Silicate and carbonate mineral weathering in soil profiles developed on Pleistocene glacial drift (Michigan, USA): Mass balances based on soil water geochemistry     

Lixin Jin  Erika L. Williams  Lynn M. Walter 《Geochimica et cosmochimica acta》2008,72(4):1027-1042

Geochemistry of soil, soil water, and soil gas was characterized in representative soil profiles of three Michigan watersheds. Because of differences in source regions, parent materials in the Upper Peninsula of Michigan (the Tahquamenon watershed) contain only silicates, while those in the Lower Peninsula (the Cheboygan and the Huron watersheds) have significant mixtures of silicate and carbonate minerals. These differences in soil mineralogy and climate conditions permit us to examine controls on carbonate and silicate mineral weathering rates and to better define the importance of silicate versus carbonate dissolution in the early stage of soil-water cation acquisition.Soil waters of the Tahquamenon watershed are the most dilute; solutes reflect amphibole and plagioclase dissolution along with significant contributions from atmospheric precipitation sources. Soil waters in the Cheboygan and the Huron watersheds begin their evolution as relatively dilute solutions dominated by silicate weathering in shallow carbonate-free soil horizons. Here, silicate dissolution is rapid and reaction rates dominantly are controlled by mineral abundances. In the deeper soil horizons, silicate dissolution slows down and soil-water chemistry is dominated by calcite and dolomite weathering, where solutions reach equilibrium with carbonate minerals within the soil profile. Thus, carbonate weathering intensities are dominantly controlled by annual precipitation, temperature and soil pCO₂. Results of a conceptual model support these field observations, implying that dolomite and calcite are dissolving at a similar rate, and further dissolution of more soluble dolomite after calcite equilibrium produces higher dissolved inorganic carbon concentrations and a Mg²⁺/Ca²⁺ ratio of 0.4.Mass balance calculations show that overall, silicate minerals and atmospheric inputs generally contribute <10% of Ca²⁺ and Mg²⁺ in natural waters. Dolomite dissolution appears to be a major process, rivaling calcite dissolution as a control on divalent cation and inorganic carbon contents of soil waters. Furthermore, the fraction of Mg²⁺ derived from silicate mineral weathering is much smaller than most of the values previously estimated from riverine chemistry.  相似文献   

Rayleigh distillation and the depth profile of C/C ratios of soil organic carbon from soils of disparate texture in Iron Range National Park, Far North Queensland, Australia     

Jonathan G. Wynn 《Geochimica et cosmochimica acta》2005,69(8):1961-1973

A depth- and particle size-specific analysis of soil organic carbon (SOC) and its isotopic composition was undertaken to investigate the effects of soil texture (or particle size) on the depth profile of stable carbon isotopic composition of SOC (δ¹³C_SOC) in two tropical soils. Depth-specific samples from two soil profiles of markedly different texture (coarse grained and fine grained) were separated into particle size classes and analyzed for the (mass/mass) concentration of SOC (C) and δ¹³C_SOC. Within 1 m of the soil surface, δ¹³C_SOC in the coarse-textured soil increases by 1.3 to 1.6‰, while δ¹³C_SOC from the fine-textured soil increase by as much as 3.8 to 5.5‰. This increasing depth trend in the coarse-textured soil is approximately linear with respect to normalized C, while the increase in the fine-textured soil follows a logarithmic function with respect to normalized C. A model of Rayleigh distillation describing isotope fractionation during decomposition of soil organic matter (SOM) accounts for the depth profile of δ¹³C_SOC in the fine-textured soil, but does not account for the depth profile observed in the coarse-textured soil despite their similar climate, vegetation, and topographic position. These results suggest that kinetic fractionation during humification of SOM leads to preferential accumulation of ¹³C in association with fine mineral particles, or aggregates of fine mineral particles in fine-textured soils. In contrast, the coarse-textured soil shows very little applicability of the Rayleigh distillation model. Rather, the depth profile of δ¹³C_SOC in the coarse-textured soil can be accounted for by mixing of soil carbon with different isotopic ratios.  相似文献   

Microbial dissolution of calcite at T = 28 °C and ambient pCO₂     

Andrew D. Jacobson  Lingling Wu 《Geochimica et cosmochimica acta》2009,73(8):2314-2331

This study used batch reactors to quantify the mechanisms and rates of calcite dissolution in the presence and absence of a single heterotrophic bacterial species (Burkholderia fungorum). Experiments were conducted at T = 28°C and ambient pCO₂ over time periods spanning either 21 or 35 days. Bacteria were supplied with minimal growth media containing either glucose or lactate as a C source, NH₄⁺ as an N source, and H₂PO₄⁻ as a P source. Combining stoichiometric equations for microbial growth with an equilibrium mass-balance model of the H₂O-CO₂-CaCO₃ system demonstrates that B. fungorum affected calcite dissolution by modifying pH and alkalinity during utilization of ionic N and C species. Uptake of NH₄⁺ decreased pH and alkalinity, whereas utilization of lactate, a negatively charged organic anion, increased pH and alkalinity. Calcite in biotic glucose-bearing reactors dissolved by simultaneous reaction with H₂CO₃ generated by dissolution of atmospheric CO₂ (H₂CO₃ + CaCO₃ → Ca²⁺ + 2HCO₃⁻) and H⁺ released during NH₄⁺ uptake (H⁺ + CaCO₃ → Ca²⁺ + HCO₃⁻). Reaction with H₂CO₃ and H⁺ supplied ∼45% and 55% of the total Ca²⁺ and ∼60% and 40% of the total HCO₃⁻, respectively. The net rate of microbial calcite dissolution in the presence of glucose and NH₄⁺ was ∼2-fold higher than that observed for abiotic control experiments where calcite dissolved only by reaction with H₂CO₃. In lactate bearing reactors, most H⁺ generated by NH₄⁺ uptake reacted with HCO₃⁻ produced by lactate oxidation to yield CO₂ and H₂O. Hence, calcite in biotic lactate-bearing reactors dissolved by reaction with H₂CO₃ at a net rate equivalent to that calculated for abiotic control experiments. This study suggests that conventional carbonate equilibria models can satisfactorily predict the bulk fluid chemistry resulting from microbe-calcite interactions, provided that the ionic forms and extent of utilization of N and C sources can be constrained. Because the solubility and dissolution rate of calcite inversely correlate with pH, heterotrophic microbial growth in the presence of nonionic organic matter and NH₄⁺ appears to have the greatest potential for enhancing calcite weathering relative to abiotic conditions.  相似文献   

Kinetics of calcite precipitation induced by ureolytic bacteria at 10 to 20°C in artificial groundwater     

F.G. Ferris  V. Phoenix  R.W. Smith 《Geochimica et cosmochimica acta》2004,68(8):1701-1710

The kinetics of calcite precipitation induced in response to the hydrolysis of urea by Bacillus pasteurii at different temperatures in artificial groundwater (AGW) was investigated. The hydrolysis of urea by B. pasteurii exhibited a temperature dependence with first order rate constants of 0.91 d⁻¹ at 20°C, 0.18 d⁻¹ at 15°C, and 0.09 d⁻¹ at 10°C. At all temperatures, the pH of the AGW increased from 6.5 to 9.3 in less than 1 d. Dissolved Ca²⁺ concentrations decreased in an asymptotic fashion after 1 d at 20°C and 15°C, and 2 d at 10°C. The loss of Ca²⁺ from solution was accompanied by the development of solid phase precipitates that were identified as calcite by X-ray diffraction. The onset of calcite precipitation at each temperature occurred after similar amounts of urea were hydrolyzed, corresponding to 8.0 mM NH₄⁺. Specific rate constants for calcite precipitation and critical saturation state were derived from time course data following a second-order chemical affinity-based rate law. The calcite precipitation rate constants and critical saturation states varied by less than 10% between the temperatures with mean values of 0.16 ± 0.01 μmoles L⁻¹ d⁻¹ and 73 ±3, respectively. The highest calcite precipitation rates (ca. 0.8 mmol L⁻¹ d⁻¹) occurred near the point of critical saturation. While unique time course trajectories of dissolved Ca²⁺ concentrations and saturation state values were observed at different temperatures, calcite precipitation rates all followed the same asymptotic profile decreasing with saturation state regardless of temperature. This emphasizes the fundamental kinetic dependence of calcite precipitation on saturation state, which connects the otherwise dissimilar temporal patterns of calcite precipitation that evolved under the different temperature and biogeochemical regimes of the experiments.  相似文献   

Carbonate dissolution in the guts of benthic deposit feeders: A numerical model     

H. Jansen  M.J. Ahrens 《Geochimica et cosmochimica acta》2004,68(20):4077-4092

We present a numerical model to quantify calcite dissolution in the guts of deposit feeding invertebrates. Deposit feeder guts were modeled as constantly stirred reactors (CSTRs) following terminology from digestion theory. Saturation state and dissolution of calcium carbonate were calculated from changes in total dissolved carbon dioxide and alkalinity resulting from sediment passage through the digestive tract, while accounting for dissolution of calcite and respiration of organic carbon. Typical dissolution rates for a gut volume of 1 ml ranged between 0.5-4 mg calcite d⁻¹. Sensitivity analysis revealed gut pH, sediment organic matter (OM) content and OM reactivity to be the critical parameters determining calcite dissolution rate. Carbonate dissolution rate was inversely related to gut pH. However, calcite dissolution was found to be possible even at alkaline gut pH due to respiration by intestinal microbes. The kinetics of calcite dissolution had only marginal influence on daily calcite dissolution rates: Varying the calcite dissolution rate constant κ by six orders of magnitude affected calcite dissolution rates by less than a factor of 10. Calcite dissolution rates were calculated for 4 different hydrographic regimes that differed in their content of sedimentary calcite and OM and furthermore in their OM reactivity. Highest dissolution rates were calculated for the shallow water setting, where relatively high OM content facilitated high microbial respiration rates depressing gut pH. However, dissolution rates for the deep sea setting were only slightly lower, due to greatly elevated ingestion rates resulting from low OM content. As a consequence of much higher faunal abundances, shallow-water benthos is likely to contribute the vast majority of gut-mediated carbonate dissolution. Nevertheless, the fraction of sedimentary calcite that dissolves during one gut passage is probably too small to be observable by simple gravimetric analysis. This may explain the notable scarcity of evidence for gut-mediated carbonate dissolution in the literature to date. Assuming depth-dependent calcite dissolution rates and deposit feeder abundances, we estimate gut-mediated carbonate dissolution to contribute approximately 5% of the annual global sedimentary carbonate dissolution rate, which corresponds to an average calcite dissolution rate of approximately 0.5 mg m⁻² d⁻¹ for the entire ocean floor.  相似文献   

Climatic dependence of stable carbon and oxygen isotope signals recorded in speleothems: From soil water to speleothem calcite   总被引：3，自引：0，他引：3  

Wolfgang Dreybrodt  Denis Scholz 《Geochimica et cosmochimica acta》2011,75(3):734-752

Understanding the relationship between stable isotope signals recorded in speleothems (δ¹³C and δ¹⁸O) and the isotopic composition of the carbonate species in the soil water is of great importance for their interpretation in terms of past climate variability. Here the evolution of the carbon isotope composition of soil water on its way down to the cave during dissolution of limestone is studied for both closed and open-closed conditions with respect to CO₂.The water entering the cave flows as a thin film towards the drip site. CO₂ degasses from this film within approx. 10 s by molecular diffusion. Subsequently, chemical and isotopic equilibrium is established on a time scale of several 10-100 s. The δ¹³C value of the drip water is mainly determined by the isotopic composition of soil CO₂. The evolution of the δ¹⁸O value of the carbonate species is determined by the long exchange time T_ex, between oxygen in carbonate and water of several 10,000 s. Even if the oxygen of the CO₂ in soil water is in isotopic equilibrium with that of the water, dissolution of limestone delivers oxygen with a different isotopic composition changing the δ¹⁸O value of the carbonate species. Consequently, the δ¹⁸O value of the rainwater will only be reflected in the drip water if it has stayed in the rock for a sufficiently long time.After the water has entered the cave, the carbon and oxygen isotope composition of the drip water may be altered by CO₂-exchange with the cave air. Exchange times, , of about 3000 s are derived. Thus, only drip water, which drips in less than 3000 s onto the stalagmite surface, is suitable to imprint climatic signals into speleothem calcite deposited from it.Precipitation of calcite proceeds with time constants, τ_p, of several 100 s. Different rate constants and equilibrium concentrations for the heavy and light isotopes, respectively, result in isotope fractionation during calcite precipitation. Since T_ex ? τ_p, exchange with the oxygen in the water can be neglected, and the isotopic evolution of carbon and oxygen proceed analogously. For drip intervals T_d < 0.1τ_p the isotopic compositions of both carbon and oxygen in the solution evolve linearly in time. The calcite precipitated at the apex of the stalagmite reflects the isotopic signal of the drip water.For long drip intervals, when calcite is deposited from a stagnant water film, long drip intervals may have a significant effect on the isotopic composition of the DIC. In this case, the isotopic composition of the calcite deposited at the apex must be determined by averaging over the drip interval. Such processes must be considered when speleothems are used as proxies of past climate variability.  相似文献   

Calcite Dissolution in Deionized Water from 50°C to 250°C at 10 MPa: Rate Equation and Reaction Order     

GONG Qingjie  DENG Jun  WANG Qingfei  YANG Liqiang  SHE Min 《《地质学报》英文版》2008,82(5):994-1001

Carbonate minerals and water （or geofluids） reactions are important for modeling of geochemical processes and have received considerable attention over the past decades. The calcite dissolution rates from 50℃ to 250℃ at 10 MPa in deionized water with a flow rate varying from 0.2 to 5 mL/min were experimentally measured in a continuous flow column pressure vessel reactor. The dissolution began near the equilibrium with c/ceq 〉 0.3 and finally reached the equilibrium at 100℃-250℃, so the corresponding solubility was also determined as 1.87, 2.02, 2.02 and 1.88×10^-4.mol/L at 100℃, 150℃, 200℃ and 250℃ respectively, which was first increasing and then switching to decreasing with temperature and the maximum value might occur between 150℃ and 200℃. The experimental dissolution rate not only increased with temperature, but also had a rapid increase between 150℃ and 200℃ at a constant flow rate of 4 mL/min. The measured dissolution rates can be described using rate equations of R = k（1-c/ceq）n or R = kc-n. In these equations the reaction order n changed with temperature, which indicates that n was a variable rather than a constant, and the activation energy was 13.4 kJ/mol calculated with R = k（1-c/ceq）n or 18.0 kJ/mol with R = kc^-n, which is a little lower than the surface controlled values. The varied reaction order and lower activation energy indicates that calcite dissolution in this study is a complex interplay of diffusion controlled and surface controlled processes.  相似文献   

Mechanism, rates, and consequences of basaltic glass dissolution: II. An experimental study of the dissolution rates of basaltic glass as a function of pH and temperature     

Sigurdur R. Gislason  Eric H. Oelkers 《Geochimica et cosmochimica acta》2003,67(20):3817-3832

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Dissolution kinetics of soil clays in sulfuric acid solutions: Ionic strength and temperature effects     

《Applied Geochemistry》2014

Significant amounts of sulfuric acid (H₂SO₄) rich saline water can be produced by the oxidation of sulfide minerals contained in inland acid sulfate soils (IASS). In the absence of carbonate minerals, the dissolution of phyllosilicate minerals is one of very few processes that can provide long-term acid neutralisation. It is therefore important to understand the acid dissolution behavior of naturally occurring clay minerals from IASS under saline–acidic solutions. The objective of this study was to investigate the dissolution of a natural clay-rich sample under saline–acidic conditions (pH 1–4; ionic strengths = 0.01 and 0.25 M; 25 °C) and over a range of temperatures (25–45 °C; pH 1 and pH 4). The clay-rich sample referred to as Bottle Bend clay (BB clay) used was from an IASS (Bottle Bend lagoon) in south-western New South Wales (Australia) and contained smectite (40%), illite (27%), kaolinite (26%) and quartz (6%). Acid dissolution of the BB clay was initially rapid, as indicated by the fast release of cations (Si, Al, K, Fe, Mg). Relatively higher Al (pH 4) and K (pH 2–4) release was obtained from BB clay dissolution in higher ionic strength solutions compared to the lower ionic strength solutions. The steady state dissolution rate (as determined from Si, Al and Fe release rates; R_Si, R_Al, R_Fe) increased with decreasing solution pH and increasing temperature. For example, the highest log R_Si value was obtained at pH 1 and 45 °C (−9.07 mol g⁻¹ s⁻¹), while the lowest log R_Si value was obtained at pH 4 and 25 °C (−11.20 mol g⁻¹ s⁻¹). A comparison of these results with pure mineral dissolution rates from the literature suggests that the BB clay dissolved at a much faster rate compared to the pure mineral samples. Apparent activation energies calculated for the clay sample varied over the range 76.6 kJ mol⁻¹ (pH 1) to 37.7 kJ mol⁻¹ (pH 4) which compare very well with the activation energy values for acidic dissolution of monomineralic samples e.g. montmorillonite from previous studies. The acid neutralisation capacity (ANC) of the clay sample was calculated from the release of all structural cations except Si (i.e. Al, Fe, K, Mg). According to these calculations an ANC of 1.11 kg H₂SO₄/tonne clay/day was provided by clay dissolution at pH 1 (I = 0.25 M, 25 °C) compared to an ANC of 0.21 kg H₂SO₄/tonne clay/day at pH 4 (I = 0.25 M, 25 °C). The highest ANC of 6.91 kg H₂SO₄/tonne clay/day was provided by clay dissolution at pH 1 and at 45 °C (I = 0.25 M), which is more than three times higher than the ANC provided under the similar solution conditions at 25 °C. In wetlands with little solid phase buffering available apart from clay minerals, it is imperative to consider the potential ANC provided by the dissolution of abundantly occurring phyllosilicate minerals in devising rehabilitation schemes.  相似文献   

The geochemical effects of benzene,toluene, and xylene (BTX) biodegradation     

《Applied Geochemistry》1997,12(3):291-303

The geochemical effects of microbially mediated degradation of aromatic hydrocarbons were observed as changes in solution composition of an artificial groundwater in packed-sand laboratory columns. Benzene, toluene, and xylene, both individually and in a combined fashion, were used as substrates in biodegradation experiments conducted under oxygenated and anoxic conditions in columns filled with quartz, calcite, or Fe³⁺-coated quartz sand. Typically, column effluent had increased concentrations of dissolved inorganic C, decreased pH, and decreased concentrations of NO₃ and dissolved O₂ relative to column influent. Efficiency of CO₂ generation was similar for the three different substrates, ranging from 22.5 to 26.6% organic C converted to CO₂. When all three substrates were combined, the percentage of CO₂ produced fell within the range observed in the single substrate experiments. Nitrate disappearance was more varied as a function of substrate identity, with greatest amounts lost when toluene was the substrate. Calcite dissolved as a result of CO₂ generated during the biodegradation reactions, and empirically calculated dissolution rates varied between 1.9 and 4.0 x 10⁻⁹ mmol cm⁻² s⁻¹. The calcite dissolution rate was slower than the biodegradation rate, as evidenced by excess generation of CO₂ relative to Ca²⁺ production. The decrease in pH was less in experiments with calcite present than in those with quartz sand present due to buffering by calcite dissolution. Dissolution of Fe oxyhydroxides was not observed under any experimental conditions.  相似文献   

A fundamental equation for calcite dissolution kinetics   总被引：1，自引：0，他引：1  

E.L. Sjöberg 《Geochimica et cosmochimica acta》1976,40(4):441-447

A fundamental rate equation for the dissolution of calcite in a pure 0.7 M KC1 solution has been determined. Between pH 8.0 and 10.1 the kinetics of the dissolution reaction can be expressed by the equation , where d[Ca²⁺]/dt is the rate in mole cm^?3s^?1, k is the apparent rate constant in s^?1 cm^?2, A is the calcite surface area and C is the square root of the calcite solubility constant. The apparent rate constant at 20°C is 9.5 × 10^?6s^?1cm^?2. The apparent activation energy for the reaction between 5 and 50°C is 8.4 kcal mole^?1.The reaction rate is pH independent above pH = 7.5. At pH values less than 8, [CO₃^2?] becomes negligible, and the rate becomes fast and should be dependent on the calcite surface area alone, if there is no change in mechanism.The stirring coefficient between 2.8 and 11.1 rev s^?1 is 0.33. This, together with the relatively high activation energy, indicates that the reaction is mainly chemically controlled.Interpolation of the experimental results into seawater systems gives a computed rate several magnitudes greater than the observed rate, but considerably less than that calculated for a diffusion-controlled reaction.  相似文献   

Crystal growth of calcite from calcium bicarbonate solutions at constant P_CO2 and 25°C: a test of a calcite dissolution model     

Michael M Reddy  L.Niel Plummer  E Busenberg 《Geochimica et cosmochimica acta》1981,45(8):1281-1289

A highly reproducible seeded growth technique was used to study calcite crystallization from calcium bicarbonate solutions at 25°C and fixed carbon dioxide partial pressures between 0.03 and 0.3 atm. The results are not consistent with empirical crystallization models that have successfully described calcite growth at low P_CO2 (< 10^?3 atm). Good agreement was found between observed crystallization rates and those calculated from the calcite dissolution rate law and mechanism proposed by Plummer et al. (1978).  相似文献