环境风险评价中的不确定性研究

在环境风险评价中经常会遇见不确定性问题,以无水氢氟酸储罐泄漏为例,分别研究了在计算事故发生概率、确定泄漏源、应用扩散模式、评价事故损伤结果等工作中遇到的不确定性问题。并以此分析了造成这些不确定性因素的原因,同时提出相应的解决方法,最后介绍了环境风险评价中不确定性问题的研究现状和方向。     

Response of ecological storage and conservation to land use transformation: A case study of a mining town in China

Rapid land use transformation shaped by agriculture, industrialization and population urbanization has a great influence on ecological environment. Based on theory of ecosystem service functions, this study aims at revealing the response of ecological storage and conservation to each unit area of land use transformation. Taking Cishan Town, a mining town in China, as a case study, this paper estimates the “past-present-future” ecological storage impacted by the process, result and possibility of land use transformation. The local land use and industrial distribution show that the active areas of land use transformation are also the areas of concentration of human (industrial) activities. Ecological storage shows the different responses to land use ways. And then this study combines the ecological storage indices with the indices of ecosystem pattern and land condition into the“5A” framework (active state, active degree, active possibility, active balance and active condition) for grading ecological conservation, and then assigns all regions of Cishan Town into different grades through membership functions for complex mapping of ecological conservation. The research results show that the ecological conservation in Cishan goes toward two extreme grades (best grade and worst grade). Uneven and unbalanced land use transformation is the main cause of that. Hence, rational and timely reflection of impact of land use transformation on ecological storage and conservation can assist land use planners and local government in adjusting land use ways and balancing regional ecology and economy.     

保护性耕作对土壤有机碳、氮储量的影响

以辽宁彰武县保护性耕作示范推广基地土壤为研究对象,通过实地调查和取样分析,对比研究了传统犁耕和6年免耕秸秆覆盖条件下的土壤有机碳、氮储量,为广泛评价保护性耕作的土壤碳、氮截获功能和合理选择农业耕作方式提供科学依据。研究结果表明,与犁耕相比,免耕覆盖不同程度地提高了0-5cm和5～15cm土层的有机碳、氮储量,对15cm以下土层没有影响,从而增加了0～100em土体总的有机碳、氮储量,证明了免耕覆盖的土壤碳、氮截获功能,年均截获率分别为1．37Mg·hm-2和0．84Mg·hm-2有机碳、氮在犁耕土壤0～30cm剖面的垂直分布较为均匀,免耕覆盖后则发生明显的分层,产生表聚现象。     

Landscape Character and Fish Assemblage Structure and Function in Western Lake Superior Streams: General Relationships and Identification of Thresholds

As part of a comparative watershed project investigating land-cover/land-use disturbance gradients for streams in the western Lake Superior Basin, we examined general relationships between landscape character and fish assemblage structure and function. We also examined the shape of those relationships to identify discontinuity thresholds where small changes in landscape character were associated with marked shifts in the fish assemblages. After completing a geographic analysis of second- and third-order watersheds in the western Lake Superior drainage, we randomly selected 48 streams along mature forest and watershed storage gradients in 2 hydrogeomorphic regions as our study sites. During the summers of 1997 and 1998, we used electrofishing to sample fish assemblages from each stream. Each of the landscape factors was significantly associated with fish assemblage structure and function based on analysis of covariance. Watershed storage was related to the greatest number of fish assemblage characteristics, but hydrogeopmorphic region and mature forest cover were strongly associated as well. The hydrogeomorphic region also mediated relationships between watershed character and fish assemblages. Discontinuity thresholds for our fish assemblages averaged 11% for watershed storage and 50% for watershed mature forest cover based on piecewise regression analysis. Although many of the landscape–fish relationships might have been manifest through effects on in-stream habitat, our results highlight the importance of management and land-use planning decisions at the watershed and landscape scales.Published online     

MANAGING UNDERGROUND STORAGE TANKS IN URBAN ENVIRONMENTS: A GEOGRAPHIC INFORMATION SYSTEMS APPROACH1

ABSTRACT: Fuels contained in underground storage tanks (USTs) are a major source of soil and ground water contamination. Effective management of the problem at the urban level is difficult due to a large number of tanks and a vast array of factors (e.g., tank characteristics, geology) that determine environmental hazards. The problem is compounded by frequent abandonment and reuse of service stations, which makes it difficult to track the status of underground tanks. Geographic information systems (GIS) are ideally suited to organizing location and attribute data for variables that are pertinent to the UST management problem. A GIS-based UST management system was developed and applied to 136 current and former gasoline service stations in Denton, Texas. The system is effective for tank inventory and can be applied in a proactive fashion to identify potentially problematic facilities. In the event of a leak or spill, the management system can support the implementation of reactive measures to mitigate subsurface contamination. Potential beneficiaries of such a system include planning departments, environmental regulatory agencies, emergency management officials, lending institutions, gasoline distributors, and oil companies.     

PRACTICAL IMPLICATIONS IN THE USE OF STOCHASTIC DYNAMIC PROGRAMMING FOR RESERVOIR OPERATION1

ABSTRACT: A stochastic dynamic programming model is applied to a small hydroelectric system. The variation in number of stage iterations and the computer time required to reach steady state conditions with changes in the number of storage states is investigated. The increase in computer time required to develop the storage probability distributions with increase in the number of storage states is reviewed. It is found that for an average of seven inflow states, the largest number of storage states for which it is computationally feasible to develop the storage probability distributions is nine. It is shown that use of the dynamic program results based on a small number of storage states results in unrealistically skewed storage probability distributions. These skewed distributions are attributed to “trapping” states at the low end of the storage range.     

三元组分图在储罐退役惰性化过程设计中的应用

储罐退役之前,一般要进行惰化处理,以降低可燃气体浓度,避免形成爆炸性混合气体。根据三元组分图,可以方便、直观地设计惰化施工的方案,包括惰化操作的程序设计和危险气体控制目标浓度的确定。本文从理论上研究了在储罐退役惰性化过程设计时,如何用三元组分图表示爆炸极限、最小含氧浓度以及在储罐稀释惰性化过程中气体组成的变化轨迹。提出了两套惰化设计方案,在分析比较的基础上,确定了储罐退役惰化时的最安全实施方案。     

Coalbed methane reservoir data and simulator parameter uncertainty modelling for CO2 storage performance assessment

Laboratory studies and a number of field pilots have demonstrated that CO₂ injection into coal seams has the potential to enhance coalbed methane (CBM) recovery with the added advantage that most of the injected CO₂ can be stored permanently in coal. The concept of storing CO₂ in geologic formations as a safe and effective greenhouse gas mitigation option requires public and regulatory acceptance. In this context it is important to develop a good understanding of the reservoir performance, uncertainties and the risks that are associated with geological storage. The paper presented refers to the sources of uncertainty involved in CO₂ storage performance assessment in coalbed methane reservoirs and demonstrates their significance using extensive digital well log data representing the Manville coals in Alberta, Canada. The spatial variability of the reservoir properties was captured through geostatistical analysis, and sequential Gaussian simulations of these provided multiple realisations for the reservoir simulator inputs. A number of CO₂ injection scenarios with variable matrix swelling coefficients were evaluated using a 2D reservoir model and spatially distributed realisations of total net thickness and permeability.     

Time-lapse carbon dioxide monitoring with pulsed neutron logging

Elevated levels of CO₂ in the atmosphere have been linked to the rise in land and sea temperature [Climate Change, 2001. In: Houghton, J.T., Ding, Y., Griggs, D.J., Noguer, M., van der Linden, P.J., Xiaosu, D. (Eds.), The Scientific Basis Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change (IPCC). Cambridge University Press, UK, p. 944]. To demonstrate geological carbon sequestration as a mitigation technique, a carbon dioxide injection experiment was conducted in East Texas. The target – Frio formation – is a highly porous, permeable and unconsolidated sandstone. The specific interval is the Frio C sand, which originally was saturated with saline formation water. At the injection location, the Frio C sand dips 18° to the south. To monitor the injected CO₂ spreading in the formation, an old well from 1956 drilled into the deeper Yegua formation was selected as the observation well. The injection well was drilled at a distance of 100 ft downdip from the monitoring well. Several borehole measurement methods were available to monitor the CO₂ injection, but the most suitable technology was thought to be the pulsed neutron logging. This logging is used widely in cased hole, and the measured macroscopic thermal absorption cross-section (Σ) is sensitive to CO₂ saturation in high porosity saline water environments. Several log examples are given demonstrating successful the monitoring of the CO₂ plume moving through the two boreholes and the resulting saturation changes.     

冰川积雪融水补给为主河流水库蓄水期起始时间的判定

如何科学合理地确定水库蓄水期起始时间对保证水库正常运行、下游灌溉、供水、河道生态需水等方面有重要的作用,尤其是以冰川积雪融水补给为主的河流水库。而目前在实际水库运行中也没有一个较好的合理确定标准和方法,只能根据流域特性水库运行管理人员主观确定,受人为因素影响较大,增加了水库正常运行的不确定性,不能充分发挥水库各方面的效益。因此提出在以MOD IS积雪监测数据基础上结合零度层高度监测数据即雪线高度合理确定水库蓄水期起始时间的方法,更具有说服力及合理性,对水库运行管理提供了一定的指导依据,有利于当地水资源的合理利用,并通过实际应用说明方法是可行的。