bluuebunny/crossref_metadata_2025_split huggingface dataset:
Biogeochemistry of billabong sediments. II. Seasonal variations in methane production
Authors: SORRELL BRIAN K. , BOON PAUL. I. 
Published: May 2006

SUMMARY1. 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

SUMMARY1. 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

SUMMARY1. 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

SUMMARY1. 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

SUMMARY1. 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

SUMMARY1. 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

SUMMARY

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

SUMMARY

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

SUMMARY

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

SUMMARY

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

SUMMARY

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

SUMMARY

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

SUMMARY

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

SUMMARY

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

SUMMARY

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.