Salinization and arsenic contamination of surface water in southwest Bangladesh

To identify the causes of salinization and arsenic contamination of surface water on an embanked island (i.e., polder) in the tidal delta plain of SW Bangladesh we collected and analyzed water samples in the dry (May) and wet (October) seasons in 2012–2013. Samples were collected from rice paddies (wet season), saltwater ponds used for brine shrimp aquaculture (dry season), freshwater ponds and tidal channels (both wet and dry season), and rainwater collectors. Continuous measurements of salinity from March 2012 to February 2013 show that tidal channel water increases from ~0.15 ppt in the wet season up to ~20 ppt in the dry season. On the polder, surface water exceeds the World Health Organization drinking water guideline of 10 μg As/L in 78% of shrimp ponds and 27% of rice paddies, raising concerns that produced shrimp and rice could have unsafe levels of As. Drinking water sources also often have unsafe As levels, with 83% of tubewell and 43% of freshwater pond samples having >10 μg As/L. Water compositions and field observations are consistent with shrimp pond water being sourced from tidal channels during the dry season, rather than the locally saline groundwater from tubewells. Irrigation water for rice paddies is also obtained from the tidal channels, but during the wet season when surface waters are fresh. Salts become concentrated in irrigation water through evaporation, with average salinity increasing from 0.43 ppt in the tidal channel source to 0.91 ppt in the rice paddies. Our observations suggest that the practice of seasonally alternating rice and shrimp farming in a field has a negligible effect on rice paddy water salinity. Also, shrimp ponds do not significantly affect the salinity of adjacent surface water bodies or subjacent groundwater because impermeable shallow surface deposits of silt and clay mostly isolate surface water bodies from each other and from the shallow groundwater aquifer. Bivariate plots of conservative element concentrations show that all surface water types lie on mixing lines between dry season tidal channel water and rainwater, i.e., all are related by varying degrees of salinization. High As concentrations in dry season tidal channel water and shrimp ponds likely result from groundwater exfiltration and upstream irrigation in the dry season. Arsenic is transferred from tidal channels to rice paddies through irrigation. Including groundwater samples from the same area (Ayers et al. in Geochem Trans 17:1–22, 2016), principal components analysis and correlation analysis reveal that salinization explains most variation in surface water compositions, whereas progressive reduction of buried surface water by dissolved organic carbon is responsible for the nonconservative behavior of S, Fe, and As and changes in Eh and alkalinity of groundwater.     

Use of discrete element modeling to study the stress and strain distribution in cyclic torsional shear tests

In this research, a torsional cyclic shear test was modeled using the 3D discrete element method (DEM). The results are compared against experimental data and micro-mechanical aspects of the soil during the loading are discussed. The aim of the work is to study the homogeneity of strains during this laboratory test and to compare the micro-mechanical behavior of the soil sample for different strain levels. The experimental investigation was performed using a synthetic soil material made of glass beads, which simplifies the modeling and calibration since normal interaction forces do not induce rotation of the particles. Both the model and experimental tests used the same grading distribution and particle size. We showed that the hysteresis cycles can be properly reproduced in terms of shape and magnitude. Thus, we obtained a robust estimation for the secant shear modulus and damping ratio at different strain levels. With this, it was possible to build stiffness degradation and damping increase curve to compare it with experimental data obtained from torsional shear tests. Based on this validation of the DEM model, we discuss the micro-mechanical behavior of the soil and its relation with the macroscopic parameters obtained. It is shown that shear strain distribution on the sample is not uniform and that large values of strains concentrate close to the top of the sample as top rotation increases, which differs from the standard assumption of a constant value across the height of the sample. Additionally, it is observed that at 0.8 times radius, the cumulative torque reaches approximately 90% of the total torque applied to sample.     

Disaster prevention,disaster preparedness and local community resilience within the context of disaster risk management in Cameroon

This paper presents a simulation of three components of near-field ground shaking recorded during the main shock at three stations of the September 16, 1978, Tabas (M _w = 7.4), Iran, earthquake, close to the causative fault. A hybrid method composed of a discrete wavenumber method developed by Bouchon (Bouchon in Bull Seismol Soc Am 71:959–971, 1981; Cotton and Coutant in Geophys J Int 128:676–688, 1997) and a stochastic finite-fault modeling based on a dynamic corner frequency proposed by Motazedian and Atkinson (Bull Seismol Soc Am 95:995–1010, 2005), modified by Assatourians and Atkinson (Bull Seismol Soc Am 97:935–1949, 2007), is used for generating the seismograms at low (0.1–1.0 Hz) and high frequencies (1.0–20.0 Hz), respectively. The results are validated by comparing the simulated peak acceleration, peak velocity, peak displacement, Arias intensity, the integral of velocity squared, Fourier spectrum and acceleration response spectrum on a frequency-by-frequency basis, the shape of the normalized integrals of acceleration and velocity squared, and the cross-correlation with the observed time-series data. Each characteristic is compared on a scale from 0 to 10, with 10 being perfect agreement. Also, the results are validated by comparing the simulated ground motions with the modified Mercalli intensity observations reported by reconnaissance teams and showed reasonable agreement. The results of the present study imply that the damage distribution pattern of the 1978 Tabas earthquake can be explained by the source directivity effect.     

Quantifying risk to agriculture from volcanic ashfall: a case study from the Bay of Plenty,New Zealand

Natural Hazards - Quantitatively assessing long-term volcanic risk can be challenging due to the many variables associated with volcanic hazard and vulnerability. This study presents a structured...     

Reassessing the invasion of South African waters by the European shore-crab Carcinus maenas

The European shore-crab Carcinus maenas has been present in South Africa since 1983. Despite this species’ international reputation as a biological invader, its distribution in this region has only been considered by three outdated ‘snapshot surveys.’ The present study is the most comprehensive to date, providing an update on the species’ range and the first temporal assessment of its abundance and demographics. Along South Africa's Cape Peninsula and surrounding areas, C. maenas was absent from 12 intertidal sites surveyed, except for Sea Point, and no crabs were found during subtidal surveys along the open coastline. Subtidal harbour populations were recorded in the Cape Town harbours of Table Bay and Hout Bay (previously estimated as comprising approximately 164 200 and 6 500 individuals, respectively). Table Bay was surveyed monthly for one year, using baited traps, crab condos and postlarvae settlement collectors, to assess size distributions and reproductive seasonality of the crab. Reproductive females were recorded throughout most of the year. These results suggest that the harbour populations could be targeted by control programmes, but provide no strong evidence to support the initiation of management action during a particular season. The lack of detection of postlarval settlement, even among well-established populations, suggests this will not be a useful monitoring tool for detecting incursions.     

Sequence of magma emplacement and sulfide saturation in the Gaojiacun–Lengshuiqing intrusive complex (SW China)

The Lengshuiqing area contains several small intrusions made up of peridotite ± quartz diorite ± granite spatially associated with the Gaojiacun pluton (gabbroids + peridotite + diorite). Ni–Cu sulfide ore occur at Lengshuiqing, hosted in peridotite. SHRIMP U–Pb zircon dating produced the ages of 803 ± 4.2 Ma (peridotite), 807 ± 2.6 Ma (oikocrystic hornblende gabbro), 809 ± 4.3 Ma (hornblende gabbronorites) for the Gaojiacun pluton and 807 ± 3.8 Ma (diorite, intrusion I), 817 ± 6.3 Ma (quartz diorite, intrusion II) and 817 ± 5 Ma (peridotite, intrusion 101) for Lengshuiqing. These ages suggest the emplacement of the Gaojiacun pluton later than the intrusions from Lengshuiqing. The olivine from Lengshuiqing does not contain sulfide inclusions and is relatively Ni-rich (1,150–1,550 ppm Ni), suggesting its crystallisation before the sulfide saturation that generated the Ni–Cu deposits. The olivine of the gabbros in the Gaojiacun pluton is Ni-poor (250–800 ppm), which indicates crystallisation from a severely metal-depleted magma after a sulfide saturation event. The olivine in the peridotites from the Gaojiacun pluton has 800–1,150 ppm Ni and contains sulfide inclusions. Moreover, geological evidence suggests the genesis of the peridotites from Gaojiacun in conduits that were ascending through the gabbroids. A sequence of at least three stages of magma emplacement is proposed: (1) Lengshuiqing; (2) gabbroids from Gaojiacun; (3) peridotites from Gaojiacun. Given the age differences, the intrusions at Lengshuiqing and the Gaojiacun pluton might have been produced by different magmatic events.     

Concentration-dependent Stable Isotope Analysis of Consumers in the Upper Reaches of a Freshwater-dominated Estuary: Apalachicola Bay,FL, USA

