Metal adsorption on mosses: Toward a universal adsorption model

AbstractThis study quantifies the adsorption of heavy metals on 4 typical moss species used for environmental monitoring in the moss bag technique. The adsorption of Cu2+, Cd2+, Ni2+, Pb2+ and Zn2+ onto Hypnum sp., Sphagnum sp., Pseudoscleropodium purum and Brachytecium rutabulum has been investigated using a batch reactor in a wide range of pH (1.3–11.0) and metal concentrations in solution (1.6μM–3.8mM). A Linear Programming Model (LPM) was applied for the experimental data to derive equilibrium constants and the number of surface binding sites. The surface acid–base titration performed for 4 mosses at a pH range of 3–10 in 0.1M NaNO3 demonstrated that Sphagnum sp. is the most efficient adsorbent as it has the maximal number of proton-binding sites on the surface (0.65mmolg−1). The pKa computed for all the moss species suggested the presence of 5 major functional groups: phosphodiester, carboxyl, phosphoryl, amine and polyphenols. The results of pH-edge experiments demonstrated that B. rutabulum exhibits the highest percentage of metal adsorption and has the highest number of available sites for most of the metals studied. However, according to the results of the constant pH “Langmuirian” isotherm, Sphagnum sp. can be considered as the strongest adsorbent, although the relative difference from other mosses is within 20%. The LPM was found to satisfactorily fit the experimental data in the full range of the studied solution parameters. The results of this study demonstrate a rather similar pattern of five metal adsorptions on mosses, both as a function of pH and as a metal concentration, which is further corroborated by similar values of adsorption constants. Therefore, despite the species and geographic differences between the mosses, a universal adsorption edge and constant pH adsorption isotherm can be recommended for 4 studied mosses. The quantitative comparison of metal adsorption with other common natural organic and inorganic materials demonstrates that mosses are among the most efficient natural adsorbents of heavy metals

Biomass offsets little or none of permafrost carbon release from soils, streams, and wildfire: an expert assessment

As the permafrost region warms, its large organic carbon pool will be increasingly vulnerable to decomposition, combustion, and hydrologic export. Models predict that some portion of this release will be offset by increased production of Arctic and boreal biomass; however, the lack of robust estimates of net carbon balance increases the risk of further overshooting international emissions targets. Precise empirical or model-based assessments of the critical factors driving carbon balance are unlikely in the near future, so to address this gap, we present estimates from 98 permafrost-region experts of the response of biomass, wildfire, and hydrologic carbon flux to climate change. Results suggest that contrary to model projections, total permafrost-region biomass could decrease due to water stress and disturbance, factors that are not adequately incorporated in current models. Assessments indicate that end-of-the-century organic carbon release from Arctic rivers and collapsing coastlines could increase by 75% while carbon loss via burning could increase four-fold. Experts identified water balance, shifts in vegetation community, and permafrost degradation as the key sources of uncertainty in predicting future system response. In combination with previous findings, results suggest the permafrost region will become a carbon source to the atmosphere by 2100 regardless of warming scenario but that 65%–85% of permafrost carbon release can still be avoided if human emissions are actively reduced

Homogeneous precipitation of magnesium phosphates from seawater solutions

International audienceHomogeneous (unseeded) nucleation of Mg phosphate from modified Ca-free seawater solutions was investigated at 20°C and pH of 8. Precipitated solid phase was characterized using chemical analysis, X-ray diffraction, scanning electron microscopy, and IR-spectroscopy. Effect of aqueous phosphate and ammonia concentrations and the intensity of stirring on the induction period time ( τ) of Mg phosphates nucleation were studied. A linear relationship between logarithm of bobbierite (Mg 3(PO 4) 2 · 8H 2O) saturation index and log τ was established with a slope close to 2. Aqueous NH 4+ (up to 0.002 M) has no effect on the nucleation kinetics and does not incorporate in the precipitated solid phase. Stirring of solution has a dramatic effect on nucleation kinetics: the induction period decreases by a factor of 100-10 000 in unstirred solutions compared to stirred ones. The relative diffusion/chemical reaction control mechanism of Mg phosphates precipitation from supersaturated solutions is discussed. It is shown that spontaneous inorganic precipitation of Mg-(ammonium) phosphates (struvite and bobbierite) in modern marine environment is impossible because of very sluggish kinetics

Experimental study of terrestrial plant litter interaction with aqueous solutions

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Basalt weathering in Central Siberia under permafrost conditions

Chemical weathering of basalts in the Putorana Plateau, Central Siberia, has been studied by combining chemical and mineralogical analysis of solids (rocks, soils, river sediments, and suspended matter) and fluid solution chemistry. Altogether, 70 large and small rivers, 30 soil pore waters and groundwaters and over 30 solids were sampled during July to August 2001. Analysis of multiannual data on discharge and chemical composition of several rivers of the region available from the Russian Hydrological Survey allowed rigorous estimation of mean annual major element concentrations, and dissolved and suspended fluxes associated with basalt weathering. For the rivers Tembenchi and Taimura that drain monolithologic basic volcanic rocks, the mean multiannual flux of total dissolved cations (TDS_c = Ca + Mg + Na + K) corrected for atmospheric input is 5.7 +/- 0.5 t/km(2)/yr. For the largest river Nizhniya Tunguska-draining essentially basic rocks-the TDS_c is 6.1 +/- 1.5 t/km(2)/yr. The overall CO2 consumption flux associated with basalt weathering in the studied region (similar to 700,000 km(2)) achieves 0.08 x 10(12) mol/yr, which represents only 2.6% of the total CO2 consumption associated with basalt weathering at the Earth's surface. The fluxes of suspended matter were estimated as 3.1 +/- 0.5, 9.0 +/- 0.8, and 6.5 +/- 2.0 t/km(2)/yr for rivers Taimura, Eratchimo, and Nizhniya Tunguska, respectively. Based on chemical analyses of river solutes and suspended matter, the relative dissolved versus particulate annual transport of major components is C-inorg >= C-org > Na + K > Ca > Mg > Si > Fe >= Mn >= Ti >= Al which reflects the usual order of element mobility during weathering. According to chemical and mineralogical soil and sediment analyses, alteration of basalt consists of (1) replacement of the original basaltic glass by Si-Al-Fe rich amorphous material, (2) mechanical desegregation and grinding of parent rocks, leading to accumulation of "primary" hydrothermal trioctahedral smectite, and (3) transformation of these trioctahedral (oxy)smectites and mixed-layer chlorite-smectite, into secondary dioctahedral smectite accompanied by removal of Ca, Mg, and Fe, and enrichment in Al. No vertical chemical differentiation of fluid and solid phases within the soil profile was identified. All sampled soil pore waters and groundwaters were found to be close to equilibrium with respect to chalcedony, gibbsite, halloysite, and allophanes, but strongly supersaturated with respect to goethite, nontronite, and montmorillonite. Over the annual cycle, the contribution of atmospheric precipitation, permafrost melting, underground reservoirs, litter degradation, and rock and soil mineral weathering for the overall TDS_c transport in the largest river of the region (Nizhniya Tunguska) is 9.3 +/- 3, 10 +/- 5, 10.5 +/- 5, 25 +/- 20, and 45 +/- 30%, respectively. In the summertime, direct contribution of rocks and soil mineral weathering via solid/fluid interaction does not exceed 20%. The main unknown factors of element mobilization from basalt to the river is litter degradation in the upper soil horizon and parameters of element turnover in the vegetation. Copyright (c) 2005 Elsevier Ltd

Copper isotope fractionation during its interaction with soil and aquatic microorganisms and metal oxy(hydr)oxides: Possible structural control

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Experimental determination of calcite solubility and the stability of aqueous Ca– and Na–carbonate and –bicarbonate complexes at 100–160 °C and 1–50 bar pCO2 using in situ pH measurements

International audienceThe solubility of calcite was measured at 100, 120, 140 and 160°C at 1-50 bar pCO2 in10-3-0.1 mol·kg-1 NaCl solutions using a new experimental setup involving in situ pH measurements with high-temperature solid-contact H-selective glass and two types of reference electrodes: i) Ag/AgCl in 3.5 M KCl, saturated AgCl placed in a Teflon extensible container with liquid junction, and ii) solid-contact high-T Na-selective glass electrode in the cell without liquid junction. The stability constants of NaHCO3° and NaCO3-aqueous complexes formation were determined in NaCl-Na2CO3/NaHCO3 solutions in CO2-free media and under 10 bar pCO2 from 100 to 160 °C. These values allowed calculation of the pH of the calibration solution in the system NaCl-CO2-H2O used in the cell without liquid junction with Na+-selective electrode as a reference. This highly stable, low-cost electrode system can be recommended for routine pH measurements at 4 < pH < 10 in sodium-bearing solutions up to 160°C and the critical point of CO2. The values of the stability constants of CaCO3° and CaHCO3+ aqueous complexes and calcite solubility product were generated at 100, 120, 140 and 160 °C allowing a description of the solubility of calcite in a wide range of pH and pCO2

Effect of the heterotrophic bacterium Pseudomonas reactans on olivine dissolution kinetics and implications for CO2 storage in basalts

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Recovery potential of periphytic biofilms translocated in artificial streams after industrial contamination (Cd and Zn)

International audienceMetal wastes can significantly disturb aquatic communities, particularly photosynthetic organisms, the main primary producers in freshwater running ecosystems. In this study, biofilms and diatoms were used as bioindicators to characterize the kinetics of biofilm recovery. An experimental decontamination study was conducted under laboratory conditions, after biofilm colonisation at a site subject to discharge of industrial metals (Zn and Cd) and in parallel at an upstream site, metal-free, considered as a control. After 24 days of colonisation, biofilms were translocated and maintained in the laboratory for 56 days under clean conditions (control and decontamination) or metal contamination. Various tests were conducted from the community level—measures of metal bioaccumulation, cell densities and taxonomic investigations, to the individual level—measures of teratological forms. After 56 days of decontamination, Zn and Cd concentrations in decontaminated biofilms showed a sharp decline, respectively ranging from 6.7 ± 2 to 4 ± 2.5 mg Zn g-1 DW and from 207.6 ± 24.5 to 45.4 ± 9.9 lg Cd g-1 DW. However, at the end of the experiment bioaccumulations remained significantly higher than concentrations in control biofilms. Despite a diatom evolution in biofilm assemblages, taxonomic inventories did not demonstrate a complete restoration of diatom communities in biofilms under decontamination conditions compared with controls, since metal-resistant species initially present after colonisation at the contaminated site, such as Eolimna minima, persisted in high abundance in decontaminated biofilms. Biofilms kept under metal pressure showed very high bioaccumulation capacities and a sharp decline of species diversity which allowed identification of some resistant species. Regarding these first results on the behaviour of diatom biofilms under experimental decontamination conditions, improvement of the natural hydrosystem’s chemical state appears quickly, but an eventual return to good ecological status appears delayed, with the persistence of metal-tolerant species even after 56 days