150年来青藏高原南红山湖的介形类与环境变化

青藏高原西北部南红山湖2孔湖芯沉积物中的介形类动物群计有4属4种,据其分布特征划分出5个组合,各组合间的差异表现在介形类动物群丰度和每个种的丰度变化以及特征种的出现。通过分析介形类属种生态特征和组合变化对150年来的南红山湖环境变化进行了探讨。分析结果表明:1884年前为有缓慢水流注入的滨岸浅水期;1885～1970年间为湖水相对温暖期,在这期间湖泊环境仍有次一级的变化,其中,1885～1905年湖面迅速抬升,水深增大,水温也较高,1923～1944年为湖水温度另一个稍高期,1961～1969年湖面再次出现明显上升;1970年以来湖泊退缩、咸化。     

两个相连湖泊的微生态系统——云南高原湖泊中浅水的星云湖和深水的抚仙湖研究

抚仙湖是中国云南省的一个深水湖，连接着富营养化的浅水湖－－星云湖，星云湖排放含绿藻的水进入抚仙湖。两湖位于省会昆明附近，由于地方文化、集约化农业、以及旅游业的发展，两湖已经富营养化。因为湖泊体积容量的级别差异，深水湖的富营养化几乎没被注意，抚仙湖秋季下层滞水带缺氧已经关注了20年，似乎下层滞水带是深水湖富营养化的指标或趋势。抚仙湖看起来目前情况尚好，可以说寡营养，然而，外界负荷是潜在的，且是以稳定的加速度进行的。在此对浅水湖富营养化的原因进行了讨论，包括在其它云南湖泊观察到富营养化的过程，再者，对两个连相湖的藻和蓝藻碎片的大小构成进行比照。为了与深水的抚仙湖状况进行比较，简略介绍了一个日本的深湖及其径流系统。其中，涡流和它的微生态系统，在两者中相关性很好。对于以涡流生态系统的见解判断微生态系统的深水湖富营养化问题将给予概括。     

历史时期(1803～1958年)西藏水灾分析

分析了现有灾异史料所覆盖时段（1803－1958年）西藏水灾的时空变化特征。研究指出：①1803－1958年，西藏水灾发生（县）次数波动比较大；19世纪40－80年代为西藏的水灾多发期；1924、1954年为严重水灾发生年；②西藏水灾空间分布差异显著，主要分布在“一江两河”地区。其中，日喀则、山南地区的水灾（县）次最多，其次为拉萨市、林芝地区，昌都、阿里、那曲地区则水灾发生相对较少；③高强度的持续降水为西藏水灾发生的关键诱导因子，河流暴涨、漫溢、改道为重要媒体，山崩、雪崩、山洪及泥石流等要素为特定地貌条件下的主要致灾因子，雹灾、地水上涌等也是不容忽视的致灾因子；④19世纪40－80年代西藏气候湿润。     

2500年来艾比湖的环境演变信息

通过对艾比湖缘1，8m浅孔的沉积相和孢粉组合，结合14C测年资料分析。指出近2500年来艾比湖的沉积环境总体是比较稳定的，但由于气候波动引起艾比湖水位曾发生较明显的变化。约在公元前300～400年，是艾比湖面积缩小时期；约公元前300—公元300年，即东周末至西晋，是艾比湖水位较高时期；约公元300—1400年，即东晋至15世纪初，是艾比湖的高水位时期；约15世纪初至17世纪中是艾比湖的水位下降期，但水位比现代仍然高；约17世纪中至19世纪初的小冰期是艾比湖的水位上升期。研究还提供了历史时期湖泊的盐度变化和湖周发生大火的信息。     

近150a来南红山湖的地球化学特征及环境意义

通过对西昆仑山南红山湖的沉积地球化学特征的分析，恢复了南红山湖区近150a来的环境变化。19世纪50年代初－19世纪80年代中期，气候受小冰期末次波动的影响，以冷湿为特点。19世纪80年代中期－1997年，处于小冰期后回暖期，以暖干趋势为主。其中19世纪80年代中期－20世纪20年代初，以暖干为特点；20世纪20年代初－20世纪中叶，气候较干燥，而且温度与湿度的结合较复杂，属于冷干－暖湿交替的气候类型；20世纪中叶－1997年，气候总特征以暖干为主，尤其是1990年以后，温度升高趋势明显，气候干燥。从近150a湖泊变化的整体趋势看，随着时间的推移，南红山湖在逐渐萎缩。就湖区的气候变化与西昆仑山古里雅冰芯所恢复的气温、降水变化及与较近的两个站点的气象记录进行了对比，认为该地区与古里雅冰芯地区受相同的气候系统控制；高原上区域间存在气候差异；应开展多尺度、高分辨率的多种代用资料的研究。     

西藏山南地区沉错湖泊与径流水化学特征及主控因素初探

选取枪勇冰川径流-卡鲁雄曲（河）-沉错（湖）为研究区域,开展高原湖泊及其补给河流与冰川径流的水化学特征研究,并探讨影响主离子组成的主控因素。结果表明：夏季湖水主要离子呈均匀混合状态,pH值、电导率、TDS及优势阴阳离子在整个湖泊空间上变化不显著;总体上,从上游冰川融水径流、河水至下游湖泊,离子浓度呈现上升趋势;融水径流及河水的水化学类型主要受岩石风化作用控制,表现为SO₄^2--Ca²⁺-Mg²⁺类型;沉错湖水的水化学类型主要受蒸发结晶作用控制,表现为SO₄^2--Na⁺-Ca²⁺类型,在蒸发作用下Ca²⁺逐渐沉淀析出,Na⁺浓度不断升高而成为绝对优势阳离子。     

南极拉斯曼丘陵湖泊水化学特征

本文介绍南极拉斯曼丘陵湖泊水化学特征。对１３个湖泊的调查和统计分析表明，湖水以Ｎａ＋和Ｃｌ－为主要优势离子，不含有ＣＯ３２－离子，营养物质（Ｎ、Ｐ、ＳｉＯ２）在湖水中普遍偏低，而且湖水和雪样无机氮组分均以ＮＨ４＋为主，水化学类型比较单一，都属氯化物Ｎａ＋型贫营养水体。Ｎａ＋、Ｃｌ－、ＳＯ４２－的高浓度，特别是Ｂｉｇ湖、莫愁湖和Ｈｅａｒｔ湖水中离子含量明显的高，指示拉斯曼丘陵地区的降水来源以海洋气团为主，并受海洋环境影响强烈。微量元素分布在０．０１～２．０μｇ／ｌ之间，接近于水圈这些元素的浓度值。     

青藏高原近40年来气候变化特征及湖泊环境响应

以青藏高原52个气象台站1971-2008年的逐月气温、降水资料为基础,采用因子分析、气候趋势分析、气候突变分析等方法,对高原内部不同区域的气候变化特征进行研究,并讨论了高原湖泊环境对气候变化的响应。结果表明,近40 a来,青藏高原各区域年平均气温整体持续上升,柴达木地区增温尤为显著,年平均气温增长率达0.49℃/10a;1987年和1998年各区域气温普遍由低向高突变,1998年以来增温尤为显著。年可利用降水的变化特征存在区域差异,柴达木地区、藏北南羌塘高原东部地区整体增湿。除藏东地区,青藏高原其它地区气候条件于20世纪末21世纪初由暖干向暖湿转变,受其影响,以青海湖、鄂陵湖、冬给措纳、兹格塘错为代表的高原大型湖泊表现出水位上升、湖水离子浓度减小的特征,反映了气候暖湿条件下湖泊水量的增加。     

封面照片:泸沽湖

被誉为高原明珠的泸沽湖位于青藏高原东部、川滇之间的万山丛中,为川滇两省共有,属四川省盐源县和云南省宁蒗县管辖。泸沽湖呈近圆形,水面面积大于50 km2,其中四川境内约占总面积的2/3,云南约占总面积的1/3。该湖为高原淡水湖泊,由地质构造运动形成的断裂下陷作用形成;湖面海拔大于2 680 m,平均水深约40 m,系深水湖泊;湖的基底是二叠系火山岩,湖中央残山由二叠系玄武岩构成,湖滨山脉由二叠系玄武岩和下二叠统-石炭系碳酸盐岩等岩石构成,湖周围山上喀斯特洞穴发育。湖水的补给主要来自大气降水(雨、雪等),其次为少量地表水及喀斯特地下水。封面照片:泸沽湖@山水     

可可西里地区库赛湖变化及湖水外溢成因

以库赛湖研究区地形图、Landsat TM/ETM+和中国环境与灾害监测预报卫星HJ1A/BCCD影像为基础,结合五道梁气象站气温降水资料,利用地理信息技术和数理统计方法,对2011 年9 月可可西里地区库赛湖湖水外溢成因进行分析。结果表明,库赛湖湖水外溢发生在2011 年9 月20 日至30 日期间,卓乃湖湖水进入库赛湖是后者发生变化的直接原因,而库赛湖规模近20 年来的持续增长,尤其是2006 年之后湖泊面积快速增加是其湖水外溢的基础。卓乃湖湖水外泄的主要诱因是区域持续降水,其中8 月17 日和21 日强降水使卓乃湖于8 月22 日出现漫顶溢流,8 月31 日至9 月5 日、9 月16 日至17 日期间两次持续降水导致卓乃湖水量剧增,并在9 月14 日至21 日期间形成洪水。由于水量外泄,卓乃湖面积骤降,截至11 月29 日,湖泊面积168.07 km²,仅为8 月22 日湖泊面积的62%,共减少104.88 km²。库赛湖外溢湖水流入海丁诺尔后又进入盐湖,其中海丁诺尔湖水进入盐湖时间介于10 月6 日至20 日期间。外来湖水大量进入导致海丁诺尔和盐湖在10-11月份快速扩大。     

The ostracod assemblages and their environmental significance in the Chen Co area, southern Tibet in recent 1400 years

The CC1 core, with a length of 216 cm, was drilled in the west part of the Chen Co (Lake) in southern Tibet Plateau. The 210Pb and 137Cs measurement indicated that it was a consecutive sedimentary sequence since ca. 1400 years. The ostracoda and their assemblages under the level of 1 cm samples' cutting interval were finished for this core to reveal the past environmental changes in the lake area. A total of 15 species of ostracods belonging to 7 genera in the core sediments had been identified. According to the ostracod distributions, abundances and preservations in the core, seven ostracod assemblages had been distinguished. The ostracod assemblages and their ecological features, together with the sediments dating decision were used to infer the past ca. 1400 years environmental changes of the Chen Co environmental evolutions in three stages, which had responded to the Medieval Ages Warm-period (MAW), the Little Ice Age (LIA) and modern warm period. The results show that the changes of the Chen Co environment had been mainly influenced by the climatic variations. The trend of the lake level fluctuations had been accorded with that of climatic variation during the past 1400 years.     

The ostracod assemblages and their environmental significance in the Chen Co area,southern Tibet in recent 1400 years

The CC1 core, with a length of 216 cm, was drilled in the west part of the Chen Co (Lake) in southern Tibet Plateau. The²¹⁰Pb and¹³⁷Cs measurement indicated that it was a consecutive sedimentary sequence since ca. 1400 years. The ostracoda and their assemblages under the level of 1 cm samples’ cutting interval were finished for this core to reveal the past environmental changes in the lake area. A total of 15 species of ostracods belonging to 7 genera in the core sediments had been identified. According to the ostracod distributions, abundances and preservations in the core, seven ostracod assemblages had been distinguished. The ostracod assemblages and their ecological features, together with the sediments dating decision were used to infer the past ca. 1400 years environmental changes of the Chen Co environmental evolutions in three stages, which had responded to the Medieval Ages Warm-period (MAW), the Little Ice Age (LIA) and modern warm period. The results show that the changes of the Chen Co environment had been mainly influenced by the climatic variations. The trend of the lake level fluctuations had been accorded with that of climatic variation during the past 1400 years.     

藏南沉错沉积物的粒度特征及其古环境意义

通过对藏南沉错粒度参数的分析 ,并结合与其它环境代用指标的比较 ,可以将本地区约 1 40 0年来环境变化分为四个阶段 :约 5 93A.D.～ 82 1 A.D.是湖泊水位相对较高而且变化频繁的时期 ,反映了波动较大且比较湿润的气候状况 ;约 82 1 A.D.～ 1 343A.D.是一个较长的气候相对稳定时期 ,粒度指示该阶段湖泊扩张 ,湖面升高 ,反映了湿润的气候状况 ;约 1 343A.D.～ 1 892 A.D.是一个气候波动十分剧烈且频繁的时期 ,其中约 1 60 2 A.D.前后可能出现了一次短时间的流水突然增加 ,而在这前后各有一个浅水阶段 ( 1 343A.D.～ 1 5 1 2 A.D.和 1 670 A.D.～ 1 892 A.D.) ,反映了湖泊补给程度的减弱 ;1 892 A.D.～1 998A.D.是一个相对稳定的时期 ,湖面变化不太明显 ,而 1 892 A.D.前后具有一个明显的补给水动力减弱的变化。粒度参数所反映的湖面波动与环境变化得到了其他环境代用指标较好的支持。     

1400-year cold/warm fluctuations reflected by environmental magnetism of a lake sediment core from the Chen Co, southern Tibet, China

Lake Chen Co, situated at 90°33–39E, 28°53–59N with a lake level of 4420 m asl, is an enclosed lake with 148 km² of catchment area and 40 km² of lake surface. It is mainly supplied by glacier melt water either from surface inflow or groundwater. Atmospheric precipitation is mainly concentrated in June–September. A 216-cm long lake sediment core was obtained at a site with 8 m of water depth, 800 m from the lakeshore and 1.5% of the bottom slope in this lake. The sediment core was taken by a piston sampler and was sliced with an interval of 1 cm each. ²¹⁰Pb dating measurement suggested that the average sedimentary rate was 0.16 cm yr^–1, which also was confirmed by ¹³⁷Cs peak occurrence. Magnetic analyses included low-frequency dependent susceptibility (_LF), susceptibility of anhysteretic remanent magnetism (_ARM), the saturation isothermal remanent magnetism (SIRM), the isothermal remanent magnetism (IRM) reverse and Soft and Hard contents were performed for the sediment core. Results showed that _LF was an index for reflecting the environmental conditions, but was not sufficient to reveal details of magnetic features. This had been proved by measurements of IRM Reverse percentage and Soft and Hard magnetic minerals values. The log(SIRM/_LF) had much more information to reveal environmental changes. The _ARM/_LF might be more sensitive to the local environmental conditions because it was well able to indicate the grain-size variations of magnetic particles. In the past ca. 1400 years, the warm stages were ca. 620–740 AD, 1120–1370 AD and since ca. 1900 AD. After an intensively cold stage during ca. 1550–1690 AD, a cold-humid stage from ca. 1690–1900 AD and a warm-dry stage since ca. 1900 AD followed. Among these stages, the warmest one occurred in ca. 1120–1370 AD and the coldest stage was between ca. 1550 and 1690 AD. This result might be compared with many other research results from lake cores, ice cores and the Chinese historical documents.     

Acidification and metal contamination in Whitepine Lake (Sudbury,Canada): a paleolimnological perspective

Diatom and chrysophyte assemblages from a sediment core from Whitepine Lake were examined to infer changes in lakewater pH, nickel and aluminum concentrations since pre-industrial times, and to help determine the cause of the virtual extirpation of the lake trout population from the lake during the 1960s and 1970s. Our study indicates that acidification started in the 1920s, and that the maximum inferred pH decline (from 6.2 to 5.8) occurred between 1960 and 1970, coincident with the peak in metal mining and smelting activity in the Sudbury basin. Lakewater [Al] and [Ni], as inferred from our diatom transfer functions, increased. It appears that in addition to the pH decline, elevated [Al] may have played an important role in the decline of lake trout from Whitepine Lake in the 1960s and 1970s. Diatom-inferred lakewater pH and [Ni] have recovered slightly in the recent sediments, which coincides with reductions in emissions that have occurred since the mid-1970s.     

Limnological responses to warming on the Xizang Plateau,Tibet, over the past 200 years

Paleolimnological analyses can be used to evaluate limnological responses to changing climate over decadal to centennial timescales, especially in regions with sparse lake monitoring data. We used a training set with 90 lakes to develop a diatom-based conductivity transfer function and address climate-driven changes in lakes on the Qinghai-Xizang Plateau, Tibet. This new training set is an expanded version of a previous model (Yang et al. in J Paleolimnol 30:1–19, 2003) and shows improved performance statistics for the conductivity model. The expanded training set also contains diatom species not previously identified from the region, such as Stephanodiscus sp. and Cyclotella sp., which are common eutrophic indicator species in other regions, but can also be influenced by water column conductivity. The new conductivity transfer function was applied to Lakes Nam Co and Chen Co in Tibet. Recent conductivity inferences were compared with climate data from the Dangxiong weather station and water level records from Yangzhuyong Co, which show increasing temperature and lower water levels, respectively, since AD 1960. Other studies showed that the water balance for many lakes on the Qinghai-Xizang Plateau is complex, affected by both evaporation and glacial melting. Our paleolimnological reconstructions, which include sediment particle size data, indicate that over relatively short timescales glacial meltwater can influence lake hydrology, but over decadal timescales, increases in evaporation, driven by rising temperatures, dominate. Our findings suggest that regional warming is lowering water levels at these sites and will continue to do so given predicted future climate warming.     

Geochemical processes in a Mediterranean Lake: a high-resolution study of the last 4,000 years in Zoñar Lake,southern Spain

High-resolution geochemical analysis of a 6-m-long sediment core from Zoñar Lake, southern Spain, provides a detailed characterization of major changes in lake and watershed processes during the last 4,000 years. Geochemical variables were used as paleolimnological indicators and complement Zoñar Lakes’s paleoenvironmental reconstruction based on sedimentological and biological proxies, which define periods of increasing allochthonous input to the lake and periods of dominant autochthonous sedimentation. Chemical ratios identify periods of endogenic carbonate formation (higher Ca/Al, Sr/Al and Ba/Al ratios), evaporite precipitation (higher S/Al, Sr/Al ratios), and anoxic conditions (higher Mo/Al, U/Th ratios and Eu anomaly). Higher productivity is marked by elevated organic carbon content and carbonate precipitation (Mg/Ca). Hydrological reconstruction for Zoñar Lake was based on sedimentological, mineralogical and biological proxies, and shows that lower lake levels are characterized by Sr-rich sediments (a brackish lake with aragonite) and S-rich sediments (a saline lake with gypsum), while higher lake levels are characterized by sediments enriched in elements associated with alumino-silicates (Al, K, Ti, Fe, trace and rare earth elements), reflecting fresher conditions. Geochemical indicators also mark periods of higher detrital input to the lake related to human activity in the watershed: (1) during the Iberian Roman Humid Period (650 BC–AD 300), around the onset of the Little Ice Age (AD 1400), during the relatively drier Post-Roman and Middle Ages (AD 800–1400), and over the last 50 years, due to mechanized farming practices. Heavy metal enrichment in the sediments (Cu and Ni) suggests intensification of human activities during the Iberian Roman Period, and the use of fertilizers during the last 50 years.     

Recently induced anoxia leading to the preservation of seasonal laminae in two NE-German lakes

The recent sediments of two lakes in the NE German lowland became seasonally laminated at different times. Anoxic bottom conditions resulted from a surplus of organic matter (OM), in the early stage indicated by irregularly laminated sediments comprising abundant iron-sulfide framboids. Their diagenetic formation predates the preservation of biochemical calcite varves. In the larger, deeper Lake Tiefer See near Klocksin, anoxia developed stepwise. A first anoxic pulse was contemporary with inflow narrowing by railway-dam construction and accumulation of OM. It was favored by a decrease of the intensity of lake circulation (turnover). Nutrients introduced from artificial fertilizer then increased the primary production (diatoms) to the point of OM surplus and seasonal laminae formation started 40 years later in 1924. In the smaller, shallower Lake Tiefer See in the Uckermark, a massive pulse of iron sulfide was centered around 1960, seven years after installation of piped field drainage into the lake. Anoxia developed rapidly with the nutrients drained from a fertilized groundwater catchment that is 10 times larger than the surface catchment, while surface erosion was reduced. Reducing bottom conditions became regular and the seasonal lamination was preserved after 1967. Morphological criteria to screen lakes for varved sediments should include reductions of natural lake inflow and catchment increase, such as by inflow of field drainage. Similar developments of increased nutrient input or intensity decrease of lake circulation may result from historical human activities but also from natural processes.     

Evidence for short-lived oscillations in the biological records from the sediments of Lago Albano (Central Italy) spanning the period ca. 28 to 17 k yr BP

We report the results of analyses of pigments (derived from algae and photosynthetic bacteria), diatoms and invertebrate fossil remains (ostracods, cladocerans, chironomids) in two late Pleistocene sediment cores from Lago Albano, a crater lake in Central Italy. The record contains evidence for oscillations in lake biota throughout the period ca. 28 to 17 k yr BP. The earliest of these are contained in the basal 3.5 m of light olive-gray and yellowish-gray spotted muds sampled in core PALB 94-1E from 70 m water depth. The later oscillations are best represented in the more extended sediment sequence recovered from a second core site, PALB 94-6B, in 30 m water depth. The sediments at site 1E, containing the earlier oscillations (ca. 28-24 k yr BP), predate any sedimentation at the shallower site, from which we infer an initially low lake level rising to permit sediment accumulation at site 6B from ca. 24 k yr onwards. At site 6B, massive silts rich in moss remains are interbedded with laminated silts and carbonates. These sediments span the period ca. 24 to 17 k yr and are interpreted as representing, respectively, times of shallow water alternating with higher lake stands, when the lake was stratified and bottom water was stagnant. A range of mutually independent chronological constraints on the frequency and duration of the oscillations recorded in the lake biota indicate that they were aperiodic and occurred on millennial to century timescales. We interpret them as responses to climate forcing through its impact on lake levels and changing aquatic productivity. The time span they occupy, their frequency and their duration suggest that at least some of these changes may parallel both the Dansgaard-Oeschger events recorded in Greenland Ice Cores and the contemporary oscillations in North Atlantic circulation documented in marine sediment cores.     

藏南沉错湖泊三角洲的沉积相及沉积环境

在西藏自治区沉错湖泊三角洲平原和湖内钻孔取芯 ,利用14 C和ESR测年方法建立了钻孔剖面的年代标尺。在岩芯描述、沉积物粒度分析和CaCO3含量分析基础上 ,对沉错湖泊三角洲的沉积环境和沉积相进行了解释分析。 36 7m长的岩芯大致记录了 5 5万年以来的沉积历史。全孔平均沉积速率约为 0 6 6 7mm/a。 16 92 0aBP以来三角洲的沉积速率较大 ,平均为 1 2 7mm/a。由于沉积物物质来源的多源性导致CaCO3在剖面上的无规律性变化。但是 ,沉积物粒度和沉积序列变化指示全套沉积由底部的冲积扇相向上过渡为水下扇亚相和三角洲沉积相。在大约 175 0 0aBP～ 14 0 0 0aBP时期 ,沉错存在高湖面阶段。沉积序列中记录了末次冰期最盛期 (LastGlacialMaximum )和新仙女木事件 (YoungerDryas)。沉积特征和沉积环境的变化主要受湖面涨缩变化所控制。而湖面升降变化的驱动因素主要为气候 ,尤其夏季风的强弱和冷事件