bluuebunny/crossref_metadata_2025 huggingface dataset:
Transformations and neoformations of clay in the cryogenic environment: examples from Transbaikalia (Siberia) and Patagonia (Argentina)
Authors: VOGT T. , LARQUÉ P.
Published: March 2003

Permafrost desiccates and indurates soil horizons. During summer, the perennially frozen ground under the active thawed layer creates confined conditions, Whereas in winter the closed system between the permafrost and the freezing front migrating downwards leads to irreversible changes in the soil structure and to transformation and neoformation of minerals. Two examples were studied by field observation and laboratory analyses (optical microscopy, scanning electron microscopy, X‐ray diffractometry, transmission electron microscopy and analytical electron microscopy). In Transbaikalia (southeastern Siberia) a Pleistocene cryogenic slope deposit on syenite contains detrital clays (chlorite, illite), but neoformed ferroan smectites dominate. In Patagonia, centimetre‐sized silica concretions containing spongy and spheroidal opal occur in alluvium ascribed to cold Pleistocene periods. They seem to have formed from primary detrital smectite that was transformed to fibrous clay (sepiolite) then to acicular opal, and eventually to spheroidal opal. The neoformed opal contains 27% magnesium. These features occur systematically within fossil cryoturbations not related to present conditions. It appears that clay transformation and neoformation can happen at temperatures far lower than 0°C.
Modelling cations in three acid soils with differing acid input in Germany
Authors: LUDWIG B. , PRENZEL J. , KHANNA P. K.
Published: March 2003

Prediction of concentration changes of cations in soil solutions is complex, and chemical models are necessary for the purpose. The objective of this study was to determine whether the reactions considered in a coupled equilibrium model were appropriate to predict cation concentrations when the initial equilibrium was disturbed by adding small amounts of electrolytes. Multi‐ion sorption in three acid soils (two Cambisols and a Podzol) was studied by sequentially adding small amounts of electrolytes to samples of the soils in batch experiments. A chemical equilibrium model that included inorganic complexation and multiple cation exchange was used to interpret the results. For the subsoils, the solubility of jurbanite was also included in the model.

Model results for the two Cambisol surface soils agreed well or satisfactorily with the measured pH and sorption values of Na, K, Mg, Ca, Mn, Al and Fe, with a few exceptions. Linear correlation coefficients were generally between 0.97 and 1, and the regressin coefficients for cations (modelled against measured) lay between 0.6 and 1.3. For the subsoils sorption of sulphate was described satisfactorily for the spodic dystric Cambisol and to some extent for the spodic Cambisol. Correlation coefficients for subsoils lay between 0.63 and 1, and the regression coefficients (modelled against measured) were between 0.9 and 1.6 for the Cambisols. The model did not predict pH and sorption data in surface and subsurface soils with very small amounts of exchange capacities, pointing to the significance of cation buffering resulting from exchange sites. This study showed the usefulness and limitations of equilibrium models to predict the composition of the soil solution.
Particle packing and organization of the textural porosity in clay–silt–sand mixtures
Authors: FIÈS J. C. , BRUAND A.
Published: March 2003

The packing of elementary particles in soil largely determines the properties that depend on the textural soil pore space, but is studied little. The relations between packing and size and nature of soil particles were studied using fractions of clay, silt and sand, mixed when wet and then dried. Ternary mixtures (clay:silt:sand) were compared with binary mixtures (clay:silt, clay:sand). The pore space of the mixtures was studied using mercury porosimetry and scanning electron microscopy. In all the mixtures the textural pore space was divided into two compartments: (1) lacunar pores due to the presence of skeleton particles and to the shrinkage of the clay phase between these particles, and (2) the clay–fabric pores due to the packing of the clay. In the ternary mixtures, lacunar pores could be divided into two classes: (1) those due to sand particles within the clay–slit phase considered as a single phase, and (2) those due to silt particles within this same phase. For certain mixtures, lacunar pores, referred to as hidden lacunar pores, were not interconnected but were occluded. This occurred both for hidden pores caused by the presence of sand and occluded by the clay–slit phase, and for hidden pores caused by the presence of silt and occluded by the clay phase. The relations between these types of textural pores and the proportions of different size fractions in the mixtures provide guidelines for making optimum use of the particle‐size characteristics of the soil to determine its properties.
Phosphate sorption by calcareous Vertisols and Inceptisols as evaluated from extended P‐sorption curves
Authors: CASTRO B. , TORRENT J.
Published: March 2003

The plant availability of phosphate applied to calcareous soils is affected by precipitation and adsorption reactions, the relative significance of which is not well known. We used extended P‐sorption curves obtained at phosphate addition rates up to 340 mmol P kg−1 soil to examine the relative contribution of precipitation and adsorption by 24 calcareous Spanish Vertisols and Inceptisols. Adsorption was dominant at 1 day and at small rates of addition (10–35 mmol P kg−1). With increasing clay and Fe and Al oxides contents of the soil, more phosphate was sorbed before the sorption curve bent upwards, as a result of Ca phosphate precipitation. Sorption curves showed a nearly vertical intermediate region, the length of which increased with time, suggesting that a Ca phosphate buffered the concentration of P in solution. The buffering concentration decreased with time, suggesting a progressive transformation of more to less soluble forms of Ca phosphate. A phase less soluble than octacalcium phosphate seemed to control the concentration of P in solution at 180 days in most soils. The apparent solubility of this phase decreased with increasing carbonate content in the soil. Precipitation of poorly soluble Ca phosphates apparently predominated up to a P addition dose ranging from about 30 mmol P kg−1 in some soils to more than 340 mmol P kg−1 in others. At larger doses, the way additional P was bound to the solid phase was different; phosphate was probably adsorbed, at least in part, to low‐affinity sites on silicate clays and oxides.

The proportion of sorbed phosphate that was isotopically exchangeable decreased with time, soil carbonate content and P addition dose for doses <100 mmol P kg−1. This is consistent with the idea that P in Ca phosphates is less isotopically exchangeable than P adsorbed on mineral surfaces. At larger additions of P, isotopic exchangeability was unrelated to the soil properties measured, probably because there was a variety of sorbed P forms influenced in turn by different soil components.
Neural network models to predict soil water retention
Authors: Koekkoek E. J. W. , Booltink H.
Published: March 2003

Soil water retention curves are needed to describe the availability of soil water to plants and to model movement of water through unsaturated soils. Measuring these characteristics is time‐consuming, labour‐intensive and therefore expensive. This study was conducted to develop and evaluate functions based on neural networks to predict soil water retention characteristics. Dutch and Scottish data sets were available; they contained data on 178 and 165 soil horizons, respectively. A series of three neural networks (A, B and C) was developed. Neural network A had the following input variables: topsoil, bulk density, organic matter, clay, silt and sand content. In addition neural network B had matric potential as input, and network C included soil structural data expressed as the upper and lower boundary of the ped‐size class. Neural network A had three output variables: the volumetric water content at matric potentials of 0, –100 and –15 000 hPa. Both models B and C had volumetric water content, at the matric potential given as input, as output variable. The networks were tested against independent data that were extracted from the original sets of soil profiles. Accuracy of the predictions was quantified by the root of the mean squared difference (RMSE) between the measured and the predicted water contents, and the coefficient of determination (R2). For network A the RMSE varied for the three estimated water contents from 0.0264 to 0.0476 cm3 cm–3, and R2 varied from 0.80 to 0.93 for the individual model outputs. Networks B and C had an RMSE of 0.0435 and 0.0426 cm3 cm–3, respectively. For both networks, R2 was 0.89. The neural networks performed somewhat better than previous regression functions, but the improvements were not significant.
Dynamics of dissolved organic nitrogen and carbon in a Central European Norway spruce ecosystem
Authors: Michalzik B. , Matzner E.
Published: March 2003

Dissolved organic nitrogen and carbon (DOC) are significant in the C and N cycle in terrestrial ecosystems. Little is known about their dynamics in the field and the factors regulating their concentrations and fluxes. We followed the fluxes and concentrations of the two in a Norway spruce (Picea abies (L.) Karst.) forest ecosystem in Germany from 1995 to 1997 by sampling at fortnightly intervals. Bulk precipitation, throughfall, forest floor percolates from different horizons and soil solutions from different depths were analysed for major ions, dissolved organic N and DOC. The largest fluxes and concentrations were observed in percolates of the Oi layer, which contain amino N and amino sugar N as the major components. The average ratio of dissolved organic C to N in forest floor percolates corresponded to the C/N ratio of the solid phase. Concentrations and fluxes were highly dynamic with time and decreased with depth. The largest fluxes in forest floor percolates occurred when the snow melted. The concentrations and fluxes of dissolved organic N were significantly correlated with DOC, but the correlation was weak, indicating different mechanisms of release and consumption. The dynamics of dissolved organic N and DOC in forest floor percolates were not explained by pH and ionic strength of the soil solution nor by the water flux, despite large variations in these. Furthermore, the release of these fractions from the forest floor was not related to the quality and amount of throughfall. Concentrations of dissolved organic N in forest floor percolates increased with soil temperature, while temperature effects on DOC were less pronounced, but their fluxes from the forest floor were not correlated with temperature. In the growing season concentrations of both dissolved organic N and C in forest floor percolates decreased with increasing intensity of throughfall. Thus, the average throughfall intensity was more important than the amount of percolate in regulating their concentrations in forest floor percolates. Our data emphasize the role of dissolved organic N and DOC in the N and C cycle of forest ecosystems.
Short‐range spatial variation of nitrous oxide fluxes in relation to compaction and straw residues
Authors: Ball B. C. , Horgan G. W. , Parker J. P.
Published: March 2003

