摘要:

SummaryThe zooplankton fauna of the Plover Cove Reservoir has been investigated using two sampling series. The first series involving a 3‐year investigation using 6‐ft vertical hauls at three stations in the reservoir, revealed the presence of two copepod and four cladoceran species with little variation in terms of seasonal peak occurrence and abundance in any of the stations and so no evidence of the horizontal distribution patterns referred to by other authors. In all three stations Diaptomus gracilis was the dominant copepod species and Diaphanosoma leuchtenbergianum the dominant cladoceran species.The second series, involving a 13‐month investigation of vertical sets of water samples collected both day and night at 4‐h intervals for 24‐h periods, revealed that in terms of seasonal vertical distribution, all six species occurred at all depths during the survey, but with a tendency to be concentrated in the surface waters.In terms of diurnal vertical distribution, differences in the migration pattern occurred from season to season in the case of Diaptomus gracilis. Thus, during spring, summer and autumn, concentrations occurred at the surface at 10.00 and 22.00 hours followed by migration to greater depth, whereas in winter, surface accumulations persisted even into the daylight hours. However, both Cyclops hyalinus and Diaphanosoma leuchtenbergianum showed surface accumulations at night and a movement away from the surface by day during all seasons.Investigations of the seasonal variation in environmental parameters conducted during both sampling series revealed that, as in the case of similar surveys, water temperature was the major controlling factor governing the seasonal variation in composition of the zooplankton fauna as well as its seasonal vertical distribution since in the case of Diaptomus gracilis and Ceriodaphnia reticulata low water temperatures corresponded with peak seasonal occurrence whereas in the case of the other species high water temperatures corresponded with peak seasonal occurrence, and since Diaptomus gracilis and Diaphanosoma leuchtenbergianum showed maximum concentration near the surface when surface water temperatures were high, whereas the remaining species showed their maximum concentration near the surface when lower water temperatures prevailed.It would also appear, however, that seasonal changes in zooplankton densities closely followed algal densities since Diaptomus gracilis, Diaphanosoma leuchtenbergianum and Bosmina longirostris had their maxima in late spring and Cyclops hyalinus in late summer while algal densities in this reservoir were highest in early spring and early summer.With regard to the diurnal vertical distribution of the zooplankton, light appeared to be the only factor alternating by an amount likely to be correlated with such diurnal vertical changes in zooplankto

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1976.tb01616.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

SummaryLake sediments of the last 1000 years provide a unique record of environmental changes. Methods of dating this record are reviewed and discussed. Sediments of the last 20 years, which are of particular biological significance because of their record of man‐made changes in lakes (including enrichment and pollution) have been dated successfully by the distribution within them of the fallout product137Cs, present in the atmosphere since 1954 and reaching a peak of supply in 1963. The structured pattern shown by the curve for137Cs concentration in most sediments investigated indicates that faunal mixing of the surface muds does not destroy the vertical stratification of the sediment profile.Sediments up to 120 years old have been dated by a lead isotope technique, and the results of this proved consistent with both137Cs dating and with palaeomagnetic dating where this was possible.Theoretical considerations of the application of radiocarbon dating to organic material of 18th and 19th century date are reviewed.Results of application of these radionuclide techniques to the sediments of a small lake, Blelham Tarn, near Windermere, are presented. Evidence from137Cs and210Pb dating of profiles from several different positions within the lake shows that the depth of the annual increment to the sediments varies by a factor of × 2 from place to place. The concentration within the sediment of chemical and biological variables shows no significant variation from one position to another; therefore calculated values for amounts of each variable included within unit area of the annual increment depend primarily on the thickness of this at the site chosen, and so cannot be directly related to the rates of supply of, for example, pollen grains or total organic matter, and so to rates of productivity.Results from nine14C dates on material 400–1000 years old, when correlated with analyses for pollen and sediment composition, demonstrate the profound effects of agricultural practices in the catchment (assumed to be deforestation and ploughing) in disturbing the orderly transfer to lake sediments of material eroded from the catch

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1976.tb01617.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

SummaryThe chemical composition and energy contents of four different species of cladocerans, one species of a calenoid copepod, and mixed samples of four species of cyclopoid copepods were quantitatively determined.The relative chemical composition, expressed as a percentage of the total organic matter (excluding chitin) of each of the different species analysed, were very similar. The mean relative composition for all species was 71·2% protein, 9·5% carbohydrates, 19·3% lipids, 16·5% total nitrogen and 2·1% total phosphate–phosphorus. A substantial amount of the total nitrogen was found to be non‐protein nitrogen (mean of 23·3% of total nitrogen). The calorific value was calculated from the estimated amounts of proteins, carbohydrates and lipids using conversion factors. The relationship between the calculated organic matter and the chemical oxygen demand (COD) was found to be constant and did not vary much for the different species. The ratio of total organic matter to COD has a mean value of 0·51. Calorific values ranged from 5847 to 6353 cal/g total organic matter.The amounts of chemical substances or energy contents per individual Copepoda or Cladocera were calculated. Regression lines together with their correlation coefficients have been computed to describe the relationship between the amount of chemical constituents and energy contents per individual, and the length of the individual. The results are extensively compared with those given in the literature and differences are

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1976.tb01618.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

SummaryLarvae of Plectrocnemia conspersa and Polycentropus flavomaculatus from flowing water and Cyrnus flavidus and Holocentropus picicornis from still water were selected for study.In the above sequence, these larvae are associated with increasing ranges of temperature in their natural habitats. Experimental determination of lethal temperatures and investigations on ventilation frequency indicated that the larvae were increasingly tolerant of temperature in the same sequence of species.C. flavidus and H. picicornis showed infrequent ventilation which was little affected over wide ranges of temperature and dissolved oxygen but was stimulated erratically by water flow. P. conspersa and P. flavomaculatus showed more active ventilation which was more sensitive to changes in temperature and dissolved oxygen and was decreased by water flow.Consideration of ventilation in relation to oxygen uptake in P. conspersa and P. flavomaculatus suggests that ventilation activity may account for some 60–70% of active oxygen uptake. Differences in ventilation behaviour may thus be important in limiting larval distribution in stream system

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1976.tb01619.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

SummaryA situation is described where silicon depletion affected a population of diatoms, mainly Diatoma elongatum and Melosira spp., in the shallow lake Tjeukemeer (The Netherlands). After Si‐deficiency the numbers of cells dropped quickly, whereas at least for the upper layer (0–1 m) a big increase in the percentage of biprotoplastic D. elongatum cells was observed. Probably the major part of the D. elongatum population arrived alive at the bottom. Heavy winds occurring 2 weeks later stirred up considerable numbers of both diatoms. The numbers of dead D. elongatum cells was then 40–50%, presenting some evidence that a large scale dying of D. elongatum cells occurs rather shortly after arrival at the bottom of Tjeukemeer. In the following weeks, at low Si‐concentration, numbers of D. elongatum almost doubled with once again a relatively high percentage of biprotoplastic cells, whereas numbers of Melosira spp. decreased. In the relevant conditions it seems that D. elongatum can take up silicon faster than Melos

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1976.tb01620.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

SummaryThe River Coquet is a clean, fast flowing, moderately calcareous river. It is young to mature in development and supports a typical torrential fauna. Marked trends in successional replacement along the river course are confined to the scarce species of Ephemeroptera and the absence of longitudinal zonation in the distribution of some common species is related to the topographical characteristics of the system. A distinct successional trend by one species is attributed to its intolerance to the lower temperatures at high altitudes. Major discontinuities in distribution are found between the Ephemeroptera of the main river and certain tributaries. The paucity of certain otherwise abundant species in one region is related to silt deposition resulting from sand and gravel excavation.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1976.tb01621.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

SummaryThis paper describes the construction and field operation of a trap designed to investigate the movements of larval Chironomidae in the open water of lakes. Although the trap was designed to be multidirectional, with six trapping bottles, only two directional components, vertical and horizontal, could be distinguished. This led to examination of three bottles only during later field studies, namely bottle 1 facing into the current, bottle 5 facing the substrate and bottle 6 facing the surface of the lake. Some results are presented and trap operation and sampling efficiency discussed.A major advantage of the trap is its use as a long term accumulator of planktonic organisms as opposed to traditional spot sampling techniques which tend to miss the less numerous plankters.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1976.tb01622.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

SummaryThe food of Planaria torva was examined in the laboratory by exposing a range of potential prey to the triclad and observing prey mortality. Under these conditions P. torva fed mainly upon tubificid oligochaetes and gastropods. The former activity was regarded as untypical of the field situation and due to limitations of the laboratory habitat.The food of P. torva was determined in the field by taking monthly samples from October 1967 to May 1969 of a population living in Linlithgow Loch, West Lothian, Scotland. A serological technique was used to examine the gut contents of the field triclads. For reasons explained in the text, the prey organisms tested for serologically were gastropods, oligochaetes (Tubificidae), Asellus and chironomid larvae. Planaria torva fed most extensively on Gastropoda, Asellus was the second main food while Tubificidae and Chironomidae were taken only seasonally and in small numbers. The limited extent of feeding on tubificids supports the laboratory data. Small P. torva gave proportionately fewer positive reactions to the prey antisera than large individuals. This was explained by the fact that small individuals occurred most frequently in the warmer months and took smaller meals; both of these features shorten the detection period of food in the gut and therefore give fewer reactions. The diet of small and large P. torva was similar in the field and showed considerable overlap with that of Dugesia polychroa.The food of Polycelis tenuis, Dendrocoelum lacteum and Dugesia polychroa in Linlithgow Loch was described on an annual basis and the results confirmed earlier observations.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1976.tb01623.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Golterman, H. L. (1975)Physiological Limnology. An Approach to the Physiology of Lake Ecosystems.Disney, R. H. L. (1975).A Key to the Larvae, Pupae and Adults of the British Dixidae (Diptera). The Meniscus Midges.Balon E. K. and Coche A. G. (Eds.) (1974).Lake Kariba, a Man‐made Tropical Ecosystem in Central Africa.Klasvik H. (1974).Computerised Analysis of Stream Algae.Lowe‐McConnell R. H. (1975).Fish Communities in Tropical Freshwaters.Roberts R. J. and Shepherd C. J. (1975).Handbook of Trout and Salmon Diseases.Nicholas W. L. (1975).The Biology of Free‐living Nematodes, pp. 219.Smirnov N. N. (1974).Chydoridae of the World's Fauna.Steemann Nielsen E. (1975).Marine Photosynthesis. With Special Emphasis on the Ecological As

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1976.tb01624.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY