bluuebunny/crossref_metadata_2025 huggingface dataset:
Bryophytes as invertebrate habitat in two New Zealand alpine streams
Authors: SUREN ALASTAIR M.
Published: May 2006

SUMMARY.
1. Quantitative samples of lotic benthic invertebrates and associated organic material were taken monthly for 18 months from bryophyte and gravel habitats in two New Zealand alpine streams in Arthur's Pass National Park, South Island; an unshaded site above the tree‐line and a shaded stream flowing through mountain beech forest. This was to assess the ecological role of bryophytes in these habitats and to determine the relative effects on the fauna of algal and detrital resources.

2. Bryophytes were confined to stable bedrock substrata in shallow (mean depth of 4.5 and 10.5 cm), fast water (mean velocity of 0.21 ms−1 and 0.30ms−1) at the unshaded and shaded sites. Mean ash‐free dry weight (AFDW) of organic material from bryophyte areas was similar at the unshaded and shaded sites (335.6 and 272.4 gm−2). Low stream‐bed stability of the gravel areas resulted in poor retention of organic matter, with average AFDW of 59.1 and 77.9 gm−2 at the unshaded and shaded sites, respectively. Periphyton biomass, however, was much higher at the unshaded site.

3. Within bryophytes, water velocity is reduced and large quantities of periphyton and detritus accumulate. This explains the greatly enhanced invertebrate densities within bryophytes (218400 and 53500 individuals m−2), compared with gravel areas (20900 and 7400 individuals m−2) in the unshaded and shaded sites, respectively. The higher invertebrate densities at the unshaded site reflect greater periphyton biomass there.

4. Invertebrate densities followed clear seasonal patterns, attributable to changes in chironomid densities. These reflected larval chironomid hatching following adult oviposition. This illustrates the importance of these plants as oviposition sites, and as protective nurseries for small larvae where they can obtain shelter during floods and consume the abundant food sources available to them.

5. DECORANA ordination revealed taxonomically distinct invertebrate communities in each stream, and in bryophytes and gravels. Several taxa appeared restricted to either the unshaded site (e.g. Acroperla spiniger and Hydrobiosis silvicola) or the shaded site (e.g. Zelolessica
The impact of three‐spined sticklebacks on the Zooplankton of a previously fish‐free pool
Authors: PONT D. , CRIVELLI A. J. , GUILLOT F.
Published: May 2006

SUMMARY.

In the Camargue (southern France), most invertebrates inhabiting temporary shallow oligohaline marshes and pools are large‐bodied, conspicuous and defenceless taxa that are restricted to fish‐free environments. Management practices, by creating drainage canals, strongly affect the invertebrate community by allowing colonization by fish.

Sticklebacks colonizing the study pool were sampled daily and Zooplankton sampling was carried out at weekly intervals. From early October until the pool dried in June, 1365 sticklebacks entered and only 139 stickleback's fry and seven adults left the pool. Zooplankton abundance was high during the whole study period with a mean density of 1360 ind. 100cm−2. Larger forms (Daphnia magna, Simocephalus vetulus, Arctodiaptomus wierzejskii) quickly disappeared after the first wave of sticklebacks entered the pool in November. Subsequently, smaller species (Diacyclops bicuspidatus odessanus, Chydorus sphaericus and ostracods) replaced the larger ones until the pool dried.

Food selectivity of sticklebacks and daily Zooplankton consumption were investigated under experimental conditions within the pool in spring. After introduction of sticklebacks, densities of Zooplankton species dropped quickly (D. b. odessanus, C. sphaericus) with the exception of Ostracoda. Estimates of daily Zooplankton consumption by adult sticklebacks varied between 2.8 and 10.7% of fish body weight. Examination of gut contents showed that fry mainly ingested Chydorus sphaericus.

Given that the stickleback is an annual species in the Camargue, and that few fry are able to leave the pool due to the early drying out, the colonization of such a former fish‐free pool is not beneficial for the stickleback population. However, a more serious effect of such colonization is the progressive local extinction of the most typical Zooplankton species inhabiting these formerly fish‐free environments.
Invertebrate colonization of a new, man‐made stream in southern Sweden
Authors: MALMQVIST BJÖRN , RUNDLE SIMON , BRÖNMARK CHRISTER , ERLANDSSON ANN
Published: May 2006

SUMMARY.

The invertebrate colonization of a man‐made stream, Flugströmmen, in southern Sweden was monitored for 18 months in 1988 and 1989. Benthic samples were taken on twelve occasions from three sites (upstream, middle and downstream) and community structure was compared with that at ten natural, permanent reference sites nearby.

The number of species colonizing increased rapidly during the first 3 months. The increase was most rapid upstream but levelled off during the second year at this site, while numbers continued to increase downstream.

Simuliid species were the earliest colonizers and reached high densities at upstream and middle sites during the first year. Ephemeropteran and plecopteran species also occurred early on, whereas Coleoptera, Odonata and Trichoptera were, on average, slower to colonize. Blackfly densities decreased upstream after the first year and hydropsychids became numerically dominant.

The colonization order of functional feeding groups was as predicted: filter feeders first, grazers/collectors intermediate, predators and shredders last.

After a year, the community structure in Flugströmmen closely resembled that in lake‐outlet streams situated in the area, although communities at the three sites within the stream were most similar to one another.

The possible role of competitive and predatory processes in determining the observed successional patterns are discussed.
Growth enhancement of the macrophyte Ceratophyllum demersum in the presence of the snail Planorbis planorbis: the effect of grazing and chemical conditioning
Authors: UNDERWOOD GRAHAM J.C.
Published: May 2006

The effects of epiphyton grazing and nutrient recycling by the freshwater snail Planorbis planorbis on the growth of the macrophyte Ceratophyllum demersum were examined in laboratory experiments.

Ceratophyllum plants grown in the presence of snails, or in water chemically conditioned by snails, were significantly longer, had more healthy nodes of leaves, and more growing tips than Ceratophyllum plants grown in isolation. There were no significant differences between the growth of plants that were grazed by snails, and those plants which received water chemically conditioned by snails.

Adult P. planorbis released 3.74 × 10−4μg phosphate, 23.9 × 10−4μg nitrate, 4.38 × 10−4μg ammonia, and 0.79 × 10−4μg of urea mg−1 wet weight of snail h−1. Measurements of these chemicals in the experimental systems suggested that ammonia was an important nutrient in stimulating the growth of Ceratophyllum.

Removal of epiphyton by grazing snails significantly prolonged the life of individual Ceratophyllum leaves compared to ungrazed leaves.
Patch distribution of interstitial communities: prevailing factors
Authors: DOLE‐OLIVIER M.J. , MARMONIER P.
Published: May 2006

1. Community structure of interstitial invertebrates was studied in the sediments of two gravel bars in a bypass section of the Rhone River (France), in relation to hydrological patchiness and to major geomorphological characteristics of the sampling areas. Hydrological patchiness was characterized by upweiling or downwelling zones while geomorphological characteristics were concerned mainly with position towards the head or tail of each bar, which presented different environmental conditions.

2. Longitudinal profiles of the two bars, at 0.5 and 1.0m below the substrate surface, were compared. At each station 10‐l samples were taken using mobile standpipes and a Bou—Rouch pump. During low‐water conditions, replicate samples were taken in both the head‐bar and tail‐bar regions to confirm the results. Physicochemical parameters were used to differentiate surface water from ground water (conductivity, alkalinity, silica, nitrates, sulphates and temperature) and to detect hydrological patterns.

3. Two different situations were observed within the gravel bars. In the first one, the upweiling zone was situated in the tail bar and downwelling zone in the head bar. The reverse was observed in gravel bar 2 where the head‐bar region formed the upweiling zone and the tail‐bar region formed the downwelling zone.

4. In the first situation, the distribution of interstitial assemblages corresponded with the observed hydrological patterns: epigean fauna characterized the downwelling zone and stygofauna characterized the upweiling zone. The interstitial fauna seemed to be strictly linked to the mode of water movement within the sediments. Hydrological patchiness therefore appeared to be an important factor for the structure of interstitial assemblages.

5. In the second case there was no relationship between the hydrological and the biological pattern. Epigean fauna and hypogean fauna were scattered all along the gravel bar. These results suggest that geomorphology is a second important factor governing the composition and structure of interstitial assemblages. A precise structure was obtained when hydrological and geomorphological characteristics were superimposed (case 1). When they were opposed (case 2) all the species responded according to their individual ecological requirements.
Physiological characteristics of inorganic nitrogen uptake by spatially separate algal communities in a nitrogendeficient lake
Authors: REUTER JOHN E. , AXLER RICHARD P.
Published: May 2006

1. The physiological characteristics of nitrogen uptake by sublittoral and eulittoral (splash zone) epilithic periphyton as well as epipelic periphyton in N‐deficient Castle Lake, California were determined by evaluating the half‐saturation constants (Kt) and initial slopes (Vmax/Kt) of uptake kinetics curves. These results were compared to similar studies of phytoplankton nitrogen uptake in this lake.

2. The strategies of nitrogen uptake differed among the various communities and were largely determined by the proximity of each to pools of available dissolved inorganic N (DIN).

3. The sublittoral algae did not have a high biological affinity for either NH4 or NO3 and depended on nitrogen fixation for their N supply. The eulittoral community showed an increased capacity for DIN uptake at low substrate concentration, but not as high as measured for the phytoplankton community. Epipelic algae live immediately adjacent to a large pool of interstitial sediment NH4 and showed no physiological adaptations for surviving in a N‐deficient environment.

4. Kt values for all benthic communities were approximately two orders of magnitude greater than ambient substrate levels. In contrast, the half‐saturation constants for NH4+ NO3 uptake by phytoplankton were very similar to in situ levels of these nutrients.
Plant—herbivore interactions in streams near Mount St Helens
Authors: LAMBERTI G.A. , GREGORY S.V. , HAWKINS C.P. , WILDMAN R.C. , ASHKENAS L.R. , DENICOLA D.M.
Published: May 2006

1. In four separate field experiments near Mount St Helens (Washington, U.S.A.) during 1986, the grazing effects of two large benthic herbivores, tadpoles of the tailed frog Ascaphus truei and larvae of the caddisfly Dicosmoecus gilvipes, were investigated using streamside channels and in‐stream manipulations. In the experimental channels, abundances of periphyton and small benthic invertebrates declined significantly with increasing density of these larger herbivores.

2. In eleven small, high‐gradient streams affected to varying degrees by the May 1980 eruption, in‐stream platforms were used to reduce grazing by A, truei tadpoles on tile substrates. Single platforms erected in each tributary and compared to grazed controls revealed only minor grazing effects, and no significant differences among streams varying in disturbance intensity (and, consequently, tadpole density). However, results probably were confounded by high variability among streams in factors other than tadpole abundance.

3. Grazing effects were further examined in two unshaded streams with different tadpole densities, using five platforms per stream. In the stream with five tadpoles m−2, grazing reduced periphyton biomass by 98% and chlorophyll a by 82%. In the stream lacking tadpoles, no significant grazing effects were revealed. Low algal abundance on both platforms and controls, and high invertebrate density in that stream (c. 30000m−2) suggests that grazing by small, vagile invertebrates was approximately equivalent to that of tadpoles.

4. The influence of large benthic herbivores on algal and invertebrate communities in streams of Mount St Helens can be important, but reponses vary spatially in relation to stream disturbance history, local environmental factors, and herbivore distributional patterns and abundance.
Patch dynamics of the stream macrophyte, Callitriche cophocarpa
Authors: SAND‐JENSEN KAJ , VINDBÆK MADSEN TOM
Published: May 2006

1. We examined changes in position and growth of Callitriche cophocarpa patches in a shallow section of a small Danish stream during the main expansion of plant cover between April and June. Mean upstream growth of patches was only 7.5% of downstream growth. The mean growth rate was 1,02cm day−1 in length and 0.55 cm day−1 in width and the growth rates were not significantly dependent on patch size. For patches with an area (A) above 100cm2, the growth rates in patch area (dA/dt) was proportional to patch circumference and thus √Aand the relative growth rate (dA/dt A−1) was inversely proportional to √A.The smallest patches (<100cm2), however, expanded less than expected because of their combined tendency to grow more slowly in patch length and width than larger patches.

2. The expansion of plant cover will be much more rapid in many medium‐sized patches compared to few large patches of a similar combined area, because internal selflimitation by light and space is partially relieved in smaller patches. We anticipate that recruitment and mortality of new‐formed patches are critical steps preceding areal expansion. Quantification of these processes are needed fully to evaluate patch dynamics and space occupation.
The influence of periphyton, detritus and shelter on invertebrate colonization of aquatic bryophytes
Authors: SUREN ALASTAIR M. , WINTERBOURN MICHAEL J.
Published: May 2006

1. Artificial bryophytes were placed in a shaded and an unshaded New Zealand alpine stream to investigate why invertebrates colonized these structures and, by inference, real plants. Three experiments were conducted to investigate the influence of (i) periphyton and detritus (ii) shelter, and (iii) time, on invertebrate colonization.

2. In the first experiment, seven taxa at the unshaded site displayed a preference for substrata with high detrital and periphyton biomass, presumably reflecting a food relationship. At the shaded, less stable site, only two taxa displayed such a relationship.

3. Reducing substratum ‘stem’ density (i.e. ‘shelter’) in the second experiment had little effect on the biomass of periphyton at each site, and only at the shaded site was detrital biomass reduced on low‐density substrata. Abundances of most of the twenty‐two invertebrate taxa analysed were unaffected by stem density reduction: densities of only four taxa at the unshaded site, and two at the shaded site were reduced.

4. Stepwise multiple regression showed that invertebrate abundance was little affected by stem density at either site. Indeed, shelter was the primary factor influencing abundance of only two of twenty‐two taxa at the unshaded site, and none at the shaded site. Abundances of most taxa were related to periphyton or detrital biomass at each site.

5. The third experiment investigated temporal relationships between invertebrate density, periphyton and detrital biomass, and exposure time of artificial bryophytes. Regression analyses indicated that of twenty‐two taxa at the stable, unshaded site, eight were influenced by periphyton biomass, three by detrital biomass, and two by exposure time. At the unstable shaded site, abundances of only eight of twenty‐two taxa were significantly related to the measured variables, of which exposure time was most important (four taxa).
Biogeochemistry of billabong sediments. II. Seasonal variations in methane production
Authors: SORRELL BRIAN K. , BOON PAUL. I.
Published: May 2006

1. We examined the temporal (seasonal and diel) and spatial variation in methane flux from sediments of a billabong in south‐eastern Australia, and related it to variations in the rate of organic matter decay, concentration of interstitial metabolites, and sediment redox.

2. Total gas ebullition ranged from <2 to >59mlm−2h−1, and was highest in the summer months when water temperatures were >25°C. These rates are equivalent to carbon fluxes of about 16–30gC—CH4m−2yr−1. Ebullition was greater from unvegetated sediments than from sediments colonized by the emergent macrophyte Eleockaris sphacelata, R, Br. or the submerged macrophyte Vallisneria gigantea Graeb. There were no consistent differences in the rate of ebullition over the day and the night.

3. Methane accounted for about 42–45% of total sediment gas in the vegetated sediments, but about 60% in the unvegetated sediments. These ratios did not vary greatly throughout the year. Carbon dioxide was a minor component of sediment gas, usually comprising <5% of the total. Carbon dioxide contents were highest in summer, especially in unvegetated and E. sphacelata beds.

4. In vitro methanogenesis ranged from 3 ± 0.9 to 106 ± 30 nmol g(dry weight)−1 h−1, being highest in summer and lowest in winter. Added acetate (5mM) increased the rate of methanogenesis by up to 10‐fold, with the effect being greater in summer than winter. Generally, added acetate had least effect in E. sphacelata sediments. The maximum rate of in vitro methanogenesis with added acetate was 243 ± 57 nmolg(dry weight)−1 h−1.

5. Ebullition was highly correlated with the rate of in vitro methanogenesis, with a rime lag of about 4 weeks. About 35–60% of benthic in vitro methanogenesis could be accounted for by ebullitive loss: the remainder was presumably lost via diffusion, flux through emergent plants or by oxidation. The rate of organic‐matter degradation, assessed with amylopectin azure, varied throughout the year, but there was no clear relationship between ebullition and organic‐matter decay.

6. Concentrations of interstitial ammonium, which also varied seasonally, ranged from 1 ± 0.2 to 13 ± 1 mgNl−1. There was no clear relationship between ebullition rates and ammonium concentrations, Redox potential was most positive in the E. sphacelata sediments, but there was little consistent difference in the redox potential of V. gigantea and unvegetated sediments. Redox potential appeared not to be a controlling factor in methane release.
Carotenoids, photoprotection and food web links in Lake Baikal
Authors: GREEN J. , KOSLOVA T.
Published: May 2006

1. Carotenoids were extracted from macrophytes, sponges, amphipods, fish stomachs, fish livers, fish ovaries and zooplankton in samples collected from various depths in Lake Baikal.

2. Acetone extracts from macrophytes showed a ratio of absorption at wavelengths of 430 and 665 nm consistently in the range 2.1–2.5. Sponges from very shallow water (1.5m) showed a similar ratio, but a sponge from 25m gave a ratio of 6.6, indicating a reduction in the concentration of chlorophyll relative to carotenoids.

3. Extracts from amphipods gave some support for the photoprotection hypothesis, with lower concentrations of carotenoids in amphipods from the deepest water.

4. Some fish took high concentrations of carotenoids into their stomachs, but the concentrations found in their Livers and ovaries were very much lower. Fish appear to be one of the carotenoid sinks in Lake Baikal.

5. Plankton samples showed an apparent inversion, with the highest concentration of carotenoid in the deepest sample, but this was a result of the sinking into deep water of the filamentous diatom Melosira.
Enhancing litter retention in streams
Authors: DOBSON MIKE , HILDREW ALAN G. , IBBOTSON ANTON , GARTHWAITE JULIA
Published: May 2006

1. Dobson & Hildrew (1992) enhanced leaf litter retention in four streams by placing small plastic leaf traps in manipulated stretches. Litter standing crop and the local abundance of shredders was increased, relative to control stretches, in all sites save one which was naturally highly retentive. These results could indicate food limitation in these detritivores, but might have occurred in response to an altered hydraulic regime or increased habitat availability.

2. Shear stress was characterized in the four streams manipulated by Dobson & Hildrew (1992). This was carried out on three occasions in both the manipulated and control stretches of each stream. While there was evidence that the manipulation of retention did influence near‐bed flows, these changes were not consistent enough to explain the response of shredding invertebrates to experimental manipulation.

3. In a further experiment, we exposed real and artificial leaves to colonization by invertebrates. Shredders, collectors and predators all colonized real leaves in preference to plastic substitutes.

4. These results support the hypothesis that detritivorous macroinvertebrates exploit aggregations of leaf litter primarily as sources of food, rather than as habitat or habitat modifier.
Effects of predators and food availability on activity and growth of Chironomus tentans (Chironomidae: Diptera)
Authors: MACCHIUSI FRANK , BAKER ROBERT L.
Published: May 2006

1. Larvae of Chironomus tentans Fab, decreased the amount of time they spent outside their tubes as the presence of predatory pumpkinseed sunfish (Lepomis gibbosus L.) increased. Greatest reductions in activity occurred at low levels of fish presence; above a certain level further increases in fish presence had little effect on activity.

2. Whether the pattern of predator presence was ordered or random had no effect on larval behaviour. Larvae did not habituate to short‐ or long‐term predator presence.

3. Larvae were less active when more food was available and predator‐induced reductions in activity were negatively related to food availability. Larval activity was much higher in the dark than it was in the light.

4. Over 7 days, presence of fish reduced the proportion of third‐instar larvae that moulted but did not affect head width or dry mass; low food availability reduced the number of larvae that moulted as well as head width and dry mass of larvae in the fourth instar.

5. Results indicate that the behavioural response of larval chironomids to predator presence depends strongly on environmental conditions and that estimating the developmental costs of these behavioural responses under field conditions will be complicated.
Distribution and feeding behaviour of field populations of the water cricketVelio, caprai(Hemiptera)
Authors: ERLANDSSON ANN , GILLER PAUL S.
Published: May 2006

1. The distribution of individuals, prey capture success and prey choice were studied in a water cricket (Velia caprai) population in southern Ireland. Groups of different sizes were observed in the field during the summer and all potential prey animals entering the groups were counted. Surface drift samples were collected to assess the proportion of profitable prey items.

2. Two types ofVeliagroups were observed: mixed groups (adults and juvenile instars 4 and 5) and juvenile groups (instars 1–3), A greater proportion of the available prey was captured by the mixed groups.

3. Individuals in large groups had a lower capture rate than individuals in small groups.

4. No differences in capture rates could be found between males, females and juveniles, but differences in prey choice were apparent. Females captured more large prey than expected.

5. Water cricket distribution in the stream did not follow the ‘ideal free’ model; too few individuals were found at the most profitable sites. Food might not be the limiting factor during summer, and other factors such as intraspecific interference and predator avoidance could be more important.
The nature of the fluid boundary layer and the selection of parameters for benthic ecology
Authors: CARLING P.A.
Published: May 2006

1. The nature of flow structure close to a river bed is reviewed and suggestions made as to appropriate equations to apply to given hydrodynamic regimes.

2. It is emphasized that in natural rivers the laminar sublayer observed immediately above the bed in some experimental studies is completely disrupted for flows characterized by high turbulence levels.

3. Instead of resorting to direct topographical measurement of bed undulations, the roughness of the river bed also can be quantified using hydraulic data obtained from velocity profiles.

4. Ambuhl's experimental findings of 1959 underpin modern ecological research into the nature of the benthic boundary layer. Common misconceptions concerning Ambuhl's contribution are corrected and it is shown that his results only apply to certain prescribed hydrodynamic conditions.

5. The adoption of a consistent approach to describing the benthic boundary layer is to be preferred, so that diverse studies can be usefully compared.
Kinetic changes in surface phosphatase activity of Synedra acus (Bacillariophyceae) in relation to pH variation
Authors: HANTKE BIRTE , MELZER ARNULF
Published: May 2006

The kinetics of surface phosphatase activity (PA) in the diatom Synedra acus were studied at low substrate concentrations that are frequently encountered in freshwaters and pH variations typical of hardwaters, ranging from pH 7 to pH 9. Higher pH resulted in higher values for the half saturation constant (Km) and the maximal velocity (Vmax).

 The pH optimum of PA was shown to be a linear function of the logarithm of substrate concentration.

 Similar slopes of Michaelis‐Menten curves at different pHs in the range of low substrate concentrations indicate that the species is well adapted to hardwaters. The rate of release of phosphate from enzymaticaliy hydrolysable phosphorus was calculated from Michaelis‐Menten kinetics for lake‐water samples dominated by S. acus. Algal surface phosphatases were responsible for the hydrolysis of 1.54–1.64 nm min−1 although incubation was performed at a lake temperature of only 7.3°C.
Selective predation by Lestes (Odoiiata, Lestidae) on littoral microcrustacea
Authors: HAVEL JOHN E. , LINK JASON , NIEDZWIECKI JOHN
Published: May 2006

Two experimental approaches were used to examine the predation risk of six littoral cladoceran and ostracod species to two size classes of the damselfly Lestes sp. Behavioural observations were conducted in a 2–1 arena and predation rate experiments in 1–1 jars in the laboratory.

 Behavioural observations revealed that attack and capture efficiencies by Lestes were higher on smaller cladocerans (Polyphemus and Ceriodaphnia) than on other taxa. Small Lestes had little success ingesting the small ostracod Cypridopsis, whereas larger Lestes captured and ate it easily.

 Predation‐rate experiments showed that Lestes has a clear preference for smaller cladocerans over both a large cladoceran (Simocephatus) and all three ostracods (Cypricercus, Cyclocypris, and Cypridopsis). Most Lestes were unable to consume the larger Cypricercus.

 Attack rates and predation rates were highly variable among individual predators.

 These data indicate that damselfly larvae are size selective and consume all but very large cladocerans more readily than ostracods.
The effects of prey profitability and habitat complexity on the foraging success and growth of stonefly (Plecoptera) nymphs
Authors: WILLIAMS D. DUDLEY , BARNES JULIE‐ANN , BEACH PHILIPPA C.
Published: May 2006

The feeding behaviour of nymphs of the perlid stonefly Dinocras cephalotes when presented with two different mayfly prey types on different substrates was examined in the laboratory.

 Most of the evidence suggested that Dinocras cephalotes did not choose between Baetis rhodani and Rhithrogena semicolomta as, under identical circumstances: (i) the survival of both prey types was the same; (ii) the predator's overall searching behaviour was similar in the presence of either mayfly, although B. rhodani was pursued more, especially on complex substrates; (iii) the number of attacks on both prey types was the same; and (iv) the intake of dry weight prey biomass over 24 h remained the same, irrespective of prey species.

 The predation efficiency (no. of prey captured/no, of encounters) of D. cephalotes decreased with increasing substrate complexity—but only with R. semicolorata as prey, and also when more than one stonefly was present—but only when B. rhodani was the prey. Predator efficiency was greater at low densities of R. semicolorata but highest at a medium density of B. rhodani.

 Increase in the body weight of D. cephalotes was greater when nymphs were fed a monospecific diet of R. semicolorata compared with one of B. rhodani. This was despite the findings that: (i) nymphs of B. rhodani contained 31.3% more protein (per mg dry body weight) than nymphs of R. semicolorata, whereas the latter contained 81.0% more chitin; and (ii) nymphs of R. semicolorata took 2.7 times as long to consume and almost twice as long to pass through the predator's gut. The longer gut passage time may have allowed a greater assimilation efficiency which may have led to the observed better growth.

 Dinocras cephalotes is thought to feed opportunistically, with a certain daily food biomass intake as its primary need rather than any specific prey preference. Foraging decisions, or opportunities, affect the fitness of individual nymphs and this may be reflected in the wide size range of contemporary nymphs found in field populations. Variation in foraging efficiency by predators and evasion success by prey, across substrate types, is thought to contribute to the well‐known microdistribution patterns of species observed in lotic communities.
The changing ecosystem of a shallow, brackish lake, Hickling Broad, Norfolk, U.K. I. Trophic relationships with special reference to the role of Neomysis integer
Authors: IRVINE KENNETH , MOSS BRIAN , BALES MICHAEL , SNOOK DEBORAH
Published: May 2006

Hickling Broad, a shallow, brackish lake in England, changed from dominance by submerged aquatic plants to dominance by phytoplankton in the 1970s. These changes were ascribed to the effects of guanotrophicatioh by black‐headed gulls, and increased salinity which together resulted in fish kills caused by a toxic alga, Prymnesium parvum. A mysid, Neomysis integer, was believed to be important in switching the system to plankton dominance through its presumed selective feeding on Cladocera and increasing population size as fish predation decreased.

 Studies on laboratory predation rates of the mysid on Cladocera and on the population dynamics, predation rates and diet of the mysid and the populations of the major zooplankter, Eurytemora affinis in the Broad in the 1980s, have shown that the former explanations were incomplete. The mysid could have markedly reduced the cladoceran community, for it has potentially high predation rates, but Cladocera were probably lost through salinization. Neomysis feeds efficiently on Eurytentora affinis, but the latter reproduces rapidly and its populations are unlikely to be controlled by mysid predation. Nauplii and small copepodites are selectively taken. Alternative and probably major food sources for the mysid are periphyton and benthic algae and detritus.

 Roach and bream readily take the mysid but the present fish stock in the Broad is very low and can now exert minimal pressure on the mysid population. An invertebrate predator on the mysid, Palaemometes varians, is also unlikely to have major effects. The former model of the operation of the Broad's ecosystem needs reconsideration in view of the findings.
Restoration of lowland streams: an introduction*
Authors: OSBORNE L.L. , BAYLEY P.B. , HIGLER L.W.G. , STATZNER B. , TRISKA F. , IVERSEN T. MOTH
Published: May 2006

This paper introduces the Lowland Streams Restoration Workshop that was held in Lund, Sweden in August 1991.

 Attenders at the Workshop participated in working groups which discussed and reported on the state of knowledge of stream restoration and identified critical areas of information need. Currently, most restoration efforts are emission‐orientated (i.e. waste‐water management), while the imitation of the geomorphology or of the riparian vegetation of a quasi‐natural or natural reference channel receives less attention.

 Successful stream restoration requires a multidisciplinary approach within a holistic system framework. Monitoring the outcome of past, existing and future steam‐restoration projects is required for information on the feasibility of alternative techniques and approaches.

 It was recommended that systems in pristine condition serve as a point of reference and not as a goal for most stream restoration projects. Restoration goals must be carefully defined so that everyone at every level understands the aim of the project. At the very least, all restoration programmes should consider geomorphic, hydrological, biological, aesthetic, and water quality aspects of the system.

 Restoration programmes should aim to create a system with a stable channel, or a channel in dynamic equilibrium that supports a self‐sustaining and functionally diverse community assemblage; it should not concentrate on one species or group, except at the local level. Preserving the terrestrial ‐aquatic interface by setting aside riparian land corridors is critical to all stages of restoration. Additional information on the temporal and regional variability in important system processes and functions is needed.
Effects of flow and refugia on drift loss of benthic macroinvertebrates: implications for habitat restoration in lowland streams
Authors: BORCHARDT DIETRICH
Published: May 2006

Current stream restoration practices are rarely based on sufficient knowledge of the physical‐habitat requirements of the biota. In this study the drift loss of two lowland stream benthic macroinvertebrates, Gammarus pulex (L.) (Amphipoda, Crustacea) and Ephemerella ignita (Poda) (Ephemeroptera, Insecta), was investigated over gradients of flow forces and abundance of woody debris in laboratory flume experiments.

 The losses by drift of E. ignita and G. pulex increased significantly at median flume shear stresses of approximately 11 and 31 dyn cm−2, respectively.

 Above these critical shear‐stress values the population losses of both species significantly decreased with increasing abundance of stationary woody debris.

 Ephemerella ignita exhibited high population loss in the first period of hydraulic disturbance. Gammarus pulex was affected in a different way, showing an almost constant population loss over time. In contrast to E. ignita, G. pulex used the refugium ‘woody debris’ actively and more efficiently.

 Restoration concepts of lowland running waters have to consider hydraulic disturbance by flow as a key element for potential benthic community recovery.

 Woody debris in the baseflow channel of lowland streams appears to mitigate the impact of hydraulic disturbance to benthic macroinvertebrates caused by rising discharge.
The riparian community of north‐west European lowland streams
Authors: HIGLER L.W.G.
Published: May 2006

Riparian plant communities along lowland streams have been affected by man for the past 15000 years. During this period climatological changes have also taken place. The present situation in north‐west Europe is a result of these influences so that the choice of reference situations is necessarily arbitrary.

 Dominant abiotic factors that influence riparian vegetation are local hydrology and soil composition, and the pH, lime content and nutrient concentration of the feeding ground water.

 Riparian plant communities are described as phytosociological units. Depending on abiotic characteristics, sequences from spring to lower course and from the stream bank to the boundaries of the stream valley are reported. The Pruno‐Fraxinetum association is, and has been for thousands of years, one of the main riparian vegetation types of (lowland) streams.

 In many European countries, restoration projects are being performed or planned. One of the restoration measures is the planting of trees or shrubs along streams as buffer strips. A phytosociological approach, based on knowledge of the local hydrology and nutrient/ion availability, is better by far than the general practice of standard plantation. Such an approach requires research in advance, which increases the initial costs of projects, but can be expected to provide far better results in the long term, and ultimately save money.
Potential contribution of system‐specific knowledge (SSK) to stream‐management decisions: ecological and economic aspects
Authors: STATZNER B. , SPERLING F.
Published: May 2006

Stream‐management decisions must produce an optimal cost‐effect ratio, as related to social, ecological and economic concerns. Therefore, decisions must be reached in a systematic approach by scrutinizing the system‐specific knowledge (SSK) provided by many disciplines.

 This paper is organized into five sections: following the introduction (Section 1), Section 2 sets a framework for the numerous elements of the SSK that can serve as a checklist to identify potentially important topics for a particular management decision; Section 3 illustrates errors in stream‐management policies that have been made because the SSK was not considered; Section 4 demonstrates how the SSK can be applied in formulating appropriate stream‐ and water‐management policies; finally Section 5 summarizes the major points in the context of alternative stream‐management strategies.

 Examples on limiting values in Europe, restrictions of NH4‐N emission, and the routine application of the Saprobian index demonstrate that current management practices often ignore the SSK.

 Combining trivial elements of the SSK we demonstrate how complex problems of stream management can be solved, focusing on the sources, sinks, and effects of water, organic carbon, nitrogen and phosphorus.

 On the basis of costs and effects, we rate various management options for a fictitious north German lowland catchment. If that catchment does not carry a dense human population, SSK‐based management is distinctly more efficient than traditional management, which focuses on a minor sink (sewer system plus sewage treatment plant).

 Stream management ignoring the SSK wastes financial, intellectual, and natural resources. If we project the estimated costs for water‐resource management in Germany over the forthcoming decade on to the standards of recent European Community (EC) guidelines concerning this subject, a large portion of a sum of around $US 1–2 trillion (1012) will be squandered in the EC unless practices change.

 The results of our analysis are rather disturbing and suggest that totally different practices are needed in legislation, administration and execution, monitoring, and research. Therefore, we propose that our paper be the starting point for a discussion involving representatives of all relevant disciplines about potential priorities for new management strategies.
Oxygen concentration profiles in soft sediment of Lake Baikal (Russia) near the Selenga delta
Authors: MARTIN PATRICK , GODDEERIS BOUDEWIJN , MARTENS KOEN
Published: May 2006

Microprofiles of oxygen concentration were made in soft sediments of Lake Baikal, along three transects near the Selenga delta. This is the first time the available oxygen in the sediment has been measured in this lake.

 The microprofiles had a similar and typical shape (a single exception was possibly caused by bioturbation). A positive correlation was found between the sediment oxygen penetration depth (SOP) and the bathymetric depth of the epilimnion, probably caused by a decrease in oxygen sediment consumption with increasing depth.

 The observed SOP values are generally very high, which is an indication of oligotrophy. A single low SOP value, observed in the northern transect, appears to be linked to organic pollution caused by the Selenga River.
Relationships of marsh seed banks to vegetation patterns along environmental gradients
Authors: WILSON SCOTT D. , MOORE DWAYNE R.J. , KEDDY PAUL A.
Published: May 2006

The relationship of the seed bank to the vegetation of a freshwater marsh was studied along gradients of water depth and soil organic matter content. Characters examined included standing crop, seedling density, and species composition, distribution and richness.

 The seed bank differed from the vegetation in that only nine of twenty‐seven species were present in both, abundant seed‐bank species were uncommon as adults, and adults showed different distributions along a gradient of soil organic matter content whereas their seeds were most abundant in soils with high organic matter.

