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361.
362.
363.
Geochemical and environmental magnetic studies were carried out to identify the effect of iron oxyhydroxides on arsenic mobilization
in high arsenic aquifer system. Using high arsenic sediment samples from two boreholes, specifically drilled for this study,
chemical composition and magnetic properties including magnetic susceptibility, saturation remnant magnetization, and isothermal
remnant magnetization were measured. Results of correlation analysis of element contents show that arsenic and iron are closely
associated with each other (r
2 = 0.40, α = 0.05, n = 21). In contrast, the correlation of phosphorus with iron (r = 0.11, α = 0.05, n = 21) and arsenic (r
2 = 0.18, α = 0.05, n = 21) was poor, which might result from competitive adsorption of phosphorus and arsenic on the surface of Fe-oxyhydroxides.
The high correlation coefficients between arsenic contents and magnetic parameters suggest that the ferrimagnetic minerals
including maghemite and hematite are the dominant carrier of arsenic in aquifer sediments. The results of sequential extraction
experiments also revealed the association of arsenic with reducible iron oxides, such as maghemite and hematite in aquifer
sediments. Therefore, under reducing conditions, reductive dissolution and desorption of arsenic from Fe-oxyhydroxides into
the aqueous phase should be the dominant geochemical processes for its enrichment in groundwater at Datong.
An erratum to this article can be found at 相似文献
364.
Based on rock and fossil data from the Upper Cretaceous of the El Hassana Dome (Abu Roash, Egypt), factors controlling facies architecture and the nature of biotopes are highlighted. The succession formed on a non-rimmed shelf, the architecture of which varied from an inner to an outer shelf setting upsection. Macrobenthic biotopes are reconstructed and their palaeoecological significance assessed using a novel ternary plot. Based on diversity and community structure (770 specimens assigned to 28 bivalve and gastropod taxa), four paucispecific associations are identified. These are: 1. the ‘Cucullaea’ Assemblage, a low-energy, soft-substrate, oligotrophic outer shelf environment with reduced terrigenous input dominated by infaunal bivalves and hexactinellid sponges; 2. the ‘Plicatula’ Assemblage, a low-energy, restricted inner shelf lagoonal setting with soupy substrates and dysoxia below the sediment-water interface dominated by plicatulid and ostreid bivalves, 3. the ‘Durania’ Assemblage, a high-energy, high-temperature, shoal environment dominated by elevator rudists with minor numbers of echinoids, corals and bryozoans, which together form several biostromes. and 4. The ‘Trochactaeon’ Assemblage, which share the same characteristics of the ‘Durania’ Assemblage. The paucispecific nature of these biotopes is indicative of different stress factors. Consequently, the predominant taxa exhibit different degrees of adaptive strategies. In addition to global sea level, local tectonics have significantly affected facies distribution and biotope structure. The shallower facies during the early Turonian and the dysoxia spanning the Coniacian–Santonian were linked to synsedimentary tectonics, which formed many barriers and led to circulation restrictions. 相似文献
365.
Coastal area is the region with the highest degree of economic and social development and the largest ecological stress in current China, where the proportions and the spatial patterns of developed coastal resource and environment are determined by projects planning. Ecological carrying capacity evaluation is the necessary prerequisite for sustainable utilization of natural resources and protecting ecological environment to ensure healthy and sustainable economic and social development to project planning. Based on the pressure types of projects planning on resources and environment, the concept and contents of coastal ecological carrying capacity were redefined for enhancing the practical value of ecological carrying capacity evaluation. The domestic and foreign research progress and advances related with coastal ecological carrying capacity evaluation were reviewed, which included habitat suitability evaluation, suitability assessment of construction land development, reclamation suitability evaluation and assessment of sea water environmental capacity. The conclusion noted that domestic research of coastal ecological carrying capacity needs to build a complete system of ecological carrying capacity evaluation methodology based on extensive reference to foreign research results, and quantitative evaluation and spatial visualization research related with coastal ecological carrying capacity should be carried out to provide strong support for ecological civilization process of economy and society in coustal areas. 相似文献
366.
秦岭造山带新生代构造隆升与区域环境效应研究 总被引:16,自引:0,他引:16
据沉积,构造、地貌并结合地球物理资料综合研究认为,秦岭造山带新生代构造隆升是在中生代白垩纪晚期构造隆升基础上,于晚第三纪中新世迅速隆升,而早更新世早期则是新构造活动最强烈时期。秦岭造山带的新生代构造隆升的方式主要有地垒式、掀斜式、振荡式和翘板式4种。诱发这一地区新构造抬升的主要原因和动力学机制是华北地块自北而南,扬子地块自南而北相向向秦岭造山带之下陆内俯冲和秦岭地块深部软流圈抬升共同作用所致。 相似文献
367.
In accordance with Senegal’s decentralisation policy, important forest management tasks, including the right to allocate charcoal production rights, have been transferred to rural councils. This paper investigates the impact of these institutional reforms on charcoal production practices using the environmental entitlement framework developed by Leach et al. [Environmental entitlements: dynamics and institutions in community-based natural resource management. World Development 27 (2) (1999) 225]. The councils have not been able to turn their new endowments into entitlements because they lack sufficient strength and legitimacy. Informal institutions, notably the coalition between merchants, state agents and village chiefs, continue to run the charcoal business and are hardly affected by decentralisation efforts. Most rural people, especially those relying solely on agriculture for sustenance, do not benefit at all from the charcoal trade. They do suffer from the environmental costs it brings with it, however. Although tensions between pro-exploitation actors and pro-conservation actors are evident, the pro-exploitation actors’ firm grip on the informal institutions will probably lead to a prolonged subversion of the laws that seek to enhance local control and to sustain the forest. 相似文献
368.
369.
Hollie Grant 《社会与自然资源》2019,32(7):768-789
Why do environmental defenders continue to participate in community-based efforts to protect the environment despite threats to their lives and minimal success in deterring or punishing offenders? Examining Community Forestry initiatives in Cambodia, we find that forest protection is not only a means to gain environmental, economic, or social benefits, but also a means for forest defenders to assert themselves as political actors in relation to the state and other citizens. Rather than simply repressing and disciplining forest dwelling populations, violence against defenders shapes their subjectivity and re-politicizes their lives. Distinguishing between various forms of violence associated with different illicit forest users, we highlight how forest protection becomes a means of political self-expression and rights-based resistance as forest defenders reinterpret direct violence through experiences and understandings of structural and symbolic violence. Participation in CF thus unlocks ways of being political and contesting oppressive structures while acting within sanctioned institutions. 相似文献
370.
This paper addresses some important issues related to the estimation of long-term extreme responses of marine structures. Several convolution models to establish the long-term distribution of a marine structure response parameter are available in the literature. These methods are typically based either on all short-term peaks, all extreme short-term peaks or all short-term upcrossing rates. The main assumptions and simplifications of the five models most usually found in the literature are discussed in this paper. A linear single-degree-of-freedom (SDOF) system along with a bi-lognormal probability model for significant wave heights and zero-crossing wave periods have been used for numerical tests. An improved approach to efficiently evaluate the long-term convolution integrals is also proposed in this paper. It is shown that a combination of the Inverse First Order Reliability Method (IFORM) and an Importance Sampling Monte Carlo Simulation (ISMCS) approach can be used to obtain a very good result for the exact solution of long-term integrals. 相似文献