On the relationship between the Bosmina taxa coregoni and thersites (Cladocera), as indicated by subfossil remains

A succession of morphs from Bosmina coregoni f. coregoni to B. c. f. thersites, which vary in shell and antennule characters, occurred in an undated 176 cm long sediment core from the Neversdorfer See (N. Germany).     

Horizontal distribution of crustaceans in Lake Glubokoe

A study has been made on the distribution of crustaceans along a profile of 6–9 stations from depths of less than 2 m to 20 m, in summer, autumn and early spring. The species composition, abundance, size-frequency distribution, biomass and diurnal dynamics were estimated. Many species abundant in the pelagic zone were found to be absent or scarce out to depths of 5 m. In the daytime, at depths out to 3 m, crustaceans greater than 1.0 mm were seldom found, while those 0.15–0.40 mm long were most abundant. At depths out to 5 m, not only was the total average size of crustaceans found to be smaller, but also that of individual species, including small ones: Ceriodaphnia and Chydorus. The biomass of crustaceans in shallow water and in the open lake differs in summer by more than 100 times, and in late autumn and early spring by more than 10 times. At the depth of 1 m, in none of the seasons did it exceed 0.026 mg l^-1. All the crustaceans except for nauplii and Chydorus considerably increased in numbers in the shallow water at night. The impoverishment of the littoral plankton in Lake Glubokoe is regarded as a specific case of the well-known phenomenon of ‘avoidance of the littoral’ by euplankton (Hutchinson, 1967; Kiselyov, 1980). It is pointed out that there is a possible relationship between diurnal horizontal migrations of plantivorous fish and the impoverishment of plankton near the shore. An attempt has been made to substantiate the assumption that the ‘avoidance of the littoral’ by pelagic crustaceans is due to high numbers of fish in shallow water.     

Hydrobiology and organic production in a marl lake of Kashmir Himalayan Valley

L. Naranbagh (alt. 1587 m) is a polymictic, shallow marl lake in the flood-plain valley of Kashmir, India. Macrofloral affinities resemble Potamogeton Type of Forsberg (1965) with alkaline waters, not rich in phosphorus. CaCO₃ precipitation coupled with decline in Ca²⁺ and alkalinity values are characteristic of the lake. Fluctuations in Mg²⁺, Na⁺, K⁺, and Cl^– were relatively conservative. The levels of PO _inf4 ^sup3– -P and NO _inf3 ^sup– -N indicate moderate fertility of the lake water.Persistence of a summer-autumn planktonic algal pulse is related to favourable irradiance, high water temperatures, and increased photosynthetic efficiency values. The most striking seasonality in photosynthetic rates (m^–2 h^–1) between winter minimum (3 mg C_assim) and summer maximum (75.4 mg C_assim) is determined by mainly climatic changes. Energy flow gave annual phytoplankton production of 51.95 × 10² KJ m^–2 for the ecosystem.The nutrient levels and productivity rates suggest mesotrophic status of L. Naranbagh in classic oligoeutrophic classification of lake types.     

Palynological investigations in sediments of ancient lake Duvensee,Schleswig-Holstein (North Germany)

The Duvensee originated before the Alleroed in the Late Glacial, and had its largest areal coverage during the Preboreal. After the lake retreat, which began in early Boreal times, the marginal shore areas and nearshore islands were repeatedly inhabited by man in the early Mesolithicum. Archaeological excavations of human settlements and pollen analyses of sediment cores show evidence of lake level fluctuations in the ensuing period. The results disclose that shallow water sediments such as lake marls, algal muds and coarse detrital gyttjas predominate in the sequence. In keeping with the shallow water conditions, strong lateral facies changes were observed in the cores. The early Holocene deposits have almost the same thickness irrespective of their position in the shallow or deep parts of the lake basin. The subaerial exposure of the nearshore and island areas sometimes resulted in fern and reed peats. The last remnants of the lake, which was drained in 1850, lay in the marginal areas over shallow water sediments.     

The Pleistocene lake deposits of the NE Baza Basin (Spain): salinity variations and ostracod succession

The Guadix-Baza Basin in Spain covers an area of approximately 3000 km² and yields a sedimentary sequence ranging from Lower Miocene to Pleistocene. Twenty five meters of Lower Pleistocene lacustrine sediments have been located in the NE part of the Basin at about 1000 meters in altitude. This sequence which overlies dolomitic mud flat deposits consists of limestones, calcareous and dolomitic mudstones, dolostones, silty clays, sands and gravels. Salinity fluctuations and short dry episodes, related to lake level oscillations, have been recorded by textural, mineralogical and faunal changes throughout the sequence. Ostracods, which are the most commonly encountered fossils, permit to detect recurrent changes in water salinity and regime, and solute composition. The faunal changes indicate an alternation of slightly saline and bicarbonate-rich water (when ostracods and gastropods occur) with a saline NaCl-dominant water (in which ostracods, Cerastoderma bivalves and non-marine foraminifers are found).The frequent and recurrent hydrochemical changes in the Baza Basin in the Early Pleistocene point to a climate of high contrast like in the Mediterranean region today but with a greater availability of water within the system compared to the present situation in the area.     

Uptake and tissue distribution of manganese in the white sucker (Catostomus commersoni) under conditions of low pH

Concentrations of manganese were determined in the liver, kidney, muscle and bone of white suckers (Catostomus commersoni) from five acid (pH < 5.8), and two circumneutral lakes in south-central Ontario. Manganese tissue concentrations were greater in fish captured from the most acidified lakes with the greatest concentrations of dissolved manganese. These fish had increased concentrations of manganese in the liver, as indicated by a comparison of liver:kidney manganese concentration ratios among the seven fish populations. Tissue concentrations of manganese from all populations either were negatively correlated (P < 0.05) or remained constant with fish size indicating homeostatic regulation of this metal. Manganese concentrations of the benthic fauna were positively correlated to sediment concentrations (R=0.30). Lake sediment manganese concentrations were significantly correlated to maximum lake depth (R=0.80, P < 0.03), with the concentrations in the top 0–1 cm dependent on the redox conditions in the seven lakes. Based on the seven lakes studied, manganese concentrations in the benthic-feeding white sucker correlated better with dissolved manganese, than with either the concentrations in food or surficial sediments.     

卫星影象目视解译方法在湖区植被制图中的应用——以湖南洞庭湖区水域、洲滩植被图为例

植被(包括天然植被、人工植被)作为一种可更新资源始终是遥感应用专家们热心研究的课题。植被分类是植被研究的重要方面之一。利用卫星影象进行植被分类,国内外学者都进行了许多有意义的探索。本文以洞庭湖水域、洲滩植被为对象,试用卫星影象进行植被分类。本文从植被与环境相互依赖关系及在影象上的综合反映出发,提出了影象的景观生态学分析方法;即把影象上色调、形态特征与群落生态学规律结合起来分析,并以此作为植被目视解译的方法。在此基础上,将洞庭湖水域、洲滩划分成五个景观生态模型,17个基本植被类型。     

Biomanipulation and its feasibility for water quality management in shallow eutrophic water bodies in The Netherlands

Biomanipulation as a tool for lake restoration is discussed mainly using literature data. It is based on the exploitation of the interactions both within and between the trophic levels in an aquatic ecosystem. Important among the interactions are: competition for light and nutrients between aquatic macrophytes and phytoplankton and among different phytoplankton species; grazing by planktonic and benthic filter feeders; and size-selective predation by fish. In several case studies biomanipulation has proved to be successful in restorating mildly eutrophic small waterbodies. However, for long-term stability of the restored ecosystems supplementary measures like reducing the external nutrient loadings are needed. The feasibility of the different biomanipulation measures to improve the water quality in shallow Dutch lakes is discussed. Preliminary results on biomanipulation experiments in enclosures withOscillatoria agardhii and the benthic filter feederDreissena polymorpha are given.     

Ethanol directly stimulates dihydrotestosterone conversion to 5 alpha-androstan-3 alpha, 17 beta-diol and 5 alpha-androstan-3 beta, 17 beta-diol in rat liver

The present results demonstrate for the first time in rat liver, that low ethanol concentrations (2.2 and 22 mM) directly stimulate dihydrotestosterone conversion to 5 alpha-androstan-3 alpha, 17 beta-diol and 5 alpha-androstan-3 beta, 17 beta-diol. Because this effect was blocked by 4-methylpyrazole, an alcohol dehydrogenase inhibitor, or by the addition of a saturating NADH concentration, this action probably is mediated by hepatic alcohol dehydrogenase activity through elevation of the NADH/NAD+ ratio. It remains to be determined whether this effect of ethanol actually reduces circulating and/or target tissue dihydrotestosterone levels; nevertheless, it is tempting to speculate that this action, in part, is responsible for the reported adverse effects of alcohol on male reproductive functions.     

The frequency of mutants in human fibroblasts UV-irradiated at various times during S-phase suggests that genes for thioguanine- and diphtheria toxin-resistance are replicated early

Human cells deficient in rate of excision repair of DNA damage induced by UV-radiation, i.e., xeroderma pigmentosum (XP) cells, are much more sensitive to the mutagenic effect of UV than are cells from normal persons. The lower frequency of mutants in the latter cells has been attributed to the fact that, unlike XP cells, they excise most of the potentially mutagenic lesions before these can be converted into mutations. If semi-conservative DNA synthesis on a template still containing unexcised lesions is responsible for introducing mutations and if replication of the gene of interest, e.g., hypoxanthine (guanine)phosphoribosyltransferase (HPRT) for thioguanine resistance or the elongation factor 2 (EF-2) for diphtheria toxin resistance, occurs at a particular time during S-phase, it should be possible to shorten the time available for such repair by synchronizing cells and irradiating them just as the gene is to be replicated. The predicted result would be a much higher frequency of mutants at one part in the S-phase than at other times. To test this, cells were synchronized using the alpha-polymerase inhibitor aphidicolin, which blocks cells at the G1/S border. Autoradiography, cytofluorimetry, and incorporation of tritiated thymidine studies showed that DNA synthesis started immediately after release from aphidicolin and was completed in 8-10 h. Cells irradiated with 6 J/m2 at various times post-release were assayed for survival and mutations. The frequency of thioguanine- or diphtheria toxin-resistant cells in the population was highest in cells irradiated during the first fifth of the S-phase, i.e., 0-1.5 h post-release. It was significantly lower in cells irradiated at later times. In contrast, UV-induced cytotoxicity showed no significant time dependence during S-phase. These data suggest that the HPRT and EF-2 genes are replicated early in S-phase.