The Role of CaCO<Subscript>3</Subscript> Reactions in the Contemporary Oceanic CO<Subscript>2</Subscript> Cycle

The present analysis adjusts previous estimates of global ocean CaCO₃ production rates substantially upward, to 133 × 10¹² mol yr^?1 plankton production and 42 × 10¹² mol yr^?1 shelf benthos production. The plankton adjustment is consistent with recent satellite-based estimates; the benthos adjustment includes primarily an upward adjustment of CaCO₃ production on so-called carbonate-poor sedimentary shelves and secondarily pays greater attention to high CaCO₃ mass (calcimass) and turnover of shelf communities on temperate and polar shelves. Estimated CaCO₃ sediment accumulation rates remain about the same as they have been for some years: ~20 × 10¹² mol yr^?1 on shelves and 11 × 10¹² mol yr^?1 in the deep ocean. The differences between production and accumulation of calcareous materials call for dissolution of ~22 × 10¹² mol yr^?1 (~50 %) of shelf benthonic carbonate production and 122 × 10¹² mol yr^?1 (>90 %) of planktonic production. Most CaCO₃ production, whether planktonic or benthonic, is assumed to take place in water depths of <100 m, while most dissolution is assumed to occur below this depth. The molar ratio of CO₂ release to CaCO₃ precipitation (CO₂↑/CaCO₃↓) is <1.0 and varies with depth. This ratio, Ψ, is presently about 0.66 in surface seawater and 0.85 in ocean waters deeper than about 1000 m. The net flux of CO₂ associated with CaCO₃ reactions in the global ocean in late preindustrial time is estimated to be an apparent influx from the atmosphere to the ocean, of +7 × 10¹² mol C yr^?1, at a time scale of 10²–10³ years. The CaCO₃-mediated influx of CO₂ is approximately offset by CO₂ release from organic C oxidation in the water column. Continuing ocean acidification will have effects on CaCO₃ and organic C metabolic responses to the oceanic inorganic C cycle, although those responses remain poorly quantified.     

Freshwater-Saltwater Mixing Effects on Dissolved Carbon and CO<Subscript>2</Subscript> Outgassing of a Coastal River Entering the Northern Gulf of Mexico

The delivery of dissolved carbon from rivers to coastal oceans is an important component of the global carbon budget. From November 2013 to December 2014, we investigated freshwater-saltwater mixing effects on dissolved carbon concentrations and CO₂ outgassing at six locations along an 88-km-long estuarine river entering the Northern Gulf of Mexico with salinity increasing from 0.02 at site 1 to 29.50 at site 6 near the river’s mouth. We found that throughout the sampling period, all six sites exhibited CO₂ supersaturation with respect to the atmospheric CO₂ pressure during most of the sampling trips. The average CO₂ outgassing fluxes at site 1 through site 6 were 162, 177, 165, 218, 126, and 15 mol m^?2 year^?1, respectively, with a mean of 140 mol m^?2 year^?1 for the entire river reach. In the short freshwater river reach before a saltwater barrier, 0.079 × 10⁸ kg carbon was emitted to the atmosphere during the study year. In the freshwater-saltwater mixing zone with wide channels and river lakes, however, a much larger amount of carbon (3.04 × 10⁸ kg) was emitted to the atmosphere during the same period. For the entire study period, the river’s freshwater discharged 0.25 × 10⁹ mol dissolved inorganic carbon (DIC) and 1.77 × 10⁹ mol dissolved organic carbon (DOC) into the mixing zone. DIC concentration increased six times from freshwater (0.24 mM) to saltwater (1.64 mM), while DOC showed an opposing trend, but to a lesser degree (from 1.13 to 0.56 mM). These findings suggest strong effects of freshwater-saltwater mixing on dissolved carbon dynamics, which should be taken into account in carbon processing and budgeting in the world’s estuarine systems.     

Rates of Biotite Weathering,and Clay Mineral Transformation and Neoformation,Determined from Watershed Geochemical Mass-Balance Methods for the Coweeta Hydrologic Laboratory,Southern Blue Ridge Mountains,North Carolina,USA

Biotite is a common constituent of silicate bedrock. Its weathering releases plant nutrients and consumes atmospheric CO₂. Because of its stoichiometric relationship with its transformational weathering product and sensitivity to botanical activity, calculating biotite weathering rates using watershed mass-balance methods has proven challenging. At Coweeta Hydrologic Laboratory the coupling of biotite to its transformational weathering product is only valid if the stoichiometric relationship for the two phases is known; this relationship is unlikely layer-for-layer. Rates of biotite weathering and transformation of its secondary weathering product at the Coweeta Hydrological Laboratory are comparable with other Appalachian watersheds. The magnitude and sign of the difference between field- and laboratory-determined biotite weathering rates are similar to those of other silicate minerals. The influence of major-cation proportions in biomass on the rates of biotite weathering and transformational weathering product is greatest for watersheds with high biomass aggradation rates. The watershed with the lowest bedrock reactivity and highest flushing rate yielded the highest gibbsite formation rate of ~500 mol ha^?1 year^?1 and lowest kaolin-group mineral formation rates of 4–78 mol ha^?1 year^?1. The kaolin-group mineral formation rate increases as bedrock reactivity increases and flushing rate decreases to a maximum of ~300 mol ha^?1 year^?1, with a similar minimum gibbsite formation rate. The relative differences in bedrock reactivity and flux of water through Coweeta Hydrological Laboratory watersheds studied appear to be invariant over geologic timescales.     

Weathering Processes in the Min Jiang: Major Elements, {}^{87}{\text{Sr/}}{}^{86}{\text{Sr}},\;\delta {}^{34}{\text{S}}_{{\text{SO}}_{\text{4}} } ,\;{\text{and}}\;\delta {}^{18}{\text{O}}_{{\text{SO}}_{\text{4}} }

We investigated the dissolved major elements, $ {}^{87}{\text{Sr/}}{}^{86}{\text{Sr}},\;\delta {}^{34}{\text{S}}_{{\text{SO}}_{\text{4}} } ,\;{\text{and}}\;\delta {}^{18}{\text{O}}_{{\text{SO}}_{\text{4}} } $ composition of the Min Jiang, a headwater tributary of the Chang Jiang (Yangtze River). A forward calculation method was applied to quantify the relative contribution to the dissolved load from rain, evaporite, carbonate, and silicate reservoirs. Input from carbonate weathering dominated the major element composition (58–93%) and that from silicate weathering ranged from 2 to 18% in unperturbed Min Jiang watersheds. Most samples were supersaturated with respect to calcite, and the CO₂ partial pressures were similar to or up to ～5 times higher than atmospheric levels. The Sr concentrations in our samples were low (1.3–2.5 μM) with isotopic composition ranging from 0.7108 to 0.7127, suggesting some contribution from felsic silicates. The Si/(Na^* + K) ratios ranged from 0.5 to 2.5, which indicate low to moderate silicate weathering intensity. The $ \delta {}^{34}{\text{S}}_{{\text{SO}}_{\text{4}} } \;{\text{and}}\;\delta {}^{18}{\text{O}}_{{\text{SO}}_{\text{4}} } $ for five select samples showed that the source of dissolved sulfate was combustion of locally consumed coal. The silicate weathering rates were 23–181 × 10³ mol/km²/year, and the CO₂ consumption rates were 31–246 × 10³ mol/km²/year, which are moderate on a global basis. Upon testing various climatic and geomorphic factors for correlation with the CO₂ consumption rate, the best correlation coefficients found were with water temperature (r ² = 0.284, p = 0.009), water discharge (r ² = 0.253, p = 0.014), and relief (r ² = 0.230, p = 0.019).     

Variability in Concentrations and Fluxes of Methane in the Indian Estuaries

In order to examine the fluxes of methane (CH₄) from the Indian estuaries, measurements were carried out by collecting samples from 26 estuaries along the Indian coast during high discharge (wet) and low water discharge (dry) periods. The CH₄ concentrations in the estuaries located along the west coast of India were significantly higher (113?±?40 nM) compared to the east coast of India (27?±?6 nM) during wet and dry periods (88?±?15 and 63?±?12 nM, respectively). Supersaturation of CH₄ was observed in the Indian estuaries during both periods ((0.18 to 22.3?×?10³ %). The concentrations of CH₄ showed inverse relation with salinity indicating that freshwater is a significant source. Spatial variations in CH₄ saturation were associated with the organic matter load suggesting that its decomposition may be another source in the Indian estuaries. Fluxes of CH₄ ranged from 0.01 to 298 μmol m^?2 day^?1 (mean 13.4?±?5 μmol m^?2 day^?1) which is ~30 times lower compared to European estuaries (414 μmol m^?2 day^?1). The annual emission from Indian estuaries, including Pulicat and Adyar, amounted to 0.39?×?10¹⁰ g CH₄?year^?1 with the surface area of 0.027?×?10⁶ km² which is significantly lower than that in European estuaries (2.7?±?6.8?×?10¹⁰ g CH₄?year^?1 with the surface area of 0.03?×?10⁶ km²). This study suggests that Indian estuaries are a weak source for atmospheric CH₄ than European estuaries and such low fluxes were attributed to low residence time of water and low decomposition of organic matter within the estuary. The CH₄ fluxes from the Indian estuaries are higher than those from Indian mangroves (0.01?×?10¹⁰ g CH₄?year^?1) but lower than those from Indian inland waters (210?×?10¹⁰ g CH₄?year^?1).     

CO2 Input Dynamics and Air–Sea Exchange in a Large New England Estuary

Repeated surveys of the Kennebec estuary, a macrotidal river estuary in Maine, USA, between 2004 and 2008 found spatial and temporal variability both in sources of carbon dioxide (CO₂) to the estuary and the air–sea flux of estuary CO₂. On an annual basis, the surveyed area of the Kennebec estuary had an area-weighted average partial pressure of CO₂ (pCO₂) of 559 μatm. The area-weighted average CO₂ flux to the atmosphere was 3.54 mol C m^?2 year^?1. Overall, the Kennebec estuary was an annual source of 7.2?×?10⁷ mol CO₂ to the atmosphere. Distinct seasonality in estuarine pCO₂ was observed, with shifts in the seasonal pattern evident between lower and higher salinities. Fluxes of CO₂ from the estuary were elevated following two summertime storms, and inputs of riverine CO₂ outweighed internal estuarine CO₂ inputs in nearly all months. River and estuarine inputs of CO₂ represented 68 and 32 % of the total CO₂ contributions to the estuary, respectively. This study examines the variability of CO₂ in a large New England estuary, and highlights the comparatively high contribution of CO₂ from riverine sources.     

The effect of alkalis and polymerization on the solubility of H<Subscript>2</Subscript>O and CO<Subscript>2</Subscript> in alkali-rich silicate melts

The effect of alkalis on the solubility of H₂O and CO₂ in alkali-rich silicate melts was investigated at 500 MPa and 1,250 °C in the systems with H₂O/(H₂O + CO₂) ratio varying from 0 to 1. Using a synthetic analog of phonotephritic magma from Alban Hills (AH1) as a base composition, the Na/(Na + K) ratio was varied from 0.28 (AH1) to 0.60 (AH2) and 0.85 (AH3) at roughly constant total alkali content. The obtained results were compared with the data for shoshonitic and latitic melts having similar total alkali content but different structural characteristics, e.g., NBO/T parameter (the ratio of non-bridging oxygens over tetrahedrally coordinated cations), as those of the AH compositions. Little variation was observed in H₂O solubility (melt equilibrated with pure H₂O fluid) for the whole compositional range in this study with values ranging between 9.7 and 10.2 wt. As previously shown, the maximum CO₂ content in melts equilibrated with CO₂-rich fluids increases strongly with the NBO/T from 0.29 wt % for latite (NBO/T = 0.17) to 0.45 wt % for shoshonite (NBO/T = 0.38) to 0.90 wt % for AH2 (NBO/T = 0.55). The highest CO₂ contents determined for AH3 and AH1 are 1.18 ± 0.05 wt % and 0.86 ± 0.12 wt %, respectively, indicating that Na is promoting carbonate incorporation stronger than potassium. At near constant NBO/T, CO₂ solubility increases from 0.86 ± 0.12 wt % in AH1 [Na/(Na + K)] = 0.28, to 1.18 ± 0.05 wt % in AH3 [Na/(Na + K)] = 0.85, suggesting that Na favors CO₂ solubility on an equimolar basis. An empirical equation is proposed to predict the maximum CO₂ solubility at 500 MPa and 1,100–1,300 °C in various silicate melts as a function of the NBO/T, (Na + K)/∑cations and Na/(Na + K) parameters: \({\text{wt}}\% \;{\text{CO}}_{2} = - 0.246 + 0.014\exp \left( {6.995 \cdot \frac{\text{NBO}}{T}} \right) + 3.150 \cdot \frac{{{\text{Na}} + {\text{K}}}}{{\varSigma {\text{cations}}}} + 0.222 \cdot \frac{\text{Na}}{{{\text{Na}} + {\text{K}}}}.\) This model is valid for melt compositions with NBO/T between 0.0 and 0.6, (Na + K)/∑cation between 0.08 and 0.36 and Na/(Na + K) ratio from 0.25 to 0.95 at oxygen fugacities around the quartz–fayalite–magnetite buffer and above.     

Carbon Dioxide and Methane Emissions from Mangrove-Associated Waters of the Andaman Islands,Bay of Bengal

We estimated CO₂ and CH₄ emissions from mangrove-associated waters of the Andaman Islands by sampling hourly over 24 h in two tidal mangrove creeks (Wright Myo; Kalighat) and during transects in contiguous shallow inshore waters, immediately following the northeast monsoons (dry season) and during the peak of the southwest monsoons (wet season) of 2005 and 2006. Tidal height correlated positively with dissolved O₂ and negatively with pCO₂, CH₄, total alkalinity (TAlk) and dissolved inorganic carbon (DIC), and pCO₂ and CH₄ were always highly supersaturated (330–1,627 % CO₂; 339–26,930 % CH₄). These data are consistent with a tidal pumping response to hydrostatic pressure change. There were no seasonal trends in dissolved CH₄ but pCO₂ was around twice as high during the 2005 wet season than at other times, in both the tidal surveys and the inshore transects. Fourfold higher turbidity during the wet season is consistent with elevated net benthic and/or water column heterotrophy via enhanced organic matter inputs from adjacent mangrove forest and/or the flushing of CO₂-enriched soil waters, which may explain these CO₂ data. TAlk/DIC relationships in the tidally pumped waters were most consistent with a diagenetic origin of CO₂ primarily via sulphate reduction, with additional inputs via aerobic respiration. A decrease with salinity for pCO₂, CH₄, TAlk and DIC during the inshore transects reflected offshore transport of tidally pumped waters. Estimated mean tidal creek emissions were ～23–173 mmol m^?2 day^?1 CO₂ and ～0.11–0.47 mmol m^?2 day^?1 CH₄. The CO₂ emissions are typical of mangrove-associated waters globally, while the CH₄ emissions fall at the low end of the published range. Scaling to the creek open water area (2,700 km²) gave total annual creek water emissions ～3.6–9.2?×?10¹⁰ mol CO₂ and 3.7–34?×?10⁷ mol CH₄. We estimated emissions from contiguous inshore waters at ～1.5?×?10¹¹ mol CO₂?year^?1 and 2.6?×?10⁸ mol CH₄?year^?1, giving total emissions of ～1.9?×?10¹¹ mol CO₂?year^?1 and ～3.0?×?10⁸ mol CH₄?year^?1 from a total area of mangrove-influenced water of ～3?×?10⁴ km². Evaluating such emissions in a range of mangrove environments is important to resolving the greenhouse gas balance of mangrove ecosystems globally. Future such studies should be integral to wider quantitative process studies of the mangrove carbon balance.     

