Calcium Carbonate Dissolution Research Articles

Carbon cycling in the North American coastal ocean: a synthesis

Abstract. A quantification of carbon fluxes in the coastal ocean and across its boundaries with the atmosphere, land, and the open ocean is important for assessing the current state and projecting future trends in ocean carbon uptake and coastal ocean acidification, but this is currently a missing component of global carbon budgeting. This synthesis reviews recent progress in characterizing these carbon fluxes for the North American coastal ocean. Several observing networks and high-resolution regional models are now available. Recent efforts have focused primarily on quantifying the net air–sea exchange of carbon dioxide (CO2). Some studies have estimated other key fluxes, such as the exchange of organic and inorganic carbon between shelves and the open ocean. Available estimates of air–sea CO2 flux, informed by more than a decade of observations, indicate that the North American Exclusive Economic Zone (EEZ) acts as a sink of 160±80 Tg C yr−1, although this flux is not well constrained. The Arctic and sub-Arctic, mid-latitude Atlantic, and mid-latitude Pacific portions of the EEZ account for 104, 62, and −3.7 Tg C yr−1, respectively, while making up 51 %, 25 %, and 24 % of the total area, respectively. Combining the net uptake of 160±80 Tg C yr−1 with an estimated carbon input from land of 106±30 Tg C yr−1 minus an estimated burial of 65±55 Tg C yr−1 and an estimated accumulation of dissolved carbon in EEZ waters of 50±25 Tg C yr−1 implies a carbon export of 151±105 Tg C yr−1 to the open ocean. The increasing concentration of inorganic carbon in coastal and open-ocean waters leads to ocean acidification. As a result, conditions favoring the dissolution of calcium carbonate occur regularly in subsurface coastal waters in the Arctic, which are naturally prone to low pH, and the North Pacific, where upwelling of deep, carbon-rich waters has intensified. Expanded monitoring and extension of existing model capabilities are required to provide more reliable coastal carbon budgets, projections of future states of the coastal ocean, and quantification of anthropogenic carbon contributions.

Carbonation of silica cement at high-temperature well conditions

Cements for well environments with temperatures above 110 °C are typically designed with silica additions. This is the case for many of the wells in the North Sea, which is a region promising for large-scale geological storage of CO2 from European sources. Wells are probable leakage paths in carbon capture and storage (CCS) projects, and it is therefore important to understand how CO2 interacts with cement under downhole conditions. In this study, microstructural changes associated with carbonation of cement with and without silica were followed using micro-computed tomography, X-ray diffraction and scanning electron microscopy. The rims of the cement cores exposed to CO2-saturated brine consisted of a carbonated region and a bicarbonated region. In the silica cement sample, the carbonated region consisted of two distinct layers with a rough interface region containing wormhole-like features. The formation of these two layers in the silica cement is proposed to be due to calcium carbonate dissolution and re-precipitation during exposure to CO2-saturated brine. The results illustrate the importance of the effect of additives for offshore CO2-storage well integrity.

Benthic fluxes from hypoxia-influenced Gulf of Mexico sediments: Impact on bottom water acidification

Benthic fluxes are reported from 8 sites on the shelf and slope of the Gulf of Mexico (GoM) in the region near the Mississippi River delta. Benthic landers, with the capability to incubate 3 chambers simultaneously, were deployed in August 2011 to establish the rate of phosphate, nitrate, ammonium, dissolved Si, Dissolved Inorganic Carbon (DIC) and alkalinity concentration change vs. incubation time (7–50 h) thereby providing flux estimates for these parameters. Stations located within 350 km of the Mississippi River mouth have nutrient and DIC fluxes that vary by a factor of 10 but show no longitudinal trends. Chambers deployed in low oxygen bottom water (<4 μM) do not have different flux values compared to chambers deployed in settings with higher bottom water oxygen (160 μM). At some stations, ammonium shows a change in flux with incubation time, yet no other species shows this change; hence neither a change in transport mechanism or reaction rate can explain the non-steady state behavior of ammonium. A positive correlation (r2 = 0.91) between the fluxes of dissolved Si and DIC imply a linkage between the diagenesis of biogenic Si and organic C throughout this region. The efflux of DIC and alkalinity in a ratio > 1 drives GoM bottom waters to a lower calcite and aragonite saturation state. Carbon isotopes of the DIC were measured on chamber waters and the calculated δ13C of the DIC source at 4 stations was similar, between −14 to −17‰ compared to typical δ13C values of bulk organic carbon in the GoM of −22‰. At a fifth station, the DIC added was calculated to have an isotope value of −31‰. Dissolved inorganic carbon isotope compositions that are significantly heavier or lighter than particulate organic carbon are unexpected and may be explained by a combination of inputs: the oxidation of average marine organic carbon and calcium carbonate dissolution, methanogenesis, and/or from oxidation of terrestrial lignin fractions.

Effects of different calcium sources on the mineralization and sand curing of CaCO3 by carbonic anhydrase-producing bacteria.

The deposition and dissolution of calcium carbonate can be affected by the action of biological factors, such as microbial-induced carbonate precipitation (MICP). Bacillus spp. has been isolated and applied to prevent soil erosion, increase the stability of slopes, dikes and dunes. However, previous studies have been always limited to a single calcium source (CaCl2) to evaluate the roles of bacteria, and the deposition and curing effect has not yet been quantified. Here, we designed deposition experiments to determine the effect of Bacillus cereus with different calcium sources and applied it to sand curing to measure the amount of deposition and curing. The results demonstrated that vaterite was produced when the Bacillus cereus participated. Also, more deposition was produced in the Ca(CH3COO)2 and CaCl2 groups, but the Ca(NO3)2 group showed optimal curing effects in the sand curing test due to the denser and more uniform deposition. This research will provide an important reference for the design and application of microbial-induced carbonate precipitation.

Controls on Carbonate System Dynamics in a Coastal Plain Estuary: A Modeling Study

AbstractThe study of acidification in Chesapeake Bay is challenged by the complex spatial and temporal patterns of estuarine carbonate chemistry driven by highly variable freshwater and nutrient inputs. A new module was developed within an existing coupled hydrodynamic‐biogeochemical model to understand the underlying processes controlling variations in the carbonate system. We present a validation of the model against a diversity of field observations, which demonstrated the model's ability to reproduce large‐scale carbonate chemistry dynamics of Chesapeake Bay. Analysis of model results revealed that hypoxia and acidification were observed to cooccur in midbay bottom waters and seasonal cycles in these metrics were regulated by aerobic respiration and vertical mixing. Calcium carbonate dissolution was an important buffering mechanism for pH changes in late summer, leading to stable or slightly higher pH values in this season despite persistent hypoxic conditions. Model results indicate a strong spatial gradient in air‐sea CO2 fluxes, where the heterotrophic upper bay was a strong CO2 source to atmosphere, the mid bay was a net sink with much higher rates of net photosynthesis, and the lower bay was in a balanced condition. Scenario analysis revealed that reductions in riverine nutrient loading will decrease the acid water volume (pH &lt; 7.5) as a consequence of reduced organic matter generation and subsequent respiration, while bay‐wide dissolved inorganic carbon (DIC) increased and pH declined under scenarios of continuous anthropogenic CO2 emission. This analysis underscores the complexity of carbonate system dynamics in a productive coastal plain estuary with large salinity gradients.

Secretion of niche signal molecules in conditions of osteogenic differentiation of multipotent mesenchymal stromal cells induced by textured calcium phosphate coating

Secretion of 21 cytokines, chemokines and growth factors (LIF, SCF, SDF-1a, SCGF-b, M-CSF, MCP-3, MIF, MIG, TRAIL, GRO-a; IL-1a, IL-2ra, IL-3, IL-12(p40), IL-16, IL-18, HGF, TNF-b, b-NGF, IFN-a2, CTACK) has been studied in vitro in the culture of human adipose-derived multipotent mesenchymal stromal cells (hAMMSCs) in conditions of its osteogenic differentiation caused by 14-day contact with calcium phosphate (CP) surface with different roughness. Bilateral X-ray amorphous CP coatings were prepared on the samples of commercially pure titanium in the anodal regime using a micro-arc method. An aqueous solution prepared from 20 wt% phosphoric acid, 6 wt% dissolved hydrohyapatite nanopowder (particle diameter 10-30 nm with single agglomerates up to 100 nm), and 9 wt% dissolved calcium carbonate was used to obtain CP coating. hAMMSCs isolated from lipoaspirate were co-cultured after 4 passages with the CP-coated samples at final concentration of 1.5´105 viable karyocytes per 1.5 mL of standard nutrition medium (without osteogenic stimulators) for 14 days (a determination of [CD45,34,14,20], CD73, CD90 и CD105 cell immunophenotype; an analysis of secretory activity) and 21 days (alizarin red S staining of culture) with medium replacement every 3-4 days. Under conditions of in vitro contact with rough CP coating hAMMSCs differentiated into osteoblasts synthesizing the mineralized bone matrix; this was accompanied by 2-3-fold increasing ratio of [CD45,34,14,20]+ hemopoietic cells. The following humoral factors of hemopoietic niches acted as the signal molecules escalating in vitro the hemopoietic base in 14 days of differentiating three-dimensional culture of hAMMSCs: either leukemia inhibitory factor (LIF) and stem cell factor (SCF) cytokines under mean index of CP roughness Ra=2.4-2.6 mm or stromal derived factor-1 (SDF-1a, CXCL12 chemokine) under Ra=3.1-4.4 mm.

Description of fouling population emerging after the episode of eutrophic crisis in the Mar Menor coastal lagoon

Description of fouling population emerging after the episode of eutrophic crisis in the Mar Menor coastal lagoon

Agglutinated and planktonic foraminifera of the Nariva Formation, Central Trinidad, as indicators of its age and paleoenvironment

The Nariva Formation comprises mostly non-calcareous rocks with few calcareous foraminifera, but it is sandwiched geographically in a narrow (&lt;10 km wide) band between the richly calcareous Brasso and Cipero Formations to the north and south respectively. Sixty-one samples were collected from the Nariva Formation at nine transient exposures along a transect trending NNE-SSW across southwestern Central Trinidad. The sparse planktonic foraminiferal assemblages showed the exposures to range in age between Oligocene and early middle Miocene, though many of the samples were of earliest middle Miocene age and coincident with a tectonically-induced transgressive-regressive cycle in the Brasso Formation. The Nariva assemblage at the most southerly exposure, at which the Nariva and Cipero Formations interfingered, was calcareous and of lower bathyal aspect, containing many Planulina wuellerstorfi. The assemblage at this exposure did not differ statistically between the two formations, and was thus said to be of "Cipero aspect", although the presence of rare Elphidium sp. in the Nariva parts of the exposure attests to some downslope transport. Recovery from most other exposures was typically small. Richer, predominantly agglutinated assemblages, however, were obtained from the Tarouba Community Centre, Ben Lomond Quarry, Raphael Street, and Tabaquite Heights. The assemblages were of "Brasso aspect", comprising species illustrated previously from the Brasso Formation. Three exposures were sampled at the Raphael Street site, which covered about ten hectares and had been cleared for development. The rocks at this site are patchily but richly stained with hematite and possible manganese derived from hydrothermal activity. Exposure 1 (13 samples) was subdivided into an almost barren interval (Exposure 1a, 8 samples) and an interval containing abundant Cribrostomoides carapitanus and Trochammina cf. pacifica and lesser Jarvisella karamatensis, Arenogaudryina flexilis and Glaphyrammina americana (Exposure 1b, 5 samples). This assemblage is thought to indicate low dissolved oxygen concentrations at middle to lower bathyal paleodepths. That the Brasso Formation was deposited at neritic to shallower middle bathyal paleodepths, while the Cipero Formation at lower bathyal to abyssal depths, demonstrates that the Nariva Formation was deposited on an eastward-facing paleo-slope. Exposures 2 (9 samples) and 3 (5 samples) are dominated by Simobaculites saundersi Wilson and Kaminski, n. sp., the walls of which do not incorporate calcareous particles. Many samples yielded large quantities of gypsum that, in view of (a) the paleodepth and (b) the rich planktonic foraminiferal recovery from the adjacent Brasso and Cipero Formations, is thought to reflect syndepositional dissolution of foraminiferal calcium carbonate and its precipitation as calcium sulphate. Because both the Nariva Formation and the upper Miocene to lower Pliocene Lower Cruse Member (southern Trinidad) yield primarily organically-cemented agglutinated foraminifera, a comparison is made between them. SHE analysis and different mean values of the Assemblage Turnover Index (ATI) shows the community structures in the two formations to differ. Because there is no sign of hydrothermal activity associated with the Lower Cruse Member, despite their taxonomic similarity we conclude that the agglutinated assemblages in the Nariva and Cruse Formations lived in markedly different paleoenvironments.

The effect of warming and benthic community acclimation on coral reef carbonate sediment metabolism and dissolution

Global warming (and the consequent increase in sea surface temperature) is expected to modify rates of gross primary production (GPP), respiration (R), and net calcium carbonate (CaCO3) dissolution in permeable coral reef carbonate sediments. Previous simulations of seawater warming on coral reef sediments found a decline in the GPP/R ratio and an associated increase in CaCO3 dissolution but were only conducted over a short timescale ( 24 h) effect of seawater warming on coral reef CaCO3 sediment metabolism and dissolution, which may allow the benthic community to acclimatise. This study used 600-L flume aquaria to examine the effect of seawater warming on GPP, R, and CaCO3 dissolution in the permeable coral reef CaCO3 sediments of Mo’orea, French Polynesia, over a period of 15 d. On average, when exposed to warmed seawater (+ 2.8 °C), R in the CaCO3 sediments was enhanced (+ 58%) to a greater extent than GPP (+19%), resulting in a decline in GPP/R (− 23%) and an associated increase in net CaCO3 dissolution (+ 126%). The magnitude of these warming-mediated metabolic changes increased each day until reaching a plateau after about 8 d, indicating that 24-h experiments may be underestimating the effect of warming over longer timescales. Interestingly, the increase in dissolution relative to control treatments was more striking during the day (+ 163%) than at night (+ 89%), suggesting that warming acted to both enhance geochemical dissolution and reduce biogenic calcification or inorganic precipitation. Together, these data indicate that, over the timescale observed here, photosynthesis and associated inorganic and biogenic CaCO3 precipitation do not exhibit the ability to counterbalance the warming-mediated increase in sediment heterotrophy and CaCO3 dissolution.

Seawater acidification and anthropogenic carbon distribution on the continental shelf and slope of the western South Atlantic Ocean

Abstract Increases in atmospheric carbon dioxide (CO2) concentrations since the beginning of the Industrial Revolution have led to increases in the flux of CO2 into the oceans. A large fraction of this increased flux occurs due to anthropogenic carbon (Cant), i.e., the excess carbon released by human activities. The oceans take up large amounts of Cant, and this process likely affects calcifying organisms and the formation and dissolution of calcium carbonate. In this study, we measured hydrographic and carbonate system parameters in the western South Atlantic Ocean. This region is key for understanding climate issues; however, it remains understudied, especially regarding the drivers of ocean acidification and its effects on marine organisms and ecosystems. Using novel data collected in this undersampled area of the global ocean, we (i) determined values of the marine carbonate system parameters and (ii) characterized the seawater acidification state along the western boundary current off the southeastern and southern coasts of Brazil. Specifically, we measured total alkalinity (AT) and pH and applied the TrOCA approach (to derive the Cant storage in the water masses) in the study area. Our results show that (i) AT and the dissolved inorganic carbon distribution in the study region are governed by calcification/dissolution and dilution/evaporation processes and that (ii) Cant is present in the central and intermediate water masses at an average concentration (± method precision) of 75.0 ± 6.6 μmol kg−1 and at depths of up to ~1000 m. The highest concentrations are observed in the lower levels of the Tropical Water, although we cannot exclude an overestimated Cant concentration in this layer, and the South Atlantic Central Water (SACW). These findings suggest that cross-shelf processes likely contribute to increased Cant along western boundary current systems. The storage of Cant in the SACW and the Antarctic Intermediate Water has led to long-term pH decreases of −0.17 ± 0.07 and −0.10 ± 0.06 pH units, respectively.

Mineral compositional controls on the porosity of black shales from the Wufeng and Longmaxi Formations (Southern Sichuan Basin and its surroundings) and insights into shale diagenesis

The effects of brittle minerals in shale diagenesis on shale pores remain controversial and it is difficult to quantify directly. However, the relationship between brittle minerals and shale pores could provide indirect guidance regarding diagenesis processes in post-mature marine shales. In this study, the pore size distribution was determined, and the relationship between pore volume and shale composition was examined in shale samples with different total organic carbon contents from the Wufeng and Longmaxi Formations, with the objective of distinguishing pore size ranges in organic matter and inorganic minerals, respectively, and studying shale diagenesis. The samples of the Wufeng and Longmaxi shales are composed of clay minerals, calcite, dolomite, quartz, feldspar, and some minor components. The pore size distributions, which were determined using nitrogen adsorption isotherm analysis of shale and kerogen, show similar trends for pore sizes less than approx. 6.5 nm but different trends for larger pore sizes. Mercury injection saturation shows that macropores account for 14.4–22% of the total pore volume. Based on a series of crossplots describing the relationships between shale composition and pore volume or porosity associated with different pore sizes as well as on scanning electron microscopy observations, organic matter pores were found to comprise most of the micro-mesopores (pore diameters &lt; 6.5 nm). Organic matter pores and intraparticle pores associated with carbonate constitute the majority of mesopores (pore diameters 6.5–50 nm). Finally, interparticle pores associated with quartz comprise the majority of the macropores. The mesopores associated with carbonate were formed by dissolution during diagenesis, whereas the macropores associated with quartz are the remainders of the original interparticle pores. Mesopore volumes increase with increasing carbonate content while macropore volumes decrease due to the ‘pore size controlled solubility’ effect, which causes dissolved calcium carbonate to precipitate in larger macropores.

A study on corrosion and scaling potential of drinking water supply resources in rural areas of Sarvabad, West of Iran

Corrosion is a physicochemical reaction occurring between the metal and its surroundings, which usually has an electrochemical nature and results in changes in the properties of the metal. The corrosive water dissolves the pipe’s material during flowing and this causes many problems. This study investigated the potential of corrosion and scaling of 46 water supply resources in the villages of Sarvabad, west of Iran during high-water (HW) and low-water (LW) periods. Parameters including pH, temperature, alkalinity, calcium hardness, and total dissolved solids (TDS) were measured and the Langelier, Rayznar, Aggressive, and Puchorius indices were calculated using the data collected. The zoning maps for the indices were prepared using ArcGIS (Ver. 9.3) software. The results showed that the mean value and standard deviation for the Langelier index were 0.23 and 0.28, respectively, while for the Rayznar index, they were 7.12 and 1.18, respectively. The values for the Aggressive index and Puchorius index were 11.6 and 1.84, and 7.03 and 1.45, respectively. The Langelier index in some water supplies showed a tendency to dissolve calcium carbonate, and meanwhile in some areas it tended to precipitate calcium carbonate. Moreover, based on the Rayznar index value, water potential for corrosion increases in steel pipes; based on the Aggressive index, the potential for corrosion is medium, whereas based on the Puchorius index, there is a potential for corrosion. A brief description about the zoning maps is also given.

Bio-cementation through controlled dissolution and recrystallization of calcium carbonate

We present an approach to bio-cementation of sand where the calcium source is prepared by dissolving powdered limestone (chalk) in lactic acid. Cementation is achieved through enzyme induced carbonate precipitation (EICP) with Jack Bean urease. The real-time nucleation and growth of crystals, crystal morphology and mechanical strength of consolidated samples was studied for dissolved chalk solution as well as calcium chloride (CaCl2) and calcium lactate solutions. Solutions containing lactate were found to yield spherical calcite crystals. The compressive strengths of consolidated samples ranged from 0.06 to 2.8 MPa, increasing with the amount of precipitated CaCO3.

Taking the metabolic pulse of the world's coral reefs.

Worldwide, coral reef ecosystems are experiencing increasing pressure from a variety of anthropogenic perturbations including ocean warming and acidification, increased sedimentation, eutrophication, and overfishing, which could shift reefs to a condition of net calcium carbonate (CaCO3) dissolution and erosion. Herein, we determine the net calcification potential and the relative balance of net organic carbon metabolism (net community production; NCP) and net inorganic carbon metabolism (net community calcification; NCC) within 23 coral reef locations across the globe. In light of these results, we consider the suitability of using these two metrics developed from total alkalinity (TA) and dissolved inorganic carbon (DIC) measurements collected on different spatiotemporal scales to monitor coral reef biogeochemistry under anthropogenic change. All reefs in this study were net calcifying for the majority of observations as inferred from alkalinity depletion relative to offshore, although occasional observations of net dissolution occurred at most locations. However, reefs with lower net calcification potential (i.e., lower TA depletion) could shift towards net dissolution sooner than reefs with a higher potential. The percent influence of organic carbon fluxes on total changes in dissolved inorganic carbon (DIC) (i.e., NCP compared to the sum of NCP and NCC) ranged from 32% to 88% and reflected inherent biogeochemical differences between reefs. Reefs with the largest relative percentage of NCP experienced the largest variability in seawater pH for a given change in DIC, which is directly related to the reefs ability to elevate or suppress local pH relative to the open ocean. This work highlights the value of measuring coral reef carbonate chemistry when evaluating their susceptibility to ongoing global environmental change and offers a baseline from which to guide future conservation efforts aimed at preserving these valuable ecosystems.

The impact of the geologic setting on the Quaternary aquifer, El-Tur area, Southwest Sinai, Egypt

The groundwater extracted from the unconfined Quaternary aquifer is the main source of water supply in El-Tur area. The area is bounded from the east by the elevated basement complex of Southern Sinai and from the west by El-Qabaliyat Ridge. The wadis dissecting these highlands form effective watersheds of the Quaternary aquifer. These wadis form areas of focused recharge. Recharge also occurs directly via the Quaternary sediments covering El-Qaa Plain. Subsurface lateral groundwater flow from the fractured basement contributes significant recharge to the aquifer as well. The aquifer sediment facies affect the type and quality of groundwater. In the eastern part where the aquifer is composed mainly of gravel and coarse sand with fragments of weathered basement, the Na-Cl-SO4 water dominates. In the west where the facies change is rapid and complex, many water types arise. The base exchange index (BEX) is positive in this part reflecting the role of clay minerals in changing the water types via cation exchange. In the east where clays are insignificant in the aquifer, the BEX is negative. In the western part next to El-Qabaliyat Ridge, the wells discharging from the calcareous sand zone have low groundwater salinities compared to the wells discharging from the alluvium. In general, the groundwater salinity increases in the direction of groundwater flow from the northeast to the southwest which reflects the dissolution of aquifer sediments. The concentration relationships between the major ions on one hand and chloride on the other reflect the dissolution of calcium carbonates, precipitation of K- and Mg-bearing minerals, and cation exchange of Ca for Na on clay minerals. The hydrochemical models support these reactions. In addition, they show that the effect of evaporation on the recharge water in the western catchment is about four times its effect on the eastern recharge water which reflects the rapid recharge through the wadis draining the fractured basement. Moreover, the contribution from the eastern catchment in sample No. 23 is more than four-folds the contribution from the western recharge area. The stable isotopes (2H and 18O) show that the Quaternary aquifer is recharging from recent rainfall. However, upward leakage of Paleogene groundwater (depleted in 18O) also occurs. The groundwater level map shows strong overpumping impact especially in the areas close to El-Tur city.

How Short-Lived Ikaite Affects Calcite Crystallization

The pathways of CaCO3 crystallization are manifold, often involving one or several metastable amorphous or nanocrystalline intermediate phases. The presence of such intermediates is often overlooked, because they are short-lived and/or occur at small molar fractions. However, their occurrence does not just impact the mechanisms and pathways of formation of the final stable CaCO3 phase, but also affects their crystal size, shape, and structure. Here we document the presence of a short-lived intermediate through in situ and time-resolved small and wide-angle X-ray scattering combined with high resolution electron microscope observations. When ikaite forms concomitant with the dissolution of amorphous calcium carbonate (ACC) but prior to calcite formation, fairly large glendonite-type calcite crystals grow despite the presence of citrate ligands that usually reduce crystal size. These were ideal seeding crystals for further crystallization from supersaturated ions in solution. In contrast, in the absence of ikaite the crystallization of calcite proceeds through transformation from ACC, resulting in fine-grained spherulitic calcite with sizes ∼8 times smaller than when ikaite was present. Noteworthy is that the formation of the intermediate ikaite, although it consumes less than 3 mol % of the total precipitated CaCO3, still clearly affected the calcite formation mechanism.

Comparison of hydrochemistry and organic compound transport in two non-glaciated high Arctic catchments with a permafrost regime (Bellsund Fjord, Spitsbergen)

