二万年来长江中下游自然环境变迁及其发展趋向探讨

20000～15000a.B.P.间气候最冷,生长喜冷的针叶林和干旱草原植被.在14780±700a.B.P.出现了最低海面(-154m);15000～13500a.B.P.,气候较暖湿,海面上升,生长阔叶混交林;13500～10500a.B.P.,气候有2次温暖和3次较冷,在暖期生长针阔叶混交林.较冷期则出现森林草原和草原.最低的温度比现在低5～7;一万多年来的冰后期,气候变化分为5个新冰期(包括小冰期)和5个新高温期(包括小气候最宜期).最高气温比现在高2～3℃,出现在5000～4000a.B.P.之间;最低温度比现在低3～5℃最高海面在6500～6300a.B.P.,高出现在海面4～5m.在温暖期中生长常绿一落叶阔叶林中亚热带针阔混交林;在较冷期间,生长落叶阔叶林,针叶林或草原草地.在人类影响或自然发展之结果,未来环境变化有可能向干暖气候和高海面演变,或向干冷气候和海面下降转变.这些变化将对长江中下游带来意外的灾难.     

FRESH GROUND WATER STORED IN AQUIFERS UNDER THE CONTINENTAL SHELF: IMPLICATIONS FROM A DEEP TEST,NANTUCKET ISLAND,MASSACHUSETTS1

ABSTRACT: A deep water-resource and stratigraphic test well near the center of Nantucket Island, about 40 miles (64 km) off the New England Coast, has encountered freshwater at greater depth than predicted by the Ghyben-Herzberg principle. An uppermost lens of fresh-water, which occupies relatively permeable glacial-outwash sand and gravel to a depth of 520 ft. (158 m), is probably in hydrodynamic equilibrium with the present level of the sea and the height of the water table. However, two zones of freshwater between 730-820 ft. (222-250 m) and 900-930 ft. (274-283 m) are anomalously deep. A third zone extending from 1150-1500 ft. (350-457 m) contains slightly salty ground water (2 to 3 parts per thousand dissolved solids). Several explanations are possible, but the most likely is that large areas of the Continental Shelf were exposed to recharge by precipitation during long periods of low sea level in Pleistocene time. After the last retreat of glacial ice, seawater rapidly drowned the shelf around Nantucket Island. Since then, about 8000 years ago, the deep freshwater zones which underlie dense clay layers have not had time to adjust to a new equilibrium. Under similar circumstances freshwater may remain trapped under extensive areas of the Continental Shelf wherever clay confining beds have not permitted saltwater to intrude rapidly to new positions of hydrodynamic equilibrium. The implications are far reaching because all continental shelfs were exposed to similar hydrologic influences during Pleistocene time.     

STREAM TYPES IN THE DES MOINES RIVER BASIN1

Stream tributaries in the Des Moines River basin have been classified according to the glacial terrain through which they flow. Three stream types were categorized as follows: (1) streams that flow entirely on Wisconsin drift, (2) streams that flow entirely on Kansan drift, and (3) streams that have their headwaters located on new drift but have their lower reaches flowing on older drift. Selected channel and valley characteristics were measured and used to verify the stream type classification. Five variables were chosen for use in a multiple linear discriminatory analysis, which is a statistical technique developed for the purpose of classifying observations into one of several categories which have been predetermined. The streams in each group were verified with the exception of three anomalies based on the probability associated with the largest linear discriminant function. The rationale for the three anomalous streams is not easily determined. But, they are considered to be associated with pre-glacial drainage or at least pre-Wisconsin age drainage. Otherwise, the analysis shows that the major channels and valleys in the Des Moines River basin tend to reflect the glaciated upland surface.     

太白山古冰川遗迹资源与旅游可持续开发

太白山是我国东部古冰川地貌保存较好的山地.该冰川遗迹面积较大、规模壮观、形态保存完整,主要分布在垂直带谱显著的山地顶部,景观十分奇特.在分析冰川遗迹形成的地质基础上,探讨了冰川地貌的主要分布类型,评价了冰川地质遗迹的资源特点,提出了旅游可持续开发的一些建议.     

Climatic Variation and Solute Concentration and Flux in Meltwaters Draining from an Alpine Glacier

Measurements of electrical conductivity and discharge ofmeltwaters in the Gornera, which drains from the 83%glacierised basin containing Gornergletscher, PennineAlps, Switzerland, were undertaken between May andSeptember in both 1979 and 1998. Discharge in theGornera was 43% higher in 1998, average air temperatureduring the ablation season being 2.1 °C warmer andpreceding winter precipitation 28% lower than in 1979. Mean electrical conductivity of meltwater in 1998 wasreduced by 40%. In the same 60 day period in 1998,however, solute flux was augmented by only 2% bycomparison with 1979. Year-to-year climatic variations,reflected in discharge variability, strongly affectsolute concentration in glacial meltwaters, but havelimited impact on solute flux. Climatic conditionstranslate into meltwater quality through inter-relationships between mineral reaction rates, subglacialresidence time in contact with sediment, and discharge. Annual variability in solute flux depends on the extentto which volume of flow can offset decline in soluteconcentration brought about by reducing residence time.     

地震液化流滑震害

通过地震液化的震害调查,从土种类、地形条件和坡度、液化土壤的赋存状况、地震能量和流滑的时间与空间分布等方面,简要总结了液化流滑的震害特征和规律,初步分析了液化引起流滑发生的条件、规模、剧烈程度、坡体运动规律以及流滑产生的破坏形式,分析了影响流滑的因素,可供进一步研究等参考。     

Relict Crustaceans under Conditions of Long-Term Pollution of Subarctic Lake Imandra: Results of Observations in 1930–1998

Changes in the role of relict crustaceans in the zoobenthic communities of large subarctic Lake Imandra are analyzed over the long period of economic development in its drainage area. To date, Mysis relicta as a species highly sensitive to anthropogenic pollution has apparently disappeared from the lake fauna. The currently recorded maximum values of Pontoporeia affinis abundance and biomass are more than 20 times as great as those between 1968 and 1986. As in other lakes with mass development of P. affinis, the populations of this crustacean inhibit chironomid larvae in the communities of Lake Imandra.     

Abundance and community of snow bacteria from three glaciers in the Tibetan Plateau

Bacterial abundance and diversity in snow of East Rongbuk,Laohugou and Hailuogou glaciers on the Tibetan Plateau were investigated through epifluorescence microscope and denaturing gradient gel electrophoresis.Cell abundance ranged from 4.0 × 10 3 to 290.2 × 10 3 cells/mL.The phylogenetic trees placed the 16S rRNA sequences in four major groups:Proteobacteria,Firmicutes,Actinobacteria and Bacteroidetes.Brevundimonas,Flavobacterium,Hymenobacter,Bacillus,Polaromonas,Rhodoferax and Streptomyces were widely distributed bacteria in glaciers from different cold regions.The remaining five genera of Hylemonella,Delftia,Zoogloea,Blastococcus and Rhodococcus were endemism,only recovered from our investigated glaciers.It is proposed that the three glaciers on the Tibetan Plateau provide a specific ecological niche for prolonging survival of diverse microbial lineages.     

近50 a气候变化背景下青藏高原冰川和湖泊变化

论文综述了近年来青藏高原冰川和湖泊变化研究取得的成果,并特别着重于冰川和湖泊变化的相互关系论述。在全球变暖背景下,近几十年青藏高原冰川以退缩为主,湖泊水量以增加为主。论文一方面对青藏高原冰川末端退缩、冰川面积和冰川储量变化方面的研究成果进行了综合分析,探讨了冰川变化的时空特征;另一方面从湖泊面积和水位与水量变化探讨了湖泊变化的时空规律。结果表明青藏高原冰川退缩的幅度总体上呈从青藏高原外缘向内陆呈减小的变化态势,受冰川融水补给比较大的湖泊近期面积扩张、水位上升明显。最后指出了青藏高原冰川、湖泊变化研究中存在的问题及今后的发展趋势。     

青藏高原冰川雪细菌与气候环境的关系

通过荧光显微镜测定细菌密度,利用DGGE图谱和Shannon-Weaver指数分析细菌种类多样性,对青藏高原北部老虎沟12号冰川、南部东绒布冰川和东南部海螺沟2号冰川雪坑的细菌密度和种类多样性做了差异性分析. 结果表明:老虎沟12号冰川雪坑细菌密度平均值比东绒布冰川和海螺沟2号冰川高,老虎沟12号冰川雪坑细菌种类多样性比东绒布冰川高,这与高原南、北部不同大气环流引起的大气微粒含量的差异性有关. 海螺沟2号冰川雪坑细菌种类多样性均最高,与该冰川所受的大气环流多样性最高相一致. 东绒布冰川雪坑细菌密度平均值与南极点相近,与其远离人类污染,因而大气环境本底值低有关. 海拔高的东绒布冰川雪坑细菌密度和种类多样性均比海拔低的海螺沟2号冰川和老虎沟12号冰川低,即二者与海拔高度呈反比.