SOME ASPECTS OF THE HYDRIC BALANCE OF LAKES IN THE EASTERN ROMANIAN PLAIN IN THE YEARS 1956–1970

ABSTRACT

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

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

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

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

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

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

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

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

Steady state flow with hydraulic conductivity change around large diameter wells

Darcian flow law in aquifers assumes that the aquifer hydraulic conductivity is constant and the groundwater movement is due only to the piezometric level changes through hydraulic gradient. In practice, after the well development the aquifer just around the well has comparatively larger hydraulic conductivity and gradient. Patchy aquifer solutions in the literature consider sudden hydraulic conductivity changes with distance for the steady state flow. The change of transmissivity is demonstrated by the application of slope‐matching procedure to actual field data. It is the main purpose of this paper to derive simple analytical expressions for aquifer parameter evaluations with steadily decreasing hydraulic conductivity around the well. Spatial nonlinear hydraulic conductivity changes around a large‐diameter well within the depression cone of a confined aquifer are considered as exponentially decreasing functions of the radial distance. Copyright © 2010 John Wiley & Sons, Ltd.     

Evidence of Saharan dust in upper Pleistocene reworked palaeosols of North‐west Sardinia,Italy: palaeoenvironmental implications

A multi‐disciplinary approach was followed to investigate two thick palaeosol strata that alternate with wind‐blown dominated deposits developed along the Alghero coast (North‐west Sardinia, Italy). Optically stimulated luminescence ages reveal that both palaeosols were developed during cooler drier periods: the first one at around 70 ka Marine Isotope Stage 4 and the latter around 50 ka (Marine Isotope Stage 3). In contrast, the pedological features indicate that the palaeosols underwent heavy weathering processes under warm humid to sub‐humid conditions, characteristic of the Sardinian climate during the last interglacial stage (Marine Isotope Stage 5e). To reconcile this apparent data discrepancy, a range of sedimentological and pedological analyses were conducted. These analyses reveal that the palaeosols possess a complex history, with accumulation and weathering occurring during Marine Isotope Stage 5e, and erosion, colluviation and final deposition taking place during the following cold stages. Thus, even if these reddish palaeosols were last formed during the glacial period, the sediments building up these strata probably record the climate of the last interglacial stage (Marine Isotope Stage 5e). Trace element and X‐ray diffraction analyses, together with scanning electron microscope images, reveal the presence of Saharan dust in the parent material of the palaeosols. However, no evidence of any far‐travelled African dust has been observed in the Marine Isotope Stage 4–3 aeolian deposits. It is possible to conclude that in the West Mediterranean islands, Saharan dust input, even if of modest magnitude, is preserved preferentially in soils accumulated and weathered during interglacial stages.     

A comprehensive photometric study of the Algol-type eclipsing binary: BG Pegasi

This study presents new photometric observations of classical Algol type binary BG Peg with a δ Scuti component. The light curve modeling was provided with the physical parameters of the component stars in the BG Peg system for the first time. After modeling light curves in B and V filters, the eclipse and proximity effects were removed from the light curve to analyze intrinsic variations caused by the hotter component of the system. Frequency analysis of the residuals light represents the multi-mode pulsation of the more massive component of the BG Peg system at periods of 0.039 and 0.047 days. Two frequencies could be associated with non-radial (l = 2) modes. The total amplitude of the pulsational variability in the V light curve was found to be about 0.045 mag. The long-term orbital period variation of the system was also investigated for the first time. The O–C analysis indicates periodic variation superimposed on a downward parabola. The secular period variation means that the orbital period of the system is decreasing at a rate of ?5.5 seconds per century, probably due to the magnetic activity of the cooler component. The tilted sinusoidal O–C variation may be caused by the gravitational effect of an unseen component around the system.     

Assessment of trace metal contents in water and bottom sediments from Eğirdir Lake,Turkey

The concentration of metals (Pb, As, Co, Cu, Ni, Zn, Fe and Mn) was investigated in water and sediment samples of E?irdir Lake. The Lake is the second largest fresh water lake of Turkey and it is used as drinking water in the region. The anthropogenic pollutants are primary sources of trace metals which are negatively affected lake water quality. These negative effects were observed in both lake water and bottom sediments. According to obtained data, Pb, Cu, Ni, Fe and Zn have significant enrichment in sediments samples. In addition, the hydrodynamic model of the lake was determined as effectively for Pb, Co, Cu, Ni, Zn, Fe and Mn accumulations. Also, the effect of anthropogenic pollutants was found to be more dominant than geogenic effect in metal accumulation of the lake bottom sediments. Therefore, anthropogenic pollutants within the lake basin should be consistently controlled for the sustainable usage of the lake.     

Dimensionless straight line fitting method for hydrogeological parameter determination

Aquifers may have alluvium deposits, weathered layers, fractured zones, and karstic formations separately or in mixture forms. Such geological configurations do not allow classical aquifer test applicability, due to a set of underlying assumptions that are not usually valid in nature. In practice, the Jacob straight line method is the most commonly used approach for aquifer parameter determinations. Constant transmissivity and storativity estimations depend on large time-drawdown plots on semilogarithmic paper as a straight line. A common mistake is that the appearance of a general trend as a straight line on semilogarithmic paper is taken as guaranteed for the application of Jacob method. Since Jacob straight line is the large time extension of Theis type curve, there is only one straight line on the semilogarithmic paper that can represent Jacob method, which is based on the assumption that the aquifer is porous and homogeneous. In such a case, the Jacob method slope should equal to 2.3, which shows its validity. Otherwise, a modification of Jacob method is suggested in this paper. The basis of the methodology is a dimensionless type straight line approach for the aquifer parameter assessment. Its application is presented for aquifer test data from Oude Korendjik porous medium aquifer data. The application results indicate that the classical Jacob straight line method might not be valid without a preliminary check. The dimensionless reevaluation of existing data helps to check the validity. The necessary formulations for the modification of the classical straight line method are derived, which reduce to classical Jacob method for a specific set of parameters.     

Rock quality designation-fracture intensity index method for geomechanical classification

Rock quality designation (RQD) is a simple and effective way of rock mass classification from surface scanlines or preferably borehole measurements. A major drawback in its classical use is that only one representative RQD value is obtained from the field measurements per core run. However, it is shown in this paper that the field measurements along a scanline provide detailed information about the rock quality and the fracture intensity (FI) for a given number of joints. In order to be able to extract the complete information concealed within the field data, the RQD-fracture index diagram concept is proposed and applied to actual field scanline measurements from England. The basis of the suggested procedure is to obtain a series of all possible RQD and FI values from given intact length measurements. This procedure provides additional information as to the local zones of heterogeneities within the rock mass and a new way of rock classification on the basis of the combined effects of RQD and FI. It is also possible to calculate percentages of different rock qualities within the same rock mass.     

Trace and rare-earth element behaviors during alteration and mineralization in the Attepe iron deposits (Feke-Adana,southern Turkey)

Hydrothermal-metasomatic iron ores consisting mainly of siderite, ankerite and hematite are located in the Lower–Middle Cambrian limestone marbles of the Eastern Taurus Belt. The siderite, ankerite, hematite and host rock samples from the deposits have been investigated for major, trace, and rare-earth elements (REE) to evaluate the element mobility and mass transfer during fluid–rock interactions.