The fluvial geochemistry, contributions of silicate, carbonate and saline-alkaline components to chemical weathering flux and controlling parameters: Narmada River (Deccan Traps), India

The Narmada River in India is the largest west-flowing river into the Arabian Sea, draining through the Deccan Traps, one of the largest flood basalt provinces in the world. The fluvial geochemical characteristics and chemical weathering rates (CWR) for the mainstream and its major tributaries were determined using a composite dataset, which includes four phases of seasonal field (spot) samples (during 2003 and 2004) and a decade-long (1990-2000) fortnight time series (multiannual) data. Here, we demonstrate the influence of minor lithologies (carbonates and saline-alkaline soils) on basaltic signature, as reflected in sudden increases of Ca²⁺-Mg²⁺ and Na⁺ contents at many locations along the mainstream and in tributaries. Both spot and multiannual data corrected for non-geological contributions were used to calculate the CWR. The CWR for spot samples (CWR_spot) vary between 25 and 63 ton km⁻² year⁻¹, showing a reasonable correspondence with the CWR estimated for multiannual data (CWR_multi) at most study locations. The weathering rates of silicate (SilWR), carbonate (CarbWR) and evaporite (Sal-AlkWR) have contributed ∼38-58, 28-45 and 8-23%, respectively to the CWR_spot at different locations. The estimated SilWR (11-36 ton km⁻² year⁻¹) for the Narmada basin indicates that the previous studies on the North Deccan Rivers (Narmada-Tapti-Godavari) overestimated the silicate weathering rates and associated CO₂ consumption rates. The average annual CO₂ drawdown via silicate weathering calculated for the Narmada basin is ∼0.032 × 10¹² moles year⁻¹, suggesting that chemical weathering of the entire Deccan Trap basalts consumes approximately 2% (∼0.24 × 10¹² moles) of the annual global CO₂ drawdown. The present study also evaluates the influence of meteorological parameters (runoff and temperature) and physical weathering rates (PWR) in controlling the CWR at annual scale across the basin. The CWR and the SilWR show significant correlation with runoff and PWR. On the basis of observed wide temporal variations in the CWR and their close association with runoff, temperature and physical erosion, we propose that the CWR in the Narmada basin strongly depend on meteorological variability. At most locations, the total denudation rates (TDR) are dominated by physical erosion, whereas chemical weathering constitutes only a small part (<10%). Thus, the CWR to PWR ratio for the Narmada basin can be compared with high relief small river watersheds of Taiwan and New Zealand (1-5%) and large Himalayan Rivers such as the Brahmaputra and the Ganges (8-9%).     

Chemical Weathering of Pleistocene Glacial Outwash Sediments: A Comparison of Contemporary and Long-term Rates for Soils and Groundwaters

Pore water solutes increase to depths of up to six meters in unsaturated 10 kyr-old glacial outwash sediments in the Trout Lake Basin of northern Wisconsin, USA. After correction for evapotranspiration, these increases reflect weathering gradients produced from plagioclase, calc-magnesium pyroxenes, and amphiboles. In spite of relatively abundant K-feldspar, solute K and Rb reflect negative gradients produced by nutrient plant uptake and cycling. Weathering rates are calculated from solute gradients (b _solute), hydraulic fluxes (q _h ), volumetric BET surface areas (S _v ), and mineral-specific stoichiometric coefficients (β) such that $ R_{\text{solute}} = \frac{{q_{h} }}{{b_{\text{solute}} \beta {\kern 1pt} {\kern 1pt} S_{v} }} $ Average plagioclase weathering rates (R _plag = 1.6–3.1 × 10^?15 mol m^?2 s^?1) bracket rates calculated for other Quaternary glaciated landscapes. Deeper soil pore waters are as chemically concentrated as underlying groundwaters which, based on hydrologic analyses, have traveled distances up to several kilometers over transient times of hundreds of years. Pore water recharge essentially sets solute compositions close to thermodynamic saturation, thus limiting additional weathering potential along these ground water flow paths. Solid-state elemental and mineral gradients, unlike solute gradients, are essentially invariant with soil depth, reflecting low weathering intensities produced over the relatively short geologic time since sediment deposition. A spreadsheet calculator reproduces modest mass loses from such profiles and indicates that present-day weathering is kinetically and not saturation/transport controlled.     

Dissolution sequestration mechanism of CO<Subscript>2</Subscript> at the Shiqianfeng saline aquifer in the Ordos Basin,northwestern China

This study focused on the target injection layers of deep saline aquifers in the Shiqianfeng Fm. in the Carbon Capture and Sequestration (CCS) Demonstration Projects in the Ordos Basin, northwestern China. The study employed a combination method of experiments and numerical simulation to investigate the dissolution mechanism and impact factors of CO₂ in these saline aquifers. The results showed (1) CO₂ solubility in different types of water chemistry were shown in ascending order: MgCl₂-type water < CaCl₂-type water < Na₂SO₄-type water < NaCl-type water < Na₂CO₃-type water < distilled water. These results were consistent with the calculated results undertaken by TOUGHREACT with about 5% margin of error. CO₂ solubility of Shiqianfeng Fm. saline was 1.05 mol/L; (2) compared with distilled water, the more complex the water’s chemical composition, the greater the increase in HCO₃ ^?concentration. While the water’s composition was relatively simple, the tested water’s HCO₃ ^?concentrations were in close accord with the calculated value undertaken by the TOUGHREACT code, and the more complex the water’s composition, the poorer the agreement was, probably due to the complex and unstable HCO₃ ^? complicating matters when in an aqueous solution system including both tested HCO₃ ^?concentration and calculated HCO₃ ^?concentration; (3) the CO₂ solubility in the saline at the temperature conditions of 55 °C and 70 °C were 1.17 and 1.02 mol/L. When compared with the calculated value of 1.20 and 1.05 mol/L, they were almost the same with only 1 and 3% margin of error; concentrations of HCO₃ ^? were 402.73 mg/L (0.007 mol/L) and 385.65 mg/L (0.006 mol/L), while the simulation results were 132.16 mg/L (0.002 mol/L) and 128.52 mg/L (0.002 mol/L). From the contrast between the tested data and the calculated data undertaken by the TOUGHREACT code, it was shown that TOUGHRACT code could better simulate the interaction between saline and CO₂ in the dissolution sequestration capacity. Therefore, TOUGHREACT code could be used for the inter-process prediction of CO₂ long-term geological storage of CO₂; (4) The Ca²⁺ concentration and SO₄ ^2?concentration in saline water had less effect on the solubility of CO₂ and HCO₃ ^?concentration. In addition, TDS and pH values of saline affected not only the solubility of CO₂, but also the conversion of CO₂ to HCO₃ ^? due to that they can affect the activity and acid-base balance. So in fact, we just need to consider that the TDS and pH values are main impact factors in the dissolution sequestration capacity of CO₂ geological sequestration in deep saline aquifers.     

Isotope Constraints on the Aquatic Carbon Budget: Langat Watershed,Malaysia

Langat River drains a tropical watershed in the southwest of the Malaysian Peninsula. The watershed is heavily urbanized in its downstream portion. Water samples were collected from May 2010 to December 2011, at three localities along the main stem river, 1 location at its Semenyih tributary and from an upstream groundwater source. Concentration and δ¹³C data of riverine DIC and DOC indicate the dominance of C3 plant-derived material as the primary source of carbon, with δ¹³C_DIC values enriched in ¹³C relative to that of the C3 source. This enrichment is likely due to CO₂ outgassing, as calculated concentrations of riverine CO₂ are significantly higher than ambient atmospheric values, with methanogenic activity a theoretically possible contributing factor, particularly at the upstream location. The Langat River therefore acts as a net source of CO₂, with a total sub-basin flux of 19.7 × 10³ t C year^?1. This is comparable to the sum of riverine DOC, DIC and POC loss rates from the sub-basin, calculated as 24.5 × 10³ t C year^?1, and highlights the significance of CO₂ evasion from water bodies to the atmosphere for balancing the budget of the terrestrial carbon cycle. The DIC and DOC concentration and δ¹³C data also suggests that in the more urbanized downriver areas, much of the organic carbon input may be anthropogenicaly derived due to ubiquity of sewage treatment plants and landfill sites. Such human-induced perturbations to riverine carbon cycling should be taken into account in future studies of urbanized watersheds.     

Thermoelastic properties of chromium oxide Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> (eskolaite) at high pressures and temperatures

A new synchrotron X-ray diffraction study of chromium oxide Cr₂O₃ (eskolaite) with the corundum-type structure has been carried out in a Kawai-type multi-anvil apparatus to pressure of 15 GPa and temperatures of 1873 K. Fitting the Birch–Murnaghan equation of state (EoS) with the present data up to 15 GPa yielded: bulk modulus (K _0,T0), 206 ± 4 GPa; its pressure derivative K′_0,T , 4.4 ± 0.8; (?K _0,T /?T) = ?0.037 ± 0.006 GPa K^?1; a = 2.98 ± 0.14 × 10^?5 K^?1 and b = 0.47 ± 0.28 × 10^?8 K^?2, where α _0,T  = a + bT is the volumetric thermal expansion coefficient. The thermal expansion of Cr₂O₃ was additionally measured at the high-temperature powder diffraction experiment at ambient pressure and α _0,T0 was determined to be 2.95 × 10^?5 K^?1. The results indicate that coefficient of the thermal expansion calculated from the EoS appeared to be high-precision because it is consistent with the data obtained at 1 atm. However, our results contradict α ₀ value suggested by Rigby et al. (Brit Ceram Trans J 45:137–148, 1946) widely used in many physical and geological databases. Fitting the Mie–Grüneisen–Debye EoS with the present ambient and high-pressure data yielded the following parameters: K _0,T0 = 205 ± 3 GPa, K′_0,T  = 4.0, Grüneisen parameter (γ ₀) = 1.42 ± 0.80, q = 1.82 ± 0.56. The thermoelastic parameters indicate that Cr₂O₃ undergoes near isotropic compression at room and high temperatures up to 15 GPa. Cr₂O₃ is shown to be stable in this pressure range and adopts the corundum-type structure. Using obtained thermoelastic parameters, we calculated the reaction boundary of knorringite formation from enstatite and eskolaite. The Clapeyron slope (with \({\text{d}}P/{\text{d}}T = - 0.014\) GPa/K) was found to be consistent with experimental data.     

Seasonally chemical weathering and CO<Subscript>2</Subscript> consumption flux of Lake Qinghai river system in the northeastern Tibetan Plateau

The major cation and anion compositions of waters from the Lake Qinghai river system (LQRS) in the northeastern Tibetan Plateau were measured. The waters were collected seasonally from five main rivers during pre-monsoon (late May), monsoon (late July), and post-monsoon (middle October). The LQRS waters are all very alkaline and have high concentrations of TDS (total dissolved solids) compared to rivers draining the Himalayas and the southeastern Tibetan Plateau. Seasonal variations in the water chemistry show that, except the Daotang River, the TDS concentration is high in October and low in July in the LQRS waters. The forward models were used to quantify the input of three main rivers (Buha River, Shaliu River, and Hargai River) from rain, halite, carbonates, and silicates. The results suggest that (1) atmospheric input is the first important source for the waters of the Buha River and the Shaliu River, contributing 36–57% of the total dissolved cations, (2) carbonate weathering input and atmospheric input have equal contribution to the Hargai River water, (3) carbonate weathering has higher contribution to these rivers than silicate weathering, and (4) halite is also important source for the Buha River. The Daotang River water is dominated by halite input owing to its underlying old lacustrine sediments. The water compositions of the Heima River are controlled by carbonate weathering and rainfall input in monsoon season, and groundwater input may be important in pre-monsoon and post-monsoon seasons. After being corrected the atmospheric input, average CO₂ drawdown via silicate weathering in the LQRS is 35 × 10³ mol/km² per year, with highest in monsoon season, lower than Himalayas and periphery of Tibetan Plateau rivers but higher than some rivers draining shields.     

Thermal equation of state of CaIrO<Subscript>3</Subscript> post-perovskite

The pressure–volume–temperature (P–V–T) relation of CaIrO₃ post-perovskite (ppv) was measured at pressures and temperatures up to 8.6 GPa and 1,273 K, respectively, with energy-dispersive synchrotron X-ray diffraction using a DIA-type, cubic-anvil apparatus (SAM85). Unit-cell dimensions were derived from the Le Bail full profile refinement technique, and the results were fitted using the third-order Birth-Murnaghan equation of state. The derived bulk modulus \( K_{T0} \) at ambient pressure and temperature is 168.3 ± 7.1 GPa with a pressure derivative \( K_{T0}^{\prime } \) = 5.4 ± 0.7. All of the high temperature data, combined with previous experimental data, are fitted using the high-temperature Birch-Murnaghan equation of state, the thermal pressure approach, and the Mie-Grüneisen-Debye formalism. The refined thermoelastic parameters for CaIrO₃ ppv are: temperature derivative of bulk modulus \( (\partial K_{T} /\partial T)_{P} \) = ?0.038 ± 0.011 GPa K^?1, \( \alpha K_{T} \) = 0.0039 ± 0.0001 GPa K^?1, \( \left( {\partial K_{T} /\partial T} \right)_{V} \) = ?0.012 ± 0.002 GPa K^?1, and \( \left( {\partial^{2} P/\partial T^{2} } \right)_{V} \) = 1.9 ± 0.3 × 10^?6 GPa² K^?2. Using the Mie-Grüneisen-Debye formalism, we obtain Grüneisen parameter \( \gamma_{0} \) = 0.92 ± 0.01 and its volume dependence q = 3.4 ± 0.6. The systematic variation of bulk moduli for several oxide post-perovskites can be described approximately by the relationship K _T0  = 5406.0/V(molar) + 5.9 GPa.     

Nitrous oxide (N<Subscript>2</Subscript>O) emissions from a mesotrophic reservoir on the Wujiang River,southwest China

Aquatic ecosystems have been identified as a globally significant source of nitrous oxide (N₂O) due to continuous active nitrogen involvement, but the processes and influencing factors that control N₂O production are still poorly understood, especially in reservoirs. For that, monthly N₂O variations were monitored in Dongfeng reservoir (DFR) with a mesotrophic condition. The dissolved N₂O concentration in DFR displayed a distinct spatial–temporal pattern but lower than that in the eutrophic reservoirs. During the whole sampling year, N₂O saturation ranging from 144% to 640%, indicating that reservoir acted as source of atmospheric N₂O. N₂O production is induced by the introduction of nitrogen (NO₃ ^?, NH₄ ⁺) in mesotrophic reservoirs, and is also affected by oxygen level and water temperature. Nitrification was the predominate process for N₂O production in DFR due to well-oxygenated longitudinal water layers. Mean values of estimated N₂O flux from the air–water interface averaged 0.19 µmol m^?2 h^?1 with a range of 0.01–0.61 µmol m^?2 h^?1. DFR exhibited less N₂O emission flux than that reported in a nearby eutrophic reservoir, but still acted as a moderate N₂O source compared with other reservoirs and lakes worldwide. Annual emissions from the water–air interface of DFR were estimated to be 0.32 × 10⁵ mol N–N₂O, while N₂O degassing from releasing water behind the dam during power generation was nearly five times greater. Hence, N₂O degassing behind the dam should be taken into account for estimation of N₂O emissions from artificial reservoirs, an omission that historically has probably resulted in underestimates. IPCC methodology should consider more specifically N₂O emission estimation in aquatic ecosystems, especially in reservoirs, the default EF5 model will lead to an overestimation.     

Chemistry of the heavily urbanized Bagmati River system in Kathmandu Valley, Nepal: export of organic matter, nutrients, major ions, silica, and metals

Water quality in less-developed countries is often subject to substantial degradation, but is rarely studied in a systematic way. The concentration and flux of major ions, carbon, nitrogen, silicon, and trace metals in the heavily urbanized Bagmati River within Kathmandu Valley, Nepal, are reported. The concentrations of all chemical species increased with distance downstream with the exceptions of protons and nitrate, and showed strong relationships with population density adjacent to the river. Total dissolved nitrogen (TDN), dominated by NH₄, was found in high concentrations along the Bagmati drainage system. The export of dissolved organic carbon (DOC) and TDN were 23 and 33 tons km^?2 year^?1, respectively, at the outlet point of the Kathmandu Valley, much higher than in relatively undeveloped watersheds. The cationic and silica fluxes were 106 and 18 tons km^?2 year^?1 at the outlet of the Bagmati within Kathmandu Valley, and 36 and 32 tons km^?2 year^?1 from the relatively pristine headwater area. The difference between headwaters and the urban site suggests that the apparent weathering flux is three times higher than the actual weathering rate in the heavily urbanized Bagmati basin. Fluxes of cations and silica are above the world average, as well as fluxes from densely populated North American and European watersheds. End-member composition of anthropogenic sources like sewage or agricultural runoff is needed to understand the drivers of this high rate of apparent weathering.     

Dynamics of greenhouse gases in the river–groundwater interface in a gaining river stretch (Triffoy catchment,Belgium)

This study investigates the occurrence of greenhouse gases (GHGs) and the role of groundwater as an indirect pathway of GHG emissions into surface waters in a gaining stretch of the Triffoy River agricultural catchment (Belgium). To this end, nitrous oxide (N₂O), methane (CH₄) and carbon dioxide (CO₂) concentrations, the stable isotopes of nitrate, and major ions were monitored in river and groundwater over 8 months. Results indicated that groundwater was strongly oversaturated in N₂O and CO₂ with respect to atmospheric equilibrium (50.1 vs. 0.55 μg L^?1 for N₂O and 14,569 vs. 400 ppm for CO₂), but only marginally for CH₄ (0.45 vs. 0.056 μg L^?1), suggesting that groundwater can be a source of these GHGs to the atmosphere. Nitrification seemed to be the main process for the accumulation of N₂O in groundwater. Oxic conditions prevailing in the aquifer were not prone for the accumulation of CH₄. In fact, the emissions of CH₄ from the river were one to two orders of magnitude higher than the inputs from groundwater, meaning that CH₄ emissions from the river were due to CH₄ in-situ production in riverbed or riparian zone sediments. For CO₂ and N₂O, average emissions from groundwater were 1.5?×?10⁵ kg CO₂ ha^?1 year^?1 and 207 kg N₂O ha^?1 year^?1, respectively. Groundwater is probably an important source of N₂O and CO₂ in gaining streams but when the measures are scaled at catchment scale, these fluxes are probably relatively modest. Nevertheless, their quantification would better constrain nitrogen and carbon budgets in natural systems.     

Silica gel/gold nanoparticles/(NS)<Subscript>2</Subscript> ligand nanoporous platform-modified ionic liquid carbon paste electrode for potentiometric ultratrace assessment of Ag(I)

A novel ionic liquid carbon paste electrode has been developed using sol–gel/Au nanoparticle (SGAN) involving (NS)₂ compound of N,N′-di-(cyclopentadienecarbaldehyde)-1, 2-di (o-aminophenylthio) ethane (CCAE) as an appropriate neutral ion-carrier for ultrahigh-sensitive potentiometric determination of Ag(I). Colloidal gold nanoparticles (AuNPs) also well dispersed self-assembly into the 3-(mercaptopropyl)-trimethoxysilane (MPTS)-derived sol–gel network through Au–S covalent bond engendering continuous and super-conductive nanoporous three-dimensional array. The room-temperature ionic liquid, 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMIM.PF₆), was applied as a super-conductive pasting agent (binder). The SGAN/CCAE/IL-CPE exhibited a significantly enhanced sensitivity and preferential selectivity toward Ag(I) over a wide concentration range of 2.4 × 10^?9 to 2.2 × 10^?2 mol L^?1 (R ² = 0.9996) with a lower limit of detection of 7.9 × 10^?10 M and a Nernstian slope of 58.5 (±0.3) mV decade^?1. The electrode has a short response time of ～5 s and long-time durability of about 2 months without any considerable divergence in potentials. Moreover, the potentiometric examinations could be carried out within the wide pH range of 3.5–9.5. Eventually, the practical utility of the proposed Ag(I)-sensor was evaluated by volumetric titration of AgNO₃ solution by sodium chloride and recovery of silver content in some real samples using flame atomic absorption spectroscopy as a confident reference.     

CO<Subscript>2</Subscript> flux variation and its contribution area in the debris-covered area of Koxkar Glacier,Mt. Tianshan in China

During the formation and development of glacial meltwater runoff, hydrochemical erosion is abundant, especially the hydrolysis of K/Na feldspar and carbonates, which can consume H⁺ in the water, promote the formation of bicarbonate by dissolving atmospheric CO₂, and affect the regional carbon cycle. From July 21, 2015, to July 18, 2017, the CO₂ concentration and flux were observed by the eddy covariance (EC) method in the relatively flat and open moraine cover area of Koxkar Glacier in western Mt. Tianshan, China. We found that: (1) atmospheric CO₂ fluxes ranged from ??408.95 to 81.58 mmol m^?2 day^?1 (average ? 58.68 mmol m^?2 day^?1), suggesting that the study area is a significant carbon sink, (2) the CO₂ flux footprint contribution areas were primarily within 150 m of the EC station, averaging total contribution rates of 93.30%, 91.39%, and 90.17% of the CO₂ flux in the snow accumulation, snow melting, and glacial melting periods, respectively. Therefore, the contribution areas with significant influences on CO₂ flux observed at EC stations were concentrated, demonstrating that grassland CO₂ flux around the glaciers had little effect at the EC stations, (3) in the predominant wind direction, under stable daytime atmospheric stratification, the measurement of CO₂ flux, as interpreted by the Agroscope Reckenholz Tanikon footprint tool, was 79.09% ± 1.84% in the contribution area. This was slightly more than seen at night, but significantly lower than the average under unstable atmospheric stratification across the three periods of interest (89%). The average distance of the farthest point of the flux footprint under steady state atmospheric conditions was 202.61?±?69.33 m, markedly greater than that under non-steady state conditions (68.55?±?10.34 m). This also indicates that the CO₂ flux observed using EC was affected primarily by hydrochemical erosion reactions in the glacier area, (4) a good negative correlation was found between net glacier exchange (NGE) of CO₂ and air temperature on precipitation-free days. Strong ice and snow ablation could promote hydrochemical reactions of soluble substances in the debris area and accelerated sinking of atmospheric CO₂. Precipitation events might reduce snow and ice melting, driven by reduced regional temperatures. However, a connection between NGE and precipitation, when less than 8.8 mm per day, was not obvious. When precipitation was greater than 8.8 mm per day, NGE decreased with increasing precipitation, (5) graphically, the slope of NGE, related to daily runoff, followed a trend: snow melting period?>?snow accumulation period?>?early glacial ablation period?>?late glacier ablation period?>?dramatic glacier ablation period. The slope was relatively large during snow melting, likely because of CO₂ sinking caused by water–rock interactions. The chemical reaction during elution in the snow layer might also promote atmospheric CO₂ drawdown. At the same time, the damping effect of snow cover and the almost-closed glacier hydrographic channel inhibited the formation of regional runoff, possibly providing sufficient time for the chemical reaction, thus promoting further CO₂ drawdown.