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201. 题目: A comparison of methods for the extraction of dissolved organic matter from freshwaters

Studies of dissolved organic matter (DOM) composition have used several different methods to concentrate and extract the DOM from fresh water, but the impact of these methods on the composition of the DOM is relatively unknown, as very few studies use more than one method to compare results. The aim of this study was to use several methods, frequently used in the scientific literature, to concentrate and extract DOM from fresh water and compare the elemental and functional group composition of the extracted DOM. In addition, the cost, in terms of money, resources and time, were assessed for each method. The results showed that the elemental and functional group composition of the extracted DOM varied between methods significantly. The methods that yielded the most similar and reproducible DOM results were rotary evaporation, dry-down at 60 °C and freeze-drying. Although each of these methods required a relatively expensive piece of laboratory equipment, this was a 'one-off' cost, and consumables and time per sample were relatively low. This study highlights the dangers of comparing DOM data from different studies when the DOM has been extracted via different methods. In future, it is recommended that studies of DOM composition report their methods of extraction clearly and consistently, ideally using one (or more) of the methods showing reliable results here.

202. 题目: Enhanced cometabolism of benzo(a)anthracene by the lignin monomer vanillate is related to structural and functional responses of the soil microbiome

Lignin is a natural polymer composed of phenolic units. The structural similarity between lignin monomers and recalcitrant aromatic pollutants raises the possibility of their cometabolism by soil microorganisms. Here, we explored the links between polycyclic aromatic hydrocarbon (PAH) degradation and microbiome responses in soil microcosms amended with lignin or one of its phenolic units, vanillate, by coupled amplicon and metagenomic shotgun sequencing. The transformation of the four-ring model PAH benzo(a)anthracene (BaA) was monitored by using a radiolabelled tracer. The results demonstrated that vanillate significantly promoted 14CO2 production during incubation, suggesting activation of BaA biodegradation in the soil microcosms. Lignin changed the fate of BaA mainly by increasing its adsorption to soil organic matter. In contrast to the control microcosms, the mineralization and formation of nonextractable residue (NER) from BaA in the presence of vanillate were sensitive to the fungicide cycloheximide. Lignin and vanillate consistently enriched bacterial methyl utilization and aromatic ring cleavage genes at the two sampling times, which, however, did not translate to BaA mineralization. The distinct responses of the fungal community to vanillate as well as the coupled cycloheximide-induced inhibition of BaA mineralization and 18S rRNA gene abundance suggest an essential contribution of fungi to BaA biodegradation in the vanillate-amended microcosms. Overall, these findings reveal a cometabolic mechanism between vanillate and PAHs, which contributed to the detoxification of BaA in the soil. This study also provides a scientific basis for the bioremediation of PAH-contaminated soil by modulating the soil microbiome with phenolic monomers of lignin.

203. 题目: Using Fe chemistry to predict Fe uptake rates for natural plankton assemblages from the Southern Ocean

A recent study using Fe-limited phytoplankton strains, showed that iron (Fe) uptake rates normalized by cellular surface area were best related to dissolved iron (dFe) concentrations as the inorganic Fe (Fe') supply rates were not sufficient to satisfy the Fe biological demand. Short-term (24 h) shipboard incubations with the in-situ phytoplankton community were used to measure Fe uptake rates that were normalized per biomass (as particulate organic carbon, POC). Fe uptake rates measured following 55FeCl3 additions (0.05 to 0.9 nM) were fitted to different Fe pools (dFe, Felabile, and Fe') using the Michaelis-Menten equation. Data showed a similar high conditional stability constant for biological transporters across all sites and phytoplankton size classes, with only a 2-fold variation in the concentrations of cellular transporters. These observations are in line with previous reports that eukaryotic phytoplankton takes up Fe close to the limit imposed by transporters cellular density and uses similar high-affinity Fe uptake systems. To further explore the link between Fe uptake rates and Fe chemistry, we also studied the effect of additions of preequilibrated with different Fe-binding ligands (L) including: the siderophore desferrioxamine B, two carbohydrates (glucuronic acid and carrageenan) and two different bacterial exopolycarbohydrates (L6 and L22, referred as EPS). For all stations, phytoplankton were able to acquire Fe associated to DFB as previously reported, however, different Fe:L ratios prevent quantitative comparison with previous studies. Iron bound to carbohydrates, glucuronic acid, carrageenan and EPS could enhance or decrease Fe uptake rates in comparison to equimolar FeCl3 addition. These results illustrate that the effect of such L on Fe uptake rates will depend on the in-situ plankton community and their chemical structure. The variation of the Fe' concentrations was able to explain up to 69% of the Fe uptake rates observed for the Antarctic communities. This relationship with Fe' was related to the fact that the Fe' maximal supply, due to the dissociation of FeL, was enough to satisfy the Fe uptakes rates. Calculations using previous reports in contrasted regions of the Southern Ocean, showed that Fe' maximal supply was greater than Fe uptake rates measured in 80% of the cases. Moreover, considering photo- and redox-chemistry as well as kinetical situations prevailing in the field, Fe' should not be overlooked as a pool able to satisfy most of the Fe biological demand. Finally, this study points towards the potential that the GEOTRACES Fe chemical speciation data represent to explore Fe uptake rates at a larger scale in this vast Fe-limited oceanic region.

204. 题目: Earth’s soil harbours ancient carbon

205. 题目: Size‐fractionated compositions of marine suspended particles in the Western Arctic Ocean: lateral and vertical sources

We present full water depth sections of size‐fractionated (1‐51 μm; >51 μm) concentrations of suspended particulate matter and major particle phase composition (particulate organic matter (POM), including its carbon isotopic composition (POC‐δ13C) and C:N ratio, calcium carbonate (CaCO3), opal, lithogenic particles, and iron and manganese (oxyhydr)oxides from the U.S. GEOTRACES Arctic Cruise (GN01) in the Western Arctic in 2015. Whereas biogenic particles (POM and opal) dominate the upper 1000 m, lithogenic particles are the most abundant particle type at depth. Minor phases such as manganese (Mn) oxides are higher in GN01 than in any other U.S. GEOTRACES cruises so far. Extremely depleted POC‐δ13C, as low as ~‐32‰, is ubiquitous at the surface of the Western Arctic Ocean as a result of different growth rates of phytoplankton. Moderate penetration of depleted POC‐δ13C to depth indicates active sinking of large particles in the central basin. Lateral transport from the Chukchi shelf is also of significance in the Western Arctic, as is evident from increases in biogenic silica to POC ratios and Mn oxide concentrations in the halocline, as well as lithogenic element contents in the deep waters. Our study supports previous suggestions of the near absence of CaCO3 in the Arctic Basin. This study presents the first data set of concentration and composition of suspended particles in the Western Arctic Ocean, and sheds new light on the vertical and lateral processes that govern particle distribution in this enclosed ocean basin.

206. 题目: In-situ formed N-doped bamboo-like carbon nanotubes encapsulated with Fe nanoparticles supported by biochar as highly efficient catalyst for activation of persulfate (PS) toward degradation of organic pollutants

207. 题目: Long-term high-P fertilizer input decreased the total bacterial diversity but not phoD-harboring bacteria in wheat rhizosphere soil with available-P deficiency

Appling phosphorus (P) fertilizer to agroecosystems affects not only crop yield but also associated soil microbial communities. The bacterial phoD gene encodes alkaline phosphatase (ALP) and plays an important role in organic P decomposition in soils. However, the impacts of long-term P fertilization on the bacterial phoD gene community, the total bacterial community, and the relationships of these communities with soil properties are poorly understood in loess soils with available-P deficiency. In this study, the impact of mineral P fertilization on the soil bacterial community was assessed. The 16S rRNA and phoD genes were targeted in DNA extracted from wheat rhizosphere soils subjected to five P fertilization rates (0 (P0), 50 (P50), 100 (P100), 150 (P150) and 200 (P200) kg P2O5 ha−1 yr−1) applied annually for 14 years. Compared to the P0 treatment, the P fertilization treatments increased the soil organic C (SOC), microbial biomass C (MBC) and available P (AP), and in the high-P treatments (P150 and P200) the total P (TP) and organic P (OP) increased, while the ALP activity decreased. All P fertilization treatments reduced the total bacterial diversity (Shannon index). However, only P200 decreased the number of operational taxonomic units (OTUs) with the 16S rRNA gene, and no P fertilization treatments affected phoD-harboring bacterial OTUs or diversity when compared to those in the P0 treatment. Additionally, compared to P0, the P fertilization treatments changed the 16S rRNA and phoD gene bacterial community compositions, with increased relative abundances of 3 phyla and 7 genera and decreased abundances of 1 phylum and 2 genera for the 16S rRNA gene and increased abundances of 4 genera and decreased abundances of 2 phyla and 1 genus for the phoD gene. Microbial network analysis showed that the high-P treatments (P150 and P200) reduced the number of links in the microbial network at the genus level for the 16S rRNA gene. Principal coordinate analysis (PCoA) showed that P fertilization treatments shifted the total bacterial community structure, and redundancy analysis (RDA) revealed that soil dissolved organic C (DOC) and P (AP, OP, TP and ALP) levels were significantly related to the total bacterial community structure. In conclusion, this study demonstrated that long-term P fertilization significantly affected soil C and P as well as the total and phoD-harboring bacterial community compositions in wheat rhizosphere soils and that high P fertilizer application rates reduced total bacterial OTUs, diversity and the connections, which might affect soil biogeochemical cycles.

208. 题目: High-resolution imaging of labile P & S in coastal sediment: Insight into the kinetics of P mobilization associated with sulfate reduction

The internal P cycling in coastal sediments during early diagenesis is of great importance to aquatic ecosystems, but its relationship with sulfate reduction is still unclear and lacks visualized evidence. In this study, diffusive gradients in thin films (Zr-oxide DGT and AgI DGT) techniques at a two-dimensional (2D) submillimeter resolution were utilized to synchronously characterize the in situ labile P and dissolved sulfide in coastal sediments around Xiamen Bay, China. The distributions of dissolved sulfide formed from sulfate reduction showed large vertical and horizontal variations, which are mainly controlled by the reactive organic carbon (OC) and redox conditions at different sampling sites. Multiple correlation analysis revealed that significant and linear correlations exist between dissolved sulfide and DGT-labile P, demonstrating that P mobilization is predominantly regulated by sulfide-dependent reductive dissolution of Fe(III)-bound P and sulfate reduction-associated OC mineralization. Both labile P and dissolved sulfide showed lower values at intertidal sites, due to oxic/suboxic conditions favoring weak sulfate reduction and strong P sequestration. Labile P accumulation during flood tides and removal during ebb tides on tidal timescales indicate that the mobilization and detention of P in surface sediment are regulated by tidal cycles and consequential S and Fe redox cycling. The apparent diffusion flux of P implies that the internal P loading can act as a P source to aquatic ecosystems.

209. 题目: Understanding the interaction between triclocarban and denitrifiers

The widespread use of triclocarban (TCC) has led to its substantial release into aquatic environment. As an important microbial community in wastewater treatment, denitrifying cultures likely remove TCC and also may be affected by TCC which has not been revealed. This work therefore aims to add knowledge to these questions. Experimental results showed that 71.2 %-79.4 % of TCC was removed by denitrifying sludge in stable operation when TCC concentration was 1∼20 mg/L. Mass balance analyses revealed that TCC was dominantly removed by adsorption rather than biodegradation, and non-homogeneous multilayer adsorption was responsible for this removal, with hydroxyl groups, amides and polysaccharides acting as the possible adsorption sites. Although the physicochemical properties of denitrifying cultures were unaffected after short-term exposure, long-term exposure to TCC deteriorated the settleability, dewaterability, flocculability and hydrophobicity of denitrifying biomass. It was observed that 20 mg/L TCC decreased denitrification efficiency by 70 % in long-term operation. Mechanism studies revealed that long-term exposure to TCC resulted in the increase of extracellular polymeric substances especially proteins, and the decrease of denitrifiers' activities. High-throughput sequencing revealed that TCC decreased the diversity of microbial community and the abundances of denitrifier genera such as Hyphomicrobium, Paracoccus, Saprospiraceae and unclassified-f-Rhodocyclaceae.

210. 题目: Benign zinc oxide betaine-modified biochar nanocomposites for phosphate removal from aqueous solutions

211. 题目: Substantial brown carbon emissions from wintertime residential wood burning over France

Brown carbon (BrC) is known to absorb light at subvisible wavelengths but its optical properties and sources are still poorly documented, leading to large uncertainties in climate studies. Here, we show its major wintertime contribution to total aerosol absorption at 370 nm (18–42%) at 9 different French sites. Moreover, an excellent correlation with levoglucosan (r2 = 0.9 and slope = 22.2 at 370 nm), suggesting important contribution of wood burning emissions to ambient BrC aerosols in France. At all sites, BrC peaks were mainly observed during late evening, linking to local intense residential wood burning during this time period. Furthermore, the geographic origin analysis also highlighted the high potential contribution of local and/or small-regional emissions to BrC. Focusing on the Paris region, twice higher BrC mass absorption efficiency value was obtained for less oxidized biomass burning organic aerosols (BBOA) compared to more oxidized BBOA (e.g., about 4.9 ± 0.2 vs. 2.0 ± 0.1 m2 g1, respectively, at 370 nm). Finally, the BBOA direct radiative effect was found to be 40% higher when these two BBOA fractions are treated as light-absorbing species, compared to the non-absorbing BBOA scenario.

212. 题目: Biochar as composite of phosphate fertilizer: Characterization and agronomic effectiveness

Organomineral phosphate fertilizers (OMP) may reduce phosphate release rate and its direct contact to the soil solid phase, increasing the effectiveness of phosphorus (P) fertilization. This study aimed to evaluate the effect of granulating biochar (BC) with triple superphosphate (TSP) in two forms (blend or coated) and three proportions (5, 15 and 25%, w/w) on the P release kinetics and plant growth. A successive plant trial using two soils of contrasting P buffering capacities and five P doses (0, 20, 40, 80 and 120 mg kg−1) was set to investigate the agronomic effectiveness of OMP that presented the slowest P release kinetic. The kinetic test showed that within the first 1.5 h, TSP, OMP blend and OMP coated fertilizers released 92, 82 and 36% of total P, respectively. Thereby, BC addition to TSP reduced the P release rate, mainly due to coating. The fertilizers coated with 15% and 25% BC (C15 and C25, respectively) presented the slowest P release rate. For the plant trial, C15 was chosen because it requires less BC when compared with C25 fertilizer. In the first crop, C15 provided more P to plants, especially in the soil with high P buffering capacity, which increased by 10% and 20% the P uptake and the P recovered by the plant when compared with TSP, respectively. In the sandy soil, fertilizers C15 and TSP showed the same performances regarding yield, P uptake and P recovery rate. At consecutive cultivation, regardless of the soil type, P sources (C15 and TSP) did not differ in yield, P uptake and P recovery. Therefore, biochar-based organomineral phosphate fertilizer can enhance P use efficiency in high P-fixing tropical soils, increasing P recovery and uptake when compared with TSP.

213. 题目: Biogeochemistry in an intertidal pocket beach

Sandy beaches are places of active organic matter mineralization due to water renewal providing organic matter and electron acceptors in the porous and permeable sands. Recycled biogenic compounds are efficiently transferred to the coastal marine environment via wave and tidal-driven advective flows. The biogeochemical processes in beach aquifers were mainly studied in semi enclosed systems with low tidal amplitude, and with a connection to continental aquifers contributing to solute fluxes to the coast from terrestrial groundwater. We present here the study of a pocket beach isolated from terrestrial aquifers with a high tidal amplitude and a medium energy wave regime. In situ measurements, cross-shore profiles and vertical sampling were conducted during several tidal cycles in spring and autumn. Cross-shore transects, obtained at low tide from holes that represent a mixture of the upper 20 cm of the water saturated zone, showed concentration gradients of redox and recycled compounds. Increase in pCO2, dissolved phosphate and ammonium concentrations downslope revealed that more products from organic matter mineralization accumulated in the lower beach. The related increase in total alkalinity downslope indicated that the part of anaerobic processes in organic matter oxidation was higher in the lower beach. Concentration and δ13C of dissolved inorganic carbon in pore waters suggested that the carbon mineralized in pore waters came from marine plant debris that were mixed with the sand. Continuous probe records of dissolved oxygen saturation and vertical profiles revealed a tidally-driven dynamics of pore water in the first centimetres of the lower beach aquifer. Ventilation of pore waters corresponded to wave pumping and swash-induced infiltration of seawater in the upper 10–20 cm of sediment. Nutrients and reduced compounds produced through organic matter mineralization remained stored in pore water below the layer disturbed by wave. The flux of these components to seawater is possible when this interface is eroded, for example when wave energy increases after a less energetic period. The low extension of the studied aquifer, typical of pocket beaches, limits the connection with continental groundwater. Both tidally-driven and wave-driven recirculation of seawater allows pocket beaches to be efficient bioreactors for marine organic matter mineralization. As such, they provide the coastal environment with recycled nutrients, and not new nutrients.

214. 题目: Novel ball-milled biochar-vermiculite nanocomposites effectively adsorb aqueous As(Ⅴ)

Ball milling was used to fabricate a nanocomposite of 20% hickory biochar (600 °C) and 80% expanded vermiculite (20%-BC/VE). This novel composite adsorbent had much higher removal of As(V) from aqueous solutions than ball-milled biochar and expanded vermiculite. Characterization of these adsorbents showed that the enhanced As(V) adsorption was ascribed to much larger surface area and pore volume (2–6 times), notable changes in crystallinity, activation of cations, and increased functional groups in the nanocomposite compared with the ball-milled products of their pristine counterparts. The As(V) adsorption process by the 20%-BC/VE fitted well with the pseudo-second-order kinetic model (R2 = 0.990) and Langmuir isotherm model (R2 = 0.989) with a maximum adsorption capacity of 20.1 mg g−1. The 20%-BC/VE best performed at pH about 6. The adsorption efficiency was not sensitive to the competition of $NO3-$, $Cl-$, $SO42-$, as well as the coexistence of humic acid. However, the adsorption capacity for As(V) was significantly reduced by coexisting with $PO43-$. The 20%-BC/VE composite can potentially serve as a superior low-cost adsorbent for As(V) removal in real-world applications.

215. 题目: Repeated applications of organic amendments promote beneficial microbiota, improve soil fertility and increase crop yield

Long-term adoption of intensive agricultural system negatively affects soil fertility, soil microbiome and may compromise the quality and amount of crop production. To avoid these problems, application of organic materials has been proposed as a potential alternative strategy for soil management. Therefore, the objective of this study was to compared the effects of conventional and organic soil management on crop yield of rocket (Eruca sativa), soil fertility, and microbiome structure through a 2-year long mesocosms experiment. Eight organic treatments, different in terms of organic amendment chemistry (i.e., alfalfa hay, biochar, glucose, manure) and application frequency, were compared with conventional management practices based on mineral fertilizer and chemical fumigation. Crop quality was assessed by measuring the NO3 content in leaves, whereas soil chemical and microbiological (i.e., FDA activity and functioning by BIOLOG EcoPlates™) properties were evaluated to understand their effects on soil fertility. Changes in soil microbiota were assessed by high-throughput sequencing of bacterial and fungal rRNA gene markers. Application of organic amendments significantly improved crop yield, especially when alfalfa and glucose were applied as a single dose. NO3 concentration in leaves was decreased with biochar and manure application, and this did not depend on the application frequency. Application of synthetic fertilizer and fumigation induced soil acidification, increased soil salinity, and reduced soil microbiota diversity, activity and functionality, with negative effects on crop yield. In conclusion, this study indicates that long-term application of organic amendments effectively improved soil fertility and promoted the development of a beneficial soil microbiota capable of supporting high plant yield under intensive agricultural system.

216. 题目: Filtration of Microplastic Spheres by Biochar: Removal Efficiency and Immobilisation Mechanisms

217. 题目: Molecular Mechanisms of Per- and Polyfluoroalkyl Substances on a Modified Clay: A Combined Experimental and Molecular Simulation Study

Repeated applications of aqueous film-forming foams (AFFF) in designated firefighting training areas has caused severe groundwater contamination by per- and polyfluoroalkyl substances (PFASs). Many research efforts are currently engaged for the effective removal of these chemicals from environmental waters. In this study, we demonstrate that modified clay produced by intercalating quaternary ammonium cations in the exchangeable interlayer sites of smectite clay can effectively remove PFAS pollutants in real groundwater via strong adsorption. The performance of the modified clay (with removal efficiencies 95∼99%) is superior to those of granular activated carbon or hard-wood biochar and comparable to an ion exchange resin. Removal efficiency is not impacted by potential organic co-contaminants (e.g., diesel, BTEX, TCE, and 1,4 dioxane) and or water chemistry (Ca2+ and Na+) at environmentally relevant concentrations. Furthermore, piecewise isotherms are identified to represent the uptake of PFAS by the modified clay. Based on molecular dynamics simulations, the anionic PFASs first occupy the highly polarized bare interlayer edge sites leading to a linear isotherm and then the interlayer surface sites resulting in a Langmuir isotherm. The ionic interactions between the cationic intercalant (N+) and the terminal oxygen atoms of carboxylate or sulfonate groups of PFASs play a dominant role in adsorption, and the lateral interaction in particular fluorophilic attraction among PFASs accelerate the adsorption. The strength of these interactions is quantified using Density Functional Theory calculations. Simulation results match reasonably well with the experimentally determined basal spacing and Fourier transform infrared spectroscopy of the modified clay loaded with PFASs. Overall, the combined experimental and molecular simulation studies elucidate the adsorption mechanism of PFASs on the modified clay and provide critical information to guide the use of modified clays for PFAS water treatment in the field.

218. 题目: Simulating nitrate and DON leaching to optimize water and N management practices for greenhouse vegetable production systems

Nitrate and dissolved organic nitrogen (DON) leaching are major nitrogen (N) loss pathway for intensive greenhouse vegetable production system (GVPS). Quantifying the nitrate and DON leaching is essential to develop best management practices. In this study, four seasons of tomato field experiments were conducted to test the impact of different water (furrow and drip irrigation) and N management practices and straw incorporation on N leaching and vegetable yield. A soil-crop system model (WHCNS_Veg, soil Water Heat Carbon Nitrogen Simulator for vegetables) was calibrated and evaluated, and results suggested that the model performed well for simulating soil water potential, water drainage, nitrate and DON leaching, crop N uptake, and yield. The average values of NRMSE, IA, and NSE for nitrate (or DON) leaching ranged from 12.1 % (11.3 %), 0.96 (0.94), and 0.85 (0.77), respectively. Compared with furrow irrigation and over fertilization, drip fertigation treatments reduced irrigation water use, water drainage, nitrate and DON leaching by 41 %, 60 %, 68 %, and 68 %, respectively, without compromising crop yield. Straw incorporation further reduced nitrate and DON leaching by 13.1 % and 25.7 % compared with no straw incorporation. Furthermore, we found that DON leaching accounted for 21.7 %–46.6 % of total dissolved N leaching loss in the study area. Using the model, we determined that the optimal water and N inputs ranged from 350−400 mm and 350−400 kg N ha−1 for the winter-spring season and 200−250 mm and 150−200 kg N ha−1 for the autumn-winter season. This led to an 87 % reduction in nitrate leaching and a 74 % reduction in DON leaching with only a slightly reduction in crop yield (<5 %) compared with the local farmer practice. The recommended water and N management practices achieved high crop yield with less environmental impact.

219. 题目: Variations in organic carbon sourcing along a trans-Himalayan river determined by a Bayesian mixing approach

Rivers transfer particulate organic carbon (POC) from eroding mountains into geological sinks. Organic carbon source composition and selective mobilization have been shown to affect the type and quantity of POC export, but their combined effects across complex mountain ranges remain underexplored. Here, we examine the variation in organic carbon sourcing and transport in the trans-Himalayan Kali Gandaki River catchment, along strong gradients in precipitation, rock type and vegetation. Combining bulk stable nitrogen, and stable and radioactive organic carbon isotopic composition of bedrock, litter, soil and river sediment samples with a Bayesian end-member mixing approach, we differentiate POC sources along the river and quantify their export. Our analysis shows that POC export from the Tibetan segment of the catchment, where carbon bearing shales are partially covered by aged and modern soils, is dominated by petrogenic POC. Based on our data we re-assess the presence of aged biospheric OC in this part of the catchment, and its contribution to the river load. In the High Himalayan segment, we observed low inputs of petrogenic and biospheric POC, likely due to very low organic carbon concentrations in the metamorphic bedrock, combined with erosion dominated by deep-seated landslides. Our findings show that along the Kali Gandaki River, the sourcing of sediment and organic carbon are decoupled, due to differences in rock organic carbon content, soil and above ground carbon stocks, and geomorphic process activity. While the fast eroding High Himalayas are the principal source of river sediment, the Tibetan headwaters, where erosion rates are lower, are the principal source of organic carbon. To robustly estimate organic carbon export from the Himalayas, the mountain range should be divided into tectono-physiographic zones with distinct organic carbon yields due to differences in substrate and erosion processes and rates.

220. 题目: Characteristics of CaCO3 nucleated around cyanobacteria: implications for calcification process

To evaluate the influences of cyanobacterial extracellular polymeric substances (EPS) on CaCO3 precipitation, calcification experiments were conducted for 48 h (initial values of calcite saturation state and equilibrium CO2 partial pressure were ∼5-fold and ∼600 μatm, respectively) using cultures of four filamentous strains (Leptolyngbya sp. (NIES-2104), Scytonema sp. (NIES-2130), Phormidium ambiguum (NIES-2119), and Spirulina subsalsa (NIES-598)). All cultures induced CaCO3 precipitation mainly by photosynthesis to form mono-/ poly crystalline calcite and amorphous calcium carbonate (ACC) around them. These features suggested a CaCO3 nucleation process via an ACC precursor phase on negatively charged substances generated by cyanobacteria (i.e., cell walls, EPS, and oxygen bubbles). The characteristics of the precipitated CaCO3 were strongly influenced by the surface properties of the cyanobacteria. For Leptolyngbya, which lacks EPS, a small number of CaCO3 was nucleated onto the smooth surface of negatively charged cell walls and entire cells were incorporated into a large single crystal of calcite. For Scytonema and Phormidium, which possess EPS sheaths, a relatively large number of CaCO3 was nucleated onto the rough surface of negatively charged sheaths, and their sheaths were encrusted and partially impregnated by calcite crystals. For Spirulina, which possesses a loose EPS matrix, CaCO3 nucleation was scarce and restricted to the surface of negatively charged oxygen bubbles stabilized by the EPS matrix to form hollow calcite crystals. These results suggest that chemical properties (i.e., abundance of dissociated acidic groups) primarily controlled the presence/absence of CaCO3 nucleation around cyanobacteria, while a physical property (i.e., submicron-scale structure of negatively charged substances) primarily controlled the numbers of crystal nuclei provided and stabilized ACC precursors as well as the calcification styles (sheath encrustation or impregnation).

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