Home About us Contact
|
Home About us Contact | ||
|
|
||
Level Fluctuations (level + fluctuation)
Kinds of Level Fluctuations Selected AbstractsTerrestrial invertebrates inhabiting lowland river floodplains of Central Amazonia and Central Europe: a reviewFRESHWATER BIOLOGY, Issue 4 2002JOACHIM ADIS 1.,Amazonian terrestrial invertebrates produce high population densities during favourable periods and may suffer a drastic decrease during occasional floods and droughts. However, the monomodal, predictable flood pulse of the larger Amazonian rivers favours the development of morphological (respiratory organs, wing-dimorphism), phenological (synchronization of life cycles, univoltine mode of life), physiological (flooding ability, gonad dormancy, alternating number of developmental stages), and behavioural adaptations (migration, temporal diving) with numerous interactions. 2.,In lowlands of Central Europe, the flood pulse of large rivers is less predictable than in Central Amazonia and is superimposed by the seasonal light/temperature pulse (summer/winter regime). Some terrestrial invertebrates show physiological resistance against inundation or drought, phenologies fitting the normal annual rhythm of water level fluctuation (quiescence or diapause of eggs or adult invertebrates), high dispersal ability and migration. However, most species survive simply using a `risk strategy', combining high reproduction rates, dispersal and reimmigration following catastrophic events. 3.,The diversity of species in terrestrial invertebrates is lower in lowland riverine ecosystems of Central Amazonia and Central Europe compared with the respective uplands because of flood stress in these systems. However, floodplains in Central Amazonia possess a greater number of endemic species in comparison with Central European floodplains because of long periods of fairly stable climatic conditions in comparison with large palaeoclimatic changes in Central Europe. [source] Spectral decomposition of periodic ground water fluctuation in a coastal aquiferHYDROLOGICAL PROCESSES, Issue 12 2008David Ching-Fang Shih Abstract This research accomplished by the descriptive statistics and spectral analysis of six kinds of time series data gives a complete assessment of periodic fluctuation in significant constituents for the Huakang Shan earthquake monitoring site. Spectral analysis and bandpass filtering techniques are demonstrated to accurately analyse the significant component. Variation in relative ground water heads with a period of 12·6 h is found to be highly related to seawater level fluctuation. Time lag is estimated about 3·78 h. Based on these phenomena, the coastal aquifer formed in an unconsolidated formation can be affected by the nearby seawater body for the semi-diurnal component. Fluctuation in piezometric heads is found to correspond at a rate of 1000 m h,1. Atmospheric pressure presents the significant components at periods of 10·8 h and 7·2 h in a quite different type, compared to relative ground water head and seawater level. Copyright © 2008 John Wiley & Sons, Ltd. [source] Ancient transpacific voyaging to the new world via Pleistocene South Pacific IslandsGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 6 2004Steve Wyatt How humans first arrived in America remains a mystery. Although the Beringian and coastal options have been discussed in detail, a transpacific route from the Old World to the New World via the islands of Oceania has been essentially ignored. Of the many factors involved in completing such a voyage, besides an adequate watercraft, landfall frequency and prevailing winds and currents were most important. A chain of islands in the landless eastern South Pacific, with its consequent and possibly favorable modifications of regional sea surface currents, would have been particularly beneficial to eastbound mariners. Comparing present-day bathymetry with estimated late Pleistocene glacially induced sea level fluctuations suggests that latent islands may actually exist, especially when the effects of other geological phenomena are also considered. If exposed during the last glacial maximum (LGM), such a chain of islands could have provided facilitating layover points for ancient eastbound seafaring explorers, thus making a transpacific journey more plausible. © 2004 Wiley Periodicals, Inc. [source] Modelling lake stage and water balance of Lake Tana, EthiopiaHYDROLOGICAL PROCESSES, Issue 25 2009Yirgalem A. Chebud Abstract The level of Lake Tana, Ethiopia, fluctuates annually and seasonally following the patterns of changes in precipitation. In this study, a mass balance approach is used to estimate the hydrological balance of the lake. Water influx from four major rivers, subsurface inflow from the floodplains, precipitation, outflow from the lake constituting river discharge and evapotranspiration from the lake are analysed on monthly and annual bases. Spatial interpolation of precipitation using rain gauge data was conducted using kriging. Outflow from the lake was identified as the evaporation from the lake's surface as well as discharge at the outlet where the Blue Nile commences. Groundwater inflow is estimated using MODular three-dimensional finite-difference ground-water FLOW model software that showed an aligned flow pattern to the river channels. The groundwater outflow is considered negligible based on the secondary sources that confirmed the absence of lake water geochemical mixing outside of the basin. Evaporation is estimated using Penman's, Meyer's and Thornwaite's methods to compare the mass balance and energy balance approaches. Meteorological data, satellite images and temperature perturbation simulations from Global Historical Climate Network of National Oceanographic and Atmospheric Administration are employed for estimation of evaporation input parameters. The difference of the inflow and outflow was taken as storage in depth and compared with the measured water level fluctuations. The study has shown that the monthly and annually calculated lake level replicates the observed values with root mean square error value of 0·17 and 0·15 m, respectively. Copyright © 2009 John Wiley & Sons, Ltd. [source] Simulating the response of a closed-basin lake to recent climate changes in tropical West Africa (Lake Bosumtwi, Ghana)HYDROLOGICAL PROCESSES, Issue 13 2007Timothy M. Shanahan Abstract Historical changes in the level of Lake Bosumtwi, Ghana, have been simulated using a catchment-scale hydrological model in order to assess the importance of changes in climate and land use on lake water balance on a monthly basis for the period 1939,2004. Several commonly used models for computing evaporation in data-sparse regions are compared, including the Penman, the energy budget, and the Priestley,Taylor methods. Based on a comparison with recorded lake level variations, the model with the energy-budget evaporation model subcomponent is most effective at reproducing observed lake level variations using regional climate records. A sensitivity analysis using this model indicates that Lake Bosumtwi is highly sensitive to changes in precipitation, cloudiness and temperature. However, the model is also sensitive to changes in runoff related to vegetation, and this factor needs to be considered in simulating lake level variations. Both interannual and longer-term changes in lake level over the last 65 years appear to have been caused primarily by changes in precipitation, though the model also suggests that the drop in lake level over the last few decades has been moderated by changes in cloudiness and temperature over that time. Based on its effectiveness at simulating the magnitude and rate of lake level response to changing climate over the historical record, this model offers a potential future opportunity to examine the palaeoclimatic factors causing past lake level fluctuations preserved in the geological record at Lake Bosumtwi. Copyright © 2006 John Wiley & Sons, Ltd. [source] Nitrogen fixation and denitrification in a floodplain forest near Manaus, BrazilHYDROLOGICAL PROCESSES, Issue 7 2003Heidi Kreibich Abstract The Amazon floodplain (várzea) is seasonally affected by water level fluctuations of the Solimões/Amazon River. The drastic environmental changes that occur also include microbiological processes, such as nitrogen (N2) fixation and denitrification. Both processes were measured in the soil by the acetylene reduction assay and the acetylene block method in a várzea forest on Ilha de Marchantaria, Central Amazonia, Brazil. In the surface soil horizon (0,5 cm), N2 fixation was highest during the exposed period (0·04,0·26 nmolN h,1 g,1 dry weight (dw)). In contrast, denitrification varied from 0 to 1·40 nmolN h,1 g,1 dw, with high rates during the submerged and the transition periods. No significant difference between locations with legume trees, with non-legume trees and without trees could be observed. N2 fixation rates of incubations (litter down to 450 cm depth) for samples collected during the exposed period ranged from 0 to 0·11 nmolN h,1 g,1 dw, with highest rates in the surface soil horizon (0,5 cm). Denitrification ranged from 0 to 0·05 nmolN h,1 g,1 dw, with the highest rate at 250,300 cm depth, which was just below the water table. The maximum N2 fixation rate (0·89 nmolN h,1 g,1dw) and denitrification rate (0·09 nmolN h,1 g,1 dw) occurred in the litter layer. On average, at least three times as much N is lost from the surface soil horizon via denitrification than is gained by N2 fixation annually, but the rates are strongly influenced by the flood pulse. Copyright © 2003 John Wiley & Sons, Ltd. [source] Zonal circulations over the Indian and Pacific Oceans and the level of lakes Victoria and TanganyikaINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 13 2004Laurent Bergonzini Abstract Level records of two East African Great Lakes, Lake Victoria and Lake Tanganyika, which are considered as hydro-climatic proxies, are analysed. Comparisons between the two lake signals show synchronisms, which can only be accounted for by large-scale mechanisms. Lake-level variations associated with the short rains season (October,January) appear to have a prominent effect on the annual lake levels. The relations between lake-level variations and atmospheric circulation indexes are then investigated. Over the period 1946,2000, four indexes are selected to characterize the October,December zonal circulation over the Pacific and Indian Oceans. Over the Indian Ocean two surface zonal wind indexes (ZWIs) are used. For the Pacific, the southern oscillation index (SOI) and the Niño3 index are held to account for the El Niño,southern oscillation (ENSO). It is shown that significant overall negative correlations of level fluctuations are preferentially obtained with Indian Ocean circulation indexes. Although ZWI is highly correlated with the ENSO indexes, the latter display weaker relations with East African lake levels. It is shown that, for the 1946,2000 period, the October,December zonal circulation cell over the Indian Ocean plays a key role in the equatorial lake-level anomalies, thus demonstrating their influence on the hydro-climatic interannual variability of a large region. However, lake-level variation is a function not only of regional hydro-climatic conditions, but also of the initial (October) absolute lake level. Higher correlations are evident in a multiple correlation approach taking into account the initial lake level status in addition to the ZWI and ENSO indexes. Copyright © 2004 Royal Meteorological Society [source] A study on the temporal dynamics of tourism demand in the Asia Pacific RegionINTERNATIONAL JOURNAL OF TOURISM RESEARCH, Issue 5 2009Vincent Cho Abstract Using the monthly statistics of tourists from four different origins (America, Europe, Asia and Oceania) among seven places in the Asia Pacific region for a period from January 1991 to December 2005, we investigate these 28 time series using the Holt-Winters method, artificial neural network and numerical graphical plots. Interesting comparisons on level fluctuations, trends and seasonal patterns of the time series among the Asia Pacific region are explored. These findings enable us to understand more about the temporal aspect of tourism demand in the Asia Pacific region. In sum, this paper lays out the importance of understanding the trend and seasonality indices in details. Copyright © 2009 John Wiley & Sons, Ltd. [source] Estimating natal dispersal movement rates of female European ducks with multistate modellingJOURNAL OF ANIMAL ECOLOGY, Issue 6 2003Peter Blums Summary 1We used up to 34 years of capture,recapture data from about 22 100 new releases of day-old female ducklings and multistate modelling to test predictions about the influence of environmental, habitat and management factors on natal dispersal probability of three species of ducks within the Engure Marsh, Latvia. 2The mean natal dispersal distances were very similar (c. 0·6,0·7 km) for all three species and were on average 2·7 times greater than breeding dispersal distances recorded within the same study system. 3We were unable to confirm the kinship hypothesis and found no evidence that young first-nesting females nested closer to their relatives (either mother or sister) than to the natal nest. 4Young female northern shovelers, like adults, moved from small islands to the large island when water level was high and vice versa when water level was low before the construction of elevated small islands. Movement probabilities between the two strata were much higher for young shovelers than adults, suggesting that young birds had not yet developed strong fidelity to the natal site. Movements of young female tufted ducks, unlike those of shovelers, were not dependent on water level fluctuations and reflected substantial flexibility in choice of first nesting sites. 5Data for young birds supported our earlier conclusion that common pochard nesting habitats in black-headed gull colonies were saturated during the entire study period. Young females, like the two adult age groups, moved into and out of colonies with similar probability. Fidelity probability of female pochards to each stratum increased with age, being the lowest (0·62) for young (DK) females, intermediate (0·78) for yearlings (SY) and the highest (0·84) for adult (ASY) females. 6Young female tufted ducks, like adults, showed higher probabilities of moving from islands to emergent marshes when water levels were higher both before and after habitat management. The relationship between the spring water levels and movement was much weaker for young females than for adults. 7Young female diving ducks exhibited much stronger (compared to adults) asymmetric movement with respect to proximity to water, with higher movement probabilities to near-water locations than away from these locations. 8Local survival of day-old ducklings during the first year of life was time-specific and very low (means for different strata/states 0·01,0·08) because of high rates of emigration and prefledging mortality. [source] Consequences of introducing the invasive amphipod Gmelinoides fasciatus into large shallow Lake Peipsi: present distribution and possible effects on fish foodJOURNAL OF APPLIED ICHTHYOLOGY, Issue 2010K. Kangur Summary The objective of the study was to assess the effect of the Baikalian amphipod Gmelinoides fasciatus, a successful invader into Europe, as a fish food source in Lake Peipsi to where it was introduced in the 1970s. In 2002,2006, the littoral macrozoobenthos was studied along 17 transects (0.1,4 m depth, 384 quantitative samples) to determine the recent distribution of G. fasciatus and its share in the benthic community. Earlier records on the littoral macrozoobenthos from the years 1970, 1980, 1990 and 2000 were also used for comparison. Our results indicate that the invasive G. fasciatus is the dominant species (about 43% of total macrozoobenthos abundance) in the littoral zone of Lake Peipsi, while the native gammarids Gammarus lacustris and Pallasea quadrispinosa appear to be extinct and oligochaetes seem to have declined. G. fasciatus preferred hard substrates and it was mainly distributed close to water shallow beach areas (water depth <0.2 m), where its abundance reached locally up to 29 000 ind. m,2 (97% of total macrozoobenthos abundance). This distribution pattern of the invader in summer makes it mostly inaccessible for adult fish and increases its survival rate. Being highly mobile, G. fasciatus is not sensitive to water level fluctuations in shallow lakes. These behavioural characteristic increase its population success. [source] Preferential flow and aging of NAPL in the unsaturated soil zone of a hazardous waste site: implications for contaminant transportJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 1 2003Kai U. Totsche Abstract Flow of non-aqueous phase liquids (NAPL) in the unsaturated zone is thought to be driven by gravity with a dominant vertical flow direction, and lateral spreading to be limited to the gradient of the relative permeabilities. The effect of soil profile build-up, preferential flow, aging, and groundwater level fluctuations is mostly neglected. The objective of our study was to check the effects of such processes on the fate of NAPL in the unsaturated soil zone. At a hazardous waste site, we conducted a field survey of the unsaturated soil zone and monitored the groundwater for a two year period. We conducted spatially resolved and depth dependent soil sampling and analysis and the evaluation of former ram and core drilling protocols. The samples were analyzed for the 16 EPA PAH and alkanes with GC-MS and GC-FID. 13C-NMR spectroscopy was used to assess structural changes of the NAPL phase. Flow of bulk NAPL along macropores and along preferential permeability structures, like sedimentation discontinuities, are the dominant transport pathways which cause large lateral spreading beyond those expected by the relative permeability gradient. Accumulation of NAPL was found at locations with abrupt textural changes and within the zone of capillary rise. Aging of NAPL results in the depletion in soluble and volatile compounds but also in oxidation and polymerization. It increases the chemical diversity and decreases the mobility of the NAPL. Thus, NAPL flow ceases much earlier than expected from the capillary forces. As chemical transformation is restricted to the NAPL water/air interface, a skin-like thin film is formed which encapsulates and preserves the bulk NAPL from further hardening, limiting contaminant mass transfer from the NAPL to the aqueous phase. Präferenzieller Fluss und Alterung nichtwässriger flüssiger Phasen (NAPL) in der ungesättigten Bodenzone eines Altlastenstandortes: Bedeutung für den Stofftransport Bei der Abschätzung der Tiefenverlagerung von nichtwässrigen Phasen (NAPL) in der ungesättigten Bodenzone ging man bisher davon aus, dass der Fluss im Boden eine dominante vertikale Fließkomponente besitzt. Die Bedeutung bevorzugter Fließwege, des Bodenprofils und der Alterung für die Ausbreitung der NAPL wurde bisher nicht untersucht. Ziel unserer Arbeiten war es daher, die Gültigkeit der Vorstellungen zum Transport von NAPL in der ungesättigten Bodenzone zu überprüfen. Hierzu wurde die ungesättigte Bodenzone an einem ehemaligen Teerwerkstandort untersucht und ein zweijähriges Grundwassermonitoring durchgeführt. Es wurde eine tiefendifferenzierte und räumlich aufgelöste Probenahme mit Rammkernsondierungen und Linern durchgeführt, sowie Bohrprotokolle vorhandener Gutachten ausgewertet. In den Proben wurden Alkane mittels GC-FID und PAK mittels GC-MS bestimmt. NAPL wurden 13C-NMR-spektroskopisch untersucht. Der Fluss von NAPL entlang präferenzieller Fließpfade ist der dominante Prozess der Tiefenverlagerung. Dabei kommt es zu einer starken lateralen Ausbreitung von NAPL weit über den Bereich hinaus, der aufgrund der heterogenen Verteilung der relativen Permeabilitäten erwartet werden würde. Innerhalb des Bodenprofils reichern sich NAPL oberhalb der Grenzflächen mit abruptem Texturwechsel und innerhalb der kapillaren Aufstiegszone an. Alterung der NAPL führt zu einer Zunahme der chemischen Diversität und zu einer Abnahme der Mobilität. Die Tiefenverlagerung von NAPL kommt viel früher zum Erliegen als durch Viskosität und Kapillarkräfte zu erwarten wäre. Die strukturchemischen Veränderungen beschränken sich jedoch auf die Grenzfläche NAPL/Wasser bzw. NAPL/Bodenluft: Es bildet sich eine dünne, verhärtete Grenzschicht aus, die die NAPL umhüllt, die weitere Alterung verlangsamt und den Stoffaustausch zwischen NAPL und Bodenwasser bzw. der Bodenluft verringert. [source] New data on the distribution and genetic structure of Greek moles of the genus Talpa (Mammalia, Talpidae)JOURNAL OF ZOOLOGICAL SYSTEMATICS AND EVOLUTIONARY RESEARCH, Issue 2 2010G. A. Tryfonopoulos Abstract In this work, we employed molecular markers and confirmed the occurrence of two mole species, Talpa stankovici and Talpa europaea in Greece. For the first species, all analyses revealed three major phylogroups, exhibiting great genetic divergence, possibly due to a vicariant event. This event was probably the Peloponnisos' insulation during the Pliocene and the following sea level fluctuations. A scenario of stable, large-sized populations for a long period rather than rapid growth from small-sized populations or founder events is supported. Additionally, T. stankovici's distribution area is extended to a southernmost limit. For T. europaea there is evidence of low genetic divergence between Greek and Central and North European populations. [source] Comparative assessment of the water balance and hydrology of selected Ethiopian and Kenyan Rift LakesLAKES & RESERVOIRS: RESEARCH AND MANAGEMENT, Issue 3 2008Tenalem Ayenew Abstract The study area is part of the East African Rift system, characterized by a cluster of lakes occupying an extremely faulted rift floor with geothermal manifestations. Some of the lakes illustrated contrasting water levels and size evolution over the last few decennia, believed to have been caused by various natural and anthropogenic factors. The relative importance of these factors, however, is unknown. This study attempts to present the hydrology of the lakes in a broader context, by giving more emphasis to lake water level fluctuations and to the water balance. These factors have far-reaching implications in regard to future management of the lake basin water. It also provides information on the relation of the groundwater with the lakes, and with the local and regional groundwater flow system from the adjacent highlands to the floor of the Rift. The methods utilized in this study include conventional hydrogeological field surveys, and hydrometeorological and data analyses, coupled with digital image processing and spatial analysis under a Geographic Information System environment. Ancillary supporting information has been obtained from environmental isotopes and hydrochemical data. The study results indicate the terminal Ethiopian lakes changed in size and water level significantly over the last half century. In contrast, the Kenyan lakes only exhibited slight changes. The lakes in both countries exhibit a striking similarity in their subsurface hydraulic connection, and are strongly governed by complex rift geological structures. Groundwater plays a vital role in the water balance of the study lakes. The study results indicate that future sustainable use of the study lakes demands that serious attention be given to the role of the groundwater component of the lake water balances. [source] A feed forward method for stabilizing the gain and output power of an erbium-doped fiber amplifierMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 9 2009N. Vijayakumar Abstract The gain and the output power of an erbium-doped fiber amplifier (EDFA) are found to be sensitive to input power level fluctuations. Many feed back methods have been proposed to stabilize the gain of an EDFA. These feed back methods are based on sampling and detecting output light and using it to control the pump laser. Such methods fail when the amplifier is expected to repeat a multi-gigabit data stream. It then becomes necessary to use all more complex optical feed back methods to stabilize the gain. In this article, we propose a novel feed forward technique for stabilizing the output power or gain of an EDFA. A lithium niobate (LiNbO3)-based Mach,Zehnder interferometer is used to modulate the intensity of pump light in accordance with the input signal level so as to retain constant output power or gain. We observe that the gain or output power of EDFA can be stabilized by proper selection of the parameters of EDFA and modulator. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2156,2160, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24554 [source] Rhone River flood deposits in Lake Le Bourget: a proxy for Holocene environmental changes in the NW Alps, FranceBOREAS, Issue 4 2005Emmanuel Chapron The Holocene evolution of Rhone River clastic sediment supply in Lake Le Bourget is documented by sub-bottom seismic profiling and multidisciplinary analysis of well-dated sediment cores. Six high-amplitude reflectors within the lacustrine drape can be correlated to periods of enhanced inter- and underflow deposition in sediment cores. Based on the synthesis of major environmental changes in the NW Alps and on the age-depth model covering the past 7500 years in Lake Le Bourget, periods of enhanced Rhone River flood events in the lake can be related to abrupt climate changes and/or to increasing land use since c. 2700 cal. yr BP. For example, significant land use under rather stable climate conditions during the Roman Empire may be responsible for large flood deposits in the northern part of Lake Le Bourget between AD 966 and 1093. However, during the Little Ice Age (LIA), well-documented major environmental changes in the catchment area essentially resulted from climate change and formed basin-wide major flood deposits in Lake Le Bourget. Up to five ,LIA-like' Holocene cold periods developing enhanced Rhone River flooding activity in Lake Le Bourget are documented at c. 7200, 5200, 2800, 1600 and 200 cal. yr BP. These abrupt climate changes were associated in the NW Alps with Mont Blanc glacier advances, enhanced glaciofluvial regimes and high lake levels. Correlations with European lake level fluctuations and winter precipitation regimes inferred from glacier fluctuations in western Norway suggest that these five Holocene cooling events at 45°N were associated with enhanced westerlies, possibly resulting from a persistent negative mode of the North Atlantic Oscillation. [source] | ||||||||||||||||