Estimation for partially observed Markov processes     

M. E. Thompson  T. N. Kaseke 《Stochastic Hydrology and Hydraulics》1995,9(1):33-47

Many stochastic process models for environmental data sets assume a process of relatively simple structure which is in some sense partially observed. That is, there is an underlying process (X_n, n 0) or (X_t, t 0) for which the parameters are of interest and physically meaningful, and an observable process (Y_n, n 0) or (Y_t, t 0) which depends on the X process but not otherwise on those parameters. Examples are wide ranging: the Y process may be the X process with missing observations; the Y process may be the X process observed with a noise component; the X process might constitute a random environment for the Y process, as with hidden Markov models; the Y process might be a lower dimensional function or reduction of the X process. In principle, maximum likelihood estimation for the X process parameters can be carried out by some form of the EM algorithm applied to the Y process data. In the paper we review some current methods for exact and approximate maximum likelihood estimation. We illustrate some of the issues by considering how to estimate the parameters of a stochastic Nash cascade model for runoff. In the case of k reservoirs, the outputs of these reservoirs form a k dimensional vector Markov process, of which only the kth coordinate process is observed, usually at a discrete sample of time points.  相似文献   

Environmental impact of the former Pb–Zn mining and smelting in East Belgium     

V. Cappuyns  R. Swennen  A. Vandamme  M. Niclaes 《Journal of Geochemical Exploration》2006,88(1-3):6

In the mining district of Plombières-La Calamine (East Belgium), extensive Pb–Zn mining activities resulted in an important contamination of overbank sediments along the Geul river. Moreover, a huge amount of heavy metals is stored in a dredged mine pond tailing, which is located along the river. In the dredged mine pond tailing sediments, Pb–Zn minerals control the solubility of Zn, Pb and Cd. Although Pb, Zn and Cd display a lower solubility in overbank sediments compared to the mine tailing pond sediments, elevated concentrations of Pb, Zn and Cd are still found in the porewater of the overbank sediments. The considerable ‘actual’ and ‘potential’ mobility of Zn, Pb and Cd indicates that the mine pond tailing sediments and the overbank sediments downstream from the mine pond tailing represent a considerable threat for the environment. Besides the chemical remobilisation of metals from the sediments, the erosion of overbank sediments and the reworking of riverbed sediments act as a secondary source of pollution.  相似文献   

Aragonite cycles: diagenesis caught in the act     

LARS REUNING  JOHN J.G. REIJMER  EMANUELA MATTIOLI† 《Sedimentology》2006,53(4):849-866

Organic biomarker and nannofossil assemblages are used in combination with sedimentary petrology to identify the role of diagenesis for the formation of a rhythmic calcareous succession. A record from the Early Pliocene of the Maldives (Ocean Drilling Program, ODP Leg 115) is presented containing precession and eccentricity cycles expressed as variable aragonite content. Additional sub‐Milankovitch cycles are caused by rhythmic precipitation of calcite cement in the lower part of the interval. Comparison with palaeo‐productivity indicators (nannofossils, chlorin, total organic carbon) suggests that cementation occurs preferentially in intervals characterized by increasing or decreasing productivity. The coupled variability in productivity and carbonate diagenesis is attributed to the effect of organic matter degradation in the sediment. The observed combination of primary and diagenetic factors hampers the interpretation of the cyclicity on Milankovitch and sub‐Milankovitch scales. Diagenetically stable proxies for palaeo‐productivity, such as nannofossil assemblage data, were used to distinguish between palaeoclimate and diagenetic influences.  相似文献   

Heavy metals in freshly deposited sediments of the river Subernarekha, India: an example of lithogenic and anthropogenic effects   总被引：1，自引：0，他引：1  

A. K. Upadhyay  K. K. Gupta  J. K. Sircar  M. K. Deb  G. L. Mundhara 《Environmental Geology》2006,50(3):397-403

Heavy metal distribution patterns in river sediments aid in understanding the exogenic cycling of elements as well as in assessing the effect of anthropogenic influences. In India, the Subernarekha river flows over the Precambrian terrain of the Singhbhum craton in eastern India. The rocks are of an iron ore series and the primary rock types are schist and quartzite. One main tributary, the Kharkhai, flows through granite rocks and subsequently flows through the schist and quartzite layers. The Subernarekha flows through the East Singhbhum district, which is one of India’s industrialised areas known for ore mining, steel production, power generation, cement production and other related activities. Freshly deposited river sediments were collected upstream and downstream the industrial zone. Samples were collected from four locations and analysed in <63-μm sediment fraction for heavy metals including Zn, Pb, Cd and Cu by anodic stripping voltammetry. Enrichment of these elements over and above the local natural concentration level has been calculated and reported. Sediments of the present study are classified by Muller’s geo-accumulation index (I _geo) and vary from element to element and with climatic seasons. During pre-monsoon period the maximum I _geo value for Zn is moderately to highly polluted and for Cu and Pb is moderately polluted, respectively, based on the Muller’s standard. Anthropogenic, lithogenic or cumulative effects of both components are the main reasons for such variations in I _geo values. The basic igneous rock layer through which the river flows or a seasonal rivulet that joins with the main river may be the primary source for lithogenic components.  相似文献   

Will the river Irtysh survive the year 2030? Impact of long-term unsuitable land use and water management of the upper stretch of the river catchment (North Kazakhstan)     

Zbyněk Hrkal  Alain Gadalia  Pierre Rigaudiere 《Environmental Geology》2006,50(5):717-723

The Irtysh river basin all the way from river spring in China across Kazakhstan as far as the Russian part of Siberia is among the most ecologically endangered and affected regions on our planet. The study provides a summary of the historical reasons for anthropological interventions in this area, which began with the construction of plants of the military—industrial complexes in the forties of the last century during World War II. These plants have a major share in extreme high concentrations of heavy metals in surface as well in groundwaters locally. The Semipalatinsk nuclear polygon plays a specific role as a source of contamination of local waters. The release of top secret data enabled us to gain knowledge about serious problems related to high radioactivity of groundwaters, which should spread uncontrollably through a system of secondary fissures activated by nuclear blasts. Another serious problem in this region is the quantitative aspect of contamination. Model simulations of water balance indicate that large industrial development in the spring area in China and continuously increasing water consumption in Kazakhstan may lead to desiccation of the lower stretch of this large river in Siberia during the summer months of 2030.  相似文献   

Lead, zinc, and antimony contamination of the Rio Chilco-Rio Tupiza drainage system, Southern Bolivia     

Lionel F. Villarroel  Jerry R. Miller  Paul J. Lechler  Dru Germanoski 《Environmental Geology》2006,51(2):283-299

An intense, but localized rainfall event in February 2003, led to the severe erosion and failure of a tailings disposal impoundment at the Abarόa Antimony Mine in southern Bolivia. The failure released approximately 5,500 m³ of contaminated tailings into the Rio Chilco-Rio Tupiza drainage system. The impacts of the event on sediment quality are examined and compared to contamination resulting from historic mining operations in the headwaters of the basin. Of primary concern are contaminated floodplain soils located along downstream reaches of the Rio Tupiza which were found to contain lead (Pb), zinc (Zn), and antimony (Sb) concentrations that locally exceed Canadian, German, and Dutch guidelines for agricultural use. Spatial patterns in sediment-borne trace metal concentrations, combined with Pb isotopic data, indicate that Pb, Zn, and Sb are derived from three tributary basins draining the Abarόa, Chilcobija, and Tatasi-Portugalete mining districts. Downstream of each tributary, geographical patterns in trace metal concentrations reflect local geomorphic changes throughout the drainage system. Trace metal concentrations within the Rio Chilco decrease rapidly downstream as a result of dilution by uncontaminated sediments and storage of metal enriched particles (e.g., sulfide minerals) in the channel bed as a result of ongoing aggradation. Storage in the floodplains is limited. These processes significantly reduced the dispersal and, thus, the relative environmental affects of tailings eroded from the Abarόa Mine during the 2003 flood. In contrast, storage of Pb, Zn, and Sb in floodplains along the Rio Tupiza is significant, the majority of which is derived from historic mining operations, particularly mining within the Tatasi-Portugalete district.  相似文献   

Vertical distribution and water solubility of phosphorus and heavy metals in sediments of the St. Lucie Estuary, South Florida, USA   总被引：2，自引：0，他引：2  

Z. L. He  M. Zhang  P. J. Stoffella  X. E. Yang 《Environmental Geology》2006,50(2):250-260

Accumulation and distribution of heavy metals and phosphorus in sediments impact water quality. There has been an increasing concern regarding fish health in the St. Lucie Estuary, which is related to increased inputs of nutrients and metals in recent decades. To investigate vertical changes of contaminants (P, Cd, Cr, Co, Cu, Ni, Pb, Zn, and Mn) in sediments of the St. Lucie Estuary in South Florida, 117 layer samples from six of the 210 to 420 cm depth cores were analyzed for their total and water-soluble P and heavy metals, clay, total Fe, Al, K, Ca, Mg, Na, and pH. Principal component analysis (PCA) was used in two sets of analytical data (total and water-soluble contaminant concentrations) to document changes of contaminants in each core of sediments. The PCA of total contaminants and minerals resulted in two factors (principal components). The first and second factors accounted for 61.7 and 17.2 % of the total variation in all variables, and contrast indicators associated with contaminants of P, Cd, Co, Cr, Ni, Pb, Zn, and Mn and accumulation of Fe and Al oxides, respectively. The first factor could be used for overall assessment of P and heavy metal contamination, and was higher in the upper 45–90 cm than the lower depths of each core. The concentrations of P and heavy metals in the surface layers of sediments significantly increased, as compared with those in the sediments deeper than 45–90 cm. The PCA of water-soluble contaminants developed two factors. The second factor (Cu–P) was higher in the upper than the lower depths of the sediment, whereas the highest score of the first factor (Cd–Co–Cr–Ni–Pb–Zn–Mn) occurred below 100 cm. The water-soluble Cu and P concentrations were mainly dependent on their total concentrations in the sediments, whereas the water-soluble Cd, Co, Cr, Ni, Pb, Zn, and Mn concentrations were mainly controlled by pH.  相似文献   

早涝碱咸综合治理与生态环境良性循环     

方生陈秀玲  范振铎万宝林 《地下水》2005,27(1):1-5,9

华北平原东部淡水资源短缺，旱涝碱成灾害限制了农业生产的可持续发展。海河的治理，解决了排洪排涝排咸出路。春季开发利用地下水包括微咸水和半咸水抗旱灌溉。夏季利用伏雨洗盐排咸，增大降雨入渗，减少径流流失，防治渍涝灾害，把降雨转化为地下水资源。秋冬引蓄河水，回灌地下水补源。以土壤与潜水的地层空间作为调节大气降水、土壤水、地下水、地表水的地下水库，以调控地下水埋深在临界动态为指标，最大限度地把时空分布不均的天然降雨转化为可持续利用的水资源。地表水地下水联合运用，促使水资源采补平衡，降雨灌溉淋洗脱盐强于干旱蒸发积盐过程，地下水淡化强于矿化过程。实现旱涝碱咸综合治理，水土资源可持续利用，经济社会可持续发展，生态环境良性循环。  相似文献   

水库下游河流再造床过程中的河岸侵蚀   总被引：3，自引：0，他引：3       下载免费PDF全文

张春燕  陈立  张俊勇  王志国 《水科学进展》2005,16(3):356-360

根据实测河道地形资料,分析了水库下游河床演变中的河岸侵蚀现象,包括不同横向边界约束条件、不同床沙组成和不同河型河段的河岸侵蚀的特征及规律。结果表明:①水库下游均会有河岸侵蚀发生,但初期一般以下切为主,后期以展宽为主。②对于横向边界约束较强的河段,河岸侵蚀相对较弱;相反,则河岸坍塌严重,河岸侵蚀强烈;③对不同的河床组成和边滩组成的河段:河床较粗特别是形成抗冲粗化层,且边滩组成较细的河段,河岸侵蚀现象非常剧烈;河床组成较细的河段,如果边滩抗冲性较强,则河岸侵蚀现象相对较弱,如果滩地组成较细、容易坍塌,河岸侵蚀也会较强;④不同的河型有着不同的河岸侵蚀现象。分汊河段以主汊为主;游荡段的游荡特性在初期受到抑制;弯曲河段的撇弯切滩现象较普遍。  相似文献   

自适应网格技术在MM5中的应用研究     

李红莉  沈桐立 《南京气象学院学报》2005,28(1):44-50

结合一次暴雨过程，将自适应网格技术应用于中尺度模式MM5中进行数值试验，同时对比自适应网格方案和固定网格方案的优劣，对模拟结果作了诊断分析。结果表明：对于此次降水过程，自适应网格模拟的效果取决于一些参数的选择。  相似文献