科尔沁沙地巴克窑地区近150年的环境演变*

在沉积和花粉分析的基础上,对科尔沁沙地东南部巴克窑地区过去150年的植被和环境演变进行了重建。巴克窑等湖泡的诞生时间是在上个世纪前期,约1837年前后。这个时间也正是科尔沁沙地东南部地区首次大规模人口移入和垦荒年代。突然增加的人类活动导致了沙丘植被的迅速破坏,而植被减少和沙丘活化引起区域水文循环的重新调整,即原来通过植物蒸腾作用输出的水量明显减弱,致使地下潜水位上升,形成一系列湖泡。以后,沙地系统的演化主要是在人类活动、气候和系统内部反馈机制的共同作用下完成的。     

The palaeolimnology of Lake Fidler, a meromictic lake in south-west Tasmania and the significance of recent human impact

Three meromictic lakes in the World Heritage Area of south-west Tasmania possess unusual microbiological communities. Their meromixis is maintained by periodic incursions of brackish water from the nearby Gordon River which, in its lower reaches, is a salt-wedge estuary. In 1977 the construction of a dam in the middle reaches of the river restricted penetration of the salt-wedge and meromixis rapidly declined in all three lakes. A palaeolimnological study was carried out on one of the lakes, Lake Fidler, firstly to determine the history of meromixis and its associated microbiological communities, and secondly to assess whether the recent and rapid decline of meromixis is inconsistent with natural rates of development of the Gordon River meromictic lakes. One part of this study included the analysis of the stratigraphy of fossil diatoms from a 17-metre sediment core dating back 8000 yrs. Detrended Correspondence Analysis and Analog Matching were used to compare diatom species assemblages in core samples with diatom samples from a reference dataset consisting of a selection of lake and river sites in the lower Gordon River valley. Five distinct stratigraphic zones were identified in the core. These zones indicated specific stages in the development of the Gordon River lakes from river backwaters to ectogenically-maintained meromictic lakes which will, finally, become terrestrialised by encroaching rainforest. The onset of a stratified water column was identified by the emergence of a dominant freshwater algal flora which suggested that the lake had developed a mixolimnion and become meromictic ca. 2070 ± 50 ¹⁴C yrs ago. In the context of this long history of meromixis, the rapid demise in meromictic stability following construction of the dam is judged to be inconsistent with natural rates of development. The palaeolimnological studies, of which this paper is one part, prompt recommendations for a management strategy to prevent the further decay of these meromictic lakes in the World Heritage Area.     

Constraints of Housing Age and Migration on Residential Mobility

This paper investigates the role of housing age in constraining residential mobility, measured as the percent of households that have moved into their homes in the past 15 months. The leading explanation for why mobility rates differ so much among regions of the United States has been the overall level of growth. The present analysis shows that the growth effect operates through both the newness of population (migration) and the newness of housing available for occupancy by all local residents. The posited explanation for this housing age effect is that progressively older units contain increasingly settled occupants, yielding fewer opportunities for in-movers in areas with older housing. It is empirically demonstrated that households in older housing have lower likelihood of recent mobility even after controlling for age, tenure, migration status, and state location of residence. The analysis reveals the temporal interdependency of mobility, migration, person age, and housing age.     

The organisation of fish assemblages in the regulated Lima basin, Northern Portugal

In order to understand the structure of fish assemblages in the modified Lima basin (Northern Portugal), two distinct datasets concerning the presence and abundance of fish species were subjected to multivariate analysis. On the River Lima two types of flow modification are present within kilometres of one another: (a) a reduced and constant flow due to hypolimnetic release; and (b) an intense and irregular flow. A comparison of their influence on fish assemblages revealed a gradient of assemblage types from tributaries to main river sites. The latter were characterised by a strong dominance of cyprinids, particularly Iberian barbel (Barbus bocagei). The former harboured two kinds of fish assemblages: those closer to the river mouth were dominated by the cyprinids Iberian chub (Squalius carolitertii) and Iberian nase (Chondrostoma polylepis), which were also frequently present in the main river; while in those further upstream the predominant species was the brown trout (Salmo trutta). Although explanatory variables such as distance from source, altitude, substrate coarseness and width were the primary correlates of fish assemblage composition, dam construction and flow regulation also had a significant effect upon assemblage structure, particularly by: i) reducing the importance of migratory species; ii) constraining the presence of trout in the regulated segments; and iii) simplifying the community, especially in the case of the constant and reduced flow regime.     

黄河流域水循环演变若干问题的研究

从若干方面的研究结果揭示了黄河流域水循环发生的巨大变化.水循环是水资源科学评价与合理开发利用的基本依据.水循环主要要素的变化取决于气候条件的变化与人类活动的影响.对前者宜采用适应性对策,在研究气候变化的基础上,分析水循环变动的规律并预测其趋势,制定相应的适应性措施;对于后者则应加强水资源开发利用的科学管理,以维持流域天然水资源的可更新(可再生)性.     

Mechanism of arrested charnockite formation at Nemmara, Palghat region, southern India

The formation of arrested charnockite is an excellent example of structurally controlled channellised fluid flow along specific sites accompanied by selective elemental mobility and mineralogical changes. The present paper recognises and focuses study on three types of arrested charnockite formation from Palghat region, namely, shear-controlled, foliation parallel and boudin-neck types, and address their spatio-temporal relations to regional-scale charnoenderbite. The shear-controlled and foliation parallel types post-date deformation and migmatisation. The boudin-neck type, on the contrary, is coeval with partial melting and followed the path of cooling and decreasing water activity in the gneiss. K-feldspar veining around plagioclase and quartz, symplectitic intergrowth of biotite+quartz after orthopyroxene and K-feldspar, and fluid inclusion data suggests the presence of alkalic supercritical brine and low-density CO₂-rich fluid during charnockite formation. Charnockite domains developed following the breakdown of hornblende, biotite and quartz are characterised by a more or less pronounced depletion of Fe, Ca, Mg and Ti and trace elements Y and Zr, compared to their counterpart gneiss. REE spectra indicate a subtle depletion in the HREE near the centre of the charnockite domain. Although close-pair samples of gneiss–charnockite are isochemical, on a scale of a few millimetres, bi-directional element movement, related to the formation of new mineral was noted. It is postulated that arrested charnockite formation developed in situ on local scale within the granitic domains of the hornblende-biotite gneiss, in the presence of CO₂-rich fluids and alkalic supercritical saline brine. This process post-dated the time of regional granulite (charnoenderbite) and large regional scale retrogression and migmatisation.     

科尔沁沙地土地沙漠化的历史与现状

科尔沁沙地是我国自然条件相对较好的一个沙地，有着广阔的治理前景。回顾科尔沁沙地的历史变化，认为科尔沁沙地是一个全球气候变化大趋势下由人类生产活动过度而形成的沙漠化区域，在金代至清代之间由于人为活动强度减弱，曾经发生明显的沙漠化逆转。根据全国沙漠化普查所获得的资料，研究分析了科尔沁沙地土地沙漠化现状及其特点，结合土地沙漠化发生的历史过程，讨论了这一地区沙漠化的治理策略。     

Assessing natural and cultural influence on soil in remnant tropical woodlands

Rural Hong Kong contains culturally protected enclaves of remnant woodlands that provide sanctuary for vegetation, wildlife and soil. This study focuses on the influence of natural and cultural factors on soil properties in woodlands with different human activities. At each of the nine selected sites, two pits were dug to collect soil samples for analysis of 24 physical and chemical properties. Analyses of variance between soil attributes and site factors suggest the prominence of woodland size, and important contribution of topography, aspect and parent material. Soil indicators of human impacts and the tenacity of woodland soil towards anthropogenic disturbance were demonstrated.     

发展中国家食物安全研究的新进展

本文回顾了七十年代以来食物安全概念的演变历史，特别是介绍了森(Sen)的食物权利理论在这个历史过程中的作用，评价了当前的主要研究热点，展望了将来的几个研究趋势。指出食物安全的概念不能也不应该以单一的观点、方法和尺度来定义，食物安全的研究必须要更紧密地与更广泛的人文安全和环境变化的内容联系在一起，才能更深入地进行下去。     

Channel Bed Mobility Downstream from the Elwha Dams,Washington*

Dams are a major source of fragmentation and degradation of rivers. Although substantial research has been conducted on the environmental impacts of large structures in the United States, smaller dams have received less attention. This study evaluated the impact of two dams of moderate size, the Elwha Dams, on the downstream channel system using field data collection at river cross‐sections. The relationship of average boundary shear stress (τ_o) to critical shear stress (τ_cr) served as the basis for determining channel bed material mobility under the two‐year and ten‐year flood events. The channel had the greatest channel bed mobility at the natural cross‐section upstream from the dams, low bed mobility between the structures, and an increase in channel bed mobility in the low gradient river segment near the mouth of the river. Low bed mobility tended to be associated with a lack of channel system complexity, including reduction or loss of bars and low alluvial terraces and their associated young riparian communities. Although these run‐of‐the‐river dams do not modify streamflow greatly, the loss of sediment from the channel system has had a substantial impact on bed mobility and geomorphic and biotic complexity of the Elwha River.