Abiotic Systems Research Articles

Extent of Precipitation and Sorption During Copper Removal from Synthetic Wastewater in the Presence of Sulfate-Reducing Bacteria

A sulfate-reducing bacterial culture was successfully enriched from the seed sludge of anaerobic sludge digester. Sulfate-reducing bacteria (SRB) in the enriched culture (around 42%) were characterized by fluorescence in situ hybridization (FISH) with group and genus specific 16S rRNA-targeted oligonucleotide probes. Desulfosarcina, Desulfococcus, Desulfofaba, and Desulfofrigus spp. were identified as the dominant species of the enriched SRB. Subsequently, batch experiments were conducted at initial copper and sulfate concentrations of 10 and 300 mg/L, respectively, to quantify the ability of the enriched SRB in simultaneous sulfate reduction and copper removal. Sulfate reduction efficiencies of the culture in the absence (biotic system without copper, BS-1) and the presence (biotic system with copper, BS-2) of copper were 96.8 and 98.8%, respectively, after 6 days. In BS-2, 99.2% copper removal was observed after 1 day. However, 67% of copper was removed by chemical precipitation and bioaccumulation. No significant inhibition of bacterial growth was observed at the copper concentration studied, that is, 10 mg/L. Chemical precipitation as hydroxide/carbonate caused a copper removal of 44% in AS-1 (abiotic system without lactate) and 36% in AS-2 (abiotic system with lactate), after 6 days. However, the majority of copper was removed as copper sulfide well before the occurrence of copper hydroxide precipitation. Energy dispersive X-ray spectroscopy (EDS) analysis of the precipitates obtained from biotic and abiotic systems confirmed the origin of copper sulfide as the result of SRB. As a whole, the results of this study could be useful to understand the mechanisms of copper removal, i.e. chemical precipitation, bioprecipitation and biosorption/bioaccumulation during sulfate reduction by SRB.

Marine bacterioplankton can increase evaporation and gas transfer by metabolizing insoluble surfactants from the air–seawater interface

Hydrophobic surfactants at the air-sea interface can retard evaporative and gaseous exchange between the atmosphere and the ocean.While numerous studies have examined the metabolic role of bacterioneuston at the air-sea interface, the interactions between hydrophobic surfactants and bacterioplankton are not well constrained. A novel experimental design was developed, using Vibrio natriegens and (3)H-labelled hexadecanoic acid tracer, to determine how the bacterial metabolism of fatty acids affects evaporative fluxes. In abiotic systems, >92% of the added hexadecanoic acid remained at the air-water interface. In contrast, the presence of V. natriegens cells draws down insoluble hexadecanoic acid from the air-water interface as an exponential function of time. The exponents characterizing the removal of hexadecanoic acid from the interface co-vary with the concentration of V. natriegens cells in the underlying water, with the largest exponent corresponding to the highest cell abundance. Radiochemical budgets show that evaporative fluxes from the system are linearly proportional to the quantity of hexadecanoic acid at the interface. Thus, bacterioplankton could influence the rate of evaporation and gas transfer in the ocean through the metabolism of otherwise insoluble surfactants.

Iron isotope fractionation and atom exchange during sorption of ferrous iron to mineral surfaces

The application of stable Fe isotopes as a tracer of the biogeochemical Fe cycle necessitates a mechanistic knowledge of natural fractionation processes. We studied the equilibrium Fe isotope fractionation upon sorption of Fe(II) to aluminum oxide (γ-Al 2O 3), goethite (α-FeOOH), quartz (α-SiO 2), and goethite-loaded quartz in batch experiments, and performed continuous-flow column experiments to study the extent of equilibrium and kinetic Fe isotope fractionation during reactive transport of Fe(II) through pure and goethite-loaded quartz sand. In addition, batch and column experiments were used to quantify the coupled electron transfer-atom exchange between dissolved Fe(II) (Fe(II) aq) and structural Fe(III) of goethite. All experiments were conducted under strictly anoxic conditions at pH 7.2 in 20 mM MOPS (3-( N-morpholino)-propanesulfonic acid) buffer and 23 °C. Iron isotope ratios were measured by high-resolution MC-ICP-MS. Isotope data were analyzed with isotope fractionation models. In batch systems, we observed significant Fe isotope fractionation upon equilibrium sorption of Fe(II) to all sorbents tested, except for aluminum oxide. The equilibrium enrichment factor, ε 56 / 54 eq , of the Fe(II) sorb–Fe(II) aq couple was 0.85 ± 0.10‰ (±2 σ) for quartz and 0.85 ± 0.08‰ (±2 σ) for goethite-loaded quartz. In the goethite system, the sorption-induced isotope fractionation was superimposed by atom exchange, leading to a δ 56/54Fe shift in solution towards the isotopic composition of the goethite. Without consideration of atom exchange, the equilibrium enrichment factor was 2.01 ± 0.08‰ (±2 σ), but decreased to 0.73 ± 0.24‰ (±2 σ) when atom exchange was taken into account. The amount of structural Fe in goethite that equilibrated isotopically with Fe(II) aq via atom exchange was equivalent to one atomic Fe layer of the mineral surface (∼3% of goethite-Fe). Column experiments showed significant Fe isotope fractionation with δ 56/54Fe(II) aq spanning a range of 1.00‰ and 1.65‰ for pure and goethite-loaded quartz, respectively. Reactive transport of Fe(II) under non-steady state conditions led to complex, non-monotonous Fe isotope trends that could be explained by a combination of kinetic and equilibrium isotope enrichment factors. Our results demonstrate that in abiotic anoxic systems with near-neutral pH, sorption of Fe(II) to mineral surfaces, even to supposedly non-reactive minerals such as quartz, induces significant Fe isotope fractionation. Therefore we expect Fe isotope signatures in natural systems with changing concentration gradients of Fe(II) aq to be affected by sorption.

Elucidating the Role of Electron Shuttles in Reductive Transformations in Anaerobic Sediments

Model studies have demonstrated that electron shuttles (ES) such as dissolved organic matter (DOM) can participate in the reduction of organic contaminants; however, much uncertainty exists concerning the significance of this solution phase pathway for contaminant reduction in natural systems. To compare the identity and reactivity of ES in anaerobic sediments with those in model systems, two chemical probes (4-cyano-4'-aminoazobenzene (CNAAzB) either free or covalently bound to glass beads) were synthesized that allowed for differentiation between surface-associated and solution-phase electron-transfer processes. The feasibility of these chemical probes were demonstrated in abiotic model systems (Fe(II)/Fe(III) oxide) and biotic model systems (Fe(II)/Fe(III) oxide or river sediment amended with S. putrefaciens strain cells). Experiments in the abiotic systems revealed that the addition of model hydroquinones and chemically reduced DOM increased reduction rates of free CNAAzB, whereas no enhancement in reactivity was observed with the addition of model quinones or DOM. Bound CNAAzB was also reduced by model hydroquinones and reduced DOM--but not by model quinones and untreated DOM--in the abiotic model systems, indicating that Fe(II)/Fe(III) oxides do not function as a bulk reductant forthe reduction of ES. Addition of model quinones or untreated DOM to the biotic models systems with sediment increased reduction rates of bound CNAAzB, which correlated well with the dissolved organic carbon content. In natural sediment slurries, reduction rates of bound CNAAzB correlated well with parameters for organic carbon (OC) content of both sediments and supernatants. Our results support a scenario in which reducible organic contaminants will compete with iron oxides for the electron flow generated by the microbially mediated oxidation of organic carbon and subsequent reduction of quinone functional groups associated with DOM.

Using the salinity preferences of benthic macroinvertebrates to classify running waters in brackish marshes in Germany

Abstract Marshland streams along European coastlines are typically located in the transition zone from limnic to brackish conditions. They constitute a distinct and important stream type within the German stream typology, which is predominantly characterised by tidal influence and salinity. According to the Water Framework Directive (WFD) the basis for the abiotic classification of European transitional and coastal waters is the ‘Venice System’ (Weber, M., 2005. Ergebnisse der Bestandsaufnahme 2004 zur Umsetzung der europaischen Wasserrahmenrichtlinie (WRRL) in den Kustengewassern Mecklenburg-Vorpommerns. Rostocker Meeresbiol. Beitr. 14, 7–15). However, the extreme spatial and temporal variability in salinity and tidal influence determines and controls the macroinvertebrate communities of marshland river and stream ecosystems and hampers the application of the ‘Venice System’. Earlier, purely biotic classifications of brackish waters typically classify different brackish water zones, each with a specific macroinvertebrate community, and often yield unsatisfactory results due to the extensively dynamic abiotic factors found in marshland streams. In practice, the permanent impact of tidal charge means that stable salinity zones do not exist. This effect can than be intensified by freshwater discharges after heavy rainfall or high tides in combination with strong winds that hinder discharge into the open sea. To overcome the restricted applicability of abiotic and biotic classification systems, we present a scoring system for marshland streams that combines the abiotic salinity classes of the ‘Venice System’ with the salinity preferences of the macroinvertebrate community. This proposal is based on literature data for macroinvertebrate salinity tolerances and preferences. According to the 137 references that were evaluated, 151 macroinvertebrate taxa were classified into six salinity groups. In a second step, we applied this scoring scheme to empirical data from two official quality assessment surveys. These surveys had been carried out in ten estuary tributaries of German marshland areas in Lower Saxony and Schleswig-Holstein in order to implement the WFD. Applying the scoring system to these data revealed a clear (and expected) gradient that was not expressed in the abiotic data. Thus we conclude that the biotic salinity preferences of benthic macroinvertebrates are a useful baseline metric for the ecological assessment of marshland streams and other transitional waters. Regional revision and adaptation of taxonomic salinity preferences would broaden the applicability of this assessment to transitional waters worldwide.

Natural hierarchy emerges from energy dispersal

Hierarchical organization of ‘systems within systems’ is an apparent characteristic of nature. For many biotic and abiotic systems it is known how the nested structural and functional order builds up, yet the general principle why matter evolves to hierarchies has remained unfamiliar to many. We clarify that increasingly larger integrated systems result from the quest to decrease free energy according to the 2nd law of thermodynamics. The argumentation is based on the recently derived equation of motion for natural processes. Hierarchically organized energy transduction machinery emerges naturally when it provides increased rates of energy dispersal. Likewise, a hierarchical system will dismantle into its constituents when they as independent systems will provide higher rates of entropy increase. Since energy flows via interactions, decreasing strengths of interactions over increasingly larges lengths scales mark natural boundaries for nested integrated systems.

Contemporary and preindustrial mass budgets of mercury in the Hudson Bay Marine System: The role of sediment recycling

Based on extensive sampling of the rivers, troposphere, seawater and sediments, mercury (Hg) mass budgets are constructed for both contemporary and preindustrial times in the Hudson Bay Marine System (HBS) to probe sources and pathways of Hg and their responses to the projected climate change. The contemporary total Hg inventory in the HBS is estimated to be 98 t, about 1% of which is present in the biotic systems and the remainder in the abiotic systems. The total contemporary Hg influx and outflux, around 6.3 t/yr each, represent a 2-fold increase from the preindustrial fluxes. The most notable changes are in the atmospheric flux, which has gone from a nearly neutral (0.1 t/yr) to source term (1.5 t/yr), increased river inputs (which may also reflect increased atmospheric deposition to the HBS watershed) and in the sedimentary burial flux which has increased by 2.4 t/yr over preindustrial values, implying that much of the modern Hg loading entering this system is buried in the sediments. The capacity to drive increased Hg loading from the atmosphere to sediment burial may be supported by the resuspension of an extraordinarily large flux (120 Mt/yr) of shallow water glacigenic sediments uncontaminated by anthropogenic Hg, which could scavenge Hg from the water column before being transported to the deeper accumulative basins. Under the projected climate warming in the region, the rate of the sediment recycling pump will likely increase due to enhanced Hg scavenging by increasing biological productivity, and thus strengthen atmosphere–ocean Hg exchanges in the HBS.

Biocorrosion of AISI 304 Stainless Steel by Desulfovibrio desulfuricans in Seawater

The corrosion behavior of AISI 304 stainless steel (SS304) in a batch system of enriched artificial seawater (EASW) in the presence of a sulfate-reducing bacteria (SRB) species (Desulfovibrio desulfuricans ATCC 27774) was investigated using analytical techniques including electrochemical impedance spectroscopy (EIS), atomic force microscopy (AFM), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). EIS analysis showed that the polarization resistance of SS304 decreased after immersion in EASW in the presence of the SRB for 14 days compared to the control sample (in the absence of SRB). The corrosion processes were simulated using equivalent circuit models, which provided electrochemical information on the liquid/surface interface for both abiotic and biotic systems. Using AFM, pits and cracks were observed on the stainless steel surface in the presence of SRB, and a thick biofilm produced by SRB was evident in SEM micrographs, which corroborated the EIS results for the explanat...

Soil microorganisms determine the sorption of radionuclides within organic soil systems

The potential of soil microorganisms to enhance the retention of 137Cs and 85Sr in organic systems was assessed in a series of experiments. A biologically active, ‘mineral-free’, organic material, produced under laboratory conditions from leaves, was used as the uptake matrix in all experiments to minimise potential interference from competing clay minerals. Biological uptake and release were differentiated from abiotic processes by comparing the sorption of radionuclides in sterilised organic material with sterile material inoculated with soil extracts or single fungal strains. Our results show conclusively that living components of soil systems are of primary importance in the uptake of radionuclides in organic material. The presence of soil microorganisms significantly enhanced the retention of Cs in organic systems and ∼70% of the Cs spike was strongly (irreversibly) bound (remained non-extractable) in the presence of microorganisms compared to only ∼10% in abiotic systems. Sorption of 85Sr was not significantly influenced by the presence of soil microorganisms. A non-linear temperature response was observed for the retention in biotic systems with increased uptake at between 10 and 30 °C and lower retention at temperatures above or below the optimum range. The optimum temperatures for biological uptake were between 15 and 20 °C for Cs, and 25 and 30 °C for Sr. Our results indicate that single strains of soil and saprotrophic fungi make an important contribution to the sorption of Cs and Sr in organic systems, but can only account for part of the strong, irreversible binding observed in biotic systems. Single strains of soil fungi increased the amount of non-extractable 137Cs (by ∼30%) and 85Sr (by ∼20%) in the organic systems as compared to abiotic systems, but the major fraction of 137Cs and 85Sr sorbed in systems inoculated with saprotrophic fungi remained extractable.

Micro-X-ray absorption near edge structure as a suitable probe to monitor live organisms

X-ray spectroscopies are very powerful tools to determine the chemistry of complex dilute solutes in abiotic and biotic systems. We have assayed their suitability to monitor the chemistry of complex solutions in a live biotic system. The impact of the probe on cells was quantified for 4 different cellular organisms differing in their resistance level to environmental stresses. We show that none of the organisms tested can survive the radiation doses needed for the acquisition of meaningful spectroscopic data. Therefore, on one hand, X-ray spectroscopy cannot be applied to the monitoring of single cells, and cellular damages have to be taken into account in the interpretation of the evolution of such systems. On the other hand, due to the limited extension of X-ray induced cellular damages in the culture volume, it is possible to probe a population of live cells provided that the culture to beam probe ratio is large enough to minimize the impact of mortality on the evolution of the biological system. Our results suggest that it could be possible to probe the volume in the close vicinity of a cell without affecting its activity. Using this setup we could monitor the reduction of selenite by the X-ray sensitive bacterium, Agrobacterium tumefaciens strain C58, for 24 h. This method has a great potential to monitor the respiration of various metals, such as iron, manganese and arsenic, in situ under relevant environmental conditions by live microorganisms.

Nonequilibrium dynamics of ecosystems

Based on the concept of the nonequilibrium behavior of nonlinear dissipative ecosystems with blow-up, problems of their dynamic equilibrium are examined. An analogy is drawn between the mathematical description of biological systems and systems of an inorganic origin, leading to their unity at the mathematical modeling level. Synergetic nonlinearity of the evolution of biotic and abiotic systems is found.

Potential for Identifying Abiotic Chloroalkane Degradation Mechanisms using Carbon Isotopic Fractionation

Degradation of 1,1- and 1,2-dichloroethane (1,1-DCA, 1,2-DCA) and carbon tetrachloride (CCl4) on Zn0 was investigated using compound specific isotope analysis (CSIA) to measure isotopic fractionation factors for chloroalkane degradation by hydrogenolysis, by alpha-elimination, and by beta-elimination. Significant differences in enrichment factors (epsilon) and associated apparent kinetic isotope effects (AKIE) were measured for these different reaction pathways, suggesting that carbon isotope fractionation by beta-elimination is substantially larger than fractionation by hydrogenolysis or by alpha-elimination. Specifically, for 1,1-DCA, the isotopic composition of the reductive alpha-elimination product (ethane) and the hydrogenolysis product (chloroethane) were the same, indicating that cleavage of a single C-Cl bond was the rate-limiting step in both cases. In contrast, for 1,2-DCA, epsilon = epsilon(reactive position) = -29.7 +/- 1.5% per hundred, and the calculated AKIE (1.03) indicated that beta-elimination was likely concerted, possibly involving two C-Cl bonds simultaneously. Compared to 1,1-DCA hydrogenolysis, the AKIE of 1.01 for hydrogenolysis of CCl4 was much lower, indicating that, for this highly reactive organohalide, mass transfer to the surface was likely partially rate-limiting. These findings are a first step toward delineating the relative contribution of these competing pathways in other abiotic systems such as the degradation of chlorinated ethenes on zerovalent iron (ZVI), iron sulfide, pyrite, or magnetite, and, potentially, toward distinguishing between degradation of chlorinated ethenes by abiotic versus biotic processes.

Use of In Vitro Absorption, Distribution, Metabolism, and Excretion (ADME) Data in Bioaccumulation Assessments for Fish

ABSTRACT A scientific workshop was held in 2006 to discuss the use of in vitro Absorption, Distribution, Metabolism, and Excretion (ADME) data in chemical bioaccumulation assessments for fish. Computer-based (in silico) modeling tools are widely used to estimate chemical bioaccumulation. These in silico methods have inherent limitations that result in inaccurate estimates for many compounds. Based on a review of the science, workshop participants concluded that two factors, absorption and metabolism, represent the greatest sources of uncertainty in current bioaccumulation models. Both factors can be investigated experimentally using in vitro test systems. A variety of abiotic and biotic systems have been used to predict chemical accumulation by invertebrates, and dietary absorption of drugs and xenobiotics by mammals. Research is needed to determine whether these or similar methods can be used to better predict chemical absorption across the gills and gut of fish. Scientists studying mammals have developed a stepwise approach to extrapolate in vitro hepatic metabolism data to the whole animal. A series of demonstration projects was proposed to investigate the utility of these in vitro–in vivo extrapolation procedures in bioaccumulation assessments for fish and delineate the applicability domain of different in vitro test systems. Anticipating research progress on these topics, participants developed a “decision tree” to show how in vitro information for individual compounds could be used in a tiered approach to improve bioaccumulation assessments for fish and inform the possible need for whole-animal testing.

Biological Soil Crust Rehabilitation in Theory and Practice: An Underexploited Opportunity

Abstract Biological soil crusts (BSCs) are ubiquitous lichen–bryophyte microbial communities, which are critical structural and functional components of many ecosystems. However, BSCs are rarely addressed in the restoration literature. The purposes of this review were to examine the ecological roles BSCs play in succession models, the backbone of restoration theory, and to discuss the practical aspects of rehabilitating BSCs to disturbed ecosystems. Most evidence indicates that BSCs facilitate succession to later seres, suggesting that assisted recovery of BSCs could speed up succession. Because BSCs are ecosystem engineers in high abiotic stress systems, loss of BSCs may be synonymous with crossing degradation thresholds. However, assisted recovery of BSCs may allow a transition from a degraded steady state to a more desired alternative steady state. In practice, BSC rehabilitation has three major components: (1) establishment of goals; (2) selection and implementation of rehabilitation techniques; and (3) monitoring. Statistical predictive modeling is a useful method for estimating the potential BSC condition of a rehabilitation site. Various rehabilitation techniques attempt to correct, in decreasing order of difficulty, active soil erosion (e.g., stabilization techniques), resource deficiencies (e.g., moisture and nutrient augmentation), or BSC propagule scarcity (e.g., inoculation). Success will probably be contingent on prior evaluation of site conditions and accurate identification of constraints to BSC reestablishment. Rehabilitation of BSCs is attainable and may be required in the recovery of some ecosystems. The strong influence that BSCs exert on ecosystems is an underexploited opportunity for restorationists to return disturbed ecosystems to a desirable trajectory.

Oxygen isotope fractionation between apatite and aqueous-phase phosphate: 20–45 °C

Replacement of biogenic CaCO 3 by apatite is an important mode of authigenic apatite formation in marine sediments, active along the Peru Margin today. Synthesis experiments mimicking this process were undertaken in abiotic inorganic systems in order to determine the oxygen (O) isotope fractionation between apatite and aqueous-phase inorganic phosphate [(PO 4) aq]. CaCO 3 solids were added to PO 4 3− solutions made with 18O-labeled waters and O isotope fractionations between solid- and aqueous-phase PO 4 3− were determined in a series of experiments at 20–45 °C. Results of δ 18O analyses of apatite synthesis systems indicate that O isotope fractionation between solid- and aqueous-phase PO 4 3− is: (1) not affected by variations in water δ 18O values; (2) initially non-equilibrium; and (3) relatively small (∼ + 1‰). Fractionations determined from long-term (up to 6 years) room-temperature experiments were ∼ + 1‰. Due to initial rapid precipitation, short experimental run periods (1 week to 4 months), resulted in fractionations between apatite and (PO 4) aq that were initially reversed from those of long-term experiments. Over time and with progressive recrystallization, these fractionations evolved to reach values consistent with long-term experiments.

Formation of Covellite (CuS) Under Biological Sulfate-Reducing Conditions

Sulfate-reducing bacteria (SRB) play a major role in the precipitation of metal sulfides in the environment. In this work, biogenic copper sulfide formation was examined in cultures of SRB and compared to chemically initiated Cu sulfide precipitation as a reference system. Mixed cultures of SRB were incubated at 22, 45, and 60°C in nutrient solutions that contained copper sulfate. Abiotic reference samples were produced by reacting uninoculated liquid media with Na2S solutions under otherwise identical conditions. Precipitates were collected anaerobically by centrifugation, frozen in liquid N2, and freeze-dried, followed by analysis using X-ray diffraction (XRD), X-ray fluorescence, and scanning electron microscopy. Covellite (CuS) was the only mineral found in the precipitates. Covellite was less crystalline in the biogenic precipitates than in the abiotic samples based on XRD peak widths and peak to background ratios. Poor crystallinity may be the result of slower precipitation rates in bacterial cultures as compared to the abiotic reference systems. Furthermore, bacterial cells may inhibit the nucleation steps that lead to crystal formation. Incubation at elevated temperatures improved the crystallinity of the biotic specimens.

A review of geochemical background concepts and an example using data from Poland

One of the most crucial issues of recent environmental sciences is the topic of background concentrations of elements and organic compounds in various abiotic and biotic systems. The relationship between natural and anthropogenically altered concentrations of chemical species is a question that involves many implications in the geosciences, environmental and biological sciences, toxicology, and other related disciplines. This is especially important when interpreting geochemical and biogeochemical anomalies of toxic elements and/or organic compounds in various media. To better understand the potential impact of hazardous substances in the environment, we must become more familiar with their spatial and temporal distribution and with their behavior under different physico-chemical and biotic conditions. This review presents an assessment of the geochemical background concept as used by various authors. Different assumptions and approaches to this topic are presented, including direct, statistical, and integrated methods. Based on the results derived from geochemical and biogeochemical studies performed in selected forest ecosystems of Poland, an integrated method is presented. As a consequence of data processing, a normal distribution of data points was obtained using an iterative 2σ-technique. This method of estimating geochemical background is feasible and can be used for setting environmental quality standards or for studying the impact of anthropogenic pollution sources on the environment.

Synthesis and properties of ammoniojarosites prepared with iron-oxidizing acidophilic microorganisms at 22–65 °C

Ammoniojarosite [(NH 4,H 3O)Fe 3(OH) 6(SO 4) 2], a poorly soluble basic ferric sulfate, was produced by microbiological oxidation of ferrous sulfate at pH 2.0–3.0 over a range of NH 4 + concentrations (5.4–805 mM) and temperatures (22–65 °C). Ammoniojarosites were also produced by chemical (abiotic) procedures in parallel thermal (36–95 °C) experiments. At 36 °C, schwertmannite [ideally Fe 8O 8(OH) 6(SO 4)] was the only solid product formed at <10 mM NH 4 + concentrations. Between 11.5 and 85.4 mM NH 4 + , a mixed product of ammoniojarosite and schwertmannite precipitated, as identified by X-ray diffraction. In excess of 165 mM NH 4 + , ammoniojarosite was the only solid phase produced. An increase in the incubation temperature using thermoacidophiles at 45 and 65 °C accelerated the formation of ammoniojarosite in culture solutions containing 165 mM NH 4 + . Both the biogenic and chemical ammoniojarosites were yellow (2Y–4Y in Munsell hue), low surface area (<1 m 2/g), well crystalline materials with average c o and a o unit cell parameters of 17.467 ± 0.048 Å and 7.330 ± 0.006 Å, respectively. Strong positive correlations were observed between unit cell axial ratios ( c o/ a o) and increasing synthesis temperature in both biotic and abiotic systems. All samples were N deficient compared to stoichiometric ammoniojarosite, and both chemical and X-ray data indicated partial replacement of NH 4 + by H 3O + to form solid solutions with 0.14–0.24 mole H 3O + per formula unit. The morphology of the biogenic jarosites included aggregated discs, pseudo-cubic crystals and botryoidal particles, whereas the chemical specimens prepared at 36–95 °C were composed of irregular crystals with angular edges. Morphological information may thus be useful to evaluate environmental parameters and mode of formation. The data may also have application in predicting phase boundary conditions for Fe(III) precipitation in biogeochemical processes and treatment systems involving acid sulfate waters.

Linking a cougar decline, trophic cascade, and catastrophic regime shift in Zion National Park

The strength of top-down forces in terrestrial food webs is highly debated as there are few examples illustrating the role of large mammalian carnivores in structuring biotic and abiotic systems. Based on the results of this study we hypothesize that an increase in human visitation within Zion Canyon of Zion National Park ultimately resulted in a catastrophic regime shift through pathways involving trophic cascades and abiotic environmental changes. Increases in human visitors in Zion Canyon apparently reduced cougar ( Puma concolor) densities, which subsequently led to higher mule deer ( Odocoileus hemionus) densities, higher browsing intensities and reduced recruitment of riparian cottonwood trees ( Populus fremontii), increased bank erosion, and reductions in both terrestrial and aquatic species abundance. These results may have broad implications with regard to our understanding of alternative ecosystem states where large carnivores have been removed or are being recovered.

