bluuebunny/crossref_metadata_2025 huggingface dataset:
Continuous drift samples of macroinvertebrates in a large river, the Danube in Austria
Authors: ANDERWALD P. H. , KONAR M. , HUMPESCH U. H.
Published: May 2006

SUMMARY 1. A new method is described for sampling the drift in large rivers continuously and automatically, using equipment based on the marine, continuous plankton sampler of Hardy (1936).

2. Between April and November 1989, about 790 h were sampled continuously, equivalent to a water volume of 2937m3 and the total catch was 527 drifting macroinvertebrates, in forty‐nine taxa. Twenty‐five of these taxa are recorded in the drift for the first time and twenty‐eight of the drifting taxa were present in benthos samples from the Danube.

3. Total drift density varied between 12 and 31 animals per 100m3 of water sampled throughout the year, with a maximum of 31 animals in May, The composition of major faunal groups showed a significant seasonal pattern, with Oligochaeta and Diptera predominant in spring, Crustacea and Insecta in summer and only Crustacea in autumn. The overall density of the macrozoobenthos from October 1986 to December 1987 was about 19360 animals m−2 and the proportion of total benthos animals, drifting at any instant in time, ranged from 0.0026 to 0.0064%.

4. The relationship between drift density day−1 and mean daily discharge was described by a power‐function. Total mean drift rate of macroinvertebrates in the Danube was estimated to be 13 600 000 animals per 24 h and the mean drift distance was estimated to vary between about 4 and 31 m, dependent on the animal group and the water velocity.

5. No obvious consistent diel pattern could be established from the continuous samples, and no marked diel rhythm could be detected for Oligochaeta, Diptera larvae and Crustacea.
Contribution of grazing in phytoplankton overall losses in a shallow French lake
Authors: GARNIER JOSETTE , MOURELATOS SPIROS
Published: May 2006

SUMMARY 1. Based on data for 14C‐primary production and biomass changes in a small and shallow lake (Créteil Lake, France), overall phytoplankton losses were calculated through an annual cycle (November 1985‐October 1986). The summer period in 1986 is compared with two other summer periods in 1985 and 1980, these two years corresponding to extreme levels of algal biomass.

2. Independent from the trophic state of the lake, phytoplankton populations were dominated by small‐sized species (<20 μm); their high growth rate (maximal in May and June: 0–8 day−1) was characteristic of nanoplanktonic natural populations.

3. The positive correlation between phytoplankton losses and production indicates a close coupling between growth and loss processes.

4. With a high filtering rate (0.22 day−1 as an annual average), zoo‐plankton impact is considerable at any time of the year but especially in late summer, when grazing losses exceeded primary production.

5. Despite the uncertainty concerning the meaning of 14C‐primary production, the persistence of small algae throughout the year implies that a great part of the phytoplankton production was harvested by grazers which led to a recycling of organic matter within the water column.
Analysis, purification and quantification of extracellular DNA from aquatic environments
Authors: BEEBEE TREVOR J. C.
Published: May 2006

SUMMARY 1. The presence of extracellular DNA, but not RNA, at μg 1−1 concentrations was demonstrated in seawater, river water and in a series of eutrophic lowland ponds.

2. Extracellular DNA in natural waters invariably comprised two major components: one of high molecular weight (>20 kb) derived from viruses, and another of low molecular weight (1–500 bp) and apparently free in solution. Similar species of DNA molecules were produced within 2 weeks in simple laboratory modules.

3. A purification procedure was developed which separated extracellular DNA from other components of dissolved organic matter, and which also separated viral from soluble DNA. Both types of DNA were purified sufficiently to constitute active templates for enzymes used in DNA manipulation.
The structure of a natural population of the medicinal leech, Hirudo medicinalis, at Dungeness, Kent
Authors: WILKIN P. J. , SCOFIELD A. M.
Published: May 2006

SUMMARY 1. A hot branding method was used to mark medicinal leeches (Hirudo medicinalis L.) from five samples (four in 1984, one in 1985) at agravel pit at Dungeness in Kent. Analysis of capture‐recapture data by the Fisher‐Ford and Jolly methods gave similar results and indicated a population in excess of 10000 (0.112 leeches per m2) in 1984 and 1985. Successive estimates were each higher than the last suggesting a thriving community.

2. The population structure was skewed towards the lower weight classes. This may indicate good recruitment of hatchlings, as also indicated by the presence of cocoons, or the failure to capture heavier satiated or gravid leeches because of their relative unresponsiveness to the sampling method involving water disturbance, or their complete absence from the water during cocoon laying. Gravid leeches were always above 2 g in weight. Recaptured marked leeches revealed that they migrated throughout the site, indicating active foraging for hosts.
Major ion chemistry of the lower Boro River, Okavango Delta, Botswana
Authors: SAWULA G. , MARTINS E.
Published: May 2006

SUMMARY.
1. The composition of surface waters of the Boro River, Okavango Delta, Botswana, was determined on five occasions during 1989–1990. The waters could be characterized as caicium—sodium—bicarbonate, with moderate alkalinity, and moderate to high amounts of silica. Mean values of the major ions, in mg1‐−1, were: Ca2+ 4.8, Mg2+ 1.3, Na+ 3.9, K+ 2.7, HCO3− 27, Cl− 1.0 and SiO2 38; pH c. 7.

2. The relative ionic composition of the waters changed gradually from the inlet in Seronga to the outlet at Boro/Thamalakane junction. There was a gradient of increasing concentrations of solutes resulting from the evaporative concentration of the waters in this semi‐arid region with an almost permanent water deficit, and the total dissolved solutes increased from c. 30 to 95 mg 1‐−1

3. There were seasonal differences in solute concentrations, connected with the rainfall pattern and climatic cycle and an ill‐defined relation with discharge. The chemical spectrum of the Boro, and the freshness of its waters, can be attributed to the major influence of precipitation within the basin and selective removal of solutes.

4. Chemical equilibrium models indicate that amorphous silica and sepiolite are likely to precipitate from the Boro waters. Carbonate and silicate systems are responsible for the selective removal of solutes in the swamps, islands, or flood plains, as proposed by others in recent studies, but not in the Boro River waters.
Diurnal variation in light and carbon limitation of photosynthesis by two species of submerged freshwater macrophyte with a differential ability to use bicarbonate
Authors: MADSEN TOM V. , MABERLY STEPHEN C.
Published: May 2006

SUMMARY.

Rates of photosynthetic oxygen evolution by Callitriche cophocarpa and Ranunculus peltatus in stream were measured on live occasions during the light period on 2 days at ambient light and ambient inorganic carbon, ambient light and saturating inorganic carbon, saturating light and ambient inorganic carbon, saturating light and saturating inorganic carbon and air‐equilibrium inorganic carbon and ambient light.

Despite an ambient CO2 concentration of about 220 μm, which is about ten times air‐equilibrium, the concentration of inorganic carbon was more limiting than light on all the occasions that rates were measured. On average, rates of photosynthesis at ambient concentrations of CO2 were about 130 and 425 μmol O2 g−1 DW h−1 for C. cophocarpa and R. peltatus, respectively. These rates as a percentage of carbon saturated rates were only about 35% for C. cophocarpa and about 60% for R. peltatus. Ambient rates as a percentage of light saturated rates were about 80% for C. cophocarpa and about 95% for R. peltatus. Only in early morning and late evening where the photon irradiance was below 160 μmol m−2 s−1 was there evidence for slight light limitation.

Based on results from pH‐drift experiments and from rates of photosynthesis as a function of CO2 concentration in the presence and absence of HCO3−, C. cophocarpa was unable, but R. peltatus able to use HCO3− at an ambient HCO3− concentration of about 0·84 mm. The greater rates of photosynthesis at ambient CO2 concentration and the lesser limitation by inorganic carbon shown by R. peltatus compared to C. cophocarpa was the result of HCO3−‐use as laboratory experiments showed that R. peltatus performed similarly to C. cophocarpa if the HCO3− concentration was reduced to 60 μm.
Distributions of Ephemeroptera, Plecoptera, and Trichoptera of three maritime catchments differing in pH
Authors: PETERSON R.H. , VAN EECKHAUTE L.
Published: May 2006

1. Two broad‐scale environmental influences affecting species of Ephemeroptera, Trichoptera and Plecoptera inhabiting riffle habitat of three study catchments in New Brunswick and Nova Scotia were stream size‐temperature‐related variables and acidity‐related variables.

2. Species richness was most affected by acidity in tributaries of intermediate size <0.001<0.1m3s−1).

3. Of the three insect orders investigated, mayfly species richness was affected most by acidity, and stonefly species richness affected least by this factor.

4. Zoogeographical isolation of the Nova Scotian catchments resulted in absence of some species of low general abundance, but these species had little influence on the site classification by TWINSPAN analysis.

5. Predaceous stoneflies were collected in greater numbers from circumneutral sites and predaceous caddisflies in greater numbers from the Nova Scotian sites.

6. Although the Nova Scotian catchments have probably been historically acidic, due to high concentrations of organic acids, pH currently limits the distributions of many indigenous invertebrate species. These species may be vulnerable to the more recent, additional, anthropogenic acidification of these catchments.
Feeding by blackfly larvae (Diptera: Simuliidae) forming dense aggregations at lake outlets
Authors: WOTTON R.S.
Published: May 2006

1. Larvae of Simulium noelleri formed dense aggregations (>60 larvae cm−2) at a lake outlet where water passed in a very thin film vertically over wooden planks. Despite the high densities there was sufficient space between larvae to allow water to flow within an aggregation as well as over its surface.

2. Small larvae, occluded within an aggregation, had a faster midgut throughput rate than larger larvae. Both had rates that were similar to those recorded in the literature for a range of habitats and species. The same relationship of throughput rate and larval size was maintained from upstream to downstream across 20cm of an aggregation.

3. Material passed through the midgut of larvae of a given size at a constant rate, indicating that assimilation efficiency of the whole gut contents was low.

4. By colour‐banding larval gut contents with fluorescent dye it was possible to demonstrate that faecal pellets are a component of the larval diet in the dense aggregations, especially of small larvae.