An increase in air temperature related to climate change results in the retreat of glaciers, the degradation of permafrost, and the expansion of glacier-free areas in the polar regions. All these processes lead to changes in the Arctic landscape. They influence the hydrochemistry of streams and rivers fed by glaciers and thawing permafrost. In this study, we examine eighty two water samples from two non-glaciated catchments with snow-permafrost regime: the Tyvjobekken Creek and the Reindeer Creek (NW Wedel-Jarlsberg Land, Spitsbergen). We cover hydrometeorological measurements, fluctuations of physicochemical parameters (pH, specific electrolytic conductivity (SEC)), and the presence of selected organic compounds (dissolved organic carbon (DOC), formaldehyde (HCHO), ∑phenols). The obtained levels of DOC (0.061–0.569mgCL−1) and HCHO (<LOD-0.140mgL−1) in water samples of these two high Arctic creeks confirm the role of the melting permafrost as a rich source of terrestrial organic carbon and organic pollutants, as well as the impact of rainfall on surface water chemistry. It was found that fluctuations of physicochemical indices (pH, SEC, DOC) were related to changes in mean daily discharge of Reindeer Creek (0.012–0.034m3s−1) and Tyvjobekken Creek (0.011–0.015m3s−1) (r>0.40). The Tyvjobekken Creek catchment, in contrast to Reindeer Creek catchment, turned out to be resistant to rapid changes in meteorological conditions (r<0.10) and surface runoff. The processes of permafrost thawing, calcium carbonate dissolution, and biogeochemical “breathing” of soils proved to be crucial for the development of water chemistry. In conclusion, the surface water chemistry of the Reindeer Creek was found to result from the mutual influence of hydrometeorological indices and the biogeochemical environment of the catchment.

Effect of calcium formate as an additive on desulfurization in power plants

SO2 in flue gas needs to be eliminated to alleviate air pollution. As the quality of coal decreases and environmental standard requirements become more stringent, the high-efficiency desulfurization of flue gas faces more and more challenges. As an economical and environmentally friendly solution, the effect of calcium formate as an additive on desulfurization efficiency in the wet flue gas desulfurization (WFGD) process was studied for the first time. Improvement of the desulfurization efficiency was achieved with limited change in pH after calcium formate was added into the reactor, and it was found to work better than other additives tested. The positive effects were further verified in a power plant, which showed that adding calcium formate could promote the dissolution of calcium carbonate, accelerate the growth of gypsum crystals and improve the efficiency of desulfurization. Thus, calcium formate was proved to be an effective additive and can potentially be used to reduce the amount of limestone slurry required, as well as the energy consumption and operating costs in industrial desulfurization.

A hybrid multi-time-step framework for pore-scale and continuum-scale modeling of solute transport in porous media

In this paper, we propose a computational framework, which is based on a domain decomposition technique, to employ both finite element method (which is a popular continuum modeling approach) and lattice Boltzmann method (which is a popular pore-scale modeling approach) in the same computational domain. To bridge the gap across the disparate length and time-scales, we first propose a new method to enforce continuum-scale boundary conditions (i.e., Dirichlet and Neumann boundary conditions) onto the numerical solution from the lattice Boltzmann method. This method is based on maximization of entropy and preserve the non-negativity of discrete distributions under the lattice Boltzmann method. The proposed computational framework allows different grid sizes, orders of interpolation, and time-steps in different subdomains. This allows for different desired resolutions in the numerical solution in different subdomains. Through numerical experiments, the effect of grid and time-step refinement, disparity of time-steps in different subdomains, domain partitioning, and the number of iteration steps on the accuracy and rate of convergence of the proposed methodology are studied. Finally, to showcase the performance of this framework in porous media applications, we use it to simulate the dissolution of calcium carbonate in a porous structure.

Targeted delivery and pH-responsive release of doxorubicin to cancer cells using calcium carbonate/hyaluronate/glutamate mesoporous hollow spheres

Currently, the efficacies of the existing anticancer drugs used in chemotherapy are still unsatisfactory. Therefore, drug delivery system has received considerable research interest. In the present study, calcium carbonate/hyaluronate/glutamate mesoporous hollow spheres are prepared through a facile method. The results indicate that the mesoporous hollow spheres can efficiently load the anticancer drug doxorubicin. Through the specific binding of hyaluronate on hollow spheres with CD44 receptors overexpressed on cancer cells, the drug-loaded hollow spheres can be specifically delivered to target cancer cells. Owing to the gradually dissolution of calcium carbonate in the weak acidic microenvironment of cancer cells, the loaded doxorubicin can be released over the period of 14days with pH-responsive and sustained manner to specifically and significantly treat cancers. Through loaded onto the hollow spheres, the IC50 value of doxorubicin for HeLa cancer cells is 0.0113μg/mL, much lower than that of the free doxorubicin (0.0801μg/mL). However, the IC50 value of doxorubicin for V79-4 cells is 0.2032μg/mL, obviously higher than that of the free DOX (0.1396μg/mL). The specificity of the doxorubicin between normal and cancer cells can be enhanced about 10-fold. The current study suggests the possible application of pH-responsive inorganic carriers for efficiently treatment of human cancers.