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Background and aims: Proteaceae species strongly acidify their rhizosphere to increase soil phosphorus (P) availability, which also inadvertently increases the availability of other elements, such as manganese and rare earth elements (REE). This study aimed to investigate REE (hyper) accumulation in the Proteaceae genus Helicia from Queensland, Australia, from a systematic assessment of REE concentrations in herbarium specimens and verification with field collected samples. Methods: Herbarium X-ray fluorescence (XRF) scanning (using yttrium as a proxy for REEs) was undertaken on selected Helicia species (Proteaceae) at the Queensland Herbarium, followed by Inductively coupled plasma atomic emission spectroscopy (ICP-AES) analysis and field collection of H. glabriflora samples to confirm the XRF findings. Results: The herbarium XRF analysis revealed highly anomalous REE concentrations in some Helicia species, reaching ~ 1300 µg Y g-1 in H. australasica and H. glabriflora. The ICP-AES analysis of the herbarium specimens revealed total REE concentrations (REE) of up to 2300 µg g-1 in H. australasica and H. glabriflora, with relatively higher light REEs (~ 70%) and yttrium (~ 20%) concentrations, compared to heavy REEs (~ 10%). The field collected H. glabriflora material had relatively higher total REE concentrations in the mature leaves (~ 850 µg REE g-1) and stems (~ 675 µg REE g-1), compared to young leaves (~ 130 µg REE g-1), roots (~ 220 µg REE g-1) and soil (~ 90 µg REE g-1). Conclusion: The discovery of REE (hyper)accumulation in these Helicia species suggests that the Proteaceae family may host several other REE hyperaccumulators that are hitherto undiscovered. This calls for systematic assessment of the Proteaceae using the same approach as used in this study. The findings have potential implications for (i) discovery of REE hyperaccumulator plants, (ii) investigation of REE uptake and accumulation in plants and (iii) biogeochemical exploration of buried REE ore deposits. [ABSTRACT FROM AUTHOR]

Abstract A systematic understanding of hyporheic flux (HF) and residence times (RT) is important as they are a major control of biogeochemical processing in streambeds. Previous studies addressing the effect of heterogeneity in streambed hydraulic conductivity (K) on HF and RT have come to deviating conclusions depending on the specific study design and the selection of heterogeneity cases being investigated. To more systematically evaluate the effects of conductivity heterogeneity on HF and RT, we simulated hyporheic exchange induced by idealized streambed ripples over a large range of heterogeneities. Conductivity heterogeneity was represented in the simulations in terms of 10,000 different heterogeneity realizations from a geostatistical model based on continuous Gaussian and discrete indicator random fields. We demonstrate that any isotropic homogeneous K-field, as an average of a heterogeneous K-field, can only match RT or HF of the respective heterogeneous K-field, but never both. We found exponential correlations of RT and HF with the variance of heterogeneous conductivity. Based on these correlations, an equivalent anisotropic homogeneous conductivity tensor K can be derived. This equivalent anisotropic K efficiently accounts for the effects of small scale heterogeneity on HF and RT. It can be calculated from the median and variance of the hydraulic conductivity distribution of the targeted heterogeneous sediment, without explicitly characterizing the sediment texture. [ABSTRACT FROM AUTHOR]

Watershed urbanization introduces a variety of physical, chemical, and thermal stressors to receiving streams and leads to well-documented declines in the diversity of fish and macroinvertebrates. Far less knowledge is available about how these urban stressors affect microbial communities and microbially mediated ecosystem properties. We examined 67 chemical, physical, and biological attributes of streams draining 47 watersheds in the metropolitan area surrounding Raleigh, North Carolina. Watersheds ranged from undeveloped to 99.7% developed watershed area. In contrast to prior investigators, we found no consistent changes in habitat structure, channel dimensions, or bed sediment size distributions along the urbanization gradient. Watershed urbanization led to large and consistent changes in receiving stream chemistry (increases in NO3−, bioavailable and algal-derived dissolved organic C, and the trace metals Pb, Cd, and Zn) and thermal regimes. These chemical and thermal changes were not associated with any consistent shifts in microbial community structure or taxonomic richness, based on terminal-restriction fragment length polymorphism and pyrosequencing methods, despite the fact that these urban stressors were associated with commonly reported declines in macroinvertebrate taxonomic richness and altered macroinvertebrate community composition. Chemical and thermal changes as a function of % developed watershed area also were unrelated to shifts in microbially mediated biogeochemical processes (C mineralization, denitrification potential, and substrate-induced respiration). A broad urbanization gradient sampled in this region suggests that stream ecosystem responses to watershed urbanization can follow diverse trajectories. [ABSTRACT FROM AUTHOR]

Since the 1960s, the Instituto del Mar del Perú (IMARPE) collected tens of thousands of in-situ temperature and salinity profiles in the Northern Humboldt Current System (NHCS). In this study, we blend this unique database with the historical in-situ profiles available from the World Ocean Database for the period 1960–2014 and apply a four-dimensional interpolation scheme to construct a seasonal climatology of temperature and salinity of the NHCS. The resulting interpolated temperature and salinity fields are gridded at a high spatial resolution (0.1° × 0.1° in latitude/longitude) between the surface and 1000 m depth, providing a detailed view of the hydrology and geostrophic circulation of this region. In particular, the mean distribution and characteristics of the main water-masses in the upper ocean of the NHCS are described, as well as their seasonal variations between austral summer and winter. The coastal upwelling region is well documented due to the increased data density along 3 highlighted cross-shore vertical sections off Paita (∼5°S), Chimbote (∼9°S) and San Juan (∼16.5°S). The large and long-term database also allowed us, through a composite analysis, to investigate the impact of the eastern Pacific El Niño and La Niña events on the NHCS hydrology. On average, during these periods, large temperature (±3–4 °C) and salinity (±0.1–0.2) anomalies are observed, impacting the water column of the coastal ocean off Peru down to 100–200 m depth. At 100 km from the coast, these anomalies are associated with a maximum deepening (shoaling, respectively) of the thermocline of 60 m (25 m) during composite El Niño (La Niña) events. At interdecadal scale, a similar approach reveals sea-surface temperature variations of ±0.5°C, associated with a deepening (shoaling) of the thermocline of 5–10 m during warm (cold) periods. [ABSTRACT FROM AUTHOR]

The growing economic interest in the exploitation of mineral resources on deep-ocean beds, including those in the vicinity of sensitive-rich habitats such as hydrothermal vents, raise a mounting concern about the damage that such actions might originate to these poorly-know ecosystems, which represent millions of years of evolution and adaptations to extreme environmental conditions. It has been suggested that mining may cause a major impact on vent ecosystems and other deep-sea areas. Yet, the scale and the nature of such impacts are unknown at present. Hence, building upon currently available scientific information it is crucial to develop new cost-effective technologies embedded into rigorous operating frameworks. The forward-thinking provided here will assist in the development of new technologies and tools to address the major challenges associated with deep sea-mining; technologies for in situ and ex situ observation and data acquisition, biogeochemical processes, hazard assessment of deep-sea mining to marine organisms and development of modeling tools in support of risk assessment scenarios. These technological developments are vital to validate a responsible and sustainable exploitation of the deep-sea mineral resources, based on the precautionary principle. [ABSTRACT FROM AUTHOR]

We report on the results of a regional scale biogeochemical sampling program conducted on the Yorke Peninsula, South Australia, utilising four locally occurring Eucalyptus species with mallee-form. Our purpose is to determine if there is an empirical relationship between Cu accumulation in the mallee leaves and elevated Cu in the underlying basement rocks – such that the mallee species might be a useful biogeochemical exploration tool in this area. The basement rocks of the Yorke Peninsula are prospective for iron oxide‑copper‑gold (IOCG) mineralisation but are mantled by Cambrian to Quaternary sedimentary rocks of variable thickness that inhibit traditional surface geochemical exploration techniques. There is no evidence to link Cu concentrations to dust contamination or fertiliser usage. Leaves of the four mallee species have comparable log normal population distributions of Cu, with a range between 1.6 ppm and 10 ppm. Higher concentrations of Cu (> 6 ppm) occur more commonly within 3 km of known Cu occurrences. These results suggest that all four mallee species have the ability to concentrate higher amounts of Cu in their leaves when the underlying/local geology also contains elevated Cu. The results suggest that biogeochemical sampling of multiple mallee species over large regions could be a useful exploration technique in covered areas of southern Australia where mallee species are widespread and densely populated. [ABSTRACT FROM AUTHOR]

Marine basins with oxygen-depleted deep waters provide a natural laboratory to investigate the consequences of anoxic and sulfidic (i.e. euxinic) conditions for biogeochemical processes in seawater and sediments. In this study, we investigate the dynamics of the key nutrient phosphorus (P) and associated elements such as manganese (Mn), iron (Fe) and calcium (Ca) in the euxinic deep basin of the Black Sea. By examining water column particles with scanning electron microscope – energy dispersive spectroscopy and synchrotron-based X-ray absorption spectroscopy, we show that Mn(III/IV)-P is the key form of particulate P in the redoxcline. Other forms of particulate P include organic P, Fe(III)-P, and inorganic polyphosphates. Most inorganic P particles that are formed in the redoxcline subsequently dissolve in the underlying sulfidic waters, with the exception of some particulate Fe(III)-P that accounts for <1% of all P settling onto the seafloor. Organic P is the dominant source of P to the sediment. Most of this organic P is degraded in the upper 2 cm of the sediment. Results of sequential extractions and a 33 P radiotracer experiment point towards the formation of labile Ca-P and P adsorbed onto calcium-carbonate and clays and a role of these phases as a major sink of P in the sediment. The total P burial efficiency in the sediments is ∼27%, which is relatively high when compared to estimates for sediments in other euxinic basins such as the Baltic Sea (<12%). We suggest that the abundant presence of calcium carbonate may contribute to the more efficient sequestration of P in Black Sea sediments. [ABSTRACT FROM AUTHOR]

Subsurface biogeochemistry and contaminant dynamics during the remediation of diesel-contamination by in-situ soil flushing were investigated at a site located in a coastal region. An in-situ sampler containing diesel-contaminated soils separated into two size fractions (<0.063- and <2-mm) was utilized in two monitoring wells: DH1 (located close to the injection and extraction wells for in-situ soil flushing) and DH2 (located beyond sheet piles placed to block the transport of leaked diesel). Total petroleum hydrocarbon (TPH) concentrations and biogeochemical properties were monitored both in soil and groundwater for six months. A shift occurred in the groundwater type from Ca-HCO 3 to Na-Cl due to seawater intrusion during intense pumping, while the concentrations of Ni, Cu, Co, V, Cr, and Se increased substantially following surfactant (TWEEN 80) injection. The in-situ sampler with fine particles was more sensitive to variations in conditions during the remedial soil flushing process. In both wells, soil TPH concentrations in the <0.063-mm fraction were much higher than those in the <2-mm fraction. Increases in soil TPH in DH1 were consistent with the expected outcomes following well pumping and surfactant injection used to enhance TPH extraction. However, the number of diesel-degrading microorganisms decreased after surfactant injection. 16S-rRNA gene-based analysis also showed that the community composition and diversity depended on both particle size and diesel contamination. The multidisciplinary approach to the contaminated site assessments showed that soil flushing with surfactant enhanced diesel extraction, but negatively impacted in-situ diesel biodegradation as well as groundwater quality. The results also suggest that the in-situ sampler can be an effective monitoring tool for subsurface biogeochemistry as well as contaminant dynamics. [ABSTRACT FROM AUTHOR]

While decreasing occurrence and duration of lake ice cover is well-documented, biogeochemical dynamics in frozen lakes remain poorly understood. Here, we interpret winter physical and biogeochemical time series from eutrophic Missisquoi Bay (MB) and hyper-eutrophic Shelburne Pond (SP) to describe variable drivers of under ice biogeochemistry in systems of fundamentally different lake-watershed physical configurations (lake area, lake : watershed area). The continuous cold of the 2015 winter drove the MB sediment-water interface to the most severe and persistent suboxic state ever documented at this site, promoting the depletion of redox-sensitive phases in sediments, and an expanding zone of bottom water enriched in reactive species of Mn, Fe, and P. In this context, lake sediment and water column inventories of reactive chemical species were sensitive to the severity and persistence of subfreezing temperatures. During thaws, event provenance and severity impact lake thermal structure and mixing, water column enrichment in P and Fe, and thaw capability to suppress redox front position and internal chemical loading. Nearly identical winter weather manifest differently in nearby SP, where the small surface and watershed areas promoted a warmer, less stratified water column and active phytoplankton populations, impacting biogeochemical dynamics. In SP, Fe and P behavior under ice were decoupled due to active biological cycling, and thaw impacts were different in distribution and composition due to SP's physical structure and related antecedent conditions. We find that under ice biogeochemistry is highly dynamic in both time and space and sensitive to a variety of drivers impacted by climate change. [ABSTRACT FROM AUTHOR]

The effect of weathering on changes of physical and mechanical properties of rocks is a prime concern in the perspectives of geology and engineering. These properties have been studied mostly on weathered igneous and sedimentary rocks under humid climates. Studies on weathering of metamorphic rocks, especially under a tropical climate, are rare. This study evaluates change of physical, mechanical, chemical, and mineralogical properties of metamorphic rocks that weather under tropical climatic conditions. Samanalawewa hydropower project area was selected for this study, because rapid weathering of a metamorphic rock (sillimanite garnet gneiss) was observed in the project site. Fresh rocks that are subjected to weathering have reached to completely weathered condition in a time span of less than 25 years in this area. Visually assessed weathering grades were physically and mechanically evaluated using bulk density, equotip hardness, porosity, specific gravity, point load strength, and slake durability tests. Mechanical properties, especially point load strength, change rapidly at the onset of weathering, while chemical properties show significant changes at later stages of weathering. Mineralogical changes such as appearance of secondary minerals are at the latter part of weathering. Physical properties gradually change during weathering. The observed changes in physical, mechanical and chemical properties indicate that their variations during weathering are independent of lithology and climatic conditions. [ABSTRACT FROM AUTHOR]

Despite our instinctive understanding of the importance of "identity," archaeologists and bioarchaeologists continue to struggle to rigorously investigate this complex phenomenon. Here, we present a contextualized multiscalar bioarchaeological approach to studying identities in the past—individual and group, mutable and immutable—through the mortuary record. We argue that, while many scholars have moved beyond the single-focus study, archaeological individuals themselves are still neglected. A contextualized bioarchaeological approach brings together a variety of methods to investigate aspects of individual and group identities, provides a means of accessing biological facets of identity, and allows for more nuanced understanding of the complexities of social identities. We illustrate the utility of our model with a case study using archaeological, bioarchaeological, and biogeochemical data from northern Chile, stressing both the fixed and the dynamic aspects of different identities. We focus on the tumultuous transition between the Middle Horizon (AD 500–1100) and Late Intermediate Period (AD 1100–1400) in northern Chile's San Pedro de Atacama oases and the neighboring upper Loa River Valley. Our research demonstrates a shift toward homogenizing representations of social identities as well as biological aspects of identities as societies began reformulating their social groups following the end of the complex and cosmopolitan Middle Horizon. [ABSTRACT FROM AUTHOR]

Although important for riverine solute and nutrient fluxes, the connections between biogeochemical processes and subsurface hydrology remain poorly characterized. We investigate these couplings in the East River, CO, a high-elevation shale-dominated catchment in the Rocky Mountains, using concentration-discharge (C-Q) relationships for major cations, anions, and organic carbon. Dissolved organic carbon (DOC) displays a positive C-Q relationship with clockwise hysteresis, indicating mobilization and depletion of DOC in the upper soil horizons and emphasizing the importance of shallow flow paths during snowmelt. Cation and anion concentrations demonstrate that carbonate weathering, which dominates solute fluxes, is promoted by both sulfuric acid derived from pyrite oxidation in the shale bedrock and carbonic acid derived from subsurface respiration. Sulfuric acid weathering dominates during base flow conditions when waters infiltrate below the inferred pyrite oxidation front, whereas carbonic acid weathering plays a dominant role during snowmelt as a result of shallow flow paths. Differential C-Q relationships between solutes suggest that infiltrating waters approach calcite saturation before reaching the pyrite oxidation front, after which sulfuric acid reduces carbonate alkalinity. This reduction in alkalinity results in CO2 outgassing when waters equilibrate to surface conditions, and reduces the riverine export of carbon and alkalinity by roughly 33% annually. Future changes in snowmelt dynamics that control the balance of carbonic and sulfuric acid weathering may substantially alter carbon cycling in the East River. Ultimately, we demonstrate that differential C-Q relationships between major solutes can provide unique insights into the complex subsurface flow and biogeochemical dynamics that operate at catchment scales. [ABSTRACT FROM AUTHOR]

Models test our understanding of processes and can reach beyond the spatial and temporal scales of measurements. Multi-component Reactive Transport Models (RTMs), initially developed more than three decades ago, have been used extensively to explore the interactions of geothermal, hydrologic, geochemical, and geobiological processes in subsurface systems. Driven by extensive data sets now available from intensive measurement efforts, there is a pressing need to couple RTMs with other community models to explore non-linear interactions among the atmosphere, hydrosphere, biosphere, and geosphere. Here we briefly review the history of RTM development, summarize the current state of RTM approaches, and identify new research directions, opportunities, and infrastructure needs to broaden the use of RTMs. In particular, we envision the expanded use of RTMs in advancing process understanding in the Critical Zone, the veneer of the Earth that extends from the top of vegetation to the bottom of groundwater. We argue that, although parsimonious models are essential at larger scales, process-based models offer tools to explore the highly nonlinear coupling that characterizes natural systems. We present seven testable hypotheses that emphasize the unique capabilities of process-based RTMs for (1) elucidating chemical weathering and its physical and biogeochemical drivers; (2) understanding the interactions among roots, micro-organisms, carbon, water, and minerals in the rhizosphere; (3) assessing the effects of heterogeneity across spatial and temporal scales; and (4) integrating the vast quantity of novel data, including “omics” data (genomics, transcriptomics, proteomics, metabolomics), elemental concentration and speciation data, and isotope data into our understanding of complex earth surface systems. With strong support from data-driven sciences, we are now in an exciting era where integration of RTM framework into other community models will facilitate process understanding across disciplines and across scales. [ABSTRACT FROM AUTHOR]

Parameter estimation is an important part of numerical modeling and often required when a coupled physical–biogeochemical ocean model is first deployed. However, 3-dimensional ocean model simulations are computationally expensive and models typically contain upwards of 10 parameters suitable for estimation. Hence, manual parameter tuning can be lengthy and cumbersome. Here, we present four easy to implement and flexible parameter estimation techniques and apply them to two 3-dimensional biogeochemical models of different complexities. Based on a Monte Carlo experiment, we first develop a cost function measuring the model-observation misfit based on multiple data types. The parameter estimation techniques are then applied and yield a substantial cost reduction over ∼ 100 simulations. Based on the outcome of multiple replicate experiments, they perform on average better than random, uninformed parameter search but performance declines when more than 40 parameters are estimated together. Our results emphasize the complex cost function structure for biogeochemical parameters and highlight dependencies between different parameters as well as different cost function formulations. [ABSTRACT FROM AUTHOR]

The ecohydrological impact of tree-canopy removal on moss and peat, which provide a principal carbon store, is just starting to be understood. Different mosses have contrasting contributions to carbon and water fluxes (e.g., Sphagnum fuscum, Pleurozium schreberi) and are strongly influenced by tree-canopy cover. Changes in tree-canopy cover may therefore lead to long-term shifts in species composition and associated ecohydrological function. However, the medium-term response to such disturbance, the associated lag in this transition to a new ecohydrological and biogeochemical regime, is not understood in detail. We investigate this medium-term (4 years) ecohydrological, biogeochemical, and species compositional response to tree-canopy removal using a randomized plot design within a northern peatland. This is the only study to test for the influence of increased light alone. We demonstrate that changes in treatment plots 4 years after tree-canopy removal were not significant. Notably, P. schreberi and S. fuscum remained within their respective plots post treatment, and there was no significant difference in plot resistance to evapotranspiration or carbon exchange. Results show that tree-canopy removal alone has little impact on bryophyte ecohydrology in the short or medium-term. This resistance to disturbance contrasts strongly with short-term changes observed within mineral soils, suggesting that concurrent shifts in the large scale hydrology induced within such disturbances are necessary to cause rapid ecohydrological transitions. Understanding this lagged response is critical to determine the strength of medium to long-term negative ecohydrological feedbacks within peatlands in addition to carbon and water fluxes on a decadal timescale in response to disturbance. [ABSTRACT FROM AUTHOR]

The Yellowknife City Gold Project (YCGP) is a promising Au district located in proximity to the city of Yellowknife, Northwest Territories, Canada. Positive results of a short biogeochemical survey in 2015 over the Crestaurum and Barney shears (Part 1) resulted in a broad survey over the early and advanced Au targets across the YCGP (Part 2). This survey uses a systematic two-phase statistical approach, including process discovery and process validation, to evaluate the multi-element biogeochemical dataset and identify the geochemical process controlling elemental occurrence and distribution in black spruce needles. To achieve these objectives, 2788 black spruce needle samples were collected across the Northbelt and Eastbelt of the YCGP and analyzed by ICP-MS using a multi-element determinations package for unashed vegetation. Following that, a biogeochemical dataset including Au, As, Ag, As, Bi, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Mo, Ni, P, Pb, S, Sb, Se, Tl, and Zn were prepared and analyzed using univariate and multivariate statistical analyses, including principal component analysis (PCA) and inverse distance weighted (IDW) interpolation method. The univariate statistical analysis showed that the average Au value in the black spruce needle is higher than the background level in all targets. Contiguous anomalous Au values were identified in needle samples collected proximal to the Ptarmigan & Tom mines (∼10 ppb) and Ryan Lake target (3.8 ppb). According to the robust RQ mode-PCA, PC1 and PC2 control the distribution pattern of elements in black spruce needles. PC1 includes two sets of elements indicating geochemical/mineralization factor (Au, As, Sb, Fe, Pb, and Mo) and physiological factor (Cu, Ca, Zn, K, S, P, and Mg). On the other hand, PC2 differentiates these two factors with more emphasis on the influence of the geochemical/mineralization factor. The IDW interpolation method indicates zones of Au enrichments at the YCGP are associated with different sets of pathfinder elements based on the bedrock composition and mineralization style. According to the IDW, elevated Au values associated with shear zones hosted within mafic/ultramafic bodies are accompanied by As, Sb, Pb, and Cu, while those located proximal to late felsic bodies are accompanied by Ag, As, Se, Hg, and Tl. Zones of Au enrichment located along the faulted contacts between the felsic-intermediate metavolcanics and sulphide metasediments are accompanied by Bi, Se, Hg, and Zn. The results of this study attest to the robustness of multivariate statistical analysis in detecting zones of Au enrichment using biogeochemical exploration. • Biogeochemical Prospecting for Gold. • Robust Statistical Analysis. • The Yellowknife City Gold Project (YCGP). • Principal component analysis (PCA). • Inverse distance weighted (IDW) interpolation. • Black spruce needles. • Gold pathfinder elements. [ABSTRACT FROM AUTHOR]

