bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimal reproductive strategies in age‐structured populations of zooplankton
Authors: DORAZIO ROBERT M. , LEHMAN JOHN T.
Published: May 2006

SUMMARY. We describe a model of zooplankton population dynamics that accounts for differences in mortality and physiology among animals of different ages or sizes. The model follows changes in numbers of individuals and changes in individual and egg biomass through time and it expresses mortality and net assimilation as functions of animal size.

We investigated the effect of egg size, age at first reproduction, and size at first reproduction on the per capita growth rates of populations growing under different conditions. In the absence of predation or when exposed to vertebrate predators that prefer large prey, populations achieve maximum growth rates when animals hatch from small eggs and reach maturity quickly at small sizes. Populations exposed to invertebrate predators that concentrate on small animals may increase r in two different ways. One way is for animals to increase juvenile survivorship by hatching from large eggs and by shortening the juvenile period. An alternative strategy is for animals to hatch from small eggs and to postpone maturity until they grow beyond the range of sizes available to their predators. Certain life history strategies maximize r if animals continue to grow after they reach maturity. By growing larger, non‐primiparous females are able to hatch larger clutches and thereby increase the overall rate of population growth.

The model analysis shows how to assess age‐dependent mortality rates from field data. The net rate of population increase and the age distribution of eggs together provide specific, quantitative information about mortality.
Continuous ammonium enrichment of a woodland stream: uptake kinetics, leaf decomposition, and nitrification
Authors: NEWBOLD J. DENIS , ELWOOD JERRY W. , SCHULZE MEL S. , STARK ROBERT W. , BARMEIER JUDY C.
Published: May 2006

In order to test for nitrogen limitation and examine ammonium uptake by stream sediments, ammonium hydroxide was added continuously at concentrations averaging 100 μg1‐1 for 70 days to a second‐ order reach of Walker Branch, an undisturbed woodland stream in Tennessee.

Ammonium uptake during the first 4h of addition corresponded to adsorption kinetics rather than to first‐order uptake or to Michaelis‐ Menten kinetics. However, the calculated adsorption partition coefficient was two to four orders of magnitude greater than values reported for physical adsorption of ammonium, suggesting that the uptake was largely biotic.

Mass balance indicated that the uptake of ammonium from the water could be accounted for by increased nitrogen content in benthic organic detritus. Nitrification, inferred from longitudinal gradients in NO3, began soon after enrichment and increased dramatically near the end of the experiment.

Both ammonium and nitrate concentrations dropped quickly to near background levels when input ceased, indicating little desorption or nitrification of excess nitrogen stored in the reach.

There was no evidence of nitrogen limitation as measured by weight loss, oxygen consumption, phosphorus content, and macroinvertebrate density of red oak leaf packs, or by chlorophyll content and aufwuchs biomass on plexiglass slides. A continuous phosphorus enrichment 1 year earlier had demonstrated phosphorus limitation in Walker Branch.
The macroinvertebrate fauna of the drainage channels of the Gwent Levels, South Wales
Authors: CLARE P. , EDWARDS R. W.
Published: May 2006

SUMMARY. From a survey of the fauna at sixty sites in permanent drainage channels of the Gwent Levels during the spring of 1976 and at some of these sites (thirty‐three) during the autumn, speeies and site associations were identified using classification and ordination techniques. Sites in some groups had identifiahly similar environmental characteristics and grouping seemed particularly related to the vegetational stage in the hydrosere, water How and the incidence of salt contamination from the Severn Estuary. Characteristics which were common within particular species groups and whieh, in part, explained their distributions were: adaptation to low oxygen concentrations, food preferences and dispersal mechanisms.

Whilst there was some temporal stability in site groups between the spring and autumn surveys, such associations were not idenlical. The oxygen status of channels appeared a major factor determining faunal distribution.

Twelve sites, representing a range of channel types, were sampled six times in a 12‐month period. Far more species were colleeled within the water column and on plants than in the benthos. Several oligochaetes, e.g. Aulodrilus pluriseta, Dero digitata, Limnodrilus claparedeanus, were not recorded at most sites during the summer probably because of the SUStained lack of oxygen at these sites.

Three contiguous reaches of channel were maintained during the period March—October 1977 with different plant cover (no Lemnu; complete Lemna cover: control with partial Lemna cover). The oxygen status of the reaches was different, that with complete Lemna cover being continuously anaerobic near the channel bed for several months, the control reach which had partial Lemna cover being anaerobic for a shorter period and that with no Lemna being only anaerobic at night. Whilst the distribution of macroinvertebrate species was prineipally related to this oxygen status, the control reach whieh was strueturally the most complex, having both submerged and floating plants, contained about twiee as many species as the other reaches during the summer (colleeted in the water column and on plants): benthic samples in this and the reach with complete Lemna cover contained only between zero and two species during the period May‐ September.
Effects of concentrating phytoplankton on the acetylene‐reduction assay for nitrogenase activity
Authors: LEONARDSON LARS
Published: May 2006

SUMMARY.

The consequences of concentrating freshwater phytoplankton communities prior to measurement of nitrogenase activity using the acetylene‐reduction assay were investigated.

Retention of heterocystous blue‐green algae by 10 and 45 öm plankton nets was usually much less than 100% and the percent retention differed among blue‐green algal species and varied for the same species both on different sampling dates and in different lakes. Retention of heterocyst numbers and helerocyst volume during concentration differed from that of total cell volume of heterocystous blue‐green algae.

Effects of concentration on specific nitrogcnase activity varied among the lakes studied. In Lake Bysjön activity decreased on all sampling occasions, in Lake Trummen there was no apparent effect, and in Lake Vaxjosjon both results were found.

Effects on nitrogenase activity of mechanical disturbance during concentration and of increased pH. reduced carbon availability. light inhibition and subsaturation. photorespiration and oxygen supersaturation in concentrated samples are discussed. Interactions between these factors are suggested to explain the varying responses in the three lakes.

It is concluded that phytoplankton should not be concentrated in the acetylene‐reduction assay for nitrogenase activity, since both volumetric and cell concentration factors are inadequate and effects of concentration on specific nitrogenase activity are not predictable.
Microbial heterotrophic utilization of dissolved organic matter in a piedmont stream
Authors: KAPLAN LOUISA. , BOTT THOMAS L.
Published: May 2006

SUMMARY.

The microbial heterotrophic utilization of dissolved organic matter (DOM) was determined experimentally in microcosms using stream water and stream‐bed sediments from a third order reach of White Clay Creek (Pennsylvania, U.S.A.).

Sources of DOM for the experiments included White Clay Creek water at baseflow and stormflow and cold water extracts of jewel weed (Impatiens capensis L.) and spicebush (Linderu henzoin (L.) Blume).

The heterotrophic activity of the sediments was measured as uptake of the following: dissolved organic carbon (DOC), molecular weight fractions within the DOC pool, carbohydrates, amino acids and peptides, phenolics, and dissolved oxygen (DO), all in the overlying water.

Concentrations of adenosine triphosphate (ATP), and direct microscopic counts of bacteria were used to estimate bacterial biomass in the surface sediments.

The microcosm experiments showed that specific DOC molecular size classes and DOM functional groups were selectively removed from solution, exposure to one DOM source affected responses to a different DOM source and certain DOM sources were more readily utilized than others.

Continued exposure to a DOM source increased microbial heterotrophic activity (a condition which persisted even after removal of the DOM source for several days).

Rates of biotic DOC uptake ranged from 3.6 to 242.8 mg Cm‐2h‐1.

Indirect estimates of biosynthesis calculated from DOC and DO data ranged from 1.6 at baseflow and 2.6–61.2 at stormflow to as high as 192.6 mg C m‐2 h‐1 when the community was repeatedly exposed to enriched DOM sources.

The mean generation times of bacteria in sediments, determined from direct microscopy data, ranged from 12.5 to 46.2 h at 15°C.
Production of a stream shredder, Peltoperla maria (Plecoptera: Peltoperlidae) in disturbed and undisturbed hardwood catchments
Authors: O'HOP JOE , WALLACE J. BRUCE , HAEFNER JOHN D.
Published: May 2006

SUMMARY. (1) The average benthic density of Peltoperla maria in an undisturbed southern Appalachian stream was more than twice that of a nearby stream draining a previously clear‐cul catchment in its tenth year of natural secondary succession.

(2) Peltoperla production estimates, using three methods, do not show a significant difference in production between streams draining the two catchments. We attribute these results to quicker growth and slightly higher densities of larger nymphs in the disturbed stream. Production estimates for the disturbed stream ranged from 498 to 560 mg (ash free dry weight) m−2y−1 while those for the undisturbed stream were 41–4–515 mg m−2 y−1.

(3) Our results reinforce the view that conclusions based solely upon numerical densities may lead to erroneus interpretations about the roles organisms play in ecosystems.

(4) Annual frass production by this shredder is about 20 times (10 g m−2 y−1) the secondary production of P. maria.
Macroinvertebrate–habitat relationships in the River Teifi catchment and the significance to conservation
Authors: JENKINS R. A. , WADE K. R. , PUGH E.
Published: May 2006

SUMMARY. 1. A macroinvertebrale survey of various habitats (e.g. riffles, pools, tree roots) at sixteen sites in the Teifi catchment in September 1981 yielded 217 taxa excluding Hydracarina and Chironomidae.

2. Sites with the greatest number of habitats were generally rich in taxa and supported the highest number of ‘rare’ species, the latter generally being associated with vegetation. However, species were not generally restricted to particular habitats although ecdyonurid mayflies predominated in riffles and one leptocerid caddisfly was principally collected from tree roots.

3. Four groups of taxa which characterized three habitat groups were established using classification procedures and it was concluded that three habitat types (eroding, depositing and vegetation) should be sampled to describe adequately the macroinvertebrate fauna at each site.

4. Three attributes (species richness, species rarity and site uniqueness) were used to establish the conservational value of each site; in general, the main river and one lowland tributary were of highest conservational significance.

5. Multiple regression analyses were used to establish significant relationships between the three attributes and environmental features such as number of habitats, altitude, river width, pH and total hardness. Such relationships may facilitate a rapid assessment of resource value without expensive biological survey.
Changes in sediment nutrient content in a subarctic lake subjected to lake fertilization
Authors: BJÖRK‐RAMBERG SUSANNA
Published: May 2006

SUMMARY. 1. Phosphorus and nitrogen concentration in the surface sediment was analysed before, during and after fertilization of a small, stratified, subarctic lake. During stratification most (70%) of the added nutrients were deposited in the epilimnion sediment.

2. After 2 years of fertilization there was a significant increase of both nutrients at all water depths, although values were 30–50% higher per square metre in the shallow areas.

3. Nutrient budget calculations based on the sediment analyses showed that 75% of the added phosphorus and 45% of the nitrogen were accumulated in the sediment after fertilization.
Sexual dimorphism in Gammarus pulex: the effect of current flow on pre‐copula pair formation
Authors: GREENWOOD PAUL J. , ADAMS JONATHAN
Published: May 2006

SUMMARY. 1. Male Gammarus pulex (L.) are typically twice as heavy as females in field caught pre‐copula pairs and mating is positively size assortative. Earlier work had shown that relatively large males can swim in pre‐copula at higher current speeds than males that are relatively small compared with their mates. We describe experiments on pair formation in the laboratory, in static water and in an artificial stream.

2. Pairs formed in the artificial stream had a significantly higher weight ratio than either those formed in static water or those caught in the field. In both experimental conditions, males in pairs were significantly larger than singles. In the stream, the weight ratio of pairs increased with formation sequence due to a significant decrease in the size of selected females.

3. It is concluded that these results are consistent with the hypothesis that the relatively large size of paired male G. pulex is a product of mechanical constraints rather than male–male competition.
The consumption of rainbow trout (Salmo gairdneri Richardson) eggs by macroinvertebrates in the field
Authors: BROWN ANDREW F. , DIAMOND MARK
Published: May 2006

SUMMARY. 1. Perforated boxes containing live, dead or no eggs of the rainbow trout, Salmo gairdneri Richardson, were buried in a natural spawning redd in a stream in North Wales for the duration of the natural incubation period.

2. A significant difference (P<0.001) was found between the mean number of invertebrates colonizing perforated boxes containing live eggs, dead eggs and no eggs.

3. The number of eggs retrieved from boxes originally containing dead eggs decreased as the number of invertebrates colonizing the boxes increased.

4. Using a serological method of prey identification it was demonstrated that Leuctra hippopus (Kempny), Gammarus pulex (L.) and Ptychopter‐idae sp. scavenged on trout eggs in the field.

5. There was some evidence that Rhyacophila dorsalis (Curtis) and Diura bicaudata (L.) preyed on trout eggs, but in view of their scarcity, it is suggested that they were a minor mortality factor.
Distribution of macro‐invertebrates in a ditch in relation to the vegetation
Authors: SCHEFFER MARTIN , ACHTERBERG ADRIAAN A. , BELTMAN BOUDEWIJN
Published: May 2006

SUMMARY. 1. Quantitative fauna samples were taken from four differently structured vegetations in a ditch on three dates in the summer of 1980.

2. Cluster analysis of twenty‐four samples showed that the vegetation pattern is probably the main factor in determining the spatial distribution of non‐benthic macro‐invertebrates in the ditch. Temporal heterogeneity arising from changes in the macro‐invertebrate fauna during the summer, however, appeared to be of at least the same magnitude as the observed spatial heterogeneity. Different vegetation types differed considerably in total faunal density. Species that are taxonomically related tend to have a similar distribution in the ditch.
Hatching time and growth of Nemurellapictetii (Plecoptera: Nemouridae) in the laboratory and a Lake District stream
Authors: ELLIOTT J. M.
Published: May 2006

SUMMARY. 1. Nemurella pictetii Klapæplek took 2 years to complete its life cycle in both the laboratory and a small stream in the English Lake District.

2. Hatching time (days after oviposition for 10%. 50% and 90% of the eggs to hatch) and hatching period (days between dates for 10% and 90% hatched) decreased with increasing water temperature in the laboratory, and the relationships were well described by a power‐law. Estimates of the mean time for 50% hatching in the stream varied between 16 and 31 days after oviposition. depending on temperature.

3. Larval instars numbered fifteen for males and seventeen for females with a constant ratio of 1.18 between successive instars (conformed with Dyar's rule). Larval growth was exponential at four constant temperatures in the laboratory; mean instantaneous growth rates were 0.40±0.01% day−1 at 5.9°C, 0.43±0.01% day−1 at 8.2°C, 0.46±0.01% day−1 at 12. 1°C. 0.56±0.02%day−1 at 19.8°C. No larvae survived after instar XI at 19.8°C.

4. Larval growth was exponential in the stream and was scarcely affected by variations in water temperature (range 4.2 ‐14.0°C); mean growth rates for three year‐classes were 0.41±0.02, 0.43±0.08, 0.54±0.05% day−1. Their similarity to laboratory growth rates under optimum conditions suggests that the availability of resources, such as food and space, was not restricting growth in the stream.
Diel and seasonal physico‐chemical fluctuations in a small natural West African lake
Authors: HARE LANDIS , CARTER JOHN C. H.
Published: May 2006

SUMMARY. 1. The waters of Opi Lake were very dilute (15–24 μS cm−1at 25°C) and somewhat acid (pH 6.0–6.5), probably a result of the highly leached lateritic soils in its small drainage basin.

2. Annual minimum water temperatures were recorded during the early dry season, not during the rainy season as has been observed in most other West African water bodies. This was attributed to the influence of the Harmattan winds on the lake and the absence of pronounced rainy season flooding, as might occur in reservoirs.

3. A diel cycle of daytime thermal stratification and complete or near‐complete night‐time destratification occurred throughout the year.

4. During the dry season, when prevailing winds were strong and lake depth shallow, night‐time destratification was accompanied by deep circulation. In the rainy season, when prevailing winds were weak and lake depth was greatest, deep vertical circulation apparently did not take place, as evidenced by anoxia in near‐bottom waters. This is the reverse of the pattern seen in many tropical lakes.
The microdistribution of some lotic insect predators in relation to their prey and to abiotic factors
Authors: MALMQVIST BJÖRN , SJÖSTRÖM PER
Published: May 2006

SUMMARY. 1. The microdistribution of three species of insect predators in a Swedish stream was assessed using a multivariate statistical approach. Both abiotic factors and factors pertaining to the prey community were included in the analysis.

