kuroshio region. The implication of this rather regional feature for the alternating dominance of sardine and anchovy populations on a larger spatial scale is also discussed.
The effects of short space and time scale current variability on the predictability of passive ichthyoplankton distributions: an analysis based on HF radar observations
Authors: Helbig J. A. , Pepin P. 
Published: March 2003

AbstractThe importance of small scale variations in currents on the predictability of spatial distributions of fish eggs is investigated using dense observations of surface currents. The currents were measured with HF radar and used to drive an advection–diffusion model of ichthyoplankton concentration. We first demonstrate that the model produces acceptable agreement with observed egg fields. We then use the predicted egg fields as a basis for comparison with model runs made with currents subsampled in space and filtered in time. Significant error was found for spatial sampling intervals as small as 3 km, even though most of the variance in the currents occurred at much longer length scales. This was primarily due to the loss of the rich small scale variability in horizontal divergence. Nevertheless, most of the error is due to the misfit in the egg fields at larger length scales; that is, small scale forcing is necessary in this system for the larger scale features to be reproduced. This study thus suggests that considerable caution should be exercised before assuming that circulation models, even very sophisticated and detailed ones, capture enough of the variability of marine systems to make accurate forecasts of plankton distributions.
Importance of the Shatsky Rise Area in the Kuroshio Extension as an offshore nursery ground for Japanese anchovy (Engraulis japonicus) and sardine (Sardinops melanostictus)
Authors: Komatsu Teruhisa , Sugimoto Takashige , Ishida Ken‐Ichi , Itaya Kazuhiko , Mishra Pravakar , Miura Teisuke 
Published: March 2003

AbstractRecent findings suggest that recruitment of Japanese anchovy (Engraulis japonicus) and sardine (Sardinops melanostictus) depends on survival during not only the first feeding larval stage in the Japanese coastal waters and the Kuroshio front but also during the post‐larval and juvenile stages in the Kuroshio Extension. Spatial distributions of juvenile anchovy and sardine around the Shatsky Rise area in the Kuroshio Extension region and the Kuroshio–Oyashio transition region are described, based on a field survey in the late spring using a newly developed mid‐water trawl for sampling juveniles. All stages of anchovy from post‐larvae to juveniles were obtained in the northern Shatsky Rise area. The Kuroshio Extension bifurcates west of the Shatsky Rise area and eddies are generated, leading to higher chlorophyll concentrations than in the surrounding regions in April and May. When Japanese anchovy and sardine spawn near the Kuroshio front or the coastal waters south‐east of Japan, their larvae are transported by the Kuroshio Extension and are retained in the Shatsky Rise area, which forms an important offshore nursery ground, especially during periods of high stock abundance.
Epibionts of	Asellus aquaticus(L.) (Crustacea, Isopoda): an SEM study
Authors: Cook Jane A. , Chubb James C. , Veltkamp  
Published: March 2003

1. This study presents a qualitative and quantitative survey of epibionts infesting two populations of the freshwater isopod Asellus aquaticus (L.). Using scanning electron microscopy, the prevalence, mean intensity, abundance, spatial preferences and distribution of organisms on various external surfaces were ascertained.2. A diverse community, consisting primarily of protozoa and rotifers, utilised A. aquaticus as a substrate organism. Every individual A. aquaticus supported some form of epizoic life. Peritrich species comprised 89.2% of all epibionts. Carchesium polypinum, Pseudocarchesium aselli, Pseudocarchesium asellicola, Pseudocarchesium simulans and Opercularia hebes dominated the epifauna.3. Highest epibiont burdens occurred on the mouthparts, the first few ventral segments and the gills and largely comprised the above peritrich species. Most epibionts exhibited some degree of site preference on the host. A distinct gill epifauna existed. Apart from Acineta tuberosa and Vorticella rotunda, which had equal prevalences on dorsal and ventral surfaces in one culture, most species largely avoided the dorsal surface.4. Epibionts exhibited varying degrees of adaptation to life on a living substrate. They ranged from facultative species such as A. tuberosa, which are capable of colonising abiotic substrata, to Gymnodinoides aselli whose life cycle relies on interaction with A. aquaticus. Highly specialised species tended to exhibit the most pronounced and consistent site restriction.5. Asellus aquaticus offers a highly tractable system for further study of substrate species–epibiont relationships.
A new functional model for estimating the maximum amount of invertebrate food consumed per day by brown trout, Salmo trutta
Authors: Elliott J. M. , Hurley M. A. 
Published: March 2003

1. A model developed over 20 years ago has been used to estimate daily food intake in brown trout living in streams and lakes over a wide geographical range. The chief disadvantages of this early model are that it is not continuous and requires twelve parameters, not all of which can be interpreted biologically. A new model, using a larger data set, was therefore developed to overcome these problems and estimate the mean daily energy intake.2. The two data sets used to develop the original model were also used to develop the general form of the new one, but a third data set was used to specify the model more precisely and to estimate the parameters. This third data set originated from experiments in which 185 trout (live weight range 1–350 g) were kept individually at 19 constant temperatures (range 3.8–21.7 °C) usually for 5–6 weeks. They were fed freshly killed shrimps (Gammarus pulex) and their food consumption was recorded throughout each experiment.3. Five, six and eight parameter versions of the new model were all excellent fits to the data (P < 0.001, R2 > 0.99), with the eight parameter version being slightly the best. All parameters can be interpreted in biological terms; three define threshold temperatures, three define the curvilinear slopes in the model over different temperature ranges, one is a weight exponent and one is the maximum daily energy intake of a 1 g trout. The simpler six parameter model was adequate at temperatures above 7 °C.4. An additional experiment with twenty‐eight trout feeding on six different invertebrate foods provided estimates of energy intake that were very similar to those predicted from the model. However, when daily intake was converted to dry weight, agreement with values from the model (also as dry weight) was poor. Possible reasons for this are discussed, as are other studies using the earlier model, and it is shown that different conclusions can be reached depending upon whether comparisons are based on units of energy, dry weight or wet weight.
Sediment microbial respiration in a synoptic survey of mid‐Atlantic region streams
Authors: Hill  , Herlihy  , KauFmann  , SinsabauGh  
Published: March 2003

1. The rate of microbial respiration on fine‐grained stream sediments was measured at 196 first‐ to third‐order sites in the mid‐Atlantic region of the United States.2. Sample collection took place between April and July in 1993, 1994 and 1995.3. Study streams were randomly selected from the United States Environmental Protection Agency’s (USEPA) River Reach File (RF3) using the sample design developed by USEPAs Environmental Monitoring and Assessment Programme (EMAP).4. Respiration rate ranged from 0 to 0.622 g O2 g–1 ash‐free dry mass (AFDM) h–1, and was significantly correlated with stream temperature, water chemistry and physical habitat.5. Respiration rate was significantly higher in streams from the Chesapeake drainage area compared to those from the Ohio drainage area, and in streams from the Northern Appalachian Plateau and Uplands and Central Appalachian Valleys ecoregions compared with streams from the Blue Ridge and Central Appalachian Plateau ecoregions.6. Respiration was not significantly different among stream orders or between years.
δ13C variability of benthic algae: effects of water colour via modulation by stream current
Authors: France Robert , Cattaneo And Antonella 
Published: March 2003

1. Increased water motion is expected to reduce boundary layer diffusion resistance of autotrophs, thereby enabling greater isotopic discrimination against 13C such that lower δ13C values (ratio of 13C : 12C) should ensue. A field test of this hypothesis was undertaken by sampling benthic algae in streams of differing current speed.2. Contrary to the expected negative relationship between δ13C and water motion, filamentous benthic algae were found to exhibit higher δ13C values in rapid water.3. Under conditions of low current in the streams studied, concentrations of dissolved organic carbon as measured by water colour are elevated through the microbial decomposition of largely terrestrial organic matter. Photoassimilation of this respired carbon by benthic filamentous algae generates 13C‐depletion and lower δ13C values, and appears to be substantial enough in the streams used in the present study to override the competing influence of water motion on boundary layer thickness.
Fighting the flow: downstream–upstream linkages in the ecology of diadromous fish faunas in West Coast New Zealand rivers
Authors: Mcdowall  
Published: March 2003

1. Diadromy is a dominating behavioural characteristic of fish faunas in New Zealand rivers, with amphidromy and catadromy being the most common strategies.2. Juvenile life stages of amphidromous and catadromous species migrate from the sea, through river systems, to find habitats for feeding, growth, maturation and reproduction.3. Studies of fish distributions in rivers of the West Coast of the South Island of New Zealand show that, in most species, these migrations result in more or less continuous distributions from the lower reaches to the upstream limits of each species’ range.4. Upstream penetration of rivers varies widely between species and this generates downstream–upstream trajectories of declining species richness.5. Parallel trajectories of declining downstream–upstream abundance are likely in each species.6. These patterns demonstrate the presence of downstream–upstream linkages in the community ecology of freshwater fishes in New Zealand rivers.