Setting sediment quality guidelines: a simple yet effective method     

Bjørgesaeter A  Gray JS 《Marine pollution bulletin》2008,57(6-12):221-235

Deriving sediment quality guidelines (SQGs) for marine sediments is a difficult task. It will often be a trade off between reproducibility and relevance. One of the fundamental questions in ecotoxicology is to decide what one should measure to detect response in ecosystems exposed to human disturbance. In this paper we use field data to estimate threshold levels eliciting effects on soft bottom macrobenthos collected at different sediment types and depths on the Norwegian Continental Shelf and test these against natural levels occurring levels in reference conditions. SQGs are presented from multivariate analyses based on 121 gradients (represented with Ba, THC, Cd, Cu, Pb and Zn) incorporating more than 2000 species. Clear clusters with slightly disturbed communities related to contamination loadings were evident in 35% of the gradients. We found large variations in naturally occurring contamination concentrations and in the threshold levels electing effects on the fauna at different sediment types and depths. For example, an increase in depth of only 100 m can triple the Cu and Zn concentrations that elicit effects. Lowest background and threshold levels were found in shallow, sandy sediment. Our results suggest that current SQGs are too high. We hypothesised that setting a SQG of 4-times background concentrations will give sufficient protection for the fauna from metal contamination. The overall background concentration eliciting effects on metal was 3.6x.  相似文献   

地震时隧道衬砌受力敏感性的简化理论分析   总被引：1，自引：1，他引：0       下载免费PDF全文

安永林  彭立敏  黄娟 《地震工程学报》2008,30(3):261-265

为了分析地震区隧道对各影响因素的敏感性,把隧道简化为圆形用拟静力法考虑地震的作用;围岩压力简化为均布,运用结构力学中的力法原理,结合敏感度函数的定义,推导了衬砌的内力(弯矩、轴力、剪力)关于垂直和水平地震作用力、地震作用下增加的孔隙水压力和围岩压力的敏感度函数.并对一工程实例进行了计算.结果表明:衬砌内力对各影响因素的敏感性与各因素数值的大小无关,与衬砌结构形状及侧压力系数有关;并随着侧压力系数的增加敏感性减小,表明浅埋隧道对地震的作用更敏感;衬砌对水平地震作用敏感性最大,并指出了一些最敏感的部位;孔隙水压力的存在有助于改善隧道的受力.  相似文献   

基阶与高阶瑞利波联合反演研究   总被引：9，自引：3，他引：6       下载免费PDF全文

罗银河  夏江海  刘江平  刘庆生 《地球物理学报》2008,51(1):242-249

研究了六层层状介质模型瑞利波基阶和高模式波相速度对横波速度、深度的敏感性,结果表明：基阶波较高模式波对7 m以内浅部地层的横波速度更敏感,敏感性频带在10～25 Hz范围内,峰值频带集中在18 Hz左右;高模式波较基阶波对深部地层的横波速度更敏感,敏感性频带宽,峰值分散.基阶波对浅层的敏感性和高模式波穿透深度更深的特点为近地表岩土层二维横波速度结构的联合反演提供了前提条件.利用阻尼最小二乘SVD（Singular Value Decomposition）算法联合基阶与高模式波对理论模型和实例数据进行横波速度反演,反演结果表明联合反演增强了反演的稳定性,提高了反演的精度.  相似文献   

农业气象灾害损失评估方法及其在产量预报中的应用   总被引：21，自引：2，他引：19  

宫德吉  陈素华 《应用气象学报》1999,10(1):66-71

该文提出了以无气象灾害时农作物应当达到的期望产量为基础来评估农业气象灾害损失的问题。介绍了期望产量和因灾减产量的确定方法,依据因灾减产量与相应年份农作物不同生长期所发生的气象灾害的强度、覆盖度以及作物对灾害的敏感度等关系,建立起因灾减产量的结构型统计评估模式。  相似文献   

UNCERTAINTY AND SENSITIVITY ANALYSES OF SEDIMENT TRANSPORT FORMULAS     

Keh Chia YEH  Sen Long DENG 《国际泥沙研究》1998,(1)

ＵＮＣＥＲＴＡＩＮＴＹＡＮＤＳＥＮＳＩＴＩＶＩＴＹＡＮＡＬＹＳＥＳＯＦＳＥＤＩＭＥＮＴＴＲＡＮＳＰＯＲＴＦＯＲＭＵＬＡＳＫｅｈＣｈｉａＹＥＨ１ａｎｄＳｅｎＬｏｎｇＤＥＮＧ２ＡＢＳＴＲＡＣＴＩｎｖｉｅｗｏｆｔｈｅｒａｎｄｏｍｃｈａｒａｃｔｅｒｉｓｔ...  相似文献   

土壤-植被-大气系统水分能量传输模拟和验证   总被引：21，自引：0，他引：21  

莫兴国 《气象学报》1998,56(3):323-332

本文建立了包括地下水的土壤－植被－大气系统水分能量传输综合模型,并对模型中冠层动量湍流交换反梯度传输现象的描述进行了改进。在此基础上,依据冠层内动量和热量的交换以及辐射传输过程,同时求解地表、冠层能量平衡方程,进而模拟饱和－非饱和土壤的水热传输。用浅地下水地区冬小麦田间试验资料对模型进行验证,结果表明,系统能量平衡各分量和土壤含水量的模拟与观测结果相当一致。模型敏感性分析发现,叶面积指数对总蒸散量的影响随叶面积指数的增加而逐渐减弱;叶片最小气孔阻力对总蒸散量的影响,在该阻力较小时更显著;地下水位对蒸散量的影响在它小于１．５ｍ时不显著,而在１．５～１．７５ｍ之间时,蒸散减小较快,主要由于土壤蒸发减小显著,冠层蒸腾稍有增加。  相似文献   

Simulated Sensitivity of Ozone Generation to Precursors in Beijing during a High O3 Episode     

Meng CUI  Xingqin AN  Li XING  Guohui LI  Guiqian TANG  Jianjun HE  Xin LONG  Shuman ZHAO 《大气科学进展》2021,38(7):1223-1237

This study uses the WRF-Chem model combined with the empirical kinetic modeling method (EKMA curve) to study the compound pollution event in Beijing that happened in 13-23 May 2017. Sensitivity tests are conducted to analyze ozone sensitivity to its precursors, and to develop emission reduction measures. The results suggest that the model can accurately simulate the compound pollution process of photochemistry and haze. When VOCs and NOx were reduced by the same proportion, the effect of O3 reduction at peak time was more obvious, and the effect during daytime was more significant than at night. The degree of change in ozone was peak time > daytime average. When reducing or increasing the ratio of precursors by 25％ at the same time, the effect of reducing 25％ VOCs on the average ozone concentration reduction was most significant. The degree of change in ozone decreased with increasing altitude, the location of the ozone maximum change shifted westward, and its range narrowed. As the altitude increases, the VOCs-limited zone decreases, VOCs sensitivity decreases, NOx sensitivity increases. The controlled area changed from near-surface VOCs-limited to high-altitude NOx-limited. Upon examining the EKMA curve, we have found that suburban and urban are sensitive to VOCs. The sensitivity tests indicate that when VOCs in suburban are reduced about 60％, the O3-1h concentration could reach the standard, and when VOCs of the urban decreased by about 50％, the O3-1h concentration could reach the standard. Thus, these findings could provide references for the control of compound air pollution in Beijing.  相似文献   

阿克苏河灌区作物需水量对气候变化的敏感性分析     

王志成 《沙漠与绿洲气象(新疆气象)》2018,12(3):33-39

阿克苏河灌区是中纬度干旱区典型的绿洲灌溉系统,同时也是新疆第二大灌区,了解灌区作物需水量可为灌区种植结构调整、水资源优化配置提供科学依据。本研究基于联合国粮农组织(FAO)的Penman-Monteith蒸散发模型,结合作物系数法估算了阿克苏灌区作物需水量的时空变化及其对气候因子和作物种植结构的敏感性。结果表明,1960—2015年阿克苏灌区多年平均作物需水量为586 mm,且呈显著上升趋势,上升速率为38.43 mm/10 a。随着气候变化和作物种植结构的改变,1990—2015年间作物需水量急剧增加,增加速率高达99.37 mm/10 a。对于不同作物类型,果林的需水量最大,高达829.8 mm,其次是棉花、水稻和玉米,小麦需水量最低。阿克苏灌区的作物需水量对日最高气温和日照时数较为敏感,而对最低气温、风速和水汽压的敏感度较低。当日最高气温升高2℃时,作物需水量增加4%,当日照时数增加10%时,作物需水量将增加3.2%。另外,作物需水量对作物种植结构非常敏感,当果林的种植面积比例增加10%时,作物需水量增加了12.1%。  相似文献   

Fluvial transport as a natural luminescence sensitiser of quartz   总被引：5，自引：2，他引：3  

Timothy J. Pietsch  Jonathan M. Olley  Gerald C. Nanson 《Quaternary Geochronology》2008,3(4):365-376

The optically stimulated luminescence (OSL) sensitivity of quartz sampled from the bed of the Castlereagh River in inland New South Wales increases linearly with distance downstream, through both a proportional increase in the number of luminescent grains and increases in the sensitivity of individual grains. It is argued that downstream transport provides numerous opportunities for repeated irradiation and bleaching which combine to increase sensitivity of the quartz grains. Individual quartz grains collected from the uppermost sampling site on the Castlereagh River increase in sensitivity in response to repeated cycles of laboratory irradiation, heating and illumination, providing an explanatory analogue. Furthermore, initially non-luminescent grains are shown to be ‘switched on’ by this same laboratory treatment. We conclude that downstream increases in the luminescence sensitivity of quartz observed in the Castlereagh River are due to intrinsic changes within the quartz and not due to any macro changes in the grains, for example polishing, or abrasion and loss of non-luminescent grains. We also infer that the high OSL sensitivity of sedimentary quartz from Australia is due to the predominance of environments which provide numerous opportunities for repeated irradiation, illumination and heating. Observation of the change in luminescence sensitivity of quartz bedload has the potential to provide additional information on the nature of bedload transport processes. Data from the Castlereagh River indicate that the rate of bedload transport is approximately constant along the 325 km sampled reach.  相似文献   

Probabilistic analysis of numerical simulated railway track global stiffness     

《Computers and Geotechnics》2014

  相似文献