成都经济区农业生态系统土壤镉通量研究

以四川成都经济区农业生态系统中的重金属Cd为对象,对其在土壤中的输入输出通量进行初步探索。综合各方面的因素,确定以大气干湿沉降、灌溉水、化肥为输入途径和农作物为输出途径进行研究。经过计算,经济区大气干湿沉降通量平均值为17.76g/hm2·a,灌溉水和化肥通量明显较低,三者对土壤Cd污染的贡献率分别为86%、10%和4%。对于6个不同的地区,三者比例略有差别,大气干湿沉降所占比例最高达94%,最低也达到了77%。Cd通过农作物收割输出的量相对较小。土壤Cd年净增量主要受大气干湿沉降的制约,因此大气环境质量应是重点监控的对象。以耕作土体为研究介质,经估算,当前的Cd年平均通量可引起土壤Cd的质量分数升高0.006mg/kg。     

青藏高原羌塘中部果干加年山上三叠统望湖岭组的建立及意义

在果干加年山的主脊及其以北识别出一套稳定的沉积岩系,角度不整合于蛇绿混杂岩之上,以细砂岩、硅质粉砂岩为主,其中夹有大小不等的古生代外来岩块,底砾岩成分因地而异并具有快速堆积的特点,底部夹有流纹岩。厚度大于1633m。流纹岩夹层获得的锆石SHRIMPU-Pb谐和年龄为214Ma±4Ma,时代为晚三叠世诺利期。在剖面测制和区域对比的基础上建立了上三叠统望湖岭组,代表龙木错-双湖缝合带闭合以后接受的最早的沉积盖层。望湖岭组之下的蛇绿混杂岩获得阳起石Ar-Ar年龄219.7Ma±6.5Ma。同位素定年确定构造转化事件发生在214～220Ma之间,为龙木错-双湖缝合带的闭合时间提供了确切的时间约束,望湖岭组是这一事件的沉积记录,是龙木错-双湖缝合带蛇绿混杂岩之上首次发现的沉积盖层。     

The clean development mechanism’s contribution to sustainable development: a review of the literature

The challenges of how to respond to climate change and ensure sustainable development are currently high on the political agenda among the world’s leading nations. The Clean Development Mechanism (CDM) is part of the global carbon market developing rapidly as part of the Kyoto response towards the mitigation of global warming. One of the aims of the CDM is to achieve sustainable development in developing countries, but uncertainty prevails as to whether the CDM is doing what it promises to do. Close to 200 studies on the CDM have been carried out since its birth in 1997 including peer-reviewed articles and reports from the grey literature. This review of the literature serves to assess the state of knowledge on how the CDM contributes to sustainable development (SD) including poverty alleviation. The main finding of the review is that, left to market forces, the CDM does not significantly contribute to sustainable development.     

Tropical Deforestation and Climate Change: What Does the Record Reveal?

Tropical deforestation is widely believed to directly influence the climate at a number of scales. Yet while much has been written about the tropical forest-climate relationship, there is little empirical evidence showing if and how local and regional climates are modified by deforestation. This study presents the results of an analysis of deforestation and climate change in a rain forest in southern Mexico. Records from 18 climate stations in the Selva Lacandona of Chiapas, Mexico were examined and related to an analysis of deforestation based on Landsat images. The area surrounding some stations has been deforested since the stations were established, while the area surroundings others has remained forested. Strong climatic trends were generally evident at the deforested stations, including decreases in the average daily maximum temperature and temperature range. No precipitation changes were observed. A comparison of the results with microclimatic experiments and modeling studies suggests that the climatic impacts of deforestation are overgeneralized at the local scale. Landscape heterogeneity appears to influence the biophysical mechanisms linking tropical forests and climate, and should be explicitly represented in modeling studies.     

RESERVOIR SEDIMENTATION AND LAND USE IN TAIWAN WUSHEH WATERSHED

ＲＥＳＥＲＶＯＩＲＳＥＤＩＭＥＮＴＡＴＩＯＮＡＮＤＬＡＮＤＵＳＥＩＮＴＡＩＷＡＮＷＵＳＨＥＨＷＡＴＥＲＳＨＥＤＳｕＣｈｉｎＣＨＥＮ１ＡＢＳＴＲＡＣＴＷｕｓｈｅｈＲｅｓｅｒｖｏｉｒｉｓａｇｏｒｇｅｔｙｐｅｈｙｄｒｏｐｏｗｅｒＲｅｓｅｒｖｏｉｒｏｎＷ...     

The emergence of a Galápagos shield volcano, Roca Redonda

Roca Redonda volcano is a mostly submarine shield volcano that rises nearly 3 km from the adjacent seafloor. Over twenty lava flows and palagonite tuff are exposed in a 60 meter high oblong outcrop above sea level, and several other flows are exposed in the shallow water surrounding the islet. Thick, slightly alkaline picritic flows form the base of the section. Thinner picrites interbedded with sparsely porphyritic alkali-olivine basaltic pahoehoe toes characterize the upper section. The subaerial section probably records the filling of a palagonite tuff cone with younger lavas. Numerous fumaroles that may have a magmatic component are present in the shallow (<30 m) submarine zone and indicate that the volcano is probably still active. Three lava types are exposed: the basal picrites with 19% > MgO > 14%, high-Mg basalts with MgO of about 9%, and low-Mg basalts with MgO of about 6%. The Sr and Nd isotopic ratios of the three lava types are within analytical uncertainty. Olivine compositions indicate that the picrites are basaltic liquids that have accumulated olivine whose composition is in equilibrium with the host basaltic liquid. Apparently, basaltic magmas percolated through dunite and troctolite that had crystallized from slightly older Roca Redonda basaltic magma. Lavas from Roca Redonda have enriched trace element contents and isotopic ratios relative to nearby Wolf volcano, but they are quite similar to lavas from Cerro Azul and Ecuador volcanoes. The common characteristic of these volcanoes is that they lie on the periphery of the archipelago and are in a stage of subaerial growth. This suggests that Galápagos volcanoes may go through a juvenile alkaline stage before a mature tholeiitic stage, analogous to the Loihi stage of Hawaiian volcanism. A low ³He/⁴He ratio in olivine from one of the picrites indicates a small contribution by the Galápagos mantle plume. Received: 15 December 1997 / Accepted: 6 May 1998     

The Characteristics of Spinels in Mantle-derivedXenoliths in Cenozoic Basalts from Eastern Chinaand Their Thermal States

The colours and chemical composition variations of 160 spinels in peridotite and pyroxenite xenoliths from Cenozoic basalts in eastern China and their petrogeneses have been studied in detail. The relationships between major elements of spinels are discussed. The equilibrium temperatures, pressures and oxygen fugacities of spinels and their coexisting olivines, orthopyroxenes and clinopyroxenes have been determined using the Brey-kohler' s T-P calculation methods (1990) and Ballhaus' fo2 calculation method (1991). The relationships betweenthe composition and the equilibrium temperatures, pressures or oxygen fugacities of spinels in peridotite xenoliths from the basalts and the stable field of the spinels in the upper mantle have been shown.     

Origin of crystalline,cold desert salts in the McMurdo region,Antarctica

The distribution of crystalline salt minerals in deposits in the McMurdo region of Antarctica has been examined to study the origin of these salts. Sulphate, chloride, sodium and calcium salts are most frequently encountered. Salts containing chloride and sodium ions become less common away from the coast. Sulphate salts are more regularly distributed but tend to be related isotopically to sea water sulphate. Salts containing magnesium ion tend to exist mainly on substrates composed of basic igneous rocks, whereas calcium and carbonate salts are present on all rock types in the region.These distributions show that salts of marine origin are regionally and quantitatively most important but that chemical weathering of mafic materials in rocks and soils is also significant. However, biological, volcanic and hydrothermal processes are or have been active contributing to salts in local areas, that include penguin rookeries and eastern Taylor Valley, the summit area of Erebus Volcano, and subsurface rocks, respectively.     

Mechanism of the reservoir impounding earthquakes at Hsinfengkiang and a preliminary endeavour to discuss their cause

After the filling up of the Hsinfengkiang Reservoir Kwangtung Province, seismicity was greatly increased. The majority of earthquakes occurred in the deep water gorge close to the dam, concentrated within a northwest belt. They are usually of shallow focal depths. A strong earthquake with magnitude 6.1 took place on March 19, 1962, about two and a half years since the impounding of the reservoir.

According to the results of analysis of data from geodetic leveling and the spectra of seismic waves, the fault parameters of the main shock were determined. The fault plane solutions of 150 small earthquakes, occurring within a period of 18 months before and after the main shock were determined from the amplitudes of the first motion of P wave. The directions of the earthquake generating stress of about 2000 small earthquakes were obtained by smoothing the first motion patterns. Displacement field and stress field in the rock bodies underneath the reservoir caused by the loading of the reservoir water were calculated. Variations of the velocity ratio of the P and S waves prior to the main shock and several strong aftershocks were analysed.

In consideration of the seismicity as well as the geological background, we endeavour to discuss the cause of reservoir impounding earthquakes at Hsinfengkiang. We have the opinion that the penetration of water along fissures becomes the most important cause of the main shock of March 19, 1962 at Hsinfengkiang.     

Delineation of spatial redox zones using discriminant analysis and geochemical modelling in arsenic‐affected alluvial aquifers

This study characterized the redox conditions in arsenic‐affected groundwater aquifers of the Lanyang plain, Taiwan. Discriminant analysis was adopted to delineate three redox zones (oxidative, transitional and reductive zones) in different aquifers and yielded 92·3% correctness on groundwater quality data. Arsenic is mainly distributed in the reductive zone, and arsenic distribution in the shallow aquifer is mainly affected by surface activities. According to PHREEQC modelling results, possible mechanisms for arsenic release to groundwater in Lanyang plain are explored. Arsenic released to groundwater in the oxidative zone (zone 1) is primarily caused by the oxidations of arsenic‐bearing pyrite minerals, and arsenate is the predominant species. While the reductive dissolution of Fe‐oxides are responsible for the high arsenic concentration found in the transitional and reductive zones (zones 2 and 3), arsenite is the predominant species. The reduction potential of groundwater rises as the depths and zones increase. Some sulphates may be reduced to form sulphide ions, which then react with arsenic to form arseno‐sulphide deposits (such as realgar, orpiment) and then slightly lower groundwater arsenic concentrations. A conceptual diagram which summarized the possible release processes of arsenic in different redox zones along groundwater flow in Lanyang plain is postulated. Arsenic‐bearing pyrite and arsenopyrite (FeAsS) are oxidized as they are exposed to the infiltrated oxygenated rainwater, releasing soluble arsenate Fe(II) and SO₄^2? into zone 1. The dissolution of arsenic‐rich Fe‐oxides due to the onset of reducing conditions in zones 2 and 3 is responsible for the mobility of arsenic and likely to be the primary mechanism of arsenic release to groundwater in the Lanyang plain Copyright © 2007 John Wiley & Sons, Ltd.