bluuebunny/crossref_metadata_2025_split huggingface dataset:
Growth and emergence of the stonefly Leuctra nigra in coniferous forest streams with contrasting pH
Authors: THOMSEN ANNE G. , FRIBERG NIKOLAI 
Published: March 2003

1. Growth and emergence of the acidification tolerant stonefly Leuctra nigra were studied in four coniferous forest streams with contrasting pH. Invertebrate samples were taken bimonthly during May 1997 to April 1998. Emerging L. nigra were captured in two of the streams during April to July 1998 using pyramidal emergence traps. In addition, a laboratory experiment was conducted to evaluate growth of L. nigra in response to variations in food quality (neutral or acid conditioned leaves) and water pH.2. The invertebrate community in low pH streams had lower diversity and density compared with neutral streams. Abundance of L. nigra was also lower, despite the dominance of this stonefly in the invertebrate community in the acidic streams.3. Secondary production of L. nigra was 2.04 and 3.07 g DW m–2 year–1 in the neutral streams compared with 1.02 and 1.27 g DW m–2 year–1 in the acidic streams. The P/B ratio differed only slightly among streams.4. More adult L. nigra emerged in the neutral stream compared with the acidic stream, despite the density of the pre‐emerging fifth instar nymphs of L. nigra being similar in the two streams. Adult size (expressed as wing length) and female fitness were also significantly greater in the neutral stream.5. Laboratory growth of L. nigra nymphs was significantly lower when fed acid conditioned alder leaves rather than neutral conditioned leaves. There was no difference in growth when nymphs were fed neutral conditioned leaves in acid and neutral water.6. Our study shows multiple, sub‐lethal effects on life history of the acidification tolerant stonefly L. nigra in coniferous streams with low pH. The results suggest that these effects could be mediated primarily by low food quality. These findings add to the existing evidence that coniferous plantation forestry has a negative impact on stream ecosystems.
The effects of Daphnia on nutrient stoichiometry and filamentous cyanobacteria: a mesocosm experiment in a eutrophic lake
Authors: PATERSON M. J. , FINDLAY D. L. , SALKI A. G. , HENDZEL L. L. , HESSLEIN R. H. 
Published: March 2003

1. Stoichiometric theory predicts that the nitrogen : phosphorus (N : P) ratio of recycled nutrients should increase when P‐rich zooplankton such as Daphnia become dominant. We used an enclosure study to test the hypothesis that an increased biomass of Daphnia will increase the relative availability of N versus P sufficiently to decrease the abundance of filamentous cyanobacteria. The experiment was conducted in artificially enriched Lake 227 (L227) in the Experimental Lakes Area (ELA), north‐western Ontario, Canada. Previous studies in L227 have shown that the dominance of filamentous, N‐fixing cyanobacteria is strongly affected by changes in the relative loading rates of N and P.2. We used a 2 × 2 factorial design with the addition or absence of D. pulicaria and high or low relative loading rates of N and P (+NH4, –NH4) in small enclosures as treatment variables. If Daphnia can strongly affect filamentous cyanobacteria by altering N and P availability, these impacts should be greatest with low external N : P loading rates. The phytoplankton community of L227 was predominantly composed of filamentous Aphanizomenon spp. at the start of the experiment.3. Daphnia strongly reduced filamentous cyanobacterial density in all enclosures to which they were added. The addition of NH4 had only a small impact on algal community composition. Hence, we conclude that Daphnia did not cause reductions in cyanobacteria by altering the N : P ratio of available nutrients.4. Despite the lack of evidence that Daphnia affected filamentous cyanobacteria by altering the relative availability of N and P, we found changes in nutrient cycling consistent with other aspects of stoichiometric theory. In the presence of Daphnia, total P in the water column decreased because of an increase in P sedimentation. In contrast to P, a decrease in suspended particulate N was offset by an increase in dissolved N (especially NH4). Hence, dissolved and total N : P ratios in the water column increased with Daphnia as a result of differences in the fate of suspended particulate N versus P. There was minimal accumulation and storage of P in Daphnia biomass in the enclosures.5. Our experiment demonstrated that Daphnia can strongly limit filamentous cyanobacterial abundance and affect the biogeochemical cycling of nutrients. In our study, changes in nutrient cycling were apparently insufficient to cause the changes in phytoplankton community composition that we observed. Daphnia therefore limited filamentous cyanobacteria by other mechanisms.
Reproductive traits of stream‐dwelling brown trout Salmo trutta in contrasting neighbouring rivers of central Spain
Authors: NICOLA G. G. , ALMODÓVAR A. 
Published: March 2003