Action bactérienne sur un mâchefer d'incinération d'ordure ménagère

Micro-organisms such as bacteria are likely to be present in the weathered municipal solid waste incinerator (MSWI) bottom ash that will be used as aggregates in road construction. Microbial activity may impact the weathering process of such material and thus the rate of leaching of potentially toxic elements. Indeed, the deterioration of rocks, like that of materials of anthropogenic origin (stained glasses, cements, blast-furnace slags), depends partly on organic compounds and micro-organisms. However, the exact role of micro-organisms remains poorly understood. Some authors suggest that they play a considerable part in the degradation of stained glass in cathedrals but they do not specify neither the mechanisms, nor even the type of micro-organism (bacteria, fungi, lichens) involved. Other authors are of the opinion that bacteria accelerate the deterioration of marine basaltic glasses due to the observation of “hair channels” that could represent bacterial activity. In our opinion, the exact role of micro-organisms remains to be demonstrated apart for some well-defined materials: degradation of books by fungi and metal drains by bacteria like Thiobacillus. There is no existing experimental validation of the role of bacterial action in the degradation of complex silicates such as the glass contained in MSWI bottom ash. The major difficulty is to measure in such complex media the rate of deterioration with reliable tracers.Although studies have been conducted on the role of bacterial cells, there is however, a lack of studies that compare the degradation due to bacterial biofilms (cells-exopolymers-solution) and the degradation that occurs in abiotic systems. As a consequence, our aim was to investigate the effect of Pseudomonas aeruginosa (a common bacteria found in the environment) on the weathering of MSWI bottom slag under well-defined conditions, similar to the natural environment (neutral pH and 25 °C).Experiments were carried out at 25 °C for 19 weeks. Two conditions were performed in parallel; the first one in a sterile medium and the second one in the presence of P. aeruginosa. The culture medium used (PS medium AOUAD et al., 2005), buffered at pH 6.7, has been developed in order to detect the greatest number of elements dissolved during deterioration. The bottom slag grains were placed in containers filled with 50 ml of medium which was renewed each week to ensure the production of a measurable quantity of bacterial cells and exopolysaccharides (biofilm). The renewed solutions were analyzed using ICP/AES (Jobin-Yvon JY 124 spectrometer) and ICP/MS (Fisons VG PQ2 + spectrometer). From the measured concentrations for Si, Mg, Ca and Sr (potential tracers), the rate of dissolution expressed in masses standardized to the reactive surface area (g/m2.j) was calculated. Rates obtained in sterile condition are higher than those of the biotic one, but they converge by the end of the experiments. For Mg and Si the rates are lower than those obtained for Ca and Sr. This may be a consequence of the precipitation of a magnesium silicate hydrate.The first remarkable observation is that the grains leached in biotic medium are agglomerated and form a compact cluster whereas the grains resulting from deterioration in the abiotic medium remain free. SEM observations indicate that by the end of the experiments, the surface of the grains leached in abiotic medium do not appear to be different to those initially present. Conversely, grains deteriorated in biotic experiments are systematically covered with exopolyssacharides which explains their agglomeration; the biofilm cements the bottom ash grains together.The rate of corrosion of bottom ash decreases quickly in biotic medium despite of the renewal of the growth medium. One explanation could be that the biofilm acts as a protective barrier, thus preventing dissolution. The rate also decreases although less rapidly in the absence of bacteria. This is probably due to the formation of a layer of precipitated minerals at the surface which has also protective properties. At the end of our experiments (19 weeks) both rates are equal.