摘要:

SUMMARY1. This paper provides the introduction to a special issue ofFreshwater Biologydevoted to papers dealing with aspects of the physical environment and ecology of alpine, glacial, high latitude and mountain streams.2. Eleven of the sixteen papers were included in a symposium that formed part of the scientific programme of the North American Benthological Society Annual Meeting in Calgary, Alberta, Canada, in May 1993.3. The contributions are a combination of reviews, overviews and primary research articles that deal with streams and ecological issues in Alaska, Nepal, New Zealand, Switzerland and southern Africa. Important issues considered include environmental consequences of river ice; altitudinal and temporal distributions of stream biota, especially macroinvertebrates; litter processing; and bryophyte production.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1994.tb01123.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SUMMARY1. The five major hydrologic regimes of cold regions are typically classified as proglacial, wetland, spring‐fed, arctic nival and subarctic nival. Each has a distinctive hydrograph determined by the source and timing of runoff.2. The hydrologic response of streams in cold regions is influenced significantly by the source and pathways of moisture from the landscape to the stream channel. Snow and ice masses, such as snow cover, permafrost and icings, play principal and unique roles as major moisture sources, and in affecting runoff pathways.3. Once flow has been routed from the landscape into a channel system, the effects of floating ice begin to control the flow system. Notably, many of the most significant hydrologic events in cold regions, such as floods and low flows, are more the result of in‐channel ice effects than of landscape runoff processes. This has not been adequately recognized in general assessments of cold‐regions water resources.4. Only recently have the broader environmental effects of river ice been addressed in any concerted fashion. This paper reviews the various stages of ice formation, growth and break‐up, and summarizes the major hydrologic and ecological effects associated with each. Priority research topics are also ide

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1994.tb01124.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SUMMARY1. Abiotic disturbances strongly modify spatial and temporal patterns of lotic ecosystem community structure and function. Such effects are produced because disturbances alter organic matter, nutrient and contaminant dynamics and the distribution and abundance of bacterial, algal, macroinvertebrate and fish communities.2. River ice break‐up is a seasonal disturbance in rivers at high altitudes and latitudes world‐wide and is characterized, in part, by large increases in current velocity, stage, water temperature, concentrations of suspended materials and substrate scouring.3. These abiotic factors are likely to have important effects on primary producers, consumers, and food‐web dynamics of river biota. Despite the potential importance of river ice break‐up on community structure and function, detailed information describing the magnitude of their effects and underlying causal mechanisms is scarce.4. The objective of this paper is to provide a hydrological and ecological review and perspective on the potential effects of ice break‐up on lotic ecosystems. Specifically, the potential importance of break‐up on water temperature, river sediments and geomorphology, riverine energy sources, contaminants, and its effects on river biota and food‐web dynamics

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1994.tb01125.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SUMMARY1. This review examines ecological conditions and zoobenthic communities of kryal, krenal and rhithral streams of the alpine zone. Altitudinal and biogeographical faunal patterns are also analysed.2. Kryal segments, fed by glacial meltwater, are characterized by low temperatures (Tmax4°C) and large diel flow fluctuations in summer. The water may be clear or turbid from suspended rock flour. Fishes and higher plants are absent. The macroalgaHydrurus foetidusmay be abundant in kryal and other alpine stream types of the Holarctic. The highly restricted cosmopolitan fauna of glacial brooks consists of diamesine chironomids, sometimes accompanied by simuliids. Sparse food resources include algae and allochthonous (aeolian) organic matter.3. Rhithral segments in alpine catchments are characterized by soft water, a hydrograph dominated by an extended period of snowmelt runoff, and a broader temperature range than kryal or krenal biotopes. Bryophytes, macroalgae (chrysophytes, chlorophytes, cyanophytes, rhodophytes) and epiphytic and epilithic diatoms constitute the flora. A relatively diverse zoobenthos includes four orders of insects (Flecoptera, Ephemeroptera, Trichoptera, Diptera), turbellarians, acarines, oligochaetes and nematodes.4. Krenal segments, fed by groundwater, are typically calcareous with summer‐cool and winter‐warm thermal conditions, high water clarity, and constant flow regimes. Bryophytes and macroafgae are accompanied by a rich diatom flora. The zoobenthos consists of a composite of kryal and rhithral elements with few crenobionts. Zoobenthos species richness values are intermediate between those of kryal and rhithral segments, whereas densities in perennial, well‐oxygenated springbrooks far exceed those in other alpine stream types.5. Downstream faunal changes are most predictable in kryal segments where chironomids of the genusDiamesaare the predominant, if not sole, members of the zoobenthos in the upper zone of glacial brooks, the metakryal. WhereTmaxexceeds about 2°C the transition to the hypokryal occurs andDiamesais co‐dominant with simuliids. These largely stenozonal headwater forms decline downstream whereTmaxexceeds about 4°C, concomitant with a marked increase in the euryzonal mountain fauna.6. Species occurring in alpine rhithral biotopes tend to be euryzonal forms at their upper alrirudinal limits, whereas the lower elevation mountain stream fauna consists of species with narrower distribution limits. There is, however, a precipitous drop in mean altitudinal range from the alpine rhithral to the kryat because of the stenozonal nature of the glacial brook fauna.7. The view that effects of temperature on generation time and mutation rate determine the speed at which selection proceeds is consistent with altitudinal species richness patterns exhibited by zoobenthos along the alrirudinal gradient and may provide an evolutionary explanation for the low faunal diversity in alpine headwaters.8. With increasing altitude, mountain ‘islands’ become progressively insular as area decreases and isolation increases. For a cold‐adapted stream fauna the insular nature of mountain tops is greatest in the tropics. Nonetheless, alpine stream

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1994.tb01126.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SUMMARY1. This review examines the physical habitat and ecology of glacial rivers which have been relatively unstudied compared with rivers originating from other sources.2. Typical glacial rivers have summer temperatures below 10°C, a single seasonal peak in discharge, which in the Northern Hemisphere typically occurs in July, a diel fluctuation in flow which usually peaks in late afternoon, and turbidity levels in summer that exceed 30 NTU. These variables contrast with those in snowmelt/rainfall streams, particularly in summer, and make conditions more extreme for the biota.3. Where maximum temperatures are 2°C benthic invertebrate communities are dominated byDiamcsa(Chironomidae). Downstream, temperatures increase, channels become more stable and valley floors become older. Orthocladiinae (Chironomidae), Simuliidae, Baetidae, Nemouridae and Chloroperlidae become characteristic members of the invertebrate community.4. Fauna may be displaced, or at least colonization delayed, by channel instability; the variable age structure of the valley floor will influence the faunal gradient, which may also be reset by the effects of tributaries, lakes and valley confinement.5. We propose a qualitative model that outlines zoobenthic community gradients determined by two principal variables, water temperature and channel stability, as a function of distance downstream, or time since deglaciatio

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1994.tb01127.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SUMMARY1. Hydrobiological changes were assessed along an altirudinal transect of eighteen to twenty‐three tributaries from 600 to 3750m in two adjacent river systems in east‐central Nepal. The transect incorporated catchments under terraced agriculture at the lowest altitudes in the Likhu Khola, through streams in forest, alpine scrub and tundra at higher altitudes in Langtang.2. Diatoms, bryophytes, macroinvertebrates and fish all showed pronounced altitudinal changes in assemblage composition as shown by TWINSPAN and DECORANA. A few taxa were restricted to streams at high altitude, but many more occurred only at lower altitudes where taxon richness increased substantially despite catchment disturbance by terraced agriculture.3. Diatoms characteristic of lower altitude streams were mostly motile, epipelic or episammicNaviculaandNitzschiaspp., which occur typically at greater electrolyte and nutrient concentrations. Those characteristic of higher and steeper sites included attachedFragilariaspp. and prostrateAchnanthesspp., tolerant of turbulent flow.4. Cover by bryophytes varied within catchment type; high altitude springs supported dense mats, unlike streams fed by ice and glaciers. Taxa confined to low altitudes included those characteristic of humid subtropical conditions.5. Invertebrate families occurring only at lower altitudes included a range of burrowers and pool dwellers. Numerically, filter feeding Hydropsychidae and Simuliidae dominated streams in terraced and forested catchments, whereas grazing baetid mayflies dominated higher altitude streams in scrub and tundra.6. The combined density and biomass of at least six fish species in the Likhu Khola were 23–250 (per 100m−2), and 86–1282 g wet mass (per 100 m−2), respectively. No fish were found in Langtang streams, probably because torrential headwaters prevented colonization.7. Our data confirm that altitudinal transitions in stream biota are pronounced in the Himalaya of Nepal, but are likely to reflect a wide array of potential

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1994.tb01128.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SUMMARY1. The influence of altitude and land‐use changes on macroinvertebrate assemblages from riffles in forty‐three streams in the Dolpo region of western Nepal were examined. Sampling sites ranged in altitude from 850 to 4250m, and land‐use patterns fell into five categories: alpine, forest, grassland, pasture and agricultural land.2. TWTNSPAN classification of physicochemical data separated streams into groups on the basis of climatic and physical factors. Streams from high, cold, alpine areas were separated from those in warmer, lower, agricultural areas.3. In all, 138 macroinvertebrate taxa were collected from fifty‐three insect families. Ephemeroptera were most common, especially Baetidae.4. Taxonomic richness declined with increasing altitude. Ten insect families were significantly more abundant in lowland streams, and five were more common in alpine streams.5. TWINSPAN and DECORANA revealed distinct invertebrate groupings of the forty‐three streams surveyed. A high percentage of the variance (79.3%) in ordination space was explained by DECORANA axes 1 and 2. Altitude, temperature, stream width and land use were implicated in structuring invertebrate co

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1994.tb01129.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SUMMARY1. The Buffalo River rises 1200m above sea level, drops 600m in the first 7km, and a further 100m in the next 30 river kilometres. Macroinvertebrates were sampled, and environmental variables measured monthly in 1987, at four sites along this part of the river.2. Flow at the headwater site (1120m a.s.l., 1 km from the source) was seasonal, though pools remained and subterranean flow was continuous. Twelve macroinvertebrate taxa were found exclusively at this site, where conductivity, pH and nutrient concentrations were low.3. Flow at the foothill site (530m a.s.l., 7km from the source) was perennial. The invertebrate community, although distinct from that at downstream sites, lacked the unique taxa of the headwater site. Conductivity, pH and nutrient concentrations were higher.4. The two sites downstream of the foothills (450m a.s.l., 18km from the source, and 410m a.s.l., 31 km from the source), had similar invertebrate communities. Conductivity, pH and nutrient concentrations were higher than at the upper sites.5. Community structure changed most between the headwater and foothill sites. This paralleled changes in river steepness rather than changes in measured physicochemical variables.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1994.tb01130.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SUMMARY1. A massive aquifer between the Gerstle, Tanana and Delta rivers in interior Alaska receives water from them and from smaller streams that flow from the Granite Mountains in the Alaska Range, Groundwater from the aquifer intersects the surface in a mid‐sized (20m3s−1× 10%) spring‐fed stream, Clearwater Creek.2. Mean annual air temperature is about ‐2.6°C. However, even in winter when air temperature often reaches —40°C, the stream does not form a complete ice cover. Water temperature ranges from 0 to 7.8°C. Specific conductance and the concentrations of major ions vary little throughout the year, and summed ionic salinity exceeds 250 mg1‐−1.3. Benthic algal standing crop (as chlorophylla) was at least an order of magnitude higher than that in a nearby surface‐water stream, the upper Chena River, Standing crop peaked in spring and autumn (about 20mgm−2) and averaged about half this value, although biomass of an early spring bloom ofHydrurus foetid uswas underestimated.4. Algal standing crop was inversely related to the concentrations of inorganic nitrogen and orrhophosphate‐phosphorus in the water column. The ratio of total nitrogen to total phosphorus (as mass concentrations) was always about 30. Measurements of primary production made in Clearwater Creek were among the highest reported for streams in subarctic Alaska.5. Macroinvertebrate diversity in Clearwater Creek was low. Numbers of ‘morpho‐species’ in monthly Surber samples (0.09m2) averaged nine, and ranged from three to fourteen. However, benthos and drift densities were similar to those reported from other Alaskan streams. In early spring and autumn, drifting macroinvertebrates were primarily Ephemeroptera, Plecoptera and Trichoptera, but in summer, Diptera dominated the drift. The low diversity of macroinvertebrates is hypothesized to be a consequence of the small annual range in water temperature and the relatively constant

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1994.tb01131.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SUMMARY1. The West Coast of the South Island, New Zealand (Westland) is a region of mountains, forests, high rainfall, and a history of exploitation. The Southern Alps rise to over 3000m in the east of the region, and a narrow coastal plain supports some agriculture and the main centres of population.2. Stream waters in the Southern Alps are characterized by low concentrations of major ions, and most can be described as calcium—sodium—bicarbonate waters. Brown waters with low pH and high concentrations of dissolved organic carbon are common at low and intermediate altitudes.3. Many mountain streams and rivers provide physically harsh environments for aquatic biota with their rapidly changing flows and frequent spates. Hydrological factors and low nutrient concentrations limit periphyton standing crops, and biomass of coarse detritus is often low. Invertebrate populations are usually dominated by insect larvae that feed primarily on FROM and stone surface biofilms.4. Features of the macroinvertebrate stream fauna on the West Coast are the wide range of physicochemical conditions tolerated by many common species, and the numerical dominance of the mayflyDeleatidium(Leptophlebiidae) in many streams. The Plecoptera also exhibit high diversity relative to other parts of the country, and an unusual trend towards terrestrialism is shown by larvae of Gripopterygidae.5. The West Coast has a long history of coal and gold mining, forestry and farming, activities that have had negative impacts on stream communities and water quality. We discuss some ecological and management issues associated with present day mining practices, and a proposal to take large volumes of alpine stream water for exp

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1994.tb01132.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY