排序方式： 共有29条查询结果，搜索用时 46 毫秒
1.
2.
ME Alexander CA Simon CL Griffiths K Peters S Sibanda S Miza 《African Journal of Marine Science》2016,38(1):141-144
Biological invasions continue to increase around the world, with impacts on many coastal marine systems. Here we review the South African marine invasion literature which, despite the field being relatively new, has grown to have significant presence in both the local and international arenas. Of the 79 papers reviewed, 70% focused on the establishment and spread of alien species, with modes of transport and introduction largely overlooked. An emphasis was also apparent towards field studies, in particular survey work, with few experimental studies. The overwhelming majority of papers focused on a single species, the Mediterranean mussel Mytilus galloprovincialis, reflecting the scale of this invasion and the tractable nature of rocky shores as study systems. With the exception of this one species, the impacts of marine alien species have rarely been quantified. We suggest that future research extends the taxonomic coverage of present work and develops a better understanding of the mechanisms of introduction, establishment and spread of marine alien species. Through an experimental approach, the drivers of altered ecological patterns and processes resulting from invasions should be addressed, providing insight into associated impacts. This approach will maintain the local applicability and international relevance of South African marine invasion research. 相似文献
3.
地面光斑足印的定位精度高度依赖于激光指向角的测量精度,星载激光光斑质心提取及其变化规律对激光指向角的分析具有重要的意义。本文基于ICESat/GLAS的激光剖面阵列（laser profile array,LPA）影像数据,首先利用灰度一阶矩阵法提取LPA的质心,精度优于0.3个像素,LPA相对定位精度优于0.11个像素。其次利用傅里叶变换和傅里叶级数拟合对LPA质心坐标的变化进行周期探测和建模分析,结果表明,激光光斑影像的质心坐标存在1.83×10-4 Hz、3.36×10-4 Hz、5.19×10-4 Hz和6.71×10-4 Hz 4个明显的周期变化,拟合结果的相关性R2达到了0.86,拟合精度可达0.4″,优于0.13个像素,得到了较好的结果。可为我国的高分七号和后续的卫星激光测高数据处理提供参考。 相似文献
4.
The efficacy of ocean colour remote sensing in assessing the variability of phytoplankton biomass within Saldanha Bay is examined. Satellite estimates of chlorophyll a (Chl a) were obtained using the maximum peak-height (MPH) algorithm on full-resolution (300?m) data from the Medium Resolution Imaging Spectrometer (MERIS). Subsurface Chl a maxima often occur within Saldanha Bay below the mean detection depth of the satellite (1.5?m) during periods of thermal stratification. Consequently, the MPH product was poorly correlated to in situ data from 4?m depth (r2 and average relative percentage difference [RPD] of 0.094 and 53% respectively); however, the coefficient of determination was much improved if limited to in situ data collected under conditions of mixing (r2 and RPD of 0.869 and 89%, respectively). Composites of monthly MPH Chl a data reveal mean concentrations consistent with in situ seasonal trends of phytoplankton biomass, confirming the capability of the MPH algorithm to qualitatively resolve surface Chl a distribution within the bay. 相似文献
5.
安徽省地震会商地理信息系统的研制与实现 总被引：3，自引：1，他引：2
文章结合安徽省现有分析预报手段和数学模型,以Visual Studio2005.net作为开发语言,利用GIS技术对地震地质和基础地理等数据进行管理、分析,通过快速访问前兆数据库,对前兆数据进行查询和曲线调用出图,最终研制实现了一套满足日常及紧急会商需要,集"基础数据查询""前兆数据管理""前兆数据注释""应急会商报告... 相似文献
6.
Saldanha Bay is a narrow-mouth bay on the west coast of South Africa linked to the southern Benguela upwelling system. Bay productivity was investigated by use of the conventional light-and-dark bottle oxygen method, and, for comparison, through assimilation of the stable isotope tracer 13C. Gross community production GCP and net community production NCP, as determined from the oxygen method, were respectively 2.6 and 2.4 times higher than estimates determined from the stable isotope method. Chlorophyll a (Chl a) concentrations increased with the onset of spring and well-defined subsurface maxima developed in association with increasingly stratified conditions (mean water column Chl a concentrations ranged from 5.4 to 31.5?mg m?3 [mean 15.5?mg m?3; SD 7.6]). A sharp decline in photosynthetic rates P* (GCP normalised to Chl a concentration) with depth was attributed to light limitation, as demonstrated by the high vertical attenuation coefficients for downward irradiance Kd, which varied from 0.29 to 0.70?m?1 (mean 0.48?m?1; SD 0.12). Productivity maxima were consequently near-surface despite the presence of deeper subsurface biomass maxima. The community compensation depth Zcc, where gross community production balances respiratory carbon loss for the entire community, ranged from 2.9 to 9.2?m (mean 5.8?m; SD 2.2), and was typically shallower than the 1% light depth for PAR (photosynthetically available radiation), Z1%PAR, which is traditionally assumed to be the depth of the euphotic zone and which ranged from 6.6 to 15.9?m (mean 9?m; SD 2.6). Autotrophic communities, where organic matter is produced in excess of respiratory demand, were confined on average to the upper 5.8?m of the water column, and often excluded the bulk of the phytoplankton community, where light limitation is considered to lead to heterotrophic community metabolism. Estimates of integrated water column productivity ranged from 0.84 to 8.46?g C m–2 d?1 (mean 3.35?g C m?2 d?1; SD 1.9). 相似文献
7.
工程抗震设防标准的效益分析 总被引：7，自引：3，他引：7
合理的工程抗震设入标准应该具有最佳的经济效益和社会效益。为此，本文提出了在确保地震造成的人员伤亡不超过社会可接受水平这一约束条件下，寻求经济效益最佳的设防标准的优化决策模型和方法，并采用这种效益分析方法对若干典型大中城市的设防标准进行了初步分析。 相似文献
8.
The relative significance of primary and secondary suspended sediment sources has been identified in a small (15 km2) agricultural catchment through the application of a linear unmixing model using mineral magnetic, geochemical and radionuclide signatures of fine sediments. Roads appear to be important as a secondary source of suspended sediment and in the conveyance of topsoils to the river channel. Roads also alter the source signatures of sediment in transport, especially that derived from agricultural topsoils. Modelling suggests that c. 30% of the suspended sediment collected from suspended sediment traps in the River Leadon were derived from, or transported via, roads. Relative contributions from primary sources of c. 43% and c. 27% were estimated from a combined (subsoil and channel bank) subsurface source, and a combined (arable and grassland) topsoil source, respectively. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
9.
This paper reviews the major sources and transport characteristics of heavy metals in the hydrological cycle. It is demonstrated that heavy metal releases to the environment have changed from 19th and early 20th century production-related activities to consumption-oriented factors in more recent times. The relative roles of particle size, sorption and desorption processes, partitioning and the chemical speciation of heavy metals on fine sediments are identified to understand the likely fate of heavy metals released into fluvial systems. It is argued that the spatial and temporal distribution of heavy metals in the river corridor depends not only on an understanding of metal solubility and speciation, but also on an understanding of sediment dynamics which control, for example, floodplain alluviation and the accumulation of metals in the bottom sediments of contaminated rivers, lakes and reservoirs. Existing long- and short-term records are examined to identify the current state of knowledge about the factors which affect heavy metal releases into aquatic environments. With limited exceptions, it is shown that few long-term studies of trends in heavy metal transport are available although, for some major rivers, limited data on trends in metal concentration exists. Palaeolimnological reconstruction techniques, based on an analysis of lake and reservoir sediments, are identified as a possible means of supplementing monitored records of heavy metal transport. Although numerous studies have suggested that trends in atmospheric contamination, mining and urbanization may be identified in the bottom sediment record, other research has shown that the radionuclide-based chronology and the heavy metal distribution within the sediment are more likely to be a function of post-depositional remobilization than the history of metal loading to the basin. Despite these limitations, it is shown that the incorporation of reservoir bottom sediment analysis into a heavy metal research programme, based in river corridors of Midland England, provides an opportunity to identify and quantify the relative contribution of point and non-point contributions to the heavy metal budget and to relate trends in metal contamination to specific periods of catchment disturbance. 相似文献
10.
The isotopic composition and concentration of Pb was measured in suspended particulate matter of the Irish Sea. Aerosol, surficial and pre-industrial sediment was also analysed to provide information on sources terms. Concentrations of Pb in suspended sediments were lower than previously reported which presumably reflects the international effort to reduce Pb inputs to the environment. Lead concentrations were highest in Liverpool Bay and lowest in the western Irish Sea. A significant negative relationship between Pb and salinity suggests that present inputs and the resuspension of relict lead associated with particles in areas significantly affected by freshwater discharges are the predominant sources of Pb to the Irish Sea. The isotopic composition of Pb in the stratified region of the western Irish Sea demonstrates that atmospheric sources are also significant to this region, which is consistent with current knowledge on the hydrography. Pb isotopic ratios show that water entering the Irish Sea through St George's Channel is significantly influenced by anthropogenic inputs prior to additional contamination by direct inputs to the Irish Sea. 相似文献