摘要:

SUMMARY.A description is given of a tubular phytoplankton sampler with a self‐activating closing valve. It can be constructed to any length, but a 2‐m or 3‐m sampler is convenient and allows the most important portion of a lake's vertical profile to be examined with relatively few hauls. Samples can be pooled for a single analysis of a sample representing the euphotic zone or other selected interval of depth within a lake. Alternatively, a series of taps in the sidewall of the tube enables subsampling of the contents and consequently, detailed determination of vertical inhomogeneities in phytoplankton distribution. Some data obtained with the sampler from two Ontario lakes are pres

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1979.tb01491.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SUMMARY.Statistical analysis has been carried out on 11 years (1965–75) weekly data of nitrate concentrations and discharge values from the R. Frome (Dorset). The results have shown a trend over the 11‐year period with nitrate concentrations increasing by 0.11 mg NO3‐N 1−1per year. A predictive model for nitrate concentrations for 1976 was made and even though discharge conditions were extreme, the mean predicted nitrate concentration of 3.37 ± 0.136 mgNO3‐N1−1was very close to the observed mean nitrate concentration of 3.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1979.tb01492.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SUMMARY.The rate of gastric evacuation in perchPerca fluviatiliswas studied at different mean temperatures (range 4.0–21.7°C). Gastric evacuation rates were empirically described by an exponential function and the relationship between the instantaneous evacuation rate (R) and temperature was also exponential. Evacuation rates were not significantly different (P>0.1) for the following food organisms:Gammarus pulex, Chaoborus, chironomids and zooplankton. The effects of temperature, different food organisms and fish size on the evacuation rates in different fish species are discuss

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1979.tb01493.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SUMMARY.Cell phosphorus and anthrone‐reactive carbohydrate contents were measured over a 6‐month period in the phytoplankton of Lough Neagh, N. Ireland. When all the soluble reactive phosphorus had disappeared from the water column, cell phosphorus contents began to decrease, reaching a minimum value of 0.4% ash‐free dry weight. At this time, cell carbohydrate contents greatly increased and phosphorus sorption assays showed rapid uptake of orthophosphate. Following a presumed sediment phosphorus release, cell carbohydrate and phosphorus uptake rate decreased greatly and there was a subsequent increase in cell phosphorus content to 1.6% ash‐free dry weight. As the cell phosphorus content declined, blue‐green algal filaments became progressively shorter. On the basis of these responses it is likely that phosphorus limitation occurred over a 4‐

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1979.tb01494.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SUMMARY.The oxygen uptake ofLimnephilus rhombicus, a typical inhabitant of lentic waters, was measured in three different experimental situations: in still water with a plastic mesh as a substrate, in stirred water with a plastic mesh and in still water without any substrate. Water flow caused a small increase in oxygen uptake at all temperatures but principally above 15°C. The presence or absence of the plastic substrate had little influence on oxygen uptake;L. rhombicuscan be active over the whole range of temperatures studied but its activity is always small. Its metabolism—temperature curve stands out in having a plateau between 5 and 10°C, with a steeper part between 10 and 20°C, the slope of which varies according to the conditions. Maximum oxygen uptake at high temperatures was relatively low (1235 ± 153 μl O2g dry wt‐1h‐1 at 25°C).The results are compared with those obtained previously for the larvae ofMicroptema testaceawhich inhabit flowing zones in brooks.L. rhombicuslarvae appear both as cold‐water animals and as animals from highly variable biotopes. They are in fact very ubiquitous and occupy all lentic biotopes from cold and mountainous districts to tempe

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1979.tb01495.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SUMMARY.The paper considers the forms of water movement that occur in unstratified lakes. Although not dealing directly with ecological implications, it is hoped that it will encourage the inclusion of observations of underwater weather as part of normal limnological routine. It is particularly concerned to show what observations are most effective in revealing hydraulic conditions.Relations between wind, lake geometry and wave characteristics are examined. Factors determining the steady, wind‐driven circulation are reviewed and examined in sequence: the action of wind on a water surface and the current directly generated by the wind drag; the effect of the earth's rotation; the need to balance the flow in and out of any part of the lake; the influence of lake morphometry. A simple model of lake circulation is developed that may help in the interpretation of on‐lake observations. Some other features of isothermal motion are discussed including the horizontal currents associated with unsteady wind conditions (seiches).The possible interaction between waves and currents are discussed. A tentative classification of hydraulic conditions in terms of wind speed, lake depth and fetch is suggested as a basis for forming hypotheses about the motion prior to on‐lake observations and as a possible starting point for a comparative app

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1979.tb01496.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SUMMARY.Six channels were constructed in various parts of two riffles from which chironomid exuviae were collected every 3 h for three 24‐h periods in July 1974. Diel emergence patterns were calculated for twelve abundant species and six different patterns were observed.Krenosmittiacf.camptophelepsandCorditeshad their major emergence pulse during peak light periods and it is proposed that high or increasing light intensity is a cue for their emergence.Stempellinellacf.brevisbegins its emergence in the morning and continues until after darkness. Increasing and high water temperatures are suggested as the emergence cue since emergence tracks water temperatures with little apparent effect of light.Parametriocnemussp. andPolypedilum(Tripodura) sp. begin emerging in late evening and continue into early daylight hours. These patterns indicate low and decreasing water temperatures as the emergence cue with little apparent effect of light.Corynoneurasp. andThienemanniellasp. emerged primarily during daylight hours with a minor pulse in the morning and the major pulse in late afternoon. It is proposed that the emergence cue is simply the presence of light and that water temperature determines how many individuals are able to prepare for emergence and respond to the cue.Rheotanytarsuscf.exiguusandTanytarsus(Sublettea)coffmanihave major emergence peaks just after sunset and minor pulses in the morning hours. Changes in light are proposed as their emergence cue with water temperatures determining the number of individuals able to respond to that cue.Eukiefferiella discoforipesgr. sp. andNilotanypussp. emerge continuously throughout daylight and darkness hours, showing no obvious patter

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1979.tb01497.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SUMMARY.Some authors have recently concluded that, using morphological criteria, the freshwater bryozoansPlumatella repensandP. fugosacannot be separated and should be regarded as conspecific. To test this conclusion, electrophoretic techniques have been used to examine genetic differences between the two nominate species at several enzyme loci. Significant variation at a malate dehydrogenase locus and three aminopeptidase loci establish beyond doubt thatP. repensandP. fugosaare separate but related species. No significant variation was found between two populations ofP. repens. Morphological characters for the distinction of the two species are discussed and evaluated.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1979.tb01498.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SUMMARY.Emerging adult chironomids were captured from a wet gravel‐pit in the Midlands in 1975 and 1976. The emergence period in 1976 was earlier than in 1975 and this change was attributed to the higher temperatures during the early part of 1976. Forty‐seven species were identified of which twenty‐one were found in both years. However, only eighteen species represented more than 5% of the monthly emergence from any one trap. The timing and location of emergence of the common species is discussed in relation to the physical parameters of substratum, depth of water and vegetation at each trap site. Similarity indices were used to compare samples from each trap site and revealed a progressive change in the chironomid assemblage with depth, caused by a succession of species and a change in the structure of the assemblage with ‘equitability’ decreasing with increasing depth. The predominant species in 1975 were Cricotopus sylvestris, C. intersectus and Procladius choreus with a number of Chironominae present in both May and June. A trap in the littoral zone caught maximum numbers earlier than traps in open water. In 1976 the above species were still predominant and Tanypus punctipennis and T. vilipennis were also numerous. The Chironominae became proportionally more abundant as the season progressed. The abundance of emerging midges was low compared with other surveys due to the restricted emergence period, imagines being abundant only in June, and also due to the low numbers

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1979.tb01499.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1979.tb01500.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY