bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nitrate leaching loss under annual and perennial pastures with and without lime on a duplex (texture contrast) soil in humid southeastern Australia
Authors: Ridley A. M. , White R. E. , Helyar K. R. , Morrison G. R. , Heng L. K. , Fisher R. 
Published: March 2003

SummaryMineral N accumulates in autumn under pastures in southeastern Australia and is at risk of leaching as nitrate during winter. Nitrate leaching loss and soil mineral N concentrations were measured under pastures grazed by sheep on a duplex (texture contrast) soil in southern New South Wales from 1994 to 1996. Legume (Trifolium subterraneum)‐based pastures contained either annual grass (Lolium rigidum) or perennial grasses (Phalaris aquaticaandDactylis glomerata), and had a control (soil pH 4.1 in 0.01 mCaCl2) or lime treatment (pH 5.5). One of the four replicates was monitored for surface runoff and subsurface flow (the top of the B horizon), and solution NO3–concentrations.The soil contained more mineral N in autumn (64–133 kg N ha−1to 120 cm) than in spring (51–96 kg N ha−1), with NO3–comprising 70–77%. No NO3–leached in 1994 (475 mm rainfall). In 1995 (697 mm rainfall) and 1996 (666 mm rainfall), the solution at 20 cm depth and subsurface flow contained 20–50 mg N l−1as NO3–initially but < 1 mg N l−1by spring. Nitrate‐N concentrations at 120 cm ranged between 2 and 22 mg N l−1during winter. Losses of NO3–were small in surface runoff (0–2 kg N ha−1year−1). In 1995, 9–19 kg N ha−1was lost in subsurface flow. Deep drainage losses were 3–12 kg N ha−1in 1995 and 4–10 kg N ha−1in 1996, with the most loss occurring under limed annual pasture. Averaged over 3 years, N losses were 9 and 15 kg N ha−1year−1under control and limed annual pastures, respectively, and 6 and 8 kg N ha−1year−1under control and limed perennial pastures. Nitrate losses in the wet year of 1995 were 22, 33, 13 and 19 kg N ha−1under the four respective pastures. The increased loss of N caused by liming was of a similar amount to the decreased N loss by maintaining perennial pasture as distinct from an annual pasture.
Measurement of the wettability of organic materials in relation to water content by the capillary rise method
Authors: Michel J. ‐C. , Rivière L. ‐M. , Bellon‐Fontaine M. ‐N. 
Published: March 2003

SummaryA new measuring technique based on a capillary rise method has been developed to quantify the wettability of more or less decomposed peats (the main materials used as horticultural growing media) in relation to their water content. A preliminary study of their physico‐chemical and biochemical characteristics enabled us to study the variation of their physical properties (particularly their rewetting capacity) in relation to their degree of decomposition. Analysis of these physical properties during two drying and rewetting cycles showed that the greater their degree of decomposition, the greater and more irreversible was their shrinkage. The change from hydrophilicity to hydrophobicity was measured by the increase of the water contact angle during desiccation and by the progressive change from bipolar to apolar surfaces. A strong correlation between the water retention of peats (related to their degree of decomposition) and their free energy (also called hydration energy) at the interface between solid and water ΔGSW is also shown.
Physical fractionation of soil and structural and functional complexity in organic matter turnover
Authors: Christensen B. T. 
Published: March 2003