Although there are many studies on biomineralization processes, most of them focus on the role of prokaryotes. As fungi play an important role in different geological and biogeochemical processes, it was considered of interest to evaluate their role in a natural extreme acidic environment, Río Tinto, which has a high level of fungal diversity and a high concentration of metals. In this work we report, for the first time, the generation of iron oxyhydroxide minerals by the fungal community in a specific location of the Tinto basin. Using Transmission Electron Microscopy (TEM) and High Angle Angular Dark Field coupled with Scanning Transmission Electron Microscopy (HAADF-STEM) and Energy-Dispersive X-ray Spectroscopy (EDX), we observed fungal structures involved in the formation of iron oxyhydroxide minerals in mineralized sediment samples from the Río Tinto basin. Although Río Tinto waters are supersaturated in these minerals, they do not precipitate due to their slow precipitation kinetics. The presence of fungi, which simply provide charged surfaces for metal binding, favors the precipitation of Fe oxyhydroxides by overcoming these kinetic barriers. These results prove that the fungal community of Río Tinto participates very actively in the geochemical processes that take place there. [ABSTRACT FROM AUTHOR]

The article offers information on the Ninth International Biogeochemical School session titled "Biogeochemistry of Technogenesis and Modern Problems of Geochemical Ecology" was held in Russian Academy of Sciences (IVEP) in Barnaul, Russia, from August 24-28, 2015. It informs that event discussed a report on biogeochemical evolution of biospheric taxons, a lecture on biogeochemistry of Altai-Sayan Mountain Land and lecture on biogeochemistry of living matter.

The HYCOM-NORWECOM (HYbrid Coordinate Ocean Model-NORWegian ECOlogical Model) modeling system is used both for basic research and as a part of the forecasting system for the Arctic Marine Forecasting Centre through the MyOcean project. Here we present a revised version of this model. The present model, as well as the sensitivity simulations leading up to this version, have been compared to a data set of in situ measurements of nutrient and chlorophyll from the Norwegian Sea and the Atlantic sector of the Arctic Ocean. The model revisions having the most impact included adding diatoms to the diet of microzooplankton, increasing microzooplankton grazing rate and decreasing the silicate-to-nitrate ratio in diatoms. Model runs are performed both with a coarse- ( ~ 50 km) and higher-resolution (~ 15 km) model configuration, both covering the North Atlantic and Arctic oceans. While the new model formulation improves the results in both the coarse- and high-resolution model, the nutrient bias is smaller in the highresolution model, probably as a result of the better resolution of the main processes and improved circulation. The final revised version delivers satisfactory results for all three nutrients as well as improved results for chlorophyll in terms of the annual cycle amplitude. However, for chlorophyll the correlation with in situ data remains relatively low. Besides the large uncertainties associated with observational data this is possibly caused by the fact that constant CVN- and ChlVN ratios are implemented in the model. [ABSTRACT FROM AUTHOR]

We discuss a recent theoretical approach combining catchment-scale flow and transport processes into a unified framework. The approach is designed to characterize the hydrochemistry of hydrologic systems and to meet the challenges posed by empirical evidence. StorAge Selection functions (SAS) are defined to represent the way catchment storage supplies the outflows with water of different ages, thus regulating the chemical composition of out-fluxes. Biogeochemical processes are also reflected in the evolving residence time distribution and thus in age-selection. Here we make the case for the routine use of SAS functions and look forward to areas where further research is needed. [ABSTRACT FROM AUTHOR]

t In geochemical logging, the standard capture gamma-ray spectra of Al, Mg, and K have no distinct characteristic energy peaks. This feature easily influences the spectral bands of characteristic peaks of other elements and thus affects the accuracy of calculating their concentrations. To study this influence, we constructed a model formation containing Al, Mg, and K, and employed the Monte Carlo N Particle Transport Code (MCNP) program to simulate their capture spectra. The results indicate that the calculated dry weights of Si are almost free from the influences of Mg, K, and Al. The ones of Ca and Fe are influenced, but only to a minor extent. The dry weight of S is concurrently influenced. Specifically, the K concentration causes S concentration to deviate significantly from its real concentration. By correcting for such influences, we can obtain relatively accurate values. Data processing for a real well validates the finding that Mg, Al, and K in the formation influence the precision of calculation of other elements and also testifies to the effectiveness of the correction method. [ABSTRACT FROM AUTHOR]

Biogeochemical ocean circulation models used to investigate the role of plankton ecosystems in global change rely on adjustable parameters to capture the dominant biogeochemical dynamics of a complex biological system. In principle, optimal parameter values can be estimated by fitting models to observational data, including satellite ocean colour products such as chlorophyll that achieve good spatial and temporal coverage of the surface ocean. However, comprehensive parametric analyses require large ensemble experiments that are computationally infeasible with global 3-D simulations. Site-based simulations provide an efficient alternative but can only be used to make reliable inferences about global model performance if robust quantitative descriptions of their relationships with the corresponding 3-D simulations can be established. The feasibility of establishing such a relationship is investigated for an intermediate complexity biogeochemistry model (MEDUSA) coupled with a widely used global ocean model (NEMO). A site-based mechanistic emulator is constructed for surface chlorophyll output from this target model as a function of model parameters. The emulator comprises an array of 1-D simulators and a statistical quantification of the uncertainty in their predictions. The unknown parameterdependent biogeochemical environment, in terms of initial tracer concentrations and lateral flux information required by the simulators, is a significant source of uncertainty. It is approximated by a mean environment derived from a small ensemble of 3-D simulations representing variability of the target model behaviour over the parameter space of interest. The performance of two alternative uncertainty quantification schemes is examined: a direct method based on comparisons between simulator output and a sample of known target model "truths" and an indirect method that is only partially reliant on knowledge of the target model output. In general, chlorophyll records at a representative array of oceanic sites are well reproduced. The use of lateral flux information reduces the 1-D simulator error considerably, consistent with a major influence of advection at some sites. Emulator robustness is assessed by comparing actual error distributions with those predicted. With the direct uncertainty quantification scheme, the emulator is reasonably robust over all sites. The indirect uncertainty quantification scheme is less reliable at some sites but scope for improving its performance is identified. The results demonstrate the strong potential of the emulation approach to improve the effectiveness of site-based methods. This represents important progress towards establishing a robust site-based capability that will allow comprehensive parametric analyses to be achieved for improving global models and quantifying uncertainty in their predictions. [ABSTRACT FROM AUTHOR]

Background: Bacteria of the genus Sulfobacillus are found worldwide as members of microbial communities that accelerate sulfide mineral dissolution in acid mine drainage environments (AMD), acid-rock drainage environments (ARD), as well as in industrial bioleaching operations. Despite their frequent identification in these environments, their role in biogeochemical cycling is poorly understood. Results: Here we report draft genomes of five species of the Sulfobacillus genus (AMDSBA1-5) reconstructed by cultivation-independent sequencing of biofilms sampled from the Richmond Mine (Iron Mountain, CA). Three of these species (AMDSBA2, AMDSBA3, and AMDSBA4) have no cultured representatives while AMDSBA1 is a strain of S. benefaciens, and AMDSBA5 a strain of S. thermosulfidooxidans. We analyzed the diversity of energy conservation and central carbon metabolisms for these genomes and previously published Sulfobacillus genomes. Pathways of sulfur oxidation vary considerably across the genus, including the number and type of subunits of putative heterodisulfide reductase complexes likely involved in sulfur oxidation. The number and type of nickel-iron hydrogenase proteins varied across the genus, as does the presence of different central carbon pathways. Only the AMDSBA3 genome encodes a dissimilatory nitrate reducatase and only the AMDSBA5 and S. thermosulfidooxidans genomes encode assimilatory nitrate reductases. Within the genus, AMDSBA4 is unusual in that its electron transport chain includes a cytochrome bc type complex, a unique cytochrome c oxidase, and two distinct succinate dehydrogenase complexes. Conclusions: Overall, the results significantly expand our understanding of carbon, sulfur, nitrogen, and hydrogen metabolism within the Sulfobacillus genus. [ABSTRACT FROM AUTHOR]

Small-scale geochemical gradients are a key feature of aquifer contaminant plumes, highlighting the need for functional and structural profiling of corresponding microbial communities on a similar scale. The purpose of this study was to characterize the microbial functional and structural diversity with depth across representative redox zones of a hydrocarbon plume and an adjacent wetland, at the Bemidji Oil Spill site. A combination of quantitative PCR, denaturing gradient gel electrophoresis, and pyrosequencing were applied to vertically sampled sediment cores. Levels of the methanogenic marker gene, methyl coenzyme-M reductase A ( mcrA), increased with depth near the oil body center, but were variable with depth further downgradient. Benzoate degradation N ( bzdN) hydrocarbon-degradation gene, common to facultatively anaerobic Azoarcus spp., was found at all locations, but was highest near the oil body center. Microbial community structural differences were observed across sediment cores, and bacterial classes containing known hydrocarbon degraders were found to be low in relative abundance. Depth-resolved functional and structural profiling revealed the strongest gradients in the iron-reducing zone, displaying the greatest variability with depth. This study provides important insight into biogeochemical characteristics in different regions of contaminant plumes, which will aid in improving models of contaminant fate and natural attenuation rates. [ABSTRACT FROM AUTHOR]

Rivers are an important source of mercury (Hg) to marine ecosystems. Based on an analysis of compiled observations, we estimate global present-day Hg discharges from rivers to ocean margins are 27 ± 13 Mmol a-1 (5500 ± 2700 Mg a-1), of which 28% reaches the open ocean and the rest is deposited to ocean margin sediments. Globally, the source of Hg to the open ocean from rivers amounts to 30% of atmospheric inputs. This is larger than previously estimated due to accounting for elevated concentrations in Asian rivers and variability in offshore transport across different types of estuaries. Riverine inputs of Hg to the North Atlantic have decreased several-fold since the 1970s while inputs to the North Pacific have increased. These trends have large effects on Hg concentrations at ocean margins but are too small in the open ocean to explain observed declines of seawater concentrations in the North Atlantic or increases in the North Pacific. Burial of Hg in ocean margin sediments represents a major sink in the global Hg biogeochemical cycle that has not been previously considered. We find that including this sink in a fully coupled global biogeochemical box model helps to balance the large anthropogenic release of Hg from commercial products recently added to global inventories. It also implies that legacy anthropogenic Hg can be removed from active environmental cycling on a faster time scale (centuries instead of millennia). Natural environmental Hg levels are lower than previously estimated, implying a relatively larger impact from human activity. [ABSTRACT FROM AUTHOR]

We have previously defined in situ biogeochemical transformation as the biogenic formation of reactive minerals that are capable of abiotically degrading chlorinated solvents such as trichloroethene without accumulation of degradation products such as vinyl chloride (AFCEE et al. ). This process has been implemented in biowalls used to intercept contaminated groundwater. Abiotic patterns of contaminant degradation were observed at Altus Air Force Base ( AFB) and in an associated column study, but not at other sites including Dover AFB. These abiotic patterns were associated with biogenic formation of reactive iron sulfide minerals. Iron sulfides in the form of small individual grains, coatings on magnetite, and sulfur-deficient pyrite framboids were observed in samples collected from the Altus AFB biowalls and one of the EPA columns. Larger iron sulfide grains coated with oxide layers were observed in samples collected from Dover AFB. Altus AFB and the EPA column differed from Dover AFB in that groundwater flow at Dover AFB was relatively slow and potentially reversing. High volumetric sulfate consumption rates, an abiotic pattern of trichloroethene ( TCE) degradation, and the formation of small, high surface area iron sulfide particles were associated with relatively high rates of TCE removal via an abiotic pattern. Geochemical modeling demonstrated that iron monosulfides such as mackinawite were near saturation, and iron disulfides such as pyrite were supersaturated at all sites. This environmental condition can be supportive of nucleation of small particles rather than crystal growth leading to larger particles. When nucleation is dominant, small, high surface area, and reactive particles result. When crystal growth dominates the crystals are larger and have lower specific surface area and reactivity. These results taken together suggest that creation of a dynamic environment can promote biogeochemical transformation based on generation of reactive iron sulfides. [ABSTRACT FROM AUTHOR]

The article offers information related to a study on the geochemical and geochronological analysis of granitoids, a type of rock, in Yenisei Ridge in Russia. Topics discussed include rocks of the Garevka metamorphic complex (GMC), intrusive massifs located within the Yenisei regional suture zone (YRSZ) and Chernorechenskii massif (CM) and geochemical specifics and dating of Neoproterozoic granitoid complexes.

A US National Science Foundation-funded workshop occurred 17-19 May 2013 at the University of Oklahoma to stimulate research using continental scientific drilling to explore earth's sedimentary, paleobiological and biogeochemical record. Participants submitted 3-page "pre-proposals" to highlight projects that envisioned using drill-core studies to address scientific issues in paleobiology, paleoclimatology, stratigraphy and biogeochemistry, and to identify locations where key questions can best be addressed. The workshop was also intended to encourage US scientists to take advantage of the exceptional capacity of unweathered, continuous core records to answer important questions in the history of earth's sedimentary, biogeochemical and paleobiologic systems. Introductory talks on drilling and coring methods, plus best practices in core handling and curation, opened the workshop to enable all to understand the opportunities and challenges presented by scientific drilling. Participants worked in thematic breakout sessions to consider questions to be addressed using drill cores related to glacial-interglacial and icehouse-greenhouse transitions, records of evolutionary events and extinctions, records of major biogeochemical events in the oceans, reorganization of earth's atmosphere, Lagerstätte and exceptional fossil biota, records of vegetation-landscape change, and special sampling requirements, contamination, and coring tool concerns for paleobiology, geochemistry, geochronology, and stratigraphy-sedimentology studies. Closing discussions at the workshop focused on the role drilling can play in studying overarching science questions about the evolution of the earth system. The key theme, holding the most impact in terms of societal relevance, is understanding how climate transitions have driven biotic change, and the role of pristine, stratigraphically continuous cores in advancing our understanding of this linkage. Scientific drilling, and particularly drilling applied to continental targets, provides unique opportunities to obtain continuous and unaltered material for increasingly sophisticated analyses, tapping the entire geologic record (extending through the Archean), and probing the full dynamic range of climate change and its impact on biotic history. [ABSTRACT FROM AUTHOR]

Using biogeochemical techniques based on 13C/12C and 18O/16O relationships in dental enamel, it was inferred if the diets of four Columbian mammoths (Mammuthus columbi) from Laguna de las Cruces (Salinas, San Luis Potosí, México) changed or were similar in time as a response to temperature variations. The results show that the diet of individual DP-1975 kept unchanged, whereas for mammoths DP-1976 and DP-1978 there was a small tendency for eating more C3 plants than C4 plants, possibly due to decreased temperatures, as shown by δ18O values. However, the isotopic carbon values of mammoth DP-1979 show that the specimen was first a mixed feeder C3/C4 and later ate mostly C4 plants, probably due to an increase in the temperature. Furthermore comparisons made between δ13C and δ18O values at the population level show that the two young mammoths, with 18 and 20 years old, are different from the two adults, which seem to be 43 and 47 years old respectively. Such differences may be due to different feed behaviors among young and adult, although it could also indicate that the individuals came from different areas. [ABSTRACT FROM AUTHOR]

Research experience for undergraduate (REU) programs are designed to recruit students to science and engineering research careers by allowing the students to conduct research with faculty mentors. International research experiences can enhance the research experience by allowing the student to conduct research in a unique environment and also provide the student with a more global perspective. This paper describes the outcomes of an international REU program in which students quantify hydrological and biogeochemical fluxes in a tropical montane forest in central Costa Rica. Having the students at a central research station location and focusing their research on a common research problem is an important aspect of an international REU program, to avoid a feeling of isolation and to ensure that the students remain safe in their research and during their free time. However, this shared experience can highlight differences among the faculty mentors and make the students evaluate their individual experience more critically. To better understand the relationship between the REU student and their faculty mentor(s), we conducted pre- and post-trip focus groups to understand the students' experience in the REU and the manner in which the faculty mentor can affect that experience and the desire to continue in research. Results of the pre-trip focus group suggest that the undergraduate students are most concerned about their projects and give little to no thought about the faculty mentor with whom they will be completing their research. Post-trip results from 2011 and 2012 suggest that mentors had a much greater impact on the experience than expected. Many students said that their future research/graduate school plans were affected by their REU mentor relationship, and that while they might not have considered the importance of faculty mentors before the research experience, they now recognize the mentor as a crucial aspect of a research project. Using a classification system commonly used in management research, the mentoring styles were classified with management classification styles as autocratic, democratic, or laissez-faire. The overall results suggest that the student-to-mentor relationship created through these authentic experiences is one of the most important aspects of REU programs, and that the mentoring style not only determines the research productivity of the student, but also appears to influence the decision of that student to conduct research in the future and/or attend graduate school. The mentoring style also affects research productivity and allows students to identify the characteristics they perceive as important to success in a graduate program. While this paper focuses on a single REU program, the results provide baseline data to examine the role of the faculty mentor across other REU programs and in decisions about graduate research by both the student and the faculty. Mentoring styles and student expectations of their mentors should be taken into consideration when developing a research experience and pairing mentors with prospective students. [ABSTRACT FROM AUTHOR]

Net community production (NCP) and carbon to nutrient uptake ratios were studied during a large-scale mesocosm experiment on ocean acidification in Kongsfjorden, western Svalbard, during June--July 2010. Nutrient depleted fjord water with natural plankton assemblages, enclosed in nine mesocosms of ~50m³ in volume, was exposed to pCO2 levels ranging initially from 185 to 1420 μatm. NCP estimations are the cumulative change in dissolved inorganic carbon concentrations after accounting for gas exchange and total alkalinity variations. Stoichiometric coupling between inorganic carbon and nutrient net uptake is shown as a ratio of NCP to a cumulative change in inorganic nutrients. Phytoplankton growth was stimulated by nutrient addition half way through the experiment and three distinct peaks in chlorophyll a concentration were observed during the experiment. Accordingly, the experiment was divided in three phases. Cumulative NCP was similar in all mesocosms over the duration of the experiment. However, in phases I and II, NCP was higher and in phase III lower at elevated pCO2. Due to relatively low inorganic nutrient concentration in phase I, C :N and C : P uptake ratios were calculated only for the period after nutrient addition (phase II and phase III). For the total post-nutrient period (phase II+phase III) ratios were close to Redfield, however they were lower in of NCP, C :N and C : P uptake ratios in different phases reflects the effect of increasing CO2 on phytoplankton community composition and succession. The phytoplankton community was composed predominantly of haptophytes in phase I, prasinophytes, dinoflagellates, and cryptophytes in phase II, and haptophytes, prasinophytes, dinoflagellates and chlorophytes in phase III (Schulz et al., 2013). Increasing ambient inorganic carbon concentrations have also been shown to promote primary production and carbon assimilation. For this study, it is clear that the pelagic ecosystem response to increasing CO2 is more complex than that represented in previous work, e.g. Bellerby et al. (2008). Carbon and nutrient uptake representation in models should, where possible, be more focused on individual plankton functional types as applying a single stoichiometry to a biogeochemical model with regard to the effect of increasing pCO2 may not always be optimal. The phase variability in NCP and stoichiometry may be better understood if CO2 sensitivities of the plankton's functional type biogeochemical uptake kinetics and trophic interactions are better constrained. [ABSTRACT FROM AUTHOR]

Abstract: Tropical rain forests are known for their high biological diversity, but the effects of plant diversity on important ecosystem processes in this biome remain unclear. Interspecies differences in both the demand for nutrients and in foliar and litter nutrient concentrations could drive variations in both the pool sizes and fluxes of important belowground resources, yet our understanding of the effects and importance of aboveground heterogeneity on belowground biogeochemistry is poor, especially in the species-rich forests of the wet tropics. To investigate the effects of individual tree species on belowground biogeochemical processes, we used both field and laboratory studies to examine how carbon (C), nitrogen (N), and phosphorus (P) cycles vary under nine different canopy tree species – including three legume and six non-legume species – that vary in foliar nutrient concentrations in a wet tropical forest in southwestern Costa Rica. We found significant differences in belowground C, N and P cycling under different canopy tree species: total C, N and P pools in standing litter varied by species, as did total soil and microbial C and N pools. Rates of soil extracellular acid phosphatase activity also varied significantly among species and functional groups, with higher rates of phosphatase activity under legumes. In addition, across all tree species, phosphatase activity was significantly positively correlated with litter N/P ratios, suggesting a tight coupling between relative N and P inputs and resource allocation to P acquisition. Overall, our results suggest the importance of aboveground plant community composition in promoting belowground biogeochemical heterogeneity at relatively small spatial scales. [Copyright &y& Elsevier]

The Mediterranean is a semi-enclosed sea characterized by high salinities, temperatures and densities. The net evaporation exceeds the precipitation, driving an antiestuarine circulation through the Strait of Gibraltar, contributing to very low nutrient concentrations. The Mediterranean Sea has an active overturning circulation, one shallow cell that communicates directly with the Atlantic Ocean, and two deep overturning cells, one in each of the two main basins. It is surrounded by populated areas and is thus sensitive to anthropogenic forcing. Several dramatic changes in the oceanographic and biogeochemical conditions have been observed during the past several decades, 10 emphasising the need to better monitor and understand the changing conditions and their drivers. During 2011 three oceanographic cruises were conducted in a coordinated fashion in order to produce base-line data of important physical and biogeochemical parameters that can be compared to historic data and be used as reference for future observational campaigns. In this article we provide information on the Mediterranean Sea oceanographic situation, and present a short review that will serve as background information for the special issue in Ocean Science on "Physical, chemical and biological oceanography of the Mediterranean Sea". An important contribution of this article is the set of figures showing the large-scale distributions of physical and chemical properties along the full length of the Mediterranean Sea. [ABSTRACT FROM AUTHOR]

Impacts of climate change on air-sea CO2 exchange are strongly region dependent, particularly in the Southern Ocean. Yet, in the Southern Ocean the role of water masses in the uptake of anthropogenic carbon is still debated. Here, a methodology is applied that tracks the carbon flux of each Southern Ocean water mass in response to climate change. A global marine biogeochemical model was coupled to a climate model, making 140-yr Coupled Model Intercomparison Project phase 5 (CMIP5)-type simulations, where atmospheric CO2 increased by 1% yr−1 to 4 times the preindustrial concentration (4 × CO2). Impacts of atmospheric CO2 (carbon-induced sensitivity) and climate change (climate-induced sensitivity) on the water mass carbon fluxes have been isolated performing two sensitivity simulations. In the first simulation, the atmospheric CO2 influences solely the marine carbon cycle, while in the second simulation, it influences both the marine carbon cycle and earth's climate. At 4 × CO2, the cumulative carbon uptake by the Southern Ocean reaches 278 PgC, 53% of which is taken up by modal and intermediate water masses. The carbon-induced and climate-induced sensitivities vary significantly between the water masses. The carbon-induced sensitivities enhance the carbon uptake of the water masses, particularly for the denser classes. But, enhancement strongly depends on the water mass structure. The climate-induced sensitivities either strengthen or weaken the carbon uptake and are influenced by local processes through changes in CO2 solubility and stratification, and by large-scale changes in outcrop surface (OS) areas. Changes in OS areas account for 45% of the climate-induced reduction in the Southern Ocean carbon uptake and are a key factor in understanding the future carbon uptake of the Southern Ocean. [ABSTRACT FROM AUTHOR]

Abstract: The three-dimensional biogeochemical model ECOHAM was applied to the Northwest European Continental Shelf (NECS) (47° 41′ – 63° 53′ N, 15° 5′ W – 13° 55′ E) for the years 1970–2006. The development of annual carbon fluxes was analysed for the North Sea as the inner shelf region. We divided the North Sea into several regions, the northern North Sea, the southern North Sea, the German Bight and the Southern Bight for a more detailed analysis. To separate the effect of physical and biological processes a second simulation without biology was performed. The results of our method for calculating the biological pCO2 were in good agreement with the biological pCO2 calculated after the method of . While in the standard run the North Sea acted as sink for atmospheric CO2, in the run without biology the North Sea was a continuous source for atmospheric CO2. The main drivers of the air-sea flux variability were identified as being temperature, net ecosystem production and pH. The eutrophication due to high riverine nutrient inputs during the 1980s had no significant effect on the air-sea flux of CO2 because in contrast to net primary production, net ecosystem production did not respond to the period of higher phosphate input. The increase of sea surface temperature of 0.027 °C yr−1 over the simulation period and the pH decline of 0.002 yr−1 led to a decline of the uptake of atmospheric CO2 by the North Sea of about 30% in the last decade of the simulation period. A special feature occurred in the year 1996, where a cold sea surface temperature anomaly led to an additional (physical) uptake of atmospheric CO2 and corresponded with a low primary and net ecosystem production, which on the other hand led to less biologically induced uptake of CO2. Our results indicate an ongoing decline of the uptake capacity for atmospheric carbon dioxide of the North Sea for future scenarios. [Copyright &y& Elsevier]

Abstract: This study aimed at finding efficient hyperspectral indices for estimating three leaf biochemical parameters: chlorophyll content (CHL, μgcm−2), leaf water thickness (EWT, gcm−2), and leaf mass per area (LMA, gcm−2) in typical temperate deciduous forests. These parameters are required by most biogeochemical models that describe ecosystem functions. We have identified the most efficient hyperspectral indices (both the index types and the wavelength domains) based on both a simulated data set (produced with the calibrated leaf reflectance model PROSPECT) and with data sets (I, II, and III) from measurement of field-collected leaves. Results indicated that CHL, EWT, and LMA can be estimated with high precision using a two-waveband vegetation index (Double Deference index, DDn) for all parameters, with an overall root mean square error (RMSE) of 6.87μgcm−2 for CHL, 0.0011gcm−2 for EWT, and 0.0015gcm−2 for LMA. The best overall indices for temperate deciduous forests were DDn (715, 185) for CHL, DDn (1530, 525) for EWT, and DDn (1235, 25) for LMA, although these indices were not necessarily the best for every specific data set (especially for the simulated data set). Moreover, discrepancies were obvious when the identified indices were applied to different data sets. Even if the wavelengths of calibrated indices have been accurately determined through the simulated data set, the regressions between the indices and the biochemical parameters must be calibrated with field-based measurements. The indices identified in this study are applicable to various species (data set III), various phenological stages and locations (data set I), and various leaf anatomies (data set II) and may therefore be widely applicable for temperate deciduous forests and possibly for other plant communities. [Copyright &y& Elsevier]

Abstract: The Tl concentrations and chemical speciation were determined in the surface sediments of Bohai Bay to evaluate its biogeochemical characteristics. The total Tl concentrations were in the range of 0.506–0.770 μg/g and correlated significantly with clay and total organic carbon (TOC) contents, suggesting that the grain size and TOC were major factors controlling Tl distribution. The sequential extraction performed to indicate Tl speciation and availability in Bohai Bay sediments suggested that Tl occurred mainly in the residual fraction and Tl came mainly from natural input. In the non-residual fractions, Fe–Mn oxide and organic matter fractions accounted for the main portions, suggesting that the labile Tl adsorption was dominated by Fe–Mn oxides and organic matter. In addition, according to our estimate, about 2.7 t/yr and 0.16 t/yr of Tl reached Bohai Bay via rivers and atmosphere, respectively. [Copyright &y& Elsevier]

Uranium accumulation by a Pseudomonas strain was characterized in terms of kinetics, effect on cell viability and role of various regulatory factors (viz . pH, Co ions and metabolism). This strain was identified as Pseudomonas aeruginosa based on 16S rRNA gene and Fatty Acid Methyl Ester (FAME) analyses. The bacterium exhibited rapid, concentration and pH dependent, uranium accumulation with maximum loading of 275 mg uranium g dry wt. at pH 4.0. Survival studies during the period of uranium exposure indicated a viable but non growing state of the cells. Uranium accumulation remains largely insensitive to metabolic activity and presence of other co-ions except Fe. Transmission electron microscopy (TEM) confirmed the deposition of bioaccumulated uranium by live cells within the cell envelope region. Our findings suggest that the P. aeruginosa J007 has intrinsic uranium-removal and -resistance properties. Accumulated uranium is deposited within the cell envelope region providing a possible survival strategy to the bacterium. Our study contributed significantly to gain insight into bacterial interaction with uranium and will be useful in understanding the role of native microorganisms inhabiting in uranium contaminated sites in biogeochemical cycling of uranium and in bioremediation applications. [ABSTRACT FROM AUTHOR]

The article offers information on several issues related to the International Mine Water Association (IMWA). It states that several members have been appointed to the organization, including Craig Bartels, Christopher Berryman and Nia Blackwell. It also offers information regarding several events, including a conference titled "Frontiers in Environmental Geoscience," that is going to be held from June 21-23, 2011 in Wales, Great Britain, and a short course on "Process-oriented Biogeochemical Modelling in Aquifers" that will be held from August 22 to September 16, 2011, in Dresden, Germany.

