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.     

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.     

Gas-hydrate promotion by smectite–bioproduct interactions

Gas hydrates accumulate on the Gulf of Mexico seafloor around hydrocarbon seeps in waters sufficiently deep to provide adequate pressure/temperature combinations. High microbial activities occur around the hydrate accumulations. To understand apparent catalytic effects of bioproducts on hydrate formation, the mechanism of sII hydrate nucleation in unconsolidated porous media was investigated in our laboratory. Because smectite clays interacting with biopolymers had been shown to promote laboratory hydrates by decreasing induction times, increasing formation rates and altering morphology, these materials commonly found in near-surface sediments were selected for study as possible nucleating agents. Dynamic light scattering (DLS) with a helium–neon laser was used to measure particle diameters down to about 2 nm. Scanning electron microscopy (SEM) was utilized to verify particle sizes and to give additional information on biopolymer–clay associations. This paper presents evidence that nanometer-sized particles of mineral–bioproduct associations of about 80 nm–450 nm diameter may act as nucleation sites for hydrate crystal initiations in sediments and then remain dispersed throughout the accumulated hydrate mass. Emulsan biopolymer was shown by SEM to apparently unfold and associate with the smectite (nontronite) in a backbone arrangement and to give multiple hydrate nucleation sites along a linear network. SEM and DLS measurements were in agreement on particle sizes and shapes. X-ray diffraction suggested that biopolymer intercalates the smectite interlayer, probably driven by clay associations with biopolymer hydrophilic groups. It is hypothesized that hydrocarbon gases attach to biopolymer hydrophobic fatty-acid branches protruding from clay interlayers and subsequently facilitate hydrate structure formation by interacting with nearby water associated with the hydrophilic segments of the biopolymer.     

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.     

Incidence of polychlorinated biphenyls in Clyde seaweed

PCBs accumulate in seaweeds. This survey of concentrations found in fixed algae around the Firth of Clyde reveals a similar pattern of PCB distribution to that found in mussels.     

Orbital effects on Mercury’s escaping sodium exosphere

We present results from coronagraphic imaging of Mercury’s sodium tail over a 7° field of view. Several sets of observations made at the McDonald Observatory since May 2007 show a tail of neutral sodium atoms stretching more than 1000 Mercury radii (R_m) in length, or a full degree of sky. However, no tail was observed extending beyond 120 R_m during the January 2008 MESSENGER fly-by period, or during a similar orbital phase of Mercury in July 2008. Large changes in Mercury’s heliocentric radial velocity cause Doppler shifts about the Fraunhofer absorption features; the resultant change in solar flux and radiation pressure is the primary cause of the observed variation in tail brightness. Smaller fluctuations in brightness may exist due to changing source rates at the surface, but we have no explicit evidence for such changes in this data set. The effects of radiation pressure on Mercury’s escaping atmosphere are investigated using seven observations spanning different orbital phases. Total escape rates of atmospheric sodium are estimated to be between 5 and 13 × 10²³ atoms/s and show a correlation to radiation pressure. Candidate sources of Mercury’s sodium exosphere include desorption by UV sunlight, thermal desorption, solar wind channeled along Mercury’s magnetic field lines, and micro-meteor impacts. Wide-angle observations of the full extent of Mercury’s sodium tail offer opportunities to enhance our understanding of the time histories of these source rates.     

Seasonal global mean sea level change from satellite altimeter, GRACE, and geophysical models

We estimate seasonal global mean sea level changes using different data resources, including sea level anomalies from satellite radar altimetry, ocean temperature and salinity from the World Ocean Atlas 2001, time-variable gravity observations from the Gravity Recovery and Climate Experiment (GRACE) mission, and terrestrial water storage and atmospheric water vapor changes from the NASA global land data assimilation system and National Centers for Environmental Prediction reanalysis atmospheric model. The results from all estimates are consistent in amplitude and phase at the annual period, in some cases with remarkably good agreement. The results provide a good measure of average annual variation of water stored within atmospheric, land, and ocean reservoirs. We examine how varied treatments of degree-2 and degree-1 spherical harmonics from GRACE, laser ranging, and Earth rotation variations affect GRACE mean sea level change estimates. We also show that correcting the standard equilibrium ocean pole tide correction for mass conservation is needed when using satellite altimeter data in global mean sea level studies. These encouraging results indicate that is reasonable to consider estimating longer-term time series of water storage in these reservoirs, as a way of tracking climate change.     

On the moments approximation method for constructing a Lagrangian Stochastic model

The exact Eulerian velocity probability density function (pdf) of a turbulent field is generally unknown, and one normally has available only partial information in the form of low order moments. We compare two alternative Lagrangian Stochastic (LS) approaches formed from this partial information, (i) the moments approximation approach (Kaplan and Dinar, 1993); and (ii) the well-mixed model (Thomson, 1987) that corresponds to the maximum missing information pdf formed from the available information. We show that the moments approximation model does not in general satisfy the well-mixed constraint, and can give an inferior prediction of dispersion.     

A sensitivity analysis of the PROFILE model in relation to the calculation of soil weathering rates

Recently there has been growing interest in, and use of, the PROFILE model, principally through the role of weathering rates in determining critical loads. In many cases the accuracy of the data used to run the model is not quoted. A simple sensitivity analysis of the model has been carried out by varying the input data one at a time in a systematic fashion. The variation in weathering rate that this generates for monomineralic soil profiles and for a soil profile from an acid sensitive forested catchment in Scotland has been recorded. Variations in weathering rates of over 100% can be generated using ranges of input parameters measured in field studies. The model broadly predicts the relative ease of weathering of the different minerals. Minerals which are particularly sensitive to input variations have been identified, e.g. Kfeldspar. Some input parameters exert a larger influence on the weathering rate as calculated by the model than others. The most sensitive input data are soil temperature, moisture content and exposed mineral surface area. The least sensitive input data are cation load and precipitation rate.