Dissolved Carbon Concentrations Research Articles

Effects of pockmark activity on iron cycling and mineral composition in continental shelf sediments (southern Baltic Sea)

AbstractPockmarks are formed as a result of gas (methane) or/and groundwater outflow from the sea bottom. Methane, the second most important (after CO2) greenhouse gas, has a significant impact on biogeochemical processes in the bottom sediments by affecting the cycling of some elements, e.g. C, Fe, and S. Active pockmarks may also lead to changes in water column conditions by causing nutrients release from sediments. In the present study, we have focused on the impact of biogeochemical processes in pockmarks (methanogenesis, anaerobic methane oxidation, and groundwater seepage) on the transformation of iron (Fe) and the mineral composition of the sediment. In pore water, concentrations of hydrogen sulfide, phosphate, ammonia, sulfate, chloride, dissolved inorganic carbon, iron, and methane were analyzed. In the sediment, Fe speciation was performed using sequential extraction. The mineral composition was determined using powder X-Ray diffraction and scanning electron microscopy. The results from two pockmarks (with active gas seepage and groundwater infiltration) and two reference stations in the southern Baltic Sea show that geochemical conditions in pockmark sediments are significantly different from those in the typical muddy sea bottom. Pore water in pockmarks is characterized by lower sulfate and higher dissolved carbon concentrations as compared to areas of the seafloor where such structures are absent. This is due to the outflow of groundwater, which was confirmed by lower chloride concentration. In addition, sulfate is used to oxidize methane diffusing from deeper layers. Sediments in pockmarks are enriched in Fe(II) carbonates and depleted in Fe(III) (oxy)hydroxides, resulting from the anaerobic oxidation of methane with Fe(III) (Fe-AOM). Ferrous iron produced in large quantities during Fe-AOM is precipitated with carbonates.

Effects of high wheat bran input on the performance of a biofloc system for Pacific white shrimp (Litopenaeus vannamei)

Applying an external carbohydrate source to stimulate heterotrophic bacteria growth in biofloc systems is a common practice which could be simplified by combining the carbohydrate source with the feed into one pellet. In the current study, such an approach was tested in Pacific white shrimp, Litopenaeus vannamei. Wheat bran (WB) containing non-starch polysaccharides (NSP), a hardly digestible carbohydrate, was mixed with a commercial-like shrimp diet (control; CONdiet) to create a wheat bran rich diet (WBdiet). Shrimp were fed isonitrogenously, resulting in the WBdiet group receiving equal absolute amount of nitrogen but more carbon than the CONdiet group. A digestibility trial was performed in a clear-water recirculating aquaculture system for 35 days, using 6 replicates aquaria per diet. Compared to the CONdiet, shrimp fed with the WBdiet had a reduced overall digestibility and an increased faecal carbon to nitrogen ratio (C:N ratio) from 12 to 20. Following the digestibility trial, a second experiment was performed to monitor the growth performance of the shrimp reared in biofloc systems for 42 days, using three replicate tanks per diet. The dissolved nitrogen species concentration was lower in the tanks fed the WBdiet, while the dissolved carbon concentration was similar between the diets. From a system perspective, similar amounts of nitrogen accumulated across the system compartments with both diets, with maximum 3% total nitrogen loss reached at the end of the experiment. The percentage of carbon loss per kg feed was similar between diets. Overall, diluting the CONdiet with wheat bran and feeding both diets isonitrogenously did not reduce shrimp survival and had minor effect on growth (2% reduction of the specific growth rate). Therefore, incorporating NSP-rich ingredients, such as wheat bran applied as one pellet has a potential to simplify the carbon addition management in a biofloc system.

Thermodynamic constraints on the fate of carbon mobilized from subducted sediments in the overlying mantle wedge

In subduction zones, carbon from the surface can be transported into Earth's interior. Fluids released during subduction can mobilize carbon bound in solid minerals in the subducting plate, and transport it into the overlying mantle. While there is increasing attention on the composition and redox state of carbon-bearing, subduction-mobilized fluids, the fate of fluids as they migrate through and react with overlying mantle rocks is less well characterized. Using thermodynamic modeling, we quantify the evolution of carbon-bearing aqueous fluids mobilized from subducting sedimentary rocks, as they follow several possible pathways through the overlying mantle. The extent of carbon mineralization in the overlying mantle depends on the source (siliciclastic vs carbonate rock) and composition of the fluids as well as the fluid path (isothermal, cooling, heating). A heating path towards the hot core of the mantle wedge does not favor sequestration of carbon into solid phases. Along cooling trajectories, most of the dissolved carbon (61 to 98 %) forms in solid minerals when carbon-rich, siliciclastic-equilibrated fluids react with mantle rocks. In contrast to fluids from siliciclastic sediments, less carbon is sequestered in the mantle when relatively carbon-poor, limestone-equilibrated fluids react with mantle rocks. The formation of quartz-rich (birbirite), quartz-magnesite (listvenite), talc-magnesite (soapstone), and serpentine-rich (serpentinite) parageneses is predicted at decreasing water-rock ratios. Soapstones are less favored to form along fractional crystallization paths and/or lower temperatures. Listvenite assemblages form from migrating fluids with dissolved carbon concentration > 20,000 ppm. Graphite is favored to form along closed reaction, cooling paths. Moreover, several cooling paths form reduced fluids rich in hydrogen (H2), methane (CH4), and organic species. Overall, this work provides quantitative models that can comprehensively inform studies on the movement of carbon in subduction zones and into the deep Earth.

Dissolved Carbon Concentrations and Emission Fluxes in Rivers and Lakes of Central Asia (Sayan–Altai Mountain Region, Tyva)

The carbon (C) cycle in inland waters, including carbon concentrations in and carbon dioxide (CO2) emissions from water surfaces, are at the forefront of biogeochemical studies, especially in regions strongly impacted by ongoing climate change. Towards a better understanding of C storage, transport and emission in Central Asian mountain regions, an area of knowledge that has been extremely poorly studied until now, here, we carried out systematic measurements of dissolved C and CO2 emissions in rivers and lakes located along a macrotransect of various natural landscapes in the Sayan–Altai mountain region, from the high mountains of the Western Sayan in the northwest of Tyva to the arid (dry) steppes and semideserts in the intermountain basins in the southeast of Tyva on the border with Mongolia. New data on major hydrochemical parameters and CO2 fluxes (fCO2) gathered by floating chambers and dissolved organic and inorganic carbon (DOC and DIC, respectively) concentrations collected over the four main hydrological seasons allowed us to assess the current C biogeochemical status of these water bodies in order to judge possible future changes under climate warming. We further tested the impact of permafrost, river watershed size, lake area and climate parameters as well as ‘internal’ biogeochemical drivers (pH, mineralization, organic matter quality and bacterial population) on CO2 concentration and emissions in lakes and rivers of this region and compared them with available data from other subarctic and mountain settings. We found strong environmental control of the CO2 pattern in the studied water bodies, with thermokarst lakes being drastically different from other lakes. In freshwater lakes, pCO2 negatively correlated with O2, whereas the water temperature exerted a positive impact on pCO2 in large rivers. Overall, the large complexity of counteracting external and internal drivers of CO2 exchange between the water surfaces and the atmosphere (CO2-rich underground DIC influx and lateral soil and subsurface water; CO2 production in the water column due to dissolved and particulate OC biodegradation; CO2 uptake by aquatic biota) precluded establishing simple causalities between a single environmental parameter and the fCO2 of rivers and lakes. The season-averaged CO2 emission flux from the rivers of Tyva measured in this study was comparable, with some uncertainty, to the C uptake fluxes from terrestrial ecosystems of the region, which were assessed in other works.

Concentrations of macro and microelement in Brazilian white cheeses: Evaluating sample preparation procedures and estimation of dietary intake

Two sample preparation procedures, microwave-assisted and closed digestion block, were developed to establish the nutritional content of white cheeses. A two-level full factorial design was performed to optimize the decomposition parameters. Under optimum conditions, both procedures led to low dissolved carbon content (< 11% w.w-1) employing 2 mol. L-1 HNO3. Nevertheless, the closed block presented smaller analytical throughput with approximately 11 digested samples h-1 against 20 samples h-1 for MW. Both procedures showed accuracy for Ca, K, P, Na, and Zn and precision with RSD < 10%. The limits of detection ranged from 2.2 (P) to 16 μg g-1 (Ca) (microwave) and 0.8 (K) to 14 μg g-1 (Na) (closed block). The validated procedures were employed to analyze buffalo mozzarella, minas frescal, Ricotta, Coalho, and cottage cheeses. Based on the nutritional analysis, the type of cheese influenced the variation in nutrient content. Furthermore, for all types of cheese, a discrepancy (p < 0.05) was observed between concentrations for at least one analyte, confirming the lack of uniformity in nutritional composition. The recommended daily intake evaluation demonstrated that all samples of buffalo mozzarella and minas frescal cheese analyzed could be considered sources of Ca and P.

High Dissolved Carbon Concentration in Arid Rocky Mountain Streams.

Warming in mountains is known to intensify aridity and threaten water availability globally. Its impacts on water quality, however, have remained poorly understood. Here we collate long-term (multi-year to decadal mean), baseline stream concentrations and fluxes of dissolved organic and inorganic carbon, two essential indicators of water quality and soil carbon response to warming, across more than 100 streams in the United States Rocky Mountains. Results show a universal pattern of higher mean concentrations in more arid mountain streams with lower mean discharge, a long-term climate measure. A watershed reactor model revealed less lateral export of dissolved carbon (via less water flow) out of the watersheds in more arid sites, leading to more accumulation and higher concentrations. Lower concentrations typically occur in cold, steep, and compact mountains with higher snow fraction and lower vegetation cover, which generally have higher discharge and carbon fluxes. Inferring from a space-for-time perspective, the results indicate that as warming intensifies, lateral fluxes of dissolved carbon will decrease but concentrations will increase in these mountain streams. This indicates deteriorating water quality and potentially elevated CO2 emission directly from the land (instead of streams) in the Rockies and other mountain areas in the future climate.

Simulated Impact of Ocean Alkalinity Enhancement on Atmospheric CO2 Removal in the Bering Sea

AbstractOcean alkalinity enhancement (OAE) has the potential to mitigate ocean acidification (OA) and induce atmospheric carbon dioxide (CO2) removal (CDR). We evaluate the CDR and OA mitigation impacts of a sustained point‐source OAE of 1.67 × 1010 mol total alkalinity (TA) yr−1 (equivalent to 667,950 metric tons NaOH yr−1) in Unimak Pass, Alaska. We find the alkalinity elevation initially mitigates OA by decreasing pCO2 and increasing aragonite saturation state and pH. Then, enhanced air‐to‐sea CO2 exchange follows with an approximate e‐folding time scale of 5 weeks. Meaningful modeled OA mitigation with reductions of &gt;10 μatm pCO2 (or just under 0.02 pH units) extends 100–100,000 km2 around the TA addition site. The CDR efficiency (i.e., the experimental seawater dissolved inorganic carbon (DIC) increase divided by the maximum DIC increase expected from the added TA) after the first 3 years is 0.96 ± 0.01, reflecting essentially complete air‐sea CO2 adjustment to the additional TA. This high efficiency is potentially a unique feature of the Bering Sea related to the shallow depths and mixed layer depths. The ratio of DIC increase to the TA added is also high (≥0.85) due to the high dissolved carbon content of seawater in the Bering Sea. The air‐sea gas exchange adjustment requires 3.6 months to become (&gt;95%) complete, so the signal in dissolved carbon concentrations will likely be undetectable amid natural variability after dilution by ocean mixing. We therefore argue that modeling, on a range of scales, will need to play a major role in assessing the impacts of OAE interventions.

Space-for-time substitution leads to carbon emission overestimation in eutrophic lakes

Lacustrine eutrophication is generally considered as an important contributor of carbon emissions to the atmosphere; however, there is still a huge challenge in accuracy estimating carbon emissions from lakes. To test the effect of widely used space-for-time substitution on lake carbon emissions, this study monitored different processes of carbon emissions, including the carbon production potential, dissolved carbon concentrations, and carbon release fluxes in eight lakes along the trophic gradients on a spatial scale and the typical eutrophic Lake Taihu for one year on a temporal scale. Eutrophication promoted carbon production potential, dissolved carbon concentrations, and carbon release fluxes, especially for CH4. Trophic lake index (TLI) showed positive correlations with the CH4 production potential, dissolved CH4 concentrations, and CH4 release fluxes, and also positive correlations with the CO2 production potential, dissolved CO2 concentrations, and CO2 release fluxes. The space-for-time substitution led to an overestimation for the influence of eutrophication on carbon emissions, especially the further intensification of lake eutrophication. On the spatial scale, the average CH4 production potential, dissolved CH4 concentrations and CH4 release fluxes in eutrophic lakes were 268.6, 0.96 μmol/L, and 587.6 μmol m−2·h−1, respectively, while they were 215.8, 0.79 μmol/L, and 548.6 μmol m−2·h−1 on the temporal scale. Obviously, CH4 and CO2 emissions on the spatial scale were significantly higher than those on the temporal scale in eutrophic lakes. The primary influencing factors were the seasonal changes in the physicochemical environments of lake water, including dissolved oxygen (DO) and temperature. The CH4 and CO2 release fluxes showed negative correlations with DO, while temperature displayed positive correlations, respectively. These results suggest that the effects of DO and temperature on lake carbon emissions should be considered, which may be ignored during the accurate assessment of lake carbon budget via space-for-time substitution in eutrophic lakes.

Hysteresis analysis reveals dissolved carbon concentration – discharge relationships during and between storm events

The dissolved carbon concentration, which is responsible for aquatic ecosystem productivity and water quality, is tightly coupled with hydrological processes. Excess dissolved carbon may exacerbate eutrophication and hypoxia in aquatic ecosystems and lead to deterioration of water quality. Storm events dominate the dynamics of dissolved carbon concentrations, and this nonlinear behavior exhibits significant time scale dependence. Here, we identified inter- and intra-event variability in the dissolved carbon concentration–discharge (C–Q) relationship in an agriculture-intensive catchment. The driving factors of C–Q hysteresis patterns for dissolved inorganic carbon (DIC) and organic carbon (DOC) were quantified by redundancy analysis combined with hierarchical partitioning. At the inter-event scale, DIC exhibited mainly clockwise hysteresis, indicating an exhaustible, proximal source (e.g., groundwater). However, DOC hysteresis was generally counter-clockwise, indicating distal and plentiful sources (e.g., soil water) in the agricultural catchment. Hierarchical partitioning showed that total rainfall, peak discharge and flood intensity explained 28.38% of the total variation in C–Q hysteresis for DIC and 39.87% for DOC at the inter-event scale. At the intra-event scale, time series analysis of dissolved carbon concentration and discharge indicated the interconversion of supply limitation to transport limitation, which depends on the activation of the specific DIC or DOC source zones. These findings provide significant insights into understanding the dynamics of dissolved carbon during storm periods and are important for targeted watershed management practices aimed at reducing carbon loading to surface waters.

Comprehensive improvement of soil quality and rice yield by flooding-midseason drying-flooding.

