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1.
De Beers kimberlite mine operations in South Africa (Venetia and Voorspoed) and Canada (Gahcho Kué, Victor, and Snap Lake) have the potential to sequester carbon dioxide (CO2) through weathering of kimberlite mine tailings, which can store carbon in secondary carbonate minerals (mineral carbonation). Carbonation of ca. 4.7 to 24.0 wt% (average = 13.8 wt%) of annual processed kimberlite production could offset 100% of each mine site’s carbon dioxide equivalent (CO2e) emissions. Minerals of particular interest for reactivity with atmospheric or waste CO2 from energy production include serpentine minerals, olivine (forsterite), brucite, and smectite. The most abundant minerals, such as serpentine polymorphs, provide the bulk of the carbonation potential. However, the detection of minor amounts of highly reactive brucite in tailings from Victor, as well as the likely presence of brucite at Venetia, Gahcho Kué, and Snap Lake, is also important for the mineral carbonation potential of the mine sites. 相似文献
2.
Understanding mechanisms and kinetics of mineral carbonation reactions relevant to sequestering carbon dioxide as a supercritical fluid (scCO 2) in geologic formations is crucial to accurately predicting long-term storage risks. Most attention so far has been focused on reactions occurring between silicate minerals and rocks in the aqueous dominated CO 2-bearing fluid. However, water-bearing scCO 2 also comprises a reactive fluid, and in this situation mineral carbonation mechanisms are poorly understood. Using in situ high-pressure X-ray diffraction, the carbonation of brucite [Mg(OH) 2] in wet scCO 2 was examined at pressure (82 bar) as a function of water concentration and temperature (50 and 75 °C). Exposing brucite to anhydrous scCO 2 at either temperature resulted in little or no detectable reaction over three days. However, addition of trace amounts of water resulted in partial carbonation of brucite into nesquehonite [MgCO 3·3H 2O] within a few hours at 50 °C. By increasing water content to well above the saturation level of the scCO 2, complete conversion of brucite into nesquehonite was observed. Tests conducted at 75 °C resulted in the conversion of brucite into magnesite [MgCO 3] instead, apparently through an intermediate nesquehonite step. Raman spectroscopy applied to brucite reacted with 18O-labeled water in scCO 2 show it was incorporated into carbonate at a relatively high concentration. This supports a carbonation mechanism with at least one step involving a direct reaction between the mineral and water molecules without mediation by a condensed aqueous layer. 相似文献
3.
The dehydroxylation reactions of chrysotile Mg 3Si 2O 5(OH) 4 and brucite Mg(OH) 2 were studied under inert nitrogen atmosphere using isothermal and non-isothermal approaches. The brucite decomposition was additionally studied under CO 2 in order to check the influence of a competing dehydroxylation/carbonation/decarbonisation reaction on the reaction kinetics. Isothermal experiments were conducted using in situ high-temperature X-ray powder diffraction, whereas non-isothermal experiments were performed by thermogravimetric analyses. All data were treated by model-free, isoconversional approaches (‘time to a given fraction’ and Friedman method) to avoid the influence of kinetic misinterpretation caused by model-fitting techniques. All examined reactions are characterised by a dynamic, non-constant reaction-progress-resolved (‘ α’-resolved) course of the apparent activation energy E a and indicate, therefore, multi-step reaction scenarios in case of the three studied reactions. The dehydroxylation kinetics of chrysotile can be subdivided into three different stages characterised by a steadily increasing E a ( α ≤ 15 %, 240–300 kJ/mol), before coming down and forming a plateau (15 % ≤ α ≤ 60 %, 300–260 kJ/mol). The reaction ends with an increasing E a ( α ≥ 60 %, 260–290 kJ/mol). The dehydroxylation of brucite under nitrogen shows a less dynamic, but generally decreasing trend in E a versus α (160–110 kJ/mol). In contrast to that, the decomposition of brucite under CO 2 delivers a dynamic course with a much higher apparent E a characterised by an initial stage of around 290 kJ/mol. Afterwards, the apparent E a comes down to around 250 kJ/mol at α ~ 65 % before rising up to around 400 kJ/mol. The delivered kinetic data have been investigated by the z( α) master plot and generalised time master plot methods in order to discriminate the reaction mechanism. Resulting data verify the multi-step reaction scenarios (reactions governed by more than one rate-determining step) already visible in E a versus α plots. 相似文献
4.
A detailed study of low-pressure gas-solid carbonation of chrysotile in dry and humid environments has been carried out. The evolving structure of chrysotile and its reactivity as a function of temperature (300-1200 °C), humidity (0-10 mol %) and CO 2 partial pressure (20-67 mol %), thermal preconditioning, and alkali metal doping (Li, Na, K, Cs) have been monitored through in-situ X-ray photoelectron spectroscopy, isothermal thermogravimetry/mass spectrometry, ex-situ X-ray powder diffraction, and water and nitrogen adsorption/desorption. Based on chrysotile crystalline structure and its nanofibrilar orderliness, a multistep carbonation mechanism was elaborated to explain the role of water during chrysotile partial amorphisation, formation of periclase, brucite, and hydromagnesite crystalline phases, and surface passivation thereof, during humid carbonation. The weak carbonation reactivity was rationalized in terms of incongruent CO 2 van der Waals molecular diameters with the octahedral-tetrahedral lattice constants of chrysotile. This lack of reactivity appeared to be relatively indifferent to the facilitated water crisscrossing during chrysotile core dehydroxylation/pseudo-amorphisation and surface hydroxylation induced product stabilization during humid carbonation. Thermodynamic stability domains of the species observed at low pressure have been thoroughly discussed on the basis of X-ray powder diffraction patterns and X-ray photoelectron spectroscopy evidence. The highest carbon dioxide uptake occurred at 375 °C in moist atmospheres. On the basis of chrysotile fresh N 2 BET area, nearly 15 atoms out of 100 of the surface chrysotile brucitic Mg moiety have been carbonated at this temperature which was tantamount to the carbonation of about 2.5 at. % of the total brucitic Mg moiety in chrysotile. The carbonation of brucite (Mg(OH) 2) impurities coexisting in chrysotile was minor and estimated to contribute by less than 17.6 at. % of the total converted magnesium. The presence of cesium traces (3 Cs atoms per 100 Mg atoms) was found to boost chrysotile carbonation capacity by a factor 2.7. 相似文献
5.
The dissolution behavior of two biogenic Mg-calcites, the echinoid, Tripneustes (12 mol% MgCO 3), and the red alga, Neogoniolithon (18 mol% MgCO 3 plus brucite), was studied using free-drift methods in distilled water and phosphate-spiked solutions at 25°C and PCO2 = 1 atm. Small concentrations of phosphate strongly inhibit dissolution rates. Inhibition increases with increased phosphate levels and with approach toward saturation. Near saturation, dissolution rates are reduced by 10 3 by the presence of 0.6 μmol adsorbed-P/m 2. The magnitude of phosphate inhibition is similar to that observed for low-Mg calcite, and like calcite, the mechanism of inhibition is probably by adsorption of P at surface kink sites. Phosphate appears to inhibit removal of Mg and Ca equally during Mg-calcite dissolution. Rates of brucite dissolution are unaffected by phosphate.Mg-calcites containing >8.5 mol% MgCO 3 should be thermodynamically unstable relative to aragonite in most natural waters. Recent work, however, shows that in contrast to its effect on the behavior of Mg-calcites. phosphate does not inhibit aragonite dissolution. The presence of phosphate might thus reverse the relative stability of these two minerals during diagenesis of shallow marine carbonate sediments. 相似文献
6.
In this paper, we demonstrated a new approach to CO 2 mineral sequestration using wollastonite carbonation assisted by sulfuric acid and ammonia. Samples were characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and 29Si nuclear magnetic resonance. The change in Gibbs free energy from ?223 kJ/mol for the leaching reaction of wollastonite to ?101 kJ/mol for the carbonation reaction indicated that these two reactions can proceed spontaneously. The leached and carbonated wollastonite showed fibrous bassanite and granular calcium carbonate, respectively, while the crystal structure of pristine wollastonite was destroyed and the majority of the Ca 2+ in pristine wollastonite leached. The chemical changes in the phases were monitored during the whole process. A high carbonation rate of 91.1 % could be obtained under the action of sulfuric acid and ammonia at 30 °C at normal atmospheric pressure, indicating its potential use for CO 2 sequestration. 相似文献
7.
The global warming of Earth’s near-surface, air and oceans in recent decades is a direct consequence of anthropogenic emission of greenhouse gases into the atmosphere such as CO 2, CH 4, N 2O and CFCs. The CO 2 emissions contribute approximately 60% to this climate change. This study investigates experimentally the aqueous carbonation mechanisms of an alkaline paper mill waste containing about 55 wt% portlandite (Ca(OH) 2) as a possible mineralogical CO 2 sequestration process. The overall carbonation reaction includes the following steps: (1) Ca release from portlandite dissolution, (2) CO 2 dissolution in water and (3) CaCO 3 precipitation. This CO 2 sequestration mechanism was supported by geochemical modelling of final solutions using PHREEQC software, and observations by scanning electron microscope and X-ray diffraction of final reaction products. According to the experimental protocol, the system proposed would favour the total capture of approx. 218 kg of CO 2 into stable calcite/ton of paper waste, independently of initial CO 2 pressure. The final product from the carbonation process is a calcite (ca. 100 wt%)-water dispersion. Indeed, the total captured CO 2 mineralized as calcite could be stored in degraded soils or even used for diverse industrial applications. This result demonstrates the possibility of using the alkaline liquid–solid waste for CO 2 mitigation and reduction of greenhouse effect gases into the atmosphere. 相似文献
8.
The global rise in atmospheric greenhouse gas concentrations calls for practicable solutions to capture CO 2. In this study, a mineral carbonation process was applied in which CO 2 reacts with alkaline lignite ash and forms stable carbonate solids. In comparison to previous studies, the assays were conducted at low temperatures and pressures and under semi-dry reaction conditions in an 8 L laboratory mixing device. In order to find optimum process conditions the pCO 2 (10-20%), stirring rate (500-3000 rpm) and the liquid to solid ratio ( L/ S = 0.03-0.36 L kg −1) were varied. In all experiments a considerable CO 2 uptake from the gas phase was observed. Concurrently the solid phase contents of Ca and Mg (hydr)oxides decreased and CaCO 3 and MgCO 3 fractions increased throughout the experiments, showing that CO 2 was stabilized as a solid carbonate. The carbonation reaction depends on three factors: Dissolution of CO 2 in the liquid phase, mobilization of Ca and Mg from the mineral surface and precipitation of the carbonate solids. Those limitations were found to depend strongly on the variation of the process parameters. Optimum reaction conditions could be found for L/ S ratios between 0.12 and 0.18, medium stirring velocities and pCO 2 between 10% and 20%.Maximum CO 2 uptake by the solid phase was 4.8 mmol g −1 after 120 min, corresponding to a carbonation efficiency for the alkaline material of 53% of the theoretical CO 2 binding capacity. In comparison to previous studies both CO 2 uptake and carbonation efficiencies were in a similar range, but the reaction times in the semi-dry process were considerably shorter. The proposed method additionally allows for a more simple carbonation setup due to low T and P, and produces an easier to handle product with low water content. 相似文献
9.
The experiment was conducted to ascertain net production and consumption rates of 15NH 4 + and 15NO 3 ? for water and sediment in a wetland. This was done using 15N isotope pool dilution methodology under ambient and elevated atmospheric CO 2 concentrations in experimental riparian wetlands to obtain the gross N transformation rates. The 15N budget for sediment was also estimated. The results suggested that the differences in high proportion of 15N concentration in the overlying water body under elevated CO 2 could be attributed to the low production and high consumption rates of 15NH 4 + in sediment. The elevated CO 2 effect on production and consumption of NH 4 + decreased by 144 % ( P = 0.014) and increased by 153 % ( P = 0.009), respectively. Thereby, 15NH 4 + production rates are negatively related with 15NO 3 ? consumption rates and this accounted for the decreases in net 15NO 3 ? consumption under CO 2 enrichment in the wetland sediment by 11 % ( P = 0.528). Therefore, 15NO 3 ? production and consumption rates may strongly depend on NH 4 + production. Inorganic 15N and total 15N exported from sediment to overlying water body by the effect of CO 2 were 41 % ( P = 0.071) and 18 % ( P = 0.000), respectively. Therefore, low net 15NH 4 + production and high 15NH 4 + consumption rates under elevated CO 2 may partly explain the significant reduction of N from the sediment. 相似文献
10.
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 (CO 2) to the estuary and the air–sea flux of estuary CO 2. On an annual basis, the surveyed area of the Kennebec estuary had an area-weighted average partial pressure of CO 2 (pCO 2) of 559 μatm. The area-weighted average CO 2 flux to the atmosphere was 3.54 mol C m ?2 year ?1. Overall, the Kennebec estuary was an annual source of 7.2?×?10 7 mol CO 2 to the atmosphere. Distinct seasonality in estuarine pCO 2 was observed, with shifts in the seasonal pattern evident between lower and higher salinities. Fluxes of CO 2 from the estuary were elevated following two summertime storms, and inputs of riverine CO 2 outweighed internal estuarine CO 2 inputs in nearly all months. River and estuarine inputs of CO 2 represented 68 and 32 % of the total CO 2 contributions to the estuary, respectively. This study examines the variability of CO 2 in a large New England estuary, and highlights the comparatively high contribution of CO 2 from riverine sources. 相似文献
11.
The Khushaym Matruk site in central Jordan may represent a natural analogue depicting the interaction of alkaline solutions with a clayey sedimentary formation or with clay-rich confining barriers at the interface with concrete structures in waste disposal sites. In this locality, past spontaneous combustion of organic matter in a clayey biomicritic formation produced a ca. 60 m-thick layer of cement-marble containing some of the high-temperature phases usually found in industrial cements (e.g., spurrite, brucite, and Ca-aluminate). A vertical cross-section of the underlying sediments was used in order to study the interaction between cement-marbles and neighbouring clayey limestones under weathering conditions. A thermodynamic approach of the alteration parageneses (calcite–jennite–afwillite–brucite and CSH phases) in the cement-marbles constrains the interacting solutions to have had pH-values between 10.5 and 12. Over 3 m, the sediments located beneath the metamorphic unit were compacted and underwent carbonation. They display large C and O isotopic variations with respect to “pristine” sediments from the bottom of the section. Low δ13C-values down to −31.4‰/PDB show the contribution of CO 2 derived from the oxidization of organic matter and from the atmosphere to the intense carbonation process affecting that particular sedimentary level. The size of the C isotopic anomalies, their geometrical extent and their coincidence with the variations of other markers like the Zn content, the structure of organic matter, the mineralogical composition, all argue that the carbonation process was induced by the percolation of high pH solutions which derived from the alteration of cement-marbles. The temperature of the carbonation process remains conjectural and some post-formation O isotopic reequilibration likely affected the newly-formed carbonate. Carbonation induced a considerable porosity reduction, both in fractures and matrixes. The Khushaym Matruk site may have some bearing to the early life of a repository site, when water saturation of the geological formations hosting the concrete structures is incomplete, enabling simultaneous diffusion of alkaline waters and gaseous CO 2 in the near field. 相似文献
12.
The present analysis adjusts previous estimates of global ocean CaCO 3 production rates substantially upward, to 133 × 10 12 mol yr ?1 plankton production and 42 × 10 12 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 CaCO 3 production on so-called carbonate-poor sedimentary shelves and secondarily pays greater attention to high CaCO 3 mass (calcimass) and turnover of shelf communities on temperate and polar shelves. Estimated CaCO 3 sediment accumulation rates remain about the same as they have been for some years: ~20 × 10 12 mol yr ?1 on shelves and 11 × 10 12 mol yr ?1 in the deep ocean. The differences between production and accumulation of calcareous materials call for dissolution of ~22 × 10 12 mol yr ?1 (~50 %) of shelf benthonic carbonate production and 122 × 10 12 mol yr ?1 (>90 %) of planktonic production. Most CaCO 3 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 CO 2 release to CaCO 3 precipitation (CO 2↑/CaCO 3↓) 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 CO 2 associated with CaCO 3 reactions in the global ocean in late preindustrial time is estimated to be an apparent influx from the atmosphere to the ocean, of +7 × 10 12 mol C yr ?1, at a time scale of 10 2–10 3 years. The CaCO 3-mediated influx of CO 2 is approximately offset by CO 2 release from organic C oxidation in the water column. Continuing ocean acidification will have effects on CaCO 3 and organic C metabolic responses to the oceanic inorganic C cycle, although those responses remain poorly quantified. 相似文献
13.
Based on the analyses and comparisons of water chemistry, stable carbon isotopes and deposition rates of speleothems, the
authors found that there are two kinds of speleothems in the tunnels at the Wujiangdu Dam site, Guizhou, China, namely the
CO 2-outgassing type and the CO 2-absorbing type. The former is natural, as observed in general karst caves, and the product of karst processes under natural
conditions. The latter, however, is special, resulting from the carbonation of a cement-grouting curtain and concrete. Due
to the quick absorption of CO 2 from the surrounding atmosphere, evidenced by the low CO 2 content in the air and the high deposition rate of speleothems (as high as 10 cm/a) in the tunnels, the contribution of the
carbonation process to the sink of CO 2 in the atmosphere is important (in the order of magnitude of 10 8 tons c/a) and should be taken into consideration in the study of the global carbon cycle because of the use of cement on
a worldwide scale.
Received: 21 July 1997 · Accepted: 13 January 1997 相似文献
14.
The history of life on Earth is critically dependent on the carbon, sulfur and oxygen cycles of the lithosphere – hydrosphere – atmosphere – biosphere system. An Archean oxygen-poor greenhouse atmosphere developed through: (i) accumulation of CO 2 and CH 4 from episodic injections of CO 2 from volcanic activity, volatilised crust impacted by asteroids and comets, metamorphic devolatilisation processes and release of methane from sediments; and (ii) little CO 2 weathering-capture due to both high temperatures of the hydrosphere (low CO 2 solubility) and a low ratio of exposed continents to oceans. In the wake of the Sturtian glaciation, enrichment in oxygen and appearance of multicellular eukaryotes heralded the onset of the Phanerozoic where greenhouse conditions were interrupted by periods of strong CO 2-sequestration through intensified capture of CO 2 by marine plants, onset of land plants and burial of carbonaceous shale and coal (Late Ordovician; Carboniferous – Permian; Late Jurassic; Late Tertiary – Quaternary). The progression from Late Mesozoic and Early Tertiary greenhouse conditions to Late Tertiary – Quaternary ice ages was related to the sequestration of CO 2 by rapid weathering of the emerging Alpine and Himalayan mountain chains. A number of peak warming and sea-level-rise events include the Late Oligocene, mid-Miocene, mid-Pliocene and Pleistocene glacial terminations. The Late Tertiary – Quaternary ice ages were dominated by cyclic orbital-forcing-triggered terminations which involved CO 2-feedback effects from warming seas and the biosphere and albedo flips due to ice-sheet melting. Since ca AD 1750 human emissions were ~305 Gt of carbon, as compared with ~750 Gt C in the atmosphere. The emissions constitute ~12% of the terrestrial biosphere and ~10% of the known global fossil fuel reserve of ~4000 Gt C, whose combustion would compare to the ~ 4600 Gt C released to the atmosphere during the K – T impact event 65 million years ago, with associated ~65% mass extinction of species. The current growth rate of atmospheric greenhouse gases and global mean temperatures exceed those of Pleistocene glacial terminations by one to two orders of magnitude. The relationship between temperatures and sea-levels for the last few million years project future sea-level rises toward time-averaged values of at least 5 m per 1°C. The instability of ice sheets suggested by the Dansgaard – Oeschinger glacial cycles during 50 – 20 ka, observed ice melt lag effects of glacial terminations, spring ice collapse dynamics and the doubling per-decade of Greenland and west Antarctic ice melt suggest that the Intergovernmental Panel on Climate Change's projected sea-level rises (<59 cm) for the 21st century may be exceeded. The biological and philosophical rationale underlying climate change and mass extinction perpetrated by an intelligent carbon-emitting mammal species may never be known. 相似文献
15.
The objective of this study is to understand cement alteration processes with the evolution of porosity and hardness under geologic CO 2 storage conditions. For this study, the cylindrical cement cores (class G) were reacted with CO 2–saturated water in a vessel (40 °C and 8 MPa) for 10 and 100 days. After the experiment, the CO 2 concentration and Vickers hardness were measured in the hydrated cement core to estimate the carbonation depth and to identify the change in hardness, respectively. Diffusive-reactive transport modeling was also performed to trace the alteration processes and subsequent porosity changes. The results show that cement alteration mainly results from carbonation. With alteration processes, four different reaction zones are developed: degradation zone, carbonation zone, portlandite depletion zone, and unreacted zone. In the degradation zone, the re-dissolution of calcite formed in the carbonation zone leads to the increase of porosity. In contrast, the carbonation zone is characterized by calcite formation resulting mainly from the dissolution of portlandite. The carbonation zone acts as a barrier to CO 2 intrusion by consuming dissolved CO 2. Especially in this zone, although the porosity decreases, the Vickers hardness increases. Our results show that cement alteration processes can affect the physical and hydrological properties of the hydrated cement under CO 2-saturated conditions. Further long-term observation is required to confirm our results under in-situ fluid chemistry of a CO 2 storage reservoir. Nonetheless, this study would be helpful to understand alteration processes of wellbore cements under CO 2 storage conditions. 相似文献
16.
Two natural CO 2-rich cordierite samples (1.00 wt% CO 2, 0.38 wt% H 2O, and 1.65 wt% CO 2, 0.15 wt% H 2O, respectively) were investigated by means of Raman spectroscopy and single-crystal X-ray diffraction at ambient and high pressures. The effect of heavy-ion irradiation (Au 2.2 GeV, fluence of 1 × 10 12 ions cm ?2) on the crystal structure was investigated to characterize the structural alterations complementary to results reported on hydrous cordierite. The linear CO 2 molecules sustained irradiation-induced breakdown with small CO 2-to-CO conversion rates in contrast to the distinct loss of channel H 2O. The maximum CO 2 depletion rate corresponds to ~12 ± 5 % (i.e. ~0.87 and ~1.49 wt% CO 2 according to the two samples, respectively). The elastic properties of CO 2-rich cordierite reveal stiffening due to the CO 2 molecules (non-irradiated: isothermal bulk modulus K 0 = 120.3 ± 3.7 GPa, irradiated: K 0 = 109.7 ± 3.7 GPa), but show the equivalent effect of hydrous cordierite to get softer when irradiated. The degree of anisotropy of axial compressibilities and the anomalous elastic softening at increasing pressure agrees with those reported for hydrous cordierite. Nevertheless, the experimental high-pressure measurements using ethanol–methanol reveal a small hysteresis between compression and decompression, together with the noticeable effect of pressure-induced over-hydration at pressures between 4 and 5 GPa. 相似文献
17.
Carbon dioxide (CO 2) emission from the river-type reservoir is an hotspot of carbon cycle within inland waters. However, related studies on the different types of reservoirs are still inadequate. Therefore, we sampled the Three Gorges Reservoir (TGR), a typical river-type reservoir having both river and lake characteristics, using an online system (HydroCTM/CO 2) and YSI-6600v2 meter to determine the partial pressure of carbon dioxide ( pCO 2) and physical chemical parameters in 2013. The results showed that the CO 2 flux from the mainstream ranged from 26.1 to 92.2 mg CO 2/m 2 h with average CO 2 fluxes of 50.0 mg/m 2 h. The CO 2 fluxes from the tributary ranged from ?10.91 to 53.95 mg CO 2/m 2 h with area-weighted average CO 2 fluxes of 11.4 mg/m 2 h. The main stream emits CO 2 to the atmosphere the whole year; however, the surface water of the tributary can sometimes act as a sink of CO 2 for the atmosphere. As the operation of the TGR, the tributary became more favorable to photosynthetic uptake of CO 2 especially in summer. The total CO 2 flux was estimated to be 0.34 and 0.03 Tg CO 2/year from the mainstream and the tributaries, respectively. Our emission rates are lower than previous estimates, but they are in agreement with the average CO 2 flux from temperate reservoirs estimated by Barros et al. (Nat Geosci 4(9):593–596, 2011). 相似文献
18.
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 CO 2 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 CO 2 supersaturation with respect to the atmospheric CO 2 pressure during most of the sampling trips. The average CO 2 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 × 10 8 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 × 10 8 kg) was emitted to the atmosphere during the same period. For the entire study period, the river’s freshwater discharged 0.25 × 10 9 mol dissolved inorganic carbon (DIC) and 1.77 × 10 9 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. 相似文献
20.
The carbon cycle of global inland waters is quantitatively comparable to other components in the global carbon budget. Among inland waters, a significant part is man-made lakes formed by damming rivers. Man-made lakes are undergoing a rapid increase in number and size. Human impacts and frequent algae blooms lead to it necessary to make a better constraint on their carbon cycles. Here, we make a primary estimation on the air–water CO 2 transfer flux through an algae bloom year for a subtropical man-made lake—Hongfeng Lake, Southwest China. To do this a new type of glass bottles was designed for content and isotopic analysis of DIC and other environmental parameters. At the early stage of algae bloom, CO 2 was transferred from the atmosphere to the lake with a net flux of 1.770 g·C·m ?2. Later, the partial pressure ( pCO 2) of the aqueous CO 2 increased rapidly and the lake outgassed to the atmosphere with a net flux of 95.727 g·C·m ?2. In the remaining days, the lake again took up CO 2 from the atmosphere with a net flux of 14.804 g·C·m ?2. As a whole, Lake Hongfeng released 4527 t C to the atmosphere, accounting for one-third of the atmosphere/soil CO 2 sequestered by chemical weathering in the whole drainage. With an empirical mode decomposition method, we found air temperature plays a major role in controlling water temperature, aqueous pCO 2 and hence CO 2 flux. This work indicates a necessity to make detailed and comprehensive carbon budgets in man-made lakes. 相似文献
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