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971.
We present a paleolimnological record spanning the Holocene from a small lake on Russell Island (Lake PW02), in the central
Canadian Arctic Archipelago (74.07° N, 97.77° W, 182 m asl). Fragilarioid diatom types in the genera Pseudostaurosira, Staurosira and Staurosirella constitute >90% of valves in fossil samples. Using modern biogeographic data which specify the temperature optima of the
Fragilarioid diatom taxa, we present new inferences about the timing of paleoclimatic changes in the central Arctic islands.
The early Holocene was characterized by maximum values for sediment organic matter, and lower ratios of Staurosirella pinnata to Staurosira construens v. venter, suggesting warm summer air temperatures between about 9500−6500 cal year BP. Influxes of biogenic silica and diatom valves
decreased following 4000 cal year BP, the sediment accumulation rate slowed and diatom taxa of the littoral zone diversified,
suggesting cooler summers and more persistent lake ice. Variations in the species composition of the assemblages indicate
paleoclimatic changes that are in broad agreement with other paleoenvironmental records from the Arctic including melt records
from the Agassiz Ice Cap. Although autecological data remain incomplete for Fragilarioid taxa, our results indicate differences
in these taxa in responses to paleoenvironmental change and underline the potential for the increased use of these taxa in
paleoenvironmental reconstructions. The record from Lake PW02, as in other records from Arctic lakes with low algal diversity
throughout the Holocene, shows a pronounced increase in diatom diversity since the 1920s, and diatom production since the
1970s far exceeds any recorded during the Holocene. 相似文献
972.
The water quality of Dianchi Lake declines quickly and the eutrophication is getting serious. To identify the internal pollution
load of Dianchi Lake it is necessary to evaluate its sediment accumulation. Sedimentation rates of Dianchi Lake are determined
by 137Cs dating. However, 137Cs vertical distribution in sediment cores of Dianchi Lake has special characteristics because Dianchi Lake is located on
the southeast of the Qinghai-Tibet Plateau, the Kunming quasi-stationary front is over the borders of Yunnan and Guizhou where
the specific precipitation is distributed. Besides 1954, 1963 and 1986 137Cs marks can be determined in sediment cores, a 137Cs mark of 1976 representing the major period of 137Cs released from China unclear test can be determined and used for an auxiliary dating mark. Meanwhile Dianchi Lake is divided
into seven sections based on the water depth, basin topography, hydrological features and supplies of silt and the lakebed
area of each section is calculated. The mean annual sedimentation rates for seven sections are 0.0810, 0.1352, 0.1457, 0.1333,
0.0904, 0.1267 and 0.1023 g/cm2a in 1963–2003, respectively. The gross sediment accumulation of the lake is 26.18×104 t/a in recent 17 years and 39.86×104 t/a in recent 50 years.
Foundation: National Natural Science Foundation of China, No.40771186; The Key Project of the State Key Laboratory of Soil Sustainable
Agriculture, Nanjing Institute of Soil Sciences, Chinese Academy of Sciences, No.5022505
Author: Zhang Yan (1962–), Ph.D and Associate Professor, specialized in environmental change. 相似文献
973.
《Limnologica》2019
Lake Baikal is facing several environmental stressors, including climate change and nearshore eutrophication. To assess recent ecological changes in Lake Baikal and provide a baseline for future comparisons, we sampled spring plankton communities from the pelagic zone of the lake in 2016 and compared these data with unpublished and published historical information going back to 1990. In 2016, one pelagic long-term monitoring station was sampled in early spring (March) during ice cover and 21 long-term monitoring stations located throughout the lake were sampled in late spring (May-June). We measured water chemistry parameters at most stations and the abundance, taxonomic composition and biomass of bacteria, ciliates and phytoplankton at several locations in different areas of the lake. Biotic parameters from 2016 were compared with historical data, showing significant changes in the spring pelagic microbial community since the 1990s. We show increased quantities of small species, mixotrophic ciliates, and the appearance (or increasing number) of small coloured and colourless flagellates. We also show substantially decreased densities of formerly dominant heavily silicified diatoms such as Aulacoseira spp. Since 2007, Synedra acus subsp. radians, a smaller and weakly silicified diatom, has dominated the spring plankton of the lake. These results suggest that Lake Baikal’s pelagic plankton community may be changing, with climate likely playing a dominant role in these changes. 相似文献
974.
Analysis of the distribution of ore-bodies in space can be useful generally in the estimation of mineral resources or the management of exploration. This study is directed to analysis of the undiscovered potential of well known areas of mining district size, referred to as metallogenic units (MUs). The analysis employs an effort-adjusted and truncated probability model for number of occurrences within a subdivision (quadrat) of a MU and Monte Carlo sampling to generate an approximation to the probability distribution for number of occurrences and number of mines within an MU when it is totally explored. Exploration potential for Monitor, Bodie, Aurora, and Camp Douglas MUs (Walker Lake quadrangle of Nevada and California) are estimated to be 9, 4, 7, and 4 mines, respectively. 相似文献
975.
西藏自治区扎仓茶卡盐湖是我国重要的超大型固体硼镁矿产地,经多年开采,高品位硼矿资源(B_2O_3≥28%)已采掘殆尽,但矿区内仍堆有大量低品位矿石,这不仅是对环境的威胁,也是对资源的浪费。在采集样品的基础上,开展了基于X射线衍射与扫描电镜的矿物组成的鉴定和化学组分分析,为低品位矿石的综合利用提供理论依据。研究结果表明,扎仓茶卡盐湖低品位硼矿的矿物种类有库水硼镁石、柱硼镁石、石英、钠长石、微斜长石、方解石、白云母、文石、水菱镁矿、石膏和锰热臭石共11种,其中仅有库水硼镁石和柱硼镁石两种硼矿物,平均含量分别为21.14%与8.99%,且硼矿样品中B_2O_3平均含量高达13.50%,有巨大的经济利用价值。考虑到扎仓茶卡有着丰富的卤水资源,且低品位硼矿主要为库水硼镁石,可利用卤水及矿物的密度差来进行重选,该库水硼镁石为易选型。这种方法不仅能实现矿区内低品位矿的回收利用,而且生产成本低廉、绿色环保,将进一步促进区域经济发展。 相似文献
976.
977.
近800a来内蒙古岱海湖水的盐度定量及其气候意义 总被引:6,自引:0,他引:6
在干旱半干旱地区 ,封闭湖泊的湖水盐度对气候变化反应敏感。首先通过现生介形类 (Lim nocytherecf.inopinata)壳体与湖水Sr/Ca比值的测定确定了Sr/Ca的分配系数 ;然后测试现代岱海湖水盐度与湖水Sr/Ca比值 ,建立湖水盐度与湖水Sr/Ca比值的函数关系 ;最后利用湖泊沉积剖面中介形类壳体的Sr/Ca比值定量恢复了岱海湖水近 80 0a来的盐度。通过分析岱海湖水盐度变化过程 ,揭示了研究区小冰期前期降水增加的冷湿气候 ,这明显不同于东部其它地区的冷干气候 ;研究区在小冰期中后期以偏干旱气候为主 ,这与东部其它地区干冷气候相一致 ;推测了 2 1世纪初 10~ 2 0a ,岱海地区降水将有所增加 ,干旱趋于缓和。 相似文献
978.
979.
Based on the δ13C and δ18O fluctuation of lacustrine carbonate, CaCO3 content and sporo-pollen data, a palaeoclimatic history of Bosten Lake during the Holocene has been outlined, several stages
of climatic changes are divided, and the following result es are obtained: (1) Palaeoclimatic changes revealed by carbonate
isotope around Bosten Lake are basically identical with that revealed by other geological records in Xinjiang. Environmental
changes presented apparent Westlies Style model: during cold period, relative humidity increased, δ18O, δ13C and CaCO3 appeared low; but in warm periods, the dry regime aggravated. (2) The temperature reflected by δ18O exist evident features being increase in the late period during the Holocene. Together with the δ13C, pollen and CaCO3 analyses, several cold and warm phases which are of broad regional significance can be identified. The warm peaks occurred
at about 11.0 ka B.P., 9.4 ka B.P., 7.5 ka B.P., 5.0 ka B.P., 3.0 ka B.P. and 2.0 ka B.P.; the cold peaks at 11.5 ka B.P.,
10.5 ka B.P., 8.8 ka B.P., 5.5 ka B.P., 3.3 ka B.P., 2.2 ka B.P. and 1.5 ka B.P.. (3) Several climatic events with the nature
of “abrupt climatic changes” are revealed in the periods of 11.0 ka B.P. −10.5 ka B.P., 9.4 ka B.P. −8.8 ka B.P., 5.5 ka B.P.
−5.0 ka B.P. and 2.0 ka B.P. −1.5 ka B.P.. (4) The results show that carbonate isotopic record of lacustrine sediment in arid
area is very sensitive to climatic changes, and may be play a very important role in understanding the features and mechanism
of palaeoclimatic changes. 相似文献
980.
滇池表层沉积物铵态氮吸附特征 总被引:1,自引:0,他引:1
为研究滇池内源污染特征,2013年利用GIS软件针对滇池全湖布设36个采样点,采集表层沉积物,研究滇池表层沉积物铵态氮(NH_4+-N)吸附特征,同时分析沉积物的理化性质对NH_4+-N吸附特性的影响.结果表明:滇池表层沉积物对NH_4+-N的吸附量在前2 h之内呈增长趋势,吸附速率较大,之后沉积物对NH_4+-N的吸附量不随时间变化而变化,基本达到平衡,最大吸附速率均发生在0~5 min内;不同区域表层沉积物NH_4+-N最大吸附速率平均值表现为:外海南部湖心区外海北部草海,最大吸附量平均值表现为:湖心区外海南部外海北部草海,吸附效率平均值表现为:外海北部草海湖心区外海南部;沉积物对NH4+-N的吸附量与NH_4+-N的初始浓度大致呈线性关系,并且低浓度下表现出很好的吸附/解吸特征;滇池表层沉积物NH_4+-N的吸附解吸平衡浓度(ENC0)高于上覆水中NH_4+-N浓度,表明沉积物中NH_4+-N有向上覆水中释放的风险,沉积物在很长一段时间内起到水体污染"源"的作用;ENC0与沉积物中总氮、NH_4+-N含量呈显著正相关,本底吸附量和有机质总量呈显著负相关,沉积物吸附NH_4+-N主要受有机质的影响. 相似文献