摘要:

SUMMARY.Velocity measurements at fourteen hydrometric stations in the Tweed basin are described and analysed. Along‐stream velocity variations are examined and it is shown that at most flow levels the highest velocities occur at the lower, flatter end of the river system. Estimates of the frequency with which velocities of different magnitudes can be expected to occur in the river are also presented. These indicate that the velocity at most stations rarely exceeds 3.0 m s−1and for most of the time it lies between 0.25 and 1.0 m s−1. The inadequacy of subjective velocity assessment is stressed and a method suggested whereby data similar to those presented could readily be produced for almost any cross‐section along a river like th

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1981.tb01238.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARY.The ecology of the phytoplankton of Heywood Lake, Signy Island, South Orkney Islands, Antarctica was investigated during 1969–72. The lake, which is ice‐covered for 8–10 months per year, is moderately eutrophic due to enrichment by seal excreta.The annual cycle of the phytoplankton is described. During the winter (approximately May‐September), very few algal cells could be detected in the water column and14C fixation was below measurable limits. In spring (October‐November), a rapidly‐growing population of algae caused a large increase in the chlorophyll‐aconcentration (maximum value 170 mg m−2) but carbon fixation remained low, with values3 g C m−2day−1were measured on bright days. Values for Assimilation Number were very high (maximum value 10.5 mg C h−1mg−1(chlorophyll‐a) in January (1971) though temperatures never exceeded 8°C. In autumn, the phytoplankton regressed to winter levels. Both spring and summer algal populations p

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1981.tb01239.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARY.The feeding rate ofG. pseudolimnaeuswas measured monthly for 7 months in the field by monitoring the decline in weight of gut contents when the amphipod was starved. This decline was modelled by an exponential regression of weight on time. As the amphipods appeared to be continuous feeders, feeding rate was calculated by multiplying the dry weight of a full gut by the specific rate of emptying, i.e., the slope of the exponential regression. Specific rate of emptying was independent of animal size, but increased with temperature. Therefore, food has a longer period in which to be digested at low temperatures, which suggests that assimilation efficiency may increase.However, the assimilation efficiency of amphipods feeding on decaying maple leaves in the laboratory was only 10% and did not vary with temperature. Ingestion and egestion rates were measured in the laboratory by weighing amounts eaten and defecated. The turnover time of the contents of a full gut in the laboratory often agreed very well with turnover time measured in the field, i.e., the reciprocal of the specific rate of emptying, thus confirming the use of an exponential regression.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1981.tb01240.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARY.The results of direct current measurements in the South Basin of Windermere are presented and related to wind history and horizontal variations in near‐surface water temperature. Currents were measured by Lagrangian methods using drift‐bottles and depth‐specific drogues. Except when sudden calms followed strong winds, internal seiche movements had little effect on horizontal transport in the epilimnion. The most important factor governing mass water movement was direct wind forcing. Variations in wind speed accounted for 93% of the variation in near‐surface current speed.For wind speeds between 100 and 500 cm s−1the wind factor (current speed/wind speed) decreased linearly with wind speed. At wind speeds above 500 cm s−1the wind factor remained relatively constant around 1 %.Coriolis effects deflected near‐surface currents 4–38° to the right of the wind. The degree of deflection was strongly correlated with the relative depthDE/D*(whereDEwas the depth of the epilimnion andD*the depth of frictional resistance). The influence of the Coriolis force also produced pronounced rotations, with depth, of the wind‐driven current. The circulation pattern within the epilimnion was broadly that of a distorted conveyor belt moving at some angle to the wind axis. The strength of the transverse circulation was greatest at low wind speeds with a deep thermocline.Richardson‐number calculations suggest that the thermocline generally acts as a low‐friction boundary between a turbulent epilimnion and a relatively quiescent hypolimnion. Horizontal variations in water temperature, although ranging from only 0.2 to 1.0°C per km, served as a good indirect ‘tracer’

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1981.tb01241.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARY.Wastwater (English Lake District) was sampled at monthly intervals over 1 year to compare the seasonal and vertical extents of floristic and physiological variation in an oligotrophic phytoplankton assemblage. Cellular photochemical capacity (CPC) was measured byin vivochlorophyll fluorescence before and after addition of the photosynthetic inhibitor 3(3,4‐dichlorophenyl)‐1,1‐dimethyl urea (DCMU). The CPC index proved useful to define an activity coefficient for the chlorophyll levels measured in boiling methanol extracts. Large variations in CPC over time or depth were generally correlated with major shifts in phytoplankton species composition. Highest CPC values were recorded during autumnal mixing. Both CPC and floristic composition of the community demonstrated as great a variation over depth during a period of stratification as that recorded over time throughout the year. These observations emphasize the multi‐canopy structure of the Wastwater phytoplankton community in

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1981.tb01242.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARY.A new sampler is described combining the advantages of both box and Surber samplers. The sample area is 200 × 250 mm (0.05 m2) and the device has been used to sample the benthos of rivers to a depth ofc. 60 mm where the substratum consists of particles with diameters of 50 mm or less. The basic design may be used in water up to 0.5 m in depth, but with an optional top unit this depth may be increased to 1 m. Aquatic macrophytes can also be sampled either on their own or together with the underlying substratum. Results from sampling programmes designed to estimate macrophyte biomass, the biomass of the macroinvertebrate community and the density ofGammarus pulexare given as examples of the flexibility of the sampler on a variety of biotopes

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1981.tb01243.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARY.The vertical distribution of the zoobenthos in southeastern Lake Michigan was investigated monthly from May to November 1976. The organisms could be divided into two categories: one in which the majority of the population occurred in the upper 1 cm of substrate (Pontoporeia, naidids, chironomids, cyclopoids, harpacticoids, cladocerans, turbellarians, ostracods, rotifers, sphaeriids and gastropods) and one in which the majority of the population occurred deeper (immature tubificids without hair setae,Stylodrilus heringianus, enchytraeids, nematodes, and tardigrades). The vertical distribution of these infaunal forms showed a marked seasonal variation. They were found in the superficial sediments in the spring, but deeper in the sediments in the autumn. This trend coincided with the seasonal occurrence of a detrital layer that overlay the sandy substrate in the spring but was absent in the autumn.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1981.tb01244.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Allanson, B.R.(Ed)(1979).Lake Sibaya.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1981.tb01245.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.tb01246.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY