Gas hazard assessment in a densely inhabited area of Colli Albani Volcano (Cava dei Selci, Roma)     

M. L. Carapezza  B. Badalamenti  L. Cavarra  A. Scalzo 《Journal of Volcanology and Geothermal Research》2003,123(1-2):81

The northwestern flank of the Colli Albani, a Quaternary volcanic complex near Rome, is characterised by high pCO₂ values and Rn activities in the groundwater and by the presence of zones with strong emission of gas from the soil. The most significant of these zones is Cava dei Selci where many houses are located very near to the gas emission site. The emitted gas consists mainly of CO₂ (up to 98 vol%) with an appreciable content of H₂S (0.8–2%). The He and C isotopic composition indicates, as for all fluids associated with the Quaternary Roman and Tuscany volcanic provinces, the presence of an upper mantle component contaminated by crustal fluids associated with subducted sediments and carbonates. An advective CO₂ flux of 37 tons/day has been estimated from the gas bubbles rising to the surface in a small drainage ditch and through a stagnant water pool, present in the rainy season in a topographically low central part of the area. A CO₂ soil flux survey with an accumulation chamber, carried out in February–March 2000 over a 12 000 m² surface with 242 measurement points, gave a total (mostly conductive) flux of 61 tons/day. CO₂ soil flux values vary by four orders of magnitude over a 160-m distance and by one order of magnitude over several metres. A fixed network of 114 points over 6350 m² has been installed in order to investigate temporal flux variations. Six surveys carried out from May 2000 to June 2001 have shown large variations of the total CO₂ soil flux (8–25 tons/day). The strong emission of CO₂ and H₂S, which are gases denser than air, produces dangerous accumulations in low areas which have caused a series of lethal accidents to animals and one to a man. The gas hazard near the houses has been assessed by continuously monitoring the CO₂ and H₂S concentration in the air at 75 cm from the ground by means of two automatic stations. Certain environmental parameters (wind direction and speed; atm P, T, humidity and rainfall) were also continuously recorded. At both stations, H₂S and CO₂ exceeded by several times the recommended concentration thresholds. The highest CO₂ and H₂S values were recorded always with wind speeds less than 1.5 m/s, mostly in the night hours. Our results indicate that there is a severe gas hazard for people living near the gas emission site of Cava dei Selci, and appropriate precautionary and prevention measures have been recommended both to residents and local authorities.  相似文献   

Alkaline Degradation of Dissolved Organic Matter     

Thomas Brinkmann  Gudrun Abbt‐Braun  Fritz H. Frimmel 《洁净——土壤、空气、水》2003,31(3):213-224

The degradation of dissolved organic matter (DOM) was studied in alkaline solution. The products were characterised using UV/vis spectroscopy, size‐exclusion chromatography (SEC), and by the analysis of low‐molecular‐weight organic acids (LMWOA). The degradation experiments were performed with water from a brown water lake or its isolated fulvic acid fraction and sodium hydroxide at different reaction times and temperatures. Depending on the wavelength and the reaction time, the UV/vis absorbance between 230 nm and 600 nm increased or decreased. The behaviour of model compounds during reactions in alkaline media was compared to the UV/vis spectroscopic behaviour of DOM. The release of LMWOA was described by kinetic data and compared to the data of model reactions. Evidence was given for the carboxylic esters playing a significant role in the release of LMWOA only during the beginning of the alkaline degradation. The results gained by SEC with on‐line UV and DOC detection showed that the average size of DOM was decreasing, and that a major part of the degradation products consisted of low‐molecular‐weight mono‐ and dicarboxylic acids.  相似文献   

Filtrate Quality from Different Filter Operations     

Robert I. Mackie  Micha&#x; Zielina  Wojciech Dabrowski 《洁净——土壤、空气、水》2003,31(1):25-35

A brief review of the literature on filtrate quality obtained in constant and variable declining rate operation systems is presented, with the general conclusion that both systems usually produce filtrate of similar quality, assuming the flow‐rate controllers in the constant flow rate system operate properly. A mathematical model of CR (constant rate) filters and VDR (variable declining rate) filters based on the model by Mackie and Zhao (1999) has been described and used to investigate filtrate quality under different operating conditions. A similar quality of filtrate was achieved in computations carried out for both modes of operation, while the total head loss was much lower in the VDR mode. For the same time of filter runs slightly better filtration quality resulted from CR operation, but for different filter runs resulting from the same head loss of flow just before a backwash, the VDR control system produced lower turbidity filtrate.  相似文献   

Determination of Antibiotic Residues in Manure,Soil, and Surface Waters     

Thorsten Christian  Rudolf J. Schneider  Harald A. Frber  Dirk Skutlarek  Michael T. Meyer  Heiner E. Goldbach 《洁净——土壤、空气、水》2003,31(1):36-44

In the last years more and more often detections of antimicrobially active compounds (“antibiotics”) in surface waters have been reported. As a possible input pathway in most cases municipal sewage has been discussed. But as an input from the realm of agriculture is conceivable as well, in this study it should be investigated if an input can occur via the pathway application of liquid manure on fields with the subsequent mechanisms surface run‐off/interflow, leaching, and drift. For this purpose a series of surface waters, soils, and liquid manures from North Rhine‐Westphalia (Northwestern Germany) were sampled and analyzed for up to 29 compounds by HPLC‐MS/MS. In each of the surface waters antibiotics could be detected. The highest concentrations were found in samples from spring (300 ng/L of erythromycin). Some of the substances detected (e.g., tylosin), as well as characteristics in the landscape suggest an input from agriculture in some particular cases. In the investigation of different liquid manure samples by a fast immunoassay method sulfadimidine could be detected in the range of 1…2 mg/kg. Soil that had been fertilized with this liquid manure showed a content of sulfadimidine extractable by accelerated solvent extraction (ASE) of 15 μg/kg dry weight even 7 months after the application. This indicates the high stability of some antibiotics in manure and soil.  相似文献   

Joint bulk-sound and shear tomography for Western Pacific subduction zones   总被引：7，自引：0，他引：7  

A. Gorbatov  B. L. N. Kennett 《Earth and Planetary Science Letters》2003,210(3-4):527-543

Detailed regional body wave tomographic inversion of the Western Pacific region has been performed using P and S travel times from common sources and receivers, with a joint inversion in terms of bulk-sound and shear wave-speed variations in the mantle. This technique allows the separation of the influence of bulk and shear moduli, and hence a more direct comparison with mineral physics information. The study region is parameterized with cells of side 0.5° to 2° and 19 layers to a depth of 1500 km, while the rest of the mantle was parameterized with 5×5° cells with 16 layers between the surface and the core–mantle boundary. A simultaneous inversion is made for regional and global structures to minimize the influence of surrounding structures on the regional image. A nested iterative inversion scheme is employed with local linearization and three-dimensional ray tracing through the successive model updates. The results of the regional tomographic inversion reveal the penetration of a subducted slab below the 660 km discontinuity at the Kurile–Kamchatka trench, while flattening of slabs above this depth is observed in the Japan and Izu–Bonin subduction zones on both the bulk-sound and shear wave-speed images. The penetration of a subducted slab down to a depth of at least 1200 km is seen below the southern part of the Bonin trench, Mariana, Philippine, and Java subduction zones. Fast shear wave-speed perturbations associated with the subducted slabs, down to the 410 km transition zone, are larger than the comparable bulk-sound perturbations for all these subduction zones except the Philippines. The bulk-sound signature for the subducted slab is more pronounced than for shear in the Philippines, Talaud, New Guinea, Solomon, and Tonga subduction zones, where penetration of the slab into the middle mantle is observed. Variation in the amplitude ratio between bulk-sound and shear wave-speed anomalies correlates well with the subduction parameters of the descending slab. Slabs younger than 90 Ma at the trench show bulk-sound dominance in the upper mantle, while older slabs have a stronger shear wave-speed signature. Spreading of the fast shear wave-speed zone between 800 and 1000 km is observed in the areas of deep subducted slab penetration, but has no comparable expression in the bulk-sound images. This high-velocity feature may reflect physical or chemical disequilibria introduced to the lower mantle by subducted slabs.  相似文献   

城市地下管线的测绘及数据管理     

朱春晓 《测绘与空间地理信息》2003,26(1):15-17

介绍城市地下管网从野外采集数据到内业成图一体化作业过程,并同步建立管网信息库、地理信息库,实现GIS平台上对管网的科学管理。  相似文献   

ERDAS软件在森林资源分类工作中应用   总被引：6，自引：0，他引：6  

辛海强  闻辉  张昱 《测绘科学》2003,28(2):39-41

在森林资源分类经营工作的实践中,通过ERDAS软件和3S技术与传统资源调查方法的比较,提出了应用ERDAS软件和3S技术进行资源调查的技术手段具有无可比拟的优势的观点。采用3S技术来完成林业资源分类区划项目,克服了原先调查方法上存在的周期长、工作量大、费时、费力、结果不准确的问题,具有周期短、省时、省力、数据精度高、统计结果准确的优势。ERDAS软件在项目的进行过程中起到了非常重要的作用,有将近80%的工作都是在ERDAS软件中完成的。  相似文献   

Magnitude and frequency in proglacial rivers: a geomorphological and sedimentological perspective     

Philip M.   《Earth》2005,70(3-4):203-251

Proglacial fluvial sedimentary systems receive water from a variety of sources and have variable discharges with a range of magnitudes and frequencies. Little attention has been paid to how these various magnitude and frequency regimes interact to produce a distinctive sedimentary record in modern and ancient proglacial environments. This paper reviews the concept of magnitude and frequency in relation to proglacial fluvial systems from a geomorphic and sedimentary perspective rather than a hydrological or statistical perspective. The nature of the meltwater inputs can be characterised as low-magnitude–high-frequency, primarily controlled by ablation inputs from the source glacier, or high-magnitude–low-frequency, primarily controlled by ‘exceptional’ inputs. The most important high-magnitude–low-frequency inputs are catastrophic outburst floods, often referred to by the term jökulhlaup (Icelandic for glacier-burst). Glacier surges are an additional form of cyclical variation impacting the proglacial environment, which briefly alter the volumes and patterns of meltwater input. The sedimentary consequences of low-magnitude–high-frequency discharges are related to frequent variations in stage, the greater directional variability that sediment will record, and the increased significance of channel confluence sedimentation. In contrast, the most significant characteristics of high-magnitude–low-frequency flooding include the presence of large flood bars and mid-channel ‘jökulhlaup’ bars, hyperconcentrated flows, large gravel dunes, and the formation of ice-block kettle hole structures and rip-up clasts. Glacier surges result in a redistribution of low-magnitude–high-frequency processes and products across the glacier margin, and small floods may occur at the surge termination. Criteria for distinguishing magnitude and frequency regimes in the proglacial environment are identified based on these major characteristics. Studies of Quaternary proglacial fluvial sediments are used to determine how the interaction of the various magnitude and frequency regimes might produce a distinctive sedimentary record. Consideration of sandur architecture and stratigraphy shows that the main controls on the sedimentary record of proglacial regions are the discharge magnitude and frequency regime, sediment supply, the pattern of glacier advance or retreat, and proglacial topography. A model of sandur development is suggested, which shows how discharge magnitude and frequency, in combination with sandur incision and aggradation (controlled by glacier advance and retreat) can control sandur stratigraphy.  相似文献   

陕甘宁盆地东部上三叠统含油长石砂岩的成岩特点及孔隙演化   总被引：88，自引：5，他引：88  

柳益群  李文厚 《沉积学报》1996,14(3):87-96

本文通过对三条地表剖面和２０口探井的综合研究，认为斑脱岩和火山碎屑物质是影响陕甘宁盆地东部上三叠统长６油层组含油长石砂岩成岩作用的根本原因。浊沸石、方解石、绿泥石的胶结、化学压实作用和浊沸石、长石的溶解作用是影响砂岩储集性能的主要因素。孔隙的演化与成岩史、盆地演化史密切相关，长６２—长６４是孔隙结构最好的层段。较好的储油砂体分布在子长、子北地区以及延安—延长—富县—宜川地区等利于浊沸石溶蚀的地带。  相似文献   

京津唐地区地壳结构与强震的发生──Ⅱ．S波速度结构   总被引：18，自引：5，他引：18       下载免费PDF全文

孙若昧  赵燕来 《地球物理学报》1996,39(3):347-355

利用１９８６－１９９３年发生在京津唐地区的２５１６个地震的２１９２７个Ｓ波到时进行层析成像，得出：（１）公元１０００年以来研究区强震震中在下地壳的投影大多分布在低速块体内或低速块体与高速块体相交地带偏低速块体的一侧；（２）唐山地震震源下方的物质，波速比Ｖｐ／Ｖｓ呈现高值，推测呈部分熔融状态，有热物质流从莫霍界面的下方沿通向震源下方的断裂入侵的迹象。（３）黄骅坳陷中心区的上地壳呈现低Ｖｐ／Ｖｓ值，推测那里为水－汽转变的地热系，这与在该地区所测量的高热流值一致。冀中坳陷区的高Ｖｐ／Ｖｓ值反映出其地下物质可能呈部分熔融状态。  相似文献