Algal diets and natural xenobiotics impact energy allocation in cladocerans. I. Daphnia magna

Recently emerged indications imply that particular concentrations and qualities of dissolved organic carbon (DOC) have the potential to reduce species diversity in zooplankton. In this contribution, we tested the impact of a major component of DOC, the dissolved humic substances (HSs), on two life history traits of a clone of Daphnia magna, namely lifespan and reproduction. We chose reproduction as a variable since it guarantees the persistence of the population in its habitat, and lifespan was selected as the most integrative individual variable. We found that lifespan was extended by exposure to HSs, but lifetime reproduction was clearly reduced. On the other hand, the mineral and biochemical composition of food also significantly modulated these life history traits. By feeding coccal green algae that contained linolenic acid, arginine (Arg), and histidine (His), but that lacked polyunsaturated fatty acids (PUFAs) with C-back bones >18, we examined how short-chained PUFAs, either alone or in concert with Arg and His, are able to modulate life history traits. Our expectation was that the additional challenge by HSs would shift the energy allocation in favor of reproduction. We found that the carbon and amino acid content may account for longevity, even when challenged by HSs. Reproduction appeared to be triggered by the C:P and N:P ratios of the food, particularly given the rather low P-content, which was within the range of severe growth limitation. Consequently, exposure to HSs reduced offspring numbers. Resting eggs without males occurred only in Desmodesmus armatus fed Daphnia that were simultaneously exposed to HSs. Under these conditions, the total amino acid (AA) content seemed to trigger reproduction. In summary, exposure to HSs appeared to have the potential to change the competitive ability of zooplankters by modulating the energy allocation between body maintenance and reproduction.     

The occurrence of high molecular weight humic material in recent organic-rich sediment from the Namibian shelf

The molecular size distribution of humic substances has been investigated in two recent sediment samples of different ages taken from a single core sample collected off Walvis Bay, south-west Africa. Extractable humic acids were found to be by far the major form of organic carbon in both sediments, the near-surface younger sample containing predominantly high molecular weight (>100 000 molecular weight) humic acids and little fulvic acids whilst the deeper, older sample contained relatively less humic acid and relatively more fulvic acid of a range of molecular weights. A significant age difference was found between the >300 000 molecular weight and the <30 000 molecular weight fractions of the near-surface sample, the lower molecular weight fraction being older than the higher molecular weight fraction.The data suggest that in this rapidly accumulating, organic-rich sediment the first step en route from the planktonic matter to the humic complexes is direct and rapid incorporation of the biogenic material into high molecular weight humic acids.     

Imposex levels in the dogwhelk Nucella lapillus (L.)--continuing improvement at high latitudes

In 1990, restrictions on the use of tributyltin (TBT)-based antifouling paints were implemented in Iceland. A previous study showed that the level of imposex in the dogwhelk, Nucella lapillus, in Icelandic waters had decreased significantly between 1992 and 1998. In this study, we repeated the survey on imposex in N. lapillus at 33 locations from the Icelandic coast in 2003. The results indicated that both Vas Deferens Sequence Index (VDSI) and Relative Penis Size Index (RPSI) had further declined in 13 locations since 1998. Among these 13 sites, RPSI was reduced to zero in five cases. While improvements from 1992/1993 to 1998 were seen in reduced levels of imposex near both large and small harbours, the pattern from 1998 to 2003 was somewhat different, with improvement mainly observed near smaller harbours. No significant changes in imposex levels near larger harbours occurred over this period. Although the imposex levels still remain high near the large harbour complexes in Reykjavík and Hafnarfjörður, it is evident that regulations, including the use of less toxic antifouling paints and community action, have lead to substantial improvements in the marine environment of Iceland. International Maritime Organisation’s ban on the application of TBT after 2003 is apparently necessary to allow further improvements in larger harbours. The environmental effects of new antifoulants replacing TBT need to be further evaluated.     

Origin of abnormal substances discharged from Baozhusi Dam Base, Sichuan, China

Baozhusi reservoir is a large-scale hydropower engineering project in Sichuan Province, China. After drainage wells were drilled in the dam base, white flocculent and black gel substances, accompanied by a rotten-egg odor, were found in some of the drainage water wells. On the basis of a brief introduction of the geological setting in Baozhusi Dam area, the origin of the abnormal substances were analyzed and discussed through the following procedures: (1) the abnormal substances were sampled and their chemical and mineral compositions were analyzed; (2) the origin of drainage waters were determined using the isotope method and well flux measurement results; (3) characteristics of chemical composition of drainage waters were discussed relative to other kinds of waters in the area; (4) process of formation of the abnormal substances were determined using hydrogeochemical methods; (5) laboratory immersion experiment was carried out to verify the conclusions. Results showed that the abnormal substances were formed by interactions between recharging water from the reservoir and dam base rock as well as dam building materials. Among these, the precipitation of calcite and dolomite, the dissolution of calcium hydroxide and anhydrite as well as the reduction of SO₄^–2 to H₂S by organic matter are the most important processes.     

金云母-蛭石间层矿物的酸浸取物与酸蚀机理研究

对采自新疆尉犁蛭石矿的金云母蛭石间层矿物样品进行了酸处理实验研究。在样品化学成分和XRD分析的基础上,研究了样品酸处理后酸浸取物的化学组成、含量及结构变化特征;分析讨论了金云母蛭石间层矿物在酸处理过程中不同阳离子浸出率的变化规律和酸蚀机理。结果表明,层间可交换性阳离子的氧化物CaO和Na2O的酸浸取率最高,层间不可交换性阳离子的氧化物K2O次之,八面体中阳离子的氧化物MgO、Fe2O3和Al2O3具有较高的酸浸取率,而四面体阳离子的氧化物Si O2的酸浸取率最低;金云母蛭石间层矿物中蛭石晶层含量高的样品酸浸取率高,金云母蛭石间层矿物的耐酸蚀性能不如金云母。     

Physico-chemical and biological sediment properties determining erosion resistance of contaminated riverine sediments – Temporal and vertical pattern at the Lauffen reservoir/River Neckar, Germany

In order to contribute to a reliable, easy-to-handle and economically viable erosion risk assessment of contaminated riverine sites, the present study aims to implement master-variables best characterising the sediment stability. Thus, a wide range of sediment properties was related to the critical shear stress for mass erosion, determined in the SETEG (Stroemungskanal zur Ermittlung der tiefenabhaengigen Erosionsstabilitaet von Gewaessersedimenten) pressurised channel, with special emphasis on vertical and temporal gradients in the Lauffen reservoir on the River Neckar. Over the course of 1 year, positive impacts of some macrofauna species and benthic diatoms on the sediment stability were detected for the sediment surface (0.5 cm). However, a high seasonal variability of biological parameters caused varying relations with erosion resistance in the upper sediment layers as shown for the colloidal carbohydrates. Considering only deeper sediment layers (5–35 cm), a more general pattern could be revealed with correlations between the critical shear stress and single sediment properties such as depth, grain size, total organic carbon (TOC), cation exchange coefficient (CEC), carbohydrates and proteins. Firstly, the influence of physico-chemical and biological properties on erosion resistance became evident, even over depths at 0–35 cm. Secondly, inter-particle forces are most important for erosion resistance. These are enhanced in fine-grained sediment layers, offering high binding capacities but also strengthened by polymeric substances permeating the void space and coating particles. These covariance patterns of sedimentological and biological parameters are addressed by multivariate statistical tests (principal component analysis), resulting in a higher magnitude of the correlation coefficient between critical shear stress and the master-variables in main component II (polymeric substances, grain size, TOC, CEC; R=0.77) compared to single correlations.     

南极大磷虾的生物活性物质及其用途研究进展

南极磷虾以其巨大的生物量和潜在的渔业价值而日益受到人们的重视。本文就如何综合利用南极磷虾、开发其药用价值、最大限度地增加经济效益等方面进行了综合分析 ,对目前国际上的研究动态、研究成果和发展趋势等进行了介绍和探讨