摘要:

SUMMARY.1. Water temperatures in a shallow, weedy bay of a reservoir in southern Ontario were related to depth; mid‐day temperatures in summer were approximately 30°C at the water surface and 20°C below 25 cm.2. In the laboratory, larvalIschnura verticalisreleased in a thermal gradient (warmest water near the surface) did not remain near the surface any more than larvae in isothermal conditions. However, larvae in both isothermal and gradient conditions tended to spend more time close to the surface than expected by chance.3. Larvae provided with food at all depths spent more time near the surface than did larvae with no food. Larvae provided with one feeding site in the coldest water remained near the food as much as did larvae provided with a single feeding site in the warmest water.4. Results suggest that selection of microhabitats is based primarily on food availability and secondarily on proximity to the surf

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1989.tb01093.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARY.1. The life history, horizontal distribution at the sediment surface and the effect of water flow on the microdistribution ofAllogamus auricollis(Pictet, 1834), a case‐bearing caddisfly, was investigated in a mountain brook near Lunz, Lower Austria.2. The average head‐width increment per moult was proportionately constant atc. 48%; therefore Dyar's rule was applicable.3.Allogamus auricollishas a 1‐year life cycle with first and second instars most abundant in October. It overwinters primarily as third and fourth instars; pupae were observed in August.4. Horizontal distribution patterns were investigated by means of bimonthly samples taken along the stream profile. All instars were most abundant near the banks: 86.5% of the total catch 1987–88 were collected 0–1.5 m from the banks.5. Current speeds were measured at the sites of 2191 larvae (including all instars) and eighty‐six pupae. Larvae were most abundant at current speeds of 0–5 cm s−1(i.e. 86.6% of the total catch 1987–88).6. Laboratory data on different stages of resistance to drift inA. auricollis(Waringer, 1989) were tested for their application to field conditions. 90% of the total catch 1987–88 preferred areas at the substrate surface where they could remain fully retracted within their cases, unattached, even when the large lateral case surface area was directed towards the water flow. This was also true at times of high discharge where the size of these areas was c

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1989.tb01094.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARY.1. A series of samples of interstitial water and fauna was taken along transects from the channel into the bank in two small rivers in southern Ontario, Canada. These were examined for any discontinuities which might indicate the position of the hyporheic/groundwater interface.2. There were several chemical discontinuities in Duffin Greek, with “break lines” occurring from about the river margin obliquely downwards under the bank for dissolved oxygen and carbon dioxide, B.O.D., alkalinity, suspended solids and amount of organic matter. Break lines in nitrate and sulphide concentration ran from near the margin obliquely down under the river bed. In the Rouge River, a discontinuity extending from a point approximately 1.5 m landwards from the margin obliquely down under the river was indicated by dissolved carbon dioxide, B.O.D., conductivity, suspended solids, organic matter, nitrate and alkalinity.3. Ordination (DECORANA) and community classification (TWIN‐SPAN) revealed that, in both rivers, linear distance from mid‐river was the major factor associated with community structure. In both rivers the community under the bank was distinct from the river community and these two communities were separated by another community characteristic of the river margin. In Duffin Creek the classification procedure additionally discriminated surface and interstitial sub‐sets within the river community.4. Most taxa showed no significant correlations with the chemistry of the interstitial water but. in Duffin Creek, the densities of the copepodDiacyclops crasscaudis brachycercus(Kiefer) and Oligochaeta were positively correlated with nitrate: worms were also negatively correlated with sulphide. In the Rouge River, density of hyporheic animals was negatively correlated with both conductivity and alkalinity of interstitial water; oligochactes were positively correlated with both nitrate and organic matter; and density of nematodes was positively correlated with sulphide concentration.5. The hyporheic faunas of these two rivers were dominated by insects, particularly chironomids. Compared with the hyporheos of rivers in Europe and Colorado, the two Ontario rivers lack significant numbers of harpacticoid copepods as well as bathynellacid, amphipod and isopod cr

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1989.tb01095.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARY.1. Periphyton chlorophyllaand ash free dry weight (AFDW) were monitored in nine rivers to examine the relative importance of flows and nutrients for regulating periphyton biomass in gravel bed rivers.2. Mean annual flows in the rivers ranged from 0.94 to 169 m3s−1, mean dissolved reactive phophorus (DRP) from 1.3 to 68μg 1−1, periphytic chlorophyllafrom 4.6 to 73 mg m−2. and AFDW from 2.8 to 16 g m−2.3. For eight of the nine rivers NH4‐N. DRP, total Kjeldahl nitrogen, total phosphorus and total suspended solids were correlated (P<0.01) with flow, and for seven rivers conductivity was inversely correlated (P20 g m−2occurring most frequently in flows of<20 m3s−1.5. Floods prevented the development of medium term (i.e. up to 2 months) maxima in biomass in five of the rivers, but maxima occurred over summer‐autumn and winter‐spring in the three rivers where floods were absent.6. Chlorophyllabiomass was more resistant to flooding than AFDW. Only 5993 of the forty‐six recorded floods caused chlorophyllascouring, whereas 74% of the floods caused AFDW scouring. The efficiency of scour was more influenced by the pre‐flood biomass than the magnitude of the event.7. Biomass maxima were significantly correlated (P<0.01) with mean DRP concentration during the accrual period. Overall, up to 53% of the mean annual biomass difference between rivers was explained by the mean annual DRP concentrations. However, the high correlations between nutrient concentrations and flow indicated that the nutrient data were also carrying hydrological information and that simple causal relationships between nutrients and biomass are difficult to establish in rivers.8. It is concluded that hydrological factors contribute at least equally with nutrients to the differences in periphyton biomass between the gravel‐bed study rivers. They combined to explain up to 63.3% of the variance in biomass, compared with 57.6% for nutrients. It is recommended that periphyton data from gravel‐bed rivers should always be viewed within the context of the flow history of the site, and not just as a functio

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1989.tb01096.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARY.1 Foraging of the freshwater crabPotamon fluviatilewas studied by recording the activity of seventy‐eight specimens in a 50 m2pool in a Tuscan stream during early summer. Foraging was related both to the organic content of the substrate and to the crabs’ oxygen consumption. During this period, adult females underwent “second vitellogenesis”. with abundant deposition of yolk in oocytes.2. A dispotic distribution (not accompanied by agonistic interactions, but ‘peacefully’ based on size) was observed within the foraging area. Larger animals (mostly males) fed on the rare patches of vegetable debris, which presented the highest organic content. Conversely, smaller specimens were relegated lo the poorer substrates, such as the stream banks.3. The females extended and diversified their foraging areas by also venturing into terrestrial habitats, in contrast to the more sedentary and aquatic males. This behaviour (which was not accompanied by a different energetic output) resulted in a more proteinaceous diet (even when the N‐content of vegetable debris fell drastically), and in a significant increase in fats and the hepatopancreas index.4. The reserves of energetic substances are presumed to sustain the highly expensive vitellogenesis, with the production of macrolecithal eggs. The females’ behaviour as energy maximizers’ seemed to be under a strong selective pressure, since their reproductive success is directly related to the efficient h

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1989.tb01097.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARY.1 Eighteen streams in mid‐Wales were sampled for macro‐invertebrates in both riffles and margins in April 1985–87. Stream macro‐flora, substrata and marginal habitats were surveyed in May 1988.2. TWINSPAN classification of the macroinvertebrate data indicated three major stream groups. One was distinguished by circumneutral pH and had a flora and fauna typical of such conditions. The other two groups consisted of acidic streams with moorland and conifer afforested catchments respectively. The forest streams were the more acidic but the two groups also differed significantly in the composition of their marginal habitats.3 The acidic moorland streams had more vegetation (‘soft’ features) in the margins and supported several invertebrate taxa which were relative more abundant there than in the riffles. These taxa may be excluded from forest streams because the margins are ‘hard’ due to greater erosiveness and shading.4. In view of the increasing cover by conifer afforestation in Britain, it is clearly necessary to elucidate all its effects on stream ecosystems, which include changes to the physi

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1989.tb01098.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARY.1 The vertical distribution of invertebrates (>0.053 mm) was studied in a sandy‐bottomed, first‐order stream on the Coastal Plain of Virginia, U.S.A. Invertebrate species composition, abundance and bio‐mass were determined monthly over one year at sediment depth intervals of 0–1, 1–5, 5–15,15–30 and 30–40 cm.2. The subsurface community was numerically dominated by species of Chironomidae, Nematoda and Crustacea, while much of the biomass was due to early instars of several species of Trichoptera.3. Invertebrate density and biomass decreased significantly with depth in the substrate (ANOVA;P<0.05). Annual mean density decreased from 1,346,844 individuals m−3at the surface to 13,578 individuals m−3at 15–30 cm. Annual mean biomass decreased from 66.30 g m−3at the surface to 0.44 g m−3at 15–30 cm.4. Dissolved oxygen decreased markedly from the surface to the 5 cm depth in the substrate, anaerobic conditions often occurring below 10 cm. Density and biomass both showed a significant positive relationship with dissolved oxygen concentration (Linear regression;P<0.05).5. Physical forces were important in structuring the subsurface invertebrate community. Besides low dissolved oxygen concentration, sediment scouring resulting from storm discharge dramatically

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1989.tb01099.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARY.1 Genetic (electrophoretic) and sex ratio data were used to assess the contributions of sexual and asexual reproduction to recruitment to populations of the freshwater ostracodCandonocypris novaezelandiaein temporary and permanent water bodies of varying size.2. Two distinct types of population structure were found. Populations from eight permanent ponds, a reservoir and a temporary pond, apparently comprised only females and were dominated by a few highly replicated genotypes. Significant departures from Hardy‐Weinberg equilibria were observed for at least one locus in all populations, and multi‐locus genotypic diversity ranged between 16% and 48% of that expected in a population with the same underlying gene frequencies reproducing solely by sexual means. These results were consistent with the predicted consequences of predominantly asexually derived recruitment.3. In contrast, sexual reproduction was probably most important in a population inhabiting a large temporary swamp. This population displayed 79% of the genotypic diversity expected for a sexually reproducing population, and contained both males and females.4. Most theoretical models predict that sexually reproducing individuals should have a selective advantage in unstable environments. The results of this study do not provide a perfect association of sexually derived recruitment with unstable habit

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1989.tb01100.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARY.1. A new experimental method for the study of kinetics and mechanism of reactions at the solid‐liquid interface has shown that the dissolution of calcite in acidic waters is, under conditions of high mass transport, controlled by the first order heterogeneous reaction of H+at the interface and not by diffusion as previously thought.2. The implications of this for lake liming strategies (aimed at countering the effects of ‘acid rain’) are significant in that under typical liming conditions, the rate of calcite dissolution will be surface controlled and consequently appreciably slower than previously consi

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1989.tb01101.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARY.1. Extracellular hydrolytic enzyme activities and cell densities were monitored during undisrupted biofilm formation on pristine surfaces in two contrasting river sites in North Wales: an oligotrophic mountain stream (Nant Waen) and a mildly eutrophic river (River Clywedog).2. Bacterial densities generally increased at both sites over a 33‐day monitoring period. Densities in the eutrophic site were approximately 14 times greater than in the mountain stream.3. Using fluorescent substrate analogues, biofilms from Nant Waen produced low, variable xylosidase and β‐glucosidase activities. Biofilms from the more eutrophic River Clywedog produced higher xylosidase and β‐glucosidase activities and detectable endopeptidase, though these activities also fluctuated during the colonization period.4. Unlike the other activities measured, esterase activities in the River Clywedog were correlated with cell densities (P<0.05). When extracellular esterase activities per cell were calculated, the oligotrophic biofilm was found to contain about twice as much extracellular esterase activity as the more eutrophic River Clywedog

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1989.tb01102.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY