bluuebunny/crossref_metadata_2025_split huggingface dataset:
Conservation and management of brown trout, Salmo trutta, in Ireland
Authors: FAHY EDWARD 
Published: May 2006

SUMMARY. .1. Ireland's fauna and flora are, compared with those of Britain and Continental Europe, relatively impoverished as a consequence of our glacial history. Salmonids are, however, well represented here and, because cyprinids are not. they make up a large proportion of the freshwater fish biomass.2. It may be more accurate to regard our trout fauna as a mosaic of subspecies and races rather than a single species. Two principal immigrations are thought to have contributed to the extant strains one of which includes the valuable long‐lived sea trout and freshwater ferox. Their fidelity to specific spawning areas isolates and maintains the purity of trout strains but certain aspects of spawning behaviour may leave some of them susceptible to cross fertilization with others.3. Strains of trout may take distinguishable external forms or they may not be easily recognized by eye. In spite of their great interest in the conservation and management of trout, anglers are largely unaware of their genetic status.4. Artificial restocking of salmonids has been carried out in Ireland since the nineteenth century; most effort has been expended on Atlantic salmon but, in the last 25 years, the restoration of trout populations depleted by pollution and arterial drainage has been the object of these exercises. There is concern for the consequences of wild trout strains being diluted by these efforts although, to date, evidence to support that happening is sparse.5. Problems associated with deterioration in water quality have multiplied over the past 20 years and trout is the species most affected by fish kills. These tend to be seasonal, exacerbated by low water and dry weather. The smallest streams, which may be as narrow as 30 cm, which are the stronghold of trout in many catchments, are at greatest risk.6. Ireland's cyprinid fauna results from introductions but it is rapidly developing ‐ as is coarse angling. Roach is the species spreading fastest. Studies show that roach will share the diet of trout and. possibly more significant, will compete with them for the angler's fly.
Experimental investigations of diel vertical movements by lotic mayflies over substrate surfaces
Authors: GLOZIER NANCY E. , CULP JOSEPH M. 
Published: May 2006

SUMMARY. 1. The vertical distribution within the substrate of three lotic mayflies (Rhithrogena sp., Paraleptophlebia sp. and Baetis tricaudalus Dodds) was examined in laboratory streams to determine if diel patterns of vertical movement across substrate surfaces existed and whether light intensity, temperature, substrate composition or food availability influenced the observed movement patterns.2. Rhithrogena sp. and B. tricaudatus exhibited significant diel movement from lower substrate surfaces during the day to upper surfaces at night, although >64% of B. tricaudalus occupied the upper surfaces throughout the 24 h period. In contrast, Parakplophlebia sp. larvae did not change their vertical distribution over the 24 h period.3. The proportion of mayflies occupying substrate surfaces was influenced by the amount of upper and lower surface area available in the substrate and, possibly, crevice sizes associated with lower surfaces.4. The movement of Rhiihrogena sp. from lower surfaces during the day to the upper surfaces during the night was influenced by changes in light intensity, but not by changes in food availability or water temperature.5. The diel patterns of vertical movement exhibited by lotic mayflies in this investigation raise the possibility that at least some biotic interactions may vary over a diel cycle. These could include competitive interactions or temporal cycling of prey availability to predators.
A comparison of the effects of prey and non‐prey neighbours on foraging rates of Epischura nevadensis (Copepoda: Calanoida)
Authors: FOLT CAROL L. , BYRON EARL R. 
Published: May 2006

