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1.
The global carbon cycle, one of the important biogeochemical cycles controlling the surface environment of the Earth, has been greatly affected by human activity. Anthropogenic nutrient loading from urban sewage and agricultural runoff has caused eutrophication of aquatic systems. The impact of this eutrophication and consequent photosynthetic activity on CO2 exchange between freshwater systems and the atmosphere is unclear. In this study, we focused on how nutrient loading to lakes affects their carbonate system. Here, we report results of surveys of lakes in Japan at different stages of eutrophication. Alkalization due to photosynthetic activity and decreases in PCO2 had occurred in eutrophic lakes (e.g., Lake Kasumigaura), whereas in an acidotrophic lake (Lake Inawashiro) that was impacted by volcanic hot springs, nutrient loading was changing the pH and carbon cycling. When the influence of volcanic activity was stronger in the past in Lake Inawashiro, precipitation of volcanic-derived iron and aluminum had removed nutrients by co-precipitation. During the last three decades, volcanic activity has weakened and the lake water has become alkalized. We inferred that this rapid alkalization did not result just from the reduction in acid inputs but was also strongly affected by increased photosynthetic activity during this period. Human activities affect many lakes in the world. These lakes may play an important part in the global carbon cycle through their influence on CO2 exchange between freshwater and the atmosphere. Biogeochemical changes and processes in these systems have important implications for future changes in aquatic carbonate systems on land.  相似文献   

2.
Lake-level changes inferred from seismic surveying and core sampling of the floor of Lake Baikal near the Selenga River delta can be used to constrain regional climatic history and appear to be correlated to global climate changes represented by marine oxygen isotope stages (MIS). The reflection pattern and correlation to the isotope stages indicate that the topset and progradational foreset sediments of the deltas formed during periods of stable lake levels and warm climatic conditions. During warm stages, the lake level was high, and during cold stages it was low. The drop in the lake level due to cooling from MIS 5 through MIS 4 is estimated to be 33-38 m; from MIS 3 through MIS 2, it fell an additional 11-15 m. Because the lake level is chiefly controlled by evaporation and river input, we infer that more water was supplied to Lake Baikal during warm stages.  相似文献   

3.
Climatic changes and anthropogenic activities could affect nutrients?? status significantly in the different lake ecosystems. Nutrients in Lake Hulun and Lake Taihu, two largest shallow cyanobacteria-blooming lakes in northern and southern China, respectively, were at eutrophicated levels in 2009. The concentrations of total nitrogen and total phosphorus were 3.346 and 2.250?mg/L as well as 0.435 and 0.062?mg/L, respectively, in these two lakes with different causes of eutrophication. For Lake Hulun, it was the decreased amount of water as a result of the warming and drying climate that accounted for the abrupt increase of total nitrogen and total phosphorus levels through inspissation. In addition, the icebound effects, no outflows, low nutrients sequestration by the sediment and the reduction of aquatic productivity made the situation even worse. On the contrary, high population densities, the rapid development of agriculture and industry as well as urbanization have increased the nitrogen and phosphorus loads on Lake Taihu. Therefore, higher criteria of total nitrogen and total phosphorus should be applied in Lake Hulun given the difficulties in controlling climatic changes while much more rigorous standards should be established for Lake Taihu since the anthropogenic impacts on nutrient status are relatively easy to control.  相似文献   

4.
Yiping Huang  Min Zhu 《GeoJournal》1996,40(1-2):39-44
Lake Taihu, the third largest fresh water lake of China, with a surface area of 2338 km2, is located in the Changjiang River Delta, the most advanced economic zone in China. It is a typical saucer-like shallow lake in its depth and shape. During the last decade, the rapid economic development of local agriculture and industry both in the urban and rural areas of the Taihu region has made great advances. Great quantities of pollutants have been discharged into the lake, its nutrient content has increased continuously, and phytoplankton blooms have occurred in some areas. Water quality protection in Lake Taihu is very important because of its close relation with economic development and people's daily life. It is urgent to have comprehensive pollution control in Lake Taihu. Based on water quality monitoring data in Lake Taihu from 1986 to 1993, the dynamic variations of water quality and eutrophication trends have been analyzed, showing obvious spatial and temporal variations. The main water quality factors were compared with the standards for drinking water and indicate considerable change with the seasons. Basic strategies to protect water quality and prevent eutrophication are discussed.  相似文献   

5.
Active hydrate destabilization in Lake Baikal,Siberia?   总被引：1，自引：0，他引：1  
ABSTRACT In this paper, we present new seismic and heat-flow data that show the base of the hydrate stability zone (BHSZ) in Lake Baikal to be locally characterized by abnormal variations in depth, with distinct regions of deeper-than-normal and regions of shallower-than-normal BHSZ. These variations are related to strong lateral variations in heat flow, and occur in close association with important rift-basin faults. Areas of shallow BHSZ are also characterized by the presence of several methane seeps and mud volcanoes at the lake floor. We infer that the seeps are the surface expression of escape pathways for overpressured fluids generated by the dissociation of pre-existing hydrates, in response to a thermal pulse caused by an upward flow of hydrothermal fluids towards the BHSZ. It thus seems that present-day hydrate dissociation in Lake Baikal is modulated by the tectonic activity in the rift rather than by – climatically controlled – changes in lake level or water temperature.  相似文献   

6.
安国英  郭兆成  叶佩 《现代地质》2022,36(2):406-417
依据1989年至2019年云南大理地区所辖12个气象站点的气候数据和洱海水质监测资料等文献,分析大理地区气候变化特征和洱海富营养化变化趋势,并总结洱海水质综合营养状态指数与降水量、气温的相互关系。结果表明,1989年至2019年期间,大理地区的年平均气温呈波动上升趋势,气候变暖明显,冬季气温升温幅度最大;年降水量总体呈波动下降趋势,秋季降水量减少最为显著。洱海水质的综合营养状态指数及单因子总氮、总磷、高锰酸盐指数等总体呈升高趋势,而水体透明度呈降低趋势;进一步可分成2个阶段,即2003年之前呈快速上升或下降变化趋势;2003年之后呈波动稳定趋势。洱海综合营养状态指数与年平均气温呈正相关,与年降水量呈负相关关系;总氮、水体透明度分别与年平均气温正相关和负相关,与年降水量则呈负相关和正相关;而总磷与冬季平均气温、高锰酸盐指数与夏季或冬季平均气温均呈正相关关系。年内变化上,洱海污染指数、综合营养状态指数在最近的2015—2019年期间呈现6—10月份明显增高,显示非汛期水质明显好于汛期状况。总之,1989—2019年期间,受大理地区气温升高、降水量减少导致入湖水量减少的影响,洱海综合营养状态指数呈升高趋势,湖泊富营养化进程加剧状况没有得到改善,洱海水环境仍然比较脆弱。  相似文献   

7.
The long-term data (1950–2017) on the chemical composition of the water from the source of the Angara River, which is the only run-off from Lake Baikal, a large and clean fresh water reservoir, are presented. The absence of water contamination despite the anthropogenic influence is shown. The similarity and constancy of the current composition of the waters in the lake and the Angara River are recorded. It is recommended to continue geochemical studies of this unique world heritage site.  相似文献   

8.
Lake Bogoria is a saline, alkaline, meromictic lake in a geothermally active part of the Kenya Rift Valley. Coring of the lake floor has shown two types of sedimentation – a shallow fan–deltaic clastic zone and a deeper zone with alternating organic muds and evaporites. The organic muds formed during periods of relatively high lake level and high microbial productivity, the evaporites during more arid phases. Analyses of the cores show many environmental fluctuations during the past 30000 years, related to regional climatic changes and to local tectonic and hydrological controls.  相似文献   

9.
The Bonneville Basin is a continental lacustrine system accommodating extensive microbial carbonate deposits corresponding to two distinct phases: the deep Lake Bonneville (30 000 to 11 500 14C bp ) and the shallow Great Salt Lake (since 11 500 14C bp ). A characterization of these microbial deposits and their associated sediments provides insights into their spatio‐temporal distribution patterns. The Bonneville phase preferentially displays vertical distribution of the microbial deposits resulting from high‐amplitude lake level variations. Due to the basin physiography, the microbial deposits were restricted to a narrow shoreline belt following Bonneville lake level variations. Carbonate production was more efficient during intervals of relative lake level stability as recorded by the formation of successive terraces. In contrast, the Great Salt Lake microbial deposits showed a great lateral distribution, linked to the modern flat bottom configuration. A low vertical distribution of the microbial deposits was the result of the shallow water depth combined with a low amplitude of lake level fluctuations. These younger microbial deposits display a higher diversity of fabrics and sizes. They are distributed along an extensive ‘shore to lake’ transect on a flat platform in relation to local and progressive accommodation space changes. Microbial deposits are temporally discontinuous throughout the lake history showing longer hiatuses during the Bonneville phase. The main parameters controlling the rate of carbonate production are related to the interaction between physical (kinetics of the mineral precipitation, lake water temperature and runoff), chemical (Ca2+, Mg2+ and HCO3? concentrations, Mg/Ca ratio, dilution and depletion) and/or biological (trophic) factors. The contrast in evolution of Lake Bonneville and Great Salt Lake microbial deposits during their lacustrine history leads to discussions on major chemical and climatic changes during this interval as well as the role of physiography. Furthermore, it provides novel insights into the composition, structure and formation of microbialite‐rich carbonate deposits under freshwater and hypersaline conditions.  相似文献   

10.
This paper addresses some specific features of the formation of atmospheric precipitation and soil and ground waters in the Ust’-Selenga depression on the eastern coast of Lake Baikal, where the delta of the Selenga River supplying about 50% of water into the lake has been formed. It was shown that a reducing environment was formed within this region under near-surface conditions in the zone of active water exchange, where waters with high concentrations of organic matter, ammonium, iron, manganese, nitrate, zinc, and cadmium were observed. The high contents of these components in the ground waters of the depression are related to the occurrence of both natural and anthropogenic processes. It was found that the natural hydrogeologic systems of the Ust’-Selenga depression are affected by a negative impact related to the transboundary atmospheric transport of industrial wastes discharged tens to hundreds of kilometers from its boundaries.  相似文献   

11.
Global warming is likely to have significant effect on the hydrological cycle. Some parts of the world may see significant reductions in precipitation or major alterations in the timing of wet and dry seasons. Climate change is one of the serious pressures facing water resources and their management over the next few years and decades. As part of the southern belt of Mediterranean Europe, Turkey is highly vulnerable to anticipated climate change impacts. The changes in global climate will seriously affect inland freshwater ecosystems and coastal lakes. Mogan and Eymir Lakes located in Central Turkey are shallow lakes that may be impacted significantly by climate change. The interaction between the lakes and groundwater system has been modelled in order to analyse the response of lake levels to climate change over a planning period of 96 years, beginning from October 2004 and ending in September 2100. The impacts of the emission scenarios of A2 and B1 of the Intergovernmental Panel on Climate Change (IPCC) on lake levels have been analyzed with the help of the lake-aquifer simulation model. The fluctuations in lake levels due to climate change scenarios are compared with the results of a scenario generated by the assumption of the continuation of the average recharge and discharge conditions observed for 1999 and 2004. The results show that very small, but long-term changes to precipitation and temperature have the potential to cause significant declines in lake levels and temporary drying of the lakes in the long-term. The impact of climate change on lake levels will depend on how these water resources are managed in the future.  相似文献   

12.
The elemental composition of suspended particles in surface waters of Lake Baikal has been studied by ICP MS along a transect of the zone affected by the Selenga River. The amount of terrigenous suspension in water was estimated from Al content, which decreases in a saltatory manner along the transect: 6.5–8.3 km offshore it decreases by an order of magnitude; 11–14 km offshore, by other 20 times; in the pelagic zone it remains almost unchanged. During the study period (late June 2001), the distribution limit of suspension from the Selenga River in the lake’s surface waters lays 11–14 km offshore.It has been found that pelagic suspension is more than 20 times richer in Ca, P, Zn, Cu, Ni, Sn, Mo, Bi, S, and Cd than littoral one (6.5 km offshore) in the zone affected by the Selenga River. This is mainly due to fine suspension (<1.2 μm), which was considerably richer in Ca, P, Zn, Cu, Ni, Sn, Mo, Sb, and Cd than coarser ones in the river.Fine suspension in Lake Baikal, both in the zone affected by the river and in the pelagic zone, is considerably (2–35 times) richer in most elements, except for typical terrigenous ones, than river one. This suggests that element enrichment takes place in the lake, probably owing to bioaccumulation and chemisorption. These processes may be affected by additional factors, because fine suspension from the zone affected by the river differs significantly from pelagic one in elemental composition.  相似文献   

13.
In response to the impact of climate change, the US Army Corps of Engineers proposed a large-scale implementation plan for an aquifer storage and recovery (ASR) project in the Kissimmee River Basin, Florida, in 2009. It is envisaged that the routine operation of the ASR will deliver recovered water from ASR wells into Lake Okeechobee with inherently different water quality parameters. However, the addition of ASR well water into such a large, shallow lake has raised concerns about sediment phosphorus stability, which could lead to increased eutrophication in Lake Okeechobee. This paper presents a geochemical assessment to explore possible impacts of the addition of ASR well water on lake sediment in terms of phosphorus adsorption, desorption, and diffusion processes via laboratory-scale batch and column tests. Based on five different mixing ratios of ASR well water and lake water, estimated isotherms, and piston velocity calculations, a mechanistic modeling analysis provided a better understanding of the fate of sediment phosphorus and its transport processes. A final multicriteria decision analysis suggests that the mixing ratio of 1:10 between ASR well water and lake water is deemed more applicable than others based on the given composition of ASR well water, which might buffer more external phosphorus loading in the long run.  相似文献   

14.
Lake margin sedimentary systems have been the subject of only limited study. The cyclic Middle Devonian lacustrine succession of Northern Scotland contains repeated developments of shore zone sandstones and thus provides an ideal location for the study of these units. The cycles comprise deep lake, shallow lake, playa and shore zone facies. Detailed field observations are presented alongside ground penetrating radar data which has aided large‐scale and three‐dimensional characterization of the shore zone sand bodies. Loading and discrete channel forms are recognized in thin‐bedded sandstones within the lower portion of the lake shore zone successions. Up‐section, the sandstone beds appear to become amalgamated, forming subtle low angle accretionary bar complexes. Where imaged on the radar profiles, the repeated development of shoreward migrating features succeeded by more shallow angled lakeward accreting surfaces is recognized; these are ascribed to washover and swash–backwash processes, respectively. The orientation of these features is similar to palaeocurrent measurements from oscillation ripples, suggesting an alignment of the shore zone bars perpendicular to the prevailing wind direction. Further loaded sandstone beds and sand‐filled shallow channel features overlie the bar forms. The context of the shore zone facies allows the controls on its formation to be examined. The shore zone sandstones overlie playa facies which contain abundant desiccation horizons, reflecting the most arid phase in the climatically controlled lacustrine cycle. As climatic conditions ameliorated, the rejuvenation of fluvial systems resulted in the transport of sand out into the basin. Initial deposition was limited to intermittent events where sediment was laid down on a water‐saturated substrate. High resolution fluctuations in lake level resulted in periodic short‐lived reworking events along the lake margins which produced amalgamated sands, forming low relief bars. Shore zone reworking is likely to have occurred over a wide  area as the lake margin migrated back and forth, and gradually transgressed.  相似文献   

15.
Eolian and subaqueous landforms composed of gypsum sand provide geomorphic evidence for a wet episode at the termination of glacial climate in southwestern North America. Drying of pluvial Lake Estancia, central New Mexico, occurred after ca. 12,000 14C yr B.P. Thereafter, eolian landforms on the old lake floor, constructed of gypsum sand, were overridden by rising lake water, modified by subaqueous processes, and organized into beach ridges along the lake's eastern shore. Preservation of preexisting eolian landforms in the shallow lake suggests abupt changes in lake level and climate. Available radiocarbon ages suggest that the final highstand recorded by beach ridges may have developed during the Younger Dryas (YD) stade. The beach ridges provide information about lake surface area, which was 45% of the lake area reached during the maximum highstands of the late Pleistocene. A similar proportional response has been reported for YD climate changes outside the North Atlantic region.  相似文献   

16.
This paper presents a sedimentary record from Lake ?ukie located in the southeastern part of the Central European Plain, beyond the reach of the maximum extent of the last glaciation. The lake has thermokarstic origin and developed during the last glacial termination due to subsidence of the sub‐Quaternary carbonate basement triggered by permafrost thawing. A sediment core was investigated to reconstruct water trophic state and lake depth changes during the Holocene. We aimed at showing the relationship between ecological and geochemical changes in the lake and regional/supraregional climatic and hydrological trends throughout the Holocene. Results of subfossil Cladocera analysis were combined with data on the geochemistry and stable C and O isotopes in sedimentary carbonates. Isotopic and geochemical proxies helped to detect sources of sedimentary particles in the lake and thus to reconstruct changes in the intensity of atmospheric and catchment processes (e.g. precipitation and surface runoff). The Cladocera analysis results indicated endogenic processes in the lake such as trophic changes. Our data revealed that Lake ?ukie has always been a rather eutrophic water body and the periods of particularly high productivity were in the lower Preboreal and upper Subatlantic. Periods of increased water depth were recorded in the lower Preboreal, lower Boreal and upper Subboreal, whereas low water stands were obtained during the late Preboreal, late Boreal, late Atlantic and Atlantic/Subboreal transition as well as during the lower Subboreal. The sediment succession from Lake ?ukie provides the first full Holocene record of carbon and oxygen stable isotopes in lacustrine carbonates from the eastern part of the Central European Lowland. The record is characterized by uncommonly high δ13C and δ18O values of the carbonates resulting from a combination of within‐lake processes and dissolution of the carbonate bedrock of Cretaceous age. The impact of the old carbonates on isotope values was helpful in the reconstruction of the catchment forcing on the lake.  相似文献   

17.
We combine information on the influence of temperature on the thermal physiology, growth, and survival of sockeye salmon (Oncorhynchus nerka) with projections of temperature change associated with a doubling of atmospheric CO2 concentrations (over pre-industrial levels) to determine the effect of global warming on two freshwater life history stages (lake residence of juveniles, and spawning by adults) of sockeye salmon from Adams River, British Columbia. Air temperatures are expected to increase by approximately 4.0° and 2.5° C in the summer and winter respectively in the vicinity of the Adams River. Shuswap Lake is used as a rearing area by the juvenile sockeye salmon and global warming will probably change the production characteristics of lake towards a more oligotrophic system. This will cause a reduction in the abundance and availability of food for the juvenile sockeye salmon, and hence a decrease in their freshwater growth, and freshwater and marine survival. However, the increased temperature encountered by adults on the spawning grounds of the Adams River is unlikely to result in higher rates of prespawning mortality. It is anticipated that the net effect of global warming over all freshwater life history stages will be a reduction in the freshwater production of Adams River sockeye salmon.  相似文献   

18.
Here we discuss paleoenvironmental evolution in the Baikal region during the Holocene using new records of aquatic (diatom) and terrestrial vegetation changes from Hovsgol, Mongolia's largest and deepest lake. We reconcile previous contradictory Baikal timescales by constraining reservoir corrections of AMS dates on bulk sedimentary organic carbon. Synthesis of the Holocene records in the Baikal watershed reveals a northward progression in landscape/vegetation changes and an anti-phase behavior of diatom and biogenic silica proxies in neighboring rift lakes. In Lake Baikal, these proxies appear to be responsive to annual temperature increases after 6 ka, whereas in Lake Hovsgol they respond to higher precipitation/runoff from 11 to 7 ka. Unlike around Lake Baikal, warmer summers between 6 and 3.5 ka resulted in the decline, not expansion, of forest vegetation around Lake Hovsgol, apparently as a result of higher soil temperatures and lower moisture availability. The regional climatic proxy data are consistent with a series of 500-yr time slice Holocene GCM simulations for continental Eurasia. Our results allow reevaluation of the concepts of ‘the Holocene optimum’ and a ‘maximum of the Asian summer monsoon’, as applied to paleoclimate records from continental Asia.  相似文献   

19.
人类活动和气候变化对红碱淖水面面积的影响   总被引：2，自引：0，他引：2  
李登科  卓静  王钊 《冰川冻土》2009,31(6):1110-1115
红碱淖是我国面积最大的沙漠淡水湖泊, 也是全世界最大的遗鸥繁殖与栖息地, 对该地区水面面积变化进行动态监测分析具有重要意义. 利用TM、 中巴资源卫星影像对红碱淖水面面积进行解译, 结合前人的研究成果, 对红碱淖水面面积的动态变化进行了模拟, 分析了引起红碱淖水面面积急剧萎缩的原因. 结果表明: 20世纪90年代以来红碱淖水面面积在大幅度萎缩, 水位急剧下降. 红碱淖水面面积急剧萎缩是气候变化和人为影响因素综合作用的结果, 可能的影响因素有气候变化、灌溉用水、生态环境建设、煤矿开采用水排水和水源地开采等5个方面, 其中上游河流截流是主要原因.  相似文献   

20.
Lake Kastoria is a shallow lake with many anthropogenic activities concentrated in its catchment area. Surficial runoff rich in agricultural waste and underground seepage from urban and rural areas enrich the lake with nutrients intensifying the eutrophication problem of the water.Restoration techniques, with different approach, each one are proposed to restore the lake water. Treatment with alum is very effective but needs special care during the application. Reeds harvesting is an inexpensive and effective way and in combination with the city sewage redirection will improve the water quality and the trophic status of the lake sufficiently.  相似文献   

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