Contribution to the detection of Lake Masoko (Tanzania) groundwater outflow: isotopic evidence (18O,D) / Contribution à la détection des pertes souterraines du Lac Masoko (Tanzanie): évidences isotopiques (18O,D)

Abstract

The isotopic compositions (¹⁸O and D) of groundwater, springs, rivers and lake waters are used to account for the hydrological processes in the area of the closed maar Lake Masoko in Tanzania. Springs and groundwater from the northern, western and southern parts of the lake basin display relatively stable compositions, close to those of the mean precipitation, evidencing their fast infiltration rate. Springs located in the eastern part of the basin have enriched compositions, which are on the mixing line between the ?"non evaporated? water and the evaporated lake water. This underlines the hydraulic continuity between the lake and the eastern springs and supports a previous proposition of grounwater outflow from Lake Masoko. The mixing parts of lake water calculated at each spring are constant through time, evidencing the inertia of the system. Furthermore, the mixing part of the lake water decreases linearly with the distance from the lake, suggesting an homogeneous and continuous aquifer. These observations point to a west to east groundwater flow, in agreement with the altitude of different potentials.     

蒙古国北部Gun Nuur湖表层沉积物花粉分布特征

 蒙古国北部Gun Nuur湖20个表层沉积物孢粉组合与数量分析研究揭示,孢粉组合及浓度分布存在显著空间差异。结果表明：双束松型花粉百分含量由湖泊东南向西北降低,桦属、蒿属、藜科以及禾本科百分含量增加,湖泊东南侧赤松林是造成孢粉组合空间分异的主要原因。孢粉浓度分布与湖泊水深具有良好的对应关系,体现了湖水流对孢粉的二次搬运和富集作用。现代森林草原地带Gun Nuur湖表层孢粉组合中松属含量较高,具超代表性;受松属影响蒿属和藜科花粉含量较低,代表性较低。     

Water quality and light absorption attributes of glacial lakes in Mount Qomolangma region

As they are products of glacier movement, the water body composition and water quality attributes of glacial lakes have distinct characteristics compared with inland lakes. Although satellite remote sensing provides an effective approach to monitor water quality, lack of in-situ measurement data on the status and environment surrounding glacial lakes presents a major constraint in relating satellite data to water quality indicators. This study presents findings of a preliminary investigation into water quality attributes of 3 glacial lakes in the Mount Qomolangma region. Suspended particulate matter （SPM）, light absorption attributes of phytoplankton, nonalgal particles （NAP）, and colored dissolved organic matter （CDOM） were measured. The suspended substance concentration varies markedly from 0-320 mg/L. This is considered to reflect differing stages of lake development. l-he chlorophyll concentra- tion is much lower than that found for inland lakes, as landscapes that surround these high altitude lakes have almost no vegetation growth. The phytoplankton and CDOM concentration depend on long-term stability of lake slopes. Given the lack of exogenous and endogenous inputs in the Qomolangma region, CDOM in glacial lakes is significantly lower than in inland lakes. These preliminary findings could support efforts to appraise estimates of water quality parameters using remotely sensed images.     

Calving retreat and proglacial lake growth at Hooker Glacier,Southern Alps,New Zealand

Hooker Glacier in the central Southern Alps of New Zealand has undergone significant downwasting and recession (～2.14 km) during the last two centuries. High retreat rates (51 m a^?1 1986–2001, 43 m a^?1 2001–2011) have produced a large (1.22 km²) proglacial lake. We present a retreat scenario for Hooker Glacier. A retreat scenario predicts that the glacier terminus will stabilise >3 km up‐valley of the current lake outlet after 2028 when ice velocity equals calving rate.     

九寨沟早期钙华体的岩溶作用与湖瀑景观的形成

九寨沟与四川西北部碳酸盐岩地区早期钙华体在52～3万年前的冰缘环境中形成.3万年后,区内气温在振荡中升高,使九寨冰缘退缩,岩溶水酸化并具溶蚀性,在早期钙华体上形成了湖瀑等各种溶蚀形态,渗流溶蚀和混合溶蚀是壶穴湖、梯湖和溶蚀湖形成的主要机制,溶蚀侵蚀伴有季节性钙华沉淀形成着叠水和瀑布.保护湖瀑景观的原则是抑制钙华的溶蚀强度,运用岩溶水的瀑堤效应促进CaCO3沉淀,增强瀑堤的固结,减少渗漏.     

堰塞湖溃坝控制和人工排险技术

首先阐述堰塞湖溃坝控制与人工排险的内容、原则和方案.在此基础上分析堰塞湖应急处置中安全监测的原则和内容,以及泄流、渗流控制、滑动体加固等应急工程措施适用性.最后讨论冲切和坝体稳定泄流的工程设计与应急转移措施.     

太湖沉积对流域极端降水和洪水响应的研究

认识极端洪水特征和周期,急需建立长期洪水记录和序列。过去150 a来长江下游极端降水引发了多次太湖特大洪水,太湖湖泊沉积提供了长于观测资料的洪水记录。本文利用太湖中心开阔水域的近现代沉积,采用210Pb和137Cs测年法和粒度、磁学特征分析,与区域夏季降水和长江下游洪峰流量进行相关分析,恢复了太湖流域150 a来的历史洪水事件。根据长江下游极端夏季降水（Pjja≥90%百分位）和极端径流(Q≥90%百分位)以及历史文献记载,太湖流域自1840年以来约有24次特大洪水年,而湖泊沉积物砂级粒径与低频磁化率等特征能捕获与之对应的中洪水事件15次。这表明湖泊沉积记录能较好地反演过去洪水变化,为利用沉积记录认识百年极端洪水长周期变化和特征提供了沉积学、磁学等方面的科学依据。     

试论利用青海湖介形虫体长定量恢复湖水古盐度的可靠性

以青海湖东南部湖盆钻取的长475 cm沉积岩芯（QH 2005）为材料,基于6个层位14C年代（4个总有机碳（BOC）样品年代和2个木质素样品年代）建立了晚冰期以来QH 2005钻孔的“深度-年代”模型,并对BOC样品14C年代的硬水效应（732~2475年）进行了校正。挑选沉积物中成年介形虫（Limnocythere inopinata或Eucypris inflata）壳体,对其测定了δ18O值;同时测定了L. inopinata壳体体长,在此基础上利用经验公式定量恢复了青海湖湖水古盐度;此外还对QH 2005钻孔沉积物进行了红度指标的测定。结果表明:QH 2005孔沉积物红度和介形虫壳体δ18O指标所揭示的晚冰期以来气候演化模式与前人研究结果基本一致,而L. inopinata壳体体长定量重建的湖水古盐度只在较长时间尺度上（对应较大的湖水盐度变化）与气候演化模式较为一致,但在千/百年尺度上并不能很好指示气候突变事件,可见青海湖湖水盐度是L. inopinata壳体体长变化的一个重要影响因素,但并非唯一的决定性因素。     

新疆柴窝堡湖沉积物中环境敏感粒度组分揭示的环境信息

通过对柴窝堡湖沉积物剖面和流域表层沉积物进行粒度分析,结合沉积剖面年代序列,研究了柴窝堡地区的环境演变与沙尘暴事件。首先通过主成分因子分析,对柴窝堡湖沉积物剖面粒度不同粒级组分含量进行了研究,探讨了湖泊沉积物的物质来源,获得了两个主控因子F1和F2,它们控制了湖泊沉积物近97.7%的粒度变化特征。研究表明,F2代表了以57 μm为众数粒径的次总体,主要来源于地表风沙侵蚀;而F1为以7 μm为众数粒径的次总体,主要受流水作用控制。进而通过粒径-标准偏差法,提取了湖泊沉积物中环境敏感粒度组分,风成组分C2（20~209 μm）反映了区域风沙活动的历史,并揭示了1910-1930年和1980-2000年为百年来的两个沙尘暴相对活动强烈的时期。沉积物中记录的1980年和2000年左右的沙尘事件与器测记录及历史文献记载具有很好的一致性。最后利用均值突变诊断分析,发现柴窝堡湖地区1910年前后存在近百年来最强的沙尘事件,揭示了近百年来该地区一次最强的环境突变事件。      

Seismic evidence of up to 200 m lake‐level change in Southern Patagonia since Marine Isotope Stage 4

Maar lake Laguna Potrok Aike is located north of the Strait of Magellan (south‐eastern Patagonia). Seismic reflection profiles revealed a highly dynamic palaeoclimate history. Dunes were identified in the eastern part of the lake at approximately 30 to 80 m below the lake floor, overlying older lacustrine strata, and suggest that the region experienced dry conditions probably combined with strong westerly winds. It is quite likely that this can be linked to a major dust event recorded in the Antarctic ice cores during Marine Isotope Stage 4. The dunes are overlain by a series of palaeo‐shorelines indicating a stepwise water‐level evolution of a new lake established after this dry period, and thus a change towards wetter conditions. After the initial, rapid and stepwise lake‐level rise, the basin became deeper and wider, and sediments deposited on the lake shoulder at approximately 33 m below present‐day lake level point towards a long period of lake‐level highstand between roughly 53·5 ka cal. bp and 30 ka cal. bp with a maximum lake level some 200 m higher than the desiccation horizon. This highstand was then followed by a regressional phase of uncertain age, although it must have happened some time between approximately 30 ka cal. bp and 6750 yrs cal. bp . Dryer conditions during the Mid‐Holocene are evidenced by a dropping lake level, resulting in a basin‐wide erosional unconformity on the lake shoulder. A second stepwise transgression between ca 5·8 to 5·4 ka cal. bp and ca 4·7 to 4 ka cal. bp with palaeo‐shorelines deposited on the lake shoulder unconformity again indicates a change towards wetter conditions.