Integration of aquifer geology, groundwater flow and arsenic distribution in deltaic aquifers - A unifying concept

Groundwater arsenic (As) presents a public health risk of great magnitude in densely populated Asian delta regions, most acutely in the Bengal Basin (West Bengal, India and Bangladesh). Research has focused on the sources, mobilisation, and heterogeneity of groundwater As, but a consistent explanation of As distribution from local to basin scale remains elusive. We show for the Bengal Aquifer System that the numerous, discontinuous silt‐clay layers together with surface topography impose a hierarchical pattern of groundwater flow, which constrains As penetration into the aquifer and controls its redistribution towards discharge zones, where it is re‐sequestered to solid phases. This is particularly so for the discrete periods of As release to groundwater in the shallow subsurface associated with sea level high‐stand conditions of Quaternary inter‐glacial periods. We propose a hypothesis concerning groundwater flow (Silt‐clay layers Impose Hierarchical groundwater flow patterns constraining Arsenic progression [SIHA]), which links consensus views on the As source and history of sedimentation in the basin to the variety of spatial and depth distributions of groundwater As reported in the literature. SIHA reconciles apparent inconsistencies between independent, in some cases contrasting, field observations. We infer that lithological and topographic controls on groundwater flow, inherent to SIHA, apply more generally to deltaic aquifers elsewhere. The analysis suggests that groundwater As may persist in the aquifers of Asian deltas over thousands of years, but in certain regions, particularly at deeper levels, As will not exceed low background concentrations unless groundwater flow systems are short‐circuited by excessive pumping

Securing a Future for China's Wild Plant Resources

China harbors one of the most species-rich floras in the world. This plant diversity is currently severely threatened by high levels of habitat degradation and unsustainable resource extraction, the country's exceptionally fast economic growth, an uncontrolled increase in tourism, invasive species, and climate change. Furthermore, China's current system of protected areas is ineffective at conserving the country's plant resources, with low levels of enforcement and only a few small reserves located in both the most phytodiverse regions and in areas facing the highest anthropogenic pressure. Seven strategic steps are required in order to secure a future for China's wild plants, including surveys to establish current species distributions and threat levels, the creation of an effective protected-area system focused on quality rather than quantity, resettlement of parts of the scattered rural population, control of the illegal export trade and invasive species, and a streamlining of administrative responsibilities and capacity building in conservation

Unexpected features of branched flow through high-mobility two-dimensional electron gases

GaAs-based two-dimensional electron gases (2DEGs) show a wealth of remarkable electronic states, and serve as the basis for fast transistors, research on electrons in nanostructures, and prototypes of quantum-computing schemes. All these uses depend on the extremely low levels of disorder in GaAs 2DEGs, with low-temperature mean free paths ranging from microns to hundreds of microns. Here we study how disorder affects the spatial structure of electron transport by imaging electron flow in three different GaAs/AlGaAs 2DEGs, whose mobilities range over an order of magnitude. As expected, electrons flow along narrow branches that we find remain straight over a distance roughly proportional to the mean free path. We also observe two unanticipated phenomena in high-mobility samples. In our highest-mobility sample we observe an almost complete absence of sharp impurity or defect scattering, indicated by the complete suppression of quantum coherent interference fringes. Also, branched flow through the chaotic potential of a high-mobility sample remains stable to significant changes to the initial conditions of injected electrons.Comment: 22 pages, 4 figures, 1 tabl

Synergistic interaction in simultaneous exposure to Streptomyces californicus and Stachybotrys chartarum.

The microbial exposure associated with health complaints in moldy houses consists of a heterogeneous group of components, including both living and dead bacteria, fungi, and their metabolites and active compounds. However, little is known about the interactions between different microbes and their metabolites, although the cytotoxicity and inflammatory potential of certain individual microbes have been reported. In this study, we investigated the inflammatory responses of mouse RAW264.7 macrophages after exposure to six indoor air microbes (Aspergillus versicolor, Penicillium spinulosum, Stachybotrys chartarum, Bacillus cereus, Mycobacterium terrae, and Pseudomonas fluorescens) alone and together with the actinomycete Streptomyces californicus. The production of nitric oxide, levels of the proinflammatory cytokines tumor necrosis factor alpha (TNF-alpha) and interleukin-6 (IL-6), and cytotoxicity were measured. The coexposure to Sta. chartarum and Str. californicus caused a synergistic increase in the production of IL-6 but not other cytokines. In further experiments, the metabolites from Sta. chartarum or from closely related fungi (atranones B and E, satratoxin G, trichodermin, 7-alpha-hydroxytrichodermol, staplabin, and SMTP-7) and the known fungal toxins sterigmatocystin, citrinin, and ochratoxin A were each tested with Str. californicus. The testing revealed a synergistic response in TNF-alpha and IL-6 production after coexposure to Str. californicus with both trichodermin and 7-alpha-hydroxytrichodermol. Finally, the synergistic inflammatory response caused by Str. californicus and trichodermin together was studied by analyzing for the presence of nuclear factor-kappa-B (NF-kappa-B) in nuclear extracts of the exposed cells. The exposure to Str. californicus induced the binding of NF-kappa-B proteins to the NF-kappa-B consensus sequence as well as to the natural NF-kappa-B site of the IL-6 promoter. Adding trichodermin to the exposure did not increase the DNA binding

Commentary: Selecting synaptic partners: GRASPing the role of UNC- 6/netrin

Forming synaptic connections of the appropriate strength between specific neurons is crucial for constructing neural circuits to control behavior. A recent paper in Neural Development describes the use of a synapse-specific label in Caenorhabditis elegans to implicate local UNC-6/netrin signaling in this developmental process. Thus, as well as their well known roles in cell migration and axon guidance, UNC-6/netrin signals distinguish an appropriate synaptic partner from other potential targets

How Did the Spider Cross the River? Behavioral Adaptations for River-Bridging Webs in Caerostris darwini (Araneae: Araneidae)

Interspecific coevolution is well described, but we know significantly less about how multiple traits coevolve within a species, particularly between behavioral traits and biomechanical properties of animals' "extended phenotypes". In orb weaving spiders, coevolution of spider behavior with ecological and physical traits of their webs is expected. Darwin's bark spider (Caerostris darwini) bridges large water bodies, building the largest known orb webs utilizing the toughest known silk. Here, we examine C. darwini web building behaviors to establish how bridge lines are formed over water. We also test the prediction that this spider's unique web ecology and architecture coevolved with new web building behaviors.We observed C. darwini in its natural habitat and filmed web building. We observed 90 web building events, and compared web building behaviors to other species of orb web spiders.Caerostris darwini uses a unique set of behaviors, some unknown in other spiders, to construct its enormous webs. First, the spiders release unusually large amounts of bridging silk into the air, which is then carried downwind, across the water body, establishing bridge lines. Second, the spiders perform almost no web site exploration. Third, they construct the orb capture area below the initial bridge line. In contrast to all known orb-weavers, the web hub is therefore not part of the initial bridge line but is instead built de novo. Fourth, the orb contains two types of radial threads, with those in the upper half of the web doubled. These unique behaviors result in a giant, yet rather simplified web. Our results continue to build evidence for the coevolution of behavioral (web building), ecological (web microhabitat) and biomaterial (silk biomechanics) traits that combined allow C. darwini to occupy a unique niche among spiders

Probing elastic and inelastic breakup contributions to intermediate-energy two-proton removal reactions

The two-proton removal reaction from 28Mg projectiles has been studied at 93 MeV/u at the NSCL. First coincidence measurements of the heavy 26Ne projectile residues, the removed protons and other light charged particles enabled the relative cross sections from each of the three possible elastic and inelastic proton removal mechanisms to be determined. These more final-state-exclusive measurements are key for further interrogation of these reaction mechanisms and use of the reaction channel for quantitative spectroscopy of very neutron-rich nuclei. The relative and absolute yields of the three contributing mechanisms are compared to reaction model expectations - based on the use of eikonal dynamics and sd-shell-model structure amplitudes.Comment: Accepted for publication in Physical Review C (Rapid Communication

Elastic breakup cross sections of well-bound nucleons

The 9Be(28Mg,27Na) one-proton removal reaction with a large proton separation energy of Sp(28Mg)=16.79 MeV is studied at intermediate beam energy. Coincidences of the bound 27Na residues with protons and other light charged particles are measured. These data are analyzed to determine the percentage contributions to the proton removal cross section from the elastic and inelastic nucleon removal mechanisms. These deduced contributions are compared with the eikonal reaction model predictions and with the previously measured data for reactions involving the re- moval of more weakly-bound protons from lighter nuclei. The role of transitions of the proton between different bound single-particle configurations upon the elastic breakup cross section is also quantified in this well-bound case. The measured and calculated elastic breakup fractions are found to be in good agreement.Comment: Phys. Rev. C 2014 (accepted

A note on mate allocation for dominance handling in genomic selection

Estimation of non-additive genetic effects in animal breeding is important because it increases the accuracy of breeding value prediction and the value of mate allocation procedures. With the advent of genomic selection these ideas should be revisited. The objective of this study was to quantify the efficiency of including dominance effects and practising mating allocation under a whole-genome evaluation scenario. Four strategies of selection, carried out during five generations, were compared by simulation techniques. In the first scenario (MS), individuals were selected based on their own phenotypic information. In the second (GSA), they were selected based on the prediction generated by the Bayes A method of whole-genome evaluation under an additive model. In the third (GSD), the model was expanded to include dominance effects. These three scenarios used random mating to construct future generations, whereas in the fourth one (GSD + MA), matings were optimized by simulated annealing. The advantage of GSD over GSA ranges from 9 to 14% of the expected response and, in addition, using mate allocation (GSD + MA) provides an additional response ranging from 6% to 22%. However, mate selection can improve the expected genetic response over random mating only in the first generation of selection. Furthermore, the efficiency of genomic selection is eroded after a few generations of selection, thus, a continued collection of phenotypic data and re-evaluation will be required