Desertification in the Eastern Province of Saudi Arabia

The problem of land degradation in the Eastern Province of Saudi Arabia is not a new phenomenon, but during the last decade it has grown to be a serious threat to the delicate desert ecosystems, and also to the urban and industrial areas, due to an increase in sand movement. The area under investigation is situated on the Gulf coast north of Jubail and is approximately 20 km in width centered along the coastline. The total area is almost 1000 km². Eight vegetation types were classified according to the dominant and co-dominant species. A comparative study of the vegetation in a fenced, non-grazed area and in an open grazed area showed that the impact of grazing and recreational activities have largely reduced the value of the rangelands. The reduction in species diversity and density leads to an increase in wind and sand dynamics. Exposed roots, giant ripples, changes in the extension of inland sabkhas and new active dunes could be observed in many parts of the study area. It could be proved that most inland sabkhas in the area are pure deflational features with considerable dynamic due to the reduction in vegetation cover during the recent years. The monitoring of vegetation density was carried out during helicopter flights with the help of GPS and a video camera. Image processing on a personal computer allowed accurate calculations of vegetation density. Observations on active dune fields in the area showed that the size of the dune fields almost doubled in 15 months. Tests in small enclosures showed that there is a potential for natural recovery even in severely damaged areas. In just one year without grazing and with average precipitation there is a significant difference in vegetation cover. Strict grazing management and camping regulations are required to prevent further degradation and allow the recovery of damaged ecosystems. Community involvement and education is necessary for the development of an understanding of regulations and the need for preservation.     

白洋淀浮游植物群落及其与环境因子的典范对应分析

在对湖泊生态系统健康评价研究的基础上,提出用营养状态-综合指数法（TSI-CI）对西湖进行生态系统健康评价．首先选用Chl．a、SD、TP和TN四个指标用相关加权指数法进行营养状态评价,再选择物化和生物指标无量纲化处理后计算综合指数进行综合评价．结果表明：西湖生态系统健康状况与营养状态水平的变化趋势是一致的,1—3月健康状况相对较好,7-9月相对较差．该结果客观反映了西湖的实际情况,为西湖水质管理提供科学依据。     

Geochemical fractionation and ecological risks assessment of benthic sediment-bound heavy metals from coastal ecosystems off the Equatorial Atlantic Ocean

This study determines the pollution, fractionation, and ecological risks of sediment-bound heavy metals from coastal ecosystems off the Equatorial Atlantic Ocean. Contamination Factor(CF), pollution load index(PLI), and geoaccumulation index(Igeo) were used to assess the extent of the heavy metal pollution, while the potential ecological risk was evaluated using the risks assessment code(RAC) and Hkanson potential ecological risk. The analysis revealed concentrations(mg/g, dw) of the cadmium(Cd),chromium(Cr), copper(Cu), nickel(Ni), and lead(Pb) in sediments for wet and dry seasons vary from 4.40-5.08, 14.80-21.09. 35.03-44.8, 2.14-2.28, and 172.24-196.39, respectively. The results also showed that the metal fractionation percentages in the residual, oxidizable, and reducible fractions are the most significant, while the exchangeable and carbonate bound trace metals are relatively low. The RAC values indicate no risk for Cd and Ni and low risk for other metals at all the studied sites during both seasons.Potential ecological risk analysis of the heavy metal concentrations indicates that Cd had high individual potential ecological risk, while the other metals have low risk at all investigated sites. The multi-elemental potential ecological risk indices(R_1) indicate high ecological risk in all the ecosystems.     

Study on the urban heat island effects and its relationship with surface biophysical characteristics using MODIS imageries

This study assesses surface urban heat island (UHI) and its associated surface physical characteristics using remote sensing approaches. TERRA/MODIS images acquired in 2005 in three different seasons were selected to generate land surface tem-perature and surface characteristics for the Changsha-Zhuzhou-Xiangtan metropolitan area in China. The intensity of urban heat is-land effects and its seasonal variations were examined. The result showed that UHI effects were significant both in the summer and the spri...     

内蒙古呼伦西白地区铌稀土多金属矿成矿特征及找矿标志

北山成矿带东缘的内蒙古呼伦西白地区近年来发现了多处铌稀土矿床(点),矿床(点)产于二叠纪二长花岗岩外接触带上,矿体赋存于滨浅海相碳酸盐岩-变碎屑岩内,其形态、产状、规模受构造-岩浆活动控制,并与磁异常对应,其中灰石山东北铌稀土矿区Nb2O5品位0.02%～0.56%、平均0.11%,REO品位0.13%～2.63%,平均0.93%,辉森乌拉西铌金矿区Nb2O5品位0.01%～0.1%,与白云鄂博Nb-REE-Fe超大型矿床特征类似,成矿潜力巨大。结合区域地质背景及铌稀土多金属矿成矿特征,初步认为区内该类型矿床的找矿标志为:二叠系滨浅海相碳酸盐岩-变碎屑岩地层、构造挤压形成的虚脱空间或韧-脆性转换部位、二叠纪二长花岗岩外接触带、放射性异常梯度带-磁异常位置、岩石蚀变(褐铁矿化、硅化、碳酸盐化等)和石英细网脉发育地段。对该地区铌稀土多金属矿成矿特征和找矿标志的研究有利于拓展北山地区三稀矿产的找矿思路,也可为此类矿产的找矿方向提供借鉴。     

Redox evolution of western Tianshan subduction zone and its effect on deep carbon cycle

Knowing the phase relations of carbon-bearing phases at high-pressure(HP) and high-temperature(HT) condition is essential for understanding the deep carbon cycle in the subduction zones.In particular,the phase relation of carbon-bearing phases is also strongly influenced by redox condition of subduction zones,which is poorly explored.Here we summarized the phase relations of carbon-bearing phases(calcite,aragonite,dolomite,magnesite,graphite,hydrocarbon) in HP metamorphic rocks(marble,metapelite,eclogite) from the Western Tianshan subduction zone and high-pressure experiments.During prograde progress of subduction,carbonates in altered oceanic crust change from Ca-carbonate(calcite) to Ca,Mg-carbonate(dolomite),then finally to Mgcarbonate(magnesite) via Mg-Ca cation exchange reaction between silicate and carbonate,while calcite in sedimentary calcareous ooze on oceanic crust directly transfers to high-pressure aragonite in marble or amorphous CaCO3 in subduction zones.Redox evolution also plays a significant effect on the carbon speciation in the Western Tianshan subduction zone.The prograde oxygen fugacity of the Western Tianshan subduction zone was constrained by mineral assemblage of garnet-omphacite from FMQ-1.9 to FMQ-2.5 at its metamorphic peak(maximum P-T) conditions.In comparison with redox conditions of other subduction zones,Western Tianshan has the lowest oxygen fugacity.Graphite and light hydrocarbon inclusions were ubiqutously identified in Western Tianshan HP metamorphic rocks and speculated to be formed from reduction of Fe-carbonate at low redox condition,which is also confirmed by high-pressure experimental simulation.Based on petrological observation and high-pressure simulation,a polarized redox model of reducing slab but oxidizing mantle wedge in subduction zone is proposed,and its effect on deep carbon cycle in subduction zones is further discussed.     

村镇滑移隔震建筑瞬时摩擦耗能的参数敏感性分析

给出了村镇滑移隔震建筑瞬时摩擦耗能的概念,并以此概念为响应指标。通过极差大小的对比,分析了该响应指标对刚度比、第二阶段刚度系数、隔震层屈服位移、隔震层摩擦系数、系统质量比和上部结构自振周期六个参数变化的敏感程度,阐述了上述系统参数对瞬时摩擦耗能这一响应指标的影响规律。研究表明:场地条件和地震动幅值大小对瞬时摩擦耗能均有显著影响;在所考虑的参数范围内,上部结构自振周期总是对瞬时摩擦耗能有较为显著的影响,摩擦系数对瞬时摩擦耗能的影响跟场地条件有关,Ⅰ类场地条件中摩擦系数对瞬时摩擦耗能影响不显著,而Ⅱ、Ⅲ和Ⅳ类场地条件中,摩擦系数对瞬时摩擦耗能的影响则非常显著;隔震层屈服位移、刚度比和第二阶段刚度系数总得来讲对瞬时摩擦耗能影响不显著,质量比对瞬时摩擦耗能影响居中。     

生态最相关水文指标的优选及其在洞庭湖环境流量估算中的应用

水文改变指标(IHA)能够较为全面地描述水文状况,在评估水文情势改变及其生态系统影响方面具有广泛的应用.尽管该指标体系较为完善,但是数量众多的水文变量仍然存在信息冗余问题.根据洞庭湖城陵矶水文站1955-2014年的径流量数据,采用主成分分析(PCA)筛选了生态最相关水文指标(ERHIs),结合ERHIs改进了用于估算环境流量的变化范围法(RVA),并将其应用在洞庭湖出口的环境流量估算中.基于PCA选取了年最大90日流量、年最小3日流量、年最小流量出现时间、3月流量、6月流量、流量逆转次数和低流量年内平均历时7个变量作为洞庭湖出口的ERHIs.纵向和横向的对比分析都表明选取的ERHIs是合理的.ERHIs不仅有效缓解了IHA的冗余性问题,还有利于抓住最关键的生态水文变量.根据ERHIs改进的RVA方法在设定洞庭湖出口环境流量时,极大地简化原来的众多管理目标,对生态水文研究、水资源管理和生态保护都具有重要的参考价值和借鉴意义.     

长江口外缺氧区沉积物中氧化还原敏感性元素的"粒控效应"

对长江口外缺氧区及其邻近海域表层沉积物和沉积物岩芯样品的粒度和元素（主要包括氧化还原敏感性元素简称RSE,和典型陆源碎屑元素）进行了分析,并对元素的“粒控效应”进行了深入研究.结果表明,在近岸底层水溶解氧浓度正常海区沉积物中,元素（包括典型陆源碎屑元素和RSE）的分布显示出明显的“粒控效应”,在缺氧区沉积物中,RSE与粒度之间的相关性较差,其分布不受“粒控效应”的制约,而主要受氧化还原环境的影响.另外缺氧区缺氧程度的不同会导致不同的RSE的富集.     

生态系统完整性评价研究进展

系统地介绍了生态系统完整性概念的由来,以及对生态系统完整性进行评价的指标必须满足的原则;并从指示物种,结构-功能-组成,压力-响应等方面介绍了生态系统完整性评价指标;进一步介绍了生态系统完整性等级的划分;对目前生态系统完整性评价研究中存在的问题进行了初步的讨论。