Past and future plant diversity of a coastal wetland driven by soil subsidence and climate change

On the island of Ameland (The Netherlands), natural gas has been extracted from a dune and salt marsh natural area since 1986. This has caused a soil subsidence of c. 1–25?cm, which can be used as a model to infer effects of future sea level rise. The aims of our study were (a) to relate the changes in the vegetation, and more specifically, in plant diversity, during the extraction period to soil subsidence and weather fluctuations, and (b) to use these relations to predict future changes due to the combination of ongoing soil subsidence and climate change. We characterised climate change as increases in mean sea level, storm frequency and net precipitation. Simultaneous observations were made of vegetation composition, elevation, soil chemistry, net precipitation, groundwater level, and flooding frequency over the period 1986–2001. By using multiple regression the changes in the vegetation could be decomposed into (1) an oscillatory component due to fluctuations in net precipitation, (2) an oscillatory component due to incidental flooding, (3) a monotonous component due to soil subsidence, and (4) a monotonous component not related to any measured variable but probably due to eutrophication. The changes were generally small during the observation period, but the regression model predicts large changes by the year 2100 that are almost exclusively due to sea level rise. However, although sea level rise is expected to cause a loss of species, this does not necessarily lead to a loss of conservancy value.     

Investigation of seawater intrusion using stable and radioisotopes at coastal area south of Beirut,the Capital of Lebanon

In this study, field measurements were made and environmental isotopes and radiological properties were determined in six selected wells located in the coastal area south of Beirut, the capital of Lebanon. It is one of the many district areas in Lebanon, threatened by the penetration of seawater into aquifers. Two sampling campaigns were carried out to determine possible seasonal variations. High electrical conductivity was observed, ranging from 1080 to 7900 μS/cm. The total dissolved solids values ranged from 530 to 5600 mg/L. This is attributed to a seawater intrusion confirmed by high chlorine concentrations that ranged from 400 to 3500 mg/L. Isotope data for δ¹⁸O/δ²H showed enrichment that is relatively small at the end of wet season due to recharge by local precipitation and infiltration. Carbon-14 ages and ²³⁴U/²³⁸U ratios confirmed the presence of young water. No radiological hazard was observed as all values lay below the guidance levels of the WHO.     

Discriminating four tectonic settings: Five new geochemical diagrams for basic and ultrabasic volcanic rocks based on log — ratio transformation of major-element data

We present five new discriminant function diagrams based on an extensive database representative of basic and ultrabasic rocks from four tectonic settings of island arc, continental rift, ocean-island, and mid-ocean ridge. These diagrams were obtained after log_e-transformation of concentration ratios of major-elements — a technique recommended for a correct statistical treatment of compositional data. Higher % success rates (overall values from ∼ 83 to 97%) were obtained for proposing these new diagrams as compared to those (∼82 to 94%) obtained from the discriminant analysis of the raw major-element concentration data (i.e., without the log_e-transformation and without taking ratios of the compositional data, but using exactly the same database to provide an unbiased comparison), suggesting that such a data transformation constitutes a statistically correct and recommended technique. The new diagrams also resulted in less mis-classification of basic and ultrabasic rocks from known tectonic settings than the diagrams obtained from the raw data. The use of these highly successful new discriminant function diagrams is illustrated using Miocene to Recent basic and ultrabasic rocks from three areas of Mexico with complex or controversial tectonic settings (Mexican Volcanic Belt, Los Tuxtlas volcanic field, and Eastern Alkaline Province), as well as older rocks from three areas (Deccan, Malani, and Bastar) of India. Additionally, the major-element data from two ‘known’ continental arc settings are used to show that they are similar to those from the island arc setting. Continental rift setting is inferred for all Mexican cases and for one cratonic area of India (Malani) and an IAB setting for the Bastar craton. The Deccan flood basalt province of India is used to warn against an indiscriminate use of those discrimination diagrams that do not explicitly include the likely setting of the area under evaluation. An Excel template is also provided for an easy application of these new diagrams for discriminating the four settings considered in this work.     

Well productivity controlling factors in crystalline terrains of southeastern Brazil

Over the last decades, increasing water demands have fostered research to obtain high well yields in crystalline terrains where, besides the intrinsic properties of rocks, the groundwater flow depends on several factors. The depth of the wells, the lithotypes, the presence and thickness of sedimentary coverings and weathered layers, the landforms, the geological structures, and the effects of tectonic stresses are among the most investigated factors considered as determinant of well productivity. The influence of these factors on productivity of wells that exploit the Crystalline Aquifer System in the Jundiaí River Catchment, southeastern Brazil, is investigated in this work. The largest region of the studied area is located on the Precambrian Basement, partially covered by sedimentary deposits. The results show that the sedimentary deposits and the weathered layer are important for high well yield, but it also depends on the existence of a net of open fractures, in order to maintain high productivity. The sites that have more possibility of occurrence of such structures are the regional shear and fault zones and other minor structures with NW–SE and E–W directions, which characterize areas subjected to transtensional stress related to the neotectonics.     

Management options for a multipurpose coastal aquifer in Oman

Using MODFLOW 2005, this study numerically evaluated the effects of managed aquifer recharge (MAR) using treated wastewater (TWW) in managing the Al-Khawd coastal aquifer northeast of Oman. Our primary objective is to increase the urban water supply and to sustain the aquifer service with the lowest possible damage to the aquifer. A number of managerial scenarios were simulated and progressively developed to reduce seawater intrusion and outflow of the groundwater to the sea. An economic analysis was conducted to characterize the trade-off between the benefits of MAR and seawater inflow to the aquifer under increased abstraction for domestic supply. The results show that by managing irrigation wells and relocating public wells in conjunction with MAR practices, the abstracted volume for drinking purposes could be doubled. Even though injection of TWW is more expensive (due to the injection cost), it was observed to result in greater benefits. The results indicate that managing the aquifer would produce a net benefit ranging from $8.22 million (scenario 7) to $15.21 million (scenario 4) compared to $1.57 million with the current practice. In conclusion, MAR using TWW is a feasible solution to develop water resources in arid regions, and the best scenario depends on the decision maker’s preference when weighing the benefits of MAR and the level of damage to the aquifer. MAR could help manage stressed aquifer systems in arid zones to maximize the benefit of using the water for domestic purposes while minimizing the damage to the aquifer.     

Comparison of the Performance of Fourteen Statistical Tests for Detection of Outlying Values in Geochemical Reference Material Databases

This work presents a comparison of relative efficiency of fourteen statistical tests to detect outliers in normally distributed samples. These tests include deviation/spread, Grubbs-type, Dixon-type, and high-order moment statistics. Performance for the statistical tests is evaluated using Geochemical Reference Material databases from the United States Geological Survey. Test efficiency is compared for the first application of statistics in version k = 1 and k = 2, as well as for tests in version k = 1 applied consecutively against block procedures in which k = 2, 3, or 4 values are evaluated at the same time. In both evaluations, the sensitivity of the statistical tests shows a general strong dependence on sample size. The best performance is observed for the block procedures compared to consecutive statistical tests affected by masking effects.     

Topographic stress and rock fracture: a two‐dimensional numerical model for arbitrary topography and preliminary comparison with borehole observations

Theoretical calculations indicate that elastic stresses induced by surface topography may be large enough in some landscapes to fracture rocks, which in turn could influence slope stability, erosion rates, and bedrock hydrologic properties. These calculations typically have involved idealized topographic profiles, with few direct comparisons of predicted topographic stresses and observed fractures at specific field sites. We use a numerical model to calculate the stresses induced by measured topographic profiles and compare the calculated stress field with fractures observed in shallow boreholes. The model uses a boundary element method to calculate the stress distribution beneath an arbitrary topographic profile in the presence of ambient tectonic stress. When applied to a topographic profile across the Susquehanna Shale Hills Critical Zone Observatory in central Pennsylvania, the model predicts where shear fractures would occur based on a Mohr–Coulomb criterion, with considerable differences in profiles of stresses with depth beneath ridgetops and valley floors. We calculate the minimum cohesion required to prevent shear failure, C_min, as a proxy for the potential for fracturing or reactivation of existing fractures. We compare depth profiles of C_min with structural analyses of image logs from four boreholes located on the valley floor, and find that fracture abundance declines sharply with depth in the uppermost 15 m of the bedrock, consistent with the modeled profile of C_min. In contrast, C_min increases with depth at comparable depths below ridgetops, suggesting that ridgetop fracture abundance patterns may differ if topographic stresses are indeed important. Thus, the present results are consistent with the hypothesis that topography can influence subsurface rock fracture patterns and provide a basis for further observational tests. Copyright © 2014 John Wiley & Sons, Ltd.     

Diel vertical migration of medusae in the open Southern Adriatic Sea over a short time period (July 2003)

Diel vertical migration (DVM) of medusae was investigated at a fixed station in the oligotrophic Southern Adriatic Sea at several depths during summer (July) 2003. We hypothesized that medusan DVM is considerably influenced by environmental variables such as hydrographic features, light intensities, and potential prey densities. We used short-term repetitive sampling as an approach to detail these relationships. Of the 26 species collected, the highest abundance was in the layer between the thermocline (15 m) and 100 m depth, where Rhopalonema velatum predominated, reaching the maximum count of 93 individuals per 10 m³. Seven species were observed over a wide depth range: Solmissus albescens (15–1200 m), R. velatum (0–800 m), Persa incolorata (50–1200 m), Octophialucium funerarium (200–1200 m), Arctapodema australis (200–1200 m), Amphinema rubra (100–800 m), and Rhabdoon singulare (15–600). According to the medusan weighted mean depth (WMD) calculations, the longest DVMs were noted for the deep-sea species S. albescens , O. funerarium , and A. australis . The shallowest species, Aglaura hemistoma , was primarily non-migratory. Certain medusan assemblages were associated consistently with a particular depth layer characterized by a particular light intensity. The interplay of environmental factors and trophic relationships explains some of the features of medusan migratory patterns. These findings thus contribute to understanding the variables that determine patterns of medusan vertical migratory behavior.     

Arsenic distribution, concentration and speciation in groundwater of the Osijek area, eastern Croatia

Groundwater is the main source of drinking water for the population of nearly 200,000 people in eastern Croatia. The largest town in the region is Osijek whose citizens are supplied with drinking water obtained from groundwater from the “Vinogradi” well field. This study investigated and determined As occurrence in groundwater of the Osijek area. Groundwater samples were taken from 18 water wells and 12 piezometers with a depth ranging between 21 and 200 m. Over the 10-a period to 2007, a mean As concentration of 240 μg L⁻¹ was found. There was no statistically significant secular change in concentration over that period, however small but significant seasonal variations were noted, with the highest seasonal As concentrations over the period May 2006-February 2007 being observed in summer. The predominant As species observed was As(III), constituting 85% and 93% of total As in piezometers and water wells, respectively. Higher concentrations of As tended to be found in deeper wells with the mean As concentration in shallow groundwater (<50 m) and deep groundwater (>50 m) being 27 μg L⁻¹, and 205 μg L⁻¹, respectively. Geochemically, the groundwaters show similarities to those in other parts of the Pannonian Basin. Arsenic(tot) is weakly correlated with pH and Fe, negatively correlated with Mn and has no significant correlation with any of EC, COD-Mn or alkalinity.     

Nanochemo-mechanical signature of organic-rich shales: a coupled indentation–EDX analysis

The organic–inorganic nature of organic-rich source rocks poses several challenges for the development of functional relations that link mechanical properties with geochemical composition. With this focus in mind, we herein propose a method that enables chemo-mechanical characterization of this highly heterogeneous source rock at the micron and submicron length scale through a statistical analysis of a large array of energy-dispersive X-ray spectroscopy (EDX) data coupled with nanoindentation data. The ability to include elemental composition to the indentation probe via EDX is shown to provide a means to identify pure material phases, mixture phases, and interfaces between different phases. Employed over a large array, the statistical clustering of this set of chemo-mechanical data provides access to the properties of the fundamental building blocks of clay-dominated organic-rich source rocks. The versatility of the approach is illustrated through the application to a large number of source rocks of different origin, chemical composition, and organic content. We find that the identified properties exhibit a unique scaling relation between stiffness and hardness. This suggests that organic-rich shale properties can be reduced to their elementary constituents, with several implications for the development of predictive functional relations between chemical composition and mechanical properties of organic-rich source rocks such as the intimate interplay between clay-packing, organic maturity, and mechanical properties of porous clay/organic phase.