Changes In Physicochemical Conditions Research Articles

Thermodynamic study of the association and separation of copper and gold in the Shizishan ore field, Tongling, Anhui Province, China

The Shizishan ore field is the largest gold–copper ore field in the Tongling ore district of Anhui Province, China. Copper and gold deposits in the district are present as one-commodity deposits or as deposits with both commodities. Copper and gold mineralization are either cogenetic or are temporally and spatially distinct. We present the results of systematic geochemical analysis of fluid inclusions from typical Au–Cu deposits in the Shizishan ore field; these data are used to determine the solubility of Cu and Au in the ore-forming fluids and to ascertain the mechanisms and factors that controlled variations in the association and separation of copper and gold mineralization. Our results indicate that copper in the ore-forming fluids was transported as CuCl 2 − and CuCl 0 complexes and that the solubility of copper was controlled by variations in Cl − concentration. In addition, the precipitation of copper was controlled by changes in temperature, pH, fO 2, and fO 2. In comparison, gold in the ore-forming fluids was transported as Au(HS) 2 − and Au 2S(HS) 2 2− complexes, and the solubility of gold was controlled by variations in total sulfur concentration; the precipitation of gold was controlled by temperature, pH, fO 2, and fO 2. These differences between the two elements meant that copper and gold in the ore-forming fluids responded in different ways to changes in physicochemical conditions. Copper precipitated under relatively acidic conditions at high temperatures, while gold precipitated under weakly alkaline conditions at relatively low temperatures; this dissociation resulted in the temporal and spatial separation and zonation of copper and gold mineralization in the Shizishan ore field.

Communities of purple sulfur bacteria in a Baltic Sea coastal lagoon analyzed by pufLM gene libraries and the impact of temperature and NaCl concentration in experimental enrichment cultures

Shallow coastal waters, where phototrophic purple sulfur bacteria (PSB) regularly form massive blooms, are subjected to massive diurnal and event-driven changes of physicochemical conditions including temperature and salinity. To analyze the ability of PSB to cope with these environmental factors and to compete in complex communities we have studied changes of the environmental community of PSB of a Baltic Sea lagoon under experimental enrichment conditions with controlled variation of temperature and NaCl concentration. For the first time, changes within a community of PSB were specifically analyzed using the photosynthetic reaction center genes pufL and M by RFLP and cloning experiments. The most abundant PSB phylotypes in the habitat were found along the NaCl gradient from freshwater conditions up to 7.5% NaCl. They were accompanied by smaller numbers of purple nonsulfur bacteria and aerobic anoxygenic phototrophic bacteria. Major components of the PSB community of the brackish lagoon were affiliated to PSB genera and species known as marine, halophilic or salt-tolerant, including species of M arichromatium, H alochromatium, T hiorhodococcus, A llochromatium, T hiocapsa, T hiorhodovibrio, and T hiohalocapsa. A dramatic shift occurred at elevated temperatures of 41 and 44°C when M arichromatium gracile became most prominent which was not detected at lower temperatures.

Physicochemical controls on initiation and evolution of desiccation cracks in sand–bentonite mixtures: X-ray CT imaging and stochastic modeling

The shrink-swell behavior of active clays in response to changes in physicochemical conditions creates great challenges for construction of geotechnical barriers for hazardous waste isolation, and is of significant importance for management of agricultural and natural resources. Initiation and evolution of desiccation cracks in active clays are strongly dependent on physicochemical initial and boundary conditions. To investigate effects of bentonite content (20, 40, 60%), pore fluid chemistry (0.05 and 0.5 M NaCl) and drying rates (40 and 60 °C) on cracking behavior, well-controlled dehydration experiments were conducted and X-ray Computed Tomography (CT) was applied to visualize and quantify geometrical features of evolving crack networks. A stochastic model based on the Fokker-Plank equation was adopted to describe the evolution of crack aperture distributions (CAD) and to assess the impact of physicochemical factors on cracking behavior. Analyses of crack porosity and crack specific surface area showed that both clay content and temperature had larger impact on cracking than pore fluid concentration. More cracks formed at high bentonite contents (40 and 60%) and at high drying rate (60 °C). The drift, diffusion and source terms derived from stochastic analysis indicated that evaporative demand had greater influence on the dynamics of the CAD than solution chemistry.

Freshwater Flow and Fisheries Production in Estuarine and Coastal Systems: Where a Drop of Rain Is Not Lost

This review presents a synopsis of the impacts of freshwater flow on fisheries production in estuarine and coastal systems, with particular emphasis on regional examples from eastern Australia and southern Africa. Freshwater flow impacts habitat availability, trophic interactions, and fishers’ harvesting behavior in estuarine and coastal systems. Seasonal and interannual variation in freshwater flow influences the distribution and abundance of fish and invertebrates through changes in growth, survival, and recruitment. Episodic flood and drought events have pronounced impacts on fisheries production due to rapid changes in physicochemical conditions modifying species richness and diversity. Many documented reductions in fisheries production have been attributed to river regulation modifying natural variation in freshwater flow. Protecting natural flow regimes is likely to be an effective management strategy to maintain the production of estuarine and coastal fisheries. Understanding the freshwater requirements of estuarine and coastal fisheries will become increasingly important as climate change modifies the hydrological cycle and as human population growth increases demand for water resources. One major challenge for scientists seeking to explore relationships between freshwater flow and fisheries production is to understand how variable flows influence resource availability, fishing activity, and the economic performance of commercial fisheries in estuarine and coastal systems.

Ecosystem states: Creating a data-derived, ecosystem-scale ecological response model that is explicit in space and time

Increasing difficulties associated with balancing consumptive demands for water and achieving ecological benefits in aquatic ecosystems provide opportunities for new ecosystem-scale ecological response models to assist managers. Using an Australian estuary as a case study, we developed a novel approach to create a data-derived state-and-transition model. The model identifies suites of co-occurring birds, fish, benthic invertebrates and aquatic macrophytes (as ‘states’) and the changing physico-chemical conditions that are associated with each (‘transitions’). The approach first used cluster analysis to identify sets of co-occurring biota. Differences in the physico-chemical data associated with each state were identified using classification trees, with the biotic distinctness of the resultant statistical model tested using analysis of similarities. The predictive capacity of the model was tested using new cases. Two models were created using different time-steps (annual and quarterly) and then combined to capture both longer-term trends and more-recent declines in ecological condition. We identified eight ecosystem states that were differentiated by a mix of water-quantity and water-quality variables. Each ecosystem state represented a distinct biotic assemblage under well-defined physico-chemical conditions. Two ‘basins of attraction’ were identified, with four tidally-influenced states, and another four independent of tidal influence. Within each basin, states described a continuum of relative health, manifest through declining taxonomic diversity and abundances. The main threshold determining relative health was whether freshwater flows had occurred in the region during the previous 339 days. Canonical analyses of principal coordinates tested the predictive capacity of the model and demonstrated that the variance in the environmental data set was well captured (87%) with 52% of the variance in the biological data set also captured. The latter increased to >80% when long- and short-term biological data were analysed separately, indicating that the model described the available data for the Coorong well. This approach thus created a data-derived, multivariate model, where neither states nor transitions were determined a priori. The approach did not over-fit the data, was robust to patchy or missing data, the choice of initial clustering technique and random errors in the biological data set, and was well-received by local natural resource managers. However, the model did not capture causal relationships and requires additional testing, particularly during future episodes of ecological recovery. The approach shows significant promise for simplifying management definitions of ecological condition and, via scenario analyses, can be used to assist in manager decision-making of large, complex aquatic ecosystems in the future.

Selective chemical extraction of heavy metals in tailings and soils contaminated by mining activity: Environmental implications

Total concentrations of chemical elements in soils may not be enough to understand the mobility and bioavailability of the elements. It is important to characterise the degree of association of chemical elements in different physical and chemical phases of soil. Another geochemical characterisation methodology is to apply sequential selective chemical extraction techniques. A seven-step sequential extraction procedure was used to investigate the mobility and retention behaviour of Al, Fe, Mn, Cu, Zn, Pb, Cr, Co, Ni, Mo, Cd, Bi, Sn, W, Ag, As and U in specific physical–chemical and mineral phases in mine tailings and soils in the surroundings of the abandoned Ervedosa mine. The soil geochemical data show anomalies associated with mineralised veins or influenced by mining. Beyond the tailings, the highest recorded concentrations for most elements are in soils situated in mineralised areas or under the influence of tailings. The application of principal components analysis allowed recognition of (a) element associations according to their geochemical behaviour and (b) distinction between samples representing local geochemical background and samples representing contamination. Some metal cations (Mn, Cd, Cu, Zn, Co, Cr, Ni) showed important enrichment in the most mobilisable and bioavailable (i.e., water-soluble and exchangeable) fractions due likely to the acidic conditions in the area. In contrast, oxy-anions such as Mo and As showed lower mobility because of adsorption to Fe oxy-hydroxides. The residual fraction comprised largest proportions of Sn and Al and to a lesser extent Zn, Pb, Ni, Cr, Bi, W, and Ag, which are also present at low concentrations in the bioavailable fractions. The elements in secondary mineral phases (mainly Fe, Mn, Cu, Zn, Cd, Pb, W, Bi, Mo, Cr, Ni, Co, As and U) as well as in organic matter and sulphides are temporarily withheld, suggesting that they may be released to the environment by changes in physico-chemical conditions.

Components of floating emergent macrophyte treatment wetlands influencing removal of stormwater pollutants

Floating treatment wetlands planted with emergent macrophytes (FTWs) provide an innovative option for treating urban stormwaters. Emergent plants grow on a mat floating on the water surface, rather than rooted in the bottom sediments. They are therefore able to tolerate the wide fluctuations in water depths that are typical of stormwater ponds. To better understand the treatment capabilities of FTWs, a series of replicated ( n = 3) mesocosm experiments (12 × 0.7 m 3 tanks using 0.36 m 2 floating mats) were conducted over seven day periods to examine the influence of constituent components of FTWs (floating mat, soil media, and four different emergent macrophyte species) for removal of copper, zinc, phosphorus and fine suspended solids (FSS) from synthetic stormwater. The presence of a planted floating mat significantly ( P < 0.05) improved removal of copper (>6-fold), fine suspended particles (∼3-fold reduction in turbidity) and dissolved reactive P (in the presence of FSS) compared to the control. Living plants provided a large submerged root surface-area (4.6–9.3 m 2 of primary roots m −2 mat) for biofilm development and played a key role in the removal of Cu, P and FSS. Uptake of Cu and P into plant tissues during the trials could only account for a small fraction of the additional removal found in the planted FTWs, and non-planted floating mats with artificial roots providing similar surface area generally did not provide equivalent benefits. These responses suggest that release of bioactive compounds from the plant roots, or changes in physico-chemical conditions in the water column and/or soils in the planted FTWs indirectly enhanced removal processes by modifying metal speciation (e.g. stimulating complexation or flocculation of dissolved fractions) and/or the sorption characteristics of biofilms. The removal of dissolved zinc was enhanced by the inclusion of a floating mat containing organic soil media, with reduced removal when vegetated with all except one of the test species. The results indicate that planted FTWs are capable of achieving dissolved Cu and Zn mass removal rates in the order of 5.6–7.7 mg m −2 d −1 and 25–104 mg m −2 d −1, respectively, which compare favourably to removal rates reported for conventional surface flow constructed wetlands treating urban stormwaters. Although not directly measured in the present study, the removal of particulate-bound metals is also likely to be high given that the FTWs removed approximately 34–42% of the turbidity associated with very fine suspended particulates within three days. This study illustrates the promise of FTWs for stormwater treatment, and supports the need for larger-scale, longer-term studies to evaluate their sustainable treatment performance.

Stable carbon and oxygen isotope signatures of pedogenic needle fibre calcite

Carbon and oxygen isotope compositions of the needle fibre calcite (NFC) from two soils observed in quarries (Villiers and Savagnier) in the Swiss Jura Mountains are used to investigate the processes involved in the formation of these calcite crystals in pedogenic environments. NFC occurs in soils with different macroscopic and microscopic morphologies. Three groups of microscopic morphologies are distinguished: simple needles (SN), simple needles with overgrowths (SNO), and simple needles with nanofibres (SNN), nanofibres being either organic or mineral in nature. These groups correspond to different stages in the formation and evolution of NFC. Evaluation of the δ 13C and δ 18O values of NFC and late calcite cements (LCC) in relationship to the composition of the carbonate host rock (CHR), and δ 13C DIC from the soil waters, indicate that both NFC and LCC are precipitated in isotopic equilibrium with the soil waters. Similar δ 13C and δ 18O values of the elongated NFC and the rhombohedral calcite crystals of the LCC suggest that the precipitation of these different calcite habits is not due to changes in physicochemical conditions. The growth of NFC crystals inside an organic mould formed by the fungal hyphae could explain the formation of calcite crystals in the shape of a needle in isotopic equilibrium with the local environment. The comparison of the δ 13C and δ 18O signatures of the various NFC morphological groups suggests that they likely evolve in the soil solution from calcite crystals liberated during the degradation of fungal hyphae walls. The NFC may be a proxy of the soil conditions (temperature and vegetation) during its precipitation, and also an indicator of biogenic (fungal) activity.

Effects of recent increases in salinity and nutrient concentrations on the microbialite community of Lake Clifton (Western Australia): are the thrombolites at risk?

The Yalgorup lakes, a groundwater-fed system in south-western Australia recognized as a Ramsar wetland, hold significant scientific and conservation value due to the presence of a unique range of lake systems, resident waterfowl and, on the eastern shore of Lake Clifton, the presence of the only thrombolite reef in the southern hemisphere. Recent concern over changing physico-chemical conditions in the lakes, particularly an increase in salinity, prompted this study: the current status of the inherent thrombolite community is unknown. Salinity, total phosphorous (TP), phosphate, total nitrogen (TN), nitrate, chlorophyll-a and relative abundance of the thrombolite microflora were measured in Lake Clifton to analyse changing conditions in this lake and to determine the effect of these water parameters on the thrombolite community. Comparisons with historical data revealed a significant increase in salinity since 1985 and a possible increase in phosphorus concentrations in the lake in the recent decade, although historical nutrient data are rather sparse. The increased salinity may be due to concentration of lake water through a combination of high evaporation, long-term reduction in rainfall and increased groundwater abstraction. Comparison of the composition of the thrombolite community with historical data indicates a large reduction in relative abundance of Scytonema sp. and other filamentous cyanobacterial species, which are believed to be fundamental for the thrombolite structure. It is concluded the changing physico-chemical environment of the Yalgorup Lakes may have led to the decline in important genera in the thrombolite community; however, the mechanisms underlying this change remain unknown.

Isolation and Characterization of a Stress‐Dependent Plastidial Δ12 Fatty Acid Desaturase from the Antarctic Microalga Chlorella vulgaris NJ‐7

An acclimation to the changing physicochemical conditions and high amount of Delta(12)-unsaturated fatty acids of the Antarctic Chlorella vulgaris NJ-7 prompted us to speculate about the involvement of Delta(12)-fatty acid desaturases (FAD) in its adaptation to the extremely unfavorable ambience. A full-length cDNA sequence, designated CvFAD6, was isolated from C. vulgaris NJ-7 via RT-PCR and RACE methods. Sequence alignment showed that the gene was homologous to corresponding Delta(12)-FAD from other eukaryotes. Phylogenetic analysis showed that it was grouped with plastidial Delta(12)-FAD with conserved histidine boxes. Yeast cells transformed with a plasmid construct containing CvFAD6 coding region accumulated a considerable amount of linoleic acid (18:2Delta(9,12)), normally not present in wild-type yeast cells, suggesting that the isolated gene encodes a functional Delta(12) enzyme. The correlation between the accumulation of CvFAD6 and temperature has been examined by real time PCR. The analysis showed a constant expression of CvFAD6 from 25 to 15 degrees C whereas a fourfold increased from 25 to 4 degrees C. Moreover, CvFAD6 transcription was more sensitive to saline stress since a 20-fold increase at 6% NaCl was detected. Our data demonstrate that CvFAD6 is the enzyme responsible for the Delta(12) fatty acids desaturation involved in low temperature and high salinity acclimation for Antarctic C. vulgaris NJ-7.

Sources, nature, and fate of heavy metal-bearing particles in the sewer system

A preliminary insight into metal cycling within the urban sewer was obtained by determining both the heavy metal concentrations (Cu, Zn, Pb, Cd, Ni, Cr) in sewage and sediments, and the nature of metal-bearing particles using TEM–EDX, SEM–EDX and XRD. Particles collected from tap water, sump-pit deposits, and washbasin siphons, were also examined to trace back the origin of some mineral species. The results show that the total levels in Cu, Pb, Zn, Ni, and Cr in sewage are similar to that reported in the literature, thus suggesting that a time-averaged heavy metal fingerprint of domestic sewage can be defined for most developed cities at the urban catchment scale. Household activities represent the main source of Zn and Pb, the water supply system is a significant source of Cu, and in our case, groundwater infiltration in the sewer system provides a supplementary source of Ni and Cd. Concentrations in heavy metals were much higher in sewer sediments than in sewage suspended solids, the enrichment being due to the preferential settling of metal-bearing particles of high density and/or the precipitation of neoformed mineral phases. TEM and SEM–EDX analyses indicated that suspended solids, biofilms, and sewer sediments contained similar heavy metal-bearing particles including alloys and metal fragments, oxidized metals and sulfides. Copper fragments, metal carbonates (Cu, Zn, Pb), and oxidized soldering materials are released from the erosion of domestic plumbing, whereas the precipitation of sulfides and the sulfurization of metal phases occur primarily within the household connections to the sewer trunk. Close examination of sulfide phases also revealed in most cases a complex growth history recorded in the texture of particles, which likely reflects changes in physicochemical conditions associated with successive resuspension and settling of particles within the sewer system.

Seasonality of epCO2 at different scales along an integrated river continuum within the Dee basin, NE Scotland

AbstractSpatial and temporal variations of free CO2 concentrations in surface waters are mainly controlled by dynamic processes encompassing terrestrial inputs and in‐stream biotic cycling. Free CO2 can be expressed as ‘excess partial pressure of CO2’ (epCO2), indicating supersaturation or under‐saturation with respect to atmospheric CO2. Seasonal patterns of epCO2 at sites draining nested upland catchments between 3·40 and 1837 km2 were assessed within the River Dee basin in NE Scotland. EpCO2 values ranged from 0·14 at the lowermost site on the mainstem in autumn to 12·7 on a major tributary during spring.A seasonality index was derived to describe contrasting winter/spring maxima and summer/autumn minima as annual mean epCO2 values could not clearly distinguish between different sites. Seasonal differences tended to increase downstream as progressive changes in physicochemical conditions enhanced the influence of autotrophic communities. However, perturbations to this continuum occurred as CO2 inputs from high DOC, heterotrophic tributaries and land‐use changes between open moorland and forest affected downstream continuity. Major tributaries showed reduced differences between seasons compared to the mainstem. Smaller headwaters indicated a lack of seasonality as high connectivity of responsive, peaty soils enabled continual inputs of terrestrially derived free CO2 to streams concomitant with limited autotrophic CO2 removal, maintaining epCO2 &gt; 1 throughout.Seasonality of epCO2 was mainly driven by the ability of in‐stream biota to consume CO2 during optimal conditions in summer/autumn. This was confirmed by multiple linear regression analysis, which indicated that, apart from catchment area, baseflow and biotic activity indicators were the best predictors of epCO2 seasonality characteristics at any particular stage of the river system. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Experimental study of stability and crystallization peculiarities of tourmaline in hydrothermal conditions

Tourmaline is a polygenetic mineral and often occurs in pegmatite and pneumatolyte‐hydrothermal (metasomatic) and metamorphic rocks as a rock-forming mineral [1]. Wide varieties of the tourmaline chemical composition, often within the limits of even one deposit, make it a good indication of the changing physicochemical conditions of mineral formation. Crystals of tourmaline formed in rare metal pegmatites, greisens, and hydrothermal veins are characterized by the extremely great varieties of composition. More than 14 mineral varieties of tourmaline have been identified [2], which is connected with the peculiarities of its structure. Its generalized crystal chemistry formula is the following: XY 3 Z 6 Si 6 O 18 (BO 3 ) 3 V 3 W , where X— Na + ,

Experimental growth and structural-morphological characteristics of co-tourmaline

Experiments aimed at investigating opportunities of Co-tourmaline growth onto a seed crystal in aqueous boron-chloride cobalt-containing solutions under temperatures of 400‐500 ° C and pressure up to 1000 bar were performed. Experiments were conducted under thermogradient conditions in titanium autoclaves, and in several cases with the help of a dividing diaphragm. Tourmaline growth onto a seed crystal occurs only with the use of separate tourmaline-forming components (monocrystal corundum and quartz rods) as the melting stock. The layer (up to 600 micron) of Co-tourmaline grown is intensively crimson-colored and occurs only at the face of positive monohedron {+0001}. Along with the monocrystal outgrowth, a great amount of very fine (30‐150 micron in size) tourmaline crystals of selfgeneration nucleation occurred on the seed crystals and in the melting stock. Their composition does not differ from the grown layer composition, and their unit cell parameters ( a = 15.82638 ± 0.00215 A, c = 7.09434 ± 0.00186 A) correspond to intermediate values of the tourmaline group minerals olenite and elbaite. Tourmaline is a complex borosilicate of the general crystal chemical formula XYZ , where X corresponds to large voids filled with Na, Ca, K, or a vacancy; Y corresponds to closely packed octahedrons of Mg, Fe 2+ , Li, Al, Mn, and Cr; and Z corresponds to deformed octahedrons of Al and Fe 3+ . In nature tourmaline rather often occurs in granite pegmatites and pneumatolyte‐hydrothermal and hydrothermal formations. Its presence is not unusual in such granites as well as in metasomatites and metamorphic rocks. This indicates the diversity of the tourmaline formation conditions. Interest in growing tourmaline monocrystals is connected with the task of obtaining new promising piezoelectric and pyroelectric materials possessing enhanced characteristics in comparison with those already known. Moreover, synthetic tourmaline can be used as a substitute for the natural form in the jewelry industry similar to other synthetic analogues of precious stones. There are many questions concerning the tourmaline formation conditions in nature that have remained unclear up until the present despite numerous geological, mineralogical, geochemical, and crystal chemical investigations. Safe and reproducible methods of growing its monocrystals have also not been developed. This situation is connected in general with the tourmaline complex chemical composition resulting in the existence of numerous varieties according to shades of color, which often change even within the single crystal. Obviously, this is a consequence of complex and changing physicochemical crystallization conditions of this mineral during its growth as well as special predisposition of its structure to a wide exhibition of iso- and heterovalent isomorphism. Investigations in the sphere of synthesis and growth

COLOR, MINERALOGY AND COMPOSITION OF UPPER JURASSIC WEST SIBERIAN GLAUCONITE: USEFUL INDICATORS OF PALEOENVIRONMENT

Changes in color of Upper Jurassic glauconite of the Georgiev Formation, in the West Siberian Basin, in Russia, are related to changes in physicochemical conditions that caused glauconite maturation and alteration, driven by regional paleoenvironmental evolution. Maturation produces dark green (bluish) glauconite formed from Fe-rich smectite by increasing the content of Fe 2+ together with K. Alteration produces brown rims and cracks that are enriched in Al and depleted in Fe and K with respect to the glauconite cores. The change from a yellowish green to dark green color in progressively more mature glauconite is explained by light absorption induced by enrichment in octahedrally coordinated Fe 2+ relative to the total Fe, associated with the progressive decrease in the proportion of Fe 3+ -rich smectite interleaved with glauconite. The brown color in alteration rims is due essentially to light scattered by nanometric inclusions of Fe oxyhydroxides. These, together with residual Al-rich glauconite and a subordinate Fe-rich smectite, constitute reaction products formed by leaching of K and Fe 2+ , and by the oxidation of yellowish green glauconite cores. Berthierine formed later in the brown rims on Al-rich glauconite, and pyrite formed as a result of drowning of the platform during the latest Jurassic – earliest Cretaceous and sedimentation of black shales under increasingly reducing conditions.

Development and application of a T-RFLP data analysis method using correlation coefficient matrices

Environmental microbiology studies commonly use terminal restriction fragment length polymorphism (T-RFLP) of 16S rRNA genes, for example, to analyze changes in community structure in relation to changing physicochemical and biological conditions over space and time. Although T-RFLP is most useful for comparing samples from different environments, a large number of samples makes effective analysis difficult using the Web-based tools that are currently available. To resolve this dilemma, we used a new approach for calculating data from multiple T-RFLP samples by estimating terminal fragment combinations, then applying a correlation analysis using two different fluorescent dyes generated simultaneously from all samples. This calculation was based on the expectation that the proportions of two terminal fragments from one full-length polymerase chain reaction fragment would be nearly the same in each analysis. Using this program, the oral microflora in 73 human saliva samples were analyzed, and 24 bacterial groups, with peak areas of at least 0.5% and correlation coefficients of 0.55 or greater, were identified from the T-RFs within 40 s.

GRAINS OF Pt-Fe ALLOY AND INCLUSIONS IN A Pt-Fe ALLOY FROM FLORENCE CREEK, YUKON, CANADA: EVIDENCE FOR MOBILITY OF Os IN A Na-H2O-Cl-RICH FLUID

We report results of detailed electron-microprobe analyses (EMP) of fourteen grains of Pt–Fe alloy, ca. 0.4 to 1 mm, principally droplet-shaped or roundish, from Florence Creek, Yukon. We also describe new occurrences of Pt–(Pd)–Fe alloy from Arch Creek (up to 11 wt.% Pd) and Canadian Creek, Yukon. An extensive compositional series is observed at Florence, in which values of ∑PGE/(Fe + Cu + Ni) vary from 2.2 to 5.4. Minor Ir and Os display a contrasting behavior in this series. The observed levels of Ir are generally greater than those of Os. The Ir correlates negatively with Pt (the correlation coefficient, R, is −0.81; 140 EMP point-analyses); in contrast, the correlation between Os and Pt is slightly positive (R = 0.64). Probably, at a higher temperature of crystallization, Ir readily replaces Pt in the structure of a Pt–Fe alloy. As a result, Ir did not attain its maximum, and the observed inclusions of exsolution-induced Ir-dominant alloy, hosted by the Pt–Fe alloy, are moderately enriched in Ir (52–54 at.%). An inclusion of erlichmanite (4.2 wt.% Rh) and a partial rim of Au–Ag alloy (Au 0.80 Ag 0.18 ) were observed. Droplet-like inclusions of highly aluminous silicate minerals, hosted by grains of Pt–Fe alloy, are rich in Na, K and in Cl (up to 2 wt.%). Veinlets and micrograins of an Os-rich alloy (86–92 wt.% Os) are intimately associated with micrograins of nearly pure albite, Ab 97.8 An 1.7 Or 0.5 , and with an intermediate member of the chamosite–clinochlore series. The observed association chamosite + albite + native osmium, infilling a cavity in a host grain of Pt–Fe alloy, was likely deposited from a late Na–H 2 O–(Cl)-bearing fluid phase at a postmagmatic–hydrothermal stage, at a temperature less than 700°C. The Os and Na were possibly mobilized and transported as Na–(Os)-rich complexes related to the sodium hydroxy- or oxo-osmates. The precipitation of the metallic Os phase could be related to a change in physicochemical conditions, e.g., in fluid pressure or redox potential, leading to instability of these Na–(Os)-rich hydroxy- or oxo-osmate complexes. We suggest that a mineralized zone rich in chromite–magnesiochromite and hosted by an Alaskan–Uralian-type complex is the likely provenance for grains of Pt–Fe alloy recovered in Florence Creek.

Arsenic abundance and variation in golf course lakes

Monosodium methanearsonate (MSMA) is a commonly used herbicide on golf courses. To investigate the variation in abundance of arsenic (As) after MSMA application, 28 golf course lakes were monitored monthly for one year. The As concentrations varied substantially in and between individual lakes with values up to 124 μg/L (mean = 10.9 μg/L, n = 336). This is considerably higher than the As concentrations in comparable “non-golf course” lakes (up to 100-times) in the study area. The highest values of As in the lakes were generally observed in the late spring and early summer and corresponded to the intensity of MSMA applications. Arsenic seems to be sequestered by the golf course lake sediments with concentrations as high as 302 mg/kg, which were significantly higher than the 0.1 to 3 mg/kg expected for comparable sediments in central Florida. Arsenic correlates well with Fe in the top 15 cm of the lake sediments suggesting that As is sorbed by hydrous ferric oxides (HFO). As long as conditions are in favour of HFO stability, As is retained in the lake sediments preventing its migration into the Floridan aquifer systems. However, once the loading capacity of the sediment is reached or when as a result of changing physico-chemical conditions HFO may become unstable, As may enter the Floridan aquifer.

Calcium isotope fractionation in coccoliths of cultured Calcidiscus leptoporus, Helicosphaera carteri, Syracosphaera pulchra and Umbilicosphaera foliosa

Four species of marine calcifying algae, the coccolithophores Calcidiscus leptoporus, Helicosphaera carteri, Syracosphaera pulchra and Umbilicosphaera foliosa were grown in laboratory cultures under temperatures varying between 14 and 23 °C, and one species, C. leptoporus, under varying [CO 3 2−], ranging from 105 to 219 μmol/kg. Calcium isotope compositions of the coccoliths resemble in both absolute fractionation and temperature sensitivity previous calibrations of marine calcifying species e.g. Emiliania huxleyi (coccolithophores) and Orbulina universa (planktonic foraminifera) as well as inorganically precipitated CaCO 3, but also reveal small species specific differences. In contrast to inorganically precipitated calcite, but similar to E. huxleyi and O. universa, the carbonate ion concentration of the medium has no statistically significant influence on the Ca isotope fractionation of C. leptoporus coccoliths; however, combined data of E. huxleyi and C. leptoporus indicate that the observed trends might be related to changes of the calcite saturation state of the medium. Since coccoliths constitute a significant portion of the global oceanic CaCO 3 export production, the Ca isotope fractionation in these biogenic structures is important for defining the isotopic composition of the Ca sink of the ocean, one of the key parameters for modelling changes to the marine Ca budget over time. For the present ocean our results are in general agreement with the previously postulated and applied mean value of the oceanic Ca sink (Δ sed) of about − 1.3‰, but the observed inter- and intra-species differences point to possible changes in Δ sed through earth history, due to changing physico-chemical conditions of the ocean and shifts in floral and faunal assemblages.

Are mangrove forest substrates sediments or soils? A case study in southeastern Brazil

Morphological and analytical data corresponding to several profiles from two mangrove systems in the Brazilian state of São Paulo were examined for evidence of pedogenetic processes. Plant activity exerted a strong effect on the processes occurring in mangrove substrates, especially on the intensity of these processes and, therefore, constitutes one of the major factors involved in the differentiation of sediments and soils. Colonization of substrates by vascular plants leads to drastic changes in physicochemical conditions. The redox processes were much more diverse in the soil than in the sediment (substrate without vegetation); in the former they varied with depth, with oxic or suboxic conditions being observed at the surface and anoxic conditions observed below 30 cm, whereas in the sediment, anoxic conditions were observed throughout. Likewise, the acid–base conditions were more variable in the soils, ranging from strongly acid to neutral, and in the sediment they were close to neutral. Furthermore, different pedogenetic processes were identified: (1) addition of organic matter by accumulation of vegetable debris and dead roots, with formation – in some cases – of a histic epipedon, (2) transfer of soluble iron (Fe 2+) towards the surface and precipitation in the form of Fe oxyhydroxide, and transfer of the mineral particles due to the bioturbation caused by activity of crabs, (3) transformation of elements such as iron (gleization) and sulphur (sulphidization). Changes undergone in the mangrove substrates were also characterized by simultaneity and intergradations between pedogenesis and diagenesis, especially in the lowermost layers in which authigenesis appears to intensify. Thus, the presence of smectite minerals in the clay fraction may be attributed to authigenic processes that take place in both soils and sediments.