Silicon Mobilization in Soils: the Broader Impact of Land Use

Dissolved Si (DSi) provision from land systems triggers diatom growth and CO₂ sequestration. Soils and ecosystems act as a Si “filter”, transforming DSi originated from mineral weathering into biogenic Si (BSi) after DSi uptake by plants, or into other pedogenic forms of Si (non-BSi). Land use changes the quantity of BSi and non-BSi pools along the soil profile. However, methods used to isolate Si pools include chemical extractions at high temperatures and alkaline environments and therefore are unable to provide information concerning the dissolution potential of BSi and non-BSi pools under normal conditions of temperature and pH. Here, we conducted a batch experiment where forest, pasture and cropland soil samples were mixed with water at 25 °C and pH 7. The soil samples were collected from a temperate land use gradient located in the Belgian Loess Belt. We measured dissolved Si and aluminium (Al) during 80 days. BSi and non-BSi pool contents along the soil profile were known, as they had been established previously through chemical extraction. Results show that BSi and non-BSi enriched samples present distinct Si and Al dissolution curves. While non-BSi pools contribute significantly with immediate availability of Si, BSi pools present an initial slow dissolution. Therefore, croplands that were depleted of phytoliths and had poorly organic horizons display higher concentrations of initial dissolved Si, while pastures and forests, where pedogenic pools dominate only at depths below 40 cm, have more limited initial Si release.

     

The Vegetation Silica Pool in a Developing Tidal Freshwater Marsh

Tidal marshes play an important role in the estuarine Si cycle. Dissolved silicon (DSi) is taken up by marsh diatom communities and by tidal marsh vegetation. Delivery of DSi back to the estuary after biogenic silica dissolution potentially increases the resilience of the estuary against harmful effects of DSi depletion events. Tidal freshwater marsh vegetation, often dominated by reed (Phragmites australis) has previously been hypothesized to contribute to the Si buffering function of tidal marshes, by dissolution of reed biogenic Si (BSi) into the soil pore water and consequent seepage of DSi to the estuary. In this study the Si pool in the vegetation of a restored tidal freshwater marsh was quantified using species-based cover-biomass relationships and Si analyses. The Si pool in the aboveground biomass increased from 1.2 to 6.5 t km^?2 during the first 6 years of colonization by tidal freshwater marsh species. Our results indicate that young tidal freshwater marshes have a high potential to build up a large vegetation Si pool quickly, mostly due to colonization by species that have both high Si concentrations and high biomass production (e. g. P. australis). This Si pool in vegetation could act both as a long-term sink for Si along estuaries (should Si remain buried in the sediments) or as a short-term source for DSi (should Si be dissolved to DSi).     

Silicate Release from Sand-Manipulated Sediment Cores: Biogenic or Adsorbed Si?

The influence of an addition of either sand and/or spring-bloom algae on the efflux of nutrients from intact sediment cores from the Baltic Sea was studied in a flow-through experiment. The addition of sand significantly increased the efflux of silicon (Si) from sediment, but the algal addition did not. The effects on phosphorus (P) were not as clear, and fluxes of nitrogen (NH₄ and NO_2?+?3) remained relatively unaffected by the additions. The small effect of the algal addition was caused by the short time-period covered by the experiment and possibly by adsorption of released Si by the sediment. A follow-up bottle experiment showed that despite the apparently lower content of easily available Si and biogenic silica, BSi, in the sand, the sand-induced Si efflux was caused by release of Si from the sand itself, rather than by indirectly increasing the dissolution of BSi present in the sediment.     

Factors Affecting Dissolved Silica Concentrations, and DSi and DIN Stoichiometry in a Human Impacted Watershed (Po River, Italy)

