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1.
高原咸水湖水面蒸发估算——以兹格塘错为例   总被引：12，自引：0，他引：12  
根据兹格塘错流域附近气象站（安多,那曲和班戈）的器测资料和那曲站的实测辐射资料,对兹格塘错水面蒸发进行了估算,结果表明,兹格塘错多年平均（1958－1998年）蒸发量为925．1mm,在估算的41年中,最高的为1111．5mm(1975年）,最低的仅791．9mm(1983年）,5年滑动平均结果揭示,近40年来兹格塘错蒸发存在波动变化,基本上由2个峰值期（1970－1980年和1993－1998年）,1 个下降期（1975－1980年）和2个相对平衡期组成,且总体上呈上升趋势。  相似文献   

2.
Multi-proxies of lacustrine sediments, such as total carbon (TC), total organic carbon (TOC), total inorganic carbon (TIC), total nitrogen (TN), total sulfur (TS), hydrogen index (HI), oxygen index (OI) and stable carbon isotopic composition of organic matter (δ 13Corg), were analyzed using a 7.3 m core from Zigê Tangco. The source of the organic matter in the sediment was mainly from autochthonous phytoplankton, therefore the significances of proxies can be interpreted as that high TOC, TOC/TS, HI and δ13Corg values, low TC, TIC values corresponded to warm and wet climatic condition, and vice versa. The process of climatic development in the Zigê Tangco region was hence recovered. During the early and Mid-Holocene, the climate was warm and wet and intensive cold events occurred during the periods of 8600 to 8400 cal a BP and 7400 to 7000 cal a BP. In the second half of Holocene, the climate became cold and dry gradually. The palaeoclimatic process during Holocene in Zigê Tangco region matched well with that in Co Ngoin region which is ca 40 km to the south-east. Therefore this palaeoclimatic process represents the Holocene climatic feature in the Central Tibetan Plateau which has the same pattern in the Northern Tibetan Plateau, but the time and duration of some climatic events might be different. We can conclude that in Holocene solar insolation controlled the climatic pattern on the central Tibetan Plateau.  相似文献   

3.
Kilevannet is a meromictic lake in southern Norway. The stagnant bottom water probably originates from the last post-glacial period in Norway, some 8000–9000 years ago. Close to Kilevannet lies Rørholtfjorden, which is another lake with presumably old trapped seawater at its bottom. A comparison of the two lakes shows the importance of a so-called semi-stagnant layer. This layer, with gradually increasing salinity and decreasing oxygen content, seems to have a marked influence on the stability of the stratification.  相似文献   

4.
Summary During the period of partial circulation in the Lake of Zurich at the end of 1949 and the beginning of 1950, winds blowing in general up the lake led to an accumulation of surface water rich in oxygen in the lee half and a windward drift in the lower layers of water poor in oxygen. At the beginning of February 1950 the lake was, although homothermal, only mixed to a depth of about 80 m because of the increased specific gravity of the deep water (meromictic condition). During February strong and continued winds blew up the lake; these produced gradient currents which forced oxygen-poor bottom water (lying originally at 100 to 140 m depth) to the windward end where it welled up to the 55 m level. Over a horizontal distance of 12 km this represented a rise in level of this layer of sometimes more than 50 m. Subsequent oscillations of the water masses continued for several weeks; but nothing certain can be stated about possible affects of later winds in maintaining the oscillation, as only the winds in February were constant in character and blowing along the longitudinal axis of the lake. Such movements of bottom water caused by wind are important for the aeration of the lake, for the fishery and for an assessment of the lake's condition.   相似文献   

5.
High Arctic lakes are among the most sensitive ecosystems and climate change strongly affects their physical properties, especially water temperature, and mixing processes. To study the effect of recent climate change on such a lake in the Arctic environment, we measured water chemistry and temperature from 2005 to 2010 in Kongressvatn, a crenogenic meromictic lake in Spitsbergen (Svalbard). In addition, we monitored water column temperatures during two consecutive years and compared them to regional air temperature data and physicochemical lake data from 1962 and 1968, two relatively cold years. Summer surface water temperature was highly correlated to air temperature, and both have increased by approximately 2°C since 1962. Temperature monitoring during 2?years showed that the warm summer of 2007 resulted in increased water temperatures even in the stratified, denser hypolimnion. Our water chemistry measurements showed that the chemocline position in 2005?C2010 was ca 12?m deeper than in 1962?C1968, and a second, weaker, chemocline appeared at metalimnetic depths of 7?C15?m. During the study period, the water level decreased by 4?m, and this change accelerated between 2008 and 2010. Our data support the hypothesis that water temperatures and stratification patterns are changing rapidly with air temperature, but changes in the catchment, such as glacial retreat and permafrost melting, may have an even stronger impact on lake properties.  相似文献   

6.

As revealed from recent drilling and organic geochemical testing and research, a series of lacustrine high-grade hydrocarbon source rocks was discovered in the upper section of the Chang 9 oil reservoir member of upper Triassic in Ordos Basin. The hydrocarbon source rocks show average TOC content as high as 5.03%, average bitumen “A” content as high as 0.8603%, and good quality organic precursors, which are of the sapropelic type mainly derived from lower aquatic plants and have reached the thermal evolution stage featured by oil-producing climax. Generally the lacustrine high-grade hydrocarbon source rocks were developed in local depressions of a lake basin, and the Chang 91 member was particularly formed in a depositional environment characterized by fresh water to weakly saline water, weakly oxidizing to weakly reducing setting and semi-deep lake facies, as was demonstrated by a variety of organic to inorganic geochemical parameters. As a result, high productivity constitutes the principal controlling force for generation of this series of high-grade hydrocarbon source rocks. Deposition of thinly-bedded and laminated tuffs as well as positive Eu anomaly corroborate the possible occurrence of anoxic geological event closely related to contemporaneous volcanic eruption, which would play a key part in development of the Chang 91 member of high-grade hydrocarbon source rocks.

  相似文献   

7.
Abstract

Abstract An annual water balance model of Lake Victoria is derived for the period 1925–2000. Regression techniques are used to derive annual inputs to the water balance, based on lake rainfall data, measured and derived inflows and estimated evaporation during the historical period. This approach acknowledges that runoff is a nonlinear function of lake rainfall. A longer inflow series is produced here which is representative of the whole inflow to the lake, rather than just from individual tributaries. The results show a good simulation of annual lake levels and outflows and capture the high lake level in 1997–1998. Climate change scenarios, from a recent global climate model experiment, are applied to the lake rainfall inflow series and evaporation data to estimate future water balances of the lake. The scenarios produce a potential fall in lake levels by the 2030s horizon, and a rise by the 2080s horizon. A discussion of the application of climate change data to this complex hydrological system is presented.  相似文献   

8.
Lake Zigetang is located on the central Tibetan Plateau (TP) and represents a rare but typical meromictic lake in China. The lake’s stable meromixis sustains microflora communities, and changes in these communities are relatively independent of climate. Therefore, these communities can be used as paleoclimate proxies. In this paper, the stratification properties and their relationships with the microflora of Lake Zigetang were analyzed. We found that water depth and climate conditions were two important factors for maintaining meromixis in Lake Zigetang. Generally, stratification was enhanced during warm periods, while temperature differences between the mixolimnion and monimolimnion were decreased during cold periods. The presence of anoxygenic phototrophic bacteria (APB) was demonstrated by the discovery of bacteriopheophytin-a (Bph-a) in the sediments. This bacterial community is mainly concentrated at the bottom of the chemocline and the top of the monimolimnion, where it forms a thin APB layer. Moreover, total APB productivity is mainly affected by the light intensity penetrating to the APB layer, which exponentially increases as the thermocline becomes shallow. Therefore, high Bph-a values in the lake corresponded to a shallow thermocline and warm periods, low Bph-a values corresponded to cold periods, and zero changes indicated that the water was completely mixed and reflected an extreme cold climate or low lake level period. Thus, Bph-a can be used as a climate proxy to reconstruct the history of lake stratification and climate changes.  相似文献   

9.
Saline Lake Shira (Southern Siberia, Russia) was meromictic through the observation period 2002–2015. During the under-ice periods of 2015 and 2016, complete mixing of the water column was recorded for the first time, and hydrogen sulphide temporarily disappeared from the water column of the lake; i.e. in those years the lake turned to holomixis. In the summer of 2015, a sharp increase in chlorophyll a, organic carbon, zooplankton, and phytoflagellates was observed in the lake, which was probably due to the release of nutrients from the monimolimnion. Purple sulfur bacteria completely disappeared from the lake after the first mixing in 2015, and did not reappear despite the restoration of meromixis in 2017. Thus, it was demonstrated that purple sulfur bacteria are sensitive to the weakening of the stratification of Lake Shira. Based on the data of the seasonal monitoring of temperature and salinity profiles over the period 2002–2017, it was presumed that the main cause of deep mixing in 2015 was the weakening of the salinity gradient due to strong wind impact and early ice retreat in the spring of 2014. In addition, it was shown that in previous years a significant contribution to the maintenance of meromixis was made by an additional influx of fresh water, which caused a rise in the lake level in the period 2002–2007. Thus, we identified a relationship between the stratification regime of the lake and the change in its level, which provides valuable information both for the forecast of water quality and for reconstruction of the Holocene climate humidity in this region of Southern Siberia from the sediment cores of Lake Shira.  相似文献   

10.
The results of hydrophysical studies of the soda Doroninskoe Lake (Uletovskii raion, Zabaikal’skii krai) are presented. Conclusions are presented regarding the character of heat and mass exchange and the causes of formation and stability of the meromictic regime of the water body. The main factors are revealed that affect the character of lake hydrological regime in winter and summer. The seasonal dynamics of the chemocline is shown to be determined by a joint effect of many external and internal factors and to be an integral indicator of physical, chemical, and biochemical processes in the lake.  相似文献   

11.
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.  相似文献   

12.
ABSTRACT

Because of the late withdrawal of the Levantine lake waters and because of low relief the Eastern Romanian Plain was fragmented only by big alochthonous rivers (Ialomi?a, C?lm??ui and Buz?u).

The tabular-like, 40–50-km-wide interfluve areas covered by loessoid deposits and eolian sands on the periphery are deprived of surface drainage which accounts for their present evolution.

The major relief forms in these interfluves are depressions called in Romanian ‘crov’ (sink-holes) in the central areas and short valleys formed initially by erosion processes and now modelled by mechanical and chemical weathering at their periphery: in these depressions (sink-holes) and in the secondary valleys, peripheral to the interfluve areas, lakes had started to be formed.

Because of the semiarid climate sink-hole lakes have an intermittent hydrological regime, whereas those located in the small fluviatile liman-type valleys, enjoy a permanent regime. By the absence of surface drainage, by the loss of significant amounts of water through evaporation and the degree of mineralization, these lakes fall within the group of salt lakes.

In the past few years (since 1966 and especially since 1969) the level of these lakes has continually risen and the depressions formerly lacking water started being flooded by the rising of the piezometric level.

An analysis was made of the water balance of the Amara-Ialomi?a lake to investigate this phenomenon.

Level and evaporation recordings were made in the period 1956–1970. The findings revealed that the supply of underground water to the lake amounts to 47·3 per cent exceeding the water supply produced by the rains that fell on the surface of the lake (46·7 per cent). A close relationship was established (with a lapse of 8–12 months) between the surface supply of the basin (through rainfalls) and the flow of underground water to the lake.

Extending the precipitation-induced level changes over a longer period (1896–1915 and 1921–1970) it was found that level increases are cyclic, as a direct consequence of the corresponding precipitation regime.  相似文献   

13.
Vertical distribution of fossil carotenoids in a sediment core from meromictic Mahoney Lake was studied. Besides okenone and demethylated okenone, lutein and zeaxanthin and-carotene isomers were identified. No carotenoids typical for purple nonsulfur or green sulfur bacteria were detected. The ratio of zeaxanthin to lutein (above 1:1 in all samples) indicates a dominance of cyanobacteria over green algae in the phytoplankton assemblages of the past. Okenone, which is found exclusively in Chromatiaceae, was the dominating carotenoid in all sediment zones.The oldest sediment layers containing okenone were deposited 11 000 years ago. Between 9000 and 7000 and since 3000 years b.p., Chromatiaceae reached a considerable biomass in the lake. Vertical changes in okenone concentration were not related to changes of paleotemperatures. In contrast, okenone concentrations decreased during periods of volcanic ash input. During most of the lake history, however, mean okenone concentrations were positively correlated with sedimentation rates. This indicates that vertical changes of okenone concentration in the sediment reflect past changes of purple sulfur bacterial biomass in the lake.According to these results, the past limnology of Mahoney Lake resembled that of the present with a sulfide-containing monimolimnion and a well-developed population of okenone-bearing purple sulfur bacteria.  相似文献   

14.
We have measured Ba in Dead Sea samples collected before and after the 1979 overturn, and226Ra in nine samples collected after the overturn. Before this overturn, Ba and the226Ra data measured by Chung and Craig [4] show that a distinct two-layer structure existed, with higher concentrations in the upper layer. After the overturn, both elements were uniformly distributed in the water column. The inventories of Ba and Ra calculated from these data are the same for the periods before and after the overturn. If the inventories were constant during the last meromictic phase then the input rate must be balanced by the removal rate, and a mass balance model can be constructed to estimate physical parameters based on known or deduced sources and sinks. The sources include inputs from the Jordan River, springs around the Dead Sea, and submerged springs or seepages, etc. The sinks include coprecipitation with aragonite, gypsum, precipitation of barite, coprecipitation of Ra with barite, particulate scavenging, and radioactive decay for Ra. Our data include measurements of Ba and226Ra in gypsum, aragonite and halite from the Dead Sea, as well as in some of the inflowing rivers and springs.The inclusion of particulate scavenging as a sink is a major element of the model. We find that, without inclusion of a Ba scavenging term in the deep water, the lake volume at the previous overturn as calculated from the Ba data would be unrealistically high in comparison with historical records. The inclusion of particulate scavenging for Ra in the model reduces the calculated duration of the last meromictic phase significantly.Our model excludes internal mixing between the upper and lower water masses. With this restriction, various sets of model parameters were calculated as a function of theRa/Ba scavenging rate ratio. If the ratio is one, the calculated age of the last meromictic phase is about a hundred years. A substantial increase in the Ra input rate is required to balance the removal rate by particulate scavenging as well as decay. If the ratio is zero, i.e. no particulate scavenging for Ra, the age is about 260 years, as obtained by Stiller and Chung [2].  相似文献   

15.
Current bathymetric and limnologic data on natural polar lakes of the World is discussed. The principal limnologic data on the largest polar lakes and also on the saline, cold amictic, and meromictic polar lakes are generalized. The geographic, “national”, and “administrative” distributions of polar lakes and also their distribution by the genesis of lake basins are analyzed. The distribution functions of polar lake areas and the regressions relating the water areas of lakes and the storages of lakes are calculated. The total water area and storage of polar lakes are estimated. The study is based on published data for 1432 Arctic and 174 Antarctic lakes, which are collected in the authors’ WORLDLAKE database. Attention is called to the inadequate knowledge of polar lakes.  相似文献   

16.
Abstract

Abstract MODerate-resolution Imaging Spectroradiometer (MODIS) is a new generation remote sensing (RS) sensor and its applications in hydrology and water resources have attracted much attention. To overcome the problems of slow response in flood disaster monitoring based on traditional RS techniques in China, the Flood Disaster Monitoring and Assessing System (FDMAS), based on MODIS and a Geographic Information System (GIS), was designed and applied to Dongting Lake, Hunan Province, China. The storage curve of Dongting Lake for 1995 was obtained using 1:10 000 topographic map data and then a relationship between water level at the Chenglingji hydrological station and lake area was derived. A new relationship between water level and lake area was obtained by processing MODIS images of Dongting Lake from April 2002 to April 2003 and the influence of lake area variation on water level was analysed with the 1996 flood data. It was found that the water level reduction reached 0.64 m for the 1996 flood if the original lake area curve was replaced with the area curve of 2002. This illustrates that the flood water level has been considerably reduced as a result of the increased area of Dongting Lake since the Chinese Central Government’s ?return land to lake? policy took effect in 1998.  相似文献   

17.
The full spectrum of volatile sulfur compounds was detected in the water column of the permanently stratified meromictic Lake Cadagno. Besides hydrogen sulfide it included methanethiol, carbonyl sulfide, dimethyl sulfide, carbon disulfide, and dimethyl disulfide. Their distribution in the water column suggests that these compounds are of biogenic origin. Except for carbon disulfide which is present in all layers of Lake Cadagno, these volatile organic sulfur compounds are restricted to the anoxic part of the lake. For methanethiol, dimethyl sulfide, and carbon disulfide maximum concentrations were observed in the redox transition zone and in the sediment porewater. Carbon disulfide is the most abundant volatile organic sulfur compound with concentrations of up to 60 μmol L–1. The concentrations of the methylated sulfides are in the nmolar range. Although their concentrations varied during the summer months, seasonal trends of the concentrations of volatile organic sulfur compounds did not follow a consistent pattern. The restriction of most sulfur species to the anoxic layers of the lake indicates that their production originates from anaerobic microbial degradation of biomass and not from its release from a specific precursor like dimethylsulfoniumpropionate as in marine environments.  相似文献   

18.
The progressive weakening and final disappearance (in 1979) of the long-term meromictic structure of the Dead Sea are clearly reflected in the depth profiles of210Pb and210Po. In 1977/78, prior to overturn, dissolved210Pb (35–50 dpm kg?1) predominated over particulate210Pb (1–2 dpm kg?1) in the oxic upper waters, whereas the reverse was true in the anoxic deep waters (16–20 dpm kg?1 particulate vs. 2–5 dpm kg?1 dissolved). The exact extent of the disequilibrium between210Pb and226Ra is hard to evaluate in the upper oxic layers, because the progressive deepenings resulted in mixing with deep waters. By contrast, one can estimate the residence time of dissolved210Pb in the unperturbed anoxic deepest layers, because these remained isolated, at about 3 years. Following the overturn of 1979, dissolved210Pb exceeded particulate210Pb at all depths. The210Po profiles of the stratified lake resembled in shape those of its grandparent210Pb, but with distinct characteristics of their own in the oxic upper waters where particulate210Po (8–12 dpm kg?1) was greatly in excess over particulate210Pb, while dissolved210Po (25–40 dpm kg?1) was slightly deficient. Immediately following the overturn, dissolved and particulate210Po were similar (about 15 dpm kg?1), at all depths. The destruction of the lake's meromictic structure was accompanied by a reduction of its210Pb inventory, while that of210Po was almost unaffected. Thus, at overturn a transient state was created with the inventory of210Po exceeding that of210Pb.  相似文献   

19.
In order to assess the diversity and spatial distribution of bacterial and archaeal communities in a CO2-rich and meromictic lake, samples were collected along the water column of Lake Monoun and analyzed using PCR-DGGE and quantitative analyses of the 16S rRNA gene. The retrieved sequences were affiliated to 6 bacterial phyla and two archaeal phyla which plausible environmental functions map with the physico-chemical parameters of the lake. Unclassified sequences were also detected. This suggests heterogeneity in community composition and existence of potential candidate divisions. For instance, amongst the bacterial sequences, 18.2% matched with methanotrophic bacteria of the order methylococcales and amongst the archaeal sequences, 16.6% matched with methanogenic species of the order methanomicrobiales. Hence, evidencing the existence of methane-related prokaryotes in the lake, a finding that would play a key role in our understanding of the methane puzzle of Lake Monoun. Other groups capable of a wide range of metal and nutrients transformations were also detected, as well as those of unknown functions. The layering of microbial communities also appeared to directly or indirectly depend on oxygen availability. DGGE and qPCR analyses both suggested a scarcity of archaea in the surface samples. Furthermore, qPCR revealed that bacteria were numerically more important than archaea in all the samples. The general distribution along the water column indicated that archaeal abundance increases with depth.  相似文献   

20.
Chemical studies performed in the last 50 years on the northern and southern basins of Lago di Lugano are reviewed and discussed in relation to the phosphorus and nitrogen loads from the drainage area.Both basins became eutrophic in the fifties as a consequence of the dense population and industrial activity in the drainage area; the effect of these was aggravated by the meromictic condition of the layer below 100 m in the northern basin.The reduction of phosphorus loads in progress since 1976 has resulted in a significant improvement in the chemical and biological condition of the southern basin and the upper 100 m of water in the northern basin. On the other hand, the balance between dissolved oxygen and reducing substances in the northern basin is shifting toward a decrease of the net oxygen concentration, partly as a consequence of the unusually dry conditions of the last three years.A reduction in phosphorus load down to 18 and 22 t a–1 in the northern and southern basins respectively is still necessary in order to reduce the lake phosphorus concentration to 30–35 µg O l–1.  相似文献   

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