1. Reproductive traits were studied in seven wild populations of resident brown trout in Spain. We examined whether growth, and certain environmental conditions such as water temperature or food abundance, could explain interpopulation variation in the reproductive characters.2. The results indicated that nearby populations subjected to a wide variation in environmental conditions exhibited a similar reproductive performance.3. Age distributions and sex ratios were not significantly different among populations. Age ranged from 0+ to 4+ years but the populations were dominated by the 0+ to 2+ groups. In all rivers females matured at age 2+ as opposed to age 1+ and 2+ for males. Mean length at the end of the growth period differed significantly among populations. However, annual growth rate was similar among rivers and was not significantly correlated with either biomass of the benthos or water temperature during the growth season.4. Reproductive effort, body condition, fecundity and egg size did not correlate significantly with either the abundance of benthic invertebrates or water temperature. Once the effect of body length on both egg size and number was removed, a significant negative correlation was found between these two traits among populations.
A stable isotope study of linkages between stream and terrestrial food webs through spider predation
Authors: Collier Kevin J. , Bury Sarah , Gibbs Max 
Published: March 2003

SUMMARY 1. Transfer of carbon from freshwater to terrestrial ecosystems can occur through predation on adult aquatic insects, but the significance of this trophic pathway to the energetics of riparian communities is poorly understood. We used stable isotopes of carbon and nitrogen to explore linkages between aquatic insect production and the nutrition of web‐building and free‐living spiders alongside two streams in the North Island of New Zealand.2. δ13C values for riparian tree leaves (means for each site = −32.2 and −30.3‰) were distinct from those of lichens collected from stream channel rocks and instream algae, both of which were similar (−23.4 to −22.4‰). δ15N values for leaves were similar at both sites (−3.4 and −2.7‰), but algae were considerably more depleted in δ15N atonesite suggesting significant differences in instream nitrogen sources between the twostreams.3. Isotope values for potential aquatic prey of spiders indicated that aquatic algal production was their primary carbon source at both sites. Terrestrial invertebrates collected and assumed to be potential prey reflected a range of carbon sources and represented several trophic levels.4. At one site, δ13C values indicated a primarily algae‐aquatic insect pathway of carbon transfer to both web‐building and free‐living spider guilds. The other site appeared to have a primarily terrestrial carbon pathway for the free‐living spider guild, and a mixed aquatic‐terrestrial pathway for the web‐building guild.5. Overall, web‐building spiders were estimated to obtain around 61% of their body carbon from aquatic production compared with 55% for free‐living spiders. Our findings suggest that consumption of prey derived from aquatic sources can provide significant nutrition for spiders living along some stream channels. This pathway may represent an important feedback mechanism contributing to the energetics of riparian communities at sites where aquatic insect production is high.
Comparing the responses of diatoms and macro‐ invertebrates to metals in upland streams of Wales and Cornwall
Authors: Hirst Heike , Jüttner Ingrid , Ormerod S. J. 
Published: March 2003

SUMMARY1. Surprisingly few data compare the apparent responses of diatoms and macroinvertebrates to metals in streams. We examined variation in metals, diatoms and macroinvertebrates between 51 streams in metal‐mining areas of Wales and Cornwall, U.K., using a survey design with multiple reference and polluted sites.2. To quantify variations in metals between sites, we calculated cumulative criterion unit (CCU) scores, a recently defined measure of total stream metal concentration and toxicity, to account for additive effects of each metal relative to putative toxic thresholds. We compared assemblage responses among epilithic diatoms and macroinvertebrates to CCU scores or individual metal concentrations using correlation and detrended correspondence analysis (DCA).3. Macroinvertebrate diversity, richness and total abundance declined and evenness increased with increasing copper concentrations. Trends with CCU scores were significant but less pronounced. Some individual macroinvertebrate taxa varied significantly in abundance with CCU scores, copper or zinc, but overall assemblage composition correlated only with manganese, pH and nitrate.4. Among diatoms, pH and conductivity explained the major variations in assemblage composition, and neither diversity, richness nor evenness varied with metal concentration. Nevertheless, the single strongest predictor of diatom assemblages on ordination axis 2 was the CCU score. The abundances of some macroinvertebrate taxa, particularly grazers, also explained significant variations in diatom assemblages that were linked to both metals and acid–base status.5. Diatom species apparently tolerant of high metal concentrations includedPsammothidium helveticum,Eunotia subarcuatoides,Pinnularia subcapitataandSellaphora seminulum. Of these,P. helveticum,E. subarcuatoidesandP. subcapitatawere abundant at lower pH thanS.seminulumand might indicate metal enrichment over different pH ranges. Sensitive species includedFragilaria capucinavar.rumpens,Achnanthes oblongellaandTabellaria flocculosa.6. We conclude that macroinvertebrates at these sites reflected metal pollution most strongly through variations in diversity while effects on diatoms were best reflected by changes in assemblage composition. We suggest that, with further refinement, CCU scores might be useful in evaluating the possible effects of metal pollution on benthic organisms in European rivers.
Evapotranspiration at the land/water interface in a semi‐arid drainage basin
Authors: DAHM CLIFFORD N. , CLEVERLY JAMES R. , ALLRED COONROD JULIA E. , THIBAULT JAMES R. , MCDONNELL DIANNE E. , GILROY DAVID J. 
Published: March 2003

1. Evapotranspiration (ET) is a major source of water depletion from riverine systems in arid and semiarid climates. Water budgets have produced estimates of total depletions from riparian vegetation ET for a 320‐km reach of the Middle Rio Grande, New Mexico, U.S.A., that have ranged from 20 to 50% of total depletions from the river.2. Tower‐based micrometeorological measurements of riparian zone ET throughout the growing season using three‐dimensional eddy covariance provided high quality estimates of ET at the stand scale.3. A dense stand of salt cedar (111–122 cm year–1) and a mature cottonwood (Populus deltoides ssp. wislizenia Eckenwelder) stand with an extensive understory of salt cedar (Tamaria ramosissima Ledeb) and Russian olive (Eleagnus angustifolia L.) (123 cm year–1) had the highest rates of annual ET. A mature cottonwood stand with a closed canopy had intermediate rates of ET (98 cm year–1). A less dense salt cedar stand had the lowest rates of ET (74–76 cm year–1).4. Summer leaf area index (LAI) measurements within the four stands were positively correlated with daily ET rates. LAI measurements throughout the growing season coupled to riparian vegetation classification is a promising method for improving riverine corridor estimates of total annual riparian zone ET along a reach of river.5. Combining recent estimates of the extent of riparian vegetation along the 320 km length of the Middle Rio Grande, from Landsat 7 imagery with annual growing season measurements of ET at the four riparian stands yields a first‐order riverine corridor estimate of total riparian zone ET of 150–250 × 106 m3 year–1. This is approximately 20–33% of total estimated depletions along this reach of river.
Phylogeographical lineages in brown trout (Salmo trutta): investigating microgeographical differentiation between native populations from Northern Spain
Authors: Cagigas M. Elena , Vázquez Emilia , Blanco Gloria , Sánchez José A. 
Published: March 2003

SUMMARY 1. The large microgeographical differentiation revealed by allozyme studies in brown trout (Salmo trutta) populations is one of the most striking features of this species. Additionally, allozymes showed great genetic differences between Atlantic and Mediterranean populations on a macrogeographical scale.2. This study was carried out in order to assess whether the great differences observed between Atlantic and Mediterranean populations persisted where the two are geographically close (the ‘microgeographical scale’). Sixteen populations of brown trout, S. trutta, were screened for genetic variation at 25 allozyme loci. The sampling sites, which occupied a relatively small geographical area, were distributed across Cantabrian (Atlantic) and Mediterranean drainages in Northern Spain.3. The neighbour‐joining tree, inferred from Nei's genetic distance, showed that brown trout populations clustered into two different groups. These groups corresponded to the Cantabrian and the Mediterranean groups of populations, although no clear geographical pattern emerged within each of the groups. This geographical pattern is basically caused by significant differences in the frequency distribution of the CK‐A1* locus, with a higher frequency of *115 in Cantabrian samples (0.586 ± 0.091) while allele *100 was more frequent in Mediterranean samples (0.931 ± 0.038). In addition, this study revealed alleles exclusive to the Mediterranean and Cantabrian populations, agreeing with previous findings.4. Genetic differentiation between Cantabrian and Mediterranean regions (14.19%) was similar to that estimated in Spain at a larger scale (13%), showing that most of the differences between the regions can be observed even in a small geographical area.
Predictive modelling of freshwater fish as a biomonitoring tool in New Zealand
Authors: Joy M. K. , Death R. G. 
Published: March 2003

SUMMARY 1. A challenge has been issued to ecologists to find quantitative ecological relationships that have predictive power. A predictive approach has been successful when applied to biomonitoring using stream invertebrates with the River Invertebrate Prediction and Classification System (RIVPACS). This approach, to our knowledge, has not been applied to freshwater fish assemblages.2. This paper describes the initial results of the application of a regional predictive model of freshwater fish occurrence using 200 reference sites sampled in the Manawatu–Wanganui region of New Zealand over late summer/autumn 2000. In brief (i) sites were classified into biotic groups (ii) the physical and chemical characteristics that best describe variation among these groups were determined and (iii) the relationship between these environmental variables and fish communities was used to predict the fauna expected at a site.3. Reference sites clustered into six groups based on fish density and community composition. Using 14 physical variables least influenced by human activities, a discriminant model allocated 70% of sites to the correct biological classification group. The variables that best separated the site groups were mainly large‐scale variables including altitude, distance from the coast, lotic ecoregion and map co‐ordinates.4. The model was further validated by randomly removing 20% of the sites, rebuilding the model and then determining the number of removed sites correctly allocated to their original biotic groups using environmental variables. Using this process 67% of the removed sites were correctly reassigned to the six predetermined groups.5. A further 30 sites were used to determine the ability of the model to detect anthropogenic impact. The observed over expected taxa (O/E) ratios were significantly lower than the reference site O/E ratios, indicating a response of the fish assemblages to the known stressors.
The role of phosphorus release by roach [Rutilus rutilus (L.)] in the water quality changes of a biomanipulated lake
Authors: Tarvainen M. , Sarvala J. , Helminen H. 
Published: March 2003

SUMMARY 1. Following fish removal, the water quality in biomanipulated lakes often improves concomitant with decreased phosphorus (P) levels. Because the decrease in P concentrations derives most probably either directly or indirectly from fish, which are the main target of biomanipulation, this study examined the P release of 0+, 1+ and 2+ roach [Rutilus rutilus (L.)] and changes in the P release during summer in a shallow eutrophic lake in Finland.2. The P release was separated into P derived from benthic and littoral food items and into recycled P derived from feeding on zooplankton, to estimate the contribution of net P additions to the water column by the fish to the increase in P concentrations of the lake water (75–110 mg P m−3) in summer 1991–96.3. Individual P release of roach by both egestion and excretion was estimated with a bioenergetics model. The size of the roach population was estimated with a depletion method and the proportions of different age groups from catch samples, using a programme separating mixtures of normal distributions. The sensitivity of the release estimates to variation in the growth data was estimated with the jackknife technique.4. The biomass‐specific P release by 0+ roach (0.36–0.54 mg P g−1 day−1) was higher than that by older roach (0.07–0.16 mg P g−1 day−1) throughout the summer. The P release by the whole roach population deriving from benthic and littoral food items (0.7–2.7 mg m−3 during July to August, representing a net addition to the water column) was 5–19 times lower in 1991–96 than the recycled P release deriving from zooplankton (8.9–25.7 mg m−3), and too low to explain the increase in the P concentration of the lake water during the summer. Because the biomass‐specific P release and roach diet composition vary with fish age, it is important to consider the age structure of fish populations to obtain correct estimates of P release and net additions to the water column.5. The removal of roach by fishing diminished the roach stock greatly, but the fish‐mediated P release to the water column changed little. This effect was because of the high compensation capacity of the roach population, leading to high recruitment of young fish with higher biomass‐specific P release rates.6. External loading is very low during summer months and therefore it cannot explain the increase in the P concentration of water during that time. Internal loading from the sediment might be as high as 10.2 mg P m−2 day−1, i.e. 50 times higher than the maximum net P addition by the total roach population.
Effects of piscivore‐mediated habitat use on growth, diet and zooplankton consumption of roach: an individual‐based modelling approach
Authors: Hölker Franz , Haertel Susanne S. , Steiner Silke , Mehner Thomas 
Published: March 2003

