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Márjore Antunes Maísa Trevisan Antunes Andreia Neves Fernandes Janaina da Silva Crespo Marcelo Giovanela 《Environmental Earth Sciences》2013,69(3):959-968
The nutrients, carbon, nitrogen and phosphorus, significantly affect the quality of aquatic environments, especially when present at concentrations above natural levels. In this context, the sedimentary column can act as an environment for storage or accumulation of these nutrients and for the reprocessing of such substances in the water column and aquatic biota. In this context, this study aimed to estimate the concentration of total organic carbon (TOC), total nitrogen (TN), total phosphorus (TP), inorganic phosphorus (IP) and organic phosphorus (OP) in seven sediment samples that were collected from the Marrecas Stream microbasin (Caxias do Sul, Rio Grande do Sul State, Brazil). The relationships among the sediment nutrient concentrations and the levels of organic matter (OM), fine material (silt–clay) and the concentration of the metal species, Al, Fe and Mn, as well as the possible nutrient sources to the stream studied were also evaluated. The data set suggest that the TOC and IP appear to have a direct correlation with the vast riparian vegetation present in areas adjacent to the sampling points and to the physico-chemical properties of the water and sedimentary column. Moreover, the results obtained for TN suggest that its concentration possibly suffers interference from the temperature of the water and its oxygenation, in addition to other biological activities. On the other hand, one cannot rule out human interference, mainly in the levels of OP, possibly due to the inflow of domestic sewage to the stream. 相似文献
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Aeromonas veronii, a tributyltin (TBT)-degrading bacterium isolated from an estuarine environment, Ria de Aveiro in Portugal 总被引：1，自引：0，他引：1
Organotin compounds are used in a variety of industrial processes therefore their subsequent discharge into the environment is widespread. Bacteria play an important role in biogeochemical transformations acting as natural decontamination agents. Therefore, screening for tributyltin (TBT)-resistant and -degrading bacteria is relevant for the selection of isolates with decontamination ability of these polluted areas. With this purpose, 50 strains were isolated from sediment and water from Ria de Aveiro and their tolerance to TBT, up to 3mM, was evaluated. Generally, occurrence of highly TBT-resistant bacteria was observed, and Gram negative bacteria exhibited more tolerance to TBT than Gram positive bacteria. A memory response was observed when bacteria were progressively exposed to increasingly higher TBT concentrations. One isolate, Aeromonas veronii Av27, highly resistant to TBT (3mM) uses this compound as carbon source and degrades it to less toxic compounds. 相似文献
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Travel-time inversion of wide-angle ocean-bottom seismic (OBS) data results in detailed P-wave velocity models of the shallow sub-seabed beneath the Nyegga pockmark field. The area lies on the northern flank of the Storegga Slide on the mid-Norwegian margin. Velocity anomalies indicate two low P-wave velocity zones (LVZs) providing evidence for the presence of gas-rich fluids in the subsurface at Nyegga. Integrating the velocity results with 2D and 3D reflection seismic data demonstrates that LVZs coincide with zones of high-amplitude reflections that allow mapping the extent of the fluids in the subsurface. The upper fluid accumulation zone corresponds to a velocity inversion of ∼250 m/s and occurs at a depth of about 250 mbsf. The lateral extent is documented in two distinct areas. The westward area is up to 40 m thick where gas-rich fluids beneath a bottom-simulating reflection indicate that fluids may be trapped by gas hydrates. The eastward zone is up to 60 m thick and comprises a contourite deposit infilling a paleo-slide scar. On top, glacigenic debris flow deposits provide a locally effective seal for fluids. The second velocity inversion of ∼260 m/s extends laterally at about 450 mbsf with decreasing thickness in westward direction. Based on effective-medium theory the gas saturation of pore space in both layers is estimated to be between 0.5 and <1% assuming a homogeneous distribution of gas. Fluids probably originate from deeper strata approximately at the location of the top of the Helland-Hansen Arch. Fluids migrate into the second LVZ and are distributed laterally. Fluids migrate into shallower strata or are expelled at the seabed through the formation of vertical fluid migration features (VFMFs), so-called chimneys. The distribution of the chimneys is clearly linked to the two fluid accumulation zones in the subsurface. A conceptual model draws on the major controlling factors for fluid migrations at specific locations within Nyegga. Fluid migrations vary according to their actual position with respect to the prograding Plio–Pleistocene sedimentary wedge. 相似文献
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Stephanie Koch Henning Schroeder Matthias Haeckel Christian Berndt Joerg Bialas Cord Papenberg Dirk Klaeschen Andreia Plaza-Faverola 《Geo-Marine Letters》2016,36(3):187-196
This study presents 2D seismic reflection data, seismic velocity analysis, as well as geochemical and isotopic porewater compositions from Opouawe Bank on New Zealand’s Hikurangi subduction margin, providing evidence for essentially pure methane gas seepage. The combination of geochemical information and seismic reflection images is an effective way to investigate the nature of gas migration beneath the seafloor, and to distinguish between water advection and gas ascent. The maximum source depth of the methane that migrates to the seep sites on Opouawe Bank is 1,500–2,100 m below seafloor, generated by low-temperature degradation of organic matter via microbial CO2 reduction. Seismic velocity analysis enabled identifying a zone of gas accumulation underneath the base of gas hydrate stability (BGHS) below the bank. Besides structurally controlled gas migration along conduits, gas migration also takes place along dipping strata across the BGHS. Gas migration on Opouawe Bank is influenced by anticlinal focusing and by several focusing levels within the gas hydrate stability zone. 相似文献
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Andreia Dias Elias Luiz Fernando De Ros Ana Maria Mizusaki Koji Kawashita 《Gondwana Research》2007,11(4):553-567
The isotopic composition of diagenetic carbonates, sulfates, illites and associated diagenetic constituents of the Carboniferous Juruá sandstones, Solimões Basin, largest hydrocarbon reservoirs of northern Brazil, was analyzed in conjunction with petrographic characterization and chemical composition. Eolian Juruá sandstones, deposited in a coastal sabkha of a wide cratonic sag, are the best reservoirs, but diagenetic processes introduced strong and complex heterogeneities, which affect hydrocarbon production. Dolomite and anhydrite cementation, together with compaction, exerts the main control on the quality of the reservoirs. Early dolomite cements precipitated under strong evaporation, while late dolomites are related to thermal decarboxylation. Late anhydrite cements are related to the interbedded evaporites and possibly to the oxidation of dissolved sulfide. Authigenic illite K–Ar ages are related to the voluminous Triassic basic magmatism (around 200 Ma), and to the Jurassic–Cretaceous tectonism (around 150 Ma), which may have also affected the late anhydrite and dolomite–ankerite cementation. This isotopic study revealed the major conditions of the diagenetic processes that strongly affected the Juruá reservoirs, which are essential for the development of models that will optimize the production, as well as decrease the risks in the exploration for new Juruá reservoirs. 相似文献
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