摘要:

SUMMARY.Temperature determines the growing season ofUtricularia purpurea, a common rootless, carnivorous plant at depths of 0–6.5 m in a dimictic oligotrophic lake (Mirror Lake, New Hampshire, U.S.A.). The dynamics of thermal stratification limit the growing season to 8 weeks at a depth of 6 m compared to 17 weeks at 2 m. Light may limit growth at 6 m during the short growing season, but is not limiting in midsummer at 2 m or 4 m. Plants of equivalent size produce 60–75% less biomass annually at 6 m than at 2 or 4 m. The seasonally maximal biomass (in mid‐August) is equivalent to the annual net production as calculated from periodic inventories of new, old and senescent tissue (thusP/B= 1.0). Uptake of nutrient elements (N, P, Ca, Mg, Na, K) is synchronous with biomass production. Nutrients do not become enriched in the overwintering tissue (52% of the maximum biomass). This species is unusually rich in Zn (1000 μg g dry wt−1), relatively rich in N (2.9% dry wt). but quite poor in P

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1980.tb01214.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

SUMMARY.The growth ofAustropotamobius pallipeswas studied in the River Ouse during 1976–78. Growth of mature crayfish (>2.5 cm carapace length) was followed by determining the relationship between the growth increment at moult and premoult carapace length, together with the frequency of moulting of different categories of crayfish. These data are supplemented by the recapture of marked individuals and the measurement of crayfish held in corves in the river. Growth was limited to the period May–October when water temperatures exceeded 10°C. Growth rates of male and female crayfish are similar until maturity is reached, thereafter males moult twice per year and the majority of females moult once. No crayfish in excess of 3.7 cm carapace length has been observed to moult more than once per year. Growth of juveniles (<2.5 cm carapace length) was estimated from size frequency distributions constructed from regularly taken samples. Growth rates of juveniles showed great variation both between and within year classes. In the hot dry summer of 1976, juveniles exhibited faster growth rates (instantaneous growth rates (G) for 0+ and 1 + crayfish were 0.029 and 0.013 mg mg−1day−1. respectively) than in other years. Laboratory experiments on the effect of temperature on the growth rate of 0 + crayfish were undertaken; for crayfish at 15°C.G= 0.0138 (0–53 days) and at 10°C,G= 0.0003 (0–90 days). Crayfish held at 10°C failed to undergo a single successful moult. At 20°C crayfish exhibited exponential growth over the first 40 days, withG= 0.0189. declining thereafter toG= 0.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1980.tb01215.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

SUMMARY.A device for detecting (with minimum disturbance) the sediment‐water interface in lakes is described. It is based on a commercially available slotted ‘opto‐switch’ incorporating a light emitting diode and a phototransistor. The design of an audible and visual indicator is given. Possible uses are discussed and an example of chemical micro‐profiling near to the sediment with the aid of the device is

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1980.tb01216.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

SUMMARY.This study was a large‐scale comparativein situexperiment on the fragmentation and breakdown of typical aquatic and terrestrial inputs of a chalk stream. Two similar lengths of stream were separated by screens of 5‐mm mesh across the entire stream width at their upper and lower limits. The material transported downstream was collected continuously for 3 years. The order of breakdown was:<2 weeks for the emergent herbaceous macrophyteRorippa nasturtium‐aquaticum; 2–3 months for the dominant submerged macrophyteRanunculus calcareusand 4–6 months for the terrestrial material, mainly leaves ofSalix viminalisandFraxinus excelsior. The degree of fragmentation of material varied with its structure, composition and time of availability relative to the seasonal changes of discharge. In general, fragmentation of material increased with its time of retention at or near its sites of origin, but this could be greatly modified by the date of the major autumnal increase in discharge. Thus, in a year of early rain, terrestrial leaf material was mainly whole when transported downstream but in a year with late rain, fragments predominated. The breakdown order coincided with an increasing ratio of carbon/nitrogen in the materials. The total annual movement of plant material was between 231 and 426 kg dry weight for both sites but there was considerable variation in the quantities of the individual species present. On an areal basis, with equal inputs of aquatic and terrestrial material, aquatic material was fragmented more than terrestrial material and therefore more of the latter was transported downstream. The aquatic macrophytes in the open section of the stream retarded the progress of terrestrial allochthonous material and resulted in a substantial increase in fragmentation of this material which would have been lost to this part of t

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1980.tb01217.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

SUMMARY.Surveys of the Wye catchment in March and September 1975, and July and September 1976 and 1977, yielded 227 macro‐invertebrate taxa, 77 of which were Chironomidae. Total macro‐invertebrate density ranged from 520 to 22020 m−2. Total density estimates in July 1976. during a period of severe drought, were significantly higher than in July 1977 but no differences were established between estimates on other comparable dates in 1975, 1976 and 1977. The total number of taxa and total macro‐invertebrates collected from sites with total dissolved solids concentrations less than 50 mg I−1were significantly lower than at sites with higher concentrations. In general, upstream sites were dominated numerically by Plecoptera in March; Ephemeroptera, Trichoptera and Diptera were relatively more abundant during the summer months. Sites lower in the catchment were more variable in composition with Oligochaeta, Ephemeroptera, Trichoptera and Diptera all abundant at certain sites and times. The densities of Ecdyonuridae (Ephemeroptera). Hydropsychidae (Trichoptera) and Elminthidae (Coleoptera) in the impounded R. Elan, a tributary of the R. Wye, were significantly lower than at nearby sites on the Wye although no differences in total macro‐invertebrate density were established. Average linkage clustering of Spearman rank correlation coefficients between selected taxa allowed the comparison of taxa groups with contemporary site groups by nodal analysis. Six major taxa groups were established and these characterized five sit

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1980.tb01218.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

SUMMARY.A total of 155 taxa was collected from the Ystwyth (111) and Rheidol (134) catchments and total macro‐invertebrate densities ranged from 435 to 9105 m−2and 155 to 4290 m−2in the two catchments, respectively. The fauna in each catchment was dominated by Insecta, principally Plecoptera, Ephemeroptera and Diptera. Trichoptera and Oligochaeta were proportionally more abundant in the Rheidol catchment. There was no evidence that the distribution or relative abundance of the faunas of the catchments were related simply to heavy metal contamination (mean zinc concentration up to 2.0 mg I−1and 0.34 mg I−1in the Ystwyth and Rheidol, respectively). Average linkage clusters of Spearman rank correlation coefficients suggested that community affinities were probably related principally to location within the catchment. There was no evidence in the Rheidol catchment that irregular discharges (up toc. 15 m3s−1) of water for hydroelectric purposes had any substantial effect on the invertebrate fauna although total invertebrate density below the discharge was significantly higher than at an up

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1980.tb01219.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

SUMMARY.Plastic cages containing artificial substrata were placed on the stony bottom of a stream in a section where the environmental conditions appeared to be homogeneous. The section was divided into eight equal sub‐sections (A‐H) and four cages were placed in each sub‐section. The stone‐size of the artificial substrata was similar within each cage but differed between the four cages with average diameters of 14, 24, 48 and 96 mm, respectively. The baskets were removed one month later and the catches of macro‐invertebrates were recorded.Analysis of the catches (density and number of taxa in each cage) revealed no significant differences in connection with the position of the cages in the section of stream. Cages with 48‐mm stones contained the least abundant fauna. The taxa which colonized cages with 14‐ or 24‐mrn stones were more numerous than those collected from cages with 48‐ or 96‐mm stones.Statistical analysis by laxon confirmed the preceding results. Variability in connection with the position of the cages along the section of stream was never significant. A little more than half the taxa were distributed independently of stone size but always showed a contagious type distribution. The density of the other taxa was higher, either in cages with 14‐ or 24‐mm stones (particularlyGammarus) or only in cages with 96‐mm stones (especiallyHydropsyche). Only one taxon was more abundant in cages with 48‐mm stones, the type of substratum in which the overall density was lowest.Catches in the cages were not the same as those taken with a Surber sampler because the two samplers did not take samples from the same habitats and also because the baskets offered a more specialized habitat than the surrounding bottom. The basket with 24‐mm stones gave the least distorted pict

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1980.tb01220.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

Serruya, C.(Ed.)(1978)Lake Kinneret.Reay, P.J. (1979)Aquaculture.Neff, J.M. (1979)Polycyclic Aromatic Hydrocarbons in the Aquatic Environment. Sources, Fates and Biological Effects.Thorp J.H. and Gibbons J.W.(Eds)(1978)Energy and Environmental Stress in Aquatic Systems.Mordukhai‐Boltovskoi, Ph.D. (1979)The River Volga and its Life.Welcomme, R.L. (1979)Fisheries Ecology of Floodplain Rivers.Heller, H.(Ed.)(1978)Verhandlungen, Gesellschaft für Ökologie, Kiel 1977.Elliott J.M.&Mann K.H. (1979)A key to the British freshwater leeches with notes on their life cycles and ecology.Merritt R.W.&Cummins K.W.(Eds)(1978)An Introduction to the Aquatic Insects of North Amer

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1980.tb01221.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1980.tb01222.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY