Long-term history of chesapeake bay anoxia

Stratigraphic records from four sediment cores collected along a transect across the Chesapeake Bay near the mouth of the Choptank River were used to reconstruct a 2000-year history of anoxia and eutrophication in the Chesapeake Bay. Variations in pollen, diatoms, concentration of organic carbon, nitrogen, sulfur, acid-soluble iron, and an estimate of the degree of pyritization of iron indicate that sedimentation rates, anoxic conditions and eutrophication have increased in the Chesapeake Bay since the time of European settlement.     

Turbidity maximum of the northern chesapeake bay

The turbidity maximum near the head of the Chesapeake Bay is produced primarily by the local resuspension of bottom sediments, and by the estuarine "sediment trap" which is formed in the upper reaches of the estuarine circulation regime by the net nontidal circulation.     

Microstructure of agglomerated suspended sediments in northern chesapeake bay estuary

Suspended sediments in the turbidity maximum of Chesapeake Bay include composite particles which contain platy mineral grains, arranged both in pellets (attributable to fecal pelletization) and in networks of angular configuration (attributable to electrochemical flocculation and coagulation).     

Chesapeake bay anoxia: origin, development, and significance

Anoxia occurs annually in deeper waters of the central portion of the Chesapeake Bay and presently extends from Baltimore to the mouth of the Potomac estuary. This condition, which encompasses some 5 billion cubic meters of water and lasts from May to September, is the result of increased stratification of the water column in early spring, with consequent curtailment of reoxygenation of the bottom waters across the halocline, and benthic decay of organic detritus accumulated from plankton blooms of the previous summer and fall. The Chesapeake Bay anoxia appears to have had significant ecological effects on many marine species, including several of economic importance.     

Catastrophic landslide deposits in the karakoram himalaya

In July 1986, three catastrophic landslides deposited about 20 x 10(6) cubic meters of debris on Bualtar Glacier in the Karakoram Himalaya. A sudden acceleration and superficial breakup of the glacier provided an opportunity to examine the fresh deposits in depth. Beneath a surface layer of large boulders, finer materials, mainly sand and silt, made up half of the total volume. The fine materials were formed during the rock avalanche from mostly intact, massive rock of the source zone. Velocity estimates suggest that this disaggregation occurred in less than 2 minutes. Coarse materials remained in bands of uniform lithology, but the fine materials had diffused throughout the landslides. A small amount of carbonate appears to have been calcined by frictional heating, presumably at the base of the initial sliding masses. These observations are relevant to understanding the mechanisms of catastrophic landslides. Other nearby rock avalanche deposits indicate that landslides are an important geomorphic process in the area and that they pose a continuing risk to human activity.     

伊春南部林区特大洪水的成因分析及对策

主要对伊春南部１９９６年７月２９日特大洪水灾害进行了全面的调查和研究。调查结果表明：这次洪水是５０－１００ａ一遇的大洪水，洪水发生的主要原因是大面积的集中暴雨所致，但森林起到了明显的削洪减灾作用。森林质量的好坏是影响森林减洪能力的关键因素，并提出了防治洪水的一些相应对策。     

中国农业巨灾风险评估方法研究

[目的]研究中国农业巨灾风险评估的方法.[方法]利用农作物受灾面积、成灾面积和绝收面积获得中国农业灾害损失数据,同时运用蒙特卡罗模拟技术以解决样本数据不足的难题;运用极值POT模型实现对农业灾害损失尾部分布的有效拟合,建立农业巨灾损失的广义Pareto分布模型;建立基于VaR方法的农业巨灾风险的精确度量模型;选择河南省粮食生产的旱灾巨灾风险作为中国农业巨灾风险评估的案例.[结果]构建了中国农业巨灾风险评估的基本框架;旱灾巨灾对河南省粮食生产的影响总体上相对有限,其损失的平均值在10%左右,但在面临50年一遇甚至是百年一遇的旱灾巨灾时,粮食损失率将分别高达22.60%和25.24%,须引起决策层的高度重视.[结论]本研究所提出的中国农业巨灾风险评估方法是切实可行的.     

Catastrophic drought in the Afro-Asian monsoon region during Heinrich event 1

Between 15,000 and 18,000 years ago, large amounts of ice and meltwater entered the North Atlantic during Heinrich stadial 1. This caused substantial regional cooling, but major climatic impacts also occurred in the tropics. Here, we demonstrate that the height of this stadial, about 16,000 to 17,000 years ago (Heinrich event 1), coincided with one of the most extreme and widespread megadroughts of the past 50,000 years or more in the Afro-Asian monsoon region, with potentially serious consequences for Paleolithic cultures. Late Quaternary tropical drying commonly is attributed to southward drift of the intertropical convergence zone, but the broad geographic range of the Heinrich event 1 megadrought suggests that severe, systemic weakening of Afro-Asian rainfall systems also occurred, probably in response to sea surface cooling.     

Emergence of anoxia in the California current large marine ecosystem

Eastern boundary current systems are among the world's most productive large marine ecosystems. Because upwelling currents transport nutrient-rich but oxygen-depleted water onto shallow seas, large expanses of productive continental shelves can be vulnerable to the risk of extreme low-oxygen events. Here, we report the novel rise of water-column shelf anoxia in the northern California Current system, a large marine ecosystem with no previous record of such extreme oxygen deficits. The expansion of anoxia highlights the potential for rapid and discontinuous ecosystem change in productive coastal systems that sustain a major portion of the world's fisheries.     

海湾扇贝幼体期流行性弧菌病的研究

从辽宁兴城育苗场和辽宁省海洋水产研究所育苗室患面盘解体的海湾扇贝Argopecten irradians Lamarck幼体中分离出6株菌,经感染试验表明,其中3株菌B01、Y01和Y02为病原菌。根据菌体形态及生理、生化测试,B01鉴定为需钠弧菌Vibrio natriegen,Y01和Y02具有相同的形态、生理、生化特征,鉴定为弧菌属Vibrio。需钠弧菌对庆大霉素、痢特灵、菌必治、诺氟沙星、氯霉素、环丙沙星、多粘菌素B敏感;Y01和Y02菌对诺氟沙星、菌必治、氯霉素、复方新诺明、环丙沙星、磺胺异嗯唑敏感。对海湾扇贝育苗水体中细菌总数和弧菌数量的监测结果表明,幼体发生病变之前的水体中,细菌和弧菌的密度高于正常育苗水体的。文中还对病原菌的传播途径等问题进行了讨论。