Photochemical processing of dissolved organic matter (DOM) in natural waters can alter its composition and structure, supply particulate organic matter (POM) to sediments, and deliver modified terrestrial DOM to the ocean. Our studies show that terrestrial DOM exposed to simulated sunlight is altered to produce POM with a markedly different molecular composition enriched with newly formed aliphatic and condensed aromatic molecules. This process is closely tied to the chemistry of iron, which primarily exists as dissolved Fe(II) and Fe(III)–organic complexes in initial DOM and photochemically matures to Fe(III) oxyhydroxides before coprecipitating out with POM. The newly formed condensed aromatic compounds resemble black carbon, which until now was thought to be produced by only combustion. These new molecules contribute a pool of Fe-rich, aliphatic, and black carbon-like organic matter to sediments as the terrestrial DOM is transported through rivers. We estimate that the annual global flux of this photoproduced black carbon, most of which may be preserved in sediments, is nearly equivalent to the estimated flux of dissolved black carbon to the ocean from all other sources.

Previous studies investigating organic-rich tundra have reported that increasing biodegradation of Arctic tundra soil organic carbon (SOC) under warming climate regimes will cause increasing CO 2 and CH 4 emissions. Organic-poor, mineral cryosols, which comprise 87% of Arctic tundra, are not as well characterized. This study examined biogeochemical processes of 1 m long intact mineral cryosol cores (1-6% SOC) collected in the Canadian high Arctic. Vertical profiles of gaseous and aqueous chemistry and microbial composition were related to surface CO 2 and CH 4 fluxes during a simulated spring/summer thaw under light versus dark and in situ versus water saturated treatments. CO 2 fluxes attained 0.8 ± 0.4 mmol CO 2 m À2 h À1 for in situ treatments, of which 85 ± 11% was produced by aerobic SOC oxidation, consistent with field observations and metagenomic analyses indicating aerobic heterotrophs were the dominant phylotypes. The Q 10 values of CO 2 emissions ranged from 2 to 4 over the course of thawing. CH 4 degassing occurred during initial thaw; however, all cores were CH 4 sinks at atmospheric concentration CH 4 . Atmospheric CH 4 uptake rates ranged from À126 ± 77 to À207 ± 7 nmol CH 4 m À2 h À1 with CH 4 consumed between 0 and 35 cm depth.Metagenomic and gas chemistry analyses revealed that high-affinity Type II methanotrophic sequence abundance and activity were highest between 0 and 35 cm depth. Microbial sulfate reduction dominated the anaerobic processes, outcompeting methanogenesis for H 2 and acetate. Fluxes, microbial community composition, and biogeochemical rates indicate that mineral cryosols of Axel Heiberg Island act as net CO 2 sources and atmospheric CH 4 sinks during summertime thaw under both in situ and water saturated states.

Rates of hydrolyses of p-nitrophenyl acetate, hexanoate, and octanoate in borate buffer solutions at 30 °C are 2.3-16.5 times faster in the presence of 1.2 mg mL -1 quaternary ammonium ion exchange latex particles than those obtained in water alone. The latexes were constructed by emulsion copolymerization of styrene, butyl methacrylate, or 2-ethylhexyl methacrylate with 25 wt % vinylbenzyl chloride (VBC), 1% divinylbenzene, and 1% styrylmethyl(trimethylammonium chloride) followed by quaternization of the VBC units with either trimethylamine or tributylamine. Analysis of the kinetics as a function of particle concentration, pH, and buffer concentration using an ion-exchange model provided partition coefficients of the p-nitrophenyl esters, intraparticle second-order rate constants, and ion-exchange selectivity coefficients. The major contributors to the enhanced rates are the partition coefficient favoring absorption of the p-nitrophenyl ester into the latex by a factor as large as 90 000 and intraparticle hydroxide concentrations up to 10 times higher than those obtained in the external water. The intraparticle secondorder rate constants differ little from those in water.

Elevated levels of fluoride (F(-)) in groundwaters of granitic and basaltic terrains pose a major environmental problem and are affecting millions of people all over the world. Hydroxyapatite (HA) has been shown to be a strong sorbent for F(-); however, low permeability of synthetic HA results in poor sorption efficiency. Here we provide a novel method of synthesizing nano- to micrometer sized HA on the surfaces of granular limestone to improve the sorption efficiency of the HA-based filter. Our experiments with granular limestone (38-63, 125-500 μm) and dissolved PO4(3-) (0.5-5.3 mM) as a function of pH (6-8) and temperature (25-80 °C) indicated rapid formation of nano- to micrometer sized HA crystals on granular limestone with the maximum surface coverage at lower pH and in the presence of multiple additions of aqueous PO4(3-). The HA crystal morphology varied with the above variables. The sorption kinetics and magnitude of F(-) sorption by HA-coated-fine limestone are comparable to those of pure HA, and the F(-) levels dropped to below the World Health Organization's drinking water limit of 79 μM for F(-) concentrations commonly encountered in contaminated potable waters, suggesting that these materials could be used as effective filters. Fluorine XANES spectra of synthetic HA reacted with F(-) suggest that the mode of sorption is through the formation of fluoridated-HA or fluorapatite at low F(-) levels and fluorite at high F(-) loadings.

Understanding the surface reactivity of clay minerals is necessary for accurate prediction of natural weathering rates due to the ubiquity of clays in the environment as weathering products of primary minerals. However, the reactivity of the heterogeneous surfaces of a clay can be difficult to characterize as clay mineral edge sites often react at different rates or via different mechanisms than sites on the basal planes. Ultimately, a method is needed to probe quantitatively the reactive surface sites in order to predict clay mineral dissolution rates. In this study, solid-state NMR spectroscopy has been utilized to investigate surface hydroxyl species and their relation to clay surface reactivity. The surfaces of two kaolinite samples (KGa-1b and KGa-2) and two montmorillonite samples (STx-1b and SWy-2) were reacted with the probe molecule (3,3,3-trifluoropropyl)dimethylchlorosilane (TFS), which binds selectively to reactive non-hydrogen bonded Q3Si hydroxyl sites. Quantification of 19F spins in the TFS-treated samples using 19F magic angle spinning NMR peak intensities provides a sensitive measure of the number of reactive hydroxyl sites on a mass normalized (per gram) basis. The reactive surface site densities of KGa-1b and KGa-2 were found to be proportional to published atomic force microscopy edge site fractions. An example from KGa-1b dissolution after 10 days at pH 2.9 and 21 °C revealed no significant change in Brunauer−Emmett−Teller specific surface area, but a 25% decrease in reactive surface site density. We posit this site density determined by solid-state NMR is proportional to the reactive surface area of each clay mineral and its use in future dissolution studies is warranted to investigate how changes in reactive surface area can be tied to decreases in rates of silicon and aluminum release into solution.

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The diffusion of tracers of silver and cadmium has been measured in Ag-Cd alloys over the range 31 to 37 atyo Cd, thus extending the data of Schoen to compositions near to the phase boundary, and facilitating a comparison with Zener relaxation studies by Turner, Dozier, and Williams (see preceding paper). The present diffusion results fit smoothly onto an extrapolation of Schoen's data, but the decrease in activation energies with increasing cadmium content appears to flatten out a t the higher concentrations. It is suggested that a temperature dependence of the short range order may contribute to the activation energies.

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