ANN application for prediction of atmospheric nitrogen deposition to aquatic ecosystems   总被引：1，自引：0，他引：1  

Palani S  Tkalich P  Balasubramanian R  Palanichamy J 《Marine pollution bulletin》2011,62(6):1198-1206

The occurrences of increased atmospheric nitrogen deposition (ADN) in Southeast Asia during smoke haze episodes have undesired consequences on receiving aquatic ecosystems. A successful prediction of episodic ADN will allow a quantitative understanding of its possible impacts. In this study, an artificial neural network (ANN) model is used to estimate atmospheric deposition of total nitrogen (TN) and organic nitrogen (ON) concentrations to coastal aquatic ecosystems. The selected model input variables were nitrogen species from atmospheric deposition, Total Suspended Particulates, Pollutant Standards Index and meteorological parameters. ANN models predictions were also compared with multiple linear regression model having the same inputs and output. ANN model performance was found relatively more accurate in its predictions and adequate even for high-concentration events with acceptable minimum error. The developed ANN model can be used as a forecasting tool to complement the current TN and ON analysis within the atmospheric deposition-monitoring program in the region.  相似文献   

The influence of relative sediment supply on riverine habitat heterogeneity   总被引：1，自引：0，他引：1  

Sarah M. Yarnell  Jeffrey F. Mount  Eric W. Larsen 《Geomorphology》2006,80(3-4):310-324

The diversity of aquatic habitats in streams is linked to physical processes that act at various spatial and temporal scales. Two components of many that contribute to creating habitat heterogeneity in streams are the interaction between sediment supply and transport capacity and the presence of local in-stream structures, such as large woody debris and boulders. Data from previously published flume and field studies and a new field study on tributaries to the South Yuba River in Nevada County, California, USA, were used to evaluate the relationship between habitat heterogeneity, local in-stream structural features and relative sediment supply. Habitat heterogeneity was quantified using spatial heterogeneity measures from the field of landscape ecology. Relative sediment supply, as expressed by the sediment supply/transport capacity ratio, which controls channel morphology and substrate textures, two key physical habitat characteristics, was quantified using a dimensionless bedload transport ratio, q. Calculated q values were plotted against an ecologically meaningful heterogeneity index, Shannon's Diversity Index, measured for each study reach, as well as the percent area of in-stream structural elements. The results indicate two potential mechanisms for how relative sediment supply may drive geomorphic diversity in natural river systems at the reach scale. When less mobile structural elements form a small proportion of the reach landscape, the supply/capacity ratio dictates the range of sediment textures and geomorphic features observed within the reach. In these settings, channels with a moderate relative sediment supply exhibit the highest textural and geomorphic diversity. In contrast, when less mobile structural elements are abundant, forced local scour and deposition creates high habitat heterogeneity, even in the presence of high relative sediment supply.  相似文献   

Dimorphism of Bivalved Arthropod Branchiocaris? Yunnanensis from the Early Cambrian Chengjiang Biota, South China     

WU Yu  FU Dongjing  ZHANG Xingliang  Allison C. DALEY  SHU Degan 《《地质学报》英文版》2016,90(3):818-826

The bivalved arthropod Branchiocaris? yunnanensis Hou, 1987 is redescribed on the basis of new fossil material from the early Cambrian Chengjiang biota, South China. In total, 81 specimens have been examined. The carapace comprises two identical valves, each valve are sub-circular in outline, ranging from 24 mm to 58 mm in length, and from 15 mm to 46 mm in height. The dorsal margin is straight and bears two short cardinal spines. The valve surface is either smooth or ornamented with polygonal reticular structures, which may result from different preservation conditions. Two morphotypes have been recognized based on the presence or absence of a subdorsal swelling of the valve, which is convex dorsolaterally and extends beyond the dorsal margin when it appears. Statistic and ontogenetic analyses show both morphotypes grow isometrically and have the same growth trajectory. Therefore, the two morphotypes are interpreted as dimorphism within the same species. Our results are helpful for investigating the taxonomy and ontogeny of arthropod fossils and suggest that dimorphism might be fairly common in these early arthropods.  相似文献   

2012年夏季北极浮冰生物群落结构及垂直分布特征研究          下载免费PDF全文

贾书磊 张芳林凌  贾睿何培民  何剑锋 《极地研究》2016,28(1):25-33

海冰生物群落是北极生态系统的重要组成部分,在北冰洋初级生产和碳循环中扮演着重要角色。本文利用荧光显微分析技术对2012年度夏季采集于北冰洋中心区的浮冰生物群落进行了分析,结果显示：柱总生物量平均为105.85±53.41 mgC •m^-2,其中细菌占生物量的47.2%,而后依次是硅藻（26.7%）,鞭毛虫（18.2%）,鞭毛藻（6.9%）和纤毛虫（1.0%）。最高纬站位（123°43.454′E 87°39.598′N）出现冰底鞭毛藻藻华现象,生物量可达329.6 μg C•L^-1,该站位生物群落处于硅藻藻华后期,海冰上层存在较大程度的融冰作用,底部冰芯营养盐N/P比较高,可能形成有利于鞭毛藻生长的小生境。与已有研究结果的对比表明,近年来夏季北极海冰的快速融化对浮冰生物群落结构产生了明显影响,异养类群生物量升高,细菌取代硅藻成为优势类群。  相似文献   

我国水产品市场状况分析     

车斌  孙琛 《广东海洋大学学报》2000,20(4):50-54

文章分析了我国水产品市场的基本状况 ,认为目前我国水产品市场品种丰富 ,价格稳定。究其原因 ,主要是水产品流通体制的改革 ,水产品市场的开放 ,科技贡献率的提高 ,政府在渔业发展方向上的战略性调整和水产品对外贸易的快速发展。文章针对现阶段我国水产品市场存在的问题 ,特别是渔业资源及其生态环境破坏的负面影响及解决办法做了有益的探讨  相似文献   

Self-organization of recent rhythmic iron-manganese precipitations in underground mines in the Harz mountains     

S. Dietrich  K. -H. Jacob 《International Journal of Earth Sciences》1996,85(1):29-37

A recent early diagenetic banded iron-manganese mud has been forming underground in a closed lead-zinc mine for approximately 40 years. The processes leading to the banded structure of the precipitate were studied during a period of 2 years. Therefore, 19 physical and chemical parameters were measured regularly in short intervals. The resulting time series were analysed with respect to the data sets of the monthly chemical analyses of the descendent mine water, the daily rainfall and the mineral content. The results reveal that the precipitated material undergoes internal self-organization due to interaction of redox, colloid-chemical, microbial, electrical and ripening processes, and not exclusively produced by seasonal fluctuations of material input. Thus, the primary banding of the material, caused by externally forced fluctuations of the redox conditions within the mine water, is reorganized after a short time. The finally observed bands are controlled by non-linear coupling of reaction and transport processes within the mud. A genetic model for the banded mineralization was developed and verified by numerical simulation.  相似文献   

辽宁西部九佛堂组昼蜓化石的新发现及其地质意义   总被引：1，自引：0，他引：1  

刘金远  任东  高春玲  程晓冬  李宁宁  刘正玲 《世界地质》2004,23(3):209-212,219

发现于辽宁省义县早白垩世九佛堂组上段地层中的昼蜓化石(孟氏丽昼蜓Abrohemeroscopus mengi Ren，Liu et Chen，2003)与北京西山卢尚坟组的巴依萨昼蜓(Hemeroscopus baissicus Pritykina，1977)在形态上比较相似，但在演化程度上更为原始，主要体现在后翅臀套较小(仅有6～7个翅室)，径增脉(Rspl)缺，后翅CuAa脉弯曲、带有5个明显的后分支，前翅MP脉短、终止于翅后缘近翅结处，翅痣下有一个明显的支脉，后翅CuAa和MP域基部较窄、在三角室下方仅有1排翅室。据此，九佛堂组上段的地质时代定为早白垩世早期(Berriasian-Hauterivian)较为合理。  相似文献   

The effect of riparian condition on invertebrate drift in mountain streams     

Shelley E. R. Hoover  Leanne G. W. Shannon  Josef Daniel Ackerman 《Aquatic Sciences - Research Across Boundaries》2007,69(4):544-553

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Environmental determinants of littoral paludification in boreal lakes   总被引：1，自引：0，他引：1  

Sari Partanen  Miska Luoto 《Limnologica》2006,36(2):98-109

Numerical studies of the relationships between littoral processes and environmental variables are important because they provide understanding of the impacts of natural and human factors on lake systems. In this study, littoral paludification, its occurrence, types and main environmental determinants were studied in boreal lakes with varying size (41–560 km²) and total phosphorus content (4.5–35.5 μg L⁻¹) in Finland. The relative importance of catchment characteristics, water quality and water level regulation on paludification was analysed at the lake level (n=20), whereas the importance of site morphology, soil quality and aquatic vegetation was analysed at the site level (n=289). This study utilised two novel statistical methods in numerical analyses: generalised linear mixed models and variation partitioning (VP). Bottom ward overgrowth was the main paludification type in the studied lakes. At the lake level, the magnitude of spring flooding and the altitude of the lake had a negative response to paludification, whereas the existence of water level regulation, cover of clay soil and total phosphorus content correlated positively to paludification. At the site level, the paludification was negatively related to slope angle, and positively to the occurrence of clay soil, Glyceria maxima (reed sweet-grass) and the abundance of eutrophy indicator species. However, a considerable amount of variation in littoral paludification both at lake and site levels was accounted for by the joint effects of predictors and may thus be causally related to two or all three groups of predictors.  相似文献   

Effect of macrophyte spatial variability on channel resistance     

Julian C. Green 《Advances in water resources》2006

Aquatic macrophytes can severely retard flow rates in the river channels that they occupy. Consequently, there is a need to improve our ability to model vegetation resistance, to aid flood prediction and allow for better-informed channel management. An empirical model is developed to calculate flow resistance (Manning’s resistance coefficient) of channels containing the submergent macrophyte Ranunculus (water-crowfoot). Blockage factors (the proportion of a cross-section blocked by vegetation) were determined for up to nine cross-sections at each of 35 river sites. These were used to create blockage-factor percentiles, which were regressed against vegetation resistance. An exponential best-fit relation involving the 69th blockage-factor percentile gave the best results. A parameter relating the length of the vegetated/solid boundary in contact with the open channel to the length of the conventionally-defined wetted perimeter improved the model fit by acting as a pseudo-measure of the turbulent-energy losses generated within the unvegetated stream by the macrophytes. The model was tested on three additional sites containing different macrophyte species and much higher vegetation blockages, and was found to work well.  相似文献