SUMMARY. 1. Adults of the calanoid copepod, Epischura nevadensis, aggregate in situ near the thermocline in Lake Tahoe, California‐Nevada. together with adults of another species of calanoid copepod, Diaptomus tyrelli and juveniles of both species. With a series of laboratory predation and algal clearance trials, we show that foraging rates of adult E. nevadensis are determined not only by the density of co‐occurring potential prey (small copepods), but also by the presence of co‐occurring non‐prey neighbours (large, adult copepods). These effects occur at densities and in zooplankton assemblages found naturally, emphasizing the ecological importance of neighbours other than prey on zooplankton feeding.2. Neighbours are distinguished primarily by size. Although predation rates increase linearly with the densities of small copepods. both algal clearance and predation rates decrease in the presence of large copepods. We also show, with a field predation experiment using small enclosures, that adults are size selective within species and that Diaptomus are selected over conspecifics of the same size.3. We hypothesize that by reducing foraging rates in the presence of large zooplankton. E. nevadensis avoids predators and reduces predation risk at the cost of reduced energy consumption.
Standard hemispheres as indicators of flow characteristics in lotic benthos research
Authors: STATZNER BERNHARD , MÜLLER RAINER 
Published: May 2006

SUMMARY. 1. Standard hemispheres of identical size and surface but different densities were exposed on a horizontal plane at the bottom of streams. The heaviest hemisphere moved was used as an indicator of flow conditions close to the substrate.2. Techniques of manufacture, maintenance, and use of the equipment were considered in detail.3. The method was an easily applicable and integrated indicator of key hydraulic characteristics (turbulence or force of flow prevailing at the stream bottom) previously measured in lotic benthos research, and can replace these more laborious techniques.4. The hemispheres enabled a rapid flow characterization in stream reaches, in smaller areas where the benthos was being quantitatively sampled, and in en/exclosure cages used in experimental studies.5. The method also has the potential to characterize and compare physics of flow in individual running water segments with regard to frequencies and intensities of disturbances caused by long‐term variations in discharge.6. The hemispheres could be used as a standard in benthic research. since they offer a well defined scale that is directly comparable not only between studies in running waters but also in wave‐exposed shores of lakes and oceans.
Salamander predation and vertical distributions of zooplankton
Authors: HOLOMUZKI JOSEPH R. 
Published: May 2006

SUMMARY. 1. The impact of different predation regimes of zooplanktivorous larval tiger salamanders, Ambystoma tigrinum nebulosum, on the vertical temporal distributions of Daphnia pulex, Diaptomus nudus and larval Chaoborus flavicans was studied in limnetic enclosures in a pond in east‐central Arizona. Zooplankton densities were monitored 1‐2 h before sunset, at sunset, and 1‐2 h after sunset at three depths (0‐0.4, 1.0 and 2.0 m) in four salamander treatments (0, 20, 40 salamanders per enclosure, and unenclosed limnetic areas).2. Densities and body size of Daphnia pulex were consistently greater in salamander‐free enclosures than in other treatments. More Daphnia were generally nearer the surface (0‐1.0 m) than along the bottom before and at sunset than after sunset in enclosures without salamanders. After sunset, Daphnia was by far most dense along the bottom. Densities were uniform among depths and sample times in treatments with salamanders. Salamanders moved throughout the water column. Frequencies of D. pulex spined morphs (with prominent dorsal crest) did not differ among salamander treatments.3. Chaoborus densities were positively correlated with D. pulex distributions among depths and sample times in treatments. Spatio‐temporal distributions of Chaoborus were influenced more by their daphnid prey than by risk of predation from larval salamanders.4. Densities of Diaptomus nudus were highest in open water controls and lowest in enclosures without salamanders. Diaptomus was generally more dense between 0 and 1 m than at 2.0 m depths in all treatments, and vertical distributions were not dependent on salamander density.
A model of surface water acidification in Cumbria and its uses in long‐term research
Authors: TIPPING E. 
Published: May 2006

SUMMARY. 1. A description is given of a simple process‐based model of deposition‐catchment interactions in areas of Cumbria underlain by rocks of the Borrowdale Volcanic Series. The processes considered are evapotranspiration, nitrogen uptake by plants, dissolution and precipitation of A1(OH)3, basecation weathering, hydrolysis of Al3+, reactions of the carbonate system, and water flow routing. Model parametersare estimated from 1980s data for deposition and streamwater chemistry. It is shown that the‐ model is also applicable to tarns (small lakes). Analysis of 1970s streamwater data highlights uncertainties about deposition concentrations of NH4+ and catchment transformations of nitrogen.2. Using estimates of past deposition compositions, past compositions of tarn waters are estimated and indicate declines in pH I of up to 1 unit between c. 1850 and c, 1950, These changes are similar to those estimated independently from analysis of sediment diatoms. The model also shows that the historical pH trends are consistent with other paiaeolimnological evidence that Cumbrian soils have been acid for several thousand years. The model output is also consistent with direct evidence suggesting that the chemical compositions of Cumbrian tarns have altered little during the past 30 years.3. The model is used to estimate water compositions during high‐flow episodes at various times in the past, and shows that even a small increase in depositional acidity would have made high‐flow waters sufficiently acid and aluminum‐rich to limit faunal abundance. This is consistent with the limited amount of observational evidence that is available.4. The model can be used (a) for prediction, given scenarios for future deposition compositions or catchment behaviour, and (b) as a framework for planning future studies and interpreting data. Further work on the model should improve the reliability of its parameters, find better descriptions of processes dealt with in the current version, and introduce processes currently ignored. The present analysis indicates that fieldwork is needed to study nitrogen transformations, soil properties and biological responses to changes in streamwater chemistry.
The relative effects of enrichment and climate change on the long‐term dynamics of Daphnia in Esthwaite Water, Cumbria
Authors: GEORGE D. G. , HEWITT D. P. , LUND J. W. G. , SMYLY W. J. P. 
Published: May 2006

SUMMARY. 1. The factors influencing the seasonal and inter‐annual variations in the numbers of Daphnia hyalina in Esthwaite Water between 1956 and 1972 are analysed. Esthwaite Water has always been eutrophic. but the phosphorus and nitrogen loadings to the lake increased significantly in the mid 1960s.2. Qualitatively, the phytoplankton and zooplankton populations in the lake changed relatively little during the period of study. Quantitatively, however, eutrophic species of algae became more abundant and the numbers of Eudiaptomus declined as the numbers of Daphnia increased.3. The seasonal dynamics of the Daphnia was governed partly by the seasonal temperature cycle, and partly by the periodicity of edible algae. The birth rate of the Daphnia was constrained by temperature from January to April and from October to December. At other times their rate of increase was governed by the relative abundance of edible and inedible algae.4. Edible and inedible species of algae tended 10 appear in a recurring annual sequence. Diatoms such as Asterionella were abundant in the spring, the early summer phytoplankton was dominated by edible flagellates, but inedible algae such as Aphanizomenon and Microcystis become dominant later in the year.5. Daphnia could only reproduce in late summer when there were periodic regrowths of edible algae. Such regrowths were most likely to occur when there had been some entrainment of deep nutrients by episodic wind mixing. Calm weather encouraged the growth of blue‐green algae that effectively‘blocked’the development of the Daphnia for the remainder of the summer.6. The factors that controlled the seasonal dynamics of the Daphnia also influenced the average number recorded in a particular year. The average number of Daphnia increased in the early sixties when Cryptomonas was abundant and decreased in the late sixties when blooms of Aphanizomenon appeared in mid summer. Detailed analyses showed that a similar increase in the numbers of Aphanizometion had occurred in the late fifties. The critical factor throughout was the prolonged period of calm resulting in stable stratification.7. This ‘weather’ effect was highlighted by comparing de‐trended timeseries of Daphnia and Aphanizometion numbers with a simple measure of thermocline stability. De‐trending removed the superimposed effects of progressive enrichment and revealed a 10‐year cycle of thermocline stability that matched the temperature cycle recently reported in Windermere, These cycles are related to the movement of weather systems in the Atlantic so could change if the pattern of atmospheric circulation is altered by global warming.8. The possible effects of climate change on Daphnia dynamics are discussed in relation to the findings in Esthwaite Water.
A network for long‐term ecological research in the United States
Authors: MAGNUSON J. J. , BOWSER CARL J. 
Published: May 2006

SUMMARY. 1. A network of seventeen long‐term ecological research sites funded by the National Science Foundation (NSF) and spanning sites in arctic to tropical climates, low to high altitudes and wet to dry environments, provides evidence for the increasing popularity of sustained ecological research in the U.S.A.2. The sites function as regional or national facilities for long‐term research as well as for comparative and process studies by investigators from the operating institutions and by visiting researchers.3. The aquatic habitats include a variety of lakes ponds, wetlands and a playa; montane, woodland, tundra and prairie streams; as well as salt marsh, estuary, ocean beach and inshore oceanic sites.
Comparison of biotic index values for invertebrate collections from natural and artificial substrates
Authors: MODDE TIMOTHY , DREWES HENRY G. 
Published: May 2006

SUMMARY. 1. We evaluated the use of a biotic index in a small mountain stream on the basis of collections of benthic macroinvertebrates from both artificial and natural substrates in years of above and below normal discharge.2. Invertebrate composition sampled from artificial and natural substrates exhibited inverse trends in density associated with discharge patterns.3. Biotic index values derived from artificial substrates provided a more consistent and accurate description of the water quality of a small stream between years of high and low discharge than did those determined from natural substrates.
The seasonal response of diatom communities to variable water quality in some English urban lakes
Authors: GUZKOWSKA M. A. J. , GASSE F. 
Published: May 2006

SUMMARY. 1. Five diatom assemblages and their corresponding site groups were associated with the urban lakes. When treated as a single dataset, DC A and PCA grouped these diatom assemblages along an environmental gradient from circum natural. dilute waters to strongly alkaline, concentrated, nutrient‐rich waters.2. When treated as individual datasets, 75% of the known variance was explained by the first axis of DCA in all five diatom assemblages; this indicated the existence of a strong primary environmental gradient. The PCA results showed that the identity of this primary environmental gradient can be different for each assemblage.3. The statistical analyses showed that the physicochemical gradients were continuous and not discrete. Nevertheless, fine‐scale analysis can identify smaller, more precise species and site groups.4. Two types of species response could be identified within most sub‐assemblages in the urban lakes: the first was a quasi‐seasonal response and was characterized by a gradual rise to a peak relative abundance of one dominant or several co‐dominant species which could be sustained for a period of weeks before a gradual decline. A quasi‐seasonal response was sometimes interrupted by a storm response. The storm response was characterized by a sudden increase in the relative abundance of one or more diatom species following a storm, after which the species declined to pre‐storm abundances within 7 days.5. The effects of urban runoff on the water quality of urban lakes can override the effects of true seasonal factors such as water temperature and day length on the relative abundance of species.
The distribution of micro‐arthropods in some southern English streams: the influence of physicochemistry
Authors: RUNDLE SIMON D. , HILDREW ALAN G. 
Published: May 2006

SUMMARY. 1. Micro‐arthropods were surveyed during October 1986 at thirty stony, stream riffle sites in the Ashdown Forest, southern England.2. The importance of a number of physicochemical variables in determining both the distribution of micro‐arthropod taxa and community structure was assessed.3. Acidic sites had an impoverished fauna. Total micro‐arthropod species richness and densities were highest under circumneutral conditions. and the same patterns were shown by the Hydrachnellae, Harpucticoida and Cladocera. A number of species seemed indifferent to acidic conditions and were widespread and, as a group, the cyclopoid copepods showed no relationship with pH.4. Multiple regression showed that other environmental variables, in particular annual mean temperature and maximum discharge, were also important in explaining the between‐site distribution of separate micro‐arthropod groups and individual species.5. Other multivariate techniques (ordination, classification and multiple discriminant analysis) showed that impoundment linkage, source distance and conductivity, along with pH, were the most important variables in explaining patterns of species composition between sites.
Complex and flexible life history of a freshwater benthic harpacticoid species
Authors: SARVALA JOUKO 
Published: May 2006

SUMMARY. 1. The life history of the benthic harpacticoid paracamptus schmeili (Crustacea: Copepoda) in the oligotrophic lake Pääjärvi, South Finland, was described from quantitative field data of all developmental stages. The generation time of P. schmeili was exceptionally long for a meiobenthic animal and varied with depth from 1 year in the littoral (depths of 1 and 2m) to 2 years in the upper profundal (13 and 14 m). and to 3 years in the lower profundal (40 m).2. In the littoral, egg‐bearing females were found from April to October, with peaks in spring and late summer, while in the profundal a single summer egg peak was present.3. In the littoral and in the lower profundal there were three, in the upper profundal) probably four, simultaneous parallel cohorts over‐wintering as adults, medium‐sized (at 13 m also large) copepodids and medium‐sized nauplii. Reproductive isolation of the parallel cohorts was possible at all depths.4. The between‐depth variation in the life history of P. schmeili was probably mainly a phenotypic response to the changing level and seasonal course of temperature and food supply. Growth and reproduction were confined to summer months, and the lengthening generation times with depth accompanied decreasing summer temperatures.5. The cessation of growth in winter was probably due to a shortage of food, which may also have accentuated the size differences of the overwintering groups through intraspecific competition.
Patterns in the distribution of heptageniid (Ephemeroptera) species in Saskatchewan, Canada
Authors: WHITING ERIC R. , SHEARD J. W. 
Published: May 2006

SUMMARY. 1, The distribution patterns of twenty‐one species of heptageniid mayflies were examined in Saskatchewan and west‐central Manitoba, Canada. Presence/absence data from 174 stream sites were analysed using two complementary multivariate techniques, classification (Ward's method with Euclidean distance) and ordination (detrended correspondence analysis).2. Multivariate analyses revealed two large, distinct groups of sites within the study area. The first included sites characterized by the presence of Heptagenia elegantula (Eaton) and Stenonema terminatum (Walsh). The second included sites characterized by the presence of Stenonema vicarium (Walker), Leucrocuta hebe (McDunnough) and/or Nixe species. The two groups contained, respectively, three and four subgroups.3. Groups and subgroups defined by multivariate analyses were compared using large‐scale environmental features obtained from topographic and other maps. Differences in environmental features between the two groups were mainly in stream order, terrestrial vegetation and annual number of degree‐days (calculated from air temperature). The first group could be characterized as warm, large river habitat in grassland and parkland vegetation regions. The second included cooler, small to midsized streams and rivers in boreal forest. Most differences among subgroups were also in stream order, terrestrial vegetation and degree‐days, although some subgroups in the second group differed also in stream gradient.4. The observed groups and subgroups were not associated with drainage basins.
Inhibitory effects of high molecular weight dissolved organic matter upon metabolic processes in biofilms from contrasting rivers and streams
Authors: FREEMAN CHRISTOPHER , LOCK MAURICE A. , MARXSEN JÜRGEN , JONES SUSAN E. 
Published: May 2006

SUMMARY. 1. The effect of removal of organic manor >1000 apparent molecular weight (AMW) upon biofilm processes was determined in three contrasting streams in West Germany and three contrasting rivers in the U.K. This process removed 66–85% of the dissolved organic matter supply.2. Elevations in extra cellular enzyme activity (β‐glucosidase, phosphatase and esterase), metabolic heat‐output, bacterial density and poly‐beta‐hydroxy alkanoate (PHA) content (a prokaryote storage product) were noted throughout the study in response to the removal of organic matter. This suggests that there are inhibitory substances present in the dissolved organic matter pool >1000 AMW. Evidence is presented to suggest that phenolics play a role in this inhibition.3. Decreases in metabolic heat output, β‐glucosidase activity and PHA content were noted at four sites in response to the removal of >1000 AMW material.4. The divergent responses of the six river/stream biofilms are indicative of radically differing metabolic/catabolic processes, on a spatial and/or temporal basis, to a major organic supply perturbation.