Analysis of the Major Fe Bearing Mineral Phases in Recent Lake Sediments by EXAFS Spectroscopy   总被引：1，自引：0，他引：1  

Lorenzo Spadini  Markus Bott  Bernhard Wehrli  Alain Manceau 《Aquatic Geochemistry》2003,9(1):1-17

Extended X-ray absorption fine structure (EXAFS) spectroscopy and chemical analyses were combined to determine the Fe bearing minerals in recent lake sediments from Baldeggersee (Switzerland). The upper section of a laminated sediment core, deposited under eutrophic conditions, was compared to the lower part from an oligotrophic period. Qualitative analysis of FeK EXAFS agreed well with chemical data: In the oligotrophic section Fe(II)–O and Fe(III)–O specieswere present, whereas a significant fraction of Fe(II)–S sulfides was strongly indicated in the eutrophic part. A statistical analysis was performed by least square fitting of normalized reference spectra. The set of reference minerals included Fe(III) oxides and Fe(II) sulfides, carbonates and phosphates. In the oligotrophic regime no satisfying fit was obtained using the set of reference spectra, indicating that siderite (FeCO₃) was not present in a significant amount in these carbonate-rich sediments. Simulated EXAFS spectra for a(Ca_x, Fe_1-x)CO₃solid solution allowed reconstructing the specificfeatures of the experimental spectra, suggesting that this phase was the dominant Fe carrier in the oligotrophic section of the core. In the eutrophic part, mackinawite was positively identified and represented the dominant Fe(II) sulfide phase. This finding agreed with chemical extraction, which indicated that18–40 mol% of Fe was contained in the acid volatile iron sulfide fraction. EXAFS spectra of the eutrophic section were best fitted by considering the admixture of mackinawite and the Fe–Ca carbonate phase inferred to be predominant in the oligotrophic regime.  相似文献   

Characterisation of sphalerite and pyrite flotation samples by XPS and ToF-SIMS   总被引：2，自引：0，他引：2  

A. Boulton  D. Fornasiero  J. Ralston 《International Journal of Mineral Processing》2003,70(1-4):205-219

The surface analytical techniques of X-ray Photoelectron Spectroscopy (XPS) and Time of Flight Secondary Ion Mass Spectroscopy (ToF-SIMS) have provided information on the type and concentration of species on the surface of sphalerite and pyrite particles in flotation concentrate and tail samples, but also on their distribution on each particle and across particles of different sizes. From this surface analytical study, a more accurate interpretation of the flotation results of sphalerite and pyrite minerals in a mixed mineral system could be made as a function of the concentrations of copper sulphate activator and xanthate collector, and particle size. In particular, it was found that sphalerite particles reporting to the concentrate are larger in size and contain less iron hydroxide on their surface than particles reporting to the tail. As for the pyrite particles, their lower recovery than the sphalerite particles is the result of a larger proportion of iron hydroxide on their surface inhibiting copper and collector adsorption.  相似文献   

Globalisation and the Livestock Industry in Botswana   总被引：1，自引：0，他引：1  

Michael B.K. Darkoh  & Joseph E. Mbaiwa 《Singapore journal of tropical geography》2002,23(2):149-166

The expansion of Botswana's livestock industry in recent years is partly a result of moves towards integration into the global economy. In the colonial period, livestock raising was the backbone of the national economy and in the post-colonial period remains the mainstay of the rural economy. Botswana's export-driven cattle industry has led to the establishment of a well-equipped infrastructure such as marketing and veterinary services, which rank among the most developed in Africa. The industry has much support from the government; hence, the cattle population continues to grow. Even though globalisation has generally had positive impacts on the development of Botswana's economy through beef exports, it has also generated some socioeconomic and environmental problems. Most serious are the continuing skewness of livestock holdings, increasing income disparities between the rich and poor, and accelerated overgrazing of rangelands due to overstocking of cattle by both communal and commercial farmers. The erection of veterinary cordon fences associated with the prevention of diseases and expansion of the cattle industry to meet export demands have decimated large numbers of migratory wildlife species in the country, with deleterious effects on the burgeoning tourist industry. As a result, globalisation is having both positive and negative impacts on the economy of Botswana.  相似文献   

TPOA框架在禁牧政策效果评价与优化调控中的应用——以宁夏盐池县为例     

王娅 《中国沙漠》2021,41(6):179-186

位于北方农牧交错区地形、气候、植被过渡带的宁夏盐池县是典型的农牧生产和生态敏感区。基于农户视角,应用目标-过程-结果-调控四维分析框架（TPOA）和问卷数据,分析禁牧政策的实施效果和适时调整问题,对于全面了解禁牧政策的实施效用、制定相应的调控对策具有一定的实践指导意义,可为北方农牧交错区禁牧的适时调整与草原的合理利用提供案例支撑。禁牧政策实施中,60.40%、55.38%和11.83%的受访户分别采取了扩张型、调整型和收缩型适应策略,农户从事非农产业的比例提高,夜间偷牧现象普遍,存在饲草缺口大、养殖成本高、龙头企业带动力不强、市场监管难等困境。该政策的实施实现了盐池当地草原生态恢复和沙漠化逆转,38.79%的受访户认为禁牧政策确实“达到了”生态恢复的预期目标,60.87%的农户对草原补奖表示满意,46.09%的受访户认为禁牧政策亟待调整,可从提高禁牧补偿标准、生态适宜地区适当开牧、延长补助期限等方面着手。将TPOA框架应用于禁牧政策效果评价中,为评价生态政策的实施绩效提供了理论基础。  相似文献   

社会—生态系统视角下农户对禁牧政策的适应性——以宁夏盐池县为例   总被引：2，自引：2，他引：0  

侯彩霞  周立华  文岩  陈勇 《中国沙漠》2018,38(4):872-880

为了保护草原生态环境,2002年起国家全面实施“退牧还草”工程,在草原破坏严重的地区实施禁牧政策。政策实施后,草地生态明显恢复。作为草原最主要的经济活动主体和禁牧政策的最直接承受者,农户对政策的适应性直接影响政策的顺利进行以及生态环境恢复的可持续性。基于宁夏盐池县入户调查资料,研究了不同类型农户对禁牧政策的生态环境效应感知以及对禁牧政策适应能力感知,分析了不同类型农户对禁牧政策的应对策略,探讨了影响农户适应策略选择的主要因素。结果表明：（1）盐池县社会-生态系统尚处于不理想的系统稳态,生态系统恢复明显,但社会系统的适应性较低。农户普遍认为禁牧政策实施对生态环境有很大的改善,但对禁牧政策满意度感知处于中等水平,对禁牧政策适应能力的感知处于较低水平。由于生计方式和收入水平的差异,不同类型农户对禁牧政策的适应性感知差异较大。（2）不同类型农户采取不同适应策略应对禁牧政策实施造成的影响。纯农户适应策略以收缩型为主,兼业户和非农户以调节型为主,低收入和中等收入农户以收缩型为主,高收入农户以调节型为主。（3）农户对禁牧政策的适应成本、自我效能和农户拥有的人力资本、金融资本是影响农户适应性策略类型选择的主要因素。  相似文献   

Alpine Ecosystems of Northwest Yunnan, China： an Initial Assessment for Conservation   总被引：1，自引：1，他引：0  

Ruth Sherman Renee Mullen LI Haomin FANG Zhendong WANG Yi 《山地科学学报》2007,4(3):181-192

Implementing conservation actions on-the-ground is not a straightforward process,especially when faced with high scientific uncertainty due to limited available information. This is especially acute in regions of the world that harbor many unique species that have not been well studied,such as the alpine zone of the Hengduan Mountains of Northwest Yunnan (NWY),a global biodiversity hotspot and site of The Nature Conservancy’s Yunnan Great Rivers Project. We conducted a quantitative,but rapid regional-level assessment of the alpine flora across NWY to provide a broad-based understanding of local and regional patterns of the alpine flora,the first large-scale analysis of alpine biodiversity patterns in this region. Multivariate analyses were used to classify the major plant community types and link community patterns to habitat variables. Our analysis indicated that most species had small distributions and/or small population sizes. Strong patterns emerged with higher diversity in the more northern mountains,but beta diversity was high,averaging only 10% among sites. The ordinations indicated that elevation and geographic location were the dominant environ-mental gradients underlying the differences in the species composition among communities. The high beta diversity across the alpine of these mountains implies that conservation strategies ultimately will require the protection of large numbers of species over a large geographical area. However,prioritiza-tion should be given to areas where potential payoffs are greatest. Sites with high species richness also have a greater number of endemic species,and,by focusing efforts on these sites,conservation investments would be maximized by protecting the greatest number of unique species.  相似文献   

NaCl型油田水中I^-的离子选择电极法测定          下载免费PDF全文

陈玉锋杜秀月  冉广芬 《盐湖研究》2007,15(2):30-33

采用了NaCl溶液为离子强度调节剂(TISAB),离子选择电极法测定NaCl型油田水中I-离子的含量,并对该方法进行了测定条件实验的研究。标准曲线在7.94×10-6～1.00 mol/L范围内呈良好的线形关系,相关系数R2=0.999 5,平均回收率为98.9%,RSD(n=6)=1.0%,实验结果表明,该方法测定NaCl型油田水中的I-简便、快速、准确。  相似文献   

In-situ studies of microzooplankton grazing pressure on phytoplankton in Jiaozhou Bay, China     

Wang Yong  Sun Hekun  Zhou Yi 《中国海洋湖沼学报》2004,22(2):162-165

Preliminary studies on microzooplankton grazing were conducted with dilution method in Jiaozhou Bay from summer 1998 to spring 1999. Four experiments were carried out at St. 5 located at the center of Jiaozhou Bay. Chlorophyll a concentrations were consistently dominated by netphytoplankton (net-, >20μm), except during the autumn 1998 cruise, when they were dominated by nanophytoplankton(nano-, 2–20μm). The contribution of picophytoplankton (pico-, <2μm) to total chlorophyll a concentrations (<200μm) varied considerably between cruises. Instantaneous growth coefficients(u) of phytoplankton varied from 0.098 to 1.947d⁻¹, with mean value of 0.902d⁻¹. Instantaneous coefficients(g) of microzooplankton grazing on phytoplankton ranged from 0.066 to 0.567d⁻¹, mean value of 0.265d⁻¹, which was equivalent to daily lose of 21.9% of the initial standing stock and 58.1% of the daily potential production. Project No KZCX3-SW-214 supported by Chinese Academy of Sciences.  相似文献   

Interactions between suspended organic matter and copepod grazing in the plume of the Hudson River     

Mira B. Chervin  Thomas C. Malone  Patrick J. Neale 《Estuarine, Coastal and Shelf Science》1981,13(2):169-183

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锡林郭勒草原生态恢复工程效果的评价   总被引：10，自引：1，他引：9  

卓莉  曹鑫  陈晋  陈仲新  史培军 《地理学报》2007,62(5):471-480

针对锡林郭勒草原的严重退化, 近年来启动了草原生态恢复工程, 但工程实施的效果由于范围广、时间短而很难予评价。利用锡林郭勒草原地区1999~2004 年的SPOT-VGT 10 天最大值合成NDVI 时间序列数据, 在求得各年NDVI 年最大值(NDVImax) 的基础上, 通过搜寻各像元邻域内NDVImax 的最大值以及与之相应的气候因子, 建立起了像元尺度上的气候-植被生长基准响应模型, 并以此为依据运用相对残差趋势法识别出了处于恢复阶段的草原区域。 最后, 将遥感监测结果与羊单位统计资料进行对比分析, 结果发现, 在县级行政区域尺度上的平均恢复趋势与基于羊单位和NPP 构建的放牧压力趋势具有较好的反比例关系, 初步证明了该方法在时间序列较短情况下的有效性。  相似文献