5. The abundance of four easily identifiable components of the lake seston were measured from water samples above, and below, a larval aggregation. Particles with a mean diameter of 40 μm, or greater, showed significant reductions in numbers over a stream length of 6cm. Particles of smaller size showed reductions but these were not significant.
The effects of stream acidity on benthic invertebrate communities in the south‐eastern United States
Authors: ROSEMOND A.D. , REICE S.R. , ELWOOD J.W. , MULHOLLAND P.J.
Published: May 2006

1. Patterns in invertebrate community structure were determined from analysis of benthic samples taken quarterly for 1 year from four sites in the Great Smoky Mountains National Park (GSMNP). Sites ranged in baseflow pH from 4.5 to 6.8, with a corresponding range in inorganic monomeric aluminium concentrations from 3 to 197 μgl−1.

2. Total invertebrate density (excluding Chironomidae) was correlated with pH (R2= 0.90, P<0.05). Density of Ephemeroptera was more highly correlated with pH than density of invertebrates in other taxonomic orders. Invertebrate density (total and density of different orders) was generally more strongly correlated with pH than to inorganic monomeric aluminium concentrations.

3. Species richness declined from sixty‐nine species at the highest pH site to thirty‐three species at the lowest pH site. Richness of Ephemeroptera and Trichoptera was positively correlated with pH (R2= 0.96 in both cases). Trichopteran richness was also negatively correlated with inorganic monomeric Al concentrations (R2= 0.96, P< 0.05). Plecopteran richness was not related to stream acidity.

4. Not all species of Ephemeroptera were negatively affected by low stream water pH. At low pH sites, Ameletus lineatus Traver (Family: Siphonoluridae) was relatively more abundant compared to other species of Ephemeroptera, and had greater biomass and greater weight per individual length than at higher pH sites.

5. Differences in invertebrate community parameters among sites were not based on changes in food abundance. Although grazer densities were positively correlated with pH (R2= 0.93, P < 0.05), differences in density were not related to differences in food. To the contrary, lower grazer densities occurred at the lowest pH site where measured food abundance (algae) was highest. Likewise, shredder density increased with increasing pH but was correlated with standing stocks of benthic organic matter (BOM), which had generally higher standing stocks at lower pH sites.

6. Transplants of two species of Ephemeroptera between sites differing in pH (6.4 v 5.0) resulted in increased mortality of organisms placed at lower pH sites. In another transplant experiment, differences in mortality were not observed, although surviving invertebrates at low pH sites had ×10 higher body burdens of aluminium following the transplant than invertebrates from the reference site.

7. These results indicate that direct effects of pH and Al (affecting survival) were more important than indirect effects of food availability in determining changes in invertebrate community structure between the study sites.
The relationship between pH and community structure of invertebrates in streams of the Shenandoah National Park, Virginia, U.S.A.
Authors: FELDMAN RICHARD S. , CONNOR EDWARD F.
Published: May 2006

1. A replicated natural experiment was used to assess the influence of pH and low alkalinity on abundance and richness of invertebrate families in streams draining catchments that receive acid deposition. Individual streams were used as the unit of replication, allowing conclusions to refer to a class of streams rather than to particular streams.

2. We also controlled for several factors other than pH and alkalinity, including flow and temperature, that are recognized as determinants of invertebrate distribution. Samples were from indigenous rocks, standardized for size, surface area, and geology.

3. Repeated measures analyses of variance (ANOVA) revealed that invertebrate abundance and richness were significantly lower at pH 5.8 than at pH 7.1 for the total community. Thirty per cent of the forty‐seven families exhibited significantly lower abundance at pH 5.8; thirteen families were absent at pH 5.8. Differences were greatest for Ephemeroptera: species richness was significantly lower at pH 5.8, and 71% of the twenty‐four species were either absent (seven) or found in reduced abundance (ten) in the acidic streams.

4. Stream alkalinity is projected to continue to decrease with continued acid deposition in the Shenandoah National Park. Concurrent decreases in pH may lead to the absence or continued numerical decline of certain Ephemeroptera species in streams that acidify to less than pH 6.0 and/or 50μEql−1 alkalinity.
Allochthonous coarse particulate organic material in forest and pasture reaches of two south‐eastern Australian streams
Authors: CAMPBELL IAN C. , JAMES KIM R. , HART BARRY T. , DEVEREAUX ANNE
Published: May 2006

1. Processing of five species of terrestrial leaves was compared in two summers and two winters at forest and pasture sites in each of two south‐eastern Australian streams, using leaf packs fastened with plastic buttoneers and anchored to capping bricks.

2. Soluble carbohydrate and polyphenolics were rapidly lost from the leaves, mostly within 2 days. Total phosphorus and lipid contents remained constant, and nitrogen increased by about 50% over the period to 50% of leaf weight lost.

3. Processing rates, expressed in terms of the negative exponential decay coefficient varied widely for each leaf species, but the rank ordering was consistent withPomaderris asperaandEucalyptus; viminalisprocessed at similar, rapid rates followed byCorrect lawrentiana, Acacia melanoxylonandBlechnum nudum. Abscissed leaves were processed more slowly than fresh leaves.

