Delineation of groundwater provenance in a coastal aquifer using statistical and isotopic methods,Southeast Tanzania

Rapid population growth and urbanization has placed a high demand on freshwater resources in southeast costal Tanzania. In this paper, we identify the various sources of groundwater and the major factors affecting the groundwater quality by means of multivariate statistical analyses, using chemical tracers and stable isotope signatures. The results from hierarchical cluster analyses show that the groundwater in the study area may be classified into four groups. A factor analysis indicates that groundwater composition is mainly affected by three processes, accounting for 80.6% of the total data variance: seawater intrusion, dilution of groundwater by recharge, and sewage infiltration. The hydrochemical facies of shallow groundwater was mostly of the Na–Ca–Cl type, although other water types were also observed. The deep groundwater samples were slightly to moderately mineralized and they were of the NaHCO₃ type. This water type is induced mainly by dissolution of carbonate minerals and modified by ion exchange reactions. The signal from the stable isotope composition of the groundwater samples corresponded well with the major chemical characteristics. In the shallow groundwater, both high-nitrate and high-chloride concentrations were associated with localized stable isotope enrichments which offset the meteoric isotopic signature. This is inferred to be due to the contamination by influx of sewage, as well as intrusion by seawater. The depleted stable isotope values, which coincides with a chemical signature for the deep aquifer indicates that this deep groundwater is derived from infiltration in the recharge zone followed by slow lateral percolation. This study shows that a conceptual hydrogeochemical interpretation of the results from multivariate statistical analysis (using HCA and FA) on water chemistry, including isotopic data, provides a powerful tool for classifying the sources of groundwater and identifying the significant factors governing the groundwater quality. The derived knowledge generated by this study constitutes a conceptual framework for investigating groundwater characteristics. This is a prerequisite for developing a sound management plan, which is a requirement for ensuring a sustainable exploitation of the deep aquifer water resource in the coastal area of Tanzania.     

Investigation of the geochemical impact of CO2 on shallow groundwater: design and implementation of a CO2 injection test in Northeast Germany

A small scale and temporally limited CO₂ injection test was performed in a shallow aquifer to investigate the geochemical impact of CO₂ upon such aquifers and to apply and verify different monitoring methods. Detailed site investigation coupled with multiphase simulations were necessary to design the injection experiment and to set up the monitoring network, before CO₂ was injected over a ten-day period at three injection wells, at a depth of 18?m below surface level into a quaternary sand aquifer located close to the town of Wittstock in Northeast Germany. Monitoring methods comprised groundwater sampling and standard analyses, as well as trace element analyses and isotope analyses; geoelectrical borehole monitoring; passive samplers to analyse temporally integrated for cations and multi-parameter probes that can measure continuously for dissolved CO₂, pH and electrical conductivity. Due to CO₂ injection, total inorganic carbon concentrations increased and pH decreased down to a level of 5.1. Associated reactions comprised the release of major cations and trace elements. Geoelectrical monitoring, as well as isotope analyses and multi-parameter probes proved to be suitable methods for monitoring injected CO₂ and/or the alteration of groundwater.     

KGI-XGIS supporting decision making with knowledge-based techniques

The concept of the King George Island Expert GIS (KGI-XGIS) is introduced. KGI-XGIS is a combination of a rule-based expert system and a GIS meant to form an intelligent spatial decision support system. The system provides the spatial knowledge necessary for the environmental impact assessment process as dictated by the ‘Madrid Protocol’ for King George Island (South Shetland Islands, Antarctica). It also serves as information system to the scientific user community. Topographic maps, remote sensing data, thematic maps based on field surveys and other digital data form the input data to the GIS. Given the sparseness of the available data these must be combined and used in the most efficient way. Therefore expert knowledge of different domains will be coded into a rule-based expert system which is coupled to the GIS. To handle the expert knowledge and the spatial data of different types and different quality the KGI-XGIS incorporates knowledge-based techniques and fuzzy reasoning. The selection of a camp site on the ice free area of Fildes Peninsula and data quality management are used as two examples to demonstrate the capabilities of the system.     

A direct imaging search for close stellar and sub‐stellar companions to young nearby stars

A total of 28 young nearby stars (ages ≤60 Myr) have been observed in the K_s‐band with the adaptive optics imager Naos‐Conica of the Very Large Telescope at the Paranal Observatory in Chile. Among the targets are ten visual binaries and one triple system at distances between 10 and 130 pc, all previously known. During a first observing epoch a total of 20 faint stellar or sub‐stellar companion‐candidates were detected around seven of the targets. These fields, as well as most of the stellar binaries, were re‐observed with the same instrument during a second epoch, about one year later. We present the astrometric observations of all binaries. Their analysis revealed that all stellar binaries are co‐moving. In two cases (HD 119022 AB and FG Aqr B/C) indications for significant orbital motions were found. However, all sub‐stellar companion candidates turned out to be non‐moving background objects except PZ Tel which is part of this project but whose results were published elsewhere. Detection limits were determined for all targets, and limiting masses were derived adopting three different age values; they turn out to be less than 10 Jupiter masses in most cases, well below the brown dwarf mass range. The fraction of stellar multiplicity and of the sub‐stellar companion occurrence in the star forming regions in Chamaeleon are compared to the statistics of our search, and possible reasons for the observed differences are discussed. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Spaxel analysis: probing the physics of star formation in ultraluminous infrared galaxies

This paper presents a detailed spectral pixel (spaxel) analysis of the ten Luminous Infrared Galaxies (LIRGs) previously observed with the Wide Field Spectrograph (WiFeS), an integral field spectrograph mounted on the ANU 2.3 m telescope, and for which an abundance gradient analysis has already been presented by Rich et al. (Astrophys. J., 753:5, 2012). Here we use the strong emission line analysis techniques developed by Dopita et al. (Astrophys. J. Suppl. Ser., accepted, 2013) to measure the ionisation parameter and the oxygen abundance in each spaxel. In addition, we use the observed Hα flux to determine the surface rate of star formation ( $\mathrm {M}_{\odot }{\rm yr}^{-1}$ kpc^?2) and use the [S II] λλ6717/6731 ratio to estimate the local pressure in the ionised plasma. We discuss the correlations discovered between these physical quantities, and use them to infer aspects of the physics of star formation in these extreme star forming environments. In particular, we find a correlation between the star formation rate and the inferred ionisation parameter. We examine the possible reasons for this correlation, and determine that the most likely explanation is that the more active star forming regions have a different distribution of molecular gas which favour higher ionisation parameters in the ionised plasma.     

Ground-Truthing 11- to 12-kHz side-scan sonar imagery in the Norwegian–Greenland Sea: Part II: Probable diapirs on the Bear Island fan slide valley margins and the Vøring Plateau

SeaMARC II (11- to 12-kHz) side-scan sonar revealed hundreds of small strong-backscatter spots, tens to 500?m in diameter, along the lips of the Bear Island fan slide valley. New bathymetry, deep-tow side-scan, deep-tow profiles, heatflow, and gravity cores were collected for ground-truth. These mounds are probably mud diapirs (or mud-built mounds) typically 10–75?m high, formed by glacial sediment mobilized by Late Pleistocene slide events. The mounds are arranged along NNE trending lines, suggesting control by intrasedimentary faults ca. 0.5–1 km apart. Diapirs examined on the Vøring Plateau exhibit WNW structural control. No heatflow anomaly was found in four stations on or next to diapirs in either area.     

GJ 581 update: Additional evidence for a Super‐Earth in the habitable zone

We present an analysis of the significantly expanded HARPS 2011 radial velocity data set for GJ 581 that was presented by Forveille et al. (2011). Our analysis reaches substantially different conclusions regarding the evidence for a Super‐Earth‐mass planet in the star's Habitable Zone. We were able to reproduce their reported χ²_ν and RMS values only after removing some outliers from their models and refitting the trimmed down RV set. A suite of 4000 N‐body simulations of their Keplerian model all resulted in unstable systems and revealed that their reported 3.6σ detection of e = 0.32 for the eccentricity of GJ 581e is manifestly incompatible with the system's dynamical stability. Furthermore, their Keplerian model, when integrated only over the time baseline of the observations, significantly increases the χ²_ν and demonstrates the need for including non‐Keplerian orbital precession when modeling this system. We find that a four‐planet model with all of the planets on circular or nearly circular orbits provides both an excellent self‐consistent fit to their RV data and also results in a very stable configuration. The periodogram of the residuals to a 4‐planet all‐circular‐orbit model reveals significant peaks that suggest one or more additional planets in this system. We conclude that the present 240‐point HARPS data set, when analyzed in its entirety, and modeled with fully self‐consistent stable orbits, by and of itself does offer significant support for a fifth signal in the data with a period near 32 days. This signal has a false alarm probability of <4% and is consistent with a planet of minimum mass 2.2 M_⊕, orbiting squarely in the star's habitable zone at 0.13 AU, where liquid water on planetary surfaces is a distinct possibility (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Importance of sulfate emission to sulfur deposition at urban and rural sites in China

Throughfall (TF) and wet only (WO) deposition along with SO₂ and sulfate (SO₄²⁻) concentration in air at 4 urban and rural sites in southwestern China were monitored in order to understand the role of different forms of sulfur (S) emission to the S deposition and its effect in China. The sites were located in Chongqing, Hunan, and Guizhou provinces. S deposition at the most polluted site reached 15 g S m^− 2 yr^− 1. At three of the sites, located in the vicinity of several emission sources, dry S deposition is 2.1–4.2 times that of wet deposition, which is significantly higher than what is found in most other parts of the world.Main components in airborne particles (PM₁₀) are (NH₄)₂SO₄ and CaSO₄ at the highly polluted Tie Shan Ping (TSP) site. Dust particles of gypsum (CaSO₄) in the air are partly due to direct emission and partly from the reaction of calcium oxides and carbonates with sulfuric acid in the air. To illustrate the importance of sulfate emission to total S deposition we analyzed the source of S deposition based on both measurements and models. Results indicated that direct emission of SO₄²⁻ particles could account for high proportion in total S deposition at the three most polluted sites.     

Fractionation,distribution and transport of mercury in rivers and tributaries around Wanshan Hg mining district,Guizhou province,southwestern China: Part 1 – Total mercury

The Wanshan Hg mining area in Guizhou, China, was one of the world’s largest Hg producing regions. Numerous mine-waste and calcines still remain, leaching Hg to local rivers and streams and potentially impacting the local population. Several studies have been published on local environmental impacts of these mining and retorting residues, but a comprehensive, regional survey on the distribution of Hg in the rivers in the region, as presented in this paper, has not previously been conducted. This study focuses on the regional distribution and temporal variation of aqueous Hg fractions in the five main watercourses draining the Wanshan Hg mining and retorting area, covering more than 700 km². Three sampling campaigns were carried out in 2007 and 2008, covering high flow, normal flow and low flow periods. Total (THg), particulate (PHg), dissolved (DHg) and reactive (RHg) Hg fractions were determined. All rivers had the highest Hg concentrations at sample sites about 100–500 m downstream of the mine wastes. Total Hg concentrations ranged from extremely high (up to 12,000 ng L⁻¹) at the sample site just 100 m below mine wastes, to quite low in tributary streams (1.9 ng L⁻¹, about 14 km downstream of the mine wastes). Total Hg and PHg concentrations were usually highest during high flow periods in the Hg-contaminated areas (i.e. THg ? 50 ng L⁻¹), while in the less-impacted downstream areas (with THg < 50 ng L⁻¹) the Hg concentrations were usually lowest during high flow periods. Although highly elevated concentrations of Hg in water samples were found just downstream of the mine wastes, the concentrations decreased sharply to well below 50 ng L⁻¹ (US EPA Hg concentration standard for protection of fresh water), within only 6–8 km downstream. Concentrations of THg were highly dominated by and correlated with PHg (R² = 0.996–0.999, P < 0.001); PHg constituted more than 80% of THg in Hg-contaminated areas, and could account for 99.6% of the THg close to the mine wastes.     

Anisotropic compression of edingtonite and thomsonite to 6 GPa at room temperature

Polycrystalline samples of natural edingtonite (New Brunswick, Canada) and thomsonite (Oregon, USA) were studied up to 6 GPa using monochromatic synchrotron X-ray powder diffraction and a diamond-anvil cell with a methanol:ethanol:water mixture as a penetrating pressure-transmitting fluid. Unlike natrolite, previously studied under the same conditions, edingtonite and thomsonite do not show any apparent pressure-induced hydration (PIH) or phase transitions. All these fibrous zeolites are characterized by their anisotropic compressibilities, with the linear compressibilities of the fibrous chains (c-axis) being as small as one third of those perpendicular to the chains (a-, b-axes); for edingtonite, ₀ ^a =0.0050(3) GPa^–1, ₀ ^b =0.0054(2) GPa^–1, ₀ ^c =0.0034(1) GPa^–1; for thomsonite, ₀ ^a = 0.0080(2) GPa^–1, ₀ ^b =0.0084(2) GPa^–1, ₀ ^c =0.0032(1) GPa^–1. The pressure–volume data were fitted to a second-order Birch–Murnaghan equation of state using a fixed pressure derivative of 4. As a result of the 0000-type connectivity of the chains, the bulk modulus of edingtonite is found to be about 40% larger than that of thomsonite; K^EDI ₀=73(3) GPa, K^THO ₀=52(1) GPa. Distance least-squares refinements were used to model the expected framework, following the observed linear compression behaviors. The chain-bridging T–O–T angle is proposed to be correlated with the different compressibilities across the chains in each framework type.