The spatial heterogeneity of N2O flux at short distances (0.1–2 m) was characterized in relation to various soil physical and chemical properties and the location of incorporated crop residues in arable soils. Plots were prepared with uniform compaction (either zero or compacted by a laden two‐wheel‐drive tractor) in two field experiments, one under winter barley (Hordeum vulgare), the other under oil‐seed rape (Brassica napus). Flux measurements were made of N2O using small chambers (7.3 cm diameter) placed at intervals of approximately 10 cm along a transect (c. 2 m long) across the direction of application of the treatments of compaction and residue incorporation. The flux of N2O and many other measurements showed large variation over short distances, particularly when fluxes were small. The spatial variation of the flux was not closely related to the soil properties. Correlations showed that cone resistance, air permeability and closeness to incorporated residues were as important as soil NO3, NH4 and soluble C in determining flux of N2O from non‐compacted soils. Most properties of compacted soils did not correlate with N2O flux. Correlation and multiple regression analysis failed to establish consistent relations between soil environmental variables and N2O flux, but principal component regression indicated that, overall, N2O flux increased with decreasing distance from straw residues and air permeability, and with increasing cone resistance and wet bulk density.
Modelling pH buffering and aluminium solubility in European forest soils
Authors: Lofts S. , Woof C. , Tipping E. , Clarke N. , Mulder J.
Published: March 2003

The pH buffering and aluminium solubility characteristics of acid soil are important in determining the soil's response to changes in precipitation acidity. The chemistry of soil organic matter (humic substances) plays a key role in both processes, yet is complex and still poorly understood. Nevertheless, models of humic substance chemistry have been developed, one of which is WHAM–S, which contains a model (Model V) of proton and metal binding at discrete sites on humic substances and considers electrostatic effects on the binding strength. Here we have tested the ability of WHAM–S to model solution pH and Al using batch titration studies on organic and mineral soil horizons from forested sites in Norway, Germany and Spain, with ambient pH values from 3.73 to 5.73. We optimized the model predictions by adjusting the amounts of soil aluminium and humic substances within defined limits, taking the contents of copper chloride‐extractable Al and the base‐extractable organic matter as starting values. The model simulated both pH and dissolved Al well with optimized amounts of aluminium and humic substances within the defined limits (root mean squared error for pH from 0.01 to 0.22, for p[Al]aq (total dissolved Al) from 0.03 to 0.49, five data points). Control of dissolved Al by dissolved organic matter was important particularly at above‐ambient pH. In two mineral horizons we improved the fits by assuming that Al could precipitate as Al(OH)3. The optimized model also gave reasonable predictions of pH and dissolved Al in supernatants obtained by repeated leaching of the soil horizons. The results show that humic substances dominate the control of pH and dissolved Al in most of the horizons studied. Control by Al(OH)3 occurs but is the exception.
Estimation of the phosphorus sorption capacity of acidic soils in Ireland
Authors: Maguire R. O. , Foy R. H. , Bailey J. S. , Sims J. T.
Published: March 2003

The test for the degree of phosphorus (P) saturation (DPS) of soils is used in northwest Europe to estimate the potential of P loss from soil to water. It expresses the historic sorption of P by soil as a percentage of the soil's P sorption capacity (PSC), which is taken to be α (Alox + Feox), where Alox and Feox are the amounts of aluminium and iron extracted by a single extraction of oxalate. All quantities are measured as mmol kg soil−1, and a value of 0.5 is commonly used for the scaling factor α in this equation. Historic or previously sorbed P is taken to be the quantity of P extracted by oxalate (Pox) so that DPS = Pox/PSC.

The relation between PSC and Alox, Feox and Pox was determined for 37 soil samples from Northern Ireland with relatively large clay and organic matter contents. Sorption of P, measured over 252 days, was strongly correlated with the amounts of Alox and Feox extracted, but there was also a negative correlation with Pox. When PSC was calculated as the sum of the measured sorption after 252 days and Pox, the multiple regression of PSC on Alox and Feox gave the equation PSC = 36.6 + 0.61 Alox+ 0.31 Feox with a coefficient of determination (R2) of 0.92. The regression intercept of 36.6 was significantly greater than zero. The 95% confidence limits for the regression coefficients of Alox and Feox did not overlap, indicating a significantly larger regression coefficient of P sorption on Alox than on Feox. When loss on ignition was employed as an additional variable in the multiple regression of PSC on Alox and Feox, it was positively correlated with PSC. Although the regression coefficient for loss on ignition was statistically significant (P < 0.001), the impact of this variable was small as its inclusion in the multiple regression increased R2 by only 0.028. Values of P sorption measured over 252 days were on average 2.75 (range 2.0–3.8) times greater than an overnight index of P sorption. Measures of DPS were less well correlated with water‐soluble P than either the Olsen or Morgan tests for P in soil.
A study of the factors controlling the adsorption of Cr(III) on modified montmorillonites
Authors: Bakhti A. , Derriche Z. , Iddou A. , Larid M.
Published: March 2003

We have examined the way that the metallic ion Cr(III) is held by Na‐montmorillonite and alumina pillared clay. We used several physico‐chemical methods of analysis (X‐ray powder diffraction, infrared absorption spectrometry, thermal analysis and chemical composition) to determine the structural formula of the Na‐montmorillonite, and to clarify the effect of the introduction of the Al13 polycations between the clay layers on its physico‐chemical and structural properties. Our results show that the strength of chromium retention increases with pH. This effect is more marked in pillared than in unpillared clays. It seems that the mechanism of fixing of the metallic cations on pillared clays is more complex than a simple cationic exchange and involves the surface groups of the pillars. In other words, chromium adsorption on pillared montmorillonite is more like adsorption on an amphoteric oxide surface (such as Al2O3) than on a non‐pillared clay.

Etude des facteurs contrôlant l'adsorption de Cr(III) sur des montmorillonites modifiées

Nous avons examiné les possibilités de fixation de l'ion métallique Cr(III) sur une montmorillonite sodique et pontée. Les différentes analyses physico‐chimiques (Rayons‐X, Spectroscopie Infrarouge, Analyse Thermique Différentielle et composition chimique) ont permis d'une part, d'établir la formule structurale de l'argile sodique et d'autre part de mettre en évidence l'effet du pontage de l'argile par des polycations hydroxyaluminiques sur ses propriétés physico‐chimiques et structurales. Nos résultats montrent que le pouvoir de rétention du chrome augmente avec le pH. Ce paramètre affecte davantage son comportement dans les argiles pontées. Il apparaît que le mécanisme de fixation du Cr(III) sur les argiles à piliers est différent d'un simple échange cationique. L'adsorption dans ce cas met en jeu les groupements de la surface des piliers. En d'autres termes, le mécanisme d'adsorption des cations du chrome sur une montmorillonite pontée se rapproche de l'adsorption sur une surface d'oxyde amphotère (tel que Al2O3) plutôt que l'adsorption sur une argile non pontée.
Modelling cracking stages of saturated soils as they dry and shrink
Authors: Chertkov V. Y.
Published: March 2003

Cracks that form when clay soils shrink on drying eventually form a network that determines transport properties. I propose and validate a model for (i) analysing the initial cracking stages of shrinking saturated soils, (ii) estimating the minimum dimension of quasi‐brittle cracks capable of developing in such conditions, and (iii) determining relations between the minimum crack dimension and other characteristic dimensions of the soil structure. Shrinkage cracks in soils can be classified on the concept of the minimum quasi‐brittle crack capable of developing at shrinkage. I use the model of developing a shrinkage crack in a semi‐infinite brittle medium with constant relevant properties, desiccating in conditions of shock drying. The model is generalized to the cracking of a saturated clay soil with a limited maximum crack depth. The available data justify the use of constant elastic, strength, diffusivity, and shrinkage properties of clay soil. The critical point of crack development is the existence of the minimum crack capable of developing in the particular conditions. The dimension of the crack is related to the soil properties. The crack goes through stages of delay, jump, stable growth with approximately constant velocity, and then quick decline until it stops. I show that the minimum crack dimension is related to the mean dimension of soil particles, the thickness of an upper intensive‐cracking layer, and the mean spacing of primary cracks at the soil surface.
When is a measured soil organic matter fraction equivalent to a model pool?
Authors: Smith J. U. , Smith P. , Monaghan R. , MacDonald A. J.
Published: March 2003

Dynamic simulation models are important tools for rationalizing complex changes in soil organic matter. Most such models for organic matter can be described as having either a pool structure or a continuous one. A pool structure can offer advantages in ease of use and transferability. Some pools are easily measured, whereas others cannot be measured directly. New methods of fractionation are being developed in an attempt to base models on measurable fractions. A requirement for such models is a demonstration that the measured fraction and model pool are equivalent. A measured fraction is equivalent to a model pool only if, within acceptable limits, it is unique as well as non‐composite. If the measured fraction is not unique, describing it as a separate pool adds no extra information, while the added complexity can increase propagation of errors. If it is composite then the characteristics of the fraction will change with changing environment as a result of changing proportions of subpools. This will produce a model that cannot be applied without deriving parameters afresh: such a model is of greatly reduced value. Here we develop methods to examine if a fraction is both unique and non‐composite. The tests for unique and composite pools were applied to the SUNDIAL (simulation of nitrogen dynamics in arable land) model of organic matter and nitrogen turnover in soil. Results suggest that the debris, biomass and humus pools are unique, but biomass and humus are composed of two or more subpools. This worked example illustrates how, given suitable data, any pool‐based model can be tested by these methods.
Influence of former agricultural land use on net nitrate production in forest soils
Authors: Jussy J. H. , Koerner W. , Dambrine É. , Dupouey J. L. , Benoit M.
Published: March 2003

Except where nitrate is added to the soil artificially, nitrate is leached from forest soils only if it is produced. Although the factors influencing nitrification have been widely studied, nitrification activity still cannot be simply predicted from ecosystem characteristics. In France, about half of the present forest area was agricultural in 1850. Previous work suggested that former cultivation could be a major factor influencing nitrogen availability in forest soils.

Using laboratory incubations, we compared the net production of ammonium and nitrate in soils from formerly manured lands planted with conifers 70–100 years ago with that in soils of surrounding ancient coniferous forests. Net nitrate production, available P content, and natural abundance of nitrogen 15, δ15N, were greater in soils from formerly manured plots than other land, whereas the C:N ratio of the soil was less. The difference in net nitrate production between previously manured sites and adjacent ancient forests was related to differences in δ15N values in the soil but not evidently to other soil properties. Because soil δ15N increases with the intensity of organic manuring, these results suggest that nitrification in forest soils depends on previous manurial practices under agriculture. In this context, the soil δ15N might be used as an indicator of both previous agricultural land use and potential nitrification. Because a significant proportion of West European forests grow on previously cultivated soils, past land use should be taken into account when evaluating the risks of nitrate leaching from forests.
Post‐stocking behaviour of hatchery‐reared European grayling, Thymallus thymallus (L.), and brown trout, Salmo trutta L., in a semi‐natural stream
Authors: THORFVE  , CARLSTEIN
Published: March 2003

Hatchery‐reared, juvenile European grayling, Thymallus thymallus (L.), and brown trout, Salmo trutta L., were each stocked six times into an area of a semi‐natural stream. The order in which the two species were released was switched after every second experimental stocking. Temporal and spatial post‐stocking dispersal, effects of previously stocked species, feeding behaviour and the influences of sex and size were studied. During each 48‐h experimental release period, some fish were recaptured in a trap situated 200 m downstream from the stocking site, and fish remaining in the stream after each experimental release were caught by electric fishing. Significantly more grayling than trout moved downstream and left the semi‐natural stream. Proportions of stocked grayling recaptured in the trap within 2 h and from 2 to 48 h post stocking in the stream were 36.4% and 10.0%, respectively. Corresponding recapture rates for brown trout were both 1.5%. Most of the grayling and brown trout that did not leave the stream early were recaptured in deep, slow‐moving water at low velocities in the release area. The presence of grayling at the time that the brown trout were stocked resulted in significantly fewer brown trout staying in the upper part of the stream. Within 48 h of their release, 33.3% and 22.8% of the grayling and brown trout, respectively, had eaten natural food items. The mean length of brown trout recaptured in the upper part of the stocking area was significantly lower than that of fish recaptured in the lower part and in the trap. Among brown trout, males showed a significantly greater propensity to eat and to stay in the upper part of the stream near the stocking site compared with females. Brown trout with natural food items in their stomachs had significantly lower mean length than trout without such items. No sex‐ or size‐related differences were found in the spatial distribution or feeding activity of grayling.
Review of morphological and behavioural differences between reared and wild individuals: Implications for sea‐ranching of Atlantic salmon, Salmo salar L., Atlantic cod, Gadus morhua L., and European lobster, Homarus gammarus L.
Authors: SVÅSAND T. , SKILBREI O. T. , VAN DER MEEREN G. I. , HOLM M.
Published: March 2003

Abstract The main question which must be raised when planning to enhance natural populations through sea ranching is whether reared organisms are fit for a life in the wild, or more specifically, whether there are differences between reared and naturally resident individuals. The causes and effects of these differences are reviewed, and results from the Norwegian enhancement programme, which compared reared and wild individuals of Atlantic salmon, Salmo salar L., Atlantic cod, Gadus morhua L., and European lobster, Homarus gammarus L., are discussed with emphasis on morphological and behavioural differences. It was concluded that exposure to an artificial rearing environment during ontogeny can affect both the phenotype and the behaviour of the reared individuals, and thereby, their potential for survival after release into the wild as well. Suggestions are made as to how to diminish observed differences, and thereby, improve the survival potential.
An appraisal of factors constraining the success of fish stock enhancement programmes
Authors: Li J.
Published: March 2003

Stocking and introduction of fish have been widely applied in Yunnan Province, China, for many years to mitigate for declines in natural stocks and commercial catches, and to restore or create new fisheries. The present paper assesses the results of activities concerned with stock enhancement programmes to evaluate the factors which have contributed towards the success of these projects. Factors such as natural lake conditions, stocking density, the age and size of fish stocked, and the mechanisms of stocking are discussed. Stocking density was evaluated using the equations Yp = [B(P/B)Uf]/Kf or PYp = (P × Uf)/Kf, which were based on the ecological carrying capacity of the recipient lake and other criteria. The stocking density in most lakes in Yunnan was high, but the recapture rates and total yield did not reach the predicted levels. This may have been an effect of the size of the fingerlings released (finger‐lings >10 cm have a greater chance of survival). Key management measures for stocking and the ecological impacts of overstocking grass carp, Ctenopharyngodon idella (Valenciennes), are also described.
Growth of bream, Abramis brama (L.), in Irish canals and implications for management
Authors: Tierney D. , Donnelly R. E. , Caffrey J. M.
Published: March 2003

The growth rates of bream, Abramis brama (L.), were determined in three Irish Canals: the Royal and Grand Canals, and the Barrow Line. Compared with growth patterns for other Irish and European waters, the growth of bream was fast in the Royal Canal, but slow to moderate for the Grand Canal and the Barrow Line. Significant differences in bream growth in terms of both length and weight were found between the three canal systems, and between canal levels, particularly in the Grand Canal. Associations between growth, and (1) alkalinity, (2) total fish biomass and (3) the ratio of bream biomass to total fish biomass were also found. However, it was considered that these three factors alone were not sufficient to explain the differences in growth. Productivity was implicated as the main factor controlling bream growth because fish species diversity was greater and total fish biomass was generally higher in levels of the Grand Canal with faster growing bream populations. The division between ‘fast’ and ‘slow’ growing bream also corresponded with a change in the aquatic weed community. There is evidence to suggest that there was a corresponding change in macro‐invertebrate community structure and density. Angler usage as another factor in promoting growth is discussed. The implications for the future management and development of these canals are outlined.
Winter residency and activity patterns of channel catfish, Ictalurus punctatus (Rafinesque), and common carp, Cyprinus carpio L., in a thermal discharge canal
Authors: Cooke S. J. , McKinley R. S.
Published: March 2003

Radiotelemetry was used to examine the behavioural responses of fish to dynamic environmental and operating conditions in a fossil‐generating power station discharge canal on Lake Erie. A series of seven underwater antennas continuously monitored the movements of 10 common carp, Cyprinus carpio L., and 10 channel catfish, Ictalurus punctatus (Rafinesque), in the 550‐m discharge canal between 23 December 1997 and 1 May 1998. Common carp residency values were higher (47.71±8.51%) than those of channel catfish (10.15±2.82%). While resident in the discharge canal, channel catfish spent more time in the upper reaches and were more active than carp. Carp spent more time in the lower reaches of the channel, and made more frequent movements between the canal and Lake Erie. Overall residency decreased significantly during the study period. Aside from significant negative correlations between common carp residency and daily mean influent temperature (r= −0.53), daily discharge mean (r= −0.30) and minimum water temperature (r= −0.47), and positive correlations to daily mean cooling water flow (r= 0.38), the activity and residency of tagged individuals were independent of environmental and operating conditions. There was no relationship between the total length of each fish, and any of the residency or activity indices. The implications of extended fish residency in heated discharges and the utility of radiotelemetry as a monitoring procedure are discussed.
Survival of sea‐water‐adapted trout, Salmo trutta L. ranched in a Danish fjord
Authors: Pedersen S. S. , Rasmussen G. H.
Published: March 2003

The effect of seawater adaptation on the survival of coastally released post‐smolt trout, Salmo trutta L., was investigated by release: (1) directly (with no adaptation); (2) after retention in net pens in the sea for 29–131 days (delayed release); (3) after feeding with a high‐salt diet (12–13.5% NaCl) for 4 weeks; and (4) after a combination of (2) and (3). In total, 17 640 trout (age = 1+, 1.5 and 2+ years; mean fork lengths = 18.2–25.6 cm) were released in 14 batches in the summer or autumn months of 1986–1989. All fish were of domesticated origin and Carlin tagged. Survival and instantaneous mortality rates (total and fishing mortality) were estimated from reported recaptures. Mortality rates were estimated for: (1) the post‐smolt period; (2) the period until the legal size of capture (40 cm) was attained; and (3) for larger sea‐trout. Release with a delay of 4 weeks gave an increased survival rate. A longer adaptation period did not increase survival. On average, survival was increased by 36%. Survival was not increased by high‐salt diets. Until attainment of the legal size for capture, survival was 9.6% higher on average, with extremes as low as 1.7% and as high as 38% in individual batches.
Small‐scale fisheries in the middle River Tocantins, Imperatriz (MA), Brazil
Authors: Cetra M. , Petrere Jr M.
Published: March 2003

The description of the small‐scale fisheries in the middle River Tocantins and their dynamics, in a full year cycle, was made out using questionnaires when interviewing fishermen at Imperatriz market. The landed fish exhibited a seasonal pattern related to the hydrological cycle, fishing effort and species diversity. Curimatá, Prochilodus nigricans Agassiz, is the most important commercial fish. The fishing gears used in the area are castnets, gillnets, longlines and beach seines. Thirty‐six percent of fish landed were caught exclusively by beach seine which mainly targets curimatá. Alterations in the physical and biological characteristics of the middle River Tocantins due to the building of the Tucuruí dam (2850 km2 total area) allowed the mapará, Hipophthalmus marginatus Valenciennes, to colonise this area. During the closed season for nets, Siluriformes are the target of the fisheries, caught exclusively by longlining.
An assessment of the potential for the application of two simple models to Atlantic salmon, Salmo salar, stock management in chalk rivers
Authors: Hilton J. , Welton J. S. , Clarke R. T. , Ladle M.
Published: March 2003

Many salmon populations in the UK are under threat, which is assumed to result from a combination of anthropogenic and natural factors. Positive management is required to bring them back to their former productivity levels. An attempt has been made to use two simple models to assess the suitability of several management approaches for use on chalk rivers. One model is based on the survival rates at each stage of the salmon life cycle and the other estimates the predation of young salmon by other fish. This work highlights the paucity of data available to calibrate even the simplest salmon management models. For those variables where data are available, the variability is very high. Despite the poor quality of input data, the outputs are close to observed numbers in the River Frome, a chalk river in Dorset, UK. The models were used to assess the effect of managing the fishery using reduced rod catches, pike culling, gravel cleaning and trout stocking on adult salmon and smolt numbers.
Factors influencing migration of Penaeus indicus in the Negombo lagoon on the west coast of Sri Lanka
Authors: JAYAWARDANE P. A. A. T. , MCLUSKY D. S. , TYTLER P.
Published: March 2003

Juveniles of Penaeus indicus (Milne Edwards) occur in the Negombo lagoon Sri Lanka and on maturing they return to the sea for reproduction. Cohort analysis indicated pulses of immigration to the nursery areas in February and June. The growth rates for juveniles were relatively high compared with that of adults. Three groups of prawns were identified in the lagoon: `small quick movers', `larger long stay individuals' and an `intermediate group'. There were few identifiable emigration pulses from the lagoon towards the offshore areas. It appears that osmotic stress caused by low salinity waters in the lagoon during the periods of high precipitation may be the strongest influence triggering the onset of emigration.
Year‐to‐year variations in Bering Sea ice cover and some consequences for fish distributions
Authors: WYLLIE‐ECHEVERRIA TINA , WOOSTER WARREN S.
Published: March 2003

The southernmost extension of winter ice cover varies interannually and on longer time scales, reflecting large‐scale changes in driving forces, especially in the position and intensity of the winter Aleutian Low Pressure System. A conspicuous pattern is alternating warm and cool periods of several years' duration. These variations in sea ice cover are reflected in the character of a subsurface cold pool, formed as stratification isolates the deeper cold waters from surface exchanges. The cold pool is better developed and more extensive in summers that follow deep southward penetration of winter sea ice. Interannual and decadal‐scale variations in the distributions of some fish stocks reflect those of ice and thermal conditions. In particular, the distribution of walleye pollock, Theragra chalcogramma, varies significantly with multiannual cool and warm years while Arctic cod, Boreogadus saida, is only present within the cold pool. The relation among climate variations, sea ice cover, subsurface thermal conditions, and fish distribution provides information on how climate affects marine ecosystems and may also have practical application in predicting fish distributions.
Interdecadal variations of plankton biomass and physical environment in the North Pacific
Authors: SUGIMOTO TAKASHIGE , TADOKORO KAZUAKI
Published: March 2003

In the central and western subarctic Pacific, zooplankton biomass and chlorophyll concentrations during the mid 1960s to mid 1970s were a few times higher than in the preceding and following decades, corresponding to higher values of the atmospheric Northern Hemisphere Zonal Index (NHZI). In the Alaskan Gyre, however, it was reported that biomass of zooplankton and nekton doubled after the atmospheric regime shift in the mid 1970s. In the subtropical North Pacific, chlorophyll a concentration decreased drastically after 1980, although a decrease of zooplankton biomass was clearly seen only in the northern part of the subtropical gyre. Chlorophyll concentration in the central subarctic Pacific and zooplankton biomass in the Oyashio have been decreasing since the early 1980s. Additionally, chlorophyll concentration in the western subarctic Pacific and eastern Bering Sea, and zooplankton biomass in the central subarctic Pacific and eastern Bering Sea have also been decreasing since the late 1980s. In these regime‐shift situations, there is a general tendency for intensification of wind speed or de‐stratification to cause plankton biomass to decrease in regions where the upper mixed layer is deep, such as the western subarctic and north‐western subtropical water, whereas in relatively stratified areas, such as in the eastern subarctic and south‐western subtropical water, the effect is an increase of plankton biomass.
Transport of fish larvae through a tidal inlet
Authors: Forward Jr  , Reinsel  , Peters  , Tankersley  , Churchill  , Crowder  , Hettler  , Warlen  , Green
Published: March 2003

In the South‐eastern USA many species of estuarine‐dependent fishes spawn offshore and their larvae are transported into estuaries. The present study combined physical measurements and zooplankton sampling at the Beaufort Inlet (North Carolina) to determine: (i) whether fish larvae enter the estuary inlet in different horizontal sections of the tidal stream and (ii) whether larvae use selective tidal stream transport (STST) for ingress through the inlet and for movements up the estuary. Larvae of Atlantic menhaden (Brevoortia tyrannus), spot (Leistomus xanthurus), pinfish (Lagodon rhomboides), Atlantic croaker (Micropogonias undulatus), gulf flounder (Paralichthys albigutta), summer flounder (P. dentatus), and southern flounder (P. lethostigma) were sampled over two 25‐h periods (13–14 March, 25–26 March 1996) at three locations across the Beaufort Inlet and in the three main channels receiving water from different locations in the inlet. All species, except Atlantic croaker, primarily entered the inlet on the east side with up to an order of magnitude difference in abundance across the inlet from East to West. The gradient continued in the corresponding channels in the estuary. In most cases equal sizes of larvae were caught in the East and West channels of the estuary. Most larvae were caught at night. A pattern of abundance relative to tide was least evident in the inlet, but STST was evident in the estuary. At the location of greatest larval abundance (Shackleford Channel), the greatest numbers of all species of larvae were caught during rising tides at night. This relationship was not due to passive suspension, since abundance was higher during the faster nocturnal flood tide currents than during to ebb tide currents of equal magnitude. In the Shackleford Channel, southern/gulf flounder and pinfish were distributed throughout the water column during STST, but primarily at the surface. Atlantic menhaden, spot and Atlantic croaker were distributed throughout the water column, and summer flounder were near the surface.
Evidence for a substantial increase in gelatinous zooplankton in the Bering Sea, with possible links to climate change
Authors: Brodeur Richard D. , Mills Claudia E. , Overland James E. , Walters Gary E. , Schumacher James D.
Published: March 2003