Many water-saving technologies have been developed to reduce water input and the associated irrigation costs. However, the influence of water management technologies on soil quality is unclear. Soil quality is fundamental to rice yield and sustainable productivity of ecosystems. Therefore, it is important to understand the effect of water management on soil quality and its linkage with rice yield. In this work, a field experiment was conducted to assess the influence of water management on soil physico-chemical properties, microbial biomass, bacterial community, and rice yield in paddy fields. Three water treatments were selected for the study, including flooding-rain-fed (F-RF), flooding-midseason drying-flooding (F-D-F), and continuous flooding (CF). Total nitrogen (TN), total phosphorus (TP), dissolved carbon content (DOC), available phosphorus (AP), nitrate nitrogen (NO3-), microbial biomass carbon (MBC), and microbial biomass nitrogen (MBN) contents were 11%, 20%, 29%, 30%, 11%, 183%, and 215% higher in F-D-F, respectively, than those in the CF (p < 0.05). Additionally, the bacterial diversity in F-D-F and CF was significantly higher compared to the F-RF (p < 0.05). Correspondingly, soil quality index (SQI) was higher in the F-D-F (0.8) than that of F-RF (0.53) and CF (0.5). Compared with the F-RF, water management remarkably altered bacterial community composition, with higher enrichment of anaerobic bacteria (such as Firmicutes and Chloroflexi) in flooding treatments (CF and F-D-F). Differences in the bacterial community were closely related to key soil quality indicators, such as AP. Parallel increases in soil quality and bacterial diversity resulted in increased rice yield in the F-D-F, which was 53% and 12% higher than that in F-RF and CF, respectively. Therefore, F-D-F is the suggested water management method because it can comprehensively improve soil microbial diversity, soil quality, and rice yield. KEY POINTS: • Water management changed bacterial community mainly via SMC (soil moisture content), TP, AP, and NO3-contents. • The F-D-F had greater SQI and higher rice yield in comparison with F-RF and CF.

DETERMINATION OF THE TOTAL 14C CONCENTRATION OF WATER SAMPLES USING THE COD METHOD AND AMS

ABSTRACTRadiocarbon (14C) is the one of the most important radionuclides released from the nuclear facilities to the environment. Currently, inorganic 14C is checked during regular environmental monitoring as part of the groundwater monitoring program of the Paks Nuclear Power Plant. Several studies have shown that organic 14C can be also an important and sensitive tool for detection of possible leakage of nuclear technological systems. For this reason, a wet oxidation method was developed for the accelerator mass spectrometry (AMS) 14C measurement technique to determine the 14C activity concentration of the total dissolved carbon content of water samples, coming from environmental monitoring wells. The overall efficiency of the oxidation was around 94 ± 5% for different types of tested organic compounds. The typical 14C background (1–2 pMC) is obtained by preparation of blank samples, which allows a detection level of around 5·10–5 Bq L–1. The activity of the organic fraction can be calculated using the formula presented in the study. The method was applied for water samples deriving from environmental monitoring wells of a pressurized-water reactor (PWR) type of NPP. The results of our investigations over the 14 different water samples around the Paks NPP show that DO14C contribution to the total 14C activity concentration was between 5–25%.

Pilot-scale outdoor trial of a cyanobacterial consortium at pH 11 in a photobioreactor at high latitude

The biomass of microalgae and cyanobacteria yields a variety of products. Outdoor pilot plant trials typically grow a single species at circumneutral pH and provide CO2 by gas sparging. Here a cyanobacterial consortium was grown at high pH (beyond 11) and high dissolved carbonate concentrations (0.5 M) in an outdoor 1,150 L tubular photobioreactor for 130 days in Calgary, Canada. The aim was to assess the productivity and robustness of the consortium. Importantly, the system was designed to enable future integration of air capture of CO2. Productivity was between 3.1 and 5.8 g ash-free dry weight per square metre per day, depending on biomass density and month. 16S rRNA amplicon sequencing showed that cyanobacterium Candidatus “Phormidium alkaliphilum” made up 80% of the consortium. The consortium displayed robust growth and adapted to environmental conditions. Bicarbonate uptake pushed medium pH past 11, demonstrating the ability to achieve CO2 delivery by air capture.

Evaluation of silicon effects on abrasion performance, microstructure and crystalline structure of NiHard-4 white cast iron using synchrotron X-ray diffraction

NiHard-4 is a class of abrasion-resistant white cast iron widely used in mining ore-handling operations. It has a multi-component microstructure consisting of eutectic carbides and metallic matrix, both of which can influence abrasion performance. This work investigates the influence of silicon concentration on abrasion performance, microstructure and crystalline structure. Abrasion was assessed by dry sand rubber wheel abrasion test (DS-RWAT), inner circumference abrasion test (ICAT) with quartzite, and ICAT with basalt. Abrasion performance trends were explained in terms of microstructure and crystallographic evolution, using SEM, macro-hardness, micro-hardness and nano-hardness measurements, cryogenic treatment and synchrotron X-ray diffraction (XRD). As Si content increases, duplex (M3C + M7C3) eutectic carbides are replaced with homogeneous M7C3 carbides, the latter confirmed to have significantly higher hardness. However, contrary to suggestions from literature that Si should enhance abrasion resistance, the tests found that elevated Si in NiHard-4 leads to inferior performance. In the metallic matrix, increased Si results in lower hardness, which synchrotron XRD indicates is due to reduction of dissolved carbon concentration in the austenite. It is demonstrated that the detrimental effects of Si on the matrix outweigh any beneficial effect that it may have on the eutectic carbides, leading to net inferior abrasion performance.

Effect of Deformation Structure of AISI 316L in Low-Temperature Vacuum Carburizing

The effect of plastic deformation applied to AISI 316L in low-temperature vacuum carburizing without surface activation was investigated. To create a difference in the deformation states of each specimen, solution and stress-relieving heat treatment were performed using plastically deformed AISI 316L, and the deformation structure and the carburized layer were observed with EBSD and OM. The change in lattice parameter was confirmed with XRD, and the natural oxide layers were analyzed through TEM and XPS. In this study, the carburized layer on the deformed AISI 316L was the thinnest and the dissolved carbon content of the layer was the lowest. The thickness and composition of the natural oxide layer on the surface were changed due to the deformed structure. The natural oxide layer on the deformed AISI 316L was the thickest, and the layer was formed with a bi-layer structure consisting of an upper Cr-rich layer and a lower Fe-rich layer. The thick and Cr-rich oxide layer was difficult to decompose due to the requirement for lower oxygen partial pressure. In conclusion, the oxide layer is the most influential factor, and its thickness and composition may determine carburizing efficiency in low-temperature vacuum carburizing without surface activation.

Seasonal and Spatial Variability of Dissolved Carbon Concentration and Composition in Lake Michigan Tributaries

AbstractDissolved organic matter (DOM) is a complex mixture of many compounds and its composition dictates numerous reactions in the environment. Large lakes and marine coastlines receive DOM from watersheds that differ widely in their land cover, with potential implications for both the quantity and composition of carbon inputs. Seasonal variation in DOM quantity and composition may also differ among tributaries and be mediated by land cover. Here, we quantify spatially (i.e., among tributary) and seasonal variation in DOM concentration, DOM composition based on ultraviolet‐visible spectroscopy, and alkalinity across 101 tributaries of Lake Michigan, one of the world's largest lakes, using a synoptic sampling approach. Wetland land cover has the largest effect on DOM, producing high concentrations of DOM that are more aromatic and larger in apparent molecular weight. Seasonal variation is also pronounced, with concentrations and aromaticity of DOM peaking in fall across most tributaries. Watershed lithology and land cover both affect alkalinity, with higher values associated with the geography of carbonate bedrock and urbanized watersheds. Watershed land cover has a larger effect than season on all organic carbon parameters. However, seasonal variation is especially important for DOM composition. This disparity suggests that the environmental processing of DOM within river channels mediates its composition more than its concentrations. Considering the wide range of land cover and lithology around Lake Michigan and other large water bodies, accounting for both spatial and seasonal dynamics is essential for understanding controls on DOM delivery.

