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  • 1
    ISSN: 1432-1009
    Keywords: Spatiotemporal heterogeneity ; Physical habitat template ; Streams ; Disturbance ; Recovery ; Community structure ; Natural selection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Spatial and temporal environmental heterogeneity in lotic ecosystems can be quantitatively described and identified with characteristic levels of ecological organization. The long-term pattern of physicochemical variability in conjunction with the complexity and stability of the substratum establishes a physical habitat template that theoretically influences which combinations of behavioral, physiological and life history characteristics constitute appropriate “ecological strategies” for persistence in the habitat. The combination of strategies employed will constrain ecological response to and recovery from disturbance. Physical habitat templates and associated ecological attributes differ geographically because of biogeoclimatic processes that constrain lotic habitat structure and stability and that influence physicochemical variability and disturbance patterns (frequency, magnitude, and predictability). Theoretical considerations and empirical studies suggest that recovery from natural and anthropogenic disturbance also will vary among lotic systems, depending on historical temporal variability regime, degree of habitat heterogeneity, and spatial scale of the perturbation. Characterization of physical habitat templates and associated ecological dynamics along gradients of natural disturbance would provide a geographic framework for predicting recovery from anthropogenic disturbance for individual streams. Description of lotic environmental templates at the appropriate spatial and temporal scale is therefore desirable to test theoretical expectations of biotic recovery rate from disturbance and to guide selection of appropriate reference study sites for monitoring impacts of anthropogenic disturbance. Historical streamflow data, coupled with stream-specific thermal and substratum-geomorphologic characteristics, are suggested as minimum elements needed to characterize physical templates of lotic systems.
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  • 2
    ISSN: 1432-5225
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Summary Lignin topochemistry of tracheid walls from a deformed, copper deficient Pinus radiata (D. Don) tree was examined by linescan and point analyses using a Scanning Electron Microscope and Energy Dispersive Spectrometry. Both opposite and compression wood had abnormal lignin distributions compared to those observed in normal wood from a straight tree. Lignin contents in the compound middle lamella were lower than lignin contents in the secondary wall in both opposite and compression wood tracheids.
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  • 3
    ISSN: 1432-0703
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Medicine
    Notes: Abstract The initial hypothesis that predation pressure should decrease with decreasing pH in aquatic macrobenthic communities if predatory invertebrates are more sensitive to water acidification than prey invertebrates is tested. Short-term toxicity bioassays were conducted in soft water (average value of total hardness 38.0 mg CaCO3/L) to determine the differential sensitivity of the predator, Dugesia dorotocephala (Turbellaria, Tricladida), and the prey, larvae of Cheumatopsyche pettiti (Insecta, Trichoptera), to low pH. Test pH solutions were prepared with sulfuric acid (H2SO4). Test species were also exposed to high concentrations of sulfate ion (95 mg SO4=/L for D. dorotocephala and 340 mg SO4=/L for C. pettiti) as sulfate toxicity controls, using potassium sulfate (K2SO4). No mortality was observed during these toxicity controls, indicating that toxic effects generated by low pH were fundamentally due to H+ ions. The 72 and 96-h LC50s (as pH values) and their 95% confidence limits were 4.88 (4.72–5.05) and 5.04 (4.89–5.21) for D. dorotocephala, and 3.25 (3.00–3.51) and 3.48 (3.24–3.73) for C. pettiti. Net-spinning caddisfly larvae migrated from their retreat nets and protruded their anal papillae before dying. After short-term bioassays, predation-pressure laboratory experiments were performed for 6 days. The cumulative mortality of C. pettiti by predation of D. dorotocephala decreased with decreasing sublethal pH values. The average predation rates at mean pH values of 7.7, 7.7, 6.6, 6.5, 6.2 and 6.0 were 2.5, 2.0, 1.33, 1.17, 0.67 and 0.33 larvae/day, respectively. The major biotic factor affecting predation pressure appears to be the reduction in the physiological activity of triclads at low pH. It is concluded that predation pressure can decrease in aquatic macrobenthic communities if prey are more tolerant to water acidification than predators.
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  • 4
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 335 (1988), S. 64-66 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The Flathead River, a major tributary of the Clark Fork of the Columbia, drains a catchment area of 22,241 km2 (average flow = 340 m3 s"1) in northwestern Montana and southeastern British Columbia. The morphology and surficial geology of the Kalispell Valley (Fig. 1) were largely determined by ...
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  • 5
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. Seasonal changes in longitudinal patterns of environmental conditions and macroinvertebrate community distributions were examined in an alpine glacial stream (Roseg River, Switzerland).2. Physico-chemical parameters reflected seasonal changes in glacial influence via shifts in water sources and flowpaths (glacial meltwater versus ground water), and were best described by turbidity, particulate phosphorus and specific conductance. High nitrogen concentrations indicated snowmelt was the main water source in June.3. Macroinvertebrate densities and taxon richness were highest during spring (4526 m–2 and 16 taxa, all sites combined) and late autumn/early winter (8676–13 398 m–2 with 16–18 taxa), indicating these periods may be more favourable for these animals than summer when glacial melting is maximal. Diamesa spp. (Chironomidae) dominated the fauna at the upper three sites (〉95% of zoobenthos) and were abundant at all locations. Other common taxa at lower sites (1.2–10.6 km downstream of the glacier terminus) included other chironomids (Orthocladiinae, Tanytarsini), the mayflies Baetis alpinus and Rhithrogena spp., the stoneflies Leuctra spp. and Protonemura spp., blackflies (Simulium spp., Prosimulium spp.), and Oligochaeta.4. Co-inertia analysis revealed a strong relationship between environmental conditions and benthic macroinvertebrate assemblages. Furthermore, it elucidated temporal variability in longitudinal response patterns, as well as a similarity in temporal patterns among individual sites.5. Our results suggest that zoobenthic gradients are not solely related to temperature and channel stability. Seasonal shifts in sources and pathways of water (i.e. extent of glacial influence), and periods of favourable environmental conditions (in spring and late autumn/early winter) also strongly influenced zoobenthic distributions.
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  • 6
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. Benthic macroinvertebrate assemblages were compared among a diverse array of first-order alpine tundra streams of the Swiss Alps.2. A principal components analysis separated sites into three main groups: rhithral streams, rhithral lake outlets, and kryal sites including outlets and streams. Rhithral streams contained the most diverse and taxon rich assemblages, being colonised by both non-insect taxa and Ephemeroptera, Plecoptera, Trichoptera and Diptera.3. Rhithral lake outlets supported high densities of non-insect taxa such as Oligochaeta, Nemathelminthes and crustaceans. Despite low taxon richness, kryal sites had high Ephemeroptera and Plecoptera abundances. Chironomidae were most common at all sites.4. Collector-gatherers were dominant at all sites, whereas filter-feeders were rare. Scrapers and shredders were more common in streams than lake outlets.5. Water temperature and algal standing crops were higher at rhithral lake outlets than rhithral streams, perhaps providing more favourable habitat for non-insect taxa. Glacial runoff was the dominant factor influencing macroinvertebrate assemblages of kryal streams and kryal lake outlets. Alpine lakes influenced the environmental conditions of their outlets and, consequently, their macroinvertebrate assemblages unless being constrained by a glacial influence.
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Freshwater biology 48 (2003), S. 0 
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: SUMMARY 1. We examined the thermal patterns of the surface waters in the catchment of the Roseg River, which is fed by the meltwaters of two valley glaciers. One of the glaciers has a lake at its terminus. The river corridor comprised a proglacial stream reach below one glacier, the glacier lake outlet stream, a 2.5-km long complex floodplain and a constrained reach extending to the end of the catchment.2. Temperatures were continuously measured with temperature loggers at 27 sites between 1997 and 1998. Moreover, from 1997 to 1999, spot measurements were taken at 33–165 floodplain sites (depending on water level) at monthly intervals.3. The temperature regime of glacial streams, including the glacier lake outlet, was characterised by rapidly increasing temperatures in April and May, a moderate decline from June to September (period of glacial melt) and a subsequent fast decline in autumn. During summer, the lake increased temperatures in the outlet stream by 2–4 °C, compared with the adjacent proglacial stream reach.4. In the main channel (thalweg) of the Roseg River, annual degree-days (DD) ranged from 176 DD in the upper proglacial reach to 1227 DD at the end of the catchment.5. Thermal variation among different channels within the floodplain was higher than the variation along the entire main channel. Floodplain channels lacking surface connection to the main channel accumulated up to 1661 annual DDs.6. Thermal heterogeneity within the floodplain was linked to the glacial flow pulse. With the onset of ice melt, temperatures in the main channel and in channels surface-connected to the main channel began to decline, whereas in surface-disconnected channels temperatures continued to increase; as a consequence, thermal heterogeneity at the floodplain scale rose slightly until September.7. High thermal heterogeneity was not anticipated in the harsh environment of a largely glacierised alpine catchment. The relatively wide range of thermal environments may contribute to the highly diverse zoobenthic community.
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Freshwater biology 39 (1998), S. 0 
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. A factorial experiment was conducted in artificial outdoor streams to quantify the effects of irradiance (two levels) and two mayfly grazers (four densities of each) on periphytic community structure. The mayflies were Ecdyonurus venosus (Heptageniidae), a grazer using brushing mouthparts, and Baetis spp. (Baetidae) a grazer which uses mandibles and maxilla to scrape and gather periphyton. The experiment ran for 16 days.2. Grazer densities in channels approximated those existing in a shoreline habitat in the River Sihl, Switzerland. Light treatments were natural (daily mean = 810 μmol m–2 s–1) and shaded (daily mean = 286 μmol m–2 s–1).3. Higher irradiance increased total algal abundance by a factor of 4. Algae most affected were prostrate/motile and erect diatoms, filamentous chlorophytes and Hydrurus foetidus.4. Both species of mayfly reduced periphytic and algal biomass. Mayfly–mayfly interactions, however, were associated with statistical increases in algal biovolume and chlorophyll-a content, indicating that the two grazers may have interfered with one another as their densities increased. The mayfly–mayfly interaction did not influence periphytic ash-free dry mass (AFDM). Light modified the influence of Ecdyonurus such that this mayfly produced greater reductions in algal biovolume under high irradiance.5. Despite efforts to exclude other grazers, chironomids colonized experimental channels. Chironomid biomass was approximately eight times less than mayflies across treatments and was positively correlated with all measures of periphytic abundance, suggesting that these grazers were responding to periphyton rather than controlling it. Chironomids were also associated with an increase in the abundance of diatoms having a prostrate/motile physiognomy. The only physiognomy to show a negative relationship with chironomid biomass was the thallus type, a form which comprised less than 1% of the algal biovolume across channels.6. Ecdyonurus and Baetis had distinct influences on algal physiognomy. Ecdyonurus, for example, reduced adnate, stalked and Achnanthes-type physiognomies, but was associated with a significant increase in the abundance of filamentous chlorophytes (primarily Ulothrix sp.). Baetis reduced erect, Achnanthes-type and thallus physiognomies. Neither mayfly influenced the abundance of prostrate/motile diatoms; a physiognomy that comprised 21% of the algae in channels.7. Light and mayfly interactions affected algal community structure. The interaction of Ecdyonurus with light had a negative effect on erect diatoms, filamentous chlorophytes and the thallus physiognomy, but a positive effect on stalked and Achnanthes-type physiognomies. Baetis interacting with light had a positive effect on adnate diatoms.8. Although both mayfly taxa influenced periphytic community structure, physiognomy was not a good predictor of algal susceptibility to grazing. The type of substratum to which an alga is attached (detritus or algal filaments vs hard surfaces) and location within the periphytic matrix may be better indicators of vulnerability to grazing than physiognomy.
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  • 9
    Electronic Resource
    Electronic Resource
    Oxford UK : Blackwell Science Ltd.
    Freshwater biology 47 (2002), S. 0 
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. This review is presented as a broad synthesis of riverine landscape diversity, beginning with an account of the variety of landscape elements contained within river corridors. Landscape dynamics within river corridors are then examined in the context of landscape evolution, ecological succession and turnover rates of landscape elements. This is followed by an overview of the role of connectivity and ends with a riverine landscape perspective of biodiversity.2. River corridors in the natural state are characterised by a diverse array of landscape elements, including surface waters (a gradient of lotic and lentic waterbodies), the fluvial stygoscape (alluvial aquifers), riparian systems (alluvial forests, marshes, meadows) and geomorphic features (bars and islands, ridges and swales, levees and terraces, fans and deltas, fringing floodplains, wood debris deposits and channel networks).3. Fluvial action (erosion, transport, deposition) is the predominant agent of landscape evolution and also constitutes the natural disturbance regime primarily responsible for sustaining a high level of landscape diversity in river corridors. Although individual landscape features may exhibit high turnover, largely as a function of the interactions between fluvial dynamics and successional phenomena, their relative abundance in the river corridor tends to remain constant over ecological time.4. Hydrological connectivity, the exchange of matter, energy and biota via the aqueous medium, plays a major though poorly understood role in sustaining riverine landscape diversity. Rigorous investigations of connectivity in diverse river systems should provide considerable insight into landscape-level functional processes.5. The species pool in riverine landscapes is derived from terrestrial and aquatic communities inhabiting diverse lotic, lentic, riparian and groundwater habitats arrayed across spatio-temporal gradients. Natural disturbance regimes are responsible for both expanding the resource gradient in riverine landscapes as well as for constraining competitive exclusion.6. Riverine landscapes provide an ideal setting for investigating how complex interactions between disturbance and productivity structure species diversity patterns.
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  • 10
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1.  River corridors can be visualised as a three-dimensional mosaic of surface–subsurface exchange patches over multiple spatial scales. Along major flow paths, surface water downwells into the sediment, travels for some distance beneath or along the stream, eventually mixes with ground water, and then returns to the stream.2.  Spatial variations in bed topography and sediment permeability result in a mosaic of patch types (e.g. gravel versus sandy patches) that differ in their hydrological exchange rate with the surface stream. Biogeochemical processes and invertebrate assemblages vary among patch types as a function of the flux of advected channel water that determines the supply of organic matter and terminal electron acceptors.3.  The overall effect of surface–subsurface hydrological exchanges on nutrient cycling and biodiversity in streams not only depends on the proportion of the different patch types, but also on the frequency distribution of patch size and shape.4.  Because nutrients are essentially produced or depleted at the downwelling end of hyporheic flow paths, reach-scale processing rates of nutrients should be greater in stretches with many small patches (e.g. short compact gravel bars) than in stretches with only a few large patches (e.g. large gravel bars).5.  Based on data from the Rhône River, we predict that a reach with many small bars should offer more hyporheic refugia for epigean fauna than a reach containing only a few large gravel bars because benthic organisms accumulate preferentially in sediments located at the upstream and downwelling edge of bars during floods. However, large bars are more stable and may provide the only refugia during severe flood events.6.  In river floodplain systems exhibiting pronounced expansion/contraction cycles, hyporheic assemblages within newly created patches not only depend on the intrinsic characteristics of these patches but also on their life span, hydrological connection with neighbouring patches, and movement patterns of organisms.7.  Empirical and theoretical evidence illustrate how the spatial arrangement of surface–subsurface exchange patches affects heterogeneity in stream nutrient concentration, surface water temperature, and colonisation of dry reaches by invertebrates.8.  Interactions between fluvial action and geomorphic features, resulting from seasonal and episodic flow pulses, alter surface–subsurface exchange pathways and repeatedly modify the configuration of the mosaic, thereby altering the contribution of the hyporheic zone to nutrient transformation and biodiversity in river corridors.
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