2. The factors most strongly correlated to the distribution of large Dinocras cephalotes were the densities of case less caddis larvae (Wormaldia sp. and Hydropsyche siltalai) and the median weight of stonefly prey. For small D. cephalotes, the density of H. siltalai and the percentage of moss cover were most important. Isoperla grammatica showed a significant correlation to blackfly density. Rhyacophila nubila occurred predominantly in patches with high prey biomass and with high densities and median weight of case less caddis larvae.

3. It was concluded that the quantity and quality of the prey, such as size, availability and species, influenced the predators’microdistribution. The distributional pattern differed between species of predators and was probably related to their different hunting strategies.
Reproductive phenology in Dendrocoelum lacteum (Turbellaria) in South Sweden
Authors: HERRMANN JAN
Published: May 2006

SUMMARY.

L 266 degree‐days, above a threshold of 1.0°C, were required for cocoons from the triclad Dendrocoelum lacteum to hatch. The relation is described by ln D=6.12–1.17 1nr (D=number of days, T= temperature).

Laboratory and field cocoon deposition reached a maximum in late April; peaks of hatchling occurrence were 2 weeks later. The number of hatchlings per cocoon and eocoon viability declined as spring proceeded. Cocoon deposition ceased in June, coincident with regression of the reproductive organs of the adults.

Newly hatched triclads in the field are thought to avoid stones for their first weeks.

It is suggested that the earlier and more abundant offspring production in South Sweden than in Britain could be attributed to differences in spring temperature conditions.
Changes in the concentrations of short‐chain carboxylic acids and gases during decomposition of the aquatic macrophytes, Lemna paucicostata and Ceratophyllum demersum
Authors: STERRY P. R. , THOMAS J. D. , PATIENCE R. L.
Published: May 2006

SUMMARY.

Samples of two species of aquatic macrophytes, Lemna paucicostata and Ceratophyllum demersum, with which snail hosts of schistosomes are commonly associated, were homogenized, together with their epiphytic flora, and allowed to decompose in closed systems for up to 42 days.

After 10 days of incubation it was found that populations of rod and coccoid shaped bacteria had greatly increased. Fermentation proceeded only to the acid forming stage and no methane was produced.

Despite the differences in the morphologies, habitats and epiphytic flora of the two species, it was found that the short chain carboxylic acids, acetate, propanoate, butanoate and hydrogen were the major end products of microbial decomposition in both cases. There was also some oxygen production from photosynthetically active zones within the homogenates. Most of the accumulation profiles for the acids conformed to logistic growth curves, whereas the hydrogen values fluctuated.

The reasons for the biochemical changes, the differences between the patterns of decomposition in Lemna and Ceraiophyllum. and the ecological relevance of the results to the plants, micro‐organisms and the snails are discussed.
Effects of copper on production of periphyton, nitrogen fixation and processing of leaf litter in a Sierra Nevada, California, stream
Authors: LELAND HARRY V. , CARTER JAMES L.
Published: May 2006

SUMMARY.

Production of periphyton, nitrogen fixation and processing of leaf litter were examined in an oligotrophic Sierra Nevada stream and the responses of these processes to copper (2.5, 5 and 10μg 1‐1 CuT [total filtrable copper]; approximately 12, 25 and 50 ng 1‐1 Cu2+) were determined.

Autotrophic and total production were estimated from 3‐week accumulations of biomass on artificial substrates. Mean autotrophic production in the control ranged from 0.22 to 0.58 mg C m‐2 h‐1 in summer‐autumn 1979, but declined to 0.08–0.28 mg C m 2 h‐1 after peak discharge in summer 1980, apparently due to phosphorus‐limited growth. Total production in the control ranged from 0.30 to 0.82 mg C m‐2 h ‐1 in summer‐autumn 1979 and from 0.16 to 0,68 mg C m ‐2 h ‐1 in 1980. Mean autotrophic productivity, estimated by l4C‐bicarbonate uptake in daylight, ranged from 0.30 to 2.8 mg C m‐2 h‐1.

Autotrophic productivity was reduced by 57–81% at 2.5μg 1‐1 CuT, 55–96% at 5μg 1‐1 CuT, and 81–100% at 10μg 1‐1 CUT, Heterotrophic productivity (based on dark 35S‐sulphate uptake) was inhibited to a lesser extent (28–63% at 2.5μg 1‐1 CuT, 24–84% at 5μg 1‐1 CuT, and 67–92% at 10μg 1‐1 CuT), The inhibition of autotrophic and heterotrophic productivity persisted through the year of exposure. Production in stream sections previously exposed to 2.5 and 5μg 1‐1CuT increased to control levels within 4 weeks after dosing, but remained depressed for more than 7 weeks after exposure to 10μg 1‐1 CuT.

The specific rate of photosynthesis (mg C mg chlorophyll a‐1 h‐1) of mature periphyton communities declined at all test concentrations of copper, but the rate for periphyton on newly‐colonized surfaces did not change. The species composition of benthic algae shifted during exposure to an assemblage more tolerant of copper. Achrtanthes minutissima and Fragilaria crotonensis were the primary replacement species on newly‐colonized surfaces.

The nitrogenase activity of blue‐green algae was low. with controls ranging from 2.4 to 12 nmol C2H2 m‐2 h‐1. Nitrogenase activity was inhibited during the initial weeks of exposure by 5 and 10μg 1‐1 CuT. However, after 9 months of exposure, control and copper‐treated sections did not differ.

