摘要:

SummaryChanges in discharge and chemical composition are related to biological and physical conditions at eight sites on the South Winterbourne from the source to the confluence with the River Frome. The results show a complex pattern of discharge with nitrate peaks at high discharge values. Mean phosphate values varied from 34·2 μg l−1(at the source) to 164·6 μg l−1.The Winterbourne has a rich flora of algae and higher plants of which the annual sequence is influenced by the flow regime and the effects of human interference by cutting and removal of plants and addition of nutrients. The fauna has much in common with permanent chalk streams but temporary flow conditions favour insects having prolonged resting stages or those which are able to colonize quickly from other areas when flow commences. Many non‐insect groups particularly snails, are able to withstand relatively long dr

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1976.tb01584.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

SummaryThe incorporation of inorganic carbon in particulate and dissolved organic matter by natural populations of photosynthesizing algae has been studied in Lake Kinneret, Israel, from August 1972 to December 1973. The release of dissolved organic material was directly related to the rates of particulate productivity. However, the percentage of extracellular release (PER) of dissolved organic compounds showed an inverse relationship with chlorophyll a concentrations. Mean PER values (for the trophogenic layer) over the experimental period were 3·7%, and were lowest during the exponential growth phase of the annual dinoflagellate bloom (mean PER = 1·9%). Highest PER were measured in deep, light‐limited samples (mean = 31·7%; s.d.· 21·9%). In a dense metalimnic layer of photosynthetic sulphur bacteria (Chlorobium phaeobacterioides), PER was not as extremely high as has been reported for a similar layer in Lake Wadolek, Poland. Although the amounts of dissolved organic matter released by phytoplankton in Lake Kinneret were low, they may have significance as growth modulators and as substrates for heterotrophic or

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1976.tb01585.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

SummaryThe predatory larvae of Sepedon fuscipennis (Diptera: Sciomyzidae) feed only on aquatic pulmonate snails. Under laboratory conditions these larvae utilized ingested snail tissue more efficiently when a lower snail biomass was ingested at lower snail densities. The adaptive value of this response to fluctuating prey availability is suggested.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1976.tb01586.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

SummaryA comprehensive temperature survey of the River North Tyne and its major tributaries is described. The maximum summer temperature of the main river increased downstream, and then remained more or less constant in the middle and lower reaches, whereas the minimum continued to rise throughout the length of the river. This general pattern was unaltered by flow rate, except in regions of almost stationary water. Mean water temperatures were low in winter, rose to a peak in July, and then fell during the remainder of the year. Throughout the year, three significantly different mean daily temperature ranges were demonstrated. The rate of change of temperature also varied seasonally, being greatest during July. A study of the major tributaries revealed certain differences, and these are discussed, particularly in relation to the importance of width and shading on water temperature. In conclusion, suggestions have been made concerning the possible influence of Kielder Water on downstream river temperatures.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1976.tb01587.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Summary(1) A flat substratum hung in midwater is colonized rapidly by a number of species normally found in vegetation. Some have been recorded consistently, a greater number occasionally, but only a few have not been recorded at all. Evidently most species are moving round frequently, even those, such as snails and case‐building caddis‐larvae, that cannot swim. (2) It seems likely from this that the identity of the plant cover has less influence on the structure of a community than some have thought. (3) A comparison of flat sheet, pleated sheet and artificial Littorella suspended in midwater makes possible certain statements and deductions. (i) Leptophlebia, Enallagma and chironomid larvae are more numerous on artificial Littorella; their natural habitat is within the vegetation cover. (ii) Cloeon, Cyrnus and Holocentropus are as numerous on the sheets or more numerous than in the artificial vegetation; they inhabit the surface of the plant cover where Cloeon is protected by its speed, and where the polycentropopids, protected by their nets, can trap both the true plankton and the Cladocera which feed in the vegetation. (iii) The foot of a snail and the suckers of a leech are most effective on a flat surface, which also provides a good feeding place for a snail. The higher numbers of Lymnaea and Erpobdella on the pleated compared with the flat sheets indicates the importance of cover for these two animals. (4) Flat plastic sheets hanging in the illuminated zone would improve the production of fish a little, pleating the sheets would improve it a little more, and best results would come from hanging something with a greater resemblance to natural vegetat

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1976.tb01588.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

SummaryTo obtain further evidence of the contribution of autochthonous organic matter to lake sediments, the benzene‐methanol extract of the particulate matter remaining after microbial attack upon an alga, Ceratium hirundinella, during laboratory simulation of natural decomposition processes, has been separated into its components. Comparison of each component with corresponding material isolated from the fresh alga facilitates the recognition of unchanged substances and microbial products in the decomposed sample. Certain common features in the occurrence and distribution of n‐alkanes, alkenes, n‐ and branched/cyclic alkanoic acids, alkenoic and hydroxy acids in degraded algal organic matter and in sediments of productive lakes are believed to indicate a contribution of autochthonous material to the sed

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1976.tb01589.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

SummaryTemperatures of the water column and upper 5 cm of sediment were monitored over a yearly cycle in two South Carolina lakes. Occasional supportive data were also obtained for several lakes in north central Florida. Plans are given for a new type of sediment‐interface sampler that is useful in obtaining detailed temperature or chemical profiles extending from the sediment surface upward. The sampler was used in the investigation to demonstrate the thermal microstratigraphy near the mud surface.The deep‐water (16 m) temperature for the larger of the two South Carolina lakes changes seasonally from 10·5°C in February to 18·0°C in July. The smaller, shallower (11 m) lake follows an almost identical seasonal cycle but is always 4·0°C cooler because the larger lake receives a heated effluent that has a long‐term effect on hypolimnetic temperatures. In both lakes the uppermost sediments are warmer than the overlying water by an average of 0·1 to 1·0°C during the warming period. Heat accretion near the bottom continues but is slower after stratification, probably due to the relatively low temperature (density) differential between water layers in these warm lakes. Cooling in deep water begins long before breakdown of stratification and is apparently caused by cold density currents from the shallows. The coldest water is located in a thin layer just over the sediment. There is evidence from one of the South Carolina lakes and from the Florida lakes that when the density flows begin they at first flow over a warmer water layer that is more dense due to a high electrolyte content derived from the sediment.There is a slight deep water warming in all of the lakes when stratification breaks down. After destratification, the deep water is cooled by turbulence rather than density flows. The surface sediments at this time are consistently warmer than the hypolimnion and remain so through the cooling period. There is strong evidence from one Florida lake that turbulence mixes the upper 3 cm of sediment during the isothermal period.It is concluded that the sediment‐water interface of a warm lake will in general experience greater heat flux than that of a comparable cold lake during the periods of temperature maximum and minimum. Conversely, there is likely to be less heat flux during the warming and cooling periods of warm lakes than of cold lakes. Several expected differences in seasonal patterns of temperature and water movement in the deep water of warm and cold lak

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1976.tb01590.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

SummaryAn attempt is made to illustrate some of the principles of early development of muds in two contrasting lake basins which were devoid of vegetation cover before filling. Essentially the changes involve the dispersion and redistribution of particles in the newly flooded lake bottom. Field and laboratory observations are presented to demonstrate the interaction that exists between water chemistry, wave erosion and the burrowing activity of mud‐dwelling insect larvae, and the effect of these factors on particle size sorting in the substrate. These characteristic changes in the mud during filling are compared with post‐filling stage developments in which the role of extraneous material, including organic matter, may predomin

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1976.tb01591.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

SummaryThe species composition of planktonic diatom crops in Loch Leven, Kinross, Scotland varied considerably over the years studied (1968–71) with centric forms predominating. Dense populations were often produced and rates of increase and decrease were high.Relations with dissolved silica did not appear always to be simple; instances occurred during which both diatoms and silica were increasing or decreasing. Moreover, certain rates of increase in dissolved and frustule silica exceeded the rates at which silica flows into the loch even when the inflows appeared to be the only available dissolved silica sourc

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1976.tb01592.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY