Lake Water Level Changes Research Articles

Upper crustal structure, seismicity and pore pressure variations in an extensional seismic belt through 3-D and 4-D VPand VP/VSmodels: The example of the Val d'Agri area (southern Italy)

[1] We use local earthquake tomography and background seismicity to investigate static and transient features of the crustal velocity structure in the Val d'Agri (southern Apennines, Italy), one of the regions in central Mediterranean with the highest seismogenic potential. The upper crust is dominated by two broad high-velocity anticlines of the buried Apulia Carbonate Platform ramping on two parallel high-angle thrusts interpreted as preexisting inverted normal faults. The deep core of the anticlines consists of very high VP (up to 6.9 km/s) and low VP/VS rocks, suggesting the involvement of the Apulian crystalline basement in the Apennine belt. These results provide valuable constraints on the Apennine belt tectonic evolution, supporting a thick-skinned interpretation for the Pliocene terminal phase of the compressional tectonics. The geometry of the Val d'Agri Quaternary basin is controlled by these inherited compressive features, whereas the presently active extensional tectonics barely reworked the structure. We find inconsistency between the structure of the Apulia Carbonate Platform and the location and geometry of the Quaternary normal faults mapped at the surface. This suggests either the immaturity of the normal faults or their secondary role in accommodating the extension. We observe spatiotemporal (4-D) changes of VP and VP/VS models defining transient variations of pore fluid pressure in the upper crust. A strong change in the VP/VS ratio heralds a raise in the seismicity rate that can be related to large water level changes in a nearby artificial lake. This evidence is consistent with a mechanism of reservoir-induced seismicity by fluid pressure increase and pore pressure diffusion. The 4-D velocity variations are confined in the shallow portion of the upper crust (3–6 km depth) where fluids are stored in a highly fractured medium. Pore pressure fluctuations can affect the strength of fault segments, favoring seismicity rate changes along the active faults and possibly promoting large future earthquakes.

INVESTIGATION OF WATER LEVEL CHANGES OF SOME LAKES IN TURKEY

ABSTRACT Global warming and climate changes are significant environmental issues. Especially people living in coastal areas are mostly affected from the increases or decreases at sea/lake levels occurring due to these changes. This problem has been the subject of many researches especially since the beginning of the 20th century due to large economic losses and environmental problems in the environment, when excessive descends or risse in lake levels have been observed. Changes in lake water levels are affected from the changes of many climate elements. Therefore, in this study, the changes in the minimum, maximum and average water levels of five largest lakes in Turkey were examined using non-parametric Mann-Kendall and Sen's T methods. The starting years of statistically meaningful changes were determined by non-parametric Mann Kendall Rank Correlation test.

6000 years of environmental changes recorded in Blue Lake, South Australia, based on ostracod ecology and valve chemistry

A 4 m long core taken from the freshwater Blue Lake crater near the township of Mount Gambier in southeastern South Australia provided a high-resolution palaeoclimatic record for the last six millennia. Accelerator Mass Spectrometry (AMS) radiocarbon ( 14C) dates were obtained from organic plant fibres and biogenic carbonates from the laminated sequence of the core and from a modern water sample. Large discrepancies between the radiocarbon ages determined from plant fibres and biogenic carbonates indicate the presence of a time-variable lacustrine reservoir, which is consistent with what is known of the lake's hydrology. Ostracod assemblages, associated with stable isotope (δ 13C, δ 18O) analyses and, in combination with Mg/Ca, Sr/Ca and Na/Ca analyses done on ostracod valves, infer salinity, temperature and water level changes in Blue Lake over the last 6 millenia. The influence of local aquifers through time has also been determined from the Na/Ca of ostracod valves. Approximately 900 year cycles are evident in the δ 13C record from 5.4 ka to 1.8 ka. The history of Blue Lake records an initial period of high hydrological variability around 6 ka, becoming increasingly deeper as groundwater flowed into the basin. By 4 ka, the lake had reached steady state with the lake level fluctuating by as much as 9 m, although significant geochemical variations represent temperature fluctuations until European settlement near the lake in 1839.

A modeling study of catchment discharge to Poyang Lake under future climate in China

Poyang Lake, the largest freshwater lake in China, is an important water resource and iconic ecosystem in a region that has been subjected to extreme droughts and floods in recent decades. The lake’s water level is heavily influenced by the watershed inflows and also by the Yangtze River from the north of the lake basin. Assessing the impact of future climate change on the watershed inflows and the subsequent influence on changes in the lake water level is important for developing effective management strategies for local water resources and for mitigation of future droughts and floods. In this study, the large-scale, distributed hydrological model, WATLAC, was applied to the Poyang lake watershed to study the possible impacts of future climate change on both inflow generation and changes in lake water level. The Global Circulation Model ECHAM5 was used to predict future climate conditions for the watershed. Simulations of WATLAC show that annual catchment inflow will increase by 2.9% and 6.5% for A1B and B1 scenarios, respectively, and will decrease by 5.2% for A2 scenario for 2011–2050 compared to that for 1961–2000. Further analyses demonstrate that changes in monthly distribution of catchment inflow will result in an increase of lake water level of 0.10–1.34 m from February to July and a decrease of 0.32–1.31 m from September to February under the three climate change scenarios. It is concluded that climate change impacts on Poyang Lake are expected to be manifested with more extreme droughts and floods in the future.

Climate-related changes of phytoplankton seasonality in large shallow Lake Võrtsjärv, Estonia

Water level changes (7-year moving averages) in Lake Võrtsjärv (Estonia) during 1885–2000 were correlated with winter patterns in the North Atlantic Oscillation (NAO) index. In this shallow lake (270 km2, mean depth 2.8 m), where the annual water level amplitude is 1.4 m and the absolute range is 3.2 m, hydrology is the main driving force for the ecosystem. Control of phytoplankton growth was mediated by ice conditions in spring, and by water level in summer and autumn. Winter air temperature similarly influenced the biomass of cyanobacteria and diatoms in spring; while the effect of the ice-cover duration was more pronounced on cyanobacteria. Mean depth of the lake did not affect the phytoplankton biomass in spring, but clearly controlled it in summer and autumn. The direct impact of winter conditions on biological processes was restricted to a short post-winter period, but extended indirectly as the water level for the entire growing season depended strongly on the height of the spring flood peak.

Reconstruction of palaeovegetation and sedimentation conditions in the area of ancient Lake Burtnieks, northern Latvia

Palaeobotanical investigations were carried out with the aim of reconstructing the development of palaeovegetation and formation of sediments in the northeastern area of ancient Lake Burtnieks. Pollen and plant macroremain studies provide information on vegetation development in the surroundings of the lake, including Stone Age settlements of Brauksas Ⅰ and Brauksas Ⅱ. Results of the investigations indicate that the development of vegetation together with sedimentation conditions in the palaeolake have changed since the Younger Dryas until today. Vegetation composition varies in different parts of the ancient Lake Burtnieks area due to past changes in lake water level which reached different sites at different times. Data from the northern part of ancient Lake Burtnieks indicate its gradual overgrowing since the Preboreal. Deposition of minerogenic lacustrine sediments (silt, clayey silt and sand) lasted until the Boreal or the Atlantic time, depending on the water depth of the lake locality. Clastic sediments were overlain by gyttja, which in turn was later covered by well-decomposed fen (sedge, sedge-grass) peat that started to form at the end of Atlantic time. Pollen and plant macroremain composition of lacustrine sediments and fen peat sequences suggests that people have inhabited the area since Preboreal-Boreal times. However, weak traces of possible presence of people are found already at the very end of the Younger Dryas. Fluctuating curves of broadleaved tree pollen, a significant amount of pollen of cultivated plants and charcoal dust in sediments indicate activities of an early man and refer to start of crop growing in the area in the second half of the Atlantic chronozone.

Active faults and induced seismicity in the Val d’Agri area (Southern Apennines, Italy)

SUMMARY The NW–SE trending Val d’Agri extensional basin is one of the regions in Italy with the highest seismogenic potential. Field data do not univocally define which of the fault systems bordering the basin on the two opposite sides is accommodating the active deformation. In this study, we detect and locate, by using an automatic picking procedure, almost 2000 low-magnitude earthquakes (−0.2 < ML < 2.7) recorded by a dense network during a 13-months-long seismic experiment. Events are mostly located along the southwestern flank of the basin. To the south, intense swarm-type microseismicity defines a major cluster ∼5 km wide from 1 to 5 km depth. To the west, a clear alignment of events, characterized by normal faulting kinematics, defines a NE-dipping normal fault between 1 and 6 km depth. The upward continuation of this structure, ∼5 km long, matches a mapped active normal fault recognized by field and palaeoseismological surveys. A temporal correlation found between the intense swarm-type microseismicity and the water level changes in the nearby artificial Pertusillo lake suggests that this seismicity is reservoir-induced.

Temporal monitoring of water level changes in Seyfe Lake using remote sensing

AbstractThe Earth's water resources are endangered by inconsiderate use, pollution and lack of conservation measures. Temporal monitoring is necessary for the conservation and usage planning of water resources and to make informed decisions. Seyfe Lake and its environs in Turkey is one of the most important water basins in the world, because it is a node on bird migration paths between Europe, Asia and Africa. For this reason, the International Council of Bird Preservation (ICBP) has registered 27 of the bird species living at Seyfe Lake on the conservation list. In this work, the temporal changes in the water surface area of Seyfe Lake and its environs, which are important for ecological, historical and tourism reasons, are investigated. The change of water surface in the lake is examined over a 26 year period using satellite images taken between 1975 and 2001. Landsat images from years 1975, 1987 and 2001 are used. The change is tracked from the images using an unsupervised classification method. A decrease of slightly more than 33% was observed in the water surface area this 26 year period. The temporal change indicated by the images was compared with the related meteorological data between 1975 and 2001. Over this time period, climate conditions (rainfall, temperature and evaporation) in the study area have been changed by approximately 21%. These changes could have affected the Lake surface area, but so also could external human interference around the Lake. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Plant-associated invertebrates and hydrological balance in the large volcanic Lake Bracciano (Central Italy) during two years with different water levels

Lakes in the Mediterranean region experience an altered hydrological balance with large water level reductions and/or fluctuations within and between years. To date, little is known about the reaction of invertebrate assemblages inhabiting the littoral zone to water level changes in natural lakes. Here, we present the case of the volcanic Lake Bracciano, one of the largest and deepest Italian lakes. We compared the numerical composition and taxonomic richness of plant-associated invertebrate assemblages sampled from three sites and three depth ranges (0–4 m, 4–8 m and 8–15 m) between years with different water levels. Using historical data, we built a hydrological balance model to assess the role of different water budget components on the water levels. The hydrological balance showed that the volume of water currently abstracted for human use exceeds the potential changes caused by the projected warming of climate and decreasing amount of precipitation by nearly an order of magnitude. In a low water level year, littoral macrophytes and invertebrate assemblages exhibited qualitative and quantitative differences at all sampling sites and depths. The invertebrate assemblage showed a reduced taxonomic richness and lower numerical abundance of the more sessile forms (water mites, gastropods, nematodes, naidid oligochaetes), which feed directly on living plants or epiphytic algae, and an increase of more mobile and/or detritivore taxa.

Water level changes in a large shallow lake as reflected by the plankton:periphyton-ratio of sedimentary diatoms

Biostratigraphic diatom analyses were carried out on a short sediment core from the large shallow-water Lake Vortsjarv, Estonia, in order to relate the diatom composition to the instrumental water level record. We dated the sediment core by radiometric methods (210Pb, 137Cs, 241Am) and spheroidal fly-ash particle abundance chronology and evaluated the statistical significance of the relationships between the percentage of planktonic diatoms and the water level continuously monitored since 1871. Before the 1960s, the percentage of planktonic diatoms in the sediment showed quite strong positive relationship to water level. The impact of eutrophication after the 1960s presumably masked the influence of water level changes on the diatom community. In addition, statistical analysis of the upper part of the sediment core (1970—present day) together with measured limnological parameters of the lake showed that water transparency had the strongest influence on diatoms, while temperature, pH and alkalinity had lesser impacts. Our study shows that the planktonic:periphytic diatom ratio in the sediment can be used to track overall trends of the lake-level changes in Lake Vortsjarv before the onset of cultural eutrophication; however, the results have to be interpreted carefully, taking into consideration other possible limnological factors such as water transparency, nutrients and wind.

Long-Term Water Level Changes in Closed-Basin Lakes of the Canadian Prairies

The semi-arid prairie region of Canada has many closed-basin lakes that are sensitive to climatic variability and change. Long-term water level changes in these lakes provide a measure of the dynamic balance between runoff and precipitation supplying water to the lakes and water loss from the lakes by evaporation. Historic lake water level data can help to improve understanding and prediction of the hydrologic effects of climate change and land-use changes. Water level data for sixteen closed-basin lakes in the Canadian prairies were compiled from a variety of sources and additional measurements were made at some locations. In the Canadian prairie region there is an overall pattern throughout most of the twentieth century of declining lake levels, although with notable exceptions. Possible causes of lake level changes are assessed briefly, but the main objective is to present a regional and long-term perspective on lake level records.

The changing face of the Ethiopian rift lakes and their environs: call of the time

AbstractThe Ethiopian rift is characterized by many perennial rivers, and a chain of lakes that vary in size, and hydrological and hydrogeological settings. The water resources of the Rift lakes are one of the focal points for large‐scale development in Ethiopia over the last few decades. Some of the lakes and their influent rivers are used for irrigation, soda abstraction, fish farming and recreation, and also support a wide variety of endemic birds and wild animals. Ethiopia's major mechanized irrigation farms and commercial fishery are confined within the Rift region. A few of the lakes have shrunk in surface area because of excessive water abstractions, while others have expanded because of increased surface run‐off and groundwater inflows from percolated irrigation water. Excessive land degradation, deforestation and over‐irrigation have changed the hydrological setting of a few Rift lakes. Human activities, in combination with changes in climate and geology, have influenced the hydrological setting and the water quality of the lakes, with the salinity and major ion composition dramatically changed in some of them. This study tries to address the challenges associated with development of these surface‐water resources, focusing on environmental problems arising over the past few decades on three lakes (Abiyata, Beseka and Ziway) situated along the tectonically active Rift floor. The methods utilized in this study include field hydrological and hydrogeological mapping, supported by aerial photographs and satellite imagery interpretations, as well as hydrometeorological and hydrochemical data analysis, and catchment hydrological modeling. A converging‐evidence approach was adapted to reconstruct the temporal and spatial variations of the lake water levels and surface areas. The study results revealed that the major changes in the Rift Valley are related primarily to recent improper use of water from the large rivers draining the Rift Valley floor and the lake catchments, and from direct lake water abstractions aggravated intermittently by climatic and land use changes. These changes represent grave environmental consequences on the fragile Rift ecosystem that demands urgent intervention in the context of an integrated, basin‐wide water management approach. This study emphasizes lake water level changes and human influences on these changes. It also assesses human interactions and water quality changes, including land use changes and environmental repercussions on the lakes, as well as providing recommendations on how these issues should be addressed.

Environmental biogeochemistry of mercury in Antarctic ecosystems

Polar regions are recognized as important sinks for long-range transport and deposition of Hg derived from natural and anthropogenic sources at lower latitudes. In previous studies we found enhanced Hg accumulation in soils, mosses and lichens from ice-free areas of Victoria Land facing the Terra Nova Bay coastal polynya. This study extends research to the distribution of organic C, total N, S, Hg, Al and Fe in surface soils, cyanobacterial mats and short sediment cores from four lacustrine ecosystems, each with different environmental characteristics and varying distances from the polynya. Results show that planktonic and benthic mats from lakes, along with mosses in the watershed, are the main sinks for Hg in summer meltwater. The C-normalized Hg concentrations in short sediment cores were higher in samples from lakes more exposed to marine aerosols from the coastal polynya. Reactive halogens in the aerosol promote the oxidation and deposition of atmospheric Hg in coastal ecosystems. The analysis of sediment cores did not reveal increasing Hg concentrations in recent sediments, except in the Lake 14 at Edmonson Point. The latter ice-free area is unaffected by the polynya and the increase in Hg concentrations in surface sediments could be due to local changes in lake water level and S biogeochemistry. Although change in sea ice coverage may enhance the role of Antarctic coastal ecosystems as sink in the global Hg cycle, our results seem to exclude possible risks for Antarctic terrestrial and freshwater organisms.

Extensive spatial analysis of the light environment in a subtropical shallow lake, Laguna Iber�, Argentina

Variations in the attenuation of photosynthetically available radiation were analysed using extensive spatial sampling in two seasons in a subtropical wetland lake. Simultaneously with the attenuation measurements, the principal absorption and scattering components of the water column were also measured. The elevated spatial resolution used in the study allowed the determination of spatially distinct optical water classes within the lake. Changes in dissolved organic matter, phytoplankton and tripton concentrations led to a wide variation in the vertical attenuation coefficients. These changes depended on local characteristics of the ecosystem and time of year. The spatial distribution of the attenuation coefficients was examined in relation to the hydrological and geomorphological characteristics of the littoral area of the lake. The impacts of two small rivers on the light environment and attenuation components are shown. Finally, the resulting model was used to examine the possible impacts of changes in light availability at the lake bottom in relation to recent changes in lake water level.

Human Settlements on the Northern Shores of Lake Aral and Water Level Changes

The shore of Lake Aral in Kazakhstan is a perfect area for studying the human adaptation strategy to past climate changes. New archaeological material, gathered along the northern shores during the expedition of the INTAS project ‘CLIMAN’, is briefly presented. Changes in settlement activity during the Atlantic and Subboreal are related to lake level changes of the Aral Sea. A previ-ously proposed lake level maximum needs to be revised. In particular the lake level stand at 72/73 m, with an assumed age of 5000 BP is definitely refused. Based on the presented data the maximum lake level most probably never reached beyond 57/58 mean average sea level (masl). Furthermore the regression during the 15th–16th centuries has been underestimated. It may have been lower than the present day level. Thus the present desiccation of the Aral Sea is historically not unique, as a similar regression, probably induced by man as well, has occurred at least once during history. A readjustment of the water level is, therefore, possible at any time.

Water level changes in a large Amazon lake measured with spaceborne radar interferometry and altimetry

We demonstrate that interferometric processing of JERS‐1 SAR data over an Amazon lake containing ∼1500 islands yields centimeter‐scale changes in the height of the water surface from February 14 to March 30, 1997. For the method to work, we qualitatively find that inundation of about one or two leafless trees per 25 m² multi‐look SAR pixel is sufficient to return the radar pulse to the side‐looking antenna. Validation is provided by multi‐temporal TOPEX‐POSEIDON altimetry profiles, which directly measure surface heights relative to a fixed datum. Because SAR provides an image, the water height changes (∼12 cm) can be converted to a net volume measurement (280 million m³) over the 44 days separating the JERS‐1 acquisitions. Compared to historical gauge records, removal of this volume from the lake required a ∼50% greater flow.

Palaeolimnological approaches to climate change, with special regard to the biological record

Lakes systems respond physically, chemically and biologically to changes in climate and these responses are registered in many various ways in lake sediment records. This paper focuses principally on the biological record and describes recent research that aims to reconstruct (i) past variability in effective moisture, and (ii) past variability in temperature. Changes in effective moisture are manifested especially by changes in lake water level. In closed lake basins water level change can cause significant changes in water salinity that is registered in sediments by changes in the composition of fossil assemblages, especially diatoms. In open (freshwater) lake basins changes in water level are best reconstructed from the aquatic macrofossil record and potentially from the ratio of open water to littoral species of Cladocera, ostracods and diatoms. The most promising biological method for reconstructing past temperature is chironomid analysis, and a range of new chironomid-temperature transfer functions are being developed. However, biological responses to changing temperature are usually indirect as a result of temperature effects on water-column stratification, nutrient cycling and alkalinity generation, and in most cases a correct interpretation of the climatic significance of changes in the fossil record requires an understanding of the processes that are operating in the water column. A multi-proxy, whole-lake approach is advocated as the best way forward, not only as a means of reconstructing past climate but also as a means of assessing the impact of climate change on lake systems

Gravitational effect of water circulation in the northwest Yunnan

Water circulation is the main disturbance source against precise gravimetry measurement which is one of the principal means of geodynamic study. Some scientists studied the disturbance of water level changes in lakes and rivers and groundwater activities on gravity field. Taking water circulation as a whole and combining it with the hydrogeological conditions in northwest Yunnan mountainous area and the measured gravity data, this paper studies the features, connections of water circulation in atmosphere, on surface and under ground and its effect on gravimetric data. The main conclusions are as follows: 1) The water circulation in atmosphere has little direct disturbance on gravity field; 2) The change of lake water level may cause gravitational effect of (10–20)×10−8 m · s−2; 3) In the NW Yunnan, types of the groundwater are various, and its changes are complicated, it is necessary to study point by point. In general, its disturbance on gravity field in this region is about 10×10−8 m · s−2, less than that in plain area.

European lakes as palaeohydrological and palaeoclimatic indicators

Lakes in temperate regions have fluctuated in size on annual to millenial time scales. Changes in water level or depth can be reconstructed by applying geomorphic, sedimentological and biostratigraphic methods to transects of sediment cores. This systematic, field-based approach has been used at a number of sites in Europe. It is illustrated by reconstructions of water-level changes in lakes from southern Sweden. These lakes have shown broadly synchronous changes during the Holocene. Such synchronous changes in water levels at several sites in a region reflect climatic changes. Inferences about the mechanism of the climatic change depend on identifying both synchronous changes within a region and differences in the direction, magnitude and timing of lake-level changes between regions. Continental compilations of lake-level data are therefore necessary. Detailed studies are not available from enough sites, but the interpretation of already existing stratigraphic and biostratigraphic data in terms of lake-level changes has greatly increased the number of sites available for a continental-scale synthesis in Europe. This eclectic, literature-based approach is illustrated with examples from southern Europe. Lakes in the Mediterranean region were high around the glacial maximum and again somtime during the first half of the Holocene. In the western Mediterranean, the peak of late-glacial aridity occurred at 15,000–16,000 BP and the lakes were already high again by 12,000 BP. In the east, maximum late-glacial aridity occurred between 13,000 and 11,000 BP and there was a gradual return to wetter climates during the early Holocene such that 9000 BP was more arid than 6000 BP. Most lakes in the Mediterranean region were high at 6000 BP. The transition to arid conditions after 5000 BP occurred abruptly in the west and more gradually in the east. The lakes of southern Sweden indicate drier climates in the early Holocene (ca. 9000 BP), more effective moisture between 8000 and 6000 BP, increased aridity between 5500 and 3500 BP, and increased effective moisture again during the last 3000 years. The history of lake-level changes in southern Sweden and the Mediterranean region can be partially explained in terms of changes in the direct effects of insolation, and in the strength and position of the Westerlies and of the subtropical high pressure cell during the Late Quaternary.

Lake Mullsjön ‐ a key site for understanding the final stage of the Baltic Ice Lake east of Mt. Billingen

The deglaciation pattern at Mt. Billingen, within the Middle Swedish end moraine zone, and its relationship with dramatic water level changes in the Baltic Ice Lake is a classic topic of Swedish Quaternary Geology. Based on data west of Mt. Billingen, the authors (in two earlier papers) presented a stratigraphic model associated with this subject. This study is an attempt to test the model east of Mt. Billingen, i.e. inside the Baltic Ice Lake itself. Lake Mullsjon is situated 30 km southeast of the drainage area of the Baltic Ice Lake and within the final drainage zone. About 8 m of Late Weichselian sediments (mostly varved clay) were recovered from the lake and analysed from different stratigraphic viewpoints, including lithology, grainsize, varve chronology, and pollen. These analyses show that the site was deglaciated in the later part of the Allerød Chronozone. Shortly thereafter the first drainage of the Baltice Ice Lake took place but without isolating Lake Mullsjon. After a short period of disturbed sedimentation varved clay continued to form as the glacier receded for another 120 varve years until the onset of the Younger Dryas cooling, as registered both in the pollen and in the varve stratigraphies. After c. another 120 varve years our analyses suggest that the Baltic Ice Lake was dammed once again. About 230 varve years of further ice readvance followed west of Mt. Billingen, while the ice margin in the east was more or less stationary. Rapid melting set in, at first producing coarse varves, but soon the clay was thin‐varved and fine. This continued for 140 varve years until suddenly the lake became isolated. At this isolation thick beds of silty‐sandy deposits were deposited on the lake floor. The isolation is dated to 10,400–10,500 14C years B.P., which corresponds to the assumed age of the final drainage of the Baltic Ice Lake. It was also isolated at the same time as lakes (on the same isobase) situated 20 m lower, but west of Mt. Billingen, were raised above sea level. This strongly suggests that Lake Mullsjön was isolated as an effect of the drainage of the Baltic Ice Lake. Significant differences between the clay‐varve and the 14C chronologies are also presented.