Low Si Concentration Research Articles

High Productivity Makes Mangroves Potentially Important Players in the Tropical Silicon Cycle

Over the last two decades, recognition of the important role terrestrial plants play in regulating silicon (Si) cycling has emerged. Si improves plant fitness by protecting them from abiotic (e.g., desiccation) and biotic (e.g., fungal attack) stressors. Once incorporated into plant biomass this biogenic Si is more bio-available than the lithogenic material from which it was ultimately derived. Thus plants play a key function in regulating the amount and timing of Si availability in downstream ecosystems. Recent work has highlighted the importance of salt marshes in the temperate Si cycle. However, the role of their tropical counterparts, mangroves, has largely gone unexplored. Here we report foliar concentrations of plant Si (as %Si by dry weight) for four Caribbean mangrove species: Conocarpus erectus (buttonwood), Laguncularia racemosa (white mangrove), Avicennia germinans (black mangrove), and Rhizophora mangle (red mangrove). Overall, the median Si concentration was low (0.07%) and did not vary among plant part (e.g., foliage, twig, and propagule). There was also little variation in Si among species. Using literature values of aboveground net primary production, and the concentrations reported here, we estimate an aboveground mangrove Si uptake rate of 2–10 kg Si ha–1 year–1. These rates are on par with rates reported for temperate and boreal forests as well as low nutrient salt marshes, but lower than estimates for high nutrient salt marshes. Thus, despite the low Si concentrations observed in mangroves, their high productivity appears to make them a hot spot of Si cycling in tropical coastal systems.

Theoretical Predictions Versus Environmental Observations on Serpentinization Fluids: Lessons From the Samail Ophiolite in Oman

AbstractThermodynamic calculations provide valuable insights into the reactions that drive the profound fluid transformations during serpentinization, where surface fluids are transformed into some of the most reduced and alkaline fluids on Earth. However, environmental observations usually deviate from thermodynamic predictions, especially those occurring at low temperatures where equilibrium is slowly reached. In this work, we analyzed 138 low‐temperature (<40°C) fluids from the Samail ophiolite in Oman to test thermodynamic predictions with environmental observations. Four fluid types were identified through this work. (i) Type 1 circumneutral (pH 7–9) fluids result from fluid interactions with serpentinized rocks common in the shallow subsurface. (ii) Fluids with pH ranging from 9 to 11 and low Si concentrations are products of intermediate stages of serpentinization. (iii) Type 2 hyperalkaline (pH > 11) fluids approach equilibrium with diopside, and with serpentine and brucite actively forming during advanced stages of serpentinization. Lastly, (iv) most fluids sampled in this work deviate from predicted equilibrium compositions and depict various degrees of mixing between Type 1 and 2 fluids. Mixed fluids fall within the same pH range but have considerably higher dissolved Si than intermediate‐type fluids. Hyperalkaline fluids exhibit variable degrees of mixing despite maintaining pH > 11, implying strong buffering capacity of serpentinization‐generated fluids. Overall, this work demonstrates that predicted and measured compositions of serpentinization‐derived fluids can be reconciled using a combination of equilibrium and fluid‐transport simulations. This work substantiates these calculations as useful tools in exploring serpentinization reactions in continents and perhaps in other low‐temperature environments on Earth and beyond.

Petunia (Petunia ×hybrida) Cultivars Vary in Silicon Accumulation and Distribution

