摘要:

SUMMARY.Cores of sediment from Llyn Peris and Llyn Padarn, two linked lakes in North Wales, are described. Dating of sediments by14C techniques, investigations of remanent geomagnetism and estimates of recent deposition rates from measurements of137Cs, indicate that in Padarn an unbroken record of the last 7000 years has been obtained. In Peris, the upper lake, the rate of sediment accumulation is greater than in Padarn and the sediment has been considerably disturbed. Sediment chemistry is related to the climatic and industrial history of the area. Some features of the chemical profiles in Padarn are similar to those of lakes in the English Lake District, and there is evidence to suggest that erosion has increased in the catchment sincec. 3500 years ago. This is more recent than similar increases in erosion reported for the English Lake District. In Peris, industrial activity during the past few hundred years has resulted in high levels of copper and calcium in the surface regions of sediment profiles.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01463.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

SUMMARY.The horizontal distribution of nauplii, CI‐CIII, CIV‐Cvand adult stages of the copepodPseudodiaptomus hesseiwithin the main basin of Lake Sibaya (27° 20′ S, 32° 37′ E) is described on the basis of semi‐synoptic cruises on 6 August 1971, 28 January 1972 and 11 February 1972. The distribution observed is considered in relation to variations in food availability and water temperature over this homothermal lake. It is concluded that these factors are not primarily responsible for observed patterns of distribution. Rather, wind‐induced currents appear to be of major significance in determining horizontal distribution. Stage‐related differences in the nature and extent of horizontal redistribution following severe wind are described. A consideration of the vertical distribution of groups of life‐history stages over a diel cycle in relation to the direction and relative strength of currents encountered by the copepods within their respective depth ranges provides an explanation for the differences in horizontal redist

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01464.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

SUMMARY.Atlantic salmon fry have been annually stocked into Llyn Dwythwch, North Wales, since 1969, in an attempt to increase the natural stocks of the area. The growth and survival of 1‐ and 2‐year‐old salmon were investigated, and compared with that of other lake‐reared populations and also with salmon in the natural stream environment. Lake‐reared salmon follow the same patterns of slow and rapid growth as found for river fish, but the growth rate was superior in the former. The variation in length – weight relationship with age and sex was investigated. Survival rates in general compared favourably with the survival in rivers, with high mortality rates of salmon in Llyn Dwythwch resulting from predation at spring stocking by the resident brown trout. This was later avoided by stocking larger fish in

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01465.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

SUMMARY.Cabora Bassa, a new impoundment in the Middle Zambezi River, was closed in December 1974, filling rapidly to 12m below full supply by May 1975.The lake, with five basins, lies along a west–east axis almost parallel to prevailing south‐easterly winds. Limnological records, from several stations along the lake axis, indicated homoiothermal conditions until September, the hot dry season. From then until records ceased in December, thermoclines and oxyclines were present in the deeper eastern basins. Hydrogen sulphide was recorded in hypolimnial waters towards the end of the year. Open water of the shallow, wind‐ and wave‐swept eastern basins remained oxygenated throughout the year.Water transparency increased fivefold from April to December, increasing too from east to west. pH was alkaline becoming more acid in cool winter months and in bottom waters of stratified basins. Conductivity ranged from 95 to 119 °S cm−1with higher values in shallow lake margins. Chemical content of surface waters showed little seasonal or spatial variation and was, in general, comparable with pre‐impoundment levels.Duration of the initial ‘productive phase’ will probably be shorter than Kariba due to more rapid lake water exchange but indications are that productivity will be higher in the

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01466.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

SUMMARY.Distributions of benthic diatoms and benthic floc in Lake Sibaya were examined to determine if preferential grazing by juvenileSarotherodon mossambicuson benthic detrital aggregate in shallow water maximized diatom concentrations in the diet of the fish. Between 0.1 and 12.0 m depth, the range of diatom densities was 1–60 × 104cells cm−2with high but extremely variable densities above 3 m and consistently low densities at greater depths. Light intensity and burial by wave action appear to be primary factors affecting diatom abundance, but the effect of unidentified factors causing local patchiness is also evident. Substrate stabilization by diatoms was observed between 0.3 and 1.8 m depth. Weight of benthic detrital aggregate generally increased with depth such that diatom concentrations were variable above 3 m but were extremely low in benthic detrital aggregate at greater depths. Comparison of diatom concentrations in fish stomachs and benthic detrital aggregate shows that within the shallow waters, fish do not selectively graze those areas richest in dia

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01467.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

SUMMARY.Lake Wisdom is of interest because it is large and deep, has oxygen throughout, and yet, apparently as a result of its recent formation, its biota has some surprising lacunae. It is nearly circular and fills the central caldera of Long Island, Papua New Guinea (5° 20′ S, 147° 6′ E). Its maximum length is 13.4 km, and area approximately 95 km2. A bathymetric map of the lake to depths of 300 m has been constructed from fathometer transects. Repeated soundings in the deeper parts gave depths of about 360 m. The surface of the lake is approximately 190 m above sea‐level and water samples from the deepest part of the lake are fresh, so the basin is apparently sealed. The lake level shows annual fluctuations ofc. 1.0 m.Limnological information has been collected during seven visits to Lake Wisdom over the period 1969–76. The surface temperature of the lake was constant at 28°C throughout this period and the temperature falls very gradually to 26–27°C at 60 m, except for a relatively rapid drop of approximately 1°C from 10 to 20 m. One of the most unusual features is the relatively high oxygen concentration in the deepest parts of the lake. Living chironomid larvae and molluscs were collected from the bottom in depths of 360 m. Light penetration in the lake varies greatly depending on the amount of rainfall and the volcanic activity of Motmot, a secondary cone within the lake.The biota of Lake Wisdom is rather simple. There is a low standing crop of phytoplankton. Benthic algae are abundant and diverse although they cover only a limited area because of the depth of the lake. There are no vascular aquatic plants. The pelagic fauna consists of two species of Cladocera and one species of notonectid. There is one species of sponge, four species of molluscs, and a small number of species of aquatic insects including Hemiptera. Odonata, and the larvae of chironomids, mayflies, a caddisfly, and a pyralid moth. Water birds, including ducks, grebes and waders, are fairly numerous. The lake also contains one or m

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01468.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

SUMMARY.Two species of aquatic moss (Calliergon sarmentosumandDrepanocladussp.) occur in deep water in Moss Lake, Signy Island (60° 43′S, 45° 38′W). Their elongate stems support a structurally complex community of epiphytic algae and associated invertebrates which has a greater diversity than the surrounding benthic algal communities.Qualitative differences in the distribution and abundance of the epiphytic algae are described. Two groups of algae present on both mosses are distinguished–‘habitual’ and ‘casual’ epiphytes. OnCalliergun, algae are most abundant in the leaf axil. The succession of epiphytes down the stem and the progressive deterioration of the moss plant are used to characterize six stem zones.The invertebrates are benthic and most move actively among the moss. Six species of rotifers are more or less permanently attached and show a preference for the middle stem zones where epiphyte cover is highest. Four species favour the leaf axil, the other two colonize the bare underside of the leaf.A settlement experiment has shown the importance of wind‐induced mixing in summer for the transport of some epiphytic species from shallow parts of the lake. The settlement of sessile rotifers is effected by their larvae.Photosynthesis declines from the stem apex to the dead old stem. Much of the primary production of the community is algal. The respiration maximum occurs where the highest concentration of epiphytic algae and invertebrates is found.Interrelationships between the invertebrates and the epiphytic algae are suggested and a comparison is made between these data

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01469.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

SUMMARY.Assimilation budgets (i.e. assimilation = respiration + excretion + production) are presented for cohorts ofP. zietzianain two salt lakes. Shrimps in Pink Lake had an assimilation rate of 1631.6 kJ m−2year−1, those in Lake Cundare 212.1 kJ m−2year−1. In both lakes, respiration accounted for 60–80% of assimilation. Assimilation rates for individuals (derived as assimilation = ingestion minus faecal output) are also given and compared with respiratory rates of individuals. The comparisons indicated that energy was often consumed at a higher rate by respiration than it could be supplied by assimilation. Starvation due to a low assimilation efficiency was suggested as a cause of the consistent mortality, variable growth rate of individuals and unpredictable recruitment which were characteristic of the cohorts ofP. zietzianain both lakes. An analysis of mortality showed that the young had the poorest survival, as predicted by a theoretical model of a starving zooplankter and a comparison of the increase with weight of ingestion and respiration. Gross growth efficiency (production: assimilation) was 15–30%, about the same as published data on Anostracans. Net growth efficiency (production : consumption) was 5–12% and generally lower than published values reflecting the difficultyP. zietzianahas in balanci

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01470.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

SUMMARY.In a small lake (Blelham Tarn, English Lake District) two plastic cylinders, each of which extends from the lake surface to the bottom sediments and encloses 18 000 m3of water, were used to investigate effects of enclosure on the zooplankton. This paper describes observations from March 1973 to October 1974 and is the second part of a report on a project spanning 4 years.Seasonal population densities of the more abundant species were essentially similar to those observed in the first part of the project, despite large changes in algal and predator populations. In the enclosures, fish (mostlyPerca fluviatilis) populations are known from observations by divers to have been large in the period under consideration and small in the first part of the project. Populations ofChaoboruslarvae in the enclosures were small at all seasons from March 1973 to October 1974.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01471.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

SUMMARY.Histological and electron microscopical study of the gills of fish poisoned by the anionic detergent sodium lauryl sulphate indicates that the nature of the toxic action changes at a concentration of about 120 mg I−1. Toxicity tests were conducted to determine whether this change could be detected in the test data, using brown trout (Salmo trutta) and rainbow trout (S. gairdneri).Toxicity curves showed no indication of the change in toxic action, but at concentrations of 120 and 130 mg I−1of sodium lauryl sulphate ‘split’ probit lines occurred, and the lines for 150 mg I−1consistently differed in slope from ot

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01472.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY