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1.
Paleoclimate and paleovegetation changes over the last 40 cal ka were recorded by multiple variables in a sediment core from Qingshi, Wudalianchi City, northeast China. The history of vegetation types inferred from n-C27/n-C31 and average chain length of n-alkanes indicates the paleovegetation went through several distinct stages, consistent with pollen records from the study area. Compound-specific carbon isotope composition was also determined for C27, C29 and C31 n-alkanes in the Qingshi core sediments. The relative abundance of C3 and C4 plants was calculated using a binary model and indicates that C3 plants were the dominant input during the last glacial and Holocene. There were, however, shifts in the ratio of C3 to C4 vegetation abundance that correspond to changes in climate conditions. Generally, the long-term trend towards greater C4 plant abundance from the last glacial to Holocene correlated with an increase in pCO2, higher temperature, greater precipitation and more growing season precipitation. Our results suggest that temperature and seasonality of precipitation played a strong role in altering the relative abundance of C3 and C4 plants in the study area. These results provide information for predicting future vegetation changes in response to on-going global warming.  相似文献   

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The continuously decreasing average coal rank (heating value), inadequate investment, and ever stricter air-emission controls have caused the average efficiency of electricity generation from coal in the U.S. to plummet to a mere 32% by the year 2008. The U.S. gas-fired powerplants are 30% more efficient than the coal-fired ones, with average efficiency of 43% in 2008. Replacing each 1,000 MW e generated by an average coal-fired powerplant with an average gas-fired powerplant would avoid today 7 million tonnes of CO2 emissions, 1.2 million tonnes of toxic ash, and significant issues with water contamination. The parallel upgrades to the more efficient supercritical steam turbines would decrease current emissions by up to 50% (from the current average plant efficiency of 32% to over 45%). The CO2 captured in the new combined-cycle powerplants might be used to enhance oil recovery in local fields, where feasible. The CO2 enhanced oil recovery (EOR) can never become the main sink for the gigantic CO2 volume generated each year by electric powerplants. Currently, EOR could absorb only 1% of that volume.  相似文献   

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Historically, the Sanpoil River, Washington (USA) produced spawning runs of chinook salmon (Oncorhynchus tshawytscha) and steelhead trout (O. mykiss). Lake Roberta is connected to the Sanpoil River and local oral history suggests it may have supported anadromous sockeye salmon (O. nerka) until the completion of Grand Coulee Dam in the 1940s. Post-spawning mortality of anadromous salmon provides large pulses of marine-derived nutrients to aquatic and terrestrial ecosystems in the vicinity of spawning sites. Unique isotopic ratios of these marine-derived nutrients are often transferred to freshwater algae and archived in lake sediments. However, marine-derived isotope signatures may be overpowered by large inputs of other nutrient sources such as agricultural fertilizers, reactive nitrogen deposition, nitrogen fixation, or poor trophic transfer to freshwater algae. We compared nitrogen and sulfur isotope compositions for pre-1940 and post-1940 sediments to those collected from a control lake with no history of anadromy to investigate the possible historic presence of anadromous salmon in Lake Roberta. We also analyzed carbon isotopes, carbon:nitrogen ratios, and sediment accumulation rates to determine if changes in the lake sediments resulted from eutrophication rather than salmon exclusion. If sockeye did spawn in Lake Roberta historically, and if excessive nitrogen inputs did not overpower the marine-derived signal, we would expect pre-1940 sediment organic matter isotope compositions indicative of the large pulses of marine nutrients from decomposing salmon carcasses. Isotope results and land use in the Lake Roberta watershed present no conclusive evidence to support anecdotal accounts of anadromy. There is some evidence to suggest that marine-derived nutrients transferred to riparian communities within the lake’s watershed may have moved downstream to the lake. However, most of the evidence suggests eutrophication and a switch to increased autochthonous productivity are the main causes of changes in the lake sediment isotope composition.  相似文献   

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通达性;概念,度量及应用   总被引:40,自引:0,他引:40  
在西方通达性被广泛用于解释社会现象的空间变化,该文从通达性的概念,度量方式及主要应用领域三个角度来介绍西方在通达性这一研究领域的进展。  相似文献   

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Stable oxygen isotope measurements on fossil chironomid head capsules from lake sediments show that these chitinous remains can be used to reconstruct past lake water δ18O and, indirectly, past climate change. We examined the impact of chemical pretreatment procedures on the chemical and stable oxygen isotope composition, and morphology of chironomid cuticles. Use of alkali, acids, and sodium chlorite alters the chemical composition and the morphological structure of chironomid cuticles by selective removal of chitin or proteins. Gas chromatograms of pyrolyzates show that NaClO2 causes deproteination, whereas the combined use of HCl and HF results in partial chitin removal. Head capsules pretreated with KOH contained both chitin- and protein-derived moieties, although the concentration of protein was reduced, especially after KOH treatment at high concentration (28%) and temperature (100°C). Scanning electron microscopy confirmed that a proteinaceous matrix is still present in modern and fossil head capsules after KOH treatment. This matrix, however, is largely absent in head capsules pretreated with NaClO2. A change in the proportion of chitin and proteins in our samples was associated with differences in chironomid δ18O values. Our results suggest that deproteination results in a relative increase of chironomid δ18O, whereas removal of chitin leads to decreased δ18O values. We therefore discourage the use of acids or prolonged (≥1 h) exposure to hot alkali (70°C) prior to chironomid δ18O analysis. Chitin purification by sodium chlorite causes significant weight loss, which may preclude down-core chironomid δ18O measurements. Caution and standardization are required when pretreating samples for chironomid δ18O analysis to ensure reliable, comparable, and reproducible results.  相似文献   

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This paper questions the assumptions of ‘diaspora’, ‘citizenship’ and ‘development’ underlying diaspora strategies targeting a specific pool of overseas Malaysian ‘talent’ migrants. I examine the Malaysian state's discursive attempts to construct a carefully contained economic ‘diaspora'—the ‘Malaysian diaspora'—through its talent return migration programme. In this process, there is a portion of the ‘Malaysian diaspora’, especially non‐bumiputeras (sons of soil), who are doubly neglected and excluded: first, from access to full and equal citizenship (which arguably contributed to their emigration in the first place); and second, from eligibility and recognition to participate in Malaysia's talent return migration programme. However, recent political activism calling for electoral reform and overseas voting rights challenges state‐constructed visions of the ‘diaspora’ and their expected roles in advancing ‘development’. This paper concludes by highlighting questions raised by the Malaysian case, linking these explicitly to how diaspora strategies—as they have been conceived, practised and contested—challenge the broader Migration and Development paradigm.  相似文献   

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We used elemental carbon, nitrogen, phosphorus and hydrogen ratios (C/N, N/P and H/C) with total organic carbon (TOC) and total phosphorus (TP) as well as stable carbon and nitrogen isotopes (δ13C and δ15N) to investigate the source and depositional conditions of organic matter in sediments from Zeekoevlei, the largest freshwater lake in South Africa. Typical C/N (10–12), H/C ratios (≥1.7) and δ13Corganic values (−22 to −19‰) together with the increase in TOC concentration indicate elevated primary productivity in lower middle (18–22 cm) and top (0–8 cm) sections of the sediment cores. Seepage of nutrients from a nearby waste water treatment plant, rapid urbanization and heavily fertilized farming in the catchments are responsible for the increased productivity. Consistent with this, measured δ15Norganic values (∼11‰) indicate increased raw sewage input towards the top-section of the core. Although cyanobacterial blooms are evident from the low δ15N values (∼3‰) in mid-section of the core, they did not outnumber the phytoplankton population. Low N/P ratio (∼0) and high TP (100–2,200 mg l−1) support cyanobacterial growth under N limited condition, and insignificant input of macrophytes towards the organic matter pool. Dredging in 1983, caused sub-aerial exposure of the suspended and surface sediments, and affected organic matter preservation in the upper mid-section (12–14 cm) of the core.  相似文献   

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We inferred past climate conditions from the δ13C and δ15N of organic matter (OM) in a sediment core (DP-2011-02) from the sub-alpine Daping Swamp, in the western Nanling Mountains, South China. In the study region, a 1000-m increase in altitude results in a ~0.75‰ decrease in δ13C and a ~2.2‰ increase in δ15N. Organic carbon stable isotope (δ13C) values of the dominant modern vegetation species, surface soils, and the core samples taken in the swamp exhibit a strong terrestrial C3 plant signature. Comprehensive analysis of the core indicates both terrestrial and aquatic sources contribute to the OM in sediment. Temperature and precipitation are most likely the critical factors that influence δ13C: warm and wet conditions favor lower δ13C, whereas a dry and cool climate leads to higher δ13C values. Higher δ15N values may result from greater water depth and increased primary productivity, promoted by large inputs of dissolved inorganic nitrogen, induced by high surface runoff. Lower δ15N values are associated with lower lake stage and reduced productivity, under drier conditions. Therefore, stratigraphic shifts in these stable isotopes were used to infer past regional climate. Measures of δ13C and δ15N in deglacial deposits, in combination with total organic carbon (TOC) and nitrogen (TN) concentrations, the TOC/TN ratio, coarse silt and sand fractions, dry bulk density and low-frequency mass magnetic susceptibility, reveal two dry and cold events at 15,400–14,500 and 13,000–11,000 cal a BP, which correspond to Heinrich event 1 and the Younger Dryas, respectively. A pronounced warm and wet period that occurred between those dry episodes, from 14,500 to 13,000 cal a BP, corresponds to the Bølling–Allerød. The δ13C and δ15N data, however, do not reflect a warm and wet early Holocene. The Holocene optimum occurred between ~8000 and 6000 cal a BP, which is different from inferences from the nearby Dongge cave stalagmite δ18O record, but consistent with our previous results. This study contributes to our understanding of climate-related influences on δ13C and δ15N in OM of lake sediments in South China.  相似文献   

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本项研究选取柴达木盆地尕斯库勒盐湖区作为研究区,筛选出了9种优势盐生植物,开展了盐生植物生长区土体颗粒、容重、含水量等物理性质指标,以及土体中HCO<sub>3</sub><sub><sup>-</sup></sub>、Cl<sub><sup>-</sup></sub>、SO<sub>4</sub><sub><sup>2-</sup></sub>、K<sub><sup>+</sup></sub>、Na<sub><sup>+</sup></sub>、Ca<sub><sup>2+</sup></sub>和Mg<sub><sup>2+ </sup></sub>7种易溶盐离子含量试验测试,分析了区内芦苇、海韭菜等9种盐生植物茎叶和根系部分HCO<sub>3</sub><sub><sup>-</sup></sub>、Cl<sub><sup>-</sup></sub>等7种易溶盐离子含量及其分布规律。在此基础上,探讨了区内9种盐生植物对易溶盐离子吸收作用及其差异性;采用盐生植物地上茎叶部分K<sub><sup>+</sup></sub>/Na<sub><sup>+</sup></sub>值结果,定量评价了区内9种盐生植物耐盐性及变化规律,结果表明,区内9种盐生植物茎叶部分K<sub><sup>+</sup></sub>/Na<sub><sup>+</sup></sub>比值,其由大至小依次为:小花棘豆0.84、羊齿天门冬0.58、白刺0.55、盐地风毛菊0.52、海韭菜0.50、无脉苔草0.47、洽草0.41、芦苇0.39和赖草0.34。本项研究结果,利用为尕斯库勒湖区及其周边地区,利用盐生植物有效改良土壤盐渍化方面提供理论支撑。  相似文献   

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朱连奇 《地理研究》2021,40(8):2397-2398
新时代的中国地理学是推动可持续发展和促进构建人类命运共同体的应用基础学科,不仅要建构和完善现代地理学学科体系,而且要在服务国家需求方面担当重要角色.福建师范大学朱鹤健教授总结长期教学和研究成果,出版了《地理学思维与实践》一书(科学出版社出版,2018).书中集成了地理学的研究范式,阐明其独特性,为建构和完善地理学现代科学体系做出了新贡献.全书对服务社会是地理学存在的生命根基、地理学研究范式的独特效应和地理学家要挺身在国民经济的主战场3个论题做了深刻阐释.敬佩作者对地理学精髓孜孜不倦地探求精神.2020年12月中国地理学会发出以地理科学为主体或基础的高校院系应该将"地理"或"地理科学"置于机构名称中的呼吁书,强调地理学回归学科、回归本分、回归初心、回归梦想.这使我对本书增添了新感觉,认为本书还是一本地理学回归学科本色的召唤书,有其现实指导意义.由此我认为《地理学思维与实践》是地理学工作者增强学科自信的好教材,值得认真研读.  相似文献   

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“厄尼诺”(英文El Nino,俄文)是西班牙语El Nin(?)的音译。El是定冠词,可不译,所以也有译作“尼诺”的。Nino为名词,小孩之意,在这里指的是神之子即耶稣。  相似文献   

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“数字地球”的启示   总被引:1,自引:0,他引:1  
本文分析了“数字地球”这一全球战略思想带给我们的一些启示 ,这些启示包括 :战略眼光 ,大国地位 ,自主发展和技术引进 ,盲目追随、整合的意义等。笔者认为 ,宏观的、全局性的战略眼光 ,冷静思考与明确的目标 ,紧抓对地观测和国家基础信息设施建设以维护中国作为大国的形象和利益 ,在发展“数字中国”过程中走自主发展与技术引进相结合的道路 ,以及加强行政管理机制、智能化数据、科研机构和学科领域的整合 ,是我们在数字地球的挑战面前应有的基本思路。  相似文献   

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在国家自然科学基金委和教育部共同资助下,由顾朝林、于涛方、李王鸣等数十位中青年专家通力合作完成的巨著——《中国城市化格局·过程·机理》已由科学出版社出版。该书是迄今为止中国城市化领域难得见到的内容丰富、基础性较强、理论和方法有创意的科学专著。  相似文献   

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A sediment core from Lake Koucha (eastern Tibetan Plateau) was investigated using organic biomarkers and their stable carbon isotope signatures. The correlation between TOC content, total amount of aquatic macrophyte-derived n-alkanes (e.g. nC23) and δ13C values of TOC and nC23 indicates that Lake Koucha was macrophyte-dominated before 8 cal ka BP. Shortly after the lake turned from a saline to a freshwater system at 7.2 cal ka BP, a variety of algal and bacterial markers such as hopanoids and isoprenoids emerged, of which phytane, pentamethylicosene (PMI), moretene and diploptene are particularly abundant. Phytane and PMI show different isotopic signals (≈−18 and ≈−28‰, respectively), which indicates that they originated from different sources. Phytane may have been derived from cyanobacteria, while methanogenic archaea may be the source of PMI. The isotopic depletion of diploptene and moretene (≈−60‰) indicates the presence of methanotrophs. After 6.1 cal ka BP, the saturated C20 highly branched isoprenoid (HBI) became the dominant constituent of the aliphatic hydrocarbon fraction. Such dominance has rarely been reported in lacustrine environments, and indicates a strong presence of algae (most likely diatoms) or cyanobacteria. At 4.7 cal ka BP, the appearance of an unsaturated C25 HBI, which is a specific biomarker for diatoms, was noted. Furthermore, the level of nC17-alkane was observed to increase in abundance in the uppermost two samples. These results suggest that the lake was phytoplankton-dominated during the last 6.1 ka. Relatively low biomarker concentrations and δ13C values at 6.0, 3.1 and 1.8 cal ka BP indicate the occurrence of cool periods, which is in agreement with inferences from other locations on the Tibetan Plateau. The δ13C values of nC23 range from −23.5 to −12.6‰, with high values at the peak of macrophyte abundance at ca. 11 cal ka BP and at the phytoplankton maximum between ca 6.1 and 2.8 cal ka BP. Thus, aquatic macrophyte-derived mid-chain n-alkanes have been found to be excellent indicators of carbon-limiting conditions, which lead to the assimilation of isotopically-enriched carbon species. The limitation of carbon sources could be a localized phenomenon occurring in dense plant stands (as in the older section of the core), or it may be induced by high primary productivity (as in the younger section). Since the δ13C value of the inorganic carbon source may vary, the offset between the δ13C values of nC23 and TIC could serve as a more precise proxy for carbon-limiting conditions in lacustrine environments, which could in turn be interpreted with respect to lacustrine paleo-productivity.  相似文献   

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The characteristic features of the transformation of the territorial geospace structure in the African Christianity religious geospace during 1910–2010 have been revealed. African countries within the boundaries of 2010 are used as territorial cells that have been fixed retrospectively over the course of the period analyzed. We used indicators, such as Ryabtsev’s index of relative structural shifts and the trajectory of the demographic center of the Christianity to assess changes in the inertia level of the territorial structure for the entire time interval as a whole and for each of the components of its 20-year long periods. It is found that to date the adherents of Christianity are extremely unevenly distributed in the countries of Africa; however, over the course of the period under consideration there was taking place a homogenization of their settlement. In accordance with changes of the values of the indicators used, we identified two development stages of geospace of African Christianity: colonial and post-colonial. It is determined that the colonial stage (1910–1970) is characterized by a “compression” of territorial structure from east and north, and by a predominance of the south-westward direction of movement of the demographic center because of a decrease in the proportion in the Christian population of East Africa first on account of Egypt and Ethiopia and Madagascar (1910–1930) and then North Africa on account of Egypt and Algeria (1930–1950). The territorial structure of Christianity’s geospace during the post-colonial stage is characterized by a higher degree of inertia at the background of the westward ”expansion” and the “compression” from the south as well as by a change of the vector of movement of the demographic center for north-westward.  相似文献   

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