Silicon (Si) is a plant-beneficial element that can alleviate the effects of abiotic and biotic stress. Plants are typically classified as Si accumulators based on foliar Si concentrations (≥1% Si on a dry weight basis for accumulators). By this definition, most greenhouse-grown ornamentals are low Si accumulators. However, plants that accumulate low foliar Si concentrations may still accumulate high Si concentrations elsewhere in the plant. Additionally, screening cultivars for variability in Si uptake has not been investigated for low Si accumulator species. Therefore, the objective of this study was to assess cultivar variability in Si accumulation and distribution in petunia (Petunia ×hybrida). Eight cultivars (Supertunia Black Cherry, Supertunia Limoncello, Supertunia Priscilla, Supertunia Raspberry Blast, Supertunia Royal Velvet, Supertunia Sangria Charm, Supertunia Vista Silverberry, and Supertunia White Improved) were grown in a commercial peat-based soilless substrate under typical greenhouse conditions. They were supplemented with either 2 mm potassium silicate (+Si) or potassium sulfate (-Si) at every irrigation. Silicon supplementation increased leaf dry mass (4.5%) but did not affect total dry mass. In plants not receiving Si supplementation, leaf Si ranged from 243 to 1295 mg·kg−1, stem Si ranged from 48 to 380 mg·kg−1, flower Si ranged from 97 to 437 mg·kg−1, and root Si ranged from 103 to 653 mg·kg−1. Silicon supplementation increased Si throughout the plant, but most predominantly in the roots. Leaf Si in the 2 mm Si treatment ranged from 1248 to 3541 mg·kg−1 (173% to 534% increase), stem Si ranged from 195 to 654 mg·kg−1 (72% to 376% increase), flower Si ranged from 253 to 1383 mg·kg−1 (74% to 1082% increase), and root Si ranged from 4018 to 10,457 mg·kg−1 (593% to 9161% increase). The large increase in root Si following supplementation shifted Si distribution within plants. In nonsupplemented plants, it ranged from 51.2% to 76.8% in leaves, 8.2% to 40.2% in stems, 2.8% to 23.8% in flowers, and 1.2% to 13.8% in roots. In Si-supplemented plants, it ranged from 63.5% to 67.7% in leaves, 10.5% to 22.6% in roots, 9.4% to 17.7% in stems, and 1.6% to 9.6% in flowers. This study indicates that petunia, a low foliar Si accumulator, can accumulate appreciable quantities of Si in roots when provided supplemental Si.

Comparisons of Nutrients Exported From Greenlandic Glacial and Deglaciated Watersheds

AbstractRecent work demonstrates extensive nutrient exports from outlet glaciers of the Greenland Ice Sheet. In comparison, nutrient exports are poorly defined for deglaciated watersheds that were exposed during ice retreat and retain reactive comminuted glacial sediments. Nutrient exports from deglaciated watersheds may differ from glacial watersheds due to their longer exposure times, more mature chemical weathering, and ecosystem succession. To evaluate nutrient exports from glacial and deglaciated watersheds, we compare discharge and dissolved (<0.45 μm filtered) nutrient concentrations in two glacial and six non‐glacial streams in southwestern and southern Greenland. Glacial streams have orders of magnitude greater instantaneous discharge than non‐glacial streams but their specific discharges are more similar, differing by up to a factor of 10. Compared with non‐glacial streams, filtered water of glacial streams have on average (1) higher inorganic nitrogen (DIN) and PO4 concentrations, lower Si concentrations, and Fe concentrations that are not statistically different; (2) higher DIN and PO4 but lower Si specific yields; and (3) lower DIN/PO4, Si/DIN, and Fe/PO4 ratios, but indistinguishable Fe/DIN. Maximum specific yields occur in early melt season prior to maximum solar radiation for non‐glacial streams, and in mid‐melt season as solar radiation wanes for proglacial streams. Impacts to coastal ecosystems from nutrient exports depend on suspended sediment loads and processing in the estuaries, but landscape exposure during glacial terminations should decrease DIN and dissolved PO4 and increase dissolved Si exports, while increased meltwater runoff associated with future warming should increase DIN and dissolved PO4 and decrease dissolved Si exports.

Effects of Compositional Variation on the Thermal Stability of $$\theta$$′-Al2Cu Precipitates and Elevated-Temperature Strengths in Al-Cu 206 Alloys

This study explored the effects of compositional variation of Al-Cu 206 alloys (Si and Mn concentrations, 0.12 versus 0.3 wt.% each) on the precipitation and thermal stability of θ′ precipitates, and the associated elevated-temperature strengths during long-term thermal exposure at 300 °C. The results indicated that both alloys under the T7 condition exhibited comparable yield strengths at 20 and 300 °C, which were predominantly controlled by θ′ precipitates. Upon exposure at 300 °C for up to 1000 h, the θ′ precipitates in the alloy with low Si and Mn concentrations remained stable and resistