共查询到20条相似文献，搜索用时 16 毫秒
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Phytolith study is a new branch of micropaleontology with an increasingly important role in geology, archaeology, and plant taxonomy. Phytoliths have several advantages considering their characteristics of small particle size, high production, wide distribution, anti-decomposition, in situ deposition, distinctive morphologies, and element sequestrating capacity. Phytolith assemblages in modern soil have been found to be closely related to modern vegetation types and climate conditions, which forms the basis for the quantitative study of paleoecology, paleoclimate, and bio-geochemical cycles. At present, phytolith studies generally focus on the following four aspects: (1) Morphology: about 260 unduplicated types of phytoliths have been identified in modern soil, of which 110 types are from grasses, 50 types from ferns, woody plants and other angiosperms, whereas the origin plants of the remaining 100 types are still under investigation. (2) Soil phytolith assemblages and vegetation: phytolith assemblages from the topsoil have been used to distinguish surface vegetation types including different forests and grasslands over a typical region. This model has been applied to restore past vegetation conditions and monitor the dynamic evolution of specific vegetation types at different temporal and spatial scales. (3) Soil phytolith assemblages and climate: quantitative and semi-quantitative relationships between phytolith assemblages and a series of climate parameters, such as annual mean temperature, annual mean precipitation and altitude, have been established through mathematical analysis. In this manner, quantitative reconstruction of paleoclimatic parameters has been achieved through the phytolith-climate transfer function model. (4) Soil phytolith and its sequestered elements: in this topic, the content of soil PhytOC (Phytolith-occluded Organic Carbon) and the importance of PhytOC in the bio-geochemical cycle have been the focus. The study of modern soil phytoliths has provided new approaches and many successful cases for solving specific problems in various fields, such as Earth science and archaeology. This study analyzed existing issues in addition to the abovementioned significant progresses, and provides directions for future research on modern soil phytoliths. 相似文献
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The effects of floodplain vegetation on river planform have been investigated for a medium‐sized river using a 2D morphodynamic model with submodels for flow resistance and plant colonization. The flow resistance was divided into a resistance exerted by the soil and a resistance exerted by the plants. In this way it was possible to reproduce both the decrease in bed shear stress, reducing the sediment transport capacity of the flow within the plants, and the increase in hydraulic resistance, reducing the flow velocities. Colonization by plants was obtained by instantaneously assigning vegetation to the areas that became dry at low water stages. This colonization presents a step forward in the modelling of bank accretion. Bank erosion was related to bed degradation at adjacent wet cells. Bank advance and retreat were reproduced as drying and wetting of the computational cells at the channel margins. The model was applied to a hypothetical case with the same characteristics as the Allier River (France). The river was allowed to develop its own geometry starting from a straight, uniform, channel. Different vegetation densities produced different planforms. With bare floodplains, the river always developed a braided planform, even if the discharge was constant and below bankfull. With the highest vegetation density (grass) the flow concentrated in a single channel and formed incipient meanders. Lower vegetation density (pioneer vegetation) led to a transitional planform, with a low degree of braiding and distinguishable incipient meanders. The results comply with flume experiments and field observations reported in the literature. 相似文献
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The fragile ecological environment of the Gurbantunggut Desert is damaged/disturbed by human activities relating to the development of oil-gas resources and the constructions of desert road and great engineering in the Jungger Basin. It was mainly represented: soil compaction, vegetation cleaning, burial of vegetation, oil polluting, and soil disturbance. With investigation and experiment, we found that when the way and intensity of engineering activities disturbing the eco-environment does not make its ecological stability disintegrated, the desert vegetation has a capacity of natural recovery. To speed and strengthen the process of vegetation recovery efficient assistant measurements, including stabilizing mobile sands promptly and sowing seeds of shrub and herb plants in good time will be needed. 相似文献
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The fragile ecological environment of the Gurbantunggut Desert is damaged/disturbedby human activities relating to the development of oil-gas resources and the constructions of de-sert road and great engineering in the Jungger Basin. It was mainly represented: soil compaction,vegetation cleaning, burial of vegetation, oil polluting, and soil disturbance. With investigation andexperiment, we found that when the way and intensity of engineering activities disturbing theeco-environment does not make its ecological stability disintegrated, the desert vegetation has acapacity of natural recovery. To speed and strengthen the process of vegetation recovery efficientassistant measurements, including stabilizing mobile sands promptly and sowing seeds of shruband herb plants in good time will be needed. 相似文献
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Julian C. Green 《水文研究》2005,19(6):1245-1259
Aquatic macrophytes are often the dominant factor influencing flow conditions within the channels they occupy. Existing knowledge of how stream plants affect the flow is outlined, and the different scales at which vegetation resistance operates are proposed. Resistance is shown to be a function of the size of the plants, their structural properties, location in the channel, and the local flow conditions. Current models to calculate this composite resistance effect are assessed in the light of theoretical considerations of the nature of vegetation resistance. New theory is also presented, which demonstrates the non‐linear relationship between channel resistance and the proportion of the channel occupied by vegetation. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
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The application of ecohydrological groundwater indicators to hydrogeological conceptual models 总被引：1，自引：0，他引：1
Lewis J 《Ground water》2012,50(5):679-689
This article reviews the application of ecohydrological indicators to hydrogeological conceptual models for earth-scientists with little or no botanical training. Ecohydrological indicators are plants whose presence or morphology can provide data about the hydrogeological setting. By examining the literature from the fields of ecohydrology, hydrogeology, geobotany, and ecology, this article summarizes what is known about groundwater indicator plants, their potential for providing information about the aquifer, and how this data can be a cost-effective addition to hydrogeological conceptual models. We conclude that the distribution and morphology of ecohydrological groundwater indicator plants can be useful to hydrogeologists in certain circumstances. They are easiest to evaluate in arid and semiarid climates. Ecohydrological groundwater indicators can provide information about the absolute depth to the water table, patterns of groundwater fluctuation, and the mineralization of the aquifer. It is shown that an understanding of the meteorological conditions of a region is often necessary to accurately interpret groundwater indicator plants and that useful data is usually obtained by observing patterns of vegetation behavior rather than interpreting individual plants. The most serious limitations to applying this source of information to hydrogeological conceptual models are the limited data in the literature and the regional nature of many indicator plants. The physical and physiological indications of the plants exist, but little effort has been made to interpret them. This article concludes by outlining several potential lines of research that could further the usefulness of ecohydrological groundwater indicators to the hydrogeological community. 相似文献
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Considering river structure and stability in the light of evolution: feedbacks between riparian vegetation and hydrogeomorphology 
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下载免费PDF全文 Dov Corenblit Neil S. Davies Johannes Steiger Martin R. Gibling Gudrun Bornette 《地球表面变化过程与地形》2015,40(2):189-207
River ecological functioning can be conceptualized according to a four‐dimensional framework, based on the responses of aquatic and riparian communities to hydrogeomorphic constraints along the longitudinal, transverse, vertical and temporal dimensions of rivers. Contemporary riparian vegetation responds to river dynamics at ecological timescales, but riparian vegetation, in one form or another, has existed on Earth since at least the Middle Ordovician (c. 450 Ma) and has been a significant controlling factor on river geomorphology since the Late Silurian (c. 420 Ma). On such evolutionary timescales, plant adaptations to the fluvial environment and the subsequent effects of these adaptations on fluvial sediment and landform dynamics resulted in the emergence, from the Silurian to the Carboniferous, of a variety of contrasted fluvial biogeomorphic types where water flow, morphodynamics and vegetation interacted to different degrees. Here we identify several of these types and describe the consequences for biogeomorphic structure and stability (i.e. resistance and resilience), along the four river dimensions, of feedbacks between riparian plants and hydrogeomorphic processes on contrasting ecological and evolutionary timescales. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
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《国际泥沙研究》2021,36(6):711-722
The current study tries a new approach to simulating interactions between waves and seagrass through Smoothed Particle Hydrodynamics (SPH). In this model, the plants are defined as a solid that respects Hooke's law, and are assumed to have direct interaction with the fluid. Given the characteristics of the SPH method, especially in terms of computational time, the dimensions of the simulations were limited. The first goal of the current study was to optimize the approach to avoid reaching certain limits such as the rupture of the simulated plant. Plant movements under waves and/or currents have been studied by several authors in various in-situ, physical, and numerical experiments concerning various vegetation species, thus proving that plant movements can be successfully reproduced by SPH 2D/3D. Manning's roughness coefficient, n, was calculated to confirm that the results were in accordance with what had been measured in flume studies. Even though there is still room for improvement, it is shown that this method can be used to estimate Manning's coefficient for coastal vegetation (seagrass and saltmarsh vegetation) and to greatly improve the modeling and forecasting of coastal erosion and storm surge risks by including the effects of vegetation in integrated models. 相似文献
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Experimental observations in a tilting flume having a bed covered with rice plants (Oryza sativa) are used to analyse the flow characteristics of flexible emergent vegetation with downward seepage. The flow velocity for no-seepage and with seepage is reduced by, on average, 52% and 33%, respectively, as the flow reaches the downstream end with vegetation. Higher Reynolds stress occurs at the start of the vegetation zone; hence, bed material transport occurs in this region. The results indicate that the bed is no longer the primary source of turbulence generation in vegetated flow; rather it is dominated by turbulence generated by the vegetation stems. The local effect of the presence of vegetation causes variations in the hydrodynamic characteristics along the vegetated portion of the channel, which leads to erosion and deposition in the vegetation zone. The experiments show that vegetation can provide considerable stability to channels by reducing channel erosion even with downward seepage. 相似文献
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Soil formation results from opposite processes of bedrock weathering and erosion, whose balance may be altered by natural events and human activities, resulting in reduced soil depth and function. The impacts of vegetation on soil production and erosion and the feedbacks between soil formation and vegetation growth are only beginning to be explored quantitatively. Since plants require suitable soil environments, disturbed soil states may support less vegetation, leading to a downward spiral of increased erosion and decline in ecosystem function. We explore these feedbacks with a minimal model of the soil–plant system described by two coupled nonlinear differential equations, which include key feedbacks, such as plant‐driven soil production and erosion inhibition. We show that sufficiently strong positive plant–soil feedback can lead to a ‘humped’ soil production function, a necessary condition for soil depth bistability when erosion is assumed to vary monotonically with vegetation biomass. In bistable plant–soil systems, the sustainable soil condition engineered by plants is only accessible above a threshold vegetation biomass and occurs in environments where the high potential rate of erosion exerts a strong control on soil production and erosion. Vegetation removal for agriculture reduces the stabilizing effect of vegetation and lowers the system resilience, thereby increasing the likelihood of transition to a degraded soil state. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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Flow resistance of one-line emergent vegetation along the floodplain edge of a compound open channel
Experiments have been conducted in straight compound channels with and without one-line emergent vegetation along the floodplain edge, in which stream-wise velocities and boundary shear stresses have been measured. The experimental results show that the velocity distribution in the vegetation case is considerably different from that in the no vegetation case and the boundary shear stress is also significantly reduced by the additional flow resistance caused by the vegetation at a similar relative water depth. The apparent shear stress distribution which has been calculated with the boundary shear stress and weight component in the vegetation case is totally different from that in the no-vegetation case. New formulae for friction factors for the with and without vegetation cases are developed using vegetation density and flow parameters. The drag force caused by the vegetation is obtained for two different vegetation density cases and the magnitude of its effect on total flow resistance is then investigated. The force balance method is used to predict discharge and this is compared with the discharge predicted by the new formula. A further analysis of the selection of vegetation spacing is carried out, determining its effect on stage-discharge. 相似文献
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太湖贡湖湾水生植被分布现状(2012年) 总被引：6，自引：2，他引：4
贡湖湾是无锡和苏州两市的重要水源地,随着近些年太湖水质的急速恶化,贡湖湾蓝藻暴发现象日益严重,危及饮水安全.为提供贡湖湾水资源管理的理论依据,于2012年开展贡湖湾水生植被野外调查.对8个断面进行为期5天的调查,结果表明:(1)共记录贡湖湾水生植物20科27属34种,单子叶植物和沉水植物分别为优势分类群和生态型;(2)贡湖湾水生植被分布区面积占总水域面积的45.35%,为典型半草型湖泊;(3)共有8种水生植物群落分布,其中马来眼子菜群落分布区面积和生物量最大;(4)贡湖湾水生植被总体表现出北部无水生植被分布,东部生物量高、群落及物种组成复杂,其他区域生物量小、群落组成单一的分布格局.水质恶化和插网捕鱼对贡湖湾水生植被分布现状存在影响,过度清淤可能是造成北部水域裸露的原因.结合贡湖湾水生植被分布现状分析结果,建议在贡湖湾水生植被管理中要开展北部裸水区植被修复,促进湾口区域马来眼子菜群落生长,加强对"引江济太"工程上游来水和贡湖湾水质的监测,并注重外来入侵植物尤其是水盾草群落的监测. 相似文献
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太湖康山湾示范区水生植物对水体氮、磷控制的适用性分析 总被引：2，自引：1，他引：1
为重建湖泊水生植被,改善太湖局部水域水质,在太湖康山湾示范区两个大型围隔进行了两种类型水生植物重建.通过2010年8月-2011年8月的现场采样及分析测定发现,人工控制条件下,浮叶植物荇菜和菱以及沉水植物马来眼子菜的重建效果较好,在其生长季节具有较高的覆盖度;研究表明,控制风浪及提高透明度是恢复水生植被的前提;植被重建区沉水植物氮、磷含量与浮叶植物差别不大,但浮叶植物重建区水体氮、磷浓度的控制比沉水植物重建区好;从经济及水环境效益角度来看,太湖敞水区的沿岸带由于风浪的控制比较困难,恢复水生植被时,应选择浮叶植物荇菜、菱、沉水植物马来眼子菜等抗风浪能力强的物种.本研究为太湖敞水区沿岸带的生态恢复方案制定提供了理论依据. 相似文献
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Liu Hongyan Jiang Zihan Dai Jingxi Wu Xiuchen Peng Jian Wang Hongya Meersmans Jeroen Green Sophie M. Quine Timothy A. 《中国科学:地球科学(英文版)》2019,62(11):1756-1763
The study of the critical zones(CZs) of the Earth link the composition and function of aboveground vegetation with the characteristics of the rock layers, providing a new way to study how the unique rock and soil conditions in karst regions affect the aboveground vegetation. Based on survey results of the rocks, soils and vegetation in the dolomite and limestone distribution areas in the karst area of central Guizhou, it was found that woody plant cover increases linearly with the number of cracks with a width of more than 1 mm, while the cover of herbaceous plants shows the opposite trend(p0.01). The dolomite distribution area is characterized by undeveloped crevices, and the thickness of the soil layer is generally less than 20 cm, which is suitable for the distribution of herbaceous plants with shallow roots. Due to the development of crevices in the limestone distribution area, the soil is deeply distributed through the crevices for the deep roots of trees, which leads to a diversified species composition and a complicated structure in the aboveground vegetation. Based on moderate resolution imaging spectroradiometer(MODIS) remote sensing data from 2001 to 2010, the normalized differentiated vegetation index(NDVI) and annual net primary productivity(NPP) results for each phase of a 16-day interval further indicate that the NDVI of the limestone distribution area is significantly higher than that in the dolomite distribution area, but the average annual NPP is the opposite. The results of this paper indicate that in karst CZs, the lithology determines the structure and distribution of the soil, which further determines the cover of woody and herbaceous plants in the aboveground vegetation. Although the amount of soil in the limestone area may be less than that in the dolomite area, the developed crevice structure is more suitable for the growth of trees with deep roots, and the vegetation activity is strong. At present, the treatment of rocky desertification in karst regions needs to fully consider the rock-soilvegetation-air interactions in karst CZs and propose vegetation restoration measures suitable for different lithologies. 相似文献
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Angela Gurnell 《地球表面变化过程与地形》2014,39(1):4-25
Plants growing within river corridors both affect and respond to fluvial processes. Their above‐ground biomass modifies the flow field and retains sediment, whereas their below‐ground biomass affects the hydraulic and mechanical properties of the substrate and consequently the moisture regime and erosion susceptibility of the land surface. This paper reviews research that dates back to the 1950s on the geomorphological influence of vegetation within fluvial systems. During the late twentieth century this research was largely pursued through field observations, but during the early years of the twenty‐first century, complementary field, flume and theoretical/modelling investigations have contributed to major advances in understanding the influence of plants on fluvial systems. Flume experiments have demonstrated the fundamental role of vegetation in determining river planform, particularly transitions from multi‐ to single‐thread forms, and have provided insights into flow–vegetation–sediment feedbacks and landform building, including processes such as channel blockage and avulsion. At the same time, modellers have incorporated factors such as moisture‐dependent plant growth, canopy and root architecture and their influence on flow resistance and sediment/bank reinforcement into morphodynamic models. Meanwhile, field investigations have revealed that vegetation has a far more important and complex influence on fluvial systems than previously realized. It is now apparent that the influence of plants on river systems is significant across space scales from individual plants to entire forested river corridors. Small plant‐scale phenomena structure patch‐scale geomorphological forms and processes, and interactions between patches are almost certainly crucial to larger‐scale and longer‐term geomorphological phenomena. The influence of plants also varies continuously through time as above‐ and below‐ground biomass change within the annual growth cycle, over longer‐term growth trajectories, and in response to external drivers of change such as climatic, hydrological and fluvial fluctuations and extremes. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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Spatiotemporal variations of Chinese Loess Plateau vegetation cover during 1981–2006 have been investigated using GIMMS and
SPOT VGT NDVI data and the cause of vegetation cover changes has been analyzed, considering the climate changes and human
activities. Vegetation cover changes on the Loess Plateau have experienced four stages as follows: (1) vegetation cover showed
a continued increasing phase during 1981–1989; (2) vegetation cover changes came into a relative steady phase with small fluctuations
during 1990–1998; (3) vegetation cover declined rapidly during 1999–2001; and (4) vegetation cover increased rapidly during
2002–2006. The vegetation cover changes of the Loess Plateau show a notable spatial difference. The vegetation cover has obviously
increased in the Inner Mongolia and Ningxia plain along the Yellow River and the ecological rehabilitated region of Ordos
Plateau, however the vegetation cover evidently decreased in the hilly and gully areas of Loess Plateau, Liupan Mountains
region and the northern hillside of Qinling Mountains. The response of NDVI to climate changes varied with different vegetation
types. NDVI of sandy land vegetation, grassland and cultivated land show a significant increasing trend, but forest shows
a decreasing trend. The results obtained in this study show that the spatiotemporal variations of vegetation cover are the
outcome of climate changes and human activities. Temperature is a control factor of the seasonal change of vegetation growth.
The increased temperature makes soil drier and unfavors vegetation growth in summer, but it favors vegetation growth in spring
and autumn because of a longer growing period. There is a significant correlation between vegetation cover and precipitation
and thus, the change in precipitation is an important factor for vegetation variation. The improved agricultural production
has resulted in an increase of NDVI in the farmland, and the implementation of large-scale vegetation construction has led
to some beneficial effect in ecology.
Supported by the National Natural Science Foundation of China (Grant No. 40671019) and the Knowledge Innovation Project of
the Institute of Geographical Sciences and Natural Resources Research of Chinese Academy of Sciences 相似文献
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Spatiotemporal variations of vegetation cover on the Chinese Loess Plateau(1981―2006):Impacts of climate changes and human activities 总被引：1，自引：0，他引：1
Spatiotemporal variations of Chinese Loess Plateau vegetation cover during 1981-2006 have been investigated using GIMMS and SPOT VGT NDVI data and the cause of vegetation cover changes has been analyzed, considering the climate changes and human activities. Vegetation cover changes on the Loess Plateau have experienced four stages as follows: (1) vegetation cover showed a continued increasing phase during 1981―1989; (2) vegetation cover changes came into a relative steady phase with small fluctuations during 1990―1998; (3) vegetation cover declined rapidly during 1999―2001; and (4) vegetation cover increased rapidly during 2002―2006. The vegetation cover changes of the Loess Plateau show a notable spatial difference. The vegetation cover has obviously increased in the Inner Mongolia and Ningxia plain along the Yellow River and the ecological rehabilitated region of Ordos Plateau, however the vegetation cover evidently decreased in the hilly and gully areas of Loess Plateau, Liupan Mountains region and the northern hillside of Qinling Mountains. The response of NDVI to climate changes varied with different vegetation types. NDVI of sandy land vegetation, grassland and cultivated land show a significant increasing trend, but forest shows a decreasing trend. The results obtained in this study show that the spatiotemporal variations of vegetation cover are the outcome of climate changes and human activities. Temperature is a control factor of the seasonal change of vegetation growth. The increased temperature makes soil drier and unfavors vegetation growth in summer, but it favors vegetation growth in spring and autumn because of a longer growing period. There is a significant correlation between vegetation cover and precipitation and thus, the change in precipitation is an important factor for vegetation variation. The improved agricultural production has resulted in an increase of NDVI in the farmland, and the implementation of large-scale vegetation construction has led to some beneficial effect in ecology. 相似文献