SUMMARY 1. We used an individual based modelling approach for roach to (i) simulate observed diel habitat shifts between the pelagic and littoral zone of a mesotrophic lake; (ii) analyse the relevance of these habitat shifts for the diet, activity costs and growth of roach; and (iii) quantify the effects of a hypothetical piscivore‐mediated (presence of pikeperch) confinement of roach to the littoral zone on roach diet, activity costs and growth.2. The model suggests that in the presence of pikeperch, roach shifts from zooplankton as the primary diet to increased consumption of less nutritious food items such as macrophytes, filamentous algae and detritus.3. The growth of roach between May and October was predicted to be significantly higher in the absence of pikeperch, although the net activity costs were about 60% higher compared with the scenario where pikeperch were present.4. These modelling results provide quantitative information for interpreting diel horizontal migrations of roach as a result from a trade‐off between food availability and predation risk in different habitats of a lake.5. Altering the habitat selection mode of planktivorous roach by piscivore stocking has the potential to reduce zooplankton consumption by fish substantially, and could therefore be used as a biomanipulation technique complementing the reduction of zooplanktivorous fish.
Biomanipulation of lake ecosystems: successful applications and expanding complexity in the underlying science
Authors: Mehner Thomas , Benndorf Jürgen , Kasprzak Peter , Koschel Rainer 
Published: March 2003

SUMMARY 1. To illustrate advances made in biomanipulation research during the last decade, seven main topics that emerged after the first biomanipulation conference in 1989 are discussed in relation to the papers included in this special issue and the general literature.2. The substantially higher success rates of biomanipulations in shallow as opposed to stratified lakes can be attributed to several positive feedback mechanisms relating mainly to the recovery of submerged macrophytes.3. The role of both nutrient loading and in‐lake concentrations in predicting the success of biomanipulations is emphasised and supported by empirically defined threshold values. Nutrient recycling by aquatic organisms (such as fish) can contribute to the bottom‐up effects on lake food webs, although the degree can vary greatly among lakes.4. Ontogenetic niche shifts and size‐structured interactions particularly of fish populations add to the complexity of lake food webs and make scientifically sound predictions of biomanipulation success more difficult than was previously envisaged.5. Consideration of appropriate temporal and spatial scales in biomanipulation research is crucial to understanding food web effects induced by changes in fish communities. This topic needs to be further developed.6. An appropriate balance between piscivorous, planktivorous and benthivorous fishes is required for long‐lasting success of biomanipulations. Recommended proportions and absolute densities of piscivorous fish are currently based on data from only a few biomanipulation experiments and need to be corroborated by additional and quantitative assessments of energy flow through lake food webs.7. Biomanipulation effects in stratified lakes can be sustained in the long term only by continued interventions. Alternate stable states of food web composition probably exist only in shallow lakes, but even here repeated interventions may be needed as long as nutrient inputs remain high.8. Biomanipulation is increasingly used as a lake restoration technique by considering the needs of all lake users (sustainability approach). The combination of water quality management and fisheries management for piscivores with positive effects for both appears to be particularly promising.9. Biomanipulation research has contributed substantially to progress in understanding complex lake food webs, which should in turn promote a higher success rate of future whole‐lake biomanipulations.