No Abstract available. [ABSTRACT FROM AUTHOR]

Robust estimation of soil hydraulic parameters is essential for predicting soil water dynamics and related biogeochemical processes; however, uncertainties in estimated parameter values limit a model's ability for prediction and application. In this study, methods of global analysis (Latin hypercube sampling, LHS) and gradient-based optimization (PEST, parameter estimation software) were explored to calibrate soil hydraulic parameters in the Root Zone Water Quality Model (RZWQM2). Six methods of estimating Brooks-Corey parameters of the soil water retention curve and saturated hydraulic conductivity were evaluated to simulate daily soil water dynamics under fallow conditions in eastern Colorado. The calibrated soil hydraulic parameters showed similar trends with soil depth for the different estimation methods in RZWQM2 but resulted in large differences between simulated and observed soil water contents. The PEST optimization based on soil type values as initial estimates gave reasonable soil water responses but with some unrealistic soil hydraulic parameters and soil evaporation. Overall, errors in simulated soil water contents were reduced by using LHS to initialize and constrain the PEST parameter space, which also stabilized the cross-validation results. Calibration results using water content measurements at four depths (30, 60, 90, and 150 cm) were similar to results using 10 depths (30, 40, 50, 60, 70, 80, 90, 120, 150, and 170 cm). Calibrating soil hydraulic parameters remains challenging, but the combined calibration procedures (LHS + PEST) with cross-validation can reduce parameter uncertainties and improve model performance. [ABSTRACT FROM AUTHOR]

Semaphorins and their receptor plexins constitute a pleiotropic cell-signalling system that is used in a wide variety of biological processes, and both protein families have been implicated in numerous human diseases. The binding of soluble or membrane-anchored semaphorins to the membrane-distal region of the plexin ectodomain activates plexin's intrinsic GTPase-activating protein (GAP) at the cytoplasmic region, ultimately modulating cellular adhesion behaviour. However, the structural mechanism underlying the receptor activation remains largely unknown. Here we report the crystal structures of the semaphorin 6A (Sema6A) receptor-binding fragment and the plexin A2 (PlxnA2) ligand-binding fragment in both their pre-signalling (that is, before binding) and signalling (after complex formation) states. Before binding, the Sema6A ectodomain was in the expected 'face-to-face' homodimer arrangement, similar to that adopted by Sema3A and Sema4D, whereas PlxnA2 was in an unexpected 'head-on' homodimer arrangement. In contrast, the structure of the Sema6A-PlxnA2 signalling complex revealed a 2:2 heterotetramer in which the two PlxnA2 monomers dissociated from one another and docked onto the top face of the Sema6A homodimer using the same interface as the head-on homodimer, indicating that plexins undergo 'partner exchange'. Cell-based activity measurements using mutant ligands/receptors confirmed that the Sema6A face-to-face dimer arrangement is physiologically relevant and is maintained throughout signalling events. Thus, homodimer-to-heterodimer transitions of cell-surface plexin that result in a specific orientation of its molecular axis relative to the membrane may constitute the structural mechanism by which the ligand-binding 'signal' is transmitted to the cytoplasmic region, inducing GAP domain rearrangements and activation. [ABSTRACT FROM AUTHOR]

The article presents a study on the snowpack and soil frost changes at the Hubbard Brook Experimental Forest (HBEF) in New Hampshire, U.S. It used simultaneous heat and water (SHAW) specific model to stimulate soil freezing and thawing and field measurements of solar radiation and wind for model input. Results show implications of short frost-covered period for forest ecosystem processes such as tree phenology and growth, hydrological flowpaths in winter, and biogeochemical processes in soil.

The contribution of carbonate‐producing benthic organisms to the global marine carbon budget has been overlooked, the prevailing view being that calcium carbonate (CaCO3) is predominantly produced and exported by marine plankton in the “biological pump.” Here, we provide the first estimation of the global contribution of echinoderms to the marine inorganic and organic carbon cycle, based on organism‐level measurements from species of the five echinoderm classes. Echinoderms' global CaCO3 contribution amounts to ~0.861 Pg CaCO3/yr (0.102 Pg C/yr of inorganic carbon) as a production rate, and ~2.11 Pg CaCO3 (0.25 Pg C of inorganic carbon) as a standing stock from the shelves, slopes, and abyssal depths. Echinoderm inorganic carbon production (0.102 Pg C/yr) is less than the global pelagic production (0.4–1.8 Pg C/yr) and similar to the estimates for carbonate shelves globally (0.024–0.120 Pg C/yr). Echinoderm CaCO3 production per unit area is ~27.01 g CaCO3·m−2·yr−1 (3.24 g C·m−2·yr−1 as inorganic carbon) on a global scale for all areas, with a standing stock of ~63.34 g CaCO3/m2 (7.60 g C/m2 as inorganic carbon), and ~7.97 g C/m2 as organic carbon. The shelf production alone is 77.91 g CaCO3·m−2·yr−1 (9.35 g C·m−2·yr−1 as inorganic carbon) in contrast to 2.05 g CaCO3·m−2·yr−1 (0.24 g C·m−2·yr−1 as inorganic carbon) for the slope on a global scale. The biogeography of the CaCO3 standing stocks of echinoderms showed strong latitudinal variability. More than 80% of the global CaCO3 production from echinoderms occurs between 0 and 800 m, with the highest contribution attributed to the shelf and upper slope. We provide a global distribution of echinoderm populations in the context of global calcite saturation horizons, since undersaturated waters with respect to mineral phases are surfacing. This shallowing is a direct consequence of ocean acidification, and in some places it may reach the shelf and upper slope permanently, where the highest CaCO3 standing stocks from echinoderms originate. These organism‐level data contribute substantially to the assessment of global carbonate inventories, which at present are poorly estimated. Additionally, it is desirable to include these benthic compartments in coupled global biogeochemical models representing the “biological pump” and its feedbacks, since at present all efforts have focused on pelagic processes, dominated by coccolithophores. The omission of the benthic processes from modeling will only diminish the understanding of elemental fluxes at large scales and any future prediction of climate change scenarios. [ABSTRACT FROM AUTHOR]

Mixing dissolution is a widely accepted process of karstification on carbonate platforms, but regional differences in climate and geology indicate that a universal application of this model is insufficient to assess water–limestone interactions in more specific island settings. A two-phase study investigating δ13C, carbon concentration, and other geochemical parameters took place on San Salvador Island, The Bahamas, to better understand its hydrologic characteristics and identify local controls on dissolution. In the initial phase, Crescent Pond and adjacent Crescent Top Cave, both with conduit connections to one another and to open marine water, were monitored over 1.5 normal tidal cycles and found to have little geochemical variation. Contrasting geochemical compositions between these two sites and the ocean illustrates the complexity of subsurface hydrology, while lower pH and δ13CDIC values in the cave suggest the potential for bacterially mediated dissolution. The second phase included a more comprehensive geochemical survey of 12 of the island’s surface/subsurface water bodies, and found that water geochemistry was governed primarily by connectivity to the ocean and secondarily by topographic and vegetative settings. Geochemical relationships illustrated by regression analyses showed that biologic activity exerted additional controls over water geochemistry, with photosynthesis removing biotically respired CO2 and elevating organic carbon in surface waters, while biotically respired CO2 accumulates and supports dissolution in the subsurface. These data underscore the importance of including the role of biotic processes with climate and geologic settings when identifying dissolution mechanisms and using them to estimate modern and historical dissolution processes. [ABSTRACT FROM AUTHOR]