4. Processing rates were significantly (P < 0.05) different between the two streams, and between leaf species, but there were no consistent differences between processing rates in winter and summer or between forest and pasture sites.

5. When decay coefficients were calculated on a degree day basis,Eucalyptus viminalisleaves were processed significantly faster (P<0.05) in summer than in winter, whereasPomaderris asperaleaves were processed significantly more rapidly in winter than summer (P<0.05); processing rates ofAcacia melanoxylonphyllodes were not significantly different between the two seasons
The drifting of invertebrates and particulate organic matter in an Austrian mountain brook
Authors: WARINGER J.A.
Published: May 2006

1. The drift of organisms and particulate organic matter in a calcareous mountain brook near Lunz, Lower Austria, was investigated for 1 year. Five sets of three drift nets (sampling at different water depths) were distributed along a cross‐section of the brook.

2. From February to March 1989, samples were taken at intervals of 2–7 days over 24‐h periods, at the end of which the drift nets were emptied. From April 1989 to March 1990, sampling was carried out at monthly intervals and the nets emptied every 3h for 1 full day.

3. Of 71 810 organisms caught, the most abundant taxa were Diptera (46.6%; mainly Chironomidae and Simuliidae), Ephemeroptera (24.0%; dominated by Baetis spp.) and Plecoptera (16.1%).

4. The drift density (mean ± 95% CL) was significantly higher (P<0.05) in spring and summer (2.50 ± 0.32 specimens m−3) than in autumn and winter (2.01 ± 0,22 specimens m−3). In terms of biomass (wet weight), drift density was also significantly higher (P < 0.001) in spring and summer (2.50 ± 0.48 mgm−3) than during the rest of the year (1.04±0.12mgm −3).

5. Total drift rates through a cross‐section of the brook ranged from 17366 organisms per day at low discharge (water depth = 10cm) to 955152 individuals per day at a water depth of 50cm in autumn and winter; in spring and summer the corresponding values were 21600 and 1188000 specimens per day.

6. Ephemeroptera, Plecoptera, Coleoptera and Simuliidae were most abundant in night samples, whereas Hydracarina, Trichoptera and Chironomidae drifted mainly during daylight hours.

7. Drift density (dry weight) of particulate organic matter was positively correlated with discharge and ranged from 2.16mgm−3 at a water depth of 10cm to 17.39mgm−3 at 50cm.
Invertebrate drift in a large, braided New Zealand river
Authors: SAGAR P.M. , GLOVA G.J.
Published: May 2006

1. The spatio‐temporal patterns of drifting macroinvertebrates in a large, braided New Zealand river were determined by sampling with drift nets, seasonally, for 1 year.

2. Drift densities were greatest in autumn, and at night in all seasons except winter. A greater proportion of larger animals drifted at night than during the day in all seasons. Mean annual drift densities were ninety‐six animals 100m−3 and 47 mg dry weight 100 m−3.

3. There were relatively few taxa in the drift, and the mayfly Deleatidium spp. comprised more than 85% of the drifting aquatic invertebrates in all seasons except autumn. Chironomidae and terrestrial forms were the only other groups to occur at densities of more than one animal 100 m−3 in all seasons.

4. Drift density was positively correlated with benthic density, which in turn was adversely affected by floods, particularly during spring and summer.
Population responses of the freshwater amphipod crustacean Gammarus pulex (L.) to copper
Authors: MAUND S.J. , TAYLOR E.J. , PASCOE D.
Published: May 2006

1. Populations of Gammarus pulex (density 4000m−2) were exposed, over a 100‐day period in a continuous‐flow dosing system, to concentrations of copper below the 240 h median lethal concentration (LC50) for juveniles.

2. There was a significant effect of copper on the resulting population density. In the control and lowest treatment (11.0μg1‐−1) it was double the initial density, but with increasing copper concentration there was a decrease in density until at the highest treatment (23.1 μg1‐−1), it was less than that of the initial population. The lowest observed effect concentration (LOEC) for population density was 14.6 μg 1‐−1.

3. Copper significantly affected the age composition of the final populations. In the control and lowest treatment concentration, the population was composed mainly of juvenile animals. With increasing copper concentration, however, there was a decrease in the number of juveniles, the LOEC being 14.6 μg1‐−1. The number of adults in the final population was also significantly reduced by copper, with an LOEC of 18.2 μg1‐−1.

4. The relationship between the body length and number of antennal segments of animals in the populations at each treatment concentration showed that growth was impaired by increased copper concentrations.
First‐year benthic recovery of a headwater stream following a 3‐year insecticide‐induced disturbance
Authors: WHILES M.R. , WALLACE J. BRUCE
Published: May 2006

1. A headwater stream (C54) was treated seasonally (twelve times from December 1985 to October 1988) with the insecticide methoxychlor for 3 years, resulting in 72 and 75% reductions of insect abundances and biomass, respectively. Following treatment, monthly benthic abundances and biomass were measured in the treated stream and a nearby reference stream (C55) in order to assess recovery. Seasonal average abundances and biomass were calculated from samples taken from December 1988—December 1989, the first post‐treatment year of C54.

