中强地震前电磁扰动异常信息量S的分析   总被引：1，自引：0，他引：1  

邓柏昌  魏焕  于立业 《地震研究》2009,32(3)

通过对2006年山东省地震电磁扰动监测台网的电磁扰动异常资料的分析,定义了地震电磁扰动异常信息量S,并用来定量研究异常信息的特征.结果表明,S值大小可能与地震的震级有关,并且反映了区域应力场的活动强度和研究区f域的地震活动.最后从物理机制和震例两个方面对S作了进一步论述.  相似文献   

Biogeochemical and ecological functioning of the low-salinity water lenses in the region of the Rhone River freshwater influence,NW Mediterranean Sea     

Frédéric Diaz  Jean-Jacques Naudin  Claude Courties  Peggy Rimmelin  Louise Oriol 《Continental Shelf Research》2008

A quasi-synoptic survey of a eulerian small grid was carried out twice during mid-spring 2002 in the Gulf of Lions, NW Mediterranean Sea. Analysis of hydrological core parameters reveal for the first time, in the region of freshwater influence (ROFI) of the Rhone River, the presence of low-salinity water (LSW) lenses. The present work details the biogeochemical and ecological functioning of the two LSW lenses from a combined analysis of nutrients and organic matter content, taxonomic assemblages of phytoplankton, primary productivity measurements and nitrogen regeneration fluxes. During the first survey, the lens observed is only detached in part from the Rhone River plume and is considered as a juvenile lens. In contrast, the second lens is totally detached from the plume forming a confined 3D structure with a large vertical development and is considered as having a more advanced maturity. A second survey, 4 days later, provided the opportunity to propose a complete sequence of ecological functioning of the LSW lenses, from their formation to a late stage of maturity just before dispersion. Nitrate contents and dissolved organic matter remain in high concentrations during the juvenile stages while the little available phosphate is rapidly exhausted. In such, an unbalanced-nutrient environment picoplankton appear to out-compete bacterioplankton for phosphate and other resources such as ammonium. In turn, the dominance of such prokaryotic assemblages could have involved the rapid development of microzooplankton. The sudden increase in phosphate observed in a more advanced stage of lens maturity is attributed to intense P-regeneration driven by the large abundance of microzooplankton. This top-down control does not seem to enable the prokaryotic assemblages to bloom again but the high concentrations of phosphate and nitrate favour the development of larger phytoplankton. These autotrophic communities rapidly exhaust nutrients and then decline in the confined ecosystem of the LSW lens that subsequently evolves towards oligotrophic conditions. In the observed last stage, small-sized phytoplankton again dominates the microbial assemblages and the trophic regime is mainly based on regenerated production. The long lifetime of the LSW lens compared to that of the Rhone River plume enables a deep transformation of the initial characteristics of the Rhone River freshwaters both in terms of nutrients balance and microbial food webs, especially through trophic cascading effects. Hence, we show that the LSW lenses have the potential to transfer nutrients and organic matter offshore but the nature (inorganic vs. organic) of the dominant compound exported will depend on the maturity of the lens at the time of its dispersion.  相似文献   

气候变暖对中国不同地区农业的影响   总被引：50，自引：2，他引：48  

刘颖杰  林而达 《气候变化研究进展》2007,3(4):229-233

摘要：利用国家统计局《中国农村统计年鉴》1984-2003年的数据和同期年平均温度的观测数据,分析了我国不同地区20年间温度变化、农业生产资料投入以及播种面积变化对粮食总产的影响。结果表明,以温度升高为主要特征的气候变化对东北地区农作物增产有明显促进作用,对华北、西北和西南地区的农作物增产有一定抑制作用,对华东和中南地区的农作物粮食产量的影响则不明显。农业投入的增加对各地区的农作物增产在早期作用均显著,后期则增长缓慢。而各地区播种面积的变化对其总产量影响不太明显,但华东和中南地区农业播种面积的持续下降对粮食总产量有较大的抑制作用。  相似文献   

黄河下游断流对沿岸地下水形成与开发的影响     

曹剑峰  王凯军  姜纪沂  冶雪艳 《吉林大学学报(地球科学版)》2007,37(5):937-942

黄河下游河段断流对沿黄地区生态环境影响严重。以1999年为基准年,利用黄河下游侧渗补给影响带地下水系统模拟模型研究了黄河断流对黄河侧渗量及地下水循环的影响。花园口-河口断流300d,黄河侧渗量减少53.8%。夹河滩-河口全年断流,黄河侧渗量减少75.2%;断流300d,黄河侧渗量减少46.3%。泺口-河口全年断流,黄河侧渗量减少25.1%;断流300d,黄河侧渗量减少19.8%。利津-河口全年断流,黄河侧渗量减少4.7%。断流对黄河侧渗补给影响带地下水流场的形态影响较小,浅层地下水系统边界的水力性质没有改变。断流对黄河下游傍河水源地开采动态水位影响较大,但宏观上对侧渗补给影响带地下水资源不会产生较大影响。  相似文献   

The Geography of Edible Insects in Sub-Saharan Africa: a study of the Mopane Caterpillar   总被引：1，自引：0，他引：1  

PETER ILLGNER  ETIENNE NEL 《The Geographical journal》2000,166(4):336-351

Entomophagy, the human consumption of insects, has not received significant attention in Western literature, despite the critical role which it plays as a protein supplement in many parts of the world. This paper explores the importance of entomophagy in Africa within the context of food security and indigenous technical knowledge. These issues are further investigated through a case study of the mopane caterpillar in Southern Africa. The findings clearly indicate the contribution which insects make to the diet of rural Africans.  相似文献   

流域水污染物排放总量控制研究--以吉林省松花江流域为例   总被引：12，自引：2，他引：10  

包存宽  张敏  尚金城 《地理科学》2000,20(1):61-64

介绍了污染物排放总量控制的３种类型：容量总量控制、目标总量控制和行业总量控制;提出了总量控制的技术路线和技术方法;并将此理论与方法具体应用到吉林省松共的总量控制研究中,着重分析了松花江中下游控制单元和吉林市子控制单元的总量控制方案;最后探讨了总量控制措施。  相似文献   

长江三角洲21世纪食物保障问题及对策   总被引：1，自引：0，他引：1  

段学军  王合生 《地域研究与开发》2000,19(1):21-24

近年来,长江三角洲粮油等主要食物的供需平衡比较困难,其它食物生产存在一些问题,保障食物供给已成为长江三角洲可持续发展的重要问题之一。文章分析了长江三角洲食物保障的现状、问题,并重新构建了长江三角洲的食物保障体系,对确保长江三角洲可持续发展的食物供给有重要的意义。  相似文献   

世纪之交我国粮食政策的反思与对策     

田建民 《地域研究与开发》2000,19(1):85-88

文章从我国目前农业生产形势及今后发展中将面临的环境和形势变化,分析到：世纪末我国的“粮改”政策有其现必要性和积极作用,但同于其有迅改革市场取向原则的地方,因此,不可能从根本上解决我国粮食生产的方向性和长远发展问题。在跨入新世纪之际,必须在对我国农业面临形势进行正确判断基础上,从转变农业目标增长方式,按照产业化目标指导农业生产;强化农业投资,改善条件,有机兼顾长短目标;加大 业科技力度,确立重点,不  相似文献   

A preliminary study on benthos food web structure of tidal zone in the Laoshan Bay by using stable carbon isotopes     

Cai Deling  Hong Xuguang  Mao Xinghu  Zhang Shufang  Gao Sulan 《海洋学报(英文版)》2000,19(4):81-89

By analyses of carbon isotopic composition(δ¹³C values) of the benthos collected in the Laoshan Bay in August 1993 and February and May 1994, it is found that the main food sources of the benthos can be divided into four groups in terms of carbon isotope composition: Particulate Organic Matter (POM),benthic diatoms, benthic macroalgae and the organic matter in sediments.The results show that the carbon isotopic composition of the benthic animals has a close relation with that of the food they take in.The carbon isotopic compositions of benthos may be useful in elucidating their food sources.The carbon isotopic data have confirmed that POM is the main food source of the benthic filter feeders such as bivalves; crustaceans have a wide range of δ¹³C values, showing their food source has diversity; benthic diatoms are an important fraction of the food for most of gastropods.A preliminary investigation of the benthic-pelagic coupling in that region using the stable carbon isotopic tracers has confirmed the importance of POM as a food source for benthos in this region,but the organic matter in sediments and benthic diatoms are also relatively important for a lot of benthic animals.The benthic-pelagic coupling in the Laoshan Bay temperate ecosystem is not so tight as that in ecosystems at higher latitudes such as north-eastern water polynya.  相似文献   

不同饵料及添加剂对中国对虾幼体的影响   总被引：1，自引：0，他引：1  

朱丽岩  郑家声  王梅林  祁自忠  徐怀恕 《海洋科学》2000,24(11):41-45

在连续两年春季中国对虾育苗期间,采用几种不同的饵料－人工饵料为主、活饵料和两种强化饵料分别培育中国对虾幼体,以存活率、体长、体重、抗感染力的缺氧耐受力等指标检验育苗效果。结果表明,人工饵料为主的喂养方式各项指标均显著劣于活饵料;强化与未强化的活饵料效果相近;强化的人工饵料在体长和耐缺氧方面显著优于人工饵料,存活率略低于后者,增重和抗感染方面与后者相近。  相似文献