Does beach seine fishery permanently alter macroinvertebrate communities and sediment characteristics in the Southern Caspian Sea?

The impacts of a beach seine fishery on macroinvertebrate communities and sediment characteristics were investigated in the Southwest Caspian Sea. Samples from a single impacted site that was regularly seined were compared with two control sites outside the fishing area. Benthic macroinvertebrates were sampled on four occasions: 6 months prior to the opening of the beach seine fishery (Time 1), 1 day immediately after the closing of beach seining (Time 2), 1 week after closing (Time 3), and 1 month after closing (Time 4). No significant differences were detected in total density, Shannon diversity, or evenness of the macroinvertebrate assemblages between impact and control sites. Unlike density, species richness increased significantly immediately after fishery closure at all sites. A significant difference was detected in the number of species between Time 2 and Time 3 at all sites and the number of species was reduced at Time 4 in all sites. Pontogammarids increased by twofold in the impact site 1 day immediately after closing beach seine fishery and leveled off toward the end of the closed season. The amplified density of pontogammarids 1 day after fishery closing at the impact site might be driven in part by an increase in sediment oxygen content resulting from disturbance of the sea floor. An alternative explanation is that the effect of fish predation on pontogammarids has largely been minimized at the impact site after 6 months of continuous fishing activity. No significant changes in the sedimentary organic content and chlorophyll‐a between the impact and control sites were observed during the courses of sampling; however, a significant change occurred between the average sedimentary pheopigment content of the control sites and that of the impact site. The conclusion from the present study is that beach seine fishery does not harm to benthic communities. The closed season also seemed to allow recovery to pre‐season levels of macroinvertebrate richness and sedimentary chlorophyll‐a.     

A Comparative Study Between Least Square and Total Least Square Methods for Time–Series Analysis and Quality Control of Sea Level Observations

In this study, the quality control of tide gauge observations is investigated by two methods of least square (LS-HE) and total least square harmonic estimation (TLS-HE). Particularly, it is shown how to deal with unexpected anomalies, including outliers, offset and gap in the time series of sea level height. To do so, at first the time series is constructed and then a method based on variance threshold is used to eliminate the possible outliers in the observations. Subsequently, a noise assessment algorithm is implemented and the signal is processed to find the possible times of offsets and to eliminate their corresponding observations from the time series. Finally, the signal is checked to find the periods of gap within the time series and then the gap area is predicted with correct observations. Gap filling analysis is performed in two contexts. In the first, only the significant frequencies of tide are considered in the modelling procedure, while in the second, all possible frequencies according to the period of observations are included. Our results show that for modelling and gap filling, the TLS-HE method has a better performance in a comparison with LS-HE method. Although, for offset and outlier detections, the LS-HE is recommended. It also indicates that the TLS-HE method provides a regular solution for gap filling analysis while LS-HE method needs a regularization scheme for which LSQR regularization is used.     

Improved Minimum Miscibility Pressure Prediction for Gas Injection Process in Petroleum Reservoir

Determination of gas–oil minimum miscibility conditions is one of the important design parameters to improve the displacement efficiency of the hydrocarbon reservoir during enhanced oil recovery with gas injection. In this work, a support vector regression (SVR) model is developed using experimental data to estimate the minimum miscibility pressure (MMP) for various reservoir fluids and injection gases. Experimental MMP data taken from the reliable literature were used as input. Each data point input includes methane and intermediate components mole percent, plus fraction properties and reservoir temperature related to reservoir fluid and CO₂, H₂S, N₂ and intermediate mole fractions, and intermediate properties of the injected gas. Experimental MMP is regarded as the model output. The database contains 135 datasets, from which 125 datasets were used for model development, and the rest were used for model evaluation. Genetic algorithm was implemented to optimize the SVR model parameters. The proposed data-driven model was verified by statistical validation data. The model results illustrate a correlation coefficient (R²) of 0.999. In addition, the SVR results demonstrate the proposed model to be a fast tool and a robust approach to map input space to output features. The SVR model was compared to popular data-driven MMP estimation models as well. This comparison presents an acceptable accuracy relative to this estimation model. Finally, the presented model was evaluated against a comprehensive theoretical model of slim tube compositional simulation on a trusted literature dataset.     

The Shear Behavior of Bedding Planes of Weakness Between Two Different Rock Types with High Strength Difference

In this article, the shear behavior of discontinuities caused by bedding planes of weakness between two different rock types with high strength difference is investigated. The effect of roughness and compressive strength of joint wall in such discontinuities are studied. The designed profiles consist of two regular and three irregular artificial joints molded by three types of plaster mortars with different uniaxial compressive strengths. Firstly, it is demonstrated that the shear behavior of discontinuities with different joint wall compressive strengths (JCS) is different from rock joints with identical wall compressive strengths by showing that Barton’s empirical criterion is not appropriate for the former discontinuities. After that, some correlation equations are proposed between the joint roughness coefficient (JRC) parameter and some surface statistical/fractal parameters, and the normal stress range of Barton’s strength criterion is also modified to be used for such discontinuities. Then, a new empirical criterion is proposed for these discontinuities in such a way that a rational function is used instead of JRC log₁₀(JCS/σ _n) as i ₀(σ _c/σ _n)^a/[b + (σ _c/σ _n) ^a ] by satisfying the peak dilation angle boundary conditions under zero and very high normal stress (physical infinite normal stress causing zero peak dilation angle). The proposed criterion has three surface parameters: i ₀, a, and b. The reason for separation of i ₀ from JRC is indicated and the method of its calculation is mentioned based on the literature. The two remaining coefficients (a and b) are discussed in detail and it is shown that a shows a power-law relationship with b, introducing the coefficient c through b = c ^a . Then, it is expressed that a is directly related to discontinuity surface topography. Finally, it is shown that the coefficient c has higher values in irregular profiles in comparison with regular profiles and is dominated by intensity of peak dilation angle reduction (majorly related to the surface irregularity and minorly related to roughness). The coefficient c is to be determined by performing regression analysis on experimental data.     

Geology,geochemistry, sulfur isotope composition,and fluid inclusion data of Farsesh barite deposit,Lorestan Province,Iran

Farsesh barite in the central part of Iranian Sanandaj-Sirjan zone is a sample of epigenetic hydrothermal mineralization in dolomitized limestone, which provides appropriate chemicophysical conditions making the passage of mineral-bearing fluids possible. Barite veins may range from a few centimeters to 2 m in thickness that increases downward. The microthermometry measurements obtained from more than 30 fluid inclusions show relative homogenization temperatures ranging from 125 to 200 °C with an average of 110 °C for Farsesh barite deposits. The mean salinity measured proves 16 times as much as weight percentage of NaCl for barite. Coexistence of liquid- and vapor-rich fluid inclusions in barite minerals may provide an evidence of boiling in ore veins. Moreover, occurrence of bladed calcite, high-grade ore zones, and presence of hydrothermal breccia are all consistent with boiling. Thermometric studies indicate that homogenization temperatures (Th) for primary and pseudosecondary fluid inclusions in barite range from 125 to 200 °C with an average of 1,100 °C. The δ³⁴S values of barite also lie between 8.88 and 16.6 %. The relatively narrow spread in δ³⁴S values may suggest uniform environmental conditions throughout the mineralization field. Thus, δ³⁴S values are lower than those of contemporaneous seawater, which indicates a contribution of magmatic sulfur to the ore-forming solution. Barite is marked by total amounts of rare Earth elements (REEs) (6.25–17.39 ppm). Moreover, chondrite-normalized REE patterns of barite indicate a fractionation of light REEs (i.e., LREEs) from La to Sm, similar to those for barite from different origins. The La_CN/Lu_CN ratios and chondrite-normalized REE patterns reveal that barite in Farsesh deposit is enriched in LREEs compared with heavy rare Earth elements (HREEs). Similarity between Ce/La ratios in barite samples and those found in deep-sea barite supports its marine origin. Lanthanum and Gd exhibit positive anomalies, which are common features of chemical marine sediments. Cerium shows a negative anomaly in most samples inherited from the negative Ce anomaly of hydrothermal fluid that is mixed with seawater at barite precipitation. The available data including tectonic setting, host rock characteristics, REE geochemistry, and sulfur isotopic compositions may support a hydrothermal submarine origin for Farsesh barite deposit.     

Source of salinity in the groundwater of Lenjanat Plain,Isfahan, Iran

The present study aimed at identifying the salinity source in the groundwater of Lenjanat Plain. To do so, non-isotopic geochemical methods were employed: groundwater samples were collected seasonally from 33 wells widespread in the area, and physicochemical parameters as well as major and minor elements were measured in the 132 samples. The data collected from the field and laboratory measurements were interpreted through statistical and hydrogeochemical graphs, mass ratios and saturation indexes obtained from modeling. The results revealed that hydrogeochemical properties of the study aquifer were controlled by rock/water interactions including ion exchange, dissolution of evaporation deposits (halite and gypsum) and precipitation/dissolution of carbonates. Based on the values of Cl/Br ratio in Lenjanat groundwater (329–4,492), dissolution of evaporation deposits in aquifer was the main cause for groundwater salinity. Considering the Lenjanat groundwater geochemical properties, the data confirm the reported Cl/Br ratios for groundwater affected by the dissolution of evaporation deposits (Cl/Br > 300) and overlaps with the range of Cl/Br ratios for domestic sewage effluent groundwater. Selecting the best chemical components and their ratios in non-isotopic geochemical methods provides an accurate distinction between sources of groundwater salinity.     

Pseudo-static Seismic Bearing Capacity of Shallow Foundations in Unsaturated Soils Employing Limit Equilibrium Method

There exist many structures founded on unsaturated soil deposits. Shear strength augmentation due to the evolution of the matric suction within the unsaturated porous media enhances the bearing capacity of the overlying foundation. This paper presents the evaluation of the pseudo-static seismic bearing capacity of the shallow foundations resting on unsaturated soil deposits using limit equilibrium method. Adopting the Coulomb failure mechanism and Bishop effective stress concept, the bearing capacity equations are solved. The distribution of the matric suction beneath the footing is assumed to be linear. The results of the bearing capacity evaluation are validated against some experimental data found in literature for the static condition. For the seismic loading consideration, the pseudo-static method is utilized. The dual effect of the earthquake acceleration vertical component is thoroughly discussed and a suction transition point is introduced in which the minimum bearing capacity is observed to bear the same value for both upward and downward directions. The increase in the matric suction throughout the soil deposit leads to the increase in the soil shear strength, thus posing more resisting forces as well as higher ultimate bearing capacity. The offered solution is deemed a consistent and useful tool for the accurate prediction of the seismic bearing capacity of shallow footings resting on unsaturated soil deposits.

     

The comparison of hydrodynamic characteristics of karst aquifers: application on two karst formations in Zagros (Asmari and Ilam-Sarvak), southwest Iran

In order to study the function, hydrodynamic behavior, and hydraulic properties of the karst aquifers in Izeh, southwest Iran, time series analysis was applied to the precipitation, spring discharge, and piezometric head data of two representative karst systems of Zagros (Ilam-Sarvak and Asmari Formations). Time series analysis was applied to two karst aquifers, those of Asmari and Ilam-Sarvak Formations. The daily precipitations of anticlines were estimated based on the precipitation–elevation function which was applied on digital elevation model (DEM) of the area. The mean estimated daily precipitations were considered in bivariate time series analysis as input data of each karst system. The total length of time series was about 2.7 years, extending from May 2007 to December 2009. During the research, several one-parameter probe data loggers were installed, which daily measure the water surfaces in karst aquifers. Time series analysis was applied for describing Izeh karst aquifers with a focus on both univariate (autocorrelation and spectral analysis) and bivariate (cross-correlation, gain function, and coherency function) methods. The results show that Asmari karst aquifer in Kamarderaz Anticline has a large storage capacity. Because of lacking a well-organized karst network, in the Asmari karst aquifer, baseflow dominates with low contribution of quick-flow. In the Ilam-Sarvak karst aquifer (Shavish and Tanush Anticlines), the karstification occurred in fractures and small diameter conduits, which caused to quick-flow between dense limestone. The Ilam-Sarvak karst aquifer could be regarded as a transition between two extreme types of karst, e.g., highly karstified system and in the opposite, extremely diffused one. The analysis of well hydrograph in Ilam-Sarvak karst aquifer shows that the karst aquifer has a low storage capacity. Unlike Asmari karst aquifer, the fractures and small diameter conduits in Ilam-Sarvak karst aquifer are more enhanced, producing a better developed karst network. Contrary to the typical karst systems, however, diffuse flow and conduit flow coexist in the Asmari Formation.     

Rock joint modeling using a visco-plastic multilaminate model at constant normal load condition

Rock joints play an important role in the behavior of rock masses under normal and shear loading conditions. Numerical simulation of the behavior of jointed rock masses is not an easy task due to complexities involved in the problem such as joint roughness, joint shear strength, hardening and softening phenomenon and mesh dependency. In this study for modeling purposes, a visco-plastic multilaminate model considering hardening and softening effects has been employed. For providing the necessary data for numerical simulation, a series of laboratory experiments have been carried out on regular tooth-shape asperities made by gypsum, under constant normal load conditions. Shear stress–shear displacement and normal displacement–shear displacement of artificial joint specimens are simulated using the proposed numerical model at constant normal load condition (CNL). The results indicate the capability of the model for simulating rock joints behavior in both strength and deformation field. Although the numerical model has been developed for simulating the behavior of artificial joints, the concept of the method can also be used for natural rock joints.     

An empirical method for design of grouted bolts in rock tunnels based on the Geological Strength Index (GSI)

The procedure presented in this paper has been developed for the design of grouted rock bolts in rock tunnels during preliminary design stage. The proposed approach provides a step-by-step procedure to set up a series of practical guidelines for optimum pattern of rock bolting in a variety of rock mass qualities. For this purpose, a new formula for the estimation of the rock load (support pressure) is recommended. Due to its wide-spread acceptance in the field of rock engineering, the Geological Strength Index (GSI) is adopted in support pressure equation. For poor and very poor rock mass where the GSI < 27, the use of Modified-GSI is, instead, recommended. The supporting action is assumed to be provided by rock bolts carrying a total load defined by the rock load height. The mechanism of bolting is assumed to rely on roof arch forming and suspension principle. Integrated with support pressure function, the bolt density parameter is modified in order to provide an optimized bolt pattern for any shape of tunnel. The modified bolt density can also be used in analysis of a reinforced tunnel in terms of Ground Reaction Curve (GRC) in such a way as to evaluate the reinforced rock mass and the tunnel convergence. By doing so, the effectiveness of the bolting pattern is well evaluated. The proposed approach based on GSI is believed to overcome constrains and limitations of existing empirical bolt design methods based on RMR or Q-system, which are doubtful in poor rock mass usage. The applicability of the proposed method is illustrated by the stability analysis and bolt design of a rail-road tunnel in Turkey.