The rate of processing of leaf litter, estimated by microbial respiration and nutrient quality of litter of resident riparian woodland taxa, was inhibited at all test concentrations of copper.
Density gradient centrifugation (DGC) in Percoll for isolation and characterization of Oscillatoria spp. from Tjeukemeer
Authors: BLOEM J. , MOED J. R.
Published: May 2006

SUMMARY.

A high degree of separation was achieved in isolating Oscillatoria redekei and O. agardhii separately from Tjeukemeer seston by density gradient centrifugation (DGC) in Percoll. When diatoms were abundant, however, a pre‐incubation in settling cyhnders was applied to obtain an optimal separation of O. redekei from diatoms.

One major band dominated by O. redekei was formed in the gradients. O. agardhii showed a varying distribution over three different bands and its banding pattern seemed to be related to the centrifugation resistance of its gas vacuoles and the turgor pressure.

Pigment ratios of O. agardhii were not affected by DGC in Percoll.
Acclimation of stream‐bed heterotrophic microflora: metabolic responses to dissolved organic matter
Authors: KAPLAN LOUIS A. , BOTT THOMAS L.
Published: May 2006

SUMMARY.

Studies were performed to assess the acclimation of the stream‐bed heterotrophic microflora to sources of dissolved organic matter (DOM) typical of its environment and microfloral responses to pulses of DOM.

Microcosm measurements of dissolved organic carbon (DOC) uptake, dissolved oxygen uptake. ATP concentration and epitluorescence microscopic counts (EMC) were performed using stream‐bed sediments and heterogeneous dissolved organic matter (DOM) sources.

Three study sites included an undisturbed woodlot spring seep, a small stream traversing a cattle pasture and a larger stream draining a catchment used for silage crops, pastures and woodlands.

The DOM sources were cold water extracts of forest floor leaf litter, bovine manure, the green alga Ulothrix and jewel weed (Impaliens capensis L.) leaves.

DOC uptake occurring in 2.5–5.0 h incubations indicated an acclimation of the microflora at each site to DOM sources generated by surrounding land use.

The sediment microflora from the larger stream did not readily metabolize bovine manure DOM and the latter was used in an acclimation experiment.

A minimum of 48 h of cumulative exposure to bovine manure DOM at 15–20°C were required to yield measurable changes in sediment microbial activity of sediment microbial biomass.

The same microflora retained an ability to readily metabolize the added DOM source after 72 h of exposure to unamended stream water.

The time frame of microfloral responses during acclimation indicated that changes leading to the metabolism of a DOM source were initially enzymatic and eventually involved growth and selection for specific decomposers within the microbial community.

We conclude that in order to utilize naturally occurring pulses of carbon and energy, stream‐bed heterotrophs must be already enzymatically prepared, induced, when the pulse occurs.
Thermal and chemical stratification and mixing in a small tropical reservoir, Solomon Dam, Australia
Authors: HAWKINS PETKR R.
Published: May 2006

SUMMARY.

The patterns of distribution of temperature, dissolved oxygen, and filterable iron in the water mass of Solomon Dam were determined at about 30 day intervals over a 2.5 year period (1981–83).

The thermal stratification, and resultant chemical differentiation of the epilimnion and hypolimnion, was the dominant limnological feature of the reservoir. A pronounced thermoline was present for most of the year and, during the stratified phase, diurnal circulation appeared to be the main mechanism for maxis.

Evidence for the presence of an internal seiche, a phenomenon commonly associated with stratified water bodies, was also observed.

An annual overturn in June‐July coincided with the minimum in solar radiation. The ‘wet’ season (January‐March) caused either partial or complete circulation depending on the volume of the reservoir and the rate of inflow. In 1982 the lake circulated once, fitting the warm monolithic pattern, but in 1983 there were two circulations, the first resulting from flood inflows.

The study illustrated the inappropriate nature of a thermally derived classification scheme for a small reservoir.
The larval diet of three anisopteran (Odonata) species
Authors: BLOIS CATHERINE
Published: May 2006

SUMMARY.

Comparisons between larval diets of three anisopteran species (Anax imperator, Aeshna cyanea and Libellula depressa) showed that their food intake changed depending on: (1) predator species, (2) time of year, and (3) developmental stage.

Although this last factor is not so important, the mean size of prey items and the range of prey species eaten by Auax imperator and Aeshna cyanea larvae increased with predator size.

Comparisons between prey availability and diets indicated differential selectivity by these predators.
Patterns of macroinvertebrate colonization on fresh and senescent alder leaves in two Michigan streams
Authors: STOUT R. JEAN , TAFT WILLIAM H. , MERRITT RICHARD W.
Published: May 2006

SUMMARY.

Communities of invertebrates colonizing senescent autumn and fresh summer alder leaves (Alnus rugosa) were compared. Leaf packs for each treatment were placed in two hardwater streams in the Upper Peninsula of Michigan in late summer and early autumn. One stream has a cobble‐bottom and the other a sand‐bottom and both receive fresh leaf inputs by beaver fellings.

Fresh leaf packs remained intact after 26 days immersion, but thereafter were processed faster than were the autumn leaf packs in both streams.

In the cobble‐bottom stream taxon richness (S), numbers of individuals and biomass were higher on fresh than on autumn leaves.

Fresh leaves in the sand‐bottom stream supported a more diverse (H'), richer (S) and more equitably distributed (J') insect fauna than did the autumn leaves.

We discuss the simultaneous lack of fresh leaf loss and the presence of more complex insect communities on those leaves during the first 26 days of the study. Invertebrates in both mid‐latitude heterotrophic streams and in tropical lowland wet forest streams may rely on fresh leaf inputs, which have received little attention.
Limnological investigations on the Rosetta branch of the Nile. I. Environmental conditions
Authors: SAAD MASSOUD A. H. , ABBAS MAHDI H.
Published: May 2006

SUMMARY.

Seasonal and local variations of some environmental conditions in the Rosetta branch of the River Nile are reported. The lowest air and water temperatures were recorded in January (winter) and the highest in July (summer). Slight decrease in water temperatures with depth is related to solar heating and mixing processes. The pH values, averaging between pH 7.5 and 8.2, showed seasonal changes which, in the main, may be related to photosynthesis.

The seasonal average chlorosity values showed very wide variation, due to fluctuations in the discharge rate of the River Nile and its effect on the estuarine sea water. Sharp increase in chlorosity values with depth at the estuarine stations was produced by the less dense river water, flowing over denser tongues of sea water. In January, however, the maximum discharge flushed out the sea water.

Minimum oxygen saturation values occurred in January and the highest values of dissolved organic matter were obtained in July. Both of these will be shown in a later publication to be related to phytoplankton abundance. Increase in dissolved organic matter near the bottom was common and is interpreted as due to the more complete decomposition of descending dead organisms and the release of organic matter from the bottom deposits.
The macroinvertebrate fauna of an acid‐stressed headwater stream system in the Adirondack Mountains, New York
Authors: SIMPSON K. W. , BODE R. W. , COLQUHOUN J. R.
Published: May 2006

SUMMARY.

The Silver Run system in the Adirondack Mountains of New York includes three first‐order streams with very different pH regimes: one moderately acidic (pH 5.8‐7.2), the others much more so (pH generally 4.4‐5.0)

The less acidic (acidophilic) site yielded a relatively diverse, well balanced fauna, with at least 10% each of midges, mayflies, stoneflies and elmid beetles. Ephemerella funcralis (Ephemeroptera) and Oulimnius latiusculus (Coleoptera) were dominant in this community. They appear to be among the most acid‐tolerant species of their respective families and may become abundant under moderately acidic conditions. Their absence or low abundance in the more acidic tributaries of the Silver Run system suggests that they arc eliminated as acidification intensifies, These species therefore may he useful indicators of advancing acidification.

The more acidic (acidobiontic) communities contained fewer Hum half as many taxa as the acidophilic communities, contained few elmid beetles or mayflies, and were heavily dominated In stoneflies. Leuctra feiruinea and Isopecrla sp. were dominant, comprising.56‐86% of the individuals. Other common constituents included black flies (Simuliumn gouldingi and S. venustum) and the caddisfly Rhyacvphila fuscula.
Macrophyte‐gastropod associations: observations and experiments on macrophyte choice by gastropods
Authors: LODGE DAVID M.
Published: May 2006

SUMMARY.

The abundance and microdistribution of thirteen gastropod and ten macrophyte species were monitored over 2 years in a 1 ha shallow eutrophic pond near Oxford, England. While areas of allochthonous leaf litter supported a depauperate and nondistinctive gastropod fauna, three different macrophyte habitats supported more diverse and distinctive assemblages of gastropods.

Most gastropod species were clearly more abundant (number m‐2pond bottom) on one macrophyte type than on other substrates. One exception, the limpetAcroloxus lacustris(Linn.) was abundantion both the water lilyNymphaea albaL. and on emergent macrophyles.Planorbis vortex(Linn.) was associated with graminoid emergent macropytes, especiallyGlyceria maxima(Hartm.) Holmberg, whileLymnaea peregra(Mull.) was associated with submersed macrophytes, perhaps more particularly withElodea canadensisMichx.

The association of, 4.lacuxtriswithN. albaand emergent macrophytes is perhaps explained by constraints of the morphology of the limpet requiring a relatively broad smooth substrate for attachment and locomotion.

The reason for the associations ofP. vortexwith G.maxima, and ofL. peregrawithE.canadensisare less obvious. Experiments giving each snail species a choice between the two macrophytes showed thatP. vortexregularly exhibited a preference for G.maximabut failed to reveal substrate selection byL. peregra.Neither snail species affected the macrophyte choice of the other. The results suggested thatL. peregradid not behave naturally in experiments.

The preference for G,maximabyP. vortexwas not affected by prior conditioning of the plant by the snail, but was affected by the emergent nature of G.maximaand by the presence/absence of a natural periphyton assemblage and associated detritus.

The distribution ofA. lacustrisis probably determined by the physical structure of the substrate, while that ofP. vortexis determined by the presence and quality of epiphytic periphyton‐detritus. The observations and experiments withL. peregrareported here leave the reasons for its distribution in doubt.
Diel feeding ecology of the nymphs of Aeshna multicolor and Lestes unguiculatus (Odonata)
Authors: JOHNSON JAMES H.
Published: May 2006

SUMMARY.

Diel feeding periodicity and diet composition of nymphs of Aeshna multicolor and Lestes unguiculatus were examined at 6 h intervals in a small pond. Feeding intensity of A. multicolor increased from 06.00 hours to approximately 18.00 hours whereas food intake by L. unguiculatus was uniformly high between 12.00 and 18.00 hours. Feeding of both species was reduced during the night.

Diel variation in diet composition was substantial in each species. Chironomid larvae were the major prey (48.9%) in the diet of A. multicolor. Zooplankton, mainly cladocerans (42.0%) and ostracods (21.1%), were the principal prey of L. unguiculatus. Detritus composed a substantial portion of the diets of both species.

Diet overlap (Cλ) at each 6 h interval was high (0.43–0.72) when detritus was included in the calculation and was low (0.48–0.54) when detrital material was omitted.
Effects of phosphorus and nitrogen enrichment on the yield of some strains of Stigeoclonium Kütz. (Chlorophyceae)
Authors: de VRIES PIERRE J. R. , de SMET STEPHAN J. M. , van der HEIDE JOOP
Published: May 2006

SUMMARY.

The combined effect of nitrate and phosphate concentrations on the yields of five selected strains of Stigeoclonium is demonstrated in a synthetic medium as well as in natural waters.

Increase of yield after addition of one nutrient depends on the concentration of the other. A graphic growth model based on the experiments in synthetic medium is presented, which allows prediction of yields at different combinations of nitrate and phosphorus concentrations.

In general, yields in natural waters before and after addition of nitrate and/or phosphate agree with the model. In some cases, other limiting factors appear to be involved.

The possible effects of nitrogen and phosphorus limitation on the phosphorus and nitrogen metabolism of the alga are discussed.

Neither an exponential model (Baule‐Mitscherlich) nor a hyperbolic model adequately describe the interaction demonstrated between nitrogen and phosphorus limitation.
The abundance and distribution of caddisflies (Insecta: Trichoptera) caught by emergence traps in the ‘Ritrodat’ research area of the Lunzer Seebach (Lower Austria) from 1980 to 1982
Authors: WARINGER J. A.
Published: May 2006

SUMMARY. 1. Adult Trichoptera were caught during 3 years (1980–82) in the ‘Ritrodat’ research area of the Upper Lunzer Seebach. a mountain brook near Lunz. Lower Austria, using a set of thirty pyramid type emergence traps. During the three collecting periods (112 collecting days) a total of 1810 specimens were caught. The most abundant species were Micrasema minimum McL. (Brachycentridae). Rhyacophila vulgaris Pictet (Rhyacophilidae), and the three Iimnephilid species Potamophylax cingulatus Steph., Allogamus auricollis Pictet and Ecclisopteryx guttulata Pictet.

2. In six species (Micrasema minimum, Rhyacophila vulgaris, Atlogamus auricollis, Ecclisopteryx guttulata, Drusus biguttatus Pictet, Chaetopteryx fusca Brauer) the sex ratio was significantly different from 1:1. In Micrasema minimum 422 females were caught but only three males.

3. In each year there were peaks in total emergence in early summer and early autumn.

4. The length of the emergence period of the most abundant species ranged from 38 days in Micrasema minimum to 210 days in Rhyacophila vulgaris (mean values 1980–82); there was also a difference in the intensity of emergence in these species: the percentage of time required for 50% of the animals to emerge (0%=onset of emergence, 100%= emergence completed) was 16% in Allogamus auricollis but 71% in Rhyacophila vulgaris (mean percentages 1980–82).

5. The distribution pattern of individuals per trap was tested against a Poisson distribution; in all three years the distribution was contagious.

6. The dry weight of specimens of Drusus biguttatus, Micrasema minimum. Ecclisopteryx guttulata and Wormaldia copiosa McL. was measured and. together with published dry weight values of other species (Malicky, 1976), these data were used to estimate the biomass emerging annually of twenty‐three species of Trichoptera (99.2% of emergence, 1980–82). This was equivalent to 35.3 kJ m−2 in 1981 and 32.5 kJ m−2 in 1982.
An indirect procedure for the estimation of assimilation efficiency of aquatic insects
Authors: PANDIAN T. J. , MARIAN M. PETER
Published: May 2006

SUMMARY. 1. From forty‐five values reported for twenty species of aquatic insect species, it was found that the nitrogen content (N) of the food was significantly and positively correlated (r=0.97. P<0.001) with assimilation efficiency (Ase).

2. Therefore, the Ase of aquatic insects can be predieted, if the nitrogen content of the food is known, using the equation: Ase (%)=9.29+8.82N.
Stream hydraulics as a major determinant of benthic invertebrate zonation patterns
Authors: STATZNER BERNHARD , HIGLER BERT
Published: May 2006

SUMMARY. 1. Studies on the zonation of benthic fauna in fourteen streams situated in a variety of latitudes from Alaska to New Zealand have been evaluated.

2. We suggest that physical characteristics of flow (‘stream hydraulics’) are the most important environmental factor governing the zonation of stream benthos on a world‐wide scale.

3. From the source to the mouth of a stream, zones of transition in stream hydraulics' occur, to which the general pattern of stream invertebrate assemblages can be related. In these zones benthic community stability and resilience must be different from those upstream and downstream of the hydraulic transition zones.
Diel activity of a boreal water beetle (Dytiscus alaskanus: Coleoptera; Dytiscidae) in the laboratory and field
Authors: AIKEN R. B.
Published: May 2006

SUMMARY. 1. The diel activity of Dytiscus alaskanus (Coleoptera: Dytiscidae) was studied by trapping in the field and by direct observation of behaviour (mounting, chasing, grappling, swimming and surfacing) in the laboratory.

2. In the field in the number of beetles trapped during the dark hours was approximately fifty‐fold greater than trapped during daylight hours.

3. In the laboratory, there was a marked increase in mounting, chasing and grappling when the ambient light level fell below 0.41mm−2. Swimming showed only a slight diel pattern and surfacing none at all.
Colloidal and dissolved organic carbon dynamics in undisturbed boreal forest catchments: a seasonal study of apparent molecular weight spectra
Authors: LOCK MAURICE A. , FORD TIME.
Published: May 2006

SUMMARY. 1. Colloidal and dissolved organic carbon (CDOC) was monitored in six pristine boreal rivers in Northern Quebec, Canada, using ultrafiltration to obtain apparent molecular weight spectra.

