摘要:

SummaryIn this study of the Lough Neagh catchment a relationship has been sought between the loads of dissolved and total silica and the flow of each of the six inflowing rivers. Two of these rivers‐the Main and Six Mile Water‐carry a higher ratio of dissolved to total silica than do the remaining four rivers due to the geology of the catchment. The multiple regressions of loads in tonnes against river flows in cubic metres show a linear relationship for dissolved but not for total silica. The explanation for this non‐linearity has been sought in the river proaies, where the fall for the last 30 m varies from 5 to 25 km depending on the river. The rivers Main and Six Mile Water are the steepest, and linear relationships were obtained in their regressions while the shallowest profile was found in the Blackwater where non‐linearity in the multiple regression was obtained.In Lough Neagh the dissolved silica content was gradually reduced from early winter through to springtime by diatom growth and a balance has been drawn up for this utilization. This reduction also compares with the quantity in the diatom crop at maximum based on cell volume measurements. The summer build up of the dissolved silica content of the lough has been shown to be greater than the quantity contributed by the inflowing rivers from late spring to autumn and the data show that the recycling of silica from some 65% of the frustules from the spring crop after its collapse would account for the summer i

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1975.tb00117.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SummaryFrom a series of experiments and measurements covering one 24‐h period in Lake George the diurnal patterns of photosynthesis, nitrogen‐fixation and stratification are described. The thermal cycle shows three distinct phases of isothermy, intense stratification and mixing. During stratification the surface water temperature reached 36°C, whereas the bottom temperature remained at 25°C. The phytoplankton are evenly distributed at dawn, sink out during the day and tend towards an even redistribution as thermal stratification breaks down. Depth‐time profiles of oxygen concentration and pH values showed that intense photosynthetic and respiratory activity occurred. The shortness of the predominant limnological cycle is thought to be instrumental in restricting species fluctuations.Changes of total CO2 concentration in situ within the euphotic zone indicated that 2.25 g C/m2.12 h were photosynthetically fixed during daytime. From changes of in situ oxygen concentration, gross photosynthesis was estimated to be 12 g O2/m2.12 h and net particulate production over 24 h as zero.Photosynthetic activity was also measured with the i^C and oxygen techniques by enclosing algal samples in light and dark bottles. The patterns of activity recorded by the two methods were similar, although quantitatively the oxygen method gave rather higher values than did the method. Daily gross photosynthesis was estimated as 15.56 g O2/m2.12 h and 4.5 gC/m2.12 h. These figures are compatible with one another and with the production estimates calculated from Tailing's model of integral daily photosynthesis.The balance between respiration and photosynthesis is described as a function of the underwater light climate and the relative rate of respiration. Both the experimental and theoretical approaches suggest that the column 24‐h net particulate production is an extremely small percentage of gross photosynthesis.Nitrogen‐fixation was measured using both the15N2and the acetylene reduction techniques. The day‐long incubation of the15N2experiment showed that 11 mg N/m2.day were fixed. The series of shorter acetylene reduction experiments gave a value of 58 mg N/m2.day. The acetylene technique showed relatively high nitro‐genase activity at very low light intensities. The15N2results indicated little N2‐fixation at low light intensities. The differences between the two techniques are discussed.Gross photosynthesis estimates calculated from seven different methods run simultaneously are compared. The figures show reasonable agreement, but since the gaseous environment in the euphotic zone is particularly suitable for photo respiration the values are not considered reliable estimates of phytoplankt

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1975.tb00118.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SummaryA serological technique was used to demonstrate that one species of trichopteran and three species of plecopteran nymphs were feeding on stream‐dwelling triclads. Observations on streams in Caernarvonshire, North Wales, suggested that, in general, these predators were not typical members of the fauna at springheads, where triclads were frequently abundant. In contrast, further downstream the presence of predators was considered to be one of a number of factors which contributed to lower population densities of triclads. However, two small stony streams were encountered where the plecopteran predator Dinocras cephalotes occurred in close proximity to stream‐dwelling triclads from the springhead downwards. In one, both predators and prey were found at all stations but highest triclad numbers were recorded where predators were few. In the second stream the population density of the predator was higher, and here, triclads were very scarce on the undersides of stones and were almost entirely confined o t patches of moss. It appears that the predators may be both limiting the micro‐distribution of the triclad and also perhaps feeding selectively on larger individuals since mature triclads were rare, except at the sprin

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1975.tb00119.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SummaryBrown trout of different weights (range 8‐358 g) were fed to satiation at fifteen different water temperatures (range 3.8–21.6°C. Both the weight of the trout (Wg) and the water temperature (T°C) affected the maximum weight of food (Q mg) consumed in a meal, and the relationship between the three variables was well described by a multiple regression equation which can be used to estimate the value of Q (with 95% confidence limits) for trout of different weights at different temperatures between 3.8°C and 21.6°C. The satiation time (with 95% confidence limits) can also be estimated from a multiple regression equation for trout of different weights at temperatures between 6.8°C and 18.1°C. Estimates from the multiple regression equations were applicable to a wide range of food organisms with the exception of larvae ofTenebrio molitor (mealworms). Appetite (measured by voluntary food intake) varied with temperature and was greatest between 13.3°C and 18.4°C. From comparisons with the results of other workers, it was concluded that the maximum amount of food consumed in a meal may provide sufficient calories for both the daily metabolic requirements and the daily maintenance requirements of a trout at temperatures between 3.8°C and 18.4°C, but not at temperatures

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1975.tb00120.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SummaryTo estimate annual production, Hamilton (1969) initially calculated mean losses/sample, as did Hynes (1961) and Hynes&Coleman (1968). While the latter failed to convert these means to annual production, Hamilton has overcome this problem by assuming a population at equilibrium. Then, production may be calculated by multiplying mean losses with the number of classes through which specimens can grow. The method was claimed to be suitable for unidentified material and not to depend strongly on growth patterns; both claims are refuted here. The main objection is that for calculations, populations must be divided into fractions. While equilibrium might be acceptable for an entire population, it is not for any of its fractions. The particular conversion factor therefore has no justification and the method becomes inapplicable.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1975.tb00121.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SummaryThe results of a quantitative study of the benthic invertebrates of a riffle area in the upper reaches of the Pawmpawm River in the forest of southern Ghana are presented. The investigation was carried out over a period of 17 months with a Surber Sampler. The seasonal fauna changes are discussed in relation to changes both in water flow and in the vegetational substrate, and a model for the succession of recolonization of the river after the resumption of flow is outlined. The earliest colonizers of the river were primary consumers, Chironomidae, Centroptilum and Simulium., which were followed after a few weeks (once a mat of vegetation had become established) by the carnivorous Cheumatopsyche (Trichoptera) and Centroptiloides (Ephemeroptera). After 2 to 3 months, the attached vegetation matured and was able to support a greater diversity of fauna. The strategy of survival in intermittent tropical rivers is discussed and it is concluded that recolonization from eggs laid by flying adults is the most important method.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1975.tb00122.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SummaryThe four periphytic communities established in Plover Cove Reservoir (the epiphyton, epihthon, epipelon and epipsammon) were investigated between November, 1970 and December, 1971. A rich flora of diatoms was found to dominate all four peri‐phytic communities, and, for this reason, assessment of diatom numbers was used to monitor each community during this survey.The standing crop of each community, measured by cell counts and by chlorophyll a determinations, showed distinct seasonal patterns. Except for the epipsammon, each community displayed a maximum growth in winter, a moderate spring and autumn growth period and a low summer growth. The episammic flora stood apart from the other attached floras in that it exhibited a prolonged maximum growth period in summer.Relatively small numbers of species were found to form the main bulk of all four communities (the so‐called ‘constant forms’) and these belonged predominantly to the pennate genera Achnanthes, Fragilaria, Nitzschia and

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1975.tb00123.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY