Spatial variation of wetlands and flux of dissolved organic carbon in boreal headwater streams     

Jan‐Olov Andersson  Lars Nyberg 《水文研究》2008,22(12):1965-1975

In order to investigate the relation between water chemistry and functional landscape elements, spatial data sets of characteristics for 68 small (0·2–1·5 km²) boreal forest catchments in western central Sweden were analysed in a geographical information system (GIS). The geographic data used were extracted from official topographic maps. Water sampled four times at different flow situations was analysed chemically. This paper focuses on one phenomenon that has an important influence on headwater quality in boreal, coniferous forest streams: generation and export of dissolved organic carbon (DOC). It is known that wetland cover (bogs and fens) in the catchment is a major source of DOC. In this study, a comparison was made between a large number of headwater catchments with varying spatial locations and areas of wetlands. How this variation, together with a number of other spatial variables, influences the DOC flux in the streamwater was analysed by statistical methods. There were significant, but not strong, correlations between the total percentages of wetland area and DOC flux measured at a medium flow situation, but not at high flow. Neither were there any significant correlations between the percentage of wetland area connected to streams, nor the percentage of wetland area within a zone 50 m from the stream and the DOC flux. There were, however, correlations between catchment mean slope and the DOC flux in all but one flow situations. This study showed that, considering geographical data retrieved from official sources, the topography of a catchment better explains the variation in DOC flux than the percentage and locations of distinct wetland areas. This emphasizes the need for high‐resolution elevation models accurate enough to reveal the sources of DOC found in headwater streams. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Simulated long-term changes in river discharge and soil moisture due to global warming / Simulations à long terme de changements d’écoulement fluvial et d’humidité du sol causés par le réchauffement global     

《水文科学杂志》2013,58(4)

Abstract

Abstract By use of a coupled ocean–atmosphere–land model, this study explores the changes of water availability, as measured by river discharge and soil moisture, that could occur by the middle of the 21st century in response to combined increases of greenhouse gases and sulphate aerosols based upon the ?IS92a? scenario. In addition, it presents the simulated change in water availability that might be realized in a few centuries in response to a quadrupling of CO₂ concentration in the atmosphere. Averaging the results over extended periods, the radiatively forced changes, which are very similar between the two sets of experiments, were successfully extracted. The analysis indicates that the discharges from Arctic rivers such as the Mackenzie and Ob’ increase by up to 20% (of the pre-Industrial Period level) by the middle of the 21st century and by up to 40% or more in a few centuries. In the tropics, the discharges from the Amazonas and Ganga-Brahmaputra rivers increase substantially. However, the percentage changes in runoff from other tropical and many mid-latitude rivers are smaller, with both positive and negative signs. For soil moisture, the results of this study indicate reductions during much of the year in many semiarid regions of the world, such as the southwestern region of North America, the northeastern region of China, the Mediterranean coast of Europe, and the grasslands of Australia and Africa. As a percentage, the reduction is particularly large during the dry season. From middle to high latitudes of the Northern Hemisphere, soil moisture decreases in summer but increases in winter.  相似文献   

小秦岭金矿区土壤重金属生物有效性与影响因素   总被引：1，自引：0，他引：1  

张开军  魏迎春  徐友宁 《地质通报》2014,33(8):1182-1187

土壤中重金属生物有效性与影响因素分析是土壤重金属风险管控的关键问题。通过实地调查、现场采样、实验测试、综合分析等方法,分析了研究区100km2内Hg、Pb、Cd、Cr、As、Cu、Zn七种重金属元素的有效态含量特征,研究了这些重金属有效态含量之间、有效态含量与全量、有效态与土壤pH、有机质含量、粒度等基本理化参数之间的相关性,分析了重金属污染来源。结果表明,土壤中Hg、Pb、Cd、Cr、As、Cu、Zn七种重金属有效态的平均含量分别为2.29mg/kg、594mg/kg、2.52mg/kg、6.30mg/kg、2.16mg/kg、48.14mg/kg、50.21mg/kg,其变异系数大小为:HgPbCuZnCdAsCr。Hg的变异系数最大,是由于金矿选矿活动采用混汞法提金排放的尾矿堆(库)分布不均。Hg、Pb、Cd、Cu、Zn有效态量与全量之间均存在显著的相关性;土壤有机质与重金属有效态之间存在显著的相关性;土壤pH与有效态重金属之间存在显著的负相关性;土壤粒度对重金属有效态的累积影响不明显。  相似文献   

Calculated mineral equilibria for eclogites in CaO–Na₂O–FeO–MgO–Al₂O₃–SiO₂–H₂O: application to the Pouébo Terrane, Pam Peninsula, New Caledonia     

Carson  Powell  & Clarke 《Journal of Metamorphic Geology》1999,17(1):9-24

The high- P , medium- T  Pouébo terrane of the Pam Peninsula, northern New Caledonia includes barroisite- and glaucophane-bearing eclogite and variably rehydrated equivalents. The metamorphic evolution of the Pouébo terrane is inferred from calculated P–T  and P–T  – X H2O pseudosections for bulk compositions appropriate to these rocks in the model system CaO–Na₂O–FeO–MgO–Al₂O₃–SiO₂–H₂O. The eclogites experienced a clockwise P–T  path that reached P ≈19  kbar and T  ≈600  °C. The eclogitic mineral assemblages are preserved because reaction consequent upon decompression consumed the rocks' fluid. Extensive reaction occurred only in rocks with fluid influx during decompression of the Pouébo terrane.  相似文献   

Hydrological sensitivity of a large Himalayan basin to climate change     

Pratap Singh  Lars Bengtsson 《水文研究》2004,18(13):2363-2385

The present study sets out to investigate the sensitivity of water availability to climate change for a large western Himalayan river (the Satluj River basin with an area of 22 275 km² and elevation range of 500 to 7000 m), which receives contributions from rain, snow and glacier melt runoff. About 65% of the basin area is covered with snow during winter, which reduces to about 11% after the ablation period. After having calibrated a conceptual hydrological model to provide accurate simulations of observed stream flow, the hydrological response of the basin was simulated using different climatic scenarios over a period of 9 years. Adopted plausible climate scenarios included three temperature scenarios (T + 1, T + 2, T + 3 °C) and four rainfall scenarios (P ? 10, P ? 5, P + 5 and P + 10%). The effect of climate change was studied on snowmelt and rainfall contribution runoff, and total stream flow. Under warmer climate, a typical feature of the study basin was found to be reduction in melt from the lower part of the basin owing to a reduction in snow covered area and shortening of the summer melting season, and, in contrast, an increase in the melt from the glacierized part owing to larger melt and an extended ablation period. Thus, on the basin scale, reduction in melt from the lower part was counteracted by the increase from melt from upper part of the basin, resulting in a decrease in the magnitude of change in annual melt runoff. The impact of climate change was found to be more prominent on seasonal rather than annual water availability. Reduction of water availability during the summer period, which contributes about 60% to the annual flow, may have severe implications on the water resources of the region, because demand of water for irrigation, hydropower and other usage is at its peak at this time. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Scenario-based assessment of future food security     

WU Wenbin  TANG Huajun  YANG Peng  YOU Liangzhi  ZHOU Qingbo  CHEN Zhongxin  SHIBASAKI Ryosuke 《地理学报》2011,21(1):3-17

This paper presents a scenario-based assessment of global future food security. To do that, the socio-economic and climate change scenarios were defined for the future and were linked to an integrated modeling framework. The crop yields simulated by the GIS-based Environmental Policy Integrated Climate (EPIC) model and crop areas simulated by the crop choice decision model were combined to calculate the total food production and per capita food availability, which was used to represent the status of food availability and stability. The per capita Gross Domestic Product (GDP) simulated by IFPSIM model was used to reflect the situation of food accessibility and affordability. Based on these two indicators, the future food security status was assessed at a global scale over a period of approximately 20 years, starting from the year 2000. The results show that certain regions such as South Asia and most African countries will likely remain hotspots of food insecurity in the future as both the per capita food availability and the capacity of being able to import food will decrease between 2000 and 2020. Low food production associated with poverty is the determining factor to starvation in these regions, and more efforts are needed to combat hunger in terms of future actions. Other regions such as China, most Eastern European countries and most South American countries where there is an increase in per capita food availability or an increase in the capacity to import food between 2000 and 2020 might be able to improve their food security situation.  相似文献   

黄山市GNSS连续运行参考站网系统性能测试与分析     

周万东  汪旸  杨铜梅 《测绘与空间地理信息》2011,34(3):116-118

介绍了黄山市GNSS连续运行参考站网系统的定位精度、时间可用性、空间可用性、定位服务时效性、兼容性等5个方面的测试情况,对系统各项性能指标进行了分析评价.  相似文献   

基于圆概率误差的RAIM可用性算法研究     

李国重  李建文  李军正  归庆明 《武汉大学学报(信息科学版)》2011,(4):461-466

把导航领域、军事领域和导航电子地图中广泛应用的圆概率误差(circular error probable,CEP)引入到HPL(horizontal protection level)的计算中,在最小二乘残差法基础上构建了基于圆概率误差的RAIM(receiver autonomous integrity monitoring)可用性算法。首先计算了在一定误警率、漏警率条件下多颗卫星发生故障时的水平定位偏差和一定置信度下的圆概率误差;然后以GPS导航星座为例,探讨了相关观测下计算HPL的新方法;最后把HPL与水平告警限差(horizontal alert limit,HAL)相比较,得到了基于圆概率误差的RAIM可用性,并通过算例验证了此方法的有效性和可行性。  相似文献   

Open for Business but at What Cost? Housing issues in ‘boomtown’ Darwin     

Gretchen Ennis  Matalena Tofa  Mary Finlayson 《The Australian geographer》2014,45(4):447-464

The Greater Darwin area has long experienced high housing costs and high rates of homelessness. Into this already stressed housing context have come large-scale, natural resource development projects, which are predicted to bring thousands of new workers to town, and exciting property investor interest. While many view these developments as positive, there is concern about the impacts upon the most vulnerable members of the population. This paper presents the findings of a qualitative research project exploring current housing issues in the Greater Darwin area. Interviews with housing support service providers and real estate agents reveal that the current population and investment growth have exacerbated longstanding housing issues. Increased housing stress in Darwin, and a myopic focus on rapid economic growth, may disenfranchise current residents and undermine service and support industries. We argue that while there may be some economic benefits from a ‘booming’ Darwin, greater planning and partnership between government, community organisations and corporates is required to ensure the benefits are spread across the population. Unfortunately, the Northern Territory government's dilatory approach to both housing issues and the social costs of the resources boom makes it highly unlikely innovative partnerships will occur.  相似文献   

Increased light availability enhances tolerance against ocean acidification-related stress in the calcifying macroalga Halimeda opuntia     

Zhangliang Wei  Yating Zhang  Fangfang Yang  Lijuan Long 《海洋学报(英文版)》2022,41(12):123-132

Although the adverse impacts of ocean acidification (OA) on marine calcifiers have been investigated extensively, the anti-stress capabilities regulated by increased light availability are unclear. Herein, the interactive effects of three light levels (30 μmol photons/(m2·s), 150 μmol photons/(m2·s), and 240 μmol photons/(m2·s) combined with two pCO₂ concentrations (400 ppmv and 1400 ppmv) on the physiological acclimation of the calcifying macroalga Halimeda opuntia were investigated using a pCO₂-light coupling experiment. The OA negatively influenced algal growth, calcification, photosynthesis, and other physiological performances in H. opuntia. The relative growth rate under elevated pCO₂ conditions significantly declined by 13.14%?41.29%, whereas net calcification rates decreased by nearly three-fold under OA conditions. Notably, increased light availability enhanced stress resistance through the accumulation of soluble organic molecules, especially soluble carbohydrate, soluble protein, and free amino acids, and in combination with metabolic enzyme-driven activities, OA stress was alleviated. The carotenoid content under low light conditions increased markedly, and the rapid light curve of the relative electron transport rate was enhanced significantly by increasing light intensities, indicating that this new organization of the photosynthetic machinery in H. opuntia accommodated light variations and elevated pCO₂ conditions. Thus, the enhanced metabolic performance of the calcifying macroalga H. opuntia mitigated OA-related stress.  相似文献