青藏高原拉昂错热力分层和混合层深度变化特征观测

湖泊热力结构不仅影响湖泊内部生态环境,而且与区域气象和气候系统相互影响,但目前对湖泊垂直温度的观测研究仍非常匮乏.本研究基于青藏高原拉昂错连续的湖温和气象观测,分析了小时尺度和日尺度热力分层规律和混合层深度的变化特征.结果表明:拉昂错为冷多次完全混合型湖泊;湖表温度8月达到最大值,湖面敞水区和沿岸的湖表温度季节震荡相同,但存在一定的空间差异;与空气温度相比,湖表温度变幅小,降温更慢,峰值滞后约1个月.同时发现,拉昂错混合层深度变化较为规律,辐射和风速是影响湖泊混合层深度的主要外界因子.探明真实的高原湖泊分层规律,有利于提高湖泊模拟能力,为优化湖泊参数化方案提供参考.     

淮河中游本世纪气候与环境波动的湖泊记录证据

为研究本世纪淮河中游气候与环境波支的湖泊沉积响应,１９９１年秋季在女山湖湖心提取了４．８ｍ沉积物。对顶部２０ｃｍ沉积物运用＾１２６Ｐｂ、＾１３７Ｃｓ的年代定位,获得１９０４－１９９１年湖泊沉积物的年序。以此通过高分辨沉积记录的代用标志提取,重建了本女山湖气候与环境的变化过程。结果表明,本世纪最初２０－３０年女山湖地区温度偏低、湿度偏大;４０、５０年代为本世纪温度最高的时段,５０至６０年代中期为延结     

云南程海和阳宗海季节性分层及其消退对冬季水华的潜在影响

基于2014年10月2016年7月在云南程海和阳宗海开展了4个季度(秋季,10月;冬季,1月;春季,4月;夏季,7月)的调查,研究了两个湖泊的水体分层特征,探讨了热力分层及其变化与其他环境因子对浮游植物生物量的潜在影响,结果显示:程海和阳宗海水体分层的特征均为冬季混合、春季形成分层、夏秋季分层稳定,两湖均属暖单次混合型湖泊;程海分层期温跃层的平均深度(顶界)、厚度和强度分别为17.70±3.89 m、5.54±4.44 m和0.67±0.43℃/m,阳宗海的分别为12.53±3.35 m、8.25±4.85 m和0.53±0.43℃/m.在热力分层稳定期,两湖底层达到缺氧甚至厌氧状态,底层的电导率总体较表层高.调查期间,两个湖泊水柱表层浮游植物生物量(以叶绿素a浓度表征)均在冬季出现峰值,程海和阳宗海的分别为19.22±11.08和45.82±9.41μg/L;进一步分析发现,热力分层的消退可能是导致水体表层无机营养盐升高(底层供给)的重要原因,加之适宜的光热条件可诱导两湖冬季水华的发生;在其他季节转化期间,浮游植物生物量变化的主要影响因子亦具有一定的共性及湖泊与季节异质性.     

乌梁素海冰封期湖泊冰盖组构特征对污染物分布的影响

为探究富营养化浅水湖泊季节性冰盖污染物分布规律,于2013-2014年冰封期,钻取乌梁素海湖泊冰盖冰芯试样,观测冰厚并对冰芯晶体结构、气泡含量、污染物浓度(总氮、总磷和COD_(Cr))进行分析.结果表明:冰盖可分为4层,中间2层冰晶体粒径较大且气泡含量较少,为冰盖热力生长区.冰盖以柱状晶体居多,粒径随深度增加而增加,气泡含量随冰盖密度增加而减少.冰盖结构特征与污染物分布具有相关关系,冰芯密度及气泡分布与总氮、总磷和COD_(Cr)相关关系分别为0.8965、0.8718、0.8184,并建立多元回归模型揭示冰封期湖泊水质特征,为季节性湖泊冰盖研究及冰封期湖泊水资源规划和管理提供理论依据.     

湖泊沉积物有机质δ13C所揭示的环境气候信息

根据我国不同纬度和高海拔地区青藏高原东部地区湖泊沉积物有机质δ＾１３Ｃ组成特征的分析,就其揭示的环境气候意义作了探讨。研究表明,湖泊沉积物有机质δ＾１３Ｃ波动间接地反映气候冷暖的波动,但高原与平原地区湖泊沉积物有机质δ＾１３Ｃ值变化具有不同的环境气候意义。这与陆生植物Ｃ３及Ｃ４植物的分布密切相关,据此初步划分为三种有机质δ＾１３Ｃ古气候类型。     

不同时间尺度青海湖沉积物总有机碳对气候变化的敏感性

湖泊沉积物总有机碳（TOC）含量通常作为表征流域和湖泊生产力的指标,在亚洲季风区也常常被当作夏季风的代用指标,被广泛应用于气候与环境变化研究.本文梳理了过去千年、全新世以及冰期-间冰期时间尺度上青海湖沉积物TOC的变化特征,并探讨了其指示气候变化的敏感性与有效性.结果表明,过去千年青海湖沉积物TOC含量与区域暖季温度和降水表现出较为一致的周期性波动.通过对比全新世区域夏季温度、基于孢粉的降水定量重建结果,以及湖泊水位、风沙活动反映的湿度状况等,发现不能简单地将青海湖沉积物TOC含量或沉积通量作为夏季风强度或者季风降水强度的代用指标.青海湖沉积物TOC含量在冰期和间冰期表现出巨大的差异,指示了冰期-间冰期时间尺度上较大的温度与降水变幅.因此,不同地域条件及不同时间尺度下,湖泊沉积物TOC对气候变化的敏感性不同,将湖泊沉积物TOC含量作为亚洲夏季风的代用指标需要特别谨慎,特别是在高寒气候区.     

青藏高原达则错近1000年来生态系统变化及可能机制

在全球变化的背景下,厘清湖泊生态系统对气候环境以及人类活动的响应机制对制定社会的适应政策非常重要.目前的研究手段如现场观测和围隔实验等可以很好地揭示湖泊生态系统在有观测记录以来的演替和变化过程,但是不能提供历史时期湖泊生态系统的变化及其对气候环境变化和人类活动的响应.古湖沼学可以为探讨湖泊生态系统的长期变化及其对气候环境变化的响应提供重要信息.本文以青藏高原中部无鱼湖泊达则错为研究对象,利用沉积物岩芯西藏拟溞（Daphnia tibetana）残体丰度和总烯酮含量重建该区过去1000年的浮游生物记录;利用总氮、总磷以及总有机碳含量重建过去1000年湖泊营养盐以及有机质变化记录;结合烯酮不饱和度重建的古温度记录,探讨达则错过去1000年生态系统变化及其对气候环境演变的响应机制.研究发现达则错湖泊生态系统尤其是生产力在自然状况和人类活动影响下存在显著变化.在自然状况下,较高的湖泊初级和次级生产力发生在温度较低和湖水营养盐浓度较高时;而在过去150年,达则错湖泊环境受到人类活动影响显著,湖泊生产力发生相应变化,较高的湖泊生产力发生在温度较高时期,其主要受由人类活动带来的营养盐元素浓度控制.研究结果表明达则错湖泊生态系统在人类活动影响下发生了显著的改变.     

中国西部湖泊水量对未来气候变化的响应--蒙特卡罗概率法在气候模拟输出的应用

基于CGCM2对未来100年气候的9个模拟试验,对中国半干旱地区青海湖、岱海和呼伦湖及其流域,运用蒙特卡罗分析法模拟湖泊水量对气候变化的响应以及相应的概率.结果表明,从2020s,2050s和2080s三个时期温度增加的发生频率高于75%的分布看,温度将稳定增加2-5℃.未来的年平均温度增幅将超过了过去50年的观测记录,与过去一万年期间高温期的变化幅度相当.三个时期75%以上发生频率的温度和降水变化将会分别引起青海湖流域为-5%至 10%,呼伦湖流域为-7%至 5%,岱海流域为 2%至 12%的降水变化.虽然未来年降水总量的变幅没有超过过去50年器测记录变幅,更不及全新世的降水变化量,但湖泊水量对气候变化的反映变率较变幅要大.模拟的气候变化在75%概率的情况下,未来3个湖泊水量将有累计30%-45%的变化,变幅在±10%之间.快速的湖泊水量变化不能不引起对不远未来的水资源状况的重视和警备.     

湖泊水体微生物四醚膜脂化合物研究进展

来源于微生物膜脂的甘油二烷基甘油四醚类(GDGTs)化合物是近年来被广泛用于古环境定量重建研究的化合物之一,究其原因在于此类化合物对环境响应敏感,特别是温度与pH值等,据此而建立的一系列GDGTs指标有效定量重建海洋、湖泊、泥炭以及土壤等不同沉积载体的环境信息.目前已在全球范围广泛开展湖泊沉积物GDGTs的研究工作,相继建立的全球以及不同区域尺度的湖泊沉积物GDGTs校正方程,已被用于湖泊古环境的定量重建研究,有效记载古湖泊环境变迁信息.相较之下,基于湖泊水体GDGTs的调查工作则起步较晚,但越来越多的研究显示,不同类型湖泊水体普遍贡献GDGTs,然而究竟此类水生来源GDGTs是否与陆源以及湖泊沉积物GDGTs具有类似的分布,以及他们对环境因素的响应如何,这都为湖泊古温度定量重建研究带来不确定性.基于此,本文总结这10年来湖泊水体GDGTs研究工作的进展,首先阐述湖泊水体不同来源(古菌以及细菌)GDGTs的分布情况,研究发现水体不同层位GDGTs浓度以及各组分之间存在差异,并且水深在不同湖泊对GDGTs浓度以及各组分相对比例的影响存在差异.此外还总结湖泊水体中古菌来源isoGDGTs以及细菌来源brGDGTs的生物来源,并进一步分析环境因素对不同深度水体GDGTs分布的影响,虽然温度依然是影响水体中GDGTs分布的首要因素之一,然而湖泊水深、温度以及水体中溶解氧浓度等因素存在着一定的耦合关系,这些因素往往协同作用于水体GDGTs,因此会为评估环境因素对水体GDGTs的影响带来难度.     

基于多源卫星数据扎日南木错湖面变化和气象成因分析

利用Landsat(MSS、TM、ETM+)系列卫星和环境减灾卫星CCD遥感影像数据以及西藏扎日南木错地区近40年(1970-2011年)气象资料,分析湖泊面积的变化特征,并探讨湖泊面积变化的可能气象成因.结果表明,扎日南木错1975-2011年间经历了先萎缩后扩张的过程,湖泊面积呈增长趋势,增长面积为7.08 km2.扎日南木错流域在过去40多年里冰川在退缩,温度升高,降水量增加,而蒸发量和最大冻土深度减少.湖泊面积与年气温之间有显著的正相关关系,气温升高可能是湖面扩大的原因之一.     

Hysteretic freezing characteristics of riparian peatlands in the Western Boreal Forest of Canada

Freezing characteristics were investigated for a sedge covered floating fen and spruce covered swamp located beside a shallow lake in the Western Boreal Forest of Canada. Thermal properties were measured in situ for one freeze‐thaw cycle, and for two freeze‐thaw cycles in laboratory columns. Thermal conductivity and liquid water content were related to a range of subsurface temperatures above and below the freezing thresholds, and clearly illustrate hysteresis between the freezing and thawing process. Thermal hysteresis occurs because of the large change in thermal conductivity between water and ice, high water content of the peat, and wide variation in pore sizes that govern ice formation. Field and laboratory results were combined to develop linear freezing functions, which were tested in a heat transfer model. For surface temperature boundary conditions, subsurface temperatures were simulated for the over‐winter period and compared with field measurements. Replication of the transient subsurface thermal regime required that freezing functions transition gradually from thawed to frozen state (spanning the ?0·25 to ?2 °C range) as opposed to a more abrupt step function. Subsurface temperatures indicate that the floating fen underwent complete phase change (from water to ice) and froze to approximately the same depth as lake ice thickness. Therefore, the floating fen peatland froze as a ‘shelf’ adjacent to the lake, whereas the spruce covered swamp had a higher capacity for thermal buffering, and subsurface freezing was both more gradual and limited in depth. These thermal properties, and the timing and duration of frozen state, are expected to control the interaction of water and nutrients between surface water and groundwater, which will be affected by changes in air temperature associated with global climate change. Copyright © 2009 John Wiley & Sons, Ltd.     

冰川融水对山地冰冻圈冰湖水文效应的影响

冰川融水通过热量、水、物质传输对山地冰冻圈冰湖水文效应产生影响,引起广泛关注.本文从山地冰冻圈冰湖的水量、物理化学性质、生物等方面系统总结冰川融水对冰湖水文效应的影响.冰川融水被冰湖滞留能在一定程度上延缓区域冰川水资源的亏损,但也直接导致了潜在危险性冰湖数量和危险程度增大.冰川融水对冰湖物理性质的影响主要表现在降低湖水温度、影响透明度/浊度、改变湖水密度、造成湖水热力分层现象等方面,对冰湖化学性质的影响主要表现在增加湖水中的氮素、溶解有机物、持久性有机污染物、各类离子和重金属等,进而影响冰湖生物的分布、组成、结构和功能.深入系统地开展冰川融水及其变化对冰湖水文效应研究,对冰川水文与水资源、山地冰冻圈生态环境研究具有重要意义.     

纳木错水温变化及热力学分层特征初步研究

水温变化是湖泊的重要物理特性,对湖泊的水质特征、湖水能量循环、水生生态系统研究具有重要意义.基于不同季节的实地观测资料,分析青藏高原高海拔、深水大湖纳木错的水温变化特征及季节差异,并着重分析湖水热力学分层的季节变化.结果显示纳木错中部、东部两个湖盆冬季封冻,夏季存在稳定分层,春、秋季混合,是一个典型双季对流、完全混合型湖泊.但两个湖盆水温变化与热力学分层又有各自的特征,东部浅湖盆湖水在春季升温快,夏季分层与秋季翻转均比中部湖盆早,且秋季翻转时水温也比中部湖盆高.初步分析认为两个湖盆不同的湖盆形状及水深分布可能是造成其热力学特征差异的主要原因.     

Climate warming alters thermal stability but not stratification phenology in a small north‐temperate lake

Recent climate change represents one of the most serious anthropogenic threats to lake ecosystems in Canada. As meteorological and hydrological conditions are altered by climate change, so too are physical, chemical and biological properties of lakes. The ability to quantify the impact of climate change on the physical properties of lakes represents an integral step in estimating future chemical and biological change. To that end, we have used the dynamic reservoir simulation model, a one‐dimensional vertical heat transfer and mixing model, to hindcast and compare lake temperature‐depth profiles against 30 years of long‐term monitoring data in Harp Lake, Ontario. These temperature profiles were used to calculate annual (June–September) thermal stability values from 1979 to 2009. Comparisons between measured and modelled lake water temperature and thermal stability over three decades showed strong correlation (r² > 0.9). However, despite significant increases in modelled thermal stability over the 30 year record, we found no significant change in the timing of the onset, breakdown or the duration of thermal stratification. Our data suggest that increased air temperature and decreased wind are the primary drivers of enhanced stability in Harp Lake since 1979. The high‐predictive ability of the Harp Lake dynamic reservoir simulation model suggests that its use as a tool in future lake management projects is appropriate. Copyright © 2013 John Wiley & Sons, Ltd.     

Sensitivity of the multiannual thermal dynamics of a deep pre‐alpine lake to climatic change

The study of the multiannual thermal dynamics of Lake Iseo, a deep lake in the Italian pre‐alpine area, is presented. Interflow was found to be the dominant river entrance mode, suggesting future susceptibility of the lake thermal structure to the overall effects of climate change expected in the upstream alpine watershed. A lake model employed the results of a long‐term hydrologic model to simulate the effects of a climate change scenario on the lake's thermal evolution for the period 2012–2050. The model predicts an overall average increase in the lake water temperature of 0.012 °C/year and a reinforced Schmidt thermal stability of the water column in the winter up to 800 J/m². Both these effects may further hinder the deep circulation process, which is vital for the oxygenation of deep water. Copyright © 2014 John Wiley & Sons, Ltd.     

D/H and O/O ratios of water in the crater lake at Kusatsu-Shirane volcano, Japan

The D/H and ¹⁸O/¹⁶O ratios of water in the active crater lake situated on the Kusatsu-Shirane volcano, Japan are about 20 and 6‰, respectively, higher than local meteoric water. The ratios show seasonal variations superimposed on a gradual change over nine years. The isotopic ratios started to increase in early 1990 and decrease in the spring of 1995. The seasonal variation which is high in winter and low in summer correlates with the temperature difference between lake water and ambient air. The large temperature difference in winter enhances the evaporation of lake water and produces the enriched isotopic ratios relative to the ratios in summer. The accumulation of snow and the decrease in the flux of meteoric water into the lake strengthens the winter-time isotopic enrichment. The enriched isotopic ratios of the lake water over a long time result from the addition of an end member with heavy isotopic ratios contained in a thermal fluid supplied to the lake. Considering the water balance in the lake, the isotopic ratios of the thermal fluid were found to be close to the lake water itself, suggesting the circulation of the lake water seeping through lake floor. Based on the correlation between Cl⁻concentration and the isotopic ratios, the contribution by the heavy end member was estimated to be 25–36% relative to the enrichment by evaporation. The heavy end member could be a liquid phase evolved from a parental fluid, which is a mixture of local meteoric water and a magmatic fluid as found in high-temperature volcanic gases.     

Thermal effects of lateral supra‐permafrost water flow around a thermokarst lake on the Qinghai–Tibet Plateau

Both the inflow and outflow of supra‐permafrost water to lakes play important roles in the hydrologic process of thermokarst lakes. The accompanying thermal effects on the adjacent permafrost are required for assessing their influences on the development of thermokarst lakes. For these purposes, the lake water level, temperature dynamics, and supra‐permafrost water flow of a lake were monitored on the Qinghai‐Tibet Plateau. In addition, the spatial and temporal variation of the active layer thickness and permafrost distribution around the lake were investigated by combining ground penetrating radar, electrical resistivity tomography, and borehole temperature monitoring. The results revealed that the yearly unfrozen supra‐permafrost water flow around the lake lasted approximately 5 months. The temperature and water level measurements during this period indicate that the lake water was recharged by relatively colder supra‐permafrost water from the north‐western lakeshore and was discharged through the eastern lakeshore. This process, accompanied by heat exchange with the underlying permafrost, might cause a directional difference of the active layer thickness and permafrost characteristics around the lake. Specifically, the active layer thickness variation was minimal, and the ice‐rich permafrost was found adjacent to the lakeshore along the recharge groundwater pathways, whereas a deeper active layer and ice‐poor permafrost were observed close to the lakeshore from which the warm lake water was discharged. This study suggests that the lateral flow of warm lake water can be a major driver for the rapid expansion of thermokarst lakes and provides clues for evaluating the relationships between the thermokarst expansion process and climate warming.     

The thermal structure of a shallow lake in early winter

The thermal structure of a shallow lake in the first month of its freeze up is shown to vary widely from year to year. The rate of temperature increase at different horizons of the water mass in early winter is evaluated, and warming of shallow and deep-water areas in the lake are shown to be uneven. The distribution of near-bed temperature as a function of water depth in the first weeks of freeze up features wide variations, though this relationship becomes more regular over time. Estimates of the effective thermal diffusivity are given for different seasons. The main periods in the variations in the heat content of water column in early winter are estimated.     

Hydrological and thermal regimes in a supra-glacial lake: Imja,Khumbu, Nepal Himalaya

Abstract

Supraglacial Imja Lake (lake level, 5010 m a.m.s.l.), Khumbu, Nepal Himalaya, has increased its size on the tongue of Imja Glacier since the 1950s. In order to clarify the mechanism of the lake expansion, the physical conditions, water budget and heat budget of the lake were examined by measuring water temperature, water turbidity, lake level, meteorology and water discharge. These measurements were carried out in the monsoon season of July 1997, when the glacier melt occurred in the ablation area with air temperature of more than 0°C. Density stratification in the lake is built up by an effect of water pressure on lake water, but, neglecting the effect, lake water density is defined by suspended sediment concentration rather than temperature. Glacier-melt water from the subaqueous part of the glacier terminus mixed with lake surface water of 4–8°C, and diffused the water of about 3°C into the deeper zone of the lake. This advective, thermal diffusion occurs by sediment-laden underflow and relatively clear density interflow. The sediment-laden underflow is induced by intermittent glacier-melt sediment discharge at the terminus, while the density interflow is probably produced by continuous glacier-melt water discharge. Calculation of water budget of the lake indicates that meltwater inflow at the glacier terminus and surface water outflow at the outlet determine the hydrological conditions of the lake. The net heat transfer by melting of the terminal ice and dead ice, connected to the lake expansion, was evaluated by calculating the heat budget of the lake.