Carbonate and silicate biomineralization in a hypersaline microbial mat (Mesaieed sabkha,Qatar): Roles of bacteria,extracellular polymeric substances and viruses

In a modern peritidal microbial mat from Qatar, both biomediated carbonates and Mg‐rich clay minerals (palygorskite) were identified. The mat, ca 5 cm thick, shows a clear lamination reflecting different microbial communities. The initial precipitates within the top millimetres of the mat are composed of Ca–Mg–Si–Al–S amorphous nanoparticles (few tens of nanometres) that replace the ultrastructure of extracellular polymeric substances. The extracellular polymeric substances are enriched in the same cations and act as a substrate for mineral nucleation. Successively, crystallites of palygorskite fibres associated with carbonate nanocrystals develop, commonly surrounding bacterial bodies. Micron‐sized crystals of low‐Mg calcite are the most common precipitates, together with subordinate aragonite, very high‐Mg calcite/dolomite and ankerite. Pyrite nanocrystals and framboids are present in the deeper layers of the mat. Calcite crystallites form conical structures, circular to triangular/hexagonal in cross‐section, evolving to crystals with rhombohedral terminations; some crystallite bundles develop into dumb‐bell and stellate forms. Spheroidal organo‐mineral structures are also common within the mat. Nanospheres, a few tens of nanometres in diameter, occur attached to coccoid bacteria and within their cells; these are interpreted as permineralized viruses and could be significant as nuclei for crystallite‐crystal precipitation. Microspheres, 1 to 10 μm in diameter, result from intracellular permineralization within bacteria or the mineralization of the bacteria themselves. Carbonates and clay minerals are commonly aggregated to form peloids, tens of microns in size, surrounded by residual organic matter. Magnesium silicate and carbonate precipitation are likely to have been driven by pH – saturation index – redox changes within the mat, related to microenvironmental chemical changes induced by the microbes – extracellular polymeric substances – viruses and their degradation.     

宝珠寺水电站坝基排水孔异常逸出物及其工程危害

在阐述宝珠寺水电站工程拦河坝坝址区地质及水文地质条件的基础上,对宝珠寺水电站坝基排水孔异常逸出物的分布及其化学成分和矿物成分进行了研究,对异常逸出物的工程危害进行了讨论.结果表明,在宝珠寺水电站坝基排水孔中,异常逸出物主要出现在河床坝段,其成分主要是地层岩石中的一些常见元素及常见的成岩矿物,异常逸出物对大坝工程的危害主要体现在其本身及其形成过程中从大坝基础中携带出了大量的物质.     

铁细菌胞外多聚物对铁矿物的调控形成及其环境意义

环境介质溶液中铁的水解作用和稳定化作用主要受铁细菌及其代谢有机物质的影响。铁细菌普遍存在于自然环境中,可利用低价铁源为自身生长所需能量。铁细菌胞外有机物的主要组分如多糖和蛋白质等可与铁结合,并通过氧化或沉淀作用使铁稳定、沉积而形成铁矿物;此外铁细菌胞外多聚物可催化铁的氧化或促进铁的聚集。这些生物成因铁矿物因具有良好的表面吸附与氧化还原等化学活性,及有效固定环境中的重金属、放射性核素和催化降解有机污染物的良好环境属性,在环境生物矿物材料和环境治理研究领域被日益重视。故本文基于铁细菌及其胞外多聚物对铁矿物矿化形成的重要调控作用,介绍了环境中存在的铁细菌及其生物矿化特征,重点阐述了铁细菌胞外多聚物(组分、结构及特性)及其在铁矿物矿化过程中的作用,同时对铁细菌胞外多聚物及生物成因铁矿物的环境意义进行了概述。     

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.