Lake Level Changes Recorded by Tree Rings of Lakeshore Shrubs： A Case Study at the Lake West-Juyan, Inner Mongolia, China

Variation in water resources is a main factor influencing ecohydrological processes and sustainable development in arid regions. Lake level changes are a useful indicator of the variability in water resources. However, observational records of changes in lake levels are usually too short to give an understanding of the long-term variability. In the present study, we investigated the tree rings of shrubs growing on the lakeshore of Lake West-Juyan, the terminus of the Heihe River in western China, and found that Lake West-Juyan had undergone degradation three times over the past 200 years. The lake level decreased from 904.3 to 896.8 m above sea level （a.s.1.） during the period 1800-1900, to 892.0 m a.s.1, from around 1900 to the late 1950s, and the lake dried out in 1963. The trend for changes in lake levels, which was represented by the composite chronology of three beach bars, showed that the phases of increasing lake levels over the past 150 years were during the periods 1852-1871, 1932-1952, 1973-1982, and 1995-1999. Comparison with the history of regional economic development showed that human activity has played an important role in regulating the water resources of the lower reaches of the Heihe watershed over the past 200 years.     

Water level fluctuations in Lake Baringo,Kenya, during the 19th and 20th centuries: Evidence from lake sediments

This article presents a fossil diatom-based, semi-quantitative reconstruction of water level fluctuations for Lake Baringo over the past 200 years as a consequence of climatic variations. A 285 cm long sediment core sample was collected using a Rod-Operated Single-drive Stationary Piston corer. Lake level was inferred using indices based on the proportion of planktonic to benthic diatom taxa (P/B ratio). The sediment archive presented distinct zones dominated by planktonic and benthic diatom flora. An initial transgression in the early 19th century was characterised as a shallow water environment dominated by planktonic Aulacoseira spp. This was a response to extreme drought during the late 18th to early 19th century. Mid-19th century was defined by a high lake stand. The late 19th to early 20th centuries experienced low water level following the widely documented aridity at the time. The mid-20th century was marked by a spectacular rise in water level that coincided with remarkably wet years during the early 1960s and late 1970s. The first decade of the 21st century witnessed widespread changes in water level. The proxy records show that lake ramping and drawdown over the years follow approximately 50-year climatic cycles.     

Long-term GIS-based records of habitat changes in a Lake Erie coastal marsh

Great Lakes wetlands have lost much of their historical extent, structure and function. Their transformation was influenced by a number of factors acting over a period of decades including modifications in the basin's hydrology (watershed drainage, dikes, lake levels), biology (exotic species), geology (sediment transport and composition), and chemistry (water quality). The relative importance of each of these catalysts likely varied from region to region and depended on pre-settlement conditions and natural variability in the marshes, both generally unknown. We applied Geographic Information Systems (GIS) technology to a 120-year record (1872–1991) of images of a 2000-ha marsh system along the southwestern shore of Lake Erie, Ohio, USA. Long-term variability in aggregate characteristics of wetland vegetation was linked with environmental changes and human impact in three regions representing (1) a naturally existing open marsh with the lowest relative topograhical elevation, (2) an open marsh with a protected exposure to the lake and higher elevation, and (3) a diked marsh with manipulated water levels. The deep, open marsh lost half of its emergents, and a third of its patchiness and edge habitat in the early 1900s, when severe watershed degradations accompanied relatively low Lake Erie water levels. Nearly all remaining emergents were eliminated between 1940 and 1991 in this open marsh, following progressively higher lake levels. In the protected open marsh, the extent of emergents fluctuated with lake levels until 1977, and declined severely since then during sustained high lake levels. Habitat parameters varied little until recent decades, but declined markedly thereafter. The diked marsh maintained pre-1900 conditions for emergent plants, patchiness, and habitat edge; variability was linked to breached dikes and the presence/absence of marsh management. No landward re-establishment of the entire marsh complex since 1873 was evident on the 10 images studied. We propose the interaction of three forcing functions as the principal mechanism controlling the historical and current distribution of aquatic plants in southwestern Lake Erie marshes. These factors, collectively referred to as the Landward Advance Paradigm (LAP), include (1) the restricted ability of the marshes to advance landward, (2) sustained above-average lake levels, and (3) the presence of carp ( Cyprinus carpio) in wetlands with silt and clay sediments. Management focused on enhancing the role of Lake Erie wetlands should consider these landscape-level alterations and attempt to maximize wetland functions within the context of the LAP.     

Combining monitoring,models and palaeolimnology to assess ecosystem response to environmental change at monthly to millennial timescales: the stability of Blue Lake,North Stradbroke Island,Australia

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Sulfate distribution in a multi-basin, saline lake

Devils Lake in northeastern North Dakota (USA) is a terminal lake of glacial origin with a substantial sulfate content. Since 1940, the lake water level has risen over 13.5m and salinity has decreased. Devils Lake consists of a series of interconnected basins with sulfate concentration increasing in an eastward direction from 450mg/l in West Bay to 3000mg/l in East Devils Lake. Using sulfate as a tracer and linking measurements of specific conductance with observed time series of water surface elevations, wind, and water velocity, this paper illustrates the magnitude and dynamics of mass transport and exchange processes between the multiple basins of Devils Lake. Measurements show small horizontal salinity gradients within the lake basins, but large salinity gradients in some of the exchange zones connecting basins. Vertical salinity gradients were observed in small basins and near exchange zones with strong horizontal salinity differentials. These instances of vertical stratification were associated with buoyancy driven exchange flows and wind sheltering. Exchange flow velocities between selected basins were correlated with wind direction and speed. Interbasin exchange flows were found to reverse direction frequently in response to the prevailing wind direction. Flow direction frequencies in one specific exchange zone were 31% west to east, 48% east to west, and 21% bidirectional (stratified). At the lake level observed in 2000, time averaged, measured interbasin exchange flow rates were 30--40m³/s compared to tributary inflow rates to the lake of 3--9m³/s.     

Ecosystem evolution of Lake Gusinoe (Transbaikal region, Russia)

Lake Gusinoe is situated on a basin originating from Paleozoic and Mesozoic deposits. The recorded history of the lake's ecosystem evolution is no more than 300 years. The present lake drainage basin was formed mainly in the Cenozoic era, but during the past century, major anthropogenic impacts on the lake have occurred. The human-influenced evolution of the ecosystem began in the 1940s with the development of opencut coal mining nearby the lake. Population increase and the building of the Gusinoozersk State Regional Power Plant, the Trans-Mongolian Railroad and an associated station, and military installations were the major sources of anthropogenic impacts. Since the early 1950s about five species of fish have been introduced into Lake Gusinoe or have invaded the lake, and at least six of the native species have disappeared or are in danger of extinction. From our recent investigations, the present environment of the Lake Gusinoe Basin (Gusinoozersk Basin) is divided into four zones hydrogeochemically: (1) ultrafreshwater, (2) freshwater, (3) mineralized water, and (4) hyposaline and saltwater. Some additional data on changes of the chemical components of the drainage basin waters, as well as on the transition of zooplankton and zoobenthic fauna, are presented in consideration of the risk of industrial development, and the perspectives are discussed.     

新疆赛里木湖流域过去373年降水变化的树轮记录

利用采自天山西部赛里木湖流域的树木年轮标准化宽度年表,重建了赛里木湖流域过去373年上年8月到当年7月的降水变化,重建序列的解释方差达到39.8%,多方验证表明,重建结果是稳定可靠的。分析历史降水变化特征表明,赛里木湖流域过去373年的降水经历了6干7湿的阶段变化,其中,持续最长的干旱阶段为1762—1791年,而最为干旱的阶段为1841—1865年;持续最长的湿润阶段为1794—1840年,而最为湿润的阶段为1734—1761年间;赛里木流域历史降水存在3个极端湿润年(1749,1876和1924年)和4个极端干旱年(1714,1775,1847和1917年),1910年代为最干旱的十年;降水变化存在11—12a、3.0a、2.5a、2.1a和2.0a的变化准周期;赛里木湖流域过去373年的降水的阶段变化、周期变化和极端降水年份均与天山北坡中西部和中亚天山山区降水变化具有很好的一致性,本研究的降水重建序列能较好的代表天山北坡中西部和中亚大部分区域历史降水变化。     

星云湖硅藻群落响应近现代人类活动与气候变化的过程

随着人类活动的增强与全球气候变暖的持续,近年来云南湖泊的生态系统功能持续退化,而目前对云南湖泊生态系统的研究还主要集中于单一环境压力的生态效应。以星云湖为研究对象,通过沉积物记录与现代监测资料,识别在湖泊富营养化、气候变化以及人类强烈干扰下硅藻群落结构响应的过程,并甄别驱动群落变化的主要环境压力及其强度。结果显示随着湖泊生产力水平(如沉积物叶绿素a浓度)的增加,硅藻物种组成发生了明显的变化,主成分分析表明了水体富营养化是驱动群落变化的主要环境因子(r=-0.63,P0.001)。简约模型与方差分解的结果表明近200年来(钻孔长度38cm),湖泊营养水平和水动力是驱动星云湖硅藻群落变化的主要环境因子,分别解释了群落变化的18.8%和2.9%;而1951年以后,湖泊营养水平和温度分别解释了硅藻群落结构变化的31.4%和26.8%。研究结果表明了硅藻群落长期变化的主控因子是湖泊营养水平,而人类活动及气候变化等可以通过改变湖泊水动力及湖水温度来驱动硅藻群落的演替,同时抚仙湖-星云湖的连通性也对硅藻群落的演替产生了一定影响。     

近十年太湖生态系统服务功能价值变化评估

理解和把握近年来湖泊生态系统服务功能退化规律的最佳手段是评估其生态系统服务功能价值的变化。以太湖为例,基于近十年来太湖生态系统的科学调查数据,综合运用生态学及经济学方法,对太湖生态系统的四大类功能和11个亚类的服务价值进行了综合评估。研究结果表明,2000年、2003年、2007年和2009年太湖生态系统服务总价值分别为1627.98亿元、1908.68亿元、1503.99亿元和3528.73亿元,保持逐渐升高的趋势,但是在2007年却意外降低。从2000年到2009年太湖生态系统服务功能价值构成发生了一些变化,2000年以供水功能为主体,约占总价值的43%,2003年和2007年变为以航运功能为主体,分别占总价值的41.31%和38.73%,而2009年又变为以旅游功能为主体,约占总价值的52.52%,总体上由供给功能向文化功能转变。航运功能和旅游功能急剧上升而供水功能急剧下降不利于长远发挥的太湖生态服务功能。蓝藻水华的发生可能降低太湖供给功能、支持服务功能和文化服务功能,进而对太湖生态服务的总价值产生负面影响。研究认为太湖生态系统对支持和保护人类社会具有重要的作用,为管理者和决策者有效的保护和管理湖泊生态系统提供了重要的信息。     

Paleolimnological evaluation of historical trophic state conditions in hypereutrophic Lake Thonotosassa, Florida, USA

We used paleolimnological methods to evaluate historical water quality in Lake Thonotosassa, Hillsborough County, Florida, USA. Sediment mapping shows that organic deposits are unevenly distributed in the lake. Two short (<130 cm) sediment cores from the depositional zone were analyzed for radioisotopes (²¹⁰Pb, ²²⁶Ra, and ¹³⁷Cs), bulk density, organic matter concentration, nutrients (C,N,P), and diatoms. ²¹⁰Pb results indicate that the profiles represent > 100 years of sediment accumulation. There is an abrupt change in sediment composition at about the turn of the century (80 cm depth), above which bulk density decreases and concentrations of organic matter, total C, total N, total P, and ²²⁶Ra activity increase. Diatom-based reconstructions of historical water-column trophic conditions indicate progressive nutrient enrichment in the lake during the past 100 years. Stratigraphic changes in diatom assemblages suggest that anthropogenic nutrient loading converted Lake Thonotosassa from a naturally eutrophic system to a hypereutrophic waterbody after 1900. Given the edaphic setting of Lake Thonotosassa, efforts to mitigate recent anthropogenic impacts will, at best, yield the eutrophic conditions that characterized the lake prior to human disturbance. This study illustrates the importance of paleolimnological data for targeting realistic water quality conditions when lake restoration is contemplated.Journal Series No. R-05019 of the Florida Agricultural Experiment Station     

A geomorphic template for the analysis of lake districts applied to the Northern Highland Lake District, Wisconsin, U.S.A.

1. We tested the degree to which a lake's landscape position constrains the expression of limnological features and imposes a characteristic spatial pattern in a glacial lake district, the Northern Highland Lake District in north‐central Wisconsin. 2. We defined lake order as a metric to analyze the effect of landscape position on limnological features. Lake order, analogous to stream order, is based solely on geographical information and is simple to measure. 3. We examined the strength of the relationship between lake order and a set of 25 variables, which included measures of lake morphometry, water optical properties, major ions, nutrients, biology, and human settlement patterns. 4. Lake order explained a significant fraction of the variance of 21 of the 25 variables tested with ANOVA. The fraction of variance explained varied from 12% (maximum depth) to 56% (calcium concentration). The variables most strongly related to lake order were: measures of lake size and shape, concentrations of major ions (except sulfate) and silica, biological variables (chlorophyll concentration, crayfish abundance, and fish species richness), and human‐use variables (density of cottages and resorts). Lake depth, water optical properties, and nutrient concentrations (other than silica) were poorly associated with lake order. 5. Potential explanations for a relationship with lake order differed among variables. In some cases, we could hypothesize a direct link. For example, major ion concentration is a function of groundwater input, which is directly related to lake order. We see these as a direct influence of the geomorphic template left by the retreat of the glacier that led to the formation of this lake district. 6. In other cases, a set of indirect links was hypothesized. For example, the effect of lake order on lake size, water chemistry, and lake connectivity may ultimately explain the relation between lake order and fish species richness. We interpret these relationships as the result of constraints imposed by the geomorphic template on lake development over the last 12 000 years. 7. By identifying relationships between lake characteristics and a measure of landscape position, and by identifying geomorphologic constraints on lake features and lake evolution, our analysis explains an important aspect of the spatial organization of a lake district.     

The Postglacial History of Lake Flarken,Southern Sweden,Interpreted from Subfossil Insect Remains

A correlation of changes in the composition of chironomid and chaoborid remains and changes in sediment chemical composition, floristic, and other faunistic information indicate that a decreasing productivity and an increasing humic level characterized the development of the small Lake Flarken, Southern Sweden, during the postglacial period. Pronounced changes in the fauna were correlated with fluctuations of the water level in the lake, which was caused by changes in the humidity of the climate. Significant human influence on the lake has only occurred in recent years, during which a rapid acidification has caused the most dramatic change in the fauna, by far, in the whole history of the lake.     

Recent history of Lake Ladoga

Combined paleolimnological investigations of a 1.8 m sediment core from the deepest north-western part of Lake Ladoga show stratigraphic changes in granulometric and chemical composition, organic matter content, diatom species composition and chlorophyll a concentration. The sediment accumulation rate was calculated and 5 stages of lake history over the last 4 000 years were described. Changes in lake environment were mainly caused by changes in climate and lake water balance. Human impact on the lake was also traced.     

Organic Carbon Flux to a Large Salt Lake: Pyramid Lake,Nevada, USA

Energy flux to a large, deep, salt lake from phytoplankton, periphyton and macrophyte primary production as well as fluvial transport and wind-transported terrestrial vegetation and dust were quantified. Average areal phytoplankton net photosynthesis was 511 mg C m⁻² d⁻¹. Highest rates were during water-blooms of the bluegreen alga, Nodularia spumigena. Although areal daily net photosynthesis by periphyton in Pyramid Lake was comparable to other salt lakes, annual carbon influx by periphyton was small due to the lake's graben morphology and moderate euphotic depth (mean, 11.9 m). Macrophytes were uncommon and, therefore a minor source of energy. Truckee River is the only major fluvial discharge to Pyramid Lake and dissolved organic carbon was the principal organic carbon fraction in river water. Large upstream water diversions coupled with several drought years resulted in an average fluvial organic carbon load of only 7.3 g Cm⁻²y⁻¹ or 4% of median phytoplankton net photosynthesis. Tumbleweeds were the most common terrestrial plant material observed in Pyramid Lake comprising a maximum projected importance of 6% of total annual carbon input. Windborne dust represented < .1% of annual carbon input. Phytoplankton primary production is the predominant energy source to Pyramid Lake, accounting for over 80% of annual carbon influx. The relative magnitude of autochthonous and allochthonous vectors to the annual carbon budget of this desert salt lake are comparable to those of the few other large lakes for which detailed energy input budgets have been calculated.     

Extreme water level decline effects sediment distribution and composition in Lake Alexandrina,South Australia

Water level decline affects the biophysical environment of shallow lakes. Unprecedented drought in Australia’s Murray–Darling Basin resulted in extreme water level drawdown in the large, shallow Lake Alexandrina at the end of the River Murray. Surface sediment was collected from 22 sites in the lake before and after water levels declined to assess the integrated limnological changes over the period of drawdown. Results indicate an increase in the proportion of organic particles in profundal sediments, as well as an increase of fine particles (<19.9 μm) in peripheral sediments. These changes to sediment composition corresponded to higher concentrations of suspended particles at low water levels. Increased autochthony and a shift in primary production from macrophytes to phytoplankton in Lake Alexandrina support these findings. Inorganic carbon and other nutrients were lost from sandy sediments most likely through carbonate dissolution driven by a localized decrease in pore water pH from increased mineralisation of organic matter.     

The ecological relationships of aquatic plants at Lake Naivasha,Kenya

The distribution and abundance of the aquatic flora of Lake Naivasha has been constrained by two ecosystem-level processes. One is the natural and unpredictable fluctuation of water levels which the lake experiences, resulting in a drawdown zone of several vertical meters. The other is the consequence of herbivory by several alien species, linked with competition between rooted aquatic plants and phytoplankton. The effects of alien introductions in the 1960s and 1970s was to eliminate submerged vegetation from the lake completely by 1982, principally by crayfish herbivory. Vegetation has been progressively returning since 1984 and this return is coincident with a decline in crayfish population density. Concentrations of phytoplankton have progressively increased since 1982 as a result of nutrient increase caused by a decline in water level and papyrus swamp clearance for agriculture. The relationship between high levels of phytoplankton and extensive littoral weed beds is discussed.     

白洋淀最低生态水位研究

由于自然条件的变化、工农业的不合理开发、人口的剧增以及水库和涵闸水利设施的盲目建设等,引发了白洋淀一系列生态环境问题,主要表现为干淀、水污染、生态环境退化、泥沙淤积、湖泊萎缩以及航运中断等。恢复和重建已遭破坏的白洋淀湿地生态系统,并使其至少维持在最低生态水位上是至关重要的问题。在分析白洋淀生态系统功能的基础上,利用水量面积法、最低年平均水位法、年保证率设定法和功能法等4种方法对其最低生态水位进行分析和计算,计算结果分别为7.32 m、7.33m、7.2 8m和7.2 7m。通过合理性分析,认为取它们的平均值即7.30 m作为白洋淀最低生态水位是合理的,符合白洋淀实际情况。     

藏东南巴松错200年沉积过程及其对硅藻记录的影响

青藏高原东南部高寒山区广泛发育冰川湖泊,湖泊沉积过程同时受控于区域气候、流域水文、地质条件及湖泊形态特征。基于放射性²¹⁰Pb/¹³⁷Cs和¹⁴C定年法,对巴松错沉积物理(粒度、分选系数)和化学指标(TOC、TN、C/N)进行分析,发现18世纪末到19世纪末湖泊沉积过程显著变化,表现为迅速变缓趋势。通过分析区域树轮重建的气候序列(温度、降水及相对湿度)及冰川地貌调查资料,认为气候变化及流域冰川分布位置是影响该湖泊沉积过程的重要因素。小冰期末期冰川前缘靠近湖区,随后温度上升导致冰川融水激增、水动力加强,从而引起湖泊沉积粒度的粗化。随着冰川前缘不断后退,径流输送距离增长、沉积分选变好、粒度细化。此外,该地区活跃的地质活动也可能是湖泊沉积过程明显变化的重要诱因。湖泊沉积硅藻是研究气候环境变化的有力指标。过去200多年巴松错硅藻组合变化不明显(DCCA=0.47 SD),说明该地区气候环境变化未超过其生态阈值。通过与其他沉积指标进行对比分析发现,巴松错硅藻记录受到流域水文和湖泊沉积过程影响,主要表现为外源输入和/或湖岸浅水区来源...     

General Description of Partly Meromictic Hypertrophic Lake Verevi,its Ecological Status,Changes during the Past Eight Decades,and Restoration Problems

The present study describes generally the ecosystem of Lake Verevi while more detailed approaches are presented in the same issue. The main task of the article is to estimate long-term changes and find the best method for the restoration of good ecological status. Lake Verevi (surface 12.6 ha, mean depth 3.6 m, maximum depth 11 m, drainage area 1.1 km², water exchange 0.63-times per year) is a hypertrophic hard-water lake located in town Elva (6400 inhabitants). Long-term complex limnological investigations have taken place since 1929. The lake has been contaminated by irregular discharge of urban wastewaters from oxidation ponds since 1978, flood from streets, and infiltrated waters from the surrounding farms. The so-called spring meromixis occurred due to extremely warm springs in recent years. The index value of buffer capacity of Lake Verevi calculated from natural conditions is on the medium level. Water properties were analysed according to the requirements of the EU Water Framework Directive. According to the classification, water quality as a long-term average of surface layers is moderate-good, but the water quality of bottom layers is bad. Values in deeper layers usually exceed 20–30 times the calculated reference values by Vighi and Chiaudani’s model. Naturally, at the beginning of the 20th century the limnological type of the lake was moderately eutrophic. During the 1980s and 1990s the ecosystem was out of balance by abiotic characteristics as well as by plankton indicators. Rapid fluctuations of species composition and abundance can be found in recent years. Seasonal variations are considerable and species composition differs remarkably also in the water column. The dominating macrophyte species vary from year to year. Since the annual amount of precipitation from the atmosphere onto the lake surface is several times higher, the impact of swimmers could be considered irrelevant. Some restoration methods were discussed. The first step, stopping external pollution, was completed by damming the inlet. Drainage (siphoning) of the hypolimnetic water is discussed. Secondary pollution occurs because Fe:P values are below the threshold. The authors propose to use phosphorus precipitation and hypolimnetic aeration instead of siphoning.     

Evaporation and the hydrologic budget of Crater Lake, Oregon

The hydrologic budget of Crater Lake, Oregon is investigated by taking advantage of its relatively simple geometry, climatic circumstances, and the concurrent availability of many years of traditional data. Buoy data are here utilized for the first time for this purpose. The lake gains water through precipitation and delayed runoff from the caldera sides and Wizard Island. The lake loses water through evaporation and seepage. Seepage can be estimated quite well from ice-covered precipitation-free intervals in 1985, and is 127 cm/year. Evaporation has previously been determined as a residual, but is here estimated directly from the floating buoy, with an approximate value of 76 cm/year, a downward revision from previous estimates. These losses are balanced by precipitation input, nearly all in the form of snow or snowmelt runoff. Factors contributing to the uncertainty in each of the water budget components are discussed in some detail. The buoy data corroborate previous findings based on studies of stage that evaporation is greatest on the coldest days. Seasonally, the greatest evaporation occurs in the autumn and the least in spring. Proxy records are used to extend the effective length of the buoy record. Monthly estimates of evaporation are calculated for 1950–1996 and used to deduce temporal characteristics. The standard deviation of water year precipitation is 4.6 times larger than that of evaporation. Thus the water budget is controlled more by variability of precipitation than evaporation. An additional 15 years of data since earlier studies confirm that the annual lake level variations from one September 30 to the next are highly correlated (r = 0.96) with Park Headquarters water year precipitation for the 42 years from 1961–2003. The lake rises 1.4 cm for every cm of measured precipitation over equilibrium value (168.6 cm) at Park Headquarters. Sources of this “magnification” are discussed.