The goals of this study were to quantify organic matter source utilization by consumers in the freshwater-dominated region (East Bay) of a high river flow estuary and compare the results to consumers in marine-influenced sites of the same estuary to understand how organic matter utilization by consumers may be changing along the salinity gradient. We used the results from these evaluations to establish the baseline against which we isotopically determined trophic level for consumers in East Bay. Average isotope values for consumers sampled in East Bay ranged from −20.1‰ to −24.8‰ for carbon and from 8.9‰ to 14.3‰ for sulfur. These values were well-constrained by the four identified sources: plankton, benthic organic matter, macroalgae, and terrestrial detritus. Application of a concentration-corrected mixing model resulted in contributions of benthic production and detrital sources (averaged over the food web) to East Bay consumers of 41% and 33%, respectively, with the remainder made up of plankton and benthic macroalage. While benthic organic matter was an important organic matter source for consumers at both sites, we found that the influence of terrestrial detritus varied significantly throughout the bay. Terrestrial detritus contributed only 18% of average total organic matter in organisms inhabiting marine-influenced sites. Although terrestrial detritus did contribute to all consumers examined, most fish species in Apalachicola Bay reflect a greater reliance on autochthonous sources. Our results suggest that, while terrestrial detritus does appear to be a major contributor to commercially important shellfish species (most notably oysters and penaeid shrimp), it is not the major source fueling the diversity of secondary production in Apalachicola Bay. Thus, production in Apalachicola Bay is highly dependent on riverine influx in two ways: (1) economically important bivalves and crustaceans are being fueled by terrestrial organic matter supplied by river flooding and (2) secondary and above consumer fish species are supported by in situ production which, in turn, is reliant on nutrients supplied by the Apalachicola River. These findings are significant in light of decisions regarding water usage and river flow restrictions in the Apalachicola-Chattahoochee-Flint drainage basin. The results of this study confirm that in situ estuarine organic matter is the dominant source supporting secondary production in this river-dominated estuary.     

Hydrochemical and isotopic evidence of recharge,apparent age,and flow direction of groundwater in Mayo Tsanaga River Basin,Cameroon: bearings on contamination

Unplanned exploitation of groundwater constitutes emerging water-related threats to MayoTsanaga River Basin. Shallow groundwater from crystalline and detrital sediment aquifers, together with rain, dams, springs, and rivers were chemically and isotopically investigated to appraise its evolution, recharge source and mechanisms, flow direction, and age which were used to evaluate the groundwater susceptibility to contamination and the basin’s stage of salinization. The groundwater which is Ca–Na–HCO₃ type is a chemically evolved equivalent of surface waters and rain water with Ca–Mg–Cl–SO₄ chemistry. The monsoon rain recharged the groundwater preferentially at an average rate of 74 mm/year, while surface waters recharge upon evaporation. Altitude effect of rain and springs show a similar variation of −0.4‰ for δ¹⁸O/100 m, but the springs which were recharged at 452, 679, and 773 m asl show enrichment of δ¹⁸O through evaporation by 0.8‰ corresponding to 3% of water loss during recharge. The groundwater which shows both local and regional flow regimes gets older towards the basins` margin with coeval enrichment in F⁻ and depletion in NO₃ ⁻. Incidentally, younger groundwaters are susceptible to anthropogenic contamination and older groundwaters are sinks of lithologenic fluoride. The basins salinization is still at an early stage.     

The aerosol measurement and processing system (AMAPS)

As the collection of Earth science datasets continues to grow, so too grows the challenge in the ability to collect, interpret, assimilate, compare, and combine them. Stores of data, already enormous, continue to amass. New instruments are built that introduce differences in measurements and retrieval algorithms from previous ones. Data are rarely collocated either spatially or temporally, and rarely represent equivalent quantities even for similarly named parameters. Uncertainties must be understood and accounted for. Formats differ. In the realm of diverse data sources, the analyst each time must become an expert in the data from each source, and that expertise is disseminated in the form of publications (if at all), but analysis tools are not, and must be continually redeveloped. AMAPS addresses each of these areas in a way that provides a breakthrough in the analyst’s ability to efficiently and effectively make use of the vast wealth of data that continues to accumulate. AMAPS is targeted to aerosol data acquisition and analysis. Data from disparate aerosol sources, including the Multi-angle Imaging SpectroRadiometer (MISR), the Moderate Resolution Imaging Spectrometer (MODIS), and the AErosol RObotic NETwork (AERONET), are efficiently retrieved and transformed behind the scenes to a common format via SciFlo. Analysis algorithms for collocation and comparison between sources are generalized so that researchers have access to a common set of tools applied consistently to each data source. AMAPS has established a successful track record in supporting scientific research.     

Mercury: reusable metadata management, data discovery and access system

Mercury is a federated metadata harvesting, search and retrieval tool based on both open source packages and custom software developed at Oak Ridge National Laboratory (ORNL). It was originally developed for the National Aeronautics and Space Administration (NASA), and the consortium now includes funding from NASA, U.S. Geological Survey (USGS), and U.S. Department of Energy (DOE). Mercury is itself a reusable software application which uses a service-oriented architecture (SOA) approach to capturing and managing metadata in support of twelve Earth science projects. Mercury also supports the reuse of metadata by enabling searches across a range of metadata specification and standards including XML, Z39.50, FGDC, Dublin-Core, Darwin-Core, EML, and ISO-19115. It collects metadata and key data from contributing project servers distributed around the world and builds a centralized index. The Mercury search interfaces allows the users to perform simple, fielded, spatial, temporal and other hierarchical searches across these metadata sources. This centralized repository of metadata with distributed data sources provides extremely fast search results (Table 1) to the user, while allowing data providers to advertise the availability of their data and yet maintain complete control and ownership of that data.