2. The concentration and proportional contribution of small (<1K) molecular weight material (potentially microbially labile) and high (0.7μm to 300 K) molecular weight material was not significantly different between streams of order 2–9.

3. The dominant component of CDOC (0.7μm to 300 K fraction) was probably derived in streams other than first order, from surface or sub‐surface run‐off, whereas a peak concentration in the <1 K fraction during August was probably due to autochthonous exudates.

4. The two first order streams included in this survey had very low CDOC concentrations. However, further work on twelve other first order streams showed that they had high concentrations and we consider that this is the more typical situation. The finding offered a potential explanation for the otherwise anomalous longitudinal CDOC distribution pattern throughout the study area.
The role of fungi in the diet of the amphipodGammarus pulex(L.): an enzymatic study
Authors: CHAMIER ANNE‐CAROLE , WILLOUGHBY L. G.
Published: May 2006

SUMMARY.1. Sets of tenGammarus pulexfed on controlled diets of sterile alder leaves, or fungal mycelium, or alder leaves incubated for 10 days with an aquatic hyphomycete, were assayed for cellulase, β‐1,3‐glucanase an d chiitinase activity and compared with (a) animals taken directly from the stream, (b) animals starved for 2 days, and (c) enzyme activity in fungal mycelium.

2. Gut enzyme activity was compared on natural substrates of sterile leaves, mycelium and inoculated leaves as well as on model substrates.

3.G. pulexsecretes an endogenous coupled cellulase system capable of degrading native cellulose in plant cell walls. It also secretes β‐1,3‐glucanase and chitinase capable of degrading fungal cell walls thus affording access for gut enzymes to cell contents.

4. Secretion of enzymes active on native cellulose is enhanced on a diet of leaves already partially degraded by fungal enzymes. Gut enzymes extract more reducing sugar from this substrate than from sterile leaves. Specific enzyme secretion is enhanced by the presence in the diet of exposed, accessible substrates. Fungal enzymes do not appear to contribute to the digestive processes ofG. pulex.
Antarctic stream ecosystems: physiological ecology of a blue‐green algal epilithon
Authors: VINCENT WARWICK F. , HOWARD‐WILLIAMS CLIVE
Published: May 2006

SUMMARY. 1. Several dozen summer meltwater streams are located in the McMurdo Sound region (c. 78°S 165°E) of southern Victoria Land. They are characterized by a highly variable flow regime at diel, seasonal and annual times caleis; wide fluctuations in temperature and nutrient content; and a very simple epilithic community of cyanophytes (Nostoc spp., Oscillatoriaceae), bacteria, fungi and microherbivores.

2. The epilithon survives the dark Antarctic winter as dry, frozen mats which provide a large inoculum for growth the following summer. This overwintering assemblage retains a high metabolic capacity and responds rapidly to rehydration.

3. In a series of artificial substrate experiments, biomass accumulation rates were generally less than 0.1 In units d−1. Colonization and growth on the substrates was inversely related to the suspended sediment load of the stream. There was also a visual correspondence between per cent algal cover of the natural streambed and the clarity of the streamwater. Sloughing losses may limit community biomass, particularly in the turbid flowing waters.

4. During running water conditions the mature communities had very low gross photosynthetic rates per unit chlorophyll (<0,1 μg C (μg chl a.h)−1 and per unit carbon (<0,2 μg C (mg biomass C.h)−1). Respiration was generally a high percentage (up to 92%) of gross photosynthesis, which probably reflected the high population densities of microheterotrophs in the community.

5. The floristically simple epilithic mats slowly accumulate to extreme biomass levels (>20 μg chl a cm −2, <20 mg C cm−2). Production rates per unit biomass are low, probably in response to the cold temperatures of the Antarctic stream environment, and the accumulated biomass represents several seasons of growth.
Population ecology of the commensal chironomid Epoicocladius flavens on its mayfly host Ephemera danica
Authors: TOKESHI MUTSUNORI
Published: May 2006

SUMMARY. 1. Epoicocladius flavens (Diptera: Chironomidae) has a 1‐year life cycle in the River Tud in eastern England. Pupation and adult emergence occurred from the end of May until the beginning of September. Larval growth was rapid during the summer but thereafter almost ceased until the following April.1 Unlike other chironomids, the population density of E. flavens was very stable and remained at around 1000m −2 all through the year.

2. Ephemera danica (Ephemeroptera: Ephemeridae), the host of E. flavens, has a 2‐year life cycle. The proportion infested was about 90% for the older host year‐class and less than 30% for the younger year‐class from autumn until the following summer. A rapid increase in infestation occurred during the summer as a result of hatching of the E. flavens eggs. Of those infested, the older year‐class hosts harboured two or three larvae, on average, whereas the younger ones had only one.

3. When host year‐classes were treated separately, the frequency distribution of the number of E. flavens per host each month did not depart significantly from a Poisson distribution. Younger instars departed from a Poisson distribution more frequently than older instars.

4. The majority of E. flavens larvae attached to the gills of their hosts. As the instars progressed, increasing proportions were found on the thorax, legs and tails. The thorax was the preferred site for fourth instar larvae.

5. Enhanced chance of survival, rather than the supply of detrital food particles which collect on the host's body, is considered as an important benefit to accrue to E. flavens from this commensalism.