 The seed bank resembled the vegetation in that separate multivariate analyses of the communities revealed that variation in the species composition of each was significantly correlated with water depth and soil organic matter content. Further, species richness in both communities decreased with water depth and increased with soil organic matter content. Lastly, the standing crop of the vegetation and the number of seedlings both decreased with water depth and increased with soil organic matter.

 Consideration of spatial patterns and environmental gradients revealed more similarities between vegetation and seed banks than were obtained by comparing species lists. The results suggest that artificial stimulation of seed bank germination for management purposes will not produce vegetation changes as large as those suggested by differences in species lists.
Influence of submergence on growth of seedlings of Scirpus lacustris and Phragmites australis
Authors: WEISNER STEFAN E.B. , GRANÉLI WILHELM , EKSTAM BÖRJE
Published: May 2006

Seeds of Scirpus lacustris and Phragmites australis were germinated in early June, and twenty‐four seedlings of each species were subsequently exposed to submerged conditions (eight seedlings at each of the water depths 0.2, 0.4 and 0.8m), in outdoor 500–1 tanks in southern Sweden. Weight and shoot length of the plants were measured in September.

 The Phragmites seedlings did not show any significant growth when submerged. The Scirpus seedlings, however, developed submerged leaves and exhibited considerable submerged growth. One Scirpus plant, in shallow water (0.2m), had developed an aerial shoot by September. Shoot length of the remaining (submerged) Scirpus plants was positively related to plant weight within water depth treatments, and was higher, in relation to plant weight, in deeper water. Mean weight in September of the submerged Scirpus plants decreased with increased water depth.

 In south Swedish lakes with a lowered water table, Scirpus often occupies large areas on the lakeward side of the reed belt, which is generally dominated by Phragmites. The differences between the two species, in performance of submerged seedlings, suggest that this zonation may be created through successful submerged seedling establishment of Scirpus on the lakeward side of Phragmites.
Field techniques for the classification of near‐bed flow regimes
Authors: YOUNG W.J.
Published: May 2006

The equipment and methods needed for collecting the data required for near‐bed flow regime classification are detailed.

 To illustrate appropriate procedures for data analysis, data collected from four cobble bed streams are used to classify near‐bed flow regimes both at the measured depth and at estimated bankfull depth.

 Implications of the resulting classifications are discussed from a limnological perspective. It is concluded that while the biological relevance of near‐bed flow regimes has not been formally established, the terms ‘pool’, ‘run’, and ‘riffle’ are not always useful for differentiating between habitats in the near‐bed zone.
The effect of suspended clay on ciliate population growth rates
Authors: JACK JEFFREY D. , GILBERT JOHN J.
Published: May 2006

Renewed batch cultures of three algivorous and one bacterivorous ciliate showed that ciliate reproductive rates increase with increasing food concentration up to an asymptote. Maximum rm values for Strobilidium gyrans, Bursaridium difficile and Euplotes eurystomus feeding on the cryptomonad alga Rhodomonas minuta were 0.87, 0.86 and 0.45 day‐1, respectively, while Paramecium aurelia feeding on the bacterium Enterobactor aerogenes had an rm of 0.40 day‐1. B. difficile had a food threshold (rm= 0) of 0.38 μg Cml‐1 and P. aurelia had a threshold of 1.6μg Cml‐1.

 The presence of suspended fine (particle size <1 μm) and coarse (particle size 1–2μm) clay suppressed the half maximum reproductive rate of the ciliate Strobilidium gyrans by up to 69% but had no effect on B. difficile, E. eurystomus or P. aurelia. Populations of ciliates unaffected by clay may be released in situations where suspended particles negatively affect their metazooplankton predators and competitors.
Substrate interstices as a habitat for larval Thraulus bellus (Ephemeroptera) in a temporary floodplain pond
Authors: TABACCHI E. , DÉCAMPS H. , THOMAS A.
Published: May 2006

Larvae of the ephemeropteran Thraulus bellus were sampled from the substrate interstices of a floodplain pond along the River Adour (south‐west France). Quantitative sampling was carried out using traps arranged in five transects of four traps each, made up of five vertical compartments between +20 and ‐80cm from the surface of the substrate. The 100 compartments thus obtained were each 2.861 volume, and were sampled once a month from January 1988 to January 1989.

 An influx of young larvae coming from the permanently flooded deep substrate invaded the upper 80cm of the substrate on and after mid‐January. An increase in larval density and frequency of occurrence in the compartments occurred until May before emergence of the adults. A second colonization phase by young larvae took place from July to September, and was followed by reductions in larval density and frequency of occurrence during the autumn/winter drop in water level.

 Horizontal and vertical movements of the larval population within the interstitial habitat of the pond were clearly linked to the water level fluctuations. However, differences between the five transects indicated a control of these movements by factors such as slope of the substratum, macrophytic vegetation, and the influence of springs. A relationship was found between population density and probability of submergence of the compartments, indicating that the larvae avoided locations most influenced by the fluctuating water levels.

 The temporarily flooded substrate interstices appear to be a refuge for the larvae of T. bellus, preventing them from overlapping with two other abundant ephemeropterans, namely Cacnis horaria from silt habitats and Cloeon gr. simile from macrophyte beds.