Variations in the dissolved carbon concentrations of the shallow groundwater in a desert inland river basin

Due to its potentially important role in the global carbon cycle, the dissolved carbon of groundwater systems is severely affected by climate change and oasisization in desert inland river basins. However, the spatial distribution and driving mechanisms of groundwater dissolved carbon are still poorly understood. Here, we use groundwater data from 72 monitoring wells to reveal the spatial variations in the dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) concentrations of the shallow groundwater in the Tarim River basin, an arid region in northwest China. Due to the unsaturated characteristics of the groundwater recharge, the DOC concentration of groundwater increased significantly with greater lateral distance from the downstream river, rather than the DIC concentration of groundwater. There was a significant positive linear correlation between DOC and DIC. Redundancy analysis showed that groundwater depth (GD) and evapotranspiration influenced the DOC concentration, while the DIC concentration was greatly affected by the total salinity of groundwater and farmland. Likewise, both DOC and DIC concentrations were most affected by Ca2+. Further analysis showed that a decrease in the GD will lead to a decrease in the DOC concentration (dilution effect), but it has no obvious influence on the DIC concentration. High evapotranspiration in the desert region drives an increase in the DOC concentration (concentration effect) and a decrease in the DIC concentration. Our study highlights that average annual evapotranspiration and GD jointly drive the differences in the DOC and DIC concentration changes in the shallow groundwater of the Tarim River basin.

Investigation of mineral trapping processes based on coherent front propagation theory: A dawsonite-rich natural CO2 reservoir as an example

After nearly 30 years of research on geological carbon storage, studies providing an in-depth conceptual understanding of mineral trapping processes are still scarce. Based on the reaction front propagation theory, this paper developed a set of concise mathematical models for front propagation and mineral trapping in quasi-2D-advection-diffusion-dispersion-reaction-kinetics systems in the coherent state and explored the nature of long-term mineral trapping processes and the effects of hydrodynamic dispersion on the front propagation. A criterion based on dawsonite volume fraction and front propagation distance was established to determine whether the mineral trapping rate is reaction- or transport-controlled for the coherent reaction fronts. Combined with the numerical simulation, the mantle-magmatic-sourced CO2 invasion, and long-term CO2 storage was investigated for the Hailar natural CO2 reservoir. The conclusions include: (1) The relative errors of the concise models for coherent front propagation speed and mineral trapping rate are 3-10% and 0.5-10%, respectively. (2) For the complete reaction stage, mineral trapping rates are always transport-controlled and are proportional to Darcy velocity, the difference of total dissolved carbon concentrations, and the correction coefficient for the hydrodynamic dispersion; when reaction controlling, the mineral trapping rate is proportional to front propagation distance and upstream dawsonite precipitation rate. (3) Specific results related to propagation speed, front width, hydrodynamic dispersion and mineral trapping rate caused by changing the rate constants of minerals and albite volume fraction were also obtained.

Hydrochemical, isotopic, and dissolved gas characterization of groundwater in Gariz aquifer, Southwest of Yazd Province, central Iran

Here we discussed the results of the first geochemical investigation of the fluids (groundwater and the associated gases) emerging in the southwest of Yazd Province. We carried out two surveys, one in July 2019 and the second in September 2019s, in the region of the Gariz aquifer (central Iran). We focused our attention to 1) the chemistry of the water (major and minor constituents coupled to the stable isotopes of oxygen and hydrogen), 2) the chemical composition of dissolved gases in water together with 3) the isotopic composition of Helium (3He/4He) and 4) the dissolved carbon in water (δ13CTDIC). Hydrogen and oxygen isotope values of groundwater display a fairly narrow range and indicate that the waters are of meteoric origin. On the base of the major ions chemistry, the bulk of the water samples are classified as Ca-HCO3, CaCl and NaCl types. The groundwater chemistry is mainly influenced by the interaction with CO2-rich fluids, leakage of chlorinated saline water into the alluvial aquifer, and silicate dissolution. High dissolved carbon contents, mainly as bicarbonate ion, reflect the noticeable interaction of the groundwater with CO2-rich fluids. CO2 is the dominant gaseous component in most samples and its amount is always greater with respect to a water in equilibrium with the atmosphere (Air Saturated Water, ASW). Such excess of CO2 contents (more than 730 cc/l STP) dissolved in groundwater also supports the presence of a deep source of CO2-rich gas. The computed δ13C(CO2) in equilibrium with the groundwater highlight a mixing in different proportion between an inorganic deep sourced CO2 (13C-enriched) and organic CO2 (13C-depleted). We also used the helium isotopes as a tools to figure out the origin of helium in the aquifer (air vs. mantle, and crust). The collected samples show a contribution of mantle-derived He in the Gariz aquifer up to (~45%) and the crust suggesting that at regional scale the tectonic discontinuities had a connection with the mantle or magmatic intrusions migrated through the crust transporting mantle volatiles to shallow crustal layers. However, we cannot infer the timing of this possible magmatism at depth in the complex tectonic evolution of the area.