2. Non‐insect abundances and biomass were higher in the recovering stream during the winter + spring and summer periods, but were similar to the reference stream by autumn. Abundances and biomass of collector‐filterers, scrapers, and shredders were all lower in the recovering stream during winter + spring; however filterers and scrapers were similar to reference stream values by the end of the recovery year. No distinct differences were seen between collector‐gatherers and predators throughout the year.

3. Univoltine and multivoltine taxa, along with treatment‐resistant taxa, were the most important contributors to recovery of C54. Taxa with longer generation times, life histories which were more vulnerable to riming of treatments, and/or poor dispersal abilities were poorly represented during first‐year recovery.

4. Abundance data alone were not sufficient for a complete analysis of recovery. Biomass estimates reflected differences in taxonomic composition and developmental stages between streams after 1 year of recovery.
Population dynamics and resource utilization by larval Chironomidae (Diptera) in a backwater area of the River Danube
Authors: SCHMID P.E.
Published: May 2006

1. The five most abundant species of the larval chironomid community in a backwater area of the River Danube were analysed in terms of population dynamics and utilization of space from July 1985 to July 1986. The life histories of Prodiamcsa olivacea (Meigen), Cryptochironomus defectus (Kieffer), Harnischia curtilamellata (Malloch), Polypedilum laetum (Meigen) and Polypedilum scalaenum Schrank were described; the number of estimated generations per year was two for P. olivacea, H. curtilamellata, P. laetum and P. scalaenum and three for C. defectus.

A decline in larval densities of P. olivacea and P. scalaenum was significantly correlated with increasing cumulative water discharge in an area close to a dam (P<0.01).

2. Spatial overlap and resource width were estimated for these chironomid species across four ranges of water depth, in three sections of the River Danube. An increasing mean spatial overlap between larval species coincided significantly with higher mean resource utilization in all cross‐sections during the sampling period. Simulations of spatial overlap between randomized species associations were conducted for analyses of coexistence and dispersion between larval populations. On the basis of comparison with a neutral model, in which patches of individuals were randomly reassigned to habitat units, spatial segregation was significantly (P<0.05) different from chance for seventy‐three out of 263 species pairs examined through the year.

3. An analysis of the spatial dispersion of each chironomid species (using the standardized Morisita index) suggested temporally and spatially varying patterns of dispersion, whereas the mean spatial segregation between patches of larval species might have resulted from temporary formations of random patches in this backwater area of the River Danube.

4. Spatial stability estimated as the minimum positive eigenvalue of the species matrix was significantly positively related to mean spatial segregation, indicating that a lower habitat segregation between patches of larval species pairs may lead to a destabilization of the larval species assemblage.
Induction and inhibition of spine development in the rotifer Keratella tropica
Authors: ZAGARESE HORACIO E. , MARINONE MARÍA C.
Published: May 2006

1. We analysed the effect of several variables on the morphology of the rotifer Keratella tropica with the aim of accounting for its morphological variability in nature. We used field data from (i) an extensive survey of Argentine lakes, (ii) a 1.5 yr, monthly sampling of Salto Grande Reservoir, and (iii) a 3‐month, outdoor experiment in fish culture tanks. In addition, we performed a series of laboratory experiments aimed at isolating the effects of different variables.

2. The increase in crustacean biomass and the amelioration of their nutritional status (measured as the reciprocal of the starvation time) caused spine enlargement. In contrast, the presence of decomposers caused reduction of the spines. These results support the idea that a major proportion of the phenotypic expression of K. tropica depends on the concentration of an inducing factor, which in turn depends on the balance between release and decomposition rates of the chemical.

3. Food concentration was identified as a secondary factor affecting morphology. In agreement with records for other rotifers, food concentration and spine length were inversely related. Both factors, crustacean chemicals and food availability, seemed to act independently, at different developmental stages. Our experiments suggest, however, that the most exuberant individuals can only be induced through chemicals released by predators and competitors.

4. The presence of backswimmers (Notonectidae) resulted in individuals with very short or non‐existing posterior spines. Filtrates of backswimmer‐conditioned medium also produced a significant, although less striking, spine inhibition. Thus, different chemical factors seem to have opposite effects on K. tropica morphology. Those released by crustaceans induce spine elongation, while those released by backswimmers inhibit spine development.

5. Genetic differences were also identified as a source of morphological variability. Under identical laboratory conditions, different clones had spines of different length. Our experiments also suggest an inverse relationship between spine length and growth rate. The latter result, however, is based upon only three clones of K. tropica and is thus preliminary.
Enzymic and molecular analysis of microbial communities associated with lotic particulate organic matter
Authors: SINSABAUGH ROBERT L. , WEILAND TIMOTHY , LINKINS ARTHUR E.
Published: May 2006

1. Most allochthonous plant detritus moves through stream ecosystems as fine particulate organic matter (FPOM), whose associated microbial communities, unlike those of coarse detritus, have received little scrutiny.

2. Benthic POM was collected from a fourth‐order boreal river and two first‐order tributaries in northern New York during July 1991, sorted it into eight size fractions ranging from 38 to >4000 μm, and assayed each fraction for ergosterol, DNA, and the activity of nine extracellular enzymes: β‐1, 4‐glucosidase, endocellulase, cellobiohydrolase, phenol oxidase, peroxidase, β‐N‐acetylglucosaminidase, acid phosphatase, alkaline phosphatase, and aryl sulphatase. In addition, DNA‐DNA hybridization was used to investigate the structural similarity of the microbial communities associated with the FPOM fractions.

3. Various enzymes showed distinct activity patterns in relation to particle size as well as among sites. Half of the possible pairwise correlations among enzyme variables were statistically significant, but no enzyme activities were correlated with biomass indices (DNA and ergosterol concentration). DNA‐DNA dot‐blot hybridizations suggested extensive structural similarity among the microbial communities associated with FPOM fractions.

4. Cluster analysis was used to compare microbial functional similarity, measured by enzyme assays, and structural similarity, measured by DNA—DNA hybridization. Comparison of cluster coefficients showed a weak correlation between community structural similarity and functional similarity (r= 0.51) with fifteen of eighteen fractions grouped within a narrow range of distance.

5. The results suggest a convergence in microbially mediated FPOM processing despite system‐level differences in litter and water quality.
Biovolume as a tool in biomass determination of Oligochaeta and Chironomidae
Authors: SMIT HENK , VAN HEEL ESTI DUDOK , WIERSMA SASKIA
Published: May 2006

We used biovolume as a simple non‐destructive means for estimating biomass for several tubificid and chironomid species. Biovolumes were determined by treating the organisms as cylinders and measuring body lengths and diameters; estimates were verified by measuring the displacement of water by live organisms in a 5‐ml burette. In addition, factors were determined for the conversion of biovolume (V) into wet weight (WW), dry weight (DW) and ash‐free dry weight (AFDW).

 For six tubificid species, regression functions between the diameter of segment XI (D11) and the biovolume enabled the prediction of any biovolume merely by measuring D11. This method, however, underestimated biovolumes of Branchiura sowerbyi by 38–47% compared with burette measurements. This difference is largely attributable to the mountant we used during identification.

 For ten chironomid species a linear relation was found between body length and the diameter of abdominal segment 5. The biovolume of Chironomus muratensis was underestimated by an average of 12% compared with burette measurements.

 Specific gravity (WW:V) amounted to 1.07 and 1.05, DW:WW ratios were 0.20 and 0.142 and AFDW:WW ratios were 0.182 and 0.129 for Oligochaeta and Chironomidae, respectively.

 The biovolume method is not yet very accurate for Oligochaeta, but to our knowledge, it is the only practical method that can be used in natural polyspecific communities that need to be treated with elucidating media for identification. For those Chironomidae that need no elucidation for identification, this method is time saving and just as accurate as the direct body shape—biomass method.
Macroinvertebrate colonization and biofilm development on leaves and wood in a boreal river
Authors: HAX CAROLYN L. , GOLLADAY STEPHEN W.
Published: May 2006

Biofilms, the accumulation of micro‐organisms, exoenzymes, and detritus particles on submerged surfaces, may change the quality of leaves and wood as sources of food and/or habitat for invertebrates. We examined the relationship between macroinvertebrate assemblages and biofilm development on leaves and wood in a boreal river.

 Arrays of white birch ice‐cream sticks and sugar maple leaves were placed at fast‐ and slow‐current sites. Samples were collected periodically, and assayed for microbial biomass (ATP, ergosterol, chlorophyll a) and macroinvertebrate colonizers.

 Microbial biomass and macroinvertebrate density were consistently greater on wood than leaves. Taxon richness was similar for all substratum/current combinations, but taxon density (number of taxa m−2) was greater on wood. Macroinvertebrate density and taxon richness correlated with all microbial indicators when data from both substrata were pooled.

 Leaves did not support as great a density of invertebrates as wood perhaps because of their faster breakdown rate and truncated biofilm development. Greater stability and the potential for surface complexity may make wood a site of higher macroinvertebrate diversity than leaves.
Temporal variability in the impact of river regulation on thermal regime and some biological implications
Authors: WEBB B.W. , WALLING D.E.
Published: May 2006

Ten years of hourly water temperature data for three river sites in south‐west England were used to investigate the longer‐term thermal effects of river regulation. The impact of reservoir impoundment on downstream invertebrate and trout development were simulated using daily mean temperature data in conjunction with published biological models.

 The main effects of regulation on water temperature were to increase the mean value, eliminate freezing conditions, depress summer maxima, delay the annual cycle and reduce diel fluctuation. These impacts persisted over a distance of at least 5km below the dam but declined downstream, especially for seasonal and diurnal variations.

 Simulations suggested that regulation is likely to have had a greater impact on the development of brown trout (Salmo trutta) than on the development of one Ephemeroptera and four Plecoptera species. Trout fry were predicted to emerge up to 57 days earlier, and to weigh up to 67% more by the end of the year following swim‐up, in the regulated compared with the unregulated river.

 Marked inter‐annual contrasts in the physical and biological consequences of impoundment were evident, indicating that long‐term studies are required to define properly the effects of river regulation.
Contribution of space remote sensing to river studies
Authors: MULLER ETIENNE , DÉCAMPS HENRI , DOBSON MICHAEL K.
Published: May 2006

A review is presented of types of satellite remote‐sensing data currently available, and their recent uses in studies of river systems.

