Biofilms and extracellular matrices on geomaterials     

A. Kemmling  M. Kämper  C. Flies  O. Schieweck  M. Hoppert 《Environmental Geology》2004,46(3-4):429-435

Microbial biofilms are ubiquitous in aquatic and terrestric ecosystems as well as on man-made material. They are initial colonizers on all surfaces and take part in biogenic weathering on natural rocks as well as on building stone. The structure and function of the biofilm matrix, mainly extracellular polysaccharides (EP), is documented for biofilms on stone surfaces: the hydrated gel acts as glue between the organisms and the material surface. Besides EP, living cells, cell debris and mineral particles are embedded in the matrix. These particles appear to be deposited on the surfaces of cell walls and interfaces in the biofilm matrix. As an important function of the matrix, EP stabilizes the biological activity against periodic desiccation. It was demonstrated that in several polymers (alginate, dextran, levan and others) a typical extracellular enzyme, the alpha-amylase, develops enhanced resistance against desiccation stress. Consequences of EP production and biofilm development on surfaces are discussed.Special issue: Stone decay hazards  相似文献   

城市交通废气与低层大气臭氧形成和分布的数值模拟   总被引：5，自引：1，他引：5  

蒋维楣  徐振涛等 《气象科学》2001,21(4):409-416

建立了一个三维的边界层光化学模式，气象过程的模拟舍弃了静力近似的假定，模式由细网格、高分辨率并取湍流能量（E－ε）闭合的气象模式，提供较为细致的气流场和湍流场。文章中以汽车尾气和植物排放为光化学反应前体物的源，模拟了不同季节南京市的光化学过程以及臭氧随时间和空间的分布。结果表明，夏季南京市的地面臭氧浓度远远高于冬季，臭氧分布有所不同。并且在不少地方出现较高的O3浓度值，超过国家二级标准，气流对污染物浓度分布的影响在较高的高度上显得尤其明显。  相似文献   

Geomorphic activity of rabbits on a coastal sand dune,De Blink dunes,the Netherlands     

J. Rutin 《地球表面变化过程与地形》1992,17(1):85-94

A study of the erosion rate and the stability of sandy slopes was conducted on an eastern arm of a parabolic coastal sand dune, De Blink, central Netherlands. The contribution of rabbits to these processes was found to depend on two types of activity; the building of caves and sand mounds of up to 1·5 m² in area; and the digging of shallow burrows, whereby amounts of sand up to 1 kg per burrow were excavated. The burrowing activity was found over the whole dune, while cave holes were dug mainly on the northern slope. The total amount of sand actually transported on the dune due to this activity is not clear yet, but their influence on the development of stepped slopes is well established.  相似文献   

Density structure and tritium-helium age of deep hypolimnetic water in the northern basin of Lake Lugano     

A. Wüest  W. Aeschbach-Hertig  H. Baur  M. Hofer  R. Kipfer  M. Schurter 《Aquatic Sciences - Research Across Boundaries》1992,54(3-4):205-218

Long-term stratification of the deep hypolimnetic waters of the northern basin of Lake Lugano (Lago di Lugano) has resulted in a lack of deep-water renewal which has persisted for decades. Tritium-helium age measurements reveal that deep water has not been in contact with the atmosphere since the 1960s. Higher primary production associated with the significant increase in phosphorus concentration which occurred at this time resulted in greater autochthonous gross sedimentation rates, increasing the rate of mineralization and, consequently, the rate of release of dissolved solids (mainly HCO ₃ ^- and Ca²⁺) into the deep hypolimnion. This gave rise to an intensification of the stratification and to a consequent reduction in the vertical exchange of hypolimnetic water layers. Today, the density stabilizing effect of ion release due to mineralization in the deep water is four to five times greater than the destabilizing effect of the geothermal heat flux from the earth's interior. It is known from laboratory experiments that such small density gradient ratios are likely to give rise to double-diffusive instabilities. However, even rudimentary mass balance calculations of biogeochemical components indicate that shear-induced turbulence, most likely generated by bottom currents, mixes far more efficiently than double diffusion. In the future, the biogenic density stratification is likely to persist in the deep water, unless the upward ion flux, driven by primary production, decreases by a factor of four to five.  相似文献   

Biological production and utilization of N2O     

C. C. Delwiche 《Pure and Applied Geophysics》1978,116(2-3):414-422

Considering only net free energy change for the dissimilatory reduction of nitrate ion, the most efficient reaction with limited organic substrate is that resulting in the production of N₂. Under conditions of abundant organic substrate and limited electron acceptor the reduction of nitrate to the level of ammonium would be more efficient. Thus the appearance of N₂O in denitrification must reflect a metabolic accident or some reaction barrier (e.g., the activation energy of some intermediate) which prevents the full utilization of this energy.Laboratory studies with microaerophylic systems indicate that under these reducing conditions both nitrate ion and N₂O can be reduced to the level of ammonium. The quantitative significance of these processes under natural conditions has not been evaluated but they may provide a significant sink for atmospheric N₂O.  相似文献   

山西省河东煤田保德地区晚古生代生物成因构造及其环境意义     

张惠良  李宝芳 《中国煤田地质》1996,8(1):5-8

应用生物成因构造、特征遗迹化石对沉积速率、含氧量、能量级别、底质和含盐度等环境指标的解释，分析了山西省河东煤田保德地区晚古生代沉积环境，认为保德地区晚古生代沉积环境以河流沉积体系、泻湖相浅海相为主，当时沉积底质为半硬到软底，水体含氧量丰富，含盐度比其相邻地区偏低。  相似文献   

Testing Sr/Sr as a paleosalinity indicator on mixed marine, brackish-water and terrestrial vertebrate skeletal apatite in late Paleocene-early Eocene near-coastal sediments, Mississippi     

Birger Schmitz  Stephen L. Ingram  David T. Dockery  III  Gran berg 《Chemical Geology》1997,140(3-4):275-287

Mixed marine, brackish-water and terrestrial vertebrate skeletal apatite is found in the late Paleocene-early Eocene Tuscahoma and Bashi Formations of Mississippi. The co-Occurrence in these near-coastal marine deposits of skeletal apatite with different provenances offers a unique opportunity for unraveling the effects of diagenesis on apatite ⁸⁷Sr/⁸⁶Sr composition, with bearings on the use of this isotope pair as paleosalinity indicator. The results show that the Sr isotopes of all originally poorly ordered phases of skeletal apatite have extensively re-equilibrated with pore water with significantly lower ⁸⁷Sr/⁸⁶Sr ratios than late Paleocene-early Eocene seawater. For example, marine shark and ray teeth from the Bashi Formation all have clearly nonmarine ⁸⁷Sr/⁸⁶Sr ratios, 0.7073-0.7075, compared with a coeval seawater ratio in the range 0.7077-0.7078. However, separated shark tooth enamel, with a high original crystallinity, appears to have retained all or most of its in vivo Sr isotopic signature until the present. Here we also show that ⁸⁷Sr/⁸⁶Sr results on recent vertebrate skeletal material from different environments are in good agreement with expected values for respective habitat.

Earlier analyses of calcite material from the Bashi Formation indicated the existence of a shift in seawater ⁸⁷Sr/⁸⁶Sr to a lower value at the Paleocene-Eocene boundary. The strong influence of pore water with low, nonmarine ⁸⁷Sr/⁸⁶Sr on the apatite in the Bashi Formation suggests that the proposed isotopic shift may be an artifact related to diagenetic processes.  相似文献   

Oxidative Ce3+ sequestration by fungal manganese oxides with an associated Mn(II) oxidase activity     

《Applied Geochemistry》2016

Sequestration of Ce³⁺ by biogenic manganese oxides (BMOs) formed by a Mn(II)-oxidizing fungus, Acremonium strictum strain KR21-2, was examined at pH 6.0. In anaerobic Ce³⁺ solution, newly formed BMOs exhibited stoichiometric Ce³⁺ oxidation, where the molar ratio of Ce³⁺ sequestered (Ce_seq) relative to Mn²⁺ released (Mn_rel) was maintained at approximately two throughout the reaction. A similar Ce³⁺ sequestration trend was observed in anaerobic treatment of BMOs in which the associated Mn(II) oxidase was completely inactivated by heating at 85 °C for 1 h or by adding 50 mM NaN₃. Aerobic Ce³⁺ treatment of newly formed BMO (enzymatically active) resulted in excessive Ce³⁺ sequestration over Mn²⁺ release, yielding Ce_seq/Mn_rel > 200, whereas heated or poisoned BMOs released a significant amount of Mn²⁺ with lower Ce³⁺ sequestration efficiency. Consequently, self-regeneration by the Mn(II) oxidase in newly formed BMO effectively suppressed Mn²⁺ release and enhanced oxidative Ce³⁺ sequestration under aerobic conditions. Repeated treatments of heated or poisoned BMOs under aerobic conditions confirmed that oxidative Ce³⁺ sequestration continued even after most Mn oxide was released from the solid phase, indicating auto-catalytic Ce³⁺ oxidation at the solid phase produced through primary Ce³⁺ oxidation by BMO. From X-ray diffraction analysis, the resultant solid phases formed through Ce³⁺ oxidation by BMO under both aerobic and anaerobic conditions consisted of cerianite with crystal sizes of 5.00–7.23 Å. Such nano-sized CeO₂ (CeO_2,BMO) showed faster auto-catalytic Ce³⁺ oxidation than that on well-crystalized cerianite under aerobic conditions, where the normalized pseudo-first order rate constants for auto-catalytic Ce³⁺ oxidation on CeO_2,BMO was two orders of magnitude higher. Consequently, we concluded that Ce³⁺ contact with BMOs sequesters Ce³⁺ through two oxidation paths: primary Ce³⁺ oxidation by BMOs produces nano-sized crystalline cerianite, and subsequent auto-catalytic Ce³⁺ oxidation efficiently occurs using dissolved oxygen as the oxidizing agent. Pretreatment of newly formed BMOs with La³⁺ solution resulted in decreased rate constants for primary Ce³⁺ oxidation by BMO due to site blocking by La³⁺ sorption. The results presented herein increase our understanding of the role of BMO in oxidative Ce³⁺ sequestration process(es) through enzymatic and abiotic paths in natural environments and provide supporting evidence for the potential application of BMOs towards the recovery of Ce³⁺ from contaminated waters.  相似文献   

Distribution of n-alkanes and PAHs in atmospheric aerosols     

A. Gelencsr  T. Barcza  Gy. Kiss  . Molnr  J. Hlavay  E. Mszros 《Atmospheric Research》1998,46(3-4)

The concentrations of n-alkanes and polycyclic aromatic hydrocarbons (PAHs) are determined in atmospheric aerosol samples collected at a rural sampling site in Hungary. For the n-alkanes the chromatographic profiles are established and the average carbon number and carbon preference index (CPI) are calculated. An attempt is made to obtain the origin of n-alkanes found in atmospheric aerosol samples. Based on the results of the measurements the probable importance of a round-the-year biogenic source for the n-alkanes with CPIs close to unity is emphasized.  相似文献   

古赤潮与古营养状况的沉积记录研究进展   总被引：2，自引：0，他引：2  

徐杰  陈建芳  刘广深  朱岩 《海洋通报》2003,22(6):63-70

大量的研究证实，赤潮与海水的富营养化有密切的关系。近年来，国内外一些学者通过分子地层学记录来探讨赤潮演变历史及其与富营养化的关系，希望找到赤潮演化与发展的科学依据。本文综述了甾醇、生物硅、色素、孢囊、同位素等指标在古赤潮及其相关古营养研究中的应用及研究动态与进展。甾醇是重要的藻类生物标志化合物，4-甲基甾醇及其衍生物可指示沟鞭藻的输入。孢囊可用来反映生物种群、表层海水营养和生产力水平。生物硅被用来指示硅藻生产力。色素可以很好地反映水体中富营养水平及生产力高低，颤藻黄素的升高被认为是湖泊人为富营养化的重要依据。利用C、N同位素组成的变化指示水体中营养状况的变化。  相似文献