Microbial Greenhouse Gas Dynamics Associated With Warming Coastal Permafrost, Western Canadian Arctic

Permafrost sediments contain one of the largest reservoirs of organic carbon on Earth that is relatively stable when it remains frozen. As air temperatures increase, the shallow permafrost thaws which allows this organic matter to be converted into potent greenhouse gases such as methane (CH4) and carbon dioxide (CO2) through microbial processes. Along the Beaufort Sea coast in the vicinity of the Tuktoyaktuk Peninsula, Northwest Territories, Canada, warming air temperatures are causing the active layer above permafrost to deepen, and a number of active periglacial processes are causing rapid erosion of previously frozen permafrost. In this paper, we consider the biogeochemical consequences of these processes on the permafrost sediments found at Tuktoyaktuk Island. Our goals were to document the in situ carbon characteristics which can support microbial activity, and then consider rates of such activity if the permafrost material were to warm even further. Samples were collected from a 12 m permafrost core positioned on the top of the island adjacent to an eroding coastal bluff. Downcore CH4, total organic carbon and dissolved organic carbon (DOC) concentrations and stable carbon isotopes revealed variable in situ CH4 concentrations down core with a sub-surface peak just below the current active layer. The highest DOC concentrations were observed in the active layer. Controlled incubations of sediment from various depths were carried out from several depths anaerobically under thawed (5°C and 15°C) and under frozen (−20°C and −5°C) conditions. These incubations resulted in gross production rates of CH4 and CO2 that increased upon thawing, as expected, but also showed appreciable production rates under frozen conditions. This dataset presents the potential for sediments below the active layer to produce potent greenhouse gases, even under frozen conditions, which could be an important atmospheric source in the actively eroding coastal zone even prior to thawing.

The Effect of Fertilization on Biomass and Metabolism in North Carolina Salt Marshes: Modulated by Location‐Specific Factors

AbstractThe resilience of salt marshes to sea level rise depends on vertical accretion through belowground biomass production and sediment deposition to maintain elevation above sea level. Increased nitrogen (N) availability from anthropogenic sources may stimulate aboveground biomass production and sediment deposition and, thus, accretion; however, increased N may also negatively impact marsh accretion by decreasing belowground biomass and increasing net CO2 emissions. A study was conducted in Spartina alterniflora‐dominated salt marshes in North Carolina, USA, to determine how responses to fertilization vary across locations with different physical and chemical characteristics. Pore water residence time, inundation time, and proximity to tidal creeks drove spatial differences in pore water sulfide, ammonium, and dissolved carbon concentrations. Although annual respiration and gross primary production were greater at the creek edge than interior marsh sites, net ecosystem CO2 exchange (NEE) was nearly balanced at all the sites. Fertilization decreased belowground biomass in the interior sites but not on the creek edge. Aboveground biomass, respiration, gross primary production, and net CO2 emissions increased in response to fertilization, but responses were diminished in interior marsh locations with high pore water sulfide. Hourly NEE measured by chambers were similar to hourly NEE observed by a nearby eddy covariance tower, but correcting for inundation depth relative to plant height was critical for accurate extrapolation to annual fluxes. The impact of fertilization on biomass and NEE, and thus marsh resilience, varied across marsh locations depending upon location‐specific pore water sulfide concentrations.