 Broad‐scale assessments of relative water quality may be carried out, although precise indication of water quality requires samples to be taken in situ.

 In the event of flooding, the extent of inundation may be determined and damage assessed quickly. Some radar data allow measurements of flood water even when obscured by vegetation.

 Riparian vegetation may be mapped over large areas, although the recognition of specific tree species remains difficult.

 One of the most basic and widely used applications of remote‐sensing data for rivers is that of mapping, both as a single event and over time to follow changes, e.g. channels in a delta. Entire catchments may be mapped, although the efficiency of detection of low‐order streams is dependent upon the characteristics of the system used.

 Remote‐sensing data has been widely used in all of the above types of study, but is rarely employed on a long‐term basis. Several factors can explain this situation, including, for example, the absence of reliable absolute relationships between spectral data and ecological parameters.

 A clear definition of observational needs (e.g. spectral bands, ground resolution, acquisition frequency) of stream ecologists, together with the identification of ecological parameters that may be collected relatively easily from space, will improve remote sensing as an ecological tool in many restoration and management situations.
Reproductive strategy as population density varies in Daphnia magna (Cladocera)
Authors: GUISANDE C.
Published: May 2006

In this study an experiment was carried out to test whether Daphnia magna (Cladocera) changed its reproductive strategy in response to varying population density but constant food supply.

 As population density increased there was a reduction in the age at which females reproduced. Early reproduction was offset by smaller body length and clutch size (number of eggs per female) relative to later reproducing females grown at lower population densities.

 This pattern was interpreted as a strategy carried out by females to reduce the time at which they release their offspring. One potential advantage of early reproduction is to reduce the risk of severe food limitation for neonates born during a period of rapid population increase.
Quantitative trophic reconstruction from sedimentary diatom assemblages: a cautionary tale*
Authors: FRITZ S.C. , KINGSTON J.C. , ENGSTROM D.R.
Published: May 2006

The diatom stratigraphy of 210Pb‐dated sediment cores is used to reconstruct the recent trophic histories of four oligo/mesotrophic lakes in the lower peninsula of Michigan, U.S.A. Quantitative trends in total phosphorus concentrations are reconstructed from the cores with a calibration data set based on modem diatom assemblages and water‐chemistry variables in forty‐two Michigan lakes that span a range of nutrient concentrations and biological productivities.

 The total phosphorus reconstructions suggest that phosphorus concentrations have changed very little over the last 200 years, with modern values approximately equal to those at the time of settlement. Three of the four lakes, however, do show a trend to higher phosphorus concentrations at the time of logging and settlement and a subsequent decline.

 The quantitative inferences of trophic change are compared with interpretations based on diatom species composition and the accumulation of diatoms, biogenic silica and carbonate in the sediments, and some discrepancies occur among the various lines of evidence. These comparisons are used to discuss the sensitivity of various proxies for reconstructing the nature and magnitude of trophic change.
Inter‐ and intrapopulational variation in time to metamorphosis in a freshwater copepod
Authors: TWOMBLY SARAN
Published: May 2006

Adjacent populations of the copepod Cyclops scutifer Sars living in lakes in southern Norway exhibit remarkably different life cycles. A series of laboratory‐common environment experiments were used to partition variance in one life cycle trait—time to metamorphosis—among and within five populations of C. scutifer, to examine the extent to which variation in this trait has a generic basis and to test whether populations are polymorphic for development rates. The experimental populations exhibit a variety of life cycles in the field and occupy environments that represent a broad range of conditions.

 Populations with different life cycles in the field continued to express differences in time to metamorphosis in the laboratory, indicating a genetic contribution to life cycle variation. Differences in developmental rates in the laboratory were smaller, however, than differences observed in the field, suggesting that environmental conditions also contribute to observed life cycle variation.

 In addition to interpopulation variation, each population maintained substantial intrapopulation variation in time to metamorphosis; differences between individuals from the same population were often as large as or larger than differences between populations.

 Individual females in most populations produced highly variable offspring, and there often was little difference in time to metamorphosis among families within a population.

  Cyclops scutifer exhibits a hierarchy of variation in time to metamorphosis, with a major portion of this variation expressed among siblings. Intrapopulation life history variation important to natural selection may be maintained by different processes among the major groups of freshwater zooplankton.
The effects of spate‐induced disturbance, predation and environmental complexity on macroinvertebrates in a tropical stream
Authors: DUDGEON DAVID
Published: May 2006

The combined effects of fish predation, substrate complexity and flow on benthic macroinvertebrates inhabiting riffles was investigated in a Hong Kong stream. Predation was manipulated using fish inclusion/exclusion cages containing complex (= many refuges) or simple (= few refuges) substrates. Experiments were undertaken during the winter dry season, when disturbance due to flow events was minimal, and repeated during the summer monsoon, when the stream experienced spates of varying intensity and duration.

