沉积色素已经成为反映浮游植物生物量和群落结构的有效指标,被广泛应用到研究过去湖泊和海洋生态系统初级生产力变化及其对气候变化与人类活动的响应中.但是由于色素的特殊化学属性,不同的提取和分析方法对不同介质中的色素具有明显的选择性.因此,在不同区域,为获得浮游植物生物量和群落结构等信息,需要选择合适的色素提取和分析方法.本文利用L9（3^4）正交实验方案,对青藏高原中部典型半对流型湖泊（达则错）和双季对流型湖泊（江错）表层沉积物进行对比研究,选择适用于青藏高原湖泊沉积色素的提取和分析方法.对比发现提取试剂的类型及含量、色谱柱和流动相分别是影响湖泊沉积色素提取与分析过程中的关键因素.利用丙酮：甲醇：水混合试剂（80：15：5,体积比）,冰浴超声30s并低温静置6h对于青藏高原湖泊沉积色素提取具有最佳提取效率.在进行色素分析时,反相高效液相色谱（RP-HPLC）系统中采用Eclipse Plus C8色谱柱（150mm×4.6mm,粒径为3.5mm）,流动相A为甲醇：乙腈：0.25m吡啶（50：25：25,体积比）;流动相B为甲醇：乙腈：丙酮（20：60：20,体积比）,流动相A的pH利用醋酸调节为6,柱温保持40℃时,色素分离效果最好.本研究为进一步利用青藏高原湖泊沉积色素研究湖泊初级生产力变化和湖泊生态系统对气候变化和人类活动的响应提供了实验基础.
Widespread lakes on the Tibetan Plateau(TP)are valuable archives for investigating climate and environment changes, which could provide essential information on the mechanisms of past climate changes on the TP and their interaction with the global climate systems.However, there is a lack of in-depth investigation of modern limnological processes in the Tibetan lakes, which hampers the understanding of paleolimnological records and lake ecosystem succession. In this study, we performed continuous temperature monitoring at two lakes, Bangong Co, a freshwater lake in the western TP, and Dagze Co, a brackish lake in the central TP, in order to characterize the patterns of seasonal temperature variability, stratification,and mixing. Temperature data for an entire hydrological year demonstrate that Bangong Co is a dimictic lake and that Dagze Co is a meromictic lake. The higher salinity in the deep water at Dagze Co prevents the lake from overturning completely, and this finding is supported by simulations using a physical limnological model Lake Analyzer. Continuous lake water temperature monitoring provides fundamental data for classifying Tibetan lakes, as well as the hydrological basis for understanding their paleolimnological records and ecosystem succession.
Both monsoons and westerlies have exerted influence on climate dynamics over the Tibetan Plateau(TP) since the last deglaciation, producing complex patterns of paleohydroclimatic conditions. Diverse proxy records are essential to forge a robust understanding of the climate system on the TP. Currently, there is a general lack of understanding of the response of inland lakes over the TP to climate change, especially glacier-fed lakes. Paleohydrological reconstructions of such lakes could deepen our understanding of the history of lake systems and their relationship to regional climate variability. Here we use records of n-alkanes and grain size from the sediments of Bangong Co in the western TP to reconstruct paleohydrological changes over the past 16,000 years. The Paq record(the ratio of non-emergent aquatic macrophytes versus emergent aquatic macrophytes and terrestrial plants) is generally consistent with the variations in summer temperature and precipitation isotopes. The changes in grain-size distributions show a similar trend to Paq but with less pronounced fluctuations in the early-middle Holocene. The new data combined with previous results from the site demonstrate that: 1) Bangong Co experienced relatively large water-level fluctuations during the last deglaciation, with a steadily high lake-level during the early-middle Holocene and a decreasing lake-level in the late Holocene;2) The lake level fluctuations were driven by both high summer temperatures via the melting water and monsoon precipitation. However, the dominant factor controlling lake level changed over time. The lake-level history at Bangong Co deduced from the n-alkanes and grain-size records reveals the past hydrological changes in the catchment area, and stimulates more discussion about the future of glacier-fed lakes under the conditions of unprecedented warming in the region.
