Palaeolimnological Development of Lake Njargajavri, Northern Finnish Lapland, in a Changing Holocene Climate and Environment   总被引：1，自引：2，他引：1  

Kaarina Sarmaja-Korjonen  Marjut Nyman  Seija Kultti  Minna Väliranta 《Journal of Paleolimnology》2006,35(1):65-81

This study used palaeolimnological approaches to determine how Holocene climatic and environmental changes affected aquatic assemblages in a subarctic lake. Sediments of the small Lake Njargajavri, in northern Finnish Lapland above the present treeline, were studied using multi-proxy methods. The palaeolimnological development of the lake was assessed by analyses of chironomids, Cladocera and diatoms. The lake was formed in the early Holocene and was characterized by prominent erosion and leaching from poorly developed soils before the establishment of birch forests, resulting in a high pH and trophic state. The lake level started to lower as early as ca. 10,200 cal. BP. In the resulting shallow basin, rich in aquatic mosses, pH decreased and a diverse cladoceran and chironomid assemblage developed. It is likely that there was a slight rise in the water level ca. 8000 cal. BP. Later, during the mid-Holocene characterized by low effective moisture detected elsewhere in Fennoscandia, the lake probably completely dried out; this is manifest as a hiatus in the stratigraphy. The sediment record continues from ca. 5000 cal. BP onwards as the lake formed again due to increased effective moisture. The new lake was characterized by very low pH. The possible spread of pine to the catchment and the development of heath community may have contributed to the unusually steep (for northern Fennoscandia) decline in pH via change in soils, together with the natural decrease in leaching of base cations. Furthermore, the change in pH may have been driven by cooling climate, affecting the balance of dissolved inorganic carbon in the lake.  相似文献   

Geographic Perspectives of Air Transportation   总被引：1，自引：1，他引：1  

Timothy M. Vowles 《The Professional geographer》2006,58(1):12-19

Past, present, and future research directions and advances in this highly dynamic research area of air transportation are reviewed with an eye toward geographers' contributions to the air transportation industry. The study of air transportation within the field of transportation geography and the larger discipline of geography is important as geographers use air transportation to help describe concepts such as connectivity and linkages, development patterns at various scales, and the global economy. This article takes three approaches in exploring geographers' contributions to research in the field: historical, publication outlets, and topic focus. The goal of the article is to commemorate the contributions of pioneer and current researchers in the field, and open to discussion future research paths in air transportation.  相似文献   

Glacial atmospheric CO_2 decline in association with decrease of marine sedimentary phosphorus     

WENG Huanxin  ZHANG Xingmao  WU Nengyou  WANG Ying  CHEN Lihong  ZHONG Hexian  QIN Yachao 《中国科学D辑(英文版)》2006,49(3)

Since the discovery from the ice-core record of South Pole revealed that atmospheric concentration of CO2 of the last glacial was 80―100 ppm less than that of Holocene[1], many researchers[2―6] have obtained a series of important findings to seek the dominant fac- tors controlling its change from marine physical, chemical and biological processes, among which the view has gained increasing attention that phosphorus, as a macronutrient, is a crucial limitation to marine primary production, a…  相似文献   

Calculated and measured values of liquid water content in clean and polluted environments     

J. Fišák  D. Řezáčová  J. Mattanen 《Studia Geophysica et Geodaetica》2006,50(1):121-130

The relationship between liquid water content (LWC) and visibility (VIS) in a fog was examined by a field measurement of LWC values at a clean location of the meteorological observatory Sodankylä (Finland) and in a polluted region at the meteorological observatory Mile?ovka (Czech Republic). Furthermore, the use of a simple regression fog model to determine LWC from VIS is examined by comparing well-known relationships with the measurement results. The results show that the verbal characterization of environment (clean, mild polluted, polluted) is insufficient to calculate the LWC values from visibility. It is necessary to establish an additional criterion based on quantitative fog characteristics or to determine the site-related equation from the previous LWC and VIS measurement.  相似文献   

石家庄市污染日特征及其天气背景分析   总被引：8，自引：3，他引：8  

李国翠连志鸾  郭卫红陈静 《气象科技》2006,34(6):674-678

对石家庄市2002年1月到2004年12月空气质量达到中度及以上典型污染日进行了统计分析,得出典型污染日的分布特点、对应的气象要素特征及3种天气型。结果表明:典型污染日多出现在采暖季节,出现时间具有相对连续性;污染日分为沙尘和非沙尘两类,气象要素特征前者表现为风速大、湿度小、多正变压等锋后特征;后者则表现为地面风小、湿度高、多逆温层、大里查逊数等稳定大气层结,这些均为锋前特征;还侧重指出由于石家庄的特殊地形作用,高压前部型是石家庄重污染出现几率最多的天气类型。并由此提炼出中度以上污染日的预报要点,可供空气质量预报业务参考。  相似文献   

南岭山地高速公路路面温度变化特征分析   总被引：5，自引：1，他引：5  

吴晟 吴兑邓雪娇  谭浩波 《气象科技》2006,34(6):783-787

使用2003年3月至2005年8月南岭山地京珠高速公路粤境北段云岩路段3套自动气象站的逐分钟路面温度、地温、气温、湿度、风向、风速等气象资料,分析研究了南岭山地高速公路的路面温度特征及其与天气状况、气温、风速等气象条件的关系,并讨论了地形对南岭山地高速公路路面温度的影响。研究结果表明,南岭山地高速公路晴天和多云时的路面温度日变化明显,与辐射过程密切相关。路温与气温、地温的差异在晴天午后最为明显。晴天时路温、地温、气温的年变化趋势比较一致,路温与地温之间保持着明显的温差;多云天气时路温与地温的差值明显缩小,阴天时路温与地温的差值非常小。地形对路面温度有明显影响,高海拔地区路面温度相对较低,南岭北坡路面温度明显高于南坡,与局地小地形有关。高温过程时路面温度最高接近60℃,地温也超过50℃,持续高温对行车安全、路面和路基结构均有很大威胁。  相似文献   

和田市能见度变化趋势及其与空气质量的关系     

玉苏甫·阿布都拉  热依汗古丽  买买提阿布都拉  米吉提·依明  Yusup·ABDULLA  Reyhanguli  Maimaitiabudula  Mijit·IMIN 《沙漠与绿洲气象(新疆气象)》2006,29(1):24-25,29

对1963～2004年和田市各级别大气能见度进行统计分析,揭示了大气能见度的年际变化和季节变化特征。近20a来和田市大气环境质量趋于好转,造成能见度恶化的重要原因是大气中悬浮颗粒的增多,因此大气能见度是评价大气环境质量的重要指标。  相似文献   

Estimating contributions of sources of soil CO2 at the shallower layer in a Japanese larch forest area     

Wei LIU Jun MORIIZUMI Hiromi YAMAZAWA Takao IIDA 《中国地球化学学报》2006,25(B08):198-198

Soils contain about twice the amount of carbon presented in the atmosphere, so a small change in the soil carbon will influence atmospheric chemistry and heat balance. The soil carbon ultimately exchanged with the atmospheric CO2 as soil CO2, which mainly exists at the depth of 0-20 cm. The transport of soil CO2 is affected by the sources of soil CO2. Thus, separation of the contributions of sources of soil CO2 is a fundamental need to understand and predict implications of environmental change on soil carbon cycling and sequestration. It is a complicated task, so that a number of different methodological approaches such as component integration, root removal, and gap analyses have been developed. However, these methods could not avoid changing soil characteristics such as air-filled porosity, soil temperature and soil water contents. Consequently, fractional contributions of respiration of living root and decomposition of soil organic matter to the total soil CO2 cannot be estimated correctly. In this study, based on mass balance theory of both concentrations and δ^13C of soil CO2, a trenching method with a stable-isotope technique was used to determine both soil CO2 sources at the depth of 3-13 cm in a Japanese larch forest area during 30 May to 7 October 2005 and fractional contributions of these sources. Experimental results showed that the amount of atmospheric CO2 invaded the soil air was not significantly variable while its percent rate in the total soil CO2 had significantly temporal variations with the lower values between 5 August and 1 September. The litter-layer decomposition was very small. The soil CO2 derived from the respiration of living root and the decomposition of soil organic matter showed significantly temporal variations with increase from 30 May to 5 Aug. and decrease from 1 September to 7 October, 2005; and it accounted for 82%-98% of the total soil CO2 in which the respiration of living root was in the range from 32% to 62%.  相似文献   

Impact of forest fires on regional air quality in Southeast Asia     

Rajasekhar Balasubramanian Siao Wee See 《中国地球化学学报》2006,25(B08):221-222

Biomass burning, the burning of living and dead vegetation for land-clearing and land-use change, has been in practice in many tropical countries such as Brazil, Indonesia, Nigeria, and Mexico. Intense forest fires can also ignite subsurface organic soil components （e.g. peat）, which can continue to smolder long after the original surface fires are put out. Combustion of vegetation and peat has only recently been recognized as a major source of atmospheric pollution. The immediate effect of burning is the production and release of gases and particles into the atmosphere, in quantities that in some cases can be significant not only locally and regionally but also on a global scale. Vegetation fire emissions account for roughly half of the atmospheric constituents of hydrocarbon, carbon monoxide, nitrogen oxides, and precursors of tropospheric ozone and may be the second largest source of anthropogenic aerosols after the production of sulfates from SO2. As a result, there has been considerable interest in studying the contribution of forest fires to the production of air pollutants. In recent years, Southeast Asian countries have been affected repeatedly by episodes of smoke haze from forest fires in Indonesia. During 1997-1998, the region was again shrouded in a haze worsened by prolonged drought linked to the E1 Nino weather phenomenon. Satellite pictures confirmed that air pollutants, originating from fires covering an estimated 800000 hectares of southern Kalimantan, Sumatra, and Java, have been transported by southwesterly monsoon winds across neighbouring Malaysia and Singapore to as far as Thailand and the Philippines. The impact of these extensive fires on the health of the residents and ecology in the affected areas was substantial, costly, and possibly long lasting. Most of the research on the environmental aspects of biomass burning has been directed towards the tropics in Africa and America, specifically to the tropical rain forests of Brazil and to the savannas of Africa and South America.  相似文献   

Carbonation of Cl-rich scapolite boudins in Skallen, East Antarctica: evidence for changing fluid condition in the continental crust   总被引：2，自引：0，他引：2  

M. SATISH-KUMAR  J. HERMANN  T. TSUNOGAE  Y. OSANAI 《Journal of Metamorphic Geology》2006,24(3):241-261

Spectacular reaction textures in poikiloblastic scapolitite boudins, within marbles in the continental crust exposed in the Lützow–Holm Complex, East Antarctica, provide insights into the changing fluid composition and movement of fluid along grain boundaries and fractures. Petrographic and geochemical features indicate scapolite formation under contrasting fluid compositions. Core composition of scapolite poikiloblasts (Scp_I) are marialitic (Cl = 0.7 apfu) whereas rims in contact with biotite or clinopyroxene are meionite rich. Fine‐grained recrystallized equigranular scapolite (Scp_II) shows prominent chemical zoning, with a marialitic core and a meionitic rim (Cl = 0.36 apfu). Scapolite poikiloblasts are traversed by Scp_III reaction zones along fractures with compositional gradients. Pure CO₂ fluid inclusions are observed in healed fractures in scapolite poikiloblasts. These negative crystal‐shaped fluid inclusions are moderately dense, and are believed to be coeval with Scp_III formation at temperatures >600 °C and a minimum pressure of c. 3.8 kbar. Grain‐scale LA‐ICPMS studies on trace and rare earth elements on different textural types of scaplolites and a traverse through scapolite reaction zone with compositional gradient suggest a multistage fluid evolution history. Scp_I developed in the presence of an internally buffered, brine‐rich fluid derived probably from an evaporite source during prograde to peak metamorphism. Recrystallization and grain size reduction occurred in the presence of an externally sourced carbonate (CaCO₃)‐bearing fluid, resulting in the leaching of Cl, K, Rb and Ba from Scp_I along fractures and grain boundaries. Movement of fluids was enhanced by micro‐fracturing during the transformation of Scp_I to Scp_III. Fractures in fluorapatite are altered to chlorapatite proving evidence for the pathways of escaping Cl‐bearing fluids released from Scp_I. The present study thus provides evidence for the usefulness of scapolite in fingerprinting changing volatile composition and trace element contents of fluids that percolate within the continental crust.  相似文献