SummaryPhysical fractionation is used increasingly to study the turnover of organic matter in soil. This essay links the methods of fractionation to concepts of turnover by defining levels of structural and functional complexity that refer to experimentally verifiable pools of organic matter in the soil.Physical fractionation according to size and density of soil particles emphasizes the importance of interactions between organic and inorganic soil components in the turnover of organic matter. It allows the separation of free and occluded uncomplexed organic matter and of primary and secondary organomineral complexes. This methodological approach recognizes that the overall regulation of decomposer activity is through the structure of soil, which determines gas exchange, the availability of substrates and water, and the transport of solutes.Results from physical fractionations suggest three levels of structural and functional complexity in the turnover of organic matter in soil. Primary organomineral complexes isolated from fully dispersed soil account for the primary level of complexity. The clay‐, silt‐ and sand‐sized complexes are seen as the basic units in soil, surface reactions between substrates, organisms and minerals being the main regulatory mechanisms. Secondary complexes reflect the degree of aggregation of primary organomineral complexes and refer to the second level of complexity. Physical protection of uncomplexed organic matter and soil organisms and the creation of gas and moisture gradients are emergent features regulating the turnover at this level of complexity. The structurally intact soil (the soil in situ) constitutes the third level of complexity. This integrates the effects of primary and secondary complexes. Emergent structural features associated with this level are resource islands, macropores, roots, mesofauna, tillage and soil compaction, the corresponding functional features being related to the transport and exchange of solutes and gases, and the spatial distribution and comminution of litter and uncomplexed organic matter. Thus, a thorough understanding of the turnover and storage of organic matter in soil can be acquired only by considering all levels of complexity in the decomposition subsystem.
Soil solution concentration of Cd and Zn canbe predicted with a CaCl2 soil extract
Authors: Degryse F. , Broos K. , Smolders E. , Merckx R. 
Published: March 2003

SummaryRisk assessment of heavy metals in soil requires an estimate of the concentrations in the soil solution. In spite of the numerous studies on the distribution of Cd and Zn in soil, few measurements of the distribution coefficient in situ, Kd, have been reported. We determined the Kd of soils contaminated with Cd and Zn by measuring metal concentrations in the soil and in the soil solution and attempted to predict them from other soil variables by regression. Soil pH explained most of the variation in logKd (R2 = 0.55 for Cd and 0.70 for Zn). Introducing organic carbon content or cation exchange capacity (CEC) as second explanatory variable improved the prediction (R2 = 0.67 for Cd and 0.72 for Zn), but these regression models, however, left more than a factor of 10 of uncertainty in the predicted Kd. This large degree of uncertainty may partly be due to the variable degree of metal fixation in contaminated soils. The labile metal content was measured by isotopic dilution (E value). The E value ranged from 18 to 92% of the total metal content for Cd and from 5 to 68% for Zn. The prediction of Kd improved when metals in solution were assumed to be in equilibrium with the labile metal pool instead of the total metal pool. It seems necessary therefore to discriminate between ‘labile’ and ‘fixed’ pools to predict Kd for Cd and Zn in field contaminated soils accurately. Dilute salt extracts (e.g. 0.01 m CaCl2) can mimic soil solution and are unlikely to extract metals from the fixed pool. Concentrations of Cd and Zn in the soil solution were predicted from the concentrations of Cd and Zn in a 0.01 m CaCl2 extract. These predictions were better correlated with the observations for field contaminated soils than the predictions based on the regression equations relating logKd to soil properties (pH, CEC and organic C).
Two robust estimators of the cross‐variogram for multivariate geostatistical analysis of soil properties
Authors: Lark R. M. 
Published: March 2003

SummaryIf we wish to describe the coregionalization of two or more soil properties for estimation by cokriging then we must estimate and model their auto‐ and cross‐variogram(s). The conventional estimates of these variograms, obtained by the method‐of‐moments, are unduly affected by outlying data which inflate the variograms and so also the estimates of the error variance of cokriging predictions. Robust estimators are less affected. Robust estimators of the auto‐variogram and the pseudo cross‐variogram have previously been proposed and used successfully, but the multivariate problem of estimating the cross‐variogram robustly has not yet been tackled. Two robust estimators of the cross‐variogram are proposed. These use covariance estimators with good robustness properties. The robust estimators of the cross‐variogram proved more resistant to outliers than did the method‐of‐moments estimator when applied to simulated fields which were then contaminated.Organic carbon and water content of the soil was measured at 256 sites on a transect and the method‐of‐moments estimator, and the two robust estimators, were used to estimate the auto‐variograms and cross‐variogram from a prediction subset of 156 sites. The data on organic carbon included a few outliers. The method‐of‐moments estimator returned larger values of the auto‐ and cross‐variograms than did either robust estimator. The organic carbon content at the 100 validation sites on the transect was estimated by cokriging from the prediction data plus a set of variograms fitted to the method‐of‐moments estimates and two sets of variograms fitted to the robust estimates. The ratio of the actual squared prediction error to the cokriging estimate of the error variance was computed at each validation site. These results showed that cokriging using variograms obtained by the method‐of‐moments estimator overestimated the error variance of the predictions. By contrast, cokriging with the robustly estimated variograms gave reliable estimates of the error variance of the predictions.
The feeding ecology of larval Pacific hake (Merluccius productus) in the California Current region: an updated approach using a combined OPC/MOCNESS to estimate prey biovolume
Authors: Cass‐Calay Shannon L. 
Published: March 2003

AbstractA combined optical particle counter (OPC) and multiple opening and closing net and environmental sensing system (MOCNESS) was used to obtain simultaneous measurements of the fine‐scale distribution of ‘prey‐sized’ particles and the vertical distribution of larvae of Pacific hake (Merluccius productus). Physical properties were also measured. The data were used to describe the feeding ecology of Pacific hake larvae, and to explore the effects of prey abundance, time of day, temperature and depth on feeding. Pacific hake larvae consumed a wide variety of prey including copepod eggs, nauplii, copepodites, and euphausiid metanauplii. Calanoid copepodites comprised > 75% of the ingested prey volume. First‐feeding larvae were 2.5–3.0 mm SL. These larvae consumed prey 40–200 μm wide. Larvae 3.0–6.5 mm long ingested prey 40–400 μm wide and larvae > 6.5 mm long ingested prey 400–700 μm wide. There were clear diel patterns in feeding incidence and prey volume ingested. Feeding commenced between 06:01 and 08:00 hours PST and continued until ∼ 16:00 hours. Ingested prey items remained in the gut until complete gut evacuation occurred near dawn. The volume of food ingested was estimated using two indices, the cube root of the prey volume (CRPV) and the cube root of the stomach volume (CRSV). Standard length, log elapsed time since gut evacuation, depth and particle biovolume contributed significantly to variation in both indices. Temperature did not contribute to variability in either CRPV or CRSV.
The relationship between the skipjack tuna (Katsuwonus pelamis) fishery and seasonal temperature variability in the south‐western Atlantic
Authors: Andrade H. A. 
Published: March 2003

AbstractThe spatio‐temporal distribution of tuna fishing effort has been related to oceanographic circulation and features in several seas of the world. Understanding the relationship between environmental variables and fishery resource dynamics is important for management decisions and to improve fishery yields. The relationship between sea temperature variability and the pole‐and‐line skipjack tuna (Katsuwonus pelamis) fishery in the south‐western Atlantic Ocean was investigated in this work. Data from logbooks, satellite images (sea surface temperature), and oceanographic surveys were used in the analyses. Skipjack are caught in warm tropical waters of the Brazil Current (BC). The north–south displacement of fishing effort was strongly associated to seasonal variation of the surface temperature, which was coupled to the tropical BC flow. Oceanographic fronts from autumn to spring and a shallow thermocline in summer probably induces the aggregation of skipjack schools over the shelfbreak, favouring fishing operations. Hypotheses are proposed to explain the relationship between peaks of fishing events and the presence of topographic peculiarities of the shelfbreak.
Light availability as a possible regulator of cyanobacteria species composition in a shallow subtropical lake
Authors: Havens Karl E. , Phlips Edward J. , Cichra Mary F. , Li Bai‐lian 
Published: March 2003

1. Variations in the relative biovolumes of dominant cyanobacterial taxa were evaluated in the context of environmental conditions using canonical correlation analysis (CCorrA) and Redundancy Analysis (RDA). The objective was to test a conceptual model in which underwater irradiance determines dominance by bloom‐forming (high light adapted) or non‐blooming (low light adapted) taxa.2. The data set consisted of 404 contiguous observations, collected over a 3‐year period at eight pelagic sites, in shallow Lake Okeechobee, Florida, U.S.A. Data included species biovolumes, total phosphorus (TP), total nitrogen (TN), dissolved oxygen (DO) and chlorophyll a concentrations, as well as two indices: underwater irradiance (Secchi depth) and the ratio of Secchi:total depth.3. The first environmental canonical variable was strongly correlated with the two light‐related indices, and negatively correlated with TP. This reflects the predominant role of resuspended P‐rich lake sediments in controlling underwater irradiance in the shallow lake. The first species canonical variable displayed a strong negative correlation with Lyngbya limnetica and L. contorta, and positive correlations with Anabaena circinalis, Aphanizomenon flos aquae and Microcystis spp. The results support the conceptual model; the first pair of canonical variables explained 55% of the variation in the species–environmental data set. RDA results provided further support for the hypothesis that irradiance was the major force controlling community structure.4. One unexpected result was a positive association between Oscillatoria spp. dominance and indicators of high irradiance. This conflicts with past research indicating that Oscillatoria is a low light adapted taxon, and the finding that it is the most abundant taxon in Lake Okeechobee. This may reflect the fact that the two Lyngbya taxa were more strongly associated with low light conditions than Oscillatoria. CCorrA results indicated that Oscillatoria densities are strongly controlled by water temperature. There is a need for more detailed studies of cyanobacteria ecophysiology in order to explain fully the seasonality of phytoplankton in this and other shallow subtropical lakes.
Epiphytic algae and macroinvertebrates on submerged and floating‐leaved macrophytes in an Italian lake
Authors: Cattaneo Antonella , Galanti Gaetano , Gentinetta Silvia , Susana And 
Published: March 2003

1. The presence of contiguous beds of submerged (Myriophyllum spicatum, Ceratophyllum demersum and Najas marina) and floating‐leaved (Trapa natans) vegetation in a north Italian lake allowed us to test the effect of the different host architecture on epiphytic algae and invertebrates and to predict the consequences for the lake of changes in the predominant vegetation.2. Epiphyton development, measured as carbon, nitrogen, phosphorus, chlorophyll a (Chl a), phaeophytin and as algal and macroinvertebrate density, was significantly higher on submerged plants than on T. natans. The C : Chl a ratio, a proxy of the ratio of heterotrophs to autotrophs, was higher on the floating‐leaved plants. The elemental (C : N : P) and pigment (Chl a : phaeophytin) ratios were not significantly different between the two vegetation types.3. The taxonomic composition of epiphytic algae and invertebrates was similar on the different plants. The more varied morphology of the floating‐leaved T. natans resulted in a higher diversity of epiphytic algae, however, but not of macroinvertebrates.4. There was a significant inverse relationship between epiphyton biomass and the standing crop of the host plant, suggesting a key role for light and water exchange in epiphyton development.5. Replacement of floating‐leaved by submerged plants would increase the total biomass of epiphytic algae and invertebrates.
Influence of diet shifts in underyearling fish on phosphorus recycling in a hypertrophic biomanipulated reservoir
Authors: Mehner Thomas , Mattukat Frank , Bauer Dirk , Voigt Hanno , Benndorf Jürgen 
Published: March 2003