We examined quantitative catches of large medusae from summer bottom trawl surveys that sampled virtually the same grid station on the eastern Bering Sea shelf using the same methodology every year from 1979 to 1997. This series shows a gradual increase in biomass of medusae from 1979 to 1989, followed by a dramatic increase in the 1990s. The median biomass increased tenfold between the 1982–1989 and 1990–1997 periods. Most of this biomass was found within the Middle Shelf Domain (50 < z < 100 m). The greatest rate of increase occurred in the north‐west portion of this domain. Whether this dramatic increase in biomass of gelatinous zooplankton has resulted from some anthropogenic perturbation of the Bering Sea environment or is a manifestation of natural ecosystem variability is unclear. However, several large‐scale winter/spring atmospheric and oceanographic variables in the Bering Sea exhibited concomitant changes beginning around 1990, indicating that a possible regime change occurred at this time.
Mesoscale eddies and survival of late stage Pacific sardine (Sardinops sagax) larvae
Authors: Logerwell Elizabeth A. , Smith Paul E.
Published: March 2003

We examined the distribution of sardine larvae relative to environmental conditions with the purpose of identifying and characterizing habitat that encourages high larval growth and survival, based on the 1983–1998 surveys of the California Cooperative Oceanic Fisheries Investigations (CalCOFI). Long‐term averages show that sardine ‘survivors’ (spatially aggregated larvae ≥ 18 days old) were most abundant offshore, whereas sardine egg density, chlorophyll biomass and zooplankton volume were greatest inshore. In contrast, mesoscale eddies, observed in remotely sensed sea surface temperature imagery, were found only in offshore regions. To further examine the link between eddies – which often result in locally elevated chlorophyll and zooplankton – and sardine survival, we compared the distribution of larvae and eddies survey by survey. Sardine survivors were most abundant offshore in only one‐quarter of the research surveys, and when they were most abundant offshore they were associated with eddies. This indicates that the offshore eddy habitat produced exceptionally large numbers of survivors, as evidenced by the disproportionate effect on the long‐term average.
Growth of larval and early juvenile Japanese anchovy, Engraulis japonicus, in the Kuroshio‐Oyashio transition region
Authors: Takahashi M. , Watanabe Y. , Kinoshita T. , Watanabe C.
Published: March 2003

Larvae, juveniles, and adults of Japanese anchovy, Engraulis japonicus, were distributed throughout the Kuroshio‐Oyashio transition region off northern Japan as far offshore as 170°E in 1996 and 1997. The growth trajectories of individual larvae and early juveniles were backcalculated using the biological intercept method based on the allometric relationship between otolith radius and somatic length. Mean larval growth rates ranged from 0.49 to 0.71 mm day–1 in the transition region, and were comparable to those reported from the Pacific coastal waters of central Japan, which is the principal distribution range of E. japonicus. In terms of growth, the Kuroshio‐Oyashio transition region seemed to be a favourable nursery area for larval E. japonicus. Larval growth tended to decline from the inshore to the offshore waters in the transition region. Thermal conditions did not show an inshore–offshore trend in the survey area and did not explain the longitudinal trend in growth rates.
High abundance of larval rockfish over Cobb Seamount, an isolated seamount in the Northeast Pacific
Authors: Dower John F. , Perry R. Ian
Published: March 2003

The larval fish community in the region of Cobb Seamount (500 km west of Oregon) is dominated by myctophid species commonly encountered in the subarctic North Pacific. However, during a survey in June 1992, the ichthyoplankton community within 30 km of the seamount summit was almost completely dominated by larvae of various rockfish (Sebastes) species. Given their very small size (and hence very young age) and the fact that they occurred only rarely in samples collected > 30 km from the seamount summit, we conclude that these Sebastes larvae were produced locally over Cobb Seamount. Previous studies have shown that the Cobb fish fauna is dominated by various Sebastes spp. and that, unlike other fish present on the seamount, the rockfish populations may be self‐recruiting. We suggest that a persistent clockwise (i.e. downwelling) eddy, consistent with a stratified Taylor cone, plays a critical role in retaining larval rockfish over Cobb Seamount and may contribute to the process of self‐recruitment. The key to the success of rockfish on Cobb and other shallow Northeast Pacific seamounts seems to be linked to their viviparous life history.
Temporal variation of seasonality of egg production and the spawning biomass of Pacific anchovy, Engraulis japonicus, in the southern waters of Korea in 1983–1994
Authors: Kim Jinyeong , Lo Nancy C. H.
Published: March 2003

Embryonic mortality, egg production and the spawning stock biomass of Pacific anchovy, Engraulis japonicus, off Southern Korea during 1983–1994, and their biological response to oceanographic features in spring and summer, were analysed. The instantaneous mortality rate (IMR) of embryonic stages decreased in spring and increased in summer, with a range of 0.33–1.23 day–1 in spring and 0.78–1.69 day–1 in summer. Egg production in summer was three times that during spring and production was low in the late 1980s. Mean lengths of yolk‐sac larvae and adult females were greater in spring than in summer, whereas spawning fraction and spawning stock ratio (spawning biomass:adult biomass) were lower in spring than summer. Estimated mean spawning stock biomass ranged from 141 × 103 to 380 × 103 MT in spring and from 221 × 103 to 557 × 103 MT in summer. Statistically, the seasonal and long‐term trends of embryonic mortality, egg production and spawning stock biomass of Pacific anchovy can be explained largely by spring warming, summer cooling and by less abundant zooplankton in the late 1980s.