摘要:

SUMMARY.Habitat selection and interspecies associations of stream insects were evaluated from a set of quantitative benthos samples and habitat measurements (velocity, depth, substrate, quantities of fine and leafy detritus) from a mountain stream. Substrate was characterized by anin situgrid method which effectively describes the size and distribution of the larger surficial materials within each sample unit. A principal components ordination of samples as characterized by abundance data over all species accounted for 54% of the total variance in three dimensions but implied continuous rather than discrete faunal change with habitat. Gradients in the habitat could not be identified with real confidence. Canonical correlation analysis identified three significant habitat‐fauna interactions. The first corresponded to the gradient from eroding to depositing substrates and included detritus abundance, the second distinguished areas of fine from leafy detritus and the third appeared to include velocity‐stone size interactions. A graphical technique based on ordination of physical data and clustering of associated species adequately summarized the distribution of fiveEphemerellamayflies. The multivariate and interactive nature of stream bottom environments is discussed for problems involving prediction and experimental design and cont

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1981.tb01272.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARY.The vertical and horizontal distribution of electrical conductivity, soluble reactive phosphorus (SRP), total phosphorus, ammonia‐nitrogen and nitrate‐nitrogen in the South Basin of Windermere is described and related, where possible, to spatial variations in phytoplankton and zooplankton.For most variables, the maximum range of horizontal variation on a single day was greater than the maximum range of seasonal variation measured at a single station over a full year. Horizontal variations in SRP and ammonia were particularly high, with coefficients of variation often exceeding 100%. The errors associated with sampling at a single station were most pronounced when local accumulations of zooplankton or phytoplankton occurred in the lake.Horizontal variations in conductivity were primarily influenced by the discharge of treated sewage effluent into the central region and the mass transport of water from the more oligotrophic North Basin. Occasionally, more widespread variations in conductivity appeared to be related to spatial variations in photosynthetic activity. The major factor influencing the horizontal distribution of SRP was the discharge of treated effluent into the central region. Despite the intensive recycling of phosphorus, SRP concentrations were nearly always 10–30% higher near the sewage works than elsewhere in the basin. On a few occasions, significant horizontal differences in SRP concentration were also detected within downwind accumulations of crustacean zooplankton. Horizontal variations in total phosphorus were produced by spatial differences in SRP concentration or by local accumulations of phytoplankton or zooplankton. Horizontal differences in ammonia concentration appeared to be produced, both by the effluent discharge and by the turbulent transfer of nutrients from sediments in shallow water.Observations of effluent movement and dispersion demonstrate that wind‐induced water movements tend to recirculate nutrient‐rich water in the central region and limit mixing along the axis of the basin. The statistical implications of nutrient heterogeneity are discussed in relation to sampling strategy and the possible effects of persistent nutrient concentration gradients on phytoplankton patch formation are

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1981.tb01273.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARY.An increase in the trophic state and productivity of a lake is not necessarily accompanied by a decrease in epilimnetic Secchi disc transparency. In smaller lakes with sharp thermoclines the symptoms of eutrophication may be more evident as a decrease in transparency in the epilimnion but, in larger lakes with poorly defined thermoclines, symptoms of eutrophication may be more evident in the hypolimnion as shown by an increase in the rate of hypolimnetic oxygen consumption.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1981.tb01274.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARY.An extensive survey of Mirror Lake, New Hampshire, was carried out by divers with SCUBA to assess the importance of the freshwater musselElliptio complanatain this softwater lake ecosystem. Density (0.032 adults m−2), biomass (52 mg m−2as dry organic matter) and annual production (6.4 mg m−2as dry organic matter) of the mussel population are low when compared with results from other studies, corresponding with the general observation that mussels are scarce in soft, oligotrophic waters. We reject the traditional view that the low mussel density is a result of low calcium concentrations in Mirror Lake, and propose that mussel populations may be regulated by a scarcity of appropriate fish hosts in unproductive lakes.Elliptio complanatais probably not important in the metabolism or biochemistry of the Mirror Lake ecos

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1981.tb01275.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARY.Mature larvae ofEcdyonurus disparwere collected from Ennerdale Water and Windermere (English Lake District) and reared to adult males and females in the laboratory. The females were then fertilized artificially and their progeny were kept at constant temperatures (range 4.2–20.2°C). Larvae collected directly from the two lakes were also reared under the same conditions.The maximum number of instars from egg to subimago was 25, the average body length increment (mm) per moult was proportionately constant atc. 15% and Dyar's rule was applicable. The interval between moults decreased with increasing temperature and the relationship between the two variables within the temperature range 4.2–19.8°C was described by a power law. Larval growth was exponential and variations in mean specific growth rate (range 0.23–5.23% length day−1) were related to mean temperature which was the major factor affecting growth in the laboratory. A few experiments were also performed in the lake to test the adequacy of the estimated values for larval growth at different temperatures in the laboratory. There was agreement between the estimates and the actual growth rates in the lake. Therefore, the regression equations obtained from the laboratory experiments are probably applicable to larval growth in the field.Values for daily production in the laboratory ranged from 0.53 to 9.33 mg dry wt day−1m−2. The lowest value was obtained at 8.9°C and the highest at 20°C.Information on different life cycles ofE. disparis briefly reviewed and it is concluded thatE. disparfrom the lakes can only achieve one gene

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1981.tb01276.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARY.This paper describes the design, construction and testing of a portable monitoring system capable of measuring water temperature, conductivity, dissolved oxygen, light attenuation and depth of operation. The unit is powered by rechargeable batteries and can be used to provide instantaneous readings or continuous records of each variable when used with a suitable chart recorder. Circuits for measuring conductivity and light‐ratio are of a novel design. The conductivity circuit measures conductance by the voltage drop across a low‐value resistor connected in series with the conductivity cell. The light‐ratio circuit measures light intensities by digitizing signals from two photocells and comparing their ratios over short periods of time. The paper includes examples of results obtained with the instrument in a wide range of applications and compares the performance of the Mackereth oxygen electrode with, and without, a small water‐circulating att

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1981.tb01277.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARY.A comparison of the potential water fertility of two linked lakes, Llyn Peris and Llyn Padarn, was carried out over a year usingAsterionella formosaas the test organism in batch cultures. In unenriched lake water, growth was more rapid in Padarn water during autumn‐winter‐spring, but there was no significant difference between growth in water from the two lakes during the period of thermal stratification. Mean growth rates in treatments with additions of nitrogen and chelated iron were not significantly different from unenriched water samples, both between treatments and lakes during thermal stratification. Growth in water from both lakes was increased greatly by addition of phosphate. Maximum growth rates occurred on addition of nitrogen, phosphate and chelated iron, and there was no significant difference between growth rates in this treatment for the two lakes throughout the year. Comparisons of mean growth rates in bioassays by Tukey's interval estimate showed significant differences between other treatments and the two lakes. The potential fertility of water samples from the two lakes differs more during mixed water conditions than in the period of thermal stratification.Inhibition ofA. formosagrowth was recorded four times in unenriched filtered water from Peris, once on addition of nitrogen and once on addition of iron. Inhibition was alleviated by the addition of nutrients.The addition of diluted sewage effluent which enters the drainage system between the two lakes, resulted in similar rates of growth ofA. formosain water from both lakes.Results of the bioassays are discussed in relation to differences in phytoplankton between the two lakes. AlthoughA. formosawill grow in samples of unenriched lake water from Peris, other features, including a shorter retention time of water, lower level of incident radiation and, occasionally, inhibitory substances in the lake water, contribute to the rare occurrence of this diatom in Peris. Padarn is enriched by sewage effluent which aids the growth ofA. form

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1981.tb01278.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Barnes R.S.K.&Mann K.H.(Eds) (1980)Fundamentals of Aquatic Ecosystems.Brown, D.S.(1980)Freshwater Snails of Africa and their medical importance.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1981.tb01279.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1981.tb01280.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY