Seasonal and interannual dynamics of free-living bacterioplankton and microbially labile organic carbon along the salinity gradient of the Potomac River

Samples were collected at stations located in the mesohaline, oligohaline, and tidal fresh regions of the Potomac River, Maryland, between April 1998 and December 1999 to evaluate the seasonal distribution of bacterioplankton and microbially labile organic carbon (MLOC) in relation to hydrodynamic parameters (dissolved oxygen, salinity, and temperature). Bacterioplankton abundance (BA) averaged 13 × 10⁶ cells ml⁻¹ at all stations, a value that is higher than the average observed in many other temperate estuaries around the world, and were almost exclusively free-living. During the summer of 1998, BA often exceeded 30 × 10⁶ cells ml⁻¹ in the mesohaline region during periods of anoxia in subpycnocline waters. Dissolved MLOC typically accounted for 40% of total MLOC and on some occasions during summer and autumn accounted for 80%. A significant positive relationship between dissolved MLOC and BA was evident in the mesohaline Potomac River, the region where anoxia occurs each summer, but the regressions of particulate MLOC and chla on BA were not significant at this location. In the mesohaline Potomac River, BA regressed negatively and significantly on dissolved oxygen (r²=0.50, p<0.001). BA may be an important indicator of ecosystem health in this and other eutrophied estuaries, because of the relationships between BA, dissolved MLOC, and dissolved oxygen in the salinity stratified Potomac River and because free-living BA was elevated along the length of the river.     

Preliminary data on chemical changes in the Aral Sea during low-level periods from the last 9000 years

The withdrawal of the Aral Sea tributaries (Amu and Syr Daria) for cultures has led to significant falls of its level and an important increase in its salinity. During the Holocene, a succession of low and high water inputs occurred. Silty deposits correspond to the high levels and carbonates to the low levels. This study makes a distinction between the Syr Daria and the Amu Daria water inputs during low-level periods by using mineralogical and chemical compositions of the carbonates deposits. Waters from the Syr Daria are more sulphatic and have a low iron content in comparison with that of the Amu Daria. The Syr Daria was the major tributary around 7500, 4956 and 970 yr?BP, whereas around 6200 and 3610 yr?BP, inflow also from the Amu Daria is observed. To cite this article: L. Le Callonnec et al., C. R. Geoscience 337 (2005).     

Geodynamics and underlying bedrock of the magnetically active crust layer of the Lut block,Eastern Iran

The Curie point depth map of Eastern Iran was constituted from spectral analysis of the aeromagnetic data. The reduction to pole (RTP) was applied to the magnetic anomaly data. The Curie point depth values from 165 overlapping blocks, 100 × 100 km in size, have been estimated. The Curie point depth method provides a relationship between the 2-D FFT power spectrum of the magnetic anomalies and the depth of magnetic sources by transforming the spatial data into the frequency domain. The centroid and top depth of the magnetic sources (respectively Z₀ and Z_t) is calculated from radially averaged log power spectrum for each block. Finally, the Curie point depth of Eastern Iran is obtained by Z_b = 2Z₀–Z_t. The highest value of 24 km is located in eastern and western boundaries of the Lut block, and the lowest value of 12 km is located at north of study area. The shallow depths in the Curie-point depth map are well correlated with the young volcanic areas and geothermal potential fields. Geothermal gradient ranging from 24 to 45°C/km. The deduced thermal structure in eastern Iran has a relationship with orogenic collapse associated with delamination of thickened lithospheric root between the Lut and Afghan continental blocks.     

SPH approach for simulating hydro-mechanical processes with large deformations and variable permeabilities

A simulation framework based on Smoothed Particle Hydrodynamics (SPH) is introduced to model problems involving the interaction between flowing water and soil deformation. Changes in soil porosity and associated permeability are automatically adjusted within this framework. The framework’s capabilities are presented and discussed for three geotechnical problems caused by flowing water. The comparison between simulation results and experiments shows that SPH with the proposed concept is capable of quantitatively simulating the hydro-mechanical processes beyond limit state with satisfactory agreement. To improve the computational stability, a correction procedure and a new algorithm for the selection of the optimal time step are introduced.     

A Study on the Surface Wettability of Clastic Rocks with Potential Application for CO2 Storage Sites

Natural Resources Research - There have been many studies carried out in the past decades attempting to develop strategies for a safe injection of CO2 into storage sites without leakage and...     

Soil-Structure Interaction Analysis of Jack-up Platforms Subjected to Monochrome and Irregular Waves

As jack-up platforms have recently been used in deeper and harsher waters, there has been an increasing demand to understand their behaviour more accurately to develop more sophisticated analysis techniques. One of the areas of significant development has been the modelling of spudcan performance, where the load-displacement behaviour of the foundation is required to be included in any numerical model of the structure. In this study, beam on nonlinear winkler foundation (BNWF) modeling—which is based on using nonlinear springs and dampers instead of a continuum soil media—is employed for this purpose. A regular monochrome design wave and an irregular wave representing a design sea state are applied to the platform as lateral loading. By using the BNWF model and assuming a granular soil under spudcans, properties such as soil nonlinear behaviour near the structure, contact phenomena at the interface of soil and spudcan (such as uplifting and rocking), and geometrical nonlinear behaviour of the structure are studied. Results of this study show that inelastic behaviour of the soil causes an increase in the lateral displacement at the hull elevation and permanent unequal settlement in soil below the spudcans, which are increased by decreasing the friction angle of the sandy soil. In fact, spudcans and the underlying soil cause a relative fixity at the platform support, which changes the dynamic response of the structure compared with the case where the structure is assumed to have a fixed support or pinned support. For simulating this behaviour without explicit modelling of soil-structure interaction (SSI), moment-rotation curves at the end of platform legs, which are dependent on foundation dimensions and soil characteristics, are obtained. These curves can be used in a simplified model of the platform for considering the relative fixity at the soil-foundation interface.     

Random seismic noise attenuation data using the discrete and the continuous wavelet transforms

In this paper, we propose a technique of random noise attenuation from seismic data using discrete and continuous wavelet transforms. Firstly, the discrete wavelet transform (DWT) is applied to denoise seismic data using the threshold method. After, we calculate the continuous wavelet transform of the denoised seismic seismogram, the final denoised seismic seismogram is the continuous wavelet transform coefficients at the lower scale. Application to a synthetic seismogram shows the robustness of the proposed tool for random noise attenuation. Application to real vertical seismic profile recorded in Algeria clearly shows the efficiency of the proposed tool for random noise attenuation.     

Heterogeneities analysis using the generalized fractal dimensions and the continuous wavelet transform. Application to the KTB boreholes

The main goal of this paper is to identify heterogeneities from well logs data using the wavelet-based multifractal analysis. Firstly, the wavelet transform modulus maxima lines method is applied with a moving window of 128 samples to the raw well logs data. After that, the generalized fractal dimensions that correspond to the three first moments of the function of partition are estimated. Application to synthetic and real well logs data of the main and pilot Kontinentales Tiefbohrprogramm de Bundesreplik Deutschland wells shows that the information and the correlation dimensions can be used for heterogeneities analysis and lithofacies segmentation form well logs data.