Geoecological Characteristics of Lake Seliger

Data of hydrological and hydrochemical observations conducted in August 2000 at Lake Seliger and its major tributaries are presented. The analyzed characteristics included: O₂, H₂S, CH₄, microelements; mineral and organic compounds of P and N, ionic composition components (HCO₃ ^–, Cl^–, Na⁺, K⁺, dry residue, pH; color index, electrical conductivity. Bottom sediment samples were analyzed for microelement concentrations, CH₄, oil hydrocarbons. The influence of the basin on the ecological state of the lake was assessed, and tendencies in the evolution of its ecosystem are analyzed. It is shown that the ecological conditions of the lake has not changed significantly since 1960–1991, however, nutrient concentrations in the lake water was found to increase.     

Distribution of Heavy Metals in Lake Seliger Bottom Deposits

The distribution of some microelements in the surface and stratified layers of bottom sediments in Lake Seliger is studied. Data on the bottom deposit pollution by heavy metals is used to determine the anthropogenic load on the lake ecosystem. Cd, Zn, and Pb are shown to rapidly accumulate in thick (>1 m) bottom deposits that have formed during the period of lake existence. The concentrations of Cd and Zn are shown to correlate with the organic matter in thick bottom deposits.     

太湖：过去、现在和将来

The presence of roads, farm house foundations, wells and Liangzhu period cultural relics in the bottom of Lake Taihu attest to the fact that this shallow depression was probably dry between 4 and 5 thousand years ago. This interpretation is corroborated by the sudden disappearance of algal pigments at sediment depths carbon-14 dated at 4-5 thousand years before present.In winter, the stronger winds are predominantly from the northeast. These winds result in a powerful counterclockwise current that transports lake sediments and has altered the very shape of the lake over the last 300 years. Winds produce a complex mixing pattern in Lake Taihu with storm induced sediment deposition occurring near the lake''s center.During approximately 240 days of the year, the wind blows across Lake Taihu with sufficient force to mix it to its bottom. As a result, this polymictic lake rarely becomes anoxic and dissolved oxygen at the mud water interface is maintained at or above 4 mg·l^-1. The consequences of this high dissolved oxygen are quite impressive as high organic loading to the lake would otherwise render its bottom waters anaerobic killing many of its natural inhabitants.Because suspended solids reduce (attenuate) light penetration, the major primary production takes place in the top metre of the lake (mean Secchi Transparency-0.25 m). Suspended clays are slow to settle and wind mixing keeps fine-grained suspended solids in suspension in all but the most quiet backwaters of the lake.In the recent past about 23 000 metric tonnes of phytoplankton were produced in Lake Taihu. This large production represents only about 5% of the total influx of organic material entering the lake. In summer and fall, cyanobacteria such as Microcystis spp. and Anabaena spp. dominate most of the lake. Recently, however, mixotrophic flagellates displaced cyanobacteria as the dominant algae in parts of Lake Taihu with high bacteria and high suspended solids (e.g. Wuli and Meiliang Bay). In the future, facultative heterotrophs may come to dominate an ever larger portion of the lake waterc column.     

Past and present state of the ichthyofauna of Lake Lugano

The evolution of the ichthyofauna of Lake Lugano (Lago di Lugano) during the past 120 years is characterized by the introduction of eight new fish species and by the possibly natural addition of the blenny (Blennius fluviatilis) in recent years. Introduced Salmonids such as charr (Salvelinus alpinus) and whitefish (Coregonus sp.) have established strong populations during the first half of this century, but have declined drastically thereafter. Likewise, the population of the native shad (Alosa fallax lacustris) has diminished significantly. A hydroacoustic survey of the pelagic fish stock of Lake Lugano in 1989 revealed the presence of a dense bleak (Alburnus albidus) population at 0 to 14 m depth. No other fish were found to be present in the pelagic zone. Oxygen and temperature distributions seem to confine the bleak to the uppermost layer in summer. In winter, very few fish were located by echosounding. Growth of bleak and roach (Rutilus rubilio) was difficult to interpret since data for comparison are lacking. Growth of perch (Perca fluviatilis) in the littoral zone was found to be slower than in other eutrophic lakes, for no obvious reason. Possible ways of restructuring the pelagic fish community are discussed.     

龙感湖地区近3000年来的气候环境变迁

本文通过分析龙感湖沉积物中的色素、孢粉、硅藻研究结果,探讨该区近３０００年来环境气候波动特点,结果表明：３２００－２４００ａＢＰ,色素含量较高,与温度条件较好有关。该带孢粉浓度也最高,阔叶乔木绎种花粉丰富,湿生及水生植物经常出现。总体上为相对暖湿阶段,其中仍有凉湿波动。２４００－１６００ａＢＰ,具体分为两个阶段,前期约２４００－２０００ａＢＰ,ＣＤ、ＴＤ、Ｍｙｘ含量明显较低,水生、湿生草本减少,气     

Paleomagnetic Logs: A Tool for Dating Lake Erie's Past

An examination of the lithology, paleomagnetic and Mossbauer Effect Spectroscopy (MES) log data and ¹⁴C determinations of cores taken from three small basins located in western Lake Erie, in conjunction with data obtained from earlier studies, has been used to re-evaluate the postglacial history of the area. After the re-advance of the Laurentide Ice Sheet into the Huron basin and the eastern part of the Erie basin during the Port Huron stadial about 13,000 yrs B.P., lacustrine clay was deposited across much of the western Erie basin in a lake ponded against the glacial ice front to the east. However, by 12,000 yrs B.P. as the ice front retreated, the waters from the Huron basin bypassed Lake Erie, first by the Kirkfield outlet to Lake Ontario, and later by the Fossmill and North Bay outlets to the Ottawa River. This resulted in the draining of water from most of the western Erie basin. Extensive swamps choked with plants formed in the small basin areas, and the surrounding low-lying former lake bottom was subjected to subaerial weathering. It would appear that by about 9,500 yrs B.P. there was an increase in surface run off into these basins and the swamps evolved into shallow, relatively warm-water lakes in which calcareous-rich clay was deposited. Isostatic rebound of the northeastern outlets of the Huron basin led to a gradual tilting of the basin and a progressive migration of the southern shoreline of Lake Huron (Lake Stanley phase) to the southwest. By about 5000 yrs B.P. the water level in the southern Huron basin had been raised sufficiently to re-open the Port Huron outlet into the Erie basin. This resulted in a substantial rise in the lake level in the Erie basin, terminated the deposition of calcareous-rich clay in the small basins, and led to the deposition of normal lacustrine sediments in the modern phase of Lake Erie.     

洞庭湖近几十年来湖盆变化及冲淤特征

洞庭湖是我国著名的五大淡水湖泊之一,位于长江中游荆江段南岸,湖南省境内.历史时期,曾经是我国第一大淡水湖,直至新中国成立初期,湖泊面积仍然有4350km2,居我国淡水湖泊之首位.但由于洞庭湖承纳“四水”,吞吐长江,长江大量水沙涌入洞庭湖,造成了湖盆迅速淤高,加之由此诱发的人类大规模地湖泊垦殖活动,湖泊急剧萎缩.目前,洞庭湖已退居鄱阳湖之后,为我国第二大淡水湖泊.湖泊的严重泥沙淤积,已经造成了湖泊调蓄长江中游洪水功能的严重衰退,不但危及湖南省的防洪的安全,而且危及长江中下游地区的防洪安全,研究洞庭湖的湖盆冲淤演变具有重要意义.本文根据1974、1988和1998年洞庭湖125000水下地形资料,并针对洞庭湖具有显著上下游水位落差的实际,分不同高程和不同水位情况下,分析洞庭湖湖泊面积和容积演变特征,探讨洞庭湖近几十年来的湖盆变化及冲淤规律,试图揭示洞庭湖湖泊调蓄能力的变化过程.     

太湖14000年来古环境演化的湖泊记录

Two sediment cores, one 396 cm long from west Taihu Lake, another 246 cm long from east Taihu Lake, are interpreted from the analysis of their magnetic susceptibility, total organic carbon, total nitrogen, total pigments, organic carbon isotope, hydrogen index, saturated hydrocarbons, ¹⁴C dating and surficial sediment conditions. The west Taihu Lake core is the longest one studied in this lake so far, and has provided us the most complete environmental and climatic information for this lake. The results from the west Taihu lake core indicate that Taihu Lake has undergone the following stages:from ca.14 300 to 13 300 aB.P. Taihu Lake was in low lake-level, and there existed exposed features from the proxies reflecting arid paleoclimate. From ca.13 300 to 12 400 aB.P. an arid transitional stages occurred with a slightly warmer and wetter climate. From ca. 12 400 to 10 900 aB.P. a period of large climatic fluctuation occurred and from 10900-10 000 aB.P. a warm period developed with deep water and strongly reducing sediments. During ca.10 000-7 200aB.P., a cool transitional period alternating with a warm climate occurred. It was warm and wet during 7 200-5 700aB.P.; some proxies changed violently in 5 050aB.P., reflecting obvious changes in material source and a probable interruption of sedimentation. The east Taihu Lake history from ca. 6 550 to 6 450 aBP, the climate was cold and dry, and gradually turned warm and wet in ca. 6 450-6 050 aBP. It was warm and wet in ca. 6 050-5 800 aBP and had a cold tendency in 5 800-ca. 5 000 aBP. An abrupt change occurred at ca. 5 000 aBP, and the lake sediment in the uppmost part was disturbed by wave action indicating shallow water conditions.     

青海湖近900年来气候环境演化的湖泊沉积记录

通过对青海湖沉积物碳酸盐含量、磁化率、TOC等多环境指标的分析,探讨了青海湖地区近900年来的气候环境演变。结果表明青海湖地区近900年来气候变化属于暖干－冷湿的气候演替类型,经历了5次冷湿期和5次暖干期,中世纪暖期、小冰期以及20世纪以来的升温在该沉积岩芯有清晰的记录。沉积物的磁化率和沉积速率的变化忠实地记录了本世纪以来人类活动的影响。     

青海湖最近25年变化的遥感调查与研究

青海湖是我国最大的内陆水体,它及其流域的生态环境近来一直倍受广泛关注．其水位下降、湖水面积缩小、湖体分离等更是研究的热点问题．本文针对这些问题展开遥感调查与研究,收集了多时相、多种信息源的影像数据;分析了1975年至2000年25年以来湖泊的变迁及成因,湖岸变化及湖体分离状况;用遥感方法反推25年以来湖水位的变化;计算了1975、2000年两个年份的湖水面积,并遥感分析了湖水面积萎缩的原因．此外,对青海湖进行了实地调查与水深测量,建立了该湖泊水深反演模型．     

近50年来洞庭湖区的内湖变化

洞庭湖区除洞庭湖外,在圩垸内尚分布着为数众多的内湖,近50年来,由于人类活动的强烈作用,内湖与洞庭湖一样呈现出急剧萎缩的态势,1km2以上内湖的数量由20世纪50年代的255个减少到目前的122个,湖泊面积也由1534.4km2缩小至644.2km2,其衰亡的速度甚至超过了洞庭湖.分析洞庭湖区内湖急剧萎缩的原因,其主要表现为前期是围湖造田,后期为湖泊鱼塘化.     

2600年以来台湾大鬼湖中的金属通量

Sediment cores were collected from the remote subalpine Great Ghost Lake in southern Taiwan. Because the lake is anoxic the sediments are well preserved, distinctive past variations can be dated accurately. The vertical distributions of total and acid-leached metal concentrations for aluminum, arsenic, cadmium, cerium, chromium, cesium, copper, iron, magnesium, manganese, nickel, lead, rubidium, strontium, vanadium and zinc are measured and the fluxes determined. The dates of higher fluxes in the past 2600 years seem to correlate with dry spells. Further, trace metal fluxes show a large increase but Pb-206/Pb-207 ratios show a large decrease since 1950, suggesting a significant anthropogenic input.     

岱海地区近400年来的"尘暴"事件——来自岱海沉积物粒度的证据

根据高分辨率的岱海沉积物粒度分布的中值粒径和粗颗粒含量,结合区域降水、历史记载资料,重建了内蒙古岱海地区近４００年来发生的尘暴事件。结果表明,尘暴事件是受冬、夏季风的相对强弱制约的,大量尘暴事件频发于小冰期干冷的气候条件下,表现为中值粒径大,粗颗粒含量高,在转暖的现代气候下,尘暴事件很少,中值粒径也随之降低,但是近十几年尘暴事件又呈上升趋势,部分可能与人类活动造成的土地荒漠化有关。     

近30年来太湖流域湖泊岸线形态动态变化

湖泊的岸线特征是表征湖泊形态特征的一项重要内容．本文应用分形理论中的计盒维数,基于岸线长度与面积 关系的分形维数及岸线发育系数,对太湖流域主要湖泊的湖泊岸线变化进行了研究．结果表明,分形维数可以更好的对 湖泊岸线进行量化描述,太湖流域主要湖泊的岸线具有自相似性;近30年来,太湖流域湖泊的岸线曲折度降低,岸线长度 减少,岸线结构趋于单调．     

洱海地区一万多年以来气候环境演化的湖泊沉积记录

根据对洱海北部10．8m深水区ES孔沉积物高分辨率的孢粉、粒度、碳屑、藻类分析,结合AMS^14C测年数据,划分了11个阶段,恢复了一万多年以来云南洱海地区气候环境演化序列．全球性的降温事件在该地区都有明显的反映,包括9900aBP(Younger Dryas)、8500aBP、7100aBP、5100aBP左右的四次冷事件,6800—5500aBP为全新世水热配置最佳期,距今2400年开始该地区出现较为明显的人类活动．     

基于遥感技术的太湖近15年面积动态变化

本文利用80年代后期以来不同时期的LANDSAT卫星遥感图像,研究了近15年太湖的面积变化状况。研究结果表明:从1988年到2003年的15年来,太湖面积共减少9.0226km2,其中湖泊围垦了4.4584km2,湖滩地面积0.6968km2,取土围堰面积3.8674km2.     

Environment Variation in North Margin of East Asian Summer Monsoon Record in Dali Lake over Past 168 Years

Water Resources - Lakes close to the limit of East Asia summer monsoon (EASM) are sensitive to the climate changes, which record significant information about environmental changes and human...     

近2600年来内蒙古居延海湖泊沉积记录的环境变迁

根据东居延海Ｓ１孔湖泊沉积柱状岩芯的多环境指标分析结果,将近２６００年来湖泊沉积物记录的环境演化过程分为十个阶段,湖泊沉积记录的气候组合特点具有冷湿→暖湿（冷干）→暖干→冷湿的过程,现阶段处于暖干阶段,预测未来气候向偏湿方向变化。近２６００年来自然的气候变化在居延海湖泊环境演化中居于主导地位,而人类活动只在特定时段对湖泊环境产生较大影响。     

近2000年来杭州西湖藻类种群的演替与富营养化的发展过程

于１９９１年在西湖底作１５个深度１ｍ左右的钻孔,根据其内微分石藻的垂直分布探索西湖近２０００年藻类种群的演替,并藉此反映湖泊的古生境及其富营养化发展的历程,结果显示淡水西湖形成后藻类的垂直分布由下而上可分为３带：（１）附生藻带（短缝藻－桥穹藻－异极藻组合）：－８５ｃｍ至－４５ｃｍ,以喜酸性及真酸性的附生藻为主,适应于当时的沼泽生境。（２）附生藻向浮游藻过渡带（水花束丝藻－直链藻组合）：通常在－３０