摘要:

SUMMARY.The freshwater littoral meiofauna along a temperature gradient in Par Pond (a cooling reservoir receiving thermal effluents from a nuclear reactor) was sampled from September 1975 to October 1976. Monthly samples were taken at three stations; ‘hot‐water’ (15–40°C), ‘warm‐water’ (13–37°C) and ambient or ‘cold‐water’ (8–37°C) sites. Total numbers of individuals at the ambient site ranged from 971 to 3674 per 10 cm2(mean = 2263), approximating the density reported from productive estuarine environments. Nematodes, rotifers, ostracods, cladocerans and mites comprised 80% of overall density. When compared to the ambient site, thermally affected sites demonstrated reduced faunal density.Contrary to other environmental perturbation studies, the Shannon‐Weaver diversity index (H') did not reflect alteration of structural complexity within the rotifer taxocene when hot‐water, warm‐water and cold‐water sites were compared. Though there was a significant reduction in number of species at the thermally altered sites, high ‘equitability’ among the reduced species resulted in H’ values comparable to those in natural communities. Distinct winter‐spring and summer‐autumn assemblages were evident in the ambient community while no seasonal clustering was apparent at the thermally affected sites. It is hypothesized that the maintenance of temperatures above ambient normals masks environmental cues that normally would elicit seasonal cha

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1979.tb01513.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SUMMARY.Organic detritus resulting from microbial attack on algal material contains lipids directly extractable by organic solvents and also contains bound lipids, obtained by solvent extraction following acid hydrolysis. Differences between the composition of bound and extractable n‐alkanes, n‐ and branched/cyclic alkanoic acids from each source are attributed to a major bacterial input to these bound lipid classes. Similarities in composition between bound lipid classes of algal detritus and corresponding classes in a lake sediment support earlier suggestions of a considerable bacterially‐derived contribution to sedimentary bound l

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1979.tb01514.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SUMMARY.Curie point pyrolysis mass‐spectrometry of freshwater fulvic acids from Tjeukemeer indicates the presence of polysaccharides, amino sugars, proteinaceous material and phenols. These results resemble those of the pyrolysis of soil fulvic acids. However, freshwater fulvic acids may be richer in aliphatic components than those from soi

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1979.tb01515.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SUMMARY.Growth ofLemna minorfronds in the River Frome during summer was found to be logarithmic with time and the growth rate (log10) was 0.066 day−1. This is equivalent to a doubling time of 4.5 days. The life expectancy of the fronds was 34 days.The net change in the density of bacteria epiphytic on the lower surface ofLemnafronds in the R. Frome was monitored using a direct microscopic technique. The observed increase in bacterial numbers has been partitioned into the components of attachment and growth, assuming that attachment occurred at a constant rate and that the bacterial population grew logarithmically. The line which fitted the data best gave an attachment rate of 5.7 × 105bacteria cm−2day−1and a growth rate (log10) for the bacteria of 0.044 day−1which is equivalent to a doubling time of 164 h.Estimates of the rate of detachment of bacteria fromLemnaplants were obtained from a laboratory experiment which assumed negligible growth of bacteria in 1 h. The number of bacteria which detached per hour and the sizes of the bacterial populations on the plants before and after detachment were estimated using a plating technique. Different detachment rates were monitored. The detachment rate (analogous to growth rate) which is judged to be most similar to anin situvalue was 0.0031 h−1(0.074 day−1). This rate added to the specific growth rate given above resulted in a corrected growth rate of 0.118 day−1equivalent to a doublin

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1979.tb01516.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SUMMARY.Chlorophyll, ATP and glucose concentrations as well as glucose uptake rate and primary production were determined every 2–4 h during three 24–h surveys in Lake Kinneret. In spite of the fluctuations in glucose uptake rate, the estimation of the daily glucose uptake rate from a single sampling carried out at 10.00 hours is justified. The same applies also for the primary production.Routine bi‐weekly determinations of primary production and glucose uptake rate were carried out from October 1976 to July 1977. No correlations were found between glucose uptake rates and ambient concentrations of ATP, chlorophyll and glucose.The glucose uptake rate showed two distinct seasonal patterns; the period which was dominated by thePeridinium(January‐April) and the rest of the year. In the former period the percentage of glucose‐carbon utilized out of the carbon formed in the water column by the photosynthetic activity, fluctuated between 1 and 9%, and in the latter period fluctuated between 5 and 37%. The yearly average was 11.1

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1979.tb01517.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SUMMARY.Buoyant nets had been developed and used for several years to sample young fish quantitatively. Tests were carried out to verify the quantitative aspect of sampling. Using nets of 1‐m and 0.5‐m mouth diameter, over several months, the catches of the two net sizes were compared. There was no significant difference in the lengths of the fish caught in the two sizes of net nor in the population estimates derived from their catches. These results indicate that there is no avoidance of the nets and that they can be considered to sample quantitativ

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1979.tb01518.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SUMMARY.A population ofAsellus aquaticusin Wistow Lake, England, was sampled at monthly intervals from September 1973 to September 1974. The mean population density was 586 m−2in autumn 1973 but it fell to 67 m−2by autumn 1974. Evidence suggests that the lower density in autumn 1974 was due to premature mortality of gravid females. The cause of this is not known.Gravid females were present from February to June and July to September, giving rise to spring and autumn cohorts. The larger members of the spring cohort reproduced in the autumn, the remainder in the following spring. The autumn cohort reproduced mainly in the following spring but later than the spring cohort. The bimodal length‐frequency curves were analysed to separate the two cohorts and to estimate growth and production of each cohort separately. The overwintering spring cohort had a faster relative growth rate than the smaller individuals of the autumn cohort. Thus the spring cohort showed aP/Bratio of 2.62 for the period September–April compared with a ratio of 1.81 for the autumn cohort. The highest ratio of 6.42 was shown by the spring cohort in the summer (May–September).Annual population production (P) was 3004.9 mg dry wt m−2from a mean biomass (B) of 757.2 mg dry wt m−2. TheP/Bratio of 3.96 is double the value reported forA. aquat

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1979.tb01519.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SUMMARY.Using a serological technique, the extent of feeding upon snails byPolycelis tenuiswas compared in habitats lacking and containingDugesia polychroawhich is the major triclad predator of snails. It was found thatP. tenuisate significantly more snails whenD. polychroawas absent. It was concluded that in the field interspecific competition for snails between these two triclad species was a more powerful process than any social feeding byP. tenuison snails captured byD. polychroa.Feeding on snails as a group byP. tenuisandP. nigrain the habitat where the two triclads co‐existed was of a similar magnitude and this was also true of their feeding on the common snail species and genera. Approximately 10% of the triclads gave a positive reaction to snail antisera.Feeding on snails byP. nigrain the three habitats lackingD. polychroawas similar in extent and did not differ from that ofP. tenuis. It was concluded thatP. nigrawould be similarly affected by the presence and absence ofD. polychroaas shown forP. tenuis.No definitive seasonal pattern was detected in the incidence of feeding upon snails by eitherPolycelisspecies but this may have been obscured by seasonal changes in the detection period of snail antigens due to temperature effects. There was some evidence that such feeding increased during the period when small snails were present in the populatio

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1979.tb01520.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SUMMARY.Levels of cellular orthophosphate concentration, alkaline phosphatase activity, photosynthesis and nitrogenase activity of natural populations of blue‐green algae collected during the summer of 1976 from the surface waters of three eutrophic lakes were determined under controlled conditions. Intracellular concentrations of surplus stored phosphorus remained high and alkaline phosphatase activity remained low during the formation and decline of the surface bloom, which indicated that available phosphorus does not become limiting to growth. In contrast, declining rates of nitrogenase activity and net photosynthesis were recorded, particularly in those blooms of shorter duration. An increase in numbers of bacteria during the summer may account for the observed fall of net photosynthetic rates, since gross rates did not change as markedly. There was appreciable nitrogenase activity proceeding and during the differentiation of akinetes, and the cellular C/N atomic ratio of sporulating populations was lower than in non‐sporulating algae. It is suggested that the onset of sporulation in surface blooms is initiated by an imbalance of the normal vegetative growth of the algal cells and of their carbon and nitrogen metabol

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1979.tb01521.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SUMMARY.The influence of exposure time upon macro‐invertebrate colonization on modified Hester‐Dendy substrate samplers was investigated over a 60‐day period. The duration of exposure affected the number of individuals, taxa and community diversity.The numbers of individuals colonizing the samplers reached a maximum after 39 days and then began to decrease, due to the emergence of adult insects. Coefficients of variation for the four replicate samples retrieved each sampling day fluctuated extensively throughout the study. No tendencies toward increasing or decreasing coefficients of variation were noted with increasing time of sampler exposure.The number of taxa colonizing the samplers increased throughout the study period. The community diversity index was calculated for each sampling day and this function tended to increase throughout the same period. This supports the hypothesis that an exposure period of 6 weeks, as recommended by the United States Environmental Protection Agency, may not always provide adequate opportunity for a truly representative community of macro‐invertebrates to colonize multiplate samplers.Many of the taxa were collected in quite substantial proportions after periods of absence or extreme sparseness. This is attributed to the growth of periphyton and the collection of other materials that created food and new habitats suitable for the colonization of new taxa.Investigation of the relationship between ‘equitability’ and length of exposure revealed that equitability did not vary like diversity with increased time

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1979.tb01522.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY