bluuebunny/crossref_metadata_2025_split huggingface dataset:
Enzymic and chemical analysis of particulate organic matter from a boreal river
Authors: SINSABAUGH ROBERT L. , LINKINS ARTHUR E. 
Published: May 2006

SUMMARY. 1. Benthic particulate organic matter (POM) was collected from a shallow pool of a fourth order boreal stream and sorted into seven size fractions ranging from 63 to >4000μm. Each size fraction was analysed for fibre, total phosphorus, and total Kjeldahl nitrogen. Microbial activity was measured by oxygen consumption and characterized by assaying for eleven classes of exoenzymes including cellulase, phenol oxidase, peroxidase, phosphatase and sulphatase.2. Indices of detritus quality such as C/N, C/P, percent lignin, and microbial respiration showed improvement with decreasing particle size. Three covarying exoenzyme groups were identified: a carbohydrase‐phosphatase group that included eight enzymes, a phenol oxidase‐peroxidase group, and sulphatase. The activity of the carbohydrase‐phosphatase group, was significantly correlated with microbial respiration and the carbohydrate content of the POM. Phenol oxidase‐peroxidase activity was correlated with lignin content for POM greater than 250 μm, but activity increased markedly in the two smallest size fractions even though the lignin content of the POM continued to decline, Sulphatase activity was inversely related to particle size over the entire range.3. The changes in microbial activity with particle size were attributed to the increasing surface area to volume ratio of smaller particles and to an ecological succession in the microbial community.
Phosphorus transformations in the epilimnion of humic lakes: biological uptake of phosphate
Authors: JONES R. I. 
Published: May 2006

SUMMARY. 1. The hypothesis that dissolved humic material (DHM) stimulates bacterial involvement in phosphorus transformations and may thus lead to decreased accessibility of phosphorus to algae was investigated by studying three small forest lakes in southern Finland representing a wide range of concentrations of DHM.2. Other chemical differences between the three lakes were slight, although the most humic lake exhibited higher concentrations of total phosphorus and of molybdate‐reactive phosphorus. Bacterial biomass did not differ significantly between the lakes, but algal biomass was significantly lower at higher DHM concentrations. Consequently the ratio of algal biomass to bacterial biomass was significantly lower in the most humic lake.3. Uptake of phosphorus from added 33PO4 was partitioned between algal and bacterial size fractions by differential filtration. No significant variation between lakes was found in the proportion of particulate 33P recovered from the algal fraction.4. Turnover times for phosphate were significantly longer in the most humic lake and also showed lower variability. In general turnover times were long in comparison with values reported from many other lakes. Only briefly in mid summmer did turnover times in two of the lakes shorten to values which would indicate that demand for phosphate was outstripping supply.5. Short‐term storage of samples from the most humic lake stimulated biological incorporation of 33P, but additions of nitrogen and iron had little effect on phosphate uptake.6. In these small forest lakes it is probable that no single nutrient consistently limits plankton development. Since no evidence was found that DHM shifts the balance of plankton phosphate uptake away from algae towards bacteria, the influence of DHM on phosphorus transformations may rather be through chemical regulation of free phosphate availability.
Phosphatase activity in relation to phytoplankton composition and pH in Swedish lakes
Authors: OLSSON HÅKAN 
Published: May 2006

SUMMARY. 1. Potential phosphatase activity and phytoplankton from several lakes of different character were compared in order to evaluate the importance of lake water pH and phytoplankton composition for the activity and pH optimum of lake water phosphatases.2. In oligotrophic lakes, in which phytoplankton biomass was most often dominated by Ochromonadaceae spp., optimum phosphate activity was found at pH values <6. In eutrophic lakes, where species of Cyanophyceae and Bacillariophyceae dominated the phytoplankton biomass, optimum phosphatase activity was found at pH 7.5 or 8.5.3. The pH optimum of phosphatase activity often differed from the corresponding lake water pH.4. Experimental variation in phosphorus availability resulted in predictable changes in phosphatase activity. However, specific phosphatase activity, calculated per biomass of phytoplankton, was dependent on plankton species composition.
Mayfly locomotory responses to endoparasitic infection and predator presence: the effects on predator encounter rate
Authors: BENTON MICHAEL J. , PRITCHARD GORDON 
Published: May 2006

SUMMARY. 1. The effects of predaceous stoneflies and endoparasilism by mermithid nematodes on the locomotory behaviour of individual mayflies were studied in the laboratory. The effects of predator‐ and parasite‐induced changes in activity on predator encounter, attack and capture rates were also examined.2. In response to predator presence non‐parasitized mayflies decreased activity, while parasitized mayflies increased activity, in comparison to a control group. As a result, the faster‐moving parasitized individuals encountered stonefly predators much more frequently. The frequency of attacks per encounter did not change.3. In view of this and other studies, two predator‐avoidance strategies based on mayfly locomotory and defensive capabilities are proposed: (a) Mayflies that are able effectively to flee a predator's attack and those able to employ a behavioural defence may decrease their mean velocity when a predator is detected, thereby reducing the likelihood of an encounter while allowing foraging to continue; (b) Slower‐moving or otherwise defenceless mayflies may immediately move away from the area in which a predator is perceived in order to avoid an encounter.4. In the absence of a predator, parasitized mayflies demonstrated greatly increased activity. This probably reflects increased foraging in response to the nutritional deficit imposed by the endoparasite. A decrease in upstream movement by parasitized mayflies may also indicate a parasite‐imposed energy stress.
The role of density in sex determination in Daphnia magna (Crustacea, Cladocera)
Authors: BARKER DAVID M. , HEBERT PAUL D. N. 
Published: May 2006

SUMMARY. 1. Cladocerans are generally believed to exhibit environmental sex determination; however, the evidence for this assertion is equivocal. Particularly, no studies have been performed which isolate potential effects of the environment on the sex of offspring (and hence sex ratio) from effects on the induction of sex (with the necessary appearance of males). We report the findings of a study of Daphnia magna Straus which is able to make this distinction.2. We examined the sexes of broods produced by asexually reproducing females collected from high and low densities of D. magna in naturally occurring populations. We looked for an effect of density, a factor frequently implicated in male induction, on offspring sex.3. We could find no effect of density on brood sex. Our results may indicate a true absence of interaction or may arise from our sampling procedure obscuring an interaction. More detailed field observations are suggested as a means of further examining the role of density in sex determination in Cladocera.
OPINION Endless summer: internal loading processes dominate nutrient cycling in tropical lakes
Authors: KILHAM PETER , KILHAM SUSAN SOLTAU 
Published: May 2006

SUMMARY. 1. Fossil diatom assemblages deposited in more than a dozen African lakes roughly 9500 years BP were dominated by a single planktonic species, Stephanodiscus astraea (Ehrcnb.) Grun. (although realistically this is likely to be a species complex). These diatoms flourished when lake‐levels were maximal. Data are included from many of (he large African lakes, and others extending from Lake Abhé0, Ethiopia, to Lake Cheshi, Zambia.2. Because the ecological physiology of Stephanodiscus species is well known one can predict the nutrient regime that must have existed when Stephanodiscus bloomed. Owing to competition for resources Stephano‐discus species dominate when the supply ratio of silicon to phosphorus (in moles) in the epilimnion is relatively low (Si:P∼1). Consequently, lakes dominated by S. astraea are often hypereutrophic.3. We propose a series of hypotheses to explain why tropical lakes have decreasing Si:P ratios as lake‐levels increase, primarily owing to internal P‐loading processes in the epilimnia. These observations appear to contradict present conceptions of the fundamental relationships governing nutrient loadings to and within lakes. Tropical lakes appear to have had increasing epilimnetic phosphorus loading as lake‐levels increased. In contrast, large, deep lakes in the temperate zone are usually oligotrophic, with high Si:P ratios.4. Our major conclusion is that regeneration rates are greater than removal rates for phosphorus in tropical lakes as compared to temperate lakes, especially where epilimnelic mixing exceeds 50 m. Biological control of the elemental cycles dominate in tropical lakes, whereas nutrient cycles in temperate lakes are dominated by physical processes for a large part of the year. This results in major differences in the fundamental mechanisms of nutrient regeneration and their relationships to morphometric features of lakes in the two regions.
Comparative study of mathematical models for the relationship between water temperature and brood development time of Gammarus fossarum and G. roeseli (Crustacea: Amphipoda)
Authors: PÖCKL M. , TIMISCHL W. 
Published: May 2006

SUMMARY. 1. The relationship between water temperature (T°C) and brood development time (d days for embryonic development time plus ‘post‐hatch time’) was investigated experimentally using animals from four populations of Gammarus fossarum (populations 1–4) and two populations of G. roeseli (populations 5 and 6) in Austrian streams.2. Eleven mathematical models were examined as suitable functions to describe the relationship between d and T. The models were compared with respect to their goodness‐of‐fit and suitability for further quantitative, statistical analyses of intra‐ and interspecific differences between natural populations of G. fossarum and G. roeseli.3. Statistical analyses were performed with logarithmically transformed values of d, in order to provide homogeneous variances between the different constant temperatures used. The following three‐parameter model was found to be the most suitable for the data:

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This equation was fitted in its linear form:
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Growth and reproduction in the freshwater crab, Potamon fluviatile (Decapoda, Brachyura)
Authors: MICHELI FIORENZA , GHERARDI FRANCESCA , VANNINI MARCO 
Published: May 2006

SUMMARY. 1. The patterns of relative and absolute growth and the reproductive biology of the freshwater crab Potamon fluviatile were studied in a natural population inhabiting a hill stream close to Florence, Italy, over an annual cycle. Periodical inspections of a stretch of the stream were made and morphological and anatomical analysis carried out.2. As in other decapods, the females are smaller than the males (they can however occasionally reach larger dimensions). This may be determined by a lengthening of the moulting interval in the females, by their higher energetic cost of reproduction (since reproduction occurs simultaneously with moulting, at least in this habitat) and/or by a higher mortality rate resulting from the risks associated with carrying eggs and vagility.3. The analysis of relative growth in secondary sexual characters (abdomen width and major chela length) with respect to carapace length, shows that the pre‐puberty and puberty ecdysis occur at 15 and 35 mm carapace length respectively, which was also confirmed by the gonad weight, vas deferens in males, and the onset of vitellogencsis in females.4. A delay between anatomical and functional (i.e. the ability to copulate successfully) maturity was observed in the males. Being larger may be an advantage in intra‐sexual competition for mating, but larger males, being more vagile, are also more likely to meet receptive females. The females may mate before their puberty moult and store sperms in their seminal receptacles for when they attain full maturity; this could be adaptive since opportunities of encountering males are few and far between in their adult phase, characterized by their vagile and amphibious habits.
Responses of zooplankton and zoobenthos to experimental acidification in a high‐elevation lake (Sierra Nevada, California, U.S.A.)
Authors: BARMUTA LEON A. , COOPER SCOTT D. , HAMILTON STEPHEN K. , KRATZ KIM W. , MELACK JOHN M. 
Published: May 2006

SUMMARY. 1. During the summer of 1987 we conducted an acidification experiment using large enclosure at Emerald Lake, a dilute, high‐elevation lake in the Sierra Nevada, California, U.S.A. The experiment was designed to examine the effects of acidification on the zooplankton and zoobenthos assemblages of Sierran lakes.2. Treatments consisted of a control (pH 6.3) and pH levels of 5.8, 5.4, 5.3, 5.0 and 4.7; each treatment was run in triplicate. The experiment lasted 35 days.3. The zooplankton assemblage was sensitive to acidification. Daphnia rosea Sars emend. Richard and Diaptomns signicauda Lilljeborg decreased in abundance below pH 5.5–5.8, and virtually disappeared below pH 5.0. Bosmina longirostris (Müller) and Keratella taurocephala Ahlstrom became more abundant with decreasing pH. although B. longirostris was rare in the pH 4.7 treatment. These species might serve as reliable indicators of early acidification in lakes such as Emerald Lake.4. The elimination of D. rosea in acidified treatments probably allowed the more acid‐tolerant taxa to increase in abundance because interspecific competition was reduced. Even slight acidification can therefore alter the structure of the zooplankton assemblage.5. In contrast to the zooplankton, there was no evidence that the zoobenthos in the enclosures was affected by acidification.
Mineralization, pore water chemistry and phosphorus release from peaty sediments in the eutrophic Loosdrecht lakes, The Netherlands
Authors: SINKE ANJA J. C. , CORNELESE ADI A. , KEIZER PEER , VAN TONGEREN ONNO F. R. , CAPPENBERG THOMAS E. 
Published: May 2006

SUMMARY. 1. Pore water chemistry in peaty sediment was monitored for a year at two representative locations of the eutrophic shallow Loosdrecht lakes. The Netherlands. Phosphorus fluxes over the sediment‐water interface were calculated using measured concentration gradients in the pore water and compared to fluxes measured under laboratory conditions. Results were analysed with Redundancy Analysis to detect patterns of variation in pore water chemistry and in measured and calculated fluxes, that could be ascribed to environmental variables.2. It was demonstrated that phosphorus fluxes measured in long‐term laboratory incubations were not correlated to any of the pore water characteristics.3. Initial phosphorus fluxes measured in sediment columns, which varied between −7.7 and 1330 μmol m−2: day−1, were correlated significantly to the calculated phosphorus flux over the sediment‐water interface.4. The high correlation between calculated fluxes of ammonia, phosphorus and methane and measured initial flux of phosphorus, conclusively pointed to mineralization of organic matter as the driving force for phosphorus release from the sediment.5. Redundancy Analysis demonstrated that the rates of mineralization and phosphorus release were only weakly related to temperature. They appeared to be especially stimulated by the autumnal decrease in temperature which was probably related to an extra input of organic matter.
Water temperature in a stream gravel bed and implications for salmonid incubation
Authors: CRISP D. T. 
Published: May 2006

SUMMARY. 1. Water temperatures were recorded at hourly intervals in the gravel of a trout spawning area in a small stony stream at depths of 0–20 cm in 1985–86 and 0– 40 cm in 1987.2. As depth within gravel increased, the size of the daily fluctuations reduced and their time of occurrence was delayed by about 12 min cm−1′ in 1985–86 and about 6 min cm−1 in 1987.3. From October to February mean temperatures at 20 cm depth were, on average, 0.5°C higher than those at the gravel surface. This reflected elevated daily minima more than it reflected elevated daily maxima.4. From March to July daily minima were lower and daily maxima were higher in the stream than in the gravel. Consequences were: (a) an appreciable increase in mean daily range at all depths in the gravel during the summer, (b) higher daily means (by an average of about 0.4°C) in the water than in the gravel in May to August.5. Some implications for the early development of salmonid fish are considered.
OPINION Manipulating lake community structure: where do we go from here?
Authors: McQUEEN D. J. 
Published: May 2006

SUMMARY. 1 More than 10 years experience with whole lake pelagic manipulation has suggested some general trends applicable to all freshwater pelagic communities and some specific trends related to lake depth.2 Among the general trends is the observation that the trophic cascade is strongly damped. This means that changes in phytoplankton biomass can be assured only when the fish community is strongly manipulated.3 Among the depth related trends is the observation that in shallow lakes, changes in fish community structure are more likely to have cascading impacts on phytoplankton than are changes in deep lakes.4 In shallow lakes, fish removal frequently results in decreased turbidity which is associated with the development of dense macrophyte populations and significant reductions of algal standing stocks. The mechanisms involve: increased grazing by zooplankton, the removal of fish induced bioturbation and nutrient recycling, and direct and indirect macrophyte effects (shading, zooplankton refuges and competition for nutrients).5 In shallow lakes, where planktivore biomass can be regulated and macrophyte development is acceptable, fish biomanipulalions are likely to result in reduced algal populations and improved water quality.6 In deep lakes, where macrophytes are not as important, long‐term effects of fish manipulations are strongly dependent upon the probability of non‐grazable algal bloom development. This is determined by many factors (chemical, physical and grazer related) which modify the impact that grazers have on phytoplankton biomass.7 In deep lakes, successful fish biomanipulations may only be effective when chemical and physical factors are altered to produce algal species compositions that permit strong top‐down control of prey by predators.
Suspension and settlement of particles in flowing water: comparison of the effects of varying water depth and velocity in circulating channels
Authors: REYNOLDS C. S. , WHITE M. L. , CLARKE R. T. , MARKER A. F 
Published: May 2006

SUMMARY. 1. An experimental study is described, designed to test the hypothesis that the loss of particles from suspension in flowing water follows an exponential decay function, the exponent of which is influenced more by water depth than water velocity. Successive experiments employed suspensions of Lycopodium spores which were introduced into one of the FBA's circulating channels maintained at its Watcrston site, Dorset, under different combinations of water depth and pumping rate.2. In each experiment, the concentration of introduced spores indeed declined exponentially through time. The bulked, transformed data‐set also conformed well to a single regression against a common time scale and which explained over 94% of the accumulated variances.3. The variance unexplained by the regression was apportioned among components distinguishing between experiments, experimental differences in starting concentration, water depth and pumping rate (velocity). This analysis revealed that, after elimination of different initial concentrations, only water depth produced a significant effect, through its relation to the settling velocity of the Lycopodium. Thus, the hypothesis was not invalidated: water depth and not Row velocity proved to be the main controlling variable determining the rale of sinking loss in these experiments. Flow velocity is, nevertheless, an important component only in the sense that it influences the horizontal distance travelled by the residual spore suspension through the time period required for complete settlement.4. The consequences of experimental findings are applied to the maintenance of planktonic diatoms in rivers: both the survival of a potential growth inoculum and its downstream dispersion are strongly time‐dependent and are enhanced by greater channel depths.
Dissolved organic carbon concentrations and fluxes along the Moisie River, Quebec
Authors: FORD T. E. , FORD S. A. , LOCK M. A. , NAIMAN R. J. 
Published: May 2006

SUMMARY. 1. The main stream and tributaries of a 145 km reach of the Moisie River, Quebec, were examined for temperature, conductivity, pH, dissolved organic carbon (DOC),%DOC>100,000 nominal molecular weight (NMW), optical density (OD350), and the ratio of OD400 to OD600 (E4:E6).2. Dissolved organic carbon concentrations correlated closely with OD350 (r2=0.92, P<0.001). However,%DOC>100,000 NMW did not correlate with the E4:E6 ratio.3. Except for a slight increase in%DOC> 100,000 NMW (r2=0.37, P<0.05), no change in any characteristic occurred down the length of the Moisie River, despite consistently higher levels of DOC in the tributaries.4. Results suggest that high concentrations of DOC in tributary waters are rapidly removed within the main river channel. These results are discussed in terms of both biotic and abiotic models of in‐strcam processing.
Home range of juvenile Atlantic salmon, Salmo salar, and brown trout, Salmo trutta, in a Norwegian stream
Authors: HESTHAGEN T. 
Published: May 2006

SUMMARY. 1. The sizes of home ranges of juvenile Atlantic salmon (age 1 +) and brown trout (age 2+ to 9+) in a Norwegian coastal stream were estimated by local movements of batch‐marked fish from 12.5 and 25 m long sections. Only recoveries made in the release section and in up‐and downstream neighbouring sections were considered.2. There was no significant difference in the average percentage of recaptures of salmon and trout between 12.5 and 25 m sections; a stream area of about 40–50 m2 defines the size of home range for stocks of both species.3. The fraction of brown trout recaptured in release sections increased with increasing fish densities, indicating a smaller home range under these conditions.