Dissolution Kinetics Of Carbonates Research Articles

Dissolution Kinetics of Carbonates in Low-Grade Microgranular Phosphate Ore Using Organic Acids as Leaching Agents

Dissolution Kinetics of Carbonates in Low-Grade Microgranular Phosphate Ore Using Organic Acids as Leaching Agents

The dissolution of metal carbonate precipitation under the external electric and magnetic fields: reactive force field molecular dynamics simulation

Abstract The dissolution of metal carbonates holds a pivotal role in diverse industrial processes, environmental occurrences, and geological formations. Grasping the fundamental mechanisms underlying these processes is imperative for enhancing industrial applications and mitigating environmental impacts. Herein, we undertake a thorough investigation employing reactive forcefieldmolecular dynamics simulations to delve into the dissolution process of metal carbonates. These simulations afford profound insights into the mechanisms and kinetics governing the process across various conditions, encompassing temperature, acidity, and external electric and magnetic fields. Although temperature itself exerts a limited influence, the study reveals a synergistic enhancement of metal carbonate dissolution kinetics when temperature is combined with static electric and magnetic fields. Our revelations offer enlightening perspectives on the intricate interplay of factors shaping dissolution processes, laying the foundation for future inquiries in this domain.

Synchronic changes of lake organic and inorganic carbon burial in response to catchment development over the past century: A case study of Shilin Karst area

有机碳和无机碳的流域输出是湖泊碳埋藏的重要驱动因子, 而喀斯特地区无机碳循环具有反应迅速且对人类活动影响敏感的特点. 在流域开发持续增强的背景下, 喀斯特地区湖泊有机碳和无机碳的来源、含量与埋藏通量可能会出现同步变化的协同模式. 本文以云南省石林喀斯特地区流域土地利用类型不同的两个中型湖泊(长湖、月湖)开展对比分析, 通过对沉积物钻孔的土壤侵蚀强度(磁化率)、流域外源输入(C∶N比值)、水动力(粒度)、营养盐(总氮、总磷)、藻类生产力(叶绿素色素)等代用指标的分析, 结合监测数据和历史资料重建了两个湖泊环境变化的近百年历史, 并定量识别了有机碳和无机碳埋藏响应流域开发的变化特征与协同模式. 沉积物磁化率和C∶N比值结果揭示了流域地表侵蚀和外源输入的阶段性特征, 同时总氮和总磷含量记录了长湖和月湖营养水平上升的长期模式. 在流域森林覆被较高(33.43%)的长湖中, 全岩和有机质C∶N比值分别与磁化率信号呈显著正相关(r=0.95和0.89, P＜0.001), 且与无机碳和有机碳含量呈显著负相关(r=-0.94, P＜0.001和r=-0.52, P=0.01), 反映了森林植被退化时流域碳输出的减少对沉积物碳含量的影响. 而在流域耕地覆被为主(60.98%)的月湖中, 全岩和有机质C∶N比值与磁化率信号呈显著负相关(r=-0.54, P＜0.01和r=-0.67, P＜0.001), 且全岩C∶N比值与无机碳含量(P=0.15)无显著关系, 反映了耕作强度的增加可能促进了水体富营养化和内源输入的增强. 在两个湖泊中, 营养水平的上升和内源生产力的增加促进了有机碳含量的快速增加. 进一步分析表明, 近百年来长湖有机碳与无机碳含量变化的同步性明显(r=0.54, P＜0.001)而在月湖中无显著关系(P=0.20, P>0.05). 两个湖泊中沉积通量的变化均与全岩C∶N比值呈显著正相关(r=0.48和0.45, P≤0.001), 且有机碳与无机碳埋藏通量均呈现同步变化的显著特征(r=0.72和0.85, P＜0.001). 其中长湖的无机碳埋藏通量显著高于有机碳埋藏通量, 而月湖的有机碳埋藏通量略高于无机碳埋藏通量, 反映了岩溶地区流域外源输入和水体富营养化的差异性驱动影响. 在流域开发增强的梯度下, 森林退化会降低流域碳输出的负荷, 而农业扩张和水体富营养化会促进藻类生长和内源有机碳的累积. 因此, 流域土地利用和水体营养水平对湖泊无机碳和有机碳埋藏变化的长期轨迹和协同模式产生了重要影响, 对喀斯特地区的碳库评估需要考虑无机碳循环的重要性.;Catchment-scale exports of organic and inorganic carbon plays an important role in affecting the lake sediment carbon burial. Inorganic carbon cycling in Karst landscapes is sensitive to human activities due to the rapid kinetics of carbonate dissolution. As with intensive watershed development, the source, content and burial loading of organic and inorganic carbon in Karst region may show a synchronous change. This study selected two medium-sized lakes (Lake Changhu and Lake Yuehu) with contrasting land uses patterns in the Shilin Karst area of central Yunnan for sediment surveys. With the proxies analyses for soil erosion (i.e. magnetic susceptibility (MS)), catchment allochthonous input (C∶N ratio), lake hydrology (particle size), nutrient levels (total phosphorus and nitrogen) and primary production (i.e. algal pigments), together with monitoring data and historical records, the history of limnological changes and catchment development over the last century for both lakes were reconstructed. Furthermore, long-term variation and synchronic pattern of sediment organic carbon (OC) and inorganic carbon (IC) burial in the context of catchment development were quantified. The sediment MS signal recorded the fluctuation in soil erosion intensity and a general pattern of long-term nutrient enrichment in both lakes. In Lake Changhu, with a higher land cover of forest (33.43%), the bulk and organic C∶N ratios were positively related with the MS signal (r=0.95 and 0.89, P < 0.001) but showed a negative relationship with sediment inorganic and organic carbon content (r=-0.94, P < 0.001 and -0.52, P=0.01), respectively, reflecting a significant impact of catchment carbon input. In Lake Yuehu, with a current land cover dominated by the cropland (60.98%), the bulk and organic C∶N ratios were negatively related with the MS signal (r=-0.54, P < 0.01 and -0.67, P < 0.001) and the bulk C∶N ratio showed no relationship with the sediment inorganic content (P=0.15), reflecting that the cropland expansion may have enhanced lake eutrophication and autochthonous input. In both lakes, nutrient enrichment and algal production enhanced the rapid OC accumulation. Additional analyses showed that there existed a significantly synchronous change between OC and IC content in Lake Changhu (r=0.54, P < 0.001) but not in Lake Yuehu (P=0.20, P>0.05). In both lakes, sediment loading was positively related with bulk C∶N ratio (r=0.48 and 0.45, P≤0.001), and there also existed a significantly synchronous change between OC and IC loadings (r=0.72 and 0.85, P < 0.001). Furthermore, the IC burial rate was significantly higher than that of OC in Lake Changhu, while IC consistently lower than OC in the nutrient-rich Lake Yuehu, reflecting differential forcing of vegetation degradation and lake eutrophication. With the intensive development in watershed, forest degradation can reduce the loading of catchment carbon export, while agricultural expansion and eutrophication would promote the growth of algae and the OC accumulation rate. Therefore, land use and lake nutrient levels can significantly impact the long-term trajectory and synchronic variation of sediment OC and IC burial. Thus, IC cycling should be considered in the regional assessment of carbon stock in karst areas.

Effects of Fe3+ on Dissolution Dynamics of Carbonate Rocks in a Shallow Burial Reservoir

Dissolution of carbonates in acidic fluids, which has attracted much research attention in recent years, is of great significance for the formation of high-quality reservoirs. The dissolution stage under low temperature and low pressure in shallow burial is one of the most important processes of reservoir dissolution and transformation. However, the dissolution dynamics of carbonate rocks in shallow burial and their formation have been controversial for a long time, and there are still disputes in the dissolution processes about how associated minerals and accessory minerals (e.g., pyrite) in carbonate reservoirs influence the formation of secondary pores. Additional metal ions in acidic fluids can change fluid properties and dissolution processes, and consequently affect reservoir quality. However, there are few laboratory studies done on the effect of associated minerals on the dissolution dynamics of carbonates. To clarify the specific impact of Fe-bearing associated minerals and Fe3+ on the dissolution of carbonates in shallow burial reservoirs, six samples of typical carbonate rocks in the Zigui area of Hubei Province, China were studied. The dissolution kinetics of carbonates in dilute hydrochloric acid and sulfuric acid solutions containing metal ions (Fe3+/Ca2+/Mn2+) at ambient temperature and pressure (T = 25 °C, P = 1 atm) were studied, by laboratory dissolution experiments combined with numerical simulations using PHREEQC. The results show that the Fe3+ is of great significance on the dissolution of carbonate rocks, while the influences of Ca2+ and Mn2+ are relatively weak. The dissolutions degrees of micritic limestone (ZG-L25), dolomitic limestone (ZG-L7) and dolomite (ZG-D9) were better than the other carbonates under the influence of metal ions (Fe3+/Ca2+/Mn2+) in acid solutions. Therefore, the dolomite reservoir of the Cambrian Qinjiamiao Formation, the dolomitic limestone reservoir of the Tianheban Formation and the limestone reservoir of the Triassic Daye Formation in the Zigui area are potential high-quality reservoirs. The carbonate reservoirs associated with Fe-bearing minerals were easier to dissolve and formed secondary pores under shallow burial. This process is beneficial to the formation of high-quality reservoirs. Moreover, the addition of Fe3+ into hydrochloric acid solution may be conducive to improving the reservoirs acidizing effect. Furthermore, the results gave innovative results from multiple perspectives of geo-material science and computational geosciences, which may provide new avenues for in-depth study of carbonate dissolution in shallow burial based on water–rock reaction, chemical dissolution, computational simulation, and geological background.

Combined unsteady denudation and climatic gradient factors constrain carbonate landscape evolution: New insights from in situ cosmogenic 36Cl

Abstract In situ cosmogenic nuclides are widely employed to quantify topographic and geomorphic landscape evolution. However, few studies are devoted to investigating possibly unsteady denudation. In this work the denudation rates of five surface bedrock and one depth profile are measured using in situ cosmogenic 36Cl in different climate zones in China; cosmogenic 36Cl is a powerful proxy for the surface denudation processes of carbonate landscapes in different climatic gradients since carbonates are more sensitive to climate change than silicates. Compiling previous worldwide surface denudation studies in different gradients, we find that: (I) denudation rate increases systematically with mean annual precipitation (MAP) in arid climatic zones (MAP lower than ~700 mm yr−1) and is dominated by long-term climatic gradients; (II) humid climatic zone (MAP greater than ~700 mm yr−1) denudation rates are about constrained to 34.1 ± 11.7 mm kyr−1 by carbonate dissolution kinetics; and (III) denudation rate is also influenced by short-term physical erosion or abrupt erosive events. Accordingly, the reconstructed evolutionary history of the Guizhou depth profile results from either a relatively high denudation rate (55.5–4.4 +5.6 mm kyr−1) and long duration exposure (274–147 +120 ka), or an alternative a low denudation rate (0.8–0.8 +13.3 mm kyr−1) and a recent abrupt erosive event (13.0–1.6 +1.9 ka). These two possible solutions suggest that assumed long-term averaged denudation rate can conceal episodic erosion events. Given tectonic quiescence we propose that climate change might mainly control an erosive event during the last glacial termination (~14 ka), which also implies that caution should be taken when determining the denudation rate of a landscape where climate change and/or tectonic activity plays an important role.

Seasonal δ13CDIC sourcing and geochemical flux in telogenetic epikarst of south‐central Kentucky

AbstractTelogenetic epikarst carbon sourcing and transport processes and their associated hydrogeochemical responses are complex and dynamic. Carbon dioxide (CO2) transport rates in the epikarst zone are often driven by hydrogeochemical responses, which influence carbonate dissolution and conduit formation. This study examines the influence of land use on carbon sourcing and carbonate dissolution kinetics through a comparative analysis of separate, but similar, epikarst systems in south‐central Kentucky. The use of high‐resolution hydrogeochemical data from multiple data loggers and isotope analysis from collected water samples reflects the processes within these epikarst aquifers, which are estimated to contribute significantly to bedrock dissolution. Results indicate that, in an agricultural setting, long‐term variability and dissolution is governed by seasonal production of CO2. In a more urbanized, shallower epikarst system, land cover may affect CO2 transport between the soil and underlying bedrock. This concentration of CO2 potentially contributes to ongoing dissolution and conduit development, irrespective of seasonality. The observed responses in telogenetic epikarst systems seem to be more similar to eogenetic settings, which is suggested to be driven by CO2 transport occurring independent of high matrix porosity. The results of this study indicate site‐specific responses with respect to both geochemical and δ13CDIC changes on a seasonal scale, despite regional geologic similarities. The results indicate that further comparative analyses between rural and urban landscapes in other karst settings is needed to delineate the impact of land use and seasonality on dissolution and carbon sourcing during karst formation processes. © 2019 John Wiley &amp; Sons, Ltd.

Equilibrium and kinetic simulation of groundwater demanganation and deironing

Analysis of chemical equilibria among iron and manganese aqueous species at various Eh-pH conditions and aqueous CO2 concentration is done. Thermodynamic and equilibrium-kinetic simulation of iron and manganese aqueous species oxidations is developed for groundwater demanganation and deironing.&#x0D; Numerical simulation of chemical interactions in the system groundwater-aqueous oxygen-rock minerals-aqueous carbon dioxide is shown that deironing is effective enough but aqueous manganese(II) concentration is increased. It occurs because (Fe,Mn)CO3 solubility rate is too slow and (Fe,Mn)CO3 dissolution and removal of aqueous iron species results in secondary MnCO3 formation.&#x0D; Using published experimental data on carbonate dissolution kinetics, iron and manganese oxidation kinetics and the critical values of rate constants of iron and manganese homogenous oxidation, iron and manganese carbonates solubility, manganese homogenous catalytical oxidation on iron hydroxide suspension are chosen. The kinetics-thermodynamics model of underground oxidation of iron and manganese by dissolved oxygen have been developed. By numerical simulation of chemical interactions in the system groundwater saturated by oxygen-stratal water-intake rock minerals shows that deironing occurs effective enough but aqueous manganese concentration increased. It happens due to aqueous manganese slow oxidation and dissolution of (Fe,Mn)CO3. Also secondary MnCO3 formation is possible due to removal of aqueous iron specis. So underground demanganation is possible if there is no (Fe,Mn)CO3 among intake rock minerals or inconvenience of water contact with it.

In-stream metabolism and atmospheric carbon sequestration in a groundwater-fed karst stream.

Atmospheric carbon sequestered in karst systems through dissolution of carbonate minerals is considered to have no net effect on long-term regional and global carbon budgets because precipitation of dissolved carbonate minerals emits CO2 back to the atmosphere. Even though recent studies have implied that rapid kinetics of carbonate dissolution coupled with the aquatic photosynthetic uptake of dissolve inorganic carbon (DIC) could facilitate a stable atmospheric C sink in karst rivers and streams, little is known about the magnitudes and long-term stability of this C sink. To assess in-stream biogeochemical processes and their role on stream C cycling, we measured diel cycles of water characteristics and chemical composition (temperature, pH, DO, SpC, DIC, Ca2+, δ13CDIC) in a groundwater-fed karst stream in southwest China. Our results show no diel variations at the groundwater discharge point (CK site) due to the absence of a sub-aquatic community (SAC). However, all hydrochemical parameters show significant diel cycle 1.3km downstream (LY site). Diel variations in pH, DO, and δ13CDIC were inversely related to diel changes in SpC, DIC, Ca2+ and pCO2. This result indicates that in-stream metabolism (photosynthesis and respiration) of SAC controls diel variations in stream water chemistry. Significant diel cycles of net ecosystem production (NEP) influences in-stream diel fluctuation of pH, DO, SIc, DIC, pCO2, Ca2+ and δ13CDIC, with gross primary production (GPP) dominating in day and ecosystem respiration (ER) dominating at the night. Absence of in-stream metabolism at CK enhances CO2 degassing from stream to the atmosphere, which is estimated to be 3-5 times higher than at LY. We estimate the carbon sink through in-stream metabolism of SAC to be 73tCkm-2a-1, which is around half the rate of the oceanic biological pump. These results imply in-stream photosynthesis sequesters DIC originating from karst weathering and controls CO2 evasion.

Experimental determination of natural carbonate rock dissolution rates with a focus on temperature dependency

The denudation of carbonate rocks at landscape scale is controlled by factors like mineral composition, temperature, precipitation, runoff, fracture spacing and vegetation cover. Knowledge on carbonate denudation is important in order to understand landscape development and long-term terrestrial/marine carbon transport, but there are few laboratory studies done on weathering rates of natural carbonate rocks under the low temperatures relevant for glacial-interglacial periods. To enhance the understanding of carbonate dissolution kinetics we studied low-temperature dissolution reactions of various natural Triassic carbonate rocks belonging to the Lower Muschelkalk in Germany. We conducted batch and flow-through experiments investigating the direct correlation of dissolution rates with temperature, and to establish whether the fine-grained carbonate rocks (micrite) are more reactive than the coarser-grained sparitic limestones. By increasing the temperature from 5 to 26°C far-from-equilibrium dissolution rates of micritic and sparitic limestone samples increased from 2.42×10−07 to 10.88×10−07 and 4.19×10−07 to 7.74×10−07molm−2s−1, respectively (Specific Surface Areas (SSA) of about 0.006–0.01m2/g). The dissolution rates of dolomite rock samples varied only slightly from 1.06×10−07 to 2.02×10−07molm−2s−1 (SSA approximately 0.002m2/g) in the temperature range 5–25°C at circum-neutral pH. The obtained apparent activation energies are in the range of earlier experiments done at higher temperatures, but there is a distinct difference between the calcite in the micrite (~51kJ/mol) and sparitic (~20–22kJ/mol) lithologies, indicating that the dissolution mechanisms are not the same. Using these activation energies in modelling of natural carbonate denudation we see that there is a clear effect of changing temperature, but this is mostly through the increased solubility at lower temperatures and not through the increasing far-from-equilibrium dissolution rates at higher temperatures. Formation of fluid pathways by preferential dissolution of framework calcite crystals is suggested to form infiltration pathways and affect denudation rates. The difference in crystal size between the micritic and sparitic limestones will affect the formation of such pathways (larger crystals may create fewer and larger conduits) and this is expected to be more important for the long-term denudation than the differences in activation energies.

Study of Calcium and Iron Carbonate Dissolution Kinetics in Order to Resolve Corrosion Problems in Carbonate Solutions

It is established that carbonate dissolution kinetics have diffusion and kinetic control, i.e., chemical reaction rate determines the transfer of calcium and carbonate ions into solution and diffusion processes determine the removal of ions into the depth of solution. Kinetics of calcite and siderite dissolution in hydrochloric acid solution in relation to medium pH are studied. Orders of dissolution reaction rate with respect to hydrogen ions n(H+) = 0.6±0.1 are calculated.

Dissolution kinetics of Devonian carbonates at circum-neutral pH, 50 bar pCO2, 105 °C, and 0.4 M: The importance of complex brine chemistry on reaction rates

The dissolution kinetics of carbonate rocks sampled from the Keg River Formation in Northeast British Columbia were measured at 50bar pCO2 and 105°C, in both natural and synthetic brines of 0.4M ionic strength. Natural brines yielded reaction rates of −12.16±0.11molcm−2s−1 for Log RCa, and −12.64±0.05 for Log RMg. Synthetic brine yielded faster rates of reaction than natural brines. Experiments performed on synthetic brines, spiked with 10mmol of either Sr or Zn, suggest that enhanced reaction rates observed in synthetic brines are due to a lack of trace ion interaction with mineral surfaces. Results were interpreted within the surface complexation model framework, allowing for the discrimination of reactive surface sites, most importantly the hydration of the >MgOH surface site. Dissolution rates extrapolated from experiments predict that CO2 injected into the Keg River Formation will dissolve a very minor portion of rock in contact with affected formation waters.

Kinetics of carbonate dissolution and its effects on the porosity and permeability of consolidated porous media

Abstract Injection of carbon dioxide into carbonate oil reservoirs is expected to promote chemical dissolution of the rock and alter its petrophysical properties. This work reports an experimental investigation on porosity and permeability alterations of carbonate samples due to the acid action of the carbonated water produced by means of solubilization of carbon dioxide in an aqueous solution. Travertine marble rocks with properties similar to Brazilian pre-salt reservoir rock were used in the tests at 9000 psi and 65 °C. Dissolution was carried out in high-pressure vessels during a total period of 240 h. Reaction was stopped at intermediate time intervals to evaluate porosity, permeability and mass loss of the samples. Results showed that the dissolution reaction between the travertine and carbonated water presents a slow kinetic, leading to a small loss of 0.2 g of sample after 240 h of reaction. However, the minor mass loss impacts strongly on the porosity and permeability of the rock. Data show that a variation of 1 wt.% on the sample mass caused by dissolution produces a change of 50% on the sample porosity and of 180% on the sample permeability. The dissolution rate is greatly faster if carbonated water is replaced by HCl aqueous solution and depends on the acid solution concentration. In addition, results lead to an exponential model that allows forecasting the mass loss as a function of time. Knowledge on the dissolution rate of carbonate samples by carbon dioxide solutions is required in EOR and CO2 storage projects to estimate the changes on the flow properties of the porous formation and the damages that can be impinged to the rock.

New progress and prospects in the study of rock-weathering-related carbon sinks

It is widely accepted that the chemical weathering of silicate potentially controls long-term climate change by providing a feedbackinteraction with atmospheric CO₂ drawdown by means of the precipitation of carbonate, while on a short time scale, the silicateweathering-related carbon sink is well matched to the carbonate-weathering-related carbon sink. However, new findings show thatowing to the rapid kinetics of carbonate dissolution and the importance of small amounts of carbonate minerals in controlling thedissolved inorganic C (DIC) of silicate watersheds, the contribution of silicate weathering to the atmospheric CO₂ sink may be only6%, while the other 94% is accounted for by carbonate weathering. On the other hand, owing to the aquatic photosynthetic uptake ofthe weathering-related DIC and burial of some of the resulting (autochthonous) organic C, the atmospheric CO₂ sink relating tocarbonate weathering might be important in controlling both short-term and long-term climate change. Another new finding is thatrock-weathering-related carbon sinks have increased with global warming and land-use change, acting as a negative mechanism forglobal warming. Future investigation should focus on the in-depth study of rock weathering processes and mechanisms in carboncapture and storage, so as to reveal the regulating potential of the carbon sink according to the climate and land use, which will servecountries in their decision making with respect to climate change. Important study topics include (1) rock weathering processes andcontrolling mechanisms of climate and land use in carbon sinks, (2) the importance of small amounts of carbonate minerals incontrolling the DIC and carbon sink of silicate watersheds, (3) the ratio of autochthonous carbon in total organic carbon, and (4) theregulating potential of rock-weathering-related carbon sinks according to climate and land use.

Atmospheric CO2 sink: Silicate weathering or carbonate weathering?

It is widely accepted that chemical weathering of Ca–silicate rocks could potentially control long-term climate change by providing feedback interaction with atmospheric CO2 drawdown by means of precipitation of carbonate, and that in contrast weathering of carbonate rocks has not an equivalent impact because all of the CO2 consumed in the weathering process is returned to the atmosphere by the comparatively rapid precipitation of carbonates in the oceans. Here, it is shown that the rapid kinetics of carbonate dissolution and the importance of small amounts of carbonate minerals in controlling the dissolved inorganic C (DIC) of silicate watersheds, coupled with aquatic photosynthetic uptake of the weatheringrelated DIC and burial of some of the resulting organic C, suggest that the atmospheric CO2 sink from carbonate weathering may previously have been underestimated by a factor of about 3, amounting to 0.477 Pg C/a. This indicates that the contribution of silicate weathering to the atmospheric CO2 sink may be only 6%, while the other 94% is by carbonate weathering. Therefore, the atmospheric CO2 sink by carbonate weathering might be significant in controlling both the short-term and long-term climate changes. This questions the traditional point of view that only chemical weathering of Ca–silicate rocks potentially controls long-term climate change.

Spatial variations in chemical weathering and CO 2 consumption in Nepalese High Himalayan catchments during the monsoon season

The major ion chemistry of the Marsyandi basin and six of its tributaries in the Nepalese Himalaya have been investigated during the monsoon months of 2002. Weekly water samples taken at 10 river monitoring stations in the Annapurna watershed over the course of 4 months provide chemical weathering data for the region at an unprecedented temporal and spatial resolution. The river chemistry of all but one basin is heavily dominated by carbonate weathering which, compared to silicate weathering, contributes 80 to 97% of the total solute load. This prevalence is due to a combination of (a) intrinsically faster dissolution kinetics of carbonates, (b) relatively high runoff and (c) glacial meltwater and low temperatures at high altitudes resulting in enhanced carbonate solubilities. Monitoring stations with headwaters in the Tethyan Sedimentary Series (TSS) are particularly carbonate-rich and slightly supersaturated with respect to calcite through half of the monsoon season. Silicate weathering in the TSS is driven largely by sulfuric acid and therefore does not contribute significantly to the drawdown of atmospheric CO 2. With respect to the tributaries in the Greater Himalayan Sequence (GHS), carbonate weathering is practically as predominant as for the TSS, in spite of the largely felsic lithology of the GHS. Relative to the TSS, the primary proton source in the GHS has shifted, with at least 80% of the protons derived from carbonic acid. Averaged over the whole field area, the CO 2 fluxes, based on silicate-derived Ca and Mg, are considerably lower than the global average. Assuming that this study area is representative of the entire range, we conclude that in situ weathering of the High Himalayas does not represent a significant sink of atmospheric carbon dioxide, despite the presence of a watershed south of the GHS that is characterized by a four times higher CO 2 consumption rate than the global average. Silicate weathering rates of all basins appear to be climate controlled, displaying a tight correlation with runoff and temperature. Given the extremely low chemical weathering under transport-limited conditions in high-altitude crystalline terrains outside of the monsoon season, this would result in virtually no chemical exhumation for 2/3 of the year in such a cold and arid climate, north of the rain shadow cast by the High Himalayas.

Inorganic carbon isotope systematics in soil profiles undergoing silicate and carbonate weathering (Southern Michigan, USA)

The upper Midwest USA features glacial-derived till materials enriched in carbonate minerals, but with the uppermost soil layer progressively leached of carbonates in the interval since glaciation. Groundwaters and groundwater-fed surface waters are profoundly influenced by carbonate mineral dissolution. Stable carbon isotope compositions of soil waters and groundwaters in two southern Michigan watersheds (Huron and Kalamazoo) were studied as a function of pH, δ 13C CO 2 , types of weathering reactions (silicate vs. carbonate), and degree of isotope equilibration. This comprehensive study of carbon isotope biogeochemistry in the vadose zone, including soil gas, soil water/groundwater, and soils (organic matter/carbonate phases), elucidates relations between the chemical weathering rates and CO 2 fluxes in the soil zone. Such information is important to evaluate responses of terrestrial ecosystems to global climate change. In shallow soil zones where only silicate weathering was occurring, respiratory CO 2 was the major source of soil water DIC with little addition from the atmospheric CO 2. Isotopic equilibration between δ 13C DIC and δ 13C CO 2 occurred in an open system with respect to soil CO 2. In the deeper soil horizons carbonate dissolution dominated soil water chemistry and saturation with respect to calcite and dolomite was attained rapidly. Mass balance calculation showed that large amounts of soil CO 2 were consumed by carbonate dissolution, such that the deeper soil zone may not have been an open system with respect to CO 2. Constant δ 13C DIC values (∼ − 11‰) were observed in these deep soil waters and also in shallow groundwaters of the Huron watershed. Thus, isotopic equilibrium might not be reached between DIC and CO 2, possibly due to a rapid kinetics of carbonate dissolution and limited gas–water exchange in the soils. If so, DIC was equally contributed by carbonate minerals ( δ 13C CaCO 3 = 0‰) in reaction with soil CO 2 ( δ 13C CO 2 = − 22‰). Soils beneath an agricultural site with a wheat/corn/soybean rotation (the Kalamazoo watershed) displayed a wide range in δ 13C CO 2 values (− 22 to − 12‰), and the δ 13C DIC of deeper soil waters in contact with carbonate minerals was controlled by seasonal variations of δ 13C CO 2 as well as by strong acids produced by nitrification and to a lesser degree by pyrite oxidation, both of which could react to dissolve carbonate minerals, in addition to carbonic acid dissolution.

Diffusional nutrient fluxes at the sediment-water interface and organic matter mineralization in an atoll lagoon (Tikehau, Tuamotu Archipelago, French Polynesia)

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 132:181-190 (1996) - doi:10.3354/meps132181 Diffusional nutrient fluxes at the sediment-water interface and organic matter mineralization in an atoll lagoon (Tikehau, Tuamotu Archipelago, French Polynesia) Charpy-Roubaud C, Charpy L, Sarazin G Fluxes of dissolved inorganic N, P and Si from the sediments were calculated using pore water gradient concentration measured using the peeper technique at 8 stations in the lagoon of Tikehau Atoll, French Polynesia. Nutrient concentrations of pore water reached maximum values of 130 uM NH4, 7 uM PO4 and 30 uM SiO2. Fluxes calculated from concentration gradients were positive at all stations. N and P fluxes represented 6 and 4% of the N and P deposition rates and between 0.1 and 6.8% of the N requirements and between 0.1 and 1.7 % of the P requirements of lagoonal primary production. Study of geochemical processes and stoichiometry of the organic matter shows that a great part of deposited organic matter is oxidized in the water column. The amount of organic matter oxidized inside the sediment is estimated to 2.5 mg kg-1 in the upper centimeter and 5.2 mg kg-1 below. Pore water was supersaturated with respect to aragonite and calcite, and the kinetics of carbonate dissolution were faster than the reverse reaction. The dissolution/precipitation of carbonate plays an important role in the composition of the pore water. Nutrient fluxes . Sediment . Pore water . Peeper . Atoll lagoon . Mineralisation Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 132. Publication date: February 29, 1996 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1996 Inter-Research.

Labormessung der Sättigungslänge als Maβ für die Lösungskinetik von Karbonaten im Grundwasser

Following the theory of Buhmann and Dreybrodt (1985a,b, 1987) a method is proposed, which allows an easy and direct determination of carbonate dissolution kinetics by measuring the saturation length in sandy aquifer material. The results are in good agreement with the measurements of other authors, who used laboratory techniques which are very difficult to apply to natural aquifer situations. Using the saturation-length-method, the dissolution kinetics of calcite, dolomite and siderite were compared. The influence of some dissolution inhibitors was quantified.