三峡水库汛期控制水位及运用条件

随着长江上游梯级水库的陆续建成投运，三峡水库的水文情势和功能需求与设计条件相比发生了显著变化，仍维持固定的汛限水位运行已不能适应新形势需求。本文通过辨析三峡水库设计阶段汛限水位的设置条件，挖掘流域洪水特性和洪水遭遇规律，论证三峡水库汛期运行水位动态控制的可行性。结果表明：① 三峡水库设计推求的汛限水位145 m的适用条件是应对流域性大洪水，而流域性洪水发生概率小且特征明显，可以通过水文水情分析提前预判。② 根据流域洪水类型、洪水分期和遭遇规律，预判发生区域性大洪水时，三峡水库6月初至梅雨期结束汛限水位按145 m设置，从梅雨期结束后逐渐提高水位，8月20日后过渡到155 m。③ 在考虑上游水库群联合调度和气象水文预报的配合下，正常年份三峡水库汛期运行水位可在155 m上下浮动，并考虑提前蓄水。④ 三峡水库汛期运行水位动态控制，不会增加防洪风险和库区淤积风险，对中下游江湖关系和水文情势有利，可显著提高发电、航运、生态保护和供水等综合利用效益。     

Historical changes in sediments of Pyramid Lake,Nevada, USA: consequences of changes in the water balance of a terminal desert lake

Sediment cores from the shallow and deep basins of Pyramid Lake, Nevada, revealed variations in composition with depth reflecting changes in lake level, river inflow, and lake productivity. Recent sediments from the period of historical record indicate: (1) CaCO₃ and organic content of sediment in the shallow basin decrease at lower lake level, (2) CaCO₃ content of deep basin sediments increases when lake level decreases rapidly, and (3) the inorganic P content of sediments increases with decreasing lake volume. Variations in sediment composition also indicate several periods for which productivity in Pyramid Lake may have been elevated over the past 1000 years. Our data provide strong evidence for increased productivity during the first half of the 20th Century, although the typical pattern for cultural eutrophication was not observed. The organic content of sediments also suggests periods of increased productivity in the lake prior to the discovery and development of the region by white settlers. Indeed, a broad peak in organic fractions during the 1800's originates as an increase starting around 1600. However, periods of changing organic content of sediments also correspond to periods when inflow to the lake was probably at extremes (e.g. drought or flood) indicating that fluctuations in river inflow may be an important factor affecting sediment composition in Pyramid Lake.     

Post glacial lacustrine event sedimentation in an ancient mountain setting: Carboniferous Lake Malanzán (Western Argentina)

Lacustrine deposits of the Malanzán Formation record sedimentation in a small and narrow mountain paleovalley. Lake Malanzán was one of several water bodies formed in the Paganzo Basin during the Late Carboniferous deglaciation. Five sedimentary facies have been recognized. Facies A (Dropstones-bearing laminated mudstones) records deposition from suspension fall-out and probably underflow currents coupled with ice-rafting processes in a basin lake setting. Facies B (Ripple cross-laminated sandstones and siltstones) was deposited from low density turbidity currents in a lobe fringe environment. Facies C (Massive or graded sandstones) is thought to represent sedimentation from high and low density turbidity currents in sand lobes. Facies D (Folded sandstones and siltstones) was formed from slumping in proximal lobe environments. Facies E (Wave-rippled sandstones) records wave reworking of sands supplied by turbidity currents above wave base level.The Lake Malanzán succession is formed by stacked turbidite sand lobe deposits. These lobes were probably formed in proximal lacustrine settings, most likely relatively high gradient slopes. Paleocurrents indicate a dominant direction from cratonic areas to the WSW. Although the overall sequence shows a regressive trend from basin fine-grained deposits to deltaic and braided fluvial facies, individual lobe packages lack of definite vertical trends in bed thickness and grain size. This fact suggests aggradation from multiple-point sources, rather than progradation from single-point sources. Sedimentologic and paleoecologic evidence indicate high depositional rate and sediment supply. Deposition within the lake was largely dominated by event sedimentation. Low diversity trace fossil assemblages of opportunistic invertebrates indicate recolonization of event beds under stressed conditions.Three stages of lake evolutionary history have been distinguished. The vertical replacement of braided fluvial deposits by basinal facies indicates high subsidence and a lacustrine transgressive episode. This flooding event was probably linked to a notable base level rise during postglacial times. The second evolutionary stage was typified by the formation of sand turbidite lobes from downslope mass-movements. Lake history culminates with the progradation of deltaic and braided fluvial systems     

Inland saline lakes with lagoonal biota: some reflections on the concept and nature of athalassic (non-marine), paralic and marine saline waters

First, some inland basins with lagoonal (or paralic) biota are brieffly described. The different kinds of saline aquatic environments are then defined and the composition of their biota are discussed. Finally, the still unknown microbiogeochemical composition of concentrated inland waters is discussed. Under arid and endorheic conditions, it seems that the wider and the more geologically complex a hydrological basin is, the more biogeochemically similar to seawater is the water of its terminal lake. The evolution of the microbiogeochemical complexity of seawater through geological times is considered.This paper has been the subject of considerable discussion among referees. Not all of the views expressed by the author are accepted by them.     

Radiometric dating of lake sediments from Signy Island (maritime Antarctic): evidence of recent climatic change

Sediment cores from three lakes (Moss, Sombre and Heywood) in the maritime Antarctic (Signy Island, South Orkney Islands) have been successfully dated radiometrically by²¹⁰Pb and¹³⁷Cs. The core inventories of both fallout radionuclides are an order of magnitude higher than that which can be supported by the direct atmospheric flux at this latitude. The elevated values may be explained by fallout onto the catchment during the winter being delivered directly to the lakes during the annual thaw. Two of the lakes (Sombre and Heywood) show marked increases in sediment accumulation afterc. 1950. This appears to be associated with a documented rise in temperature in the South Orkney Islands, which has caused extensive deglaciation at Signy Island.This is the tenth of a series of papers to be published by this journal following the 20 ^th anniversary of the first application of²¹⁰Pb dating of lake sediments. Dr P.G. Appleby is guest editing this series.     

蒙新高原盐湖资源及盆地结构

通过蒙新高原典型盐湖区的解剖研究，查清了代表性盐湖盆地的相环境及其沉积建造，将盐湖盆地环境的变化形式划分为沉陷型、抬升型和改造型，并归结了盐湖盆地相环境分异与盆地地质结构之间的相互关系，为开发大陆干旱区盆地的盐湖和卤水资源及其环境演化的理论研究提供了依据。     

新疆盐湖卤水水化学特征研究

要为深入研究新疆盐湖形成演化规律及成盐环境,根据我所历年盐湖科学考察研究结果,对该区盐湖卤水的分布及其化学组成、盐湖卤水的矿化特征和卤水水理性质及水化学类型分类等进行了研究,并通过与我国其它盐湖区盐湖水化学特征的对比分析,确认本区现代盐湖水化学成因类型具有陆相再溶盐成因特征,从而显示了该区盐湖形成演化的独特水文地球化学特点。     

Paleolimnological studies of saline lakes

Salt water lakes are located in arid to semi-arid regions where evaporation rates exceed precipitation rates. As such, saline lakes are very sensitive to changes in their hydrological cycle. Research into the current limnology of saline lakes is expanding as population growth in these regions increases. Emerging concerns include water diversions, eutrophication, and toxic substances. Paleolimnological investigations of saline lakes are providing valuable new information on paleoclimate and paleohydrology. Such studies may allow for better predictions of the environmental consequences of global warming and for a better understanding of past climate change. Paleolimnological studies may also provide some insight to more recent, anthropogenic perturbations in the arid and semi-arid regions of the world.This publication is the introduction to a series of papers presented at the Conference on Sedimentary and Paleolimnological Records of Saline Lakes. The conference was held August 13–16, 1991 at the University of Saskatchewan, Saskatoon, Canada. Dr. Evans is serving as Guest Editor.     

The protection and management of saline lakes of therapeutic value in Romania

Major limnological features and the distribution of Romanian saline lakes of therapeutic use are described. Phenomena which affect mud formation and degradation are discussed and recommendations to protect and manage the lakes are put forward.