 Predation by the fish, Oreonectes platycephalus, significantly reduced the abundance of macroinvertebrates, especially chironomids and mayflies. Because chironomids (mostly Chironominae) were the dominant cage colonists, there was also a reduction in total macroinvertebrate density.

 Predator impacts were significantly lessened during the wet season, when macroinvertebrate densities increased considerably, but significant reductions in the densities of vulnerable taxa and total macroinvertebrate abundance were nevertheless apparent.

 Substrate complexity (the presence of prey refuges) had no significant effect on the ability of predators to reduce prey abundance.

 Detritus accumulated in cages during the latter part of the study, and densities of most taxa were correlated with detrital standing stocks.

 The results of this experiment indicate that biotic interactions such as predation may be suppressed during periods of spate‐induced disturbance, although they can still influence benthic communities significantly. However, the effects of predation are highly taxon specific and may vary among streams in response to changes in predator and prey species composition, or the severity and duration of spates.
The upstream/downstream movement paradox of lotic invertebrates: quantitative evidence from a Welsh mountain stream
Authors: WILLIAMS D. DUDLEY , WILLIAMS NANCY E.
Published: May 2006

This study attempts to determine the mechanisms by which the downstream displacement of lotic invertebrates is compensated by the upstream movements of immatures and adults. To this end, submerged and aerial traps were set up at three sites, each 100 m apart on a small mountain stream (Yr Ogof) in North Wales and operated for 12 months.

 At Site 1 (the source), 19.3% of the benthic invertebrates lost as drift were replaced by the upstream movement of aquatic stages. At Site 2, the average upstream compensation was 51.1% (although there was a marked difference between the two traps at the site). At downstream Site 3 the average compensation was 55.4%. The net loss of benthos downstream over 1 year was estimated to be 261920 individuals from Site 1, 41891 from Site 2, and 40470 from Site 3.

 At Sites 1 and 2, the numbers of invertebrates drifting were positively correlated with both current speed and water depth. At Sites 2 and 3, the numbers moving upstream were positively correlated with water temperature. At all three sites, the numbers of animals drifting were positively correlated with the numbers moving upstream, under water.

 In none of the eight common species of stoneffy did females show a strong overall upstream flight preference—however, two species, Leuctra nigra and Nemoura erratica, showed a significant downstream preference.

 As with the stonefly nymphs, most of the caddisfly larvae showed a longitudinal distribution. Agapetus fuscipes larvae were most abundant at Site 1, yet females showed no preferred flight direction—this would seem to be inappropriate for maintaining this larval distribution pattern. However, females caught moving upstream at Site 2 were bigger and contained twice as many eggs, which were also larger, than females moving upstream at Site 1. The flight patterns of the other Trichoptera also seemed inappropriate for maintaining their respective larval distributions. Immature insects moved upstream at certain sites and times, but trends were not consistent. There was no correlation between female flight direction and local wind speed and direction.

 Downstream displacement of the most abundant non‐insect species, Gammarus pulex, was quite considerable at all three sites. However, at several times during the year the numbers moving upstream approached or exceeded those drifting. Maintenance of benthic population densities in this species is thought to be through a combination of upstream movement (which was highly correlated with benthic density at Sites 1 and 3) and production of young over a long (10 month) reproductive period. Maintenance of the benthic populations of the immature stages of the majority of insect species in Yr Ogof is thought to be through oviposition by females in the vicinity of their emergence sites.
Comment on ‘The nature of the fluid boundary layer and the selection of parameters for benthic ecology’ (Carling, 1992)
Authors: LAMOUROUX NICOLAS
Published: May 2006

Near‐bed flow equations and definitions have been reviewed by Carling (1992). The main errors and ambiguities in this contribution are identified.

 The hypotheses required to derive the governing equations are usually violated in complex flows of natural streams.
Interaction between chemical and tactile cues in mayfly detection of stoneflies
Authors: ODE PETER R. , WISSINGER SCOTT A.
Published: May 2006

Behavioural experiments were performed in artificial stream channels to determine if nymphs of the mayfly Paraleptophlebia adoptiva (Ephemeroptera: Leptophlebiidae) respond to (i) chemical cues from stonefly nymphs, (ii) chemical cues from disturbed conspecific mayflies, and (iii) body fluids of injured conspecifics, and (iv) whether responses to these chemical cues are different when combined with contact by foraging Acroneuria carolinensis stonefly nymphs (Plecoptera: Perlidae).

 Although none of the chemical cues elicited changes in mayfly behaviour in the absence of predator contact, stonefly chemical cues significantly enhanced the avoidance response of mayflies to stonefly contact. Mayfly nymphs swam more frequently and crawled further in response to predator encounters when chemical cues were present than when chemical cues were absent. Thus, direct stonefly precontact chemical cues appear to sensitize P. adoptiva to the potential for an encounter with A. carolinensis, enabling stronger escape or avoidance responses upon contact.

 Mayfly chemical cues that provide indirect information about the proximity of a predator (disturbed or injured conspecifics) did not stimulate increased mayfly response to stonefly contact. Indirect cues may provide less reliable information about the proximity of a stonefly than chemicals emitted directly from an adjacent predator. Mayflies might use chemical cues only in the presence of predator contact because of the high cost of premature escape in a running water system.