Multi-disciplinary earthquake researches in Western Turkey: Hints to select sites to study geochemical transients associated to seismicity

Warm and hot spring water as well as soil gas radon release patterns have been monitored in the Aegean Extensional Province of Western Turkey, alongside regional seismic events, providing a multi-disciplinary approach. In the study period of 20 months, seven moderate earthquakes with M _L between 4.0 and 4.7 occurred in this seismically very active region; two earthquakes with magnitude 5.0 also occurred near the study area. Seismic monitoring showed no foreshock activity. By contrast, hydro-geochemical anomalies were found prior to these seismic events, each lasting for weeks. The anomalies occurred foremost in conjunction with dip-slip events and seem to support the dilatancy and water diffusion hypothesis. Increased soil gas radon release was recorded before earthquakes associated with strike-slip faults, but no soil radon anomalies were seen before earthquakes associated with dip-slip faults. Geochemical anomalies were also noticeably absent at some springs throughout the postulated deformation zones of impending earthquakes. The reason for this discrepancy might be due to stress/strain anisotropies.     

Biosorption Kinetics and Isotherm Studies of Cd(II) by Dried Enteromorpha compressa Macroalgae Cells from Aqueous Solutions

For the first time ever, Enteromorpha compressa macroalgae (ECM), which is commonly found in Turkey, has been used as biosorbent by us. This study aims to investigate the biosorption of Cd²⁺ from aqueous solutions in a batch system by using an alga of ECM in different concentrations, pH levels, agitation rates (90–150 rpm), and contact periods. The maximum biosorption capacity of the ECM was found to be 9.50 mg/g at pH 6, Cd²⁺ initial concentration of 10 mg/L and agitation rate 150 rpm. Cadmium removal efficiency was about 95%. The experimental isotherm data were analyzed using the Langmuir and Freundlich equations. Isotherm parameters for both equations were determined and discussed. The stated biosorption mechanism is explained by the Freundlich isotherm (r² = 0.998) theory. Two simplified kinetic models including a pseudo‐first‐ and second‐order equation were selected to follow the biosorption process. Kinetic parameters; rate constants, equilibrium adsorption capacities and related correlation coefficients, for each kinetic model were calculated and discussed. It was shown that the biosorption of cadmium onto ECM could be described by the pseudo‐second‐order equation (r² > 0.99).     

Downstream variation in bed sediment size along the East Carpathian rivers: evidence of the role of sediment sources

Taking as an example six main rivers that drain the western flank of the Eastern Carpathians, a conceptual model has been developed, according to which fluvial bed sediment bimodality can be explained by the overlapping of two grain size distribution curves of different origins. Thus, for Carpathian tributaries of the Siret, coarse gravel joins an unimodal distribution presenting a right skewness with enhanced downstream fining. The source of the coarse material distributions is autohtonous (by abrasion and hydraulic sorting mechanisms). A second distribution with a sandy mode is, in general, skewed to the left. The source of the second distribution is allohtonous (the quantity of sand that reaches the river‐bed through the erosion of the hillslope basin terrains). The intersection of the two distributions occurs in the area of the 0·5–8 mm fractions, where, in fact, the right skewness (for gravel) and left skewness (for sand) histogram tails meet. This also explains the lack of particles in the 0·5–8 mm interval. For rivers where fine sediment sources are low, the 0·5–8 mm fractions have a higher proportion than the fractions under 1 mm. For the Siret River itself, bed sediment bimodality is greatly enhanced due to the fact that the second mode is more than 25% of the full sample. As opposed to its tributaries, the source of the first mode, of gravel, is allohtonous to the Siret river, generated by the massive input of coarse sediment through the Carpathian tributaries, while the second mode, of the sands, is local. In this case we can also observe that the two distributions of particles of different origins overlap in the 0·5–8 mm fraction domain, creating the illusion of ‘particle lack’ in the fluvial bed sediments. Copyright © 2007 John Wiley & Sons, Ltd.     

Robust representation of dry cells in single-layer MODFLOW models

Dewatered or "dry" grid cells in the USGS ground water modeling software MODFLOW may cause nonphysical artifacts, trigger convergence failures, or interfere with parameter estimation. These difficulties can be avoided in two dimensions by modifying the spatial differencing scheme and the iterative procedure used to resolve nonlinearities. Specifically, the spatial differencing scheme is modified to use the water level on the upstream side of a pair of adjacent cells to calculate the saturated thickness and hence intercell conductance for the pair. This makes it possible to explicitly constrain the water level in a cell to be at or above the cell bottom elevation without introducing nonphysical artifacts. Thus constrained, all initially active cells will remain active throughout the simulation. It was necessary to replace MODFLOW's Picard iteration method with the Newton-Raphson method to achieve convergence in demanding applications involving many dry cells. Tests using a MODFLOW variant based on the new method produced results nearly identical to conventional MODFLOW in situations where conventional MODFLOW converges. The new method is extremely robust and converged in scenarios where conventional MODFLOW failed to converge, such as when almost all cells dewatered. An example application to the Edwards Aquifer in south-central Texas further demonstrates the utility of the new method.     

Comparison of Treatment Efficiency and Energy Consumption of Batch and Continuous Electrocoagulation in Urban Wastewater

In this study, domestic wastewater was used as the electrolyte. The work was carried out with an up-flow tubular reactor, made of stainless steel that was used as cathode, while the anode electrode material was aluminum and varying values of flow regime (25, 50, 75 and 100 mL/s for continuous system), initial pH value (5, 6, 7 and 7.8) and current intensity (10, 15 and 20 A) were applied. For domestic wastewater with natural pH, the effluent pH was >9 in the batch system, while in the continuous system the pH was 8–8.5. Likewise, while the effluent temperature was up to 60°C in the batch system, it was at most 35°C in the continuous system. However, the energy consumption values in the continuous system were considerably lower compared with the batch system. At a current intensity of 10 A, 80 kWh of energy per unit volume was consumed in the batch system, while it was 50 kWh for the continuous system. The present results show that the batch system can be used for small wastewater streams whereas the continuous system can be used for large wastewater streams for domestic wastewater treatment.     

Spatial and temporal drought projections of northwestern Turkey

Theoretical and Applied Climatology - Based on the meteorological data of 60 stations above the Bengbu Sluice of Huaihe River from 1961 to 2015, Crop Water Deficit Index (CWDI) and Relative...     

Delta formation at the southern entrance of Istanbul Strait (Marmara sea, Turkey): a new interpretation based on high-resolution seismic stratigraphy

A detailed stratigraphic investigation based on high-resolution seismic profiles revealed that the delta at the southern entrance of the Istanbul Strait consists of three parasequence sets. The lowermost parasequence shows a sea-level stillstand at the beginning of the lowstand systems tract, possibly at 11,000±1,100 a b.p., whereas the upper two parasequences reflect deposition at lowstand and during the subsequent transgression. A maximum flooding surface may be developing on the delta at present. The delta is located on the eastern side of the Istanbul Strait canyon, with east–west prograding parasequences. The development of the delta is clearly associated with the Kurbağalı Stream on the east coast, and not with the Black Sea outflow through the strait. The geometry of the delta indicates a radial architecture arranged from northeast to southwest.     

Evidence and implications of massive erosion along the Strait of İstanbul (Bosphorus)

The Strait of İstanbul (SoI) (Bosphorus) is a narrow valley, which has evolved tectonically from a stream, and in which thick sediment deposits have accumulated in the course of its evolution. Detailed seismic and multi-beam bathymetric data have revealed that the upper parts of the deeper channel deposits consist of parallel strata, which have mostly been eroded subsequently to their deposition. The resulting erosion surface is represented by the present channel floor in the strait, the estimated volume of the eroded material being approximately 2×10⁸ m³ . Erosion rate and seafloor morphology indicate that the flow direction was from the south to the north. This inner channel may have been formed by an abrupt flooding of the Black Sea by Mediterranean waters at the beginning of the latest connection between the Marmara and the Black seas. Subsequently, the Mediterranean bottom current of the modern two-way flow system, which was established at about 5–4 ka b.p., has given the latest shape to the strait floor.