Summary1. In addition to effects of direct predation by planktivorous fish, nutrient recycling by fish may also contribute to structuring foodwebs in lakes. There is little evidence, however, about whether underyearling fish undergoing several ontogenetic diet shifts may have a comparable bottom‐up impact.2. This study examined seasonal patterns of phosphorus (P) concentration and external load, phytoplankton, zooplankton and benthos, and diet shifts in three underyearling fish [perch (Perca fluviatilis), roach (Rutilus rutilus) and ruffe (Gymnocephalus cernuus)] in the shallow, hypertrophic biomanipulated Bautzen reservoir, Germany. Phosphorus metabolism of fish was calculated by a balanced bioenergetics model on the basis of fish diet, growth and water temperature.3. The fish showed several shifts from planktivory to other food sources during the sampling period from May to September. These shifts were probably caused by the seasonal succession of the zooplankton community, mainly the midsummer decline of Daphnia galeata.4. The diet shifts in fish also had consequences for the amount of P consumed and released. During periods of dominant zooplanktivory, the excretion of P did not exceed the removal of P stored in pelagic prey. By contrast, if benthivory dominated, fish subsidized the pelagic P pool by excreting more P from benthic prey than had been removed from the pelagic area. This occurred predominantly in perch and ruffe during periods of low zooplankton biomass, whereas the roach ate more algae and therefore excreted less P of benthic origin.5. Phosphorus release by underyearling fish was estimated at a maximum of 0.1 mg m–3 JY day–1. This value was negligible compared with both the external load of P to Bautzen reservoir and the concentration of P in the pelagic area during summer. It is therefore concluded that both the predominance of underyearling zooplanktivorous fish and the high Daphnia biomass during certain periods of the year in the Bautzen reservoir may be the reason that nutrient release by the fish structured the foodweb only marginally. 6. This study suggests that biomanipulation has altered both top‐down and bottom‐up impacts of fish in Bautzen reservoir. The highest efficiency of foodweb manipulations may be obtained after reduction of the external P loading below a certain threshold. In turn, if external restoration of eutrophied lakes is not accompanied by changes in fish community, then the combined forces of strong zooplanktivory and high P recycling of dense stocks of zooplanktivorous and benthivorous fish may hold the water in a eutrophic‐like stage, even if external load has been significantly reduced.
An assessment of the influence of recruitment from the sediment on the development of planktonic populations of cyanobacteria in a temperate mesotrophic lake
Authors: Head R. M. , Jones R. I. , Bailey‐Watts A. E. 
Published: March 2003

1. A number of planktonic cyanobacteria species form resting stages that survive in the sediments of lakes. The significance of this life history strategy to the ecology of new planktonic populations was investigated in Esthwaite Water, a mesotrophic lake in the English Lake District.2. A simple trapping technique was used to quantify vertical movements of five species of buoyant gas‐vacuolate cyanobacteria from close to the sediments, along a depth transect.3. ‘Recruitment’ from the sediments was found to be widespread amongst the cyanobacteria species associated with the summer phytoplankton community.4. Estimates of the vertical upward fluxes of cyanobacteria based upon trap catches could not account for observed increases in the planktonic populations suggesting that ‘recruitment’ was not a significant source of biomass.5. Vertical upward movements of Anabaena solitaria were recorded prior to this species becoming established in the plankton suggesting that benthic populations might be a source of cells for initial pelagic growth of populations of this species.6. Low numbers of vegetative filaments of Anabaena flos‐aquae, Aphanizomenon flos‐aquae and Oscillatoria agardhii were observed in the plankton through the winter. These small overwintering populations appeared to be the primary source of inocula for the large summer populations of these species.
Defining and measuring river health
Authors: Karr James R. 
Published: March 2003

Summary1. Society benefits immeasurably from rivers. Yet over the past century, humans have changed rivers dramatically, threatening river health. As a result, societal well‐being is also threatened because goods and services critical to human society are being depleted.2. ‘Health’— shorthand for good condition (e.g. healthy economy, healthy communities) — is grounded in science yet speaks to citizens.3. Applying the concept of health to rivers is a logical outgrowth of scientific principles, legal mandates, and changing societal values.4. Success in protecting the condition, or health, of rivers depends on realistic models of the interactions of landscapes, rivers, and human actions.5. Biological monitoring and biological endpoints provide the most integrative view of river condition, or river health. Multimetric biological indices are an important and relatively new approach to measuring river condition.6. Effective multimetric indices depend on an appropriate classification system, the selection of metrics that give reliable signals of river condition, systematic sampling protocols that measure those biological signals, and analytical procedures that extract relevant biological patterns.7. Communicating results of biological monitoring to citizens and political leaders is critical if biological monitoring is to influence environmental policies.8. Biological monitoring is essential to identify biological responses to human actions. By using the results to describe the condition, or health, of rivers and their adjacent landscapes and to diagnose causes of degradation, we can develop restoration plans, estimate the ecological risks associated with land use plans in a watershed, or select among alternative development options to minimize river degradation.