Data on dissolved (DSi) and particulate (PSi) silica concentrations, along with DSi and DIN (dissolved inorganic nitrogen) stoichiometry in surface waters were reviewed for the Po river watershed. DSi in the cascade river and lake ecosystems followed clear upstream-downstream gradients. The DSi (77–178 kt Si y^???1) and PSi (879–1,486 kt Si y^???1) loadings from the Po river to the Adriatic Sea display strong inter-annual variability, related with the river discharge. In the lowland river reaches, the DSi to DIN ratio highlighted frequent potential Si limitation, especially in summer during diatom blooms. Since the Po river watershed is heavily inhabited and exploited with agriculture (~43 % of the total surface) and livestock husbandry (~3.4 × 10⁶ cattle heads), agriculture likely interferes with the natural silicon cycle. We present a preliminary assessment of the biogenic silica (BSi) which was fixed in and harvested with the main crop biomass. In the period 2000–2010, the total BSi in crops was 270–386 kt Si y^???1. Three main cereals (maize, wheat, rice) accounted for 70 % BSi, of which 89 % was accumulated in straw. The quantity of BSi that was annually accumulated in the cereal biomass increased 2–4 folds from 1950 to 2010. We estimated that a great part of the BSi accumulated in straw and fodder was processed by the cattle stock and returned to soil as manure. A large part of the cropland is exposed to erosion and PSi can be exported to canals and rivers at particularly high rates during flash flood events. Recent transformations of either agricultural practices or crop typology probably perturb the Si cycling.     

Base cations and micronutrients in forest soils along three clear-cut chronosequences in the northeastern United States

Determining effects of clear-cutting on base cations and micronutrients is essential for ensuring the sustainability of forestry for biofuels and wood products. The objective of this study was to quantify long-term changes in forest floor and mineral soil base cations (Ca, Mg, and K) and micronutrient (Mn, Zn, and Cu) concentrations and pools following clear-cutting in forests aged 1–120 years. We studied forest soils along three clear-cut chronosequences located in the Adirondack Ecological Center in Newcomb, NY, Bartlett Experimental Forest in Bartlett, NH, and Harvard Forest in Petersham, MA. We utilized a strong-acid extraction to quantify base cations and micronutrient concentrations and pools, which may better assess nutrients over the chronosequences than the conventional exchangeable extraction. Generalized linear mixed-effect models (GLMMs) show forest floor and mineral soil Ca, Mg, Mn, and Cu concentrations and pools decreased with increasing forest age across the three study areas. Potassium and Zn concentrations and pools were not significantly different with stand age and neither did soil C and N pools and pH using GLMMs. We calculated that 32–67% of the Ca pool decrease can be attributed to uptake by regenerating vegetation but only 0.02–9% of Mg, Mn, and Cu after harvest. Thus, leaching was likely to the dominant loss process for Mg, Mn, and Cu following clear-cutting. Our results suggest nutrient pools decreased for over a century following clear-cutting, but it is unclear if this will impact plant growth.     

Structural equation modeling for the estimation of interconnections between the P cycle and soil properties

The aim of this study was used a basic hypothetical structural model with latent variables to analyze the interconnections between the pools of stable P (inorganic P (Pi) and organic P (Po)), labile P (Pi and Po) and available P (Mehlich-1 P) and the pools of organic matter (OM) content and physicochemical properties in tropical soils of differing pedogenesis. We used structural equation modeling for designing models for two groups of soil: (1) mineral soils with low to medium organic matter content and (2) mineral soils with high organic matter content and organic soils. The proposed structural models were consistent with the hypothesis of dependence between the pools of P and organic matter as well as physicochemical properties in tropical soils. In general, stable and labile P pools acted as P sources for the available P pool; furthermore, the strength of these structural relationships was strongly associated with soil organic matter content. Yet the pool of physicochemical properties behaved as a sink of P for the labile P pool, however with a beneficial effect in maintaining the stable P pool. The pools of P and OM are strongly bonded in tropical soils under different pedogenesis. All structural models evidenced that various forms of P in different levels of lability could contribute in keeping the supply of bioavailable P, yet its magnitude would be regulated by P buffer capacity of each soil.     

Modified supercritical CO2 extraction of amine template from hexagonal mesoporous silica (HMS) materials: Effects of template identity and matrix Al/Si molar ratio

In this work, the primary amine template has been extracted from freshly synthesized hexagonal mesoporous silica (HMS) materials by means of modified supercritical carbon dioxide at 60–85 °C under 10.0–20.0 MPa. The influences of amine identity and matrix Al/Si ratio on the extraction efficiencies and structural properties of HMS thus obtained are investigated in detail. The results show that the extraction efficiency is strongly dependent on the pore size of the HMS materials produced by five different templates. For aluminium-incorporated samples, the extraction efficiency is observed to decrease with the Al/Si molar ratio since as the Al/Si molar ratio increases, more amine will get protonated and the matrix/template interactions become stronger, subsequently rendering the extraction more difficult and the efficiency decrease. The formic acid modifier has resulted in better extraction performance than methanol, yielding higher extraction efficiencies. The SFE-treated materials exhibit better structural properties like higher pore volume and specific surface area as compared to those prepared by conventional calcinations. Besides, results of pyridine adsorption and conversion of 2-propanol to propylene suggest that the SFE-treated HMS materials may have higher acidity than the directly calcined samples.     

大型塔板的模拟与板效率的研究(Ⅱ)——二维定数混合池模型

为研究大型塔板在复杂流动情况下的浓度分布与板效率计算方法,本文提出二维、固定混合池数、可调整流量的数学模型。此模型可以比较灵活地模拟大型塔板上的各种实际流动现象,并能比较方便地计算出在该流动情况下的塔板浓度分布及板效率值。     

Comparison of radioactive transmission and mechanical properties of Portland cement and a modified cement with trommel sieve waste

In this study, it was aimed to stabilize trommel sieve waste (TSW) occurring during manufacture of borax from tincal. The effects of TSW added on the mechanical properties and radioactive transmission of modified cement prepared by adding TSW to clinker was investigated. The properties which TSW as additive caused the cement to gain were tested and compared with normal Portland cement.Measurements have been made to determine variation of mass attenuation coefficients of TSW and cement by using an extremely narrow-collimated-beam transmission method in the energy range 15.746-40.930 keV with X-ray transmission method. The characteristic Kα and Kβ X-rays of the different elements (Zr, Mo, Ag, In, Sb, Ba and Pr) passed through TSW and cement were detected with a high-resolution Si(Li) detector. Results are presented and discussed in this paper.     

Experimental investigation on the influence of annular pool shape characteristics on n-heptane ring fires

The ring fire usually originates from the combustion of the annular-distributed fuel, and it may occur in the low-temperature environments such as the Arctic area and plateau area, which is kind of different from the conventional environment. In this paper, the annular pools with various shape characteristics were designed. The outside diameter ranged from 14.9 to 30.0 cm, the inside diameter increased from 0 to 24.5 cm, and the diameter ratio was from 0 to 0.858. A series of n-heptane ring fire experiments were carried out. The results showed that for the annular pools with the same outside diameter, the mass loss rate (MLR) per unit area presents a piecewise trend with the diameter ratio. When the diameter ratio increases from 0 to 0.7, the MLR per unit area increases linearly because of the domination of air entrainment effect. When the diameter ratio is larger than 0.7, the MLR per unit area is independent of the annular shape due to the strong heat dissipation effect. Finally, a parameter named the outside circumference per unit area is put forward to characterize the annular pool. A corrected pressure modeling is established to normalize the ring fire with various shape characteristics.     

VAPORIZATION OF ELEMENTAL MERCURY FROM MOLTEN LEAD AT LOW CONCENTRATIONS

Experiments were conducted to measure the rate of vaporization of elemental mercury from molten lead to provide a basis for estimating radiological source terms for the APT (Accelerator Production of Tritium project) lead blanket. These data also have application to other accelerator targets in which mercury may be created by proton spallation in lead. Molten pools of lead with from 0.01% to 0.10% mercury were prepared under inert conditions. Experiments were conducted which varied in duration from several hours to as long as a month to measure the mercury vaporization from the lead pools. The melt pools and gas atmospheres were controlled at 340 degrees C during the tests, above the melting temperature of lead. Parameters which were varied in the tests included the mercury concentrations, gas flow rates over the melt, circulation in the melts, gas atmosphere compositions and the addition of aluminum to the melts. The vaporization of mercury was found to scale roughly linearly with the concentration of mercury in the pool. Variations in the gas flow rates were not found to have any effect on the mass transfer, however circulation of the melt by a submerged stirrer did enhance the mercury vaporization rate. The rate of mercury vaporization under a high-purity argon atmosphere was found to exceed that for an air atmosphere by as much as a factor of from ten to 20; the causal factor in this variation was the formation of an oxide layer over the melt pool with the air atmosphere which retarded mass transfer across the melt-atmosphere interface. Aluminum was introduced into the melt to investigate its effect upon the mercury vaporization rate. No effect was observed for a case under a high-purity argon atmosphere, which suggests that there are no chemical effects of the aluminum on the vaporization kinetics. With an air atmosphere, the presence of aluminum in the melt reduced the mercury vaporization by a factor of six in comparison to the identical test but without aluminum, suggesting that aluminum in the lead/ mercury melt retards the vaporization of mercury by creating a surface oxide layer in addition to the lead-oxide layer or by changing the character of the lead-oxide layer, thereby increasing the mass transfer resistance.     

Vaporization of elemental mercury from molten lead at low concentrations

Experiments were conducted to measure the rate of vaporization of elemental mercury from molten lead to provide a basis for estimating radiological source terms for the APT (Accelerator Production of Tritium project) lead blanket. These data also have application to other accelerator targets in which mercury may be created by proton spallation in lead. Molten pools of lead with from 0.01% to 0.10% mercury were prepared under inert conditions. Experiments were conducted which varied in duration from several hours to as long as a month to measure the mercury vaporization from the lead pools. The melt pools and gas atmospheres were controlled at 340 degrees C during the tests, above the melting temperature of lead. Parameters which were varied in the tests included the mercury concentrations, gas flow rates over the melt, circulation in the melts, gas atmosphere compositions and the addition of aluminum to the melts. The vaporization of mercury was found to scale roughly linearly with the concentration of mercury in the pool. Variations in the gas flow rates were not found to have any effect on the mass transfer, however circulation of the melt by a submerged stirrer did enhance the mercury vaporization rate. The rate of mercury vaporization under a high-purity argon atmosphere was found to exceed that for an air atmosphere by as much as a factor of from ten to 20; the causal factor in this variation was the formation of an oxide layer over the melt pool with the air atmosphere which retarded mass transfer across the melt-atmosphere interface. Aluminum was introduced into the melt to investigate its effect upon the mercury vaporization rate. No effect was observed for a case under a high-purity argon atmosphere, which suggests that there are no chemical effects of the aluminum on the vaporization kinetics. With an air atmosphere, the presence of aluminum in the melt reduced the mercury vaporization by a factor of six in comparison to the identical test but without aluminum, suggesting that aluminum in the lead/ mercury melt retards the vaporization of mercury by creating a surface oxide layer in addition to the lead-oxide layer or by changing the character of the lead-oxide layer, thereby increasing the mass transfer resistance.     

川东北普光及周边天然气藏地质特征研究

综合运用石油地质学、地球化学、地球物理等分析测试资料,对川东北普光及其周边地区油气成藏进行了研究。分析了普光及周边地区石油地质条件,对普光、毛坝等典型气藏进行了解剖研究和对比分析,总结气藏的地质特征和成藏规律。     

Acyl-acyl carrier protein pool dynamics with oil accumulation in nitrogen-deprived Chlamydomonas reinhardtii microalgal cells

Microalgae are potential biofuel feedstocks for production of energy-dense triacylglycerols (TAG). Nitrogen deprivation is known to trigger microalgal TAG accumulation by upregulation of de novo fatty acid (FA) biosynthesis through chloroplast-localized Type II FA synthases (FAS). To gain insights into the associated FAS regulatory mechanisms, we applied a recently reported liquid chromatography–mass spectrometry method to examine acyl-acyl carrier protein (ACP) pool compositional changes of the microalga Chlamydomonas reinhardtii over a nitrogen deprivation time-course. We observed that acyl-ACP pools are highly enriched in acetyl-ACP in nutrient-rich media in photoheterotrophically grown cells. Following shift to nitrogen deprivation, acetyl-ACP markedly decreased, and long-chain palmitoyl (16:0)-, stearoyl (18:0)-, and oleoyl (18:1)-ACPs progressively predominated in acyl-ACP pools in parallel with increases in FA and TAG production. This study shows the utility of microalgal cells to study acyl-ACP pool dynamics to gain insights into plant FA biosynthetic regulation and oil enhancement strategies.     

Si/C composite lithium-ion battery anodes synthesized from coarse silicon and citric acid through combined ball milling and thermal pyrolysis

Silicon and related materials have recently received considerable attention as potential anodes in Li-ion batteries for their high theoretical specific capacities. To overcome the problem of volume variations during the Li insertion/extraction process, in this work, Si/C composites with low carbon content were synthesized from cheap coarse silicon and citric acid by simple ball milling and subsequent thermal treatment. The effects of ball milling time and calcination temperature on the structure, composition and morphology of the composites were systematically investigated by the determination of specific surface area (BET) and particle-size distribution, X-ray diffraction (XRD), O₂-TPO, and scanning electron microscopy (SEM). The capacity and cycling stability of the composites were systematically evaluated by electrochemical charge/discharge tests. It was found that both the initial capacity and the cycling stability of the composites were dependent on the milling and calcination conditions, and attractive overall electrochemical performance could be obtained by optimizing the synthesis process.     

Degassing of molten polymers

Degassing is a key-step in polymer processing. Low-molecular-weight components are removed from a polymeric system. The transport of these components takes place by diffusion to the polymer-vapour interface. This interface can be formed by free surfaces of single-phase polymer melts or by bubbles. In this study, the transport with and without bubble nucleation is investigated independently from each other in a special designed apparatus similar to a degassing extruder.The mass transport in thin films and in rotating pools with surface renewal is measured. High surface renewal rates and thick films enhance the mass transfer for single phase flow and bubbly flow. Dimensionless mass transfer coefficients are given as a function of the surface renewal rate, the area of the free surface and the total mass of the polymer. The conditions for bubble nucleation and foam formation are investigated. The bubble nucleation is observed in the rotating pool in the area of high shear velocity.     

Highly uniform silicon nanoparticle/porous carbon nanofiber hybrids towards free-standing high-performance anodes for lithium-ion batteries

Novel silicon nanoparticle/porous carbon nanofiber (Si/PCNF) hybrids with high Si loading (52 wt.%) have been designed and fabricated through a simple electrospinning. The Si/PCNF of uniform fiber diameter has exhibited high specific surface area and unique porous structure. The continuous three-dimensional porous carbon networks have effectively provided strain relaxation for Si volume expansion/shrinkage during lithium insertion/extraction. In addition, the carbon matrix could largely minimize the direct exposure of Si to the electrolyte, thus substantially improving the structural stability of Si. Moreover, the porous structure could also create efficient channels for the fast transport of lithium ions. As a consequence, this novel Si-based hybrid material has exhibited stable cycling performance (ca. 870 mAh g⁻¹ at 0.1 A g⁻¹ after 100 cycles) in the absence of binders and conducting additives, promising great potential as a free-standing anode for lithium ion batteries.     

Silica Dynamics of Tidal Marshes in the Inner Elbe Estuary, Germany

In this study the seasonal and spatial variation of dissolved silica (DSi) and biogenic silica (BSi) in tidal marshes in the inner Elbe estuary was investigated. Seasonal sampling was conducted at three sites in the dyke foreland—the stretch of land between dyke and estuary—of the Elbe estuary, Germany. To assess the potential DSi export from the dyke foreland geographic information systems were used to calculate the DSi flux. Mean annual seepage DSi concentrations increased along the salinity gradient from 270 μmol L^???1 to 380 μmol L^???1. BSi concentration of the soil showed the opposite trend decreasing from 15.8 to 4.8 mg g^???1. Temporal variations of DSi concentrations were lowest at the freshwater site. At the brackish and saline site DSi concentrations increased about 2-fold from March to November from 200 to 500 and from 300 to 550 μmol L^???1, respectively. In March a diurnal signal of DSi uptake by diatoms could be observed at the saline sampling site, highlighting the role of sampling time and irradiance for the DSi flux estimate. DSi concentrations were reduced by 18.6 % between sunrise and noon. The DSi export from the dyke foreland is significant and equals the riverine DSi input into the estuary during times of low DSi concentrations. Furthermore the marsh DSi fluxes surpass DSi fluxes from highly active weathering regions, as reported in the literature, which corroborates the importance of tidal marsh areas for the coastal silica cycle. Factors steering the seasonality of DSi export and differences between the sites (temperature, hydrology, salinity and plant uptake of DSi) are discussed.     

Interactive Effects of Silicon and Soil pH on Growth,Yield and Nutrient Uptake of Maize

Silicon - Priming crop seeds with silicon (Si) to withstand various abiotic stresses is a novel approach. As soil pH affects dissolution of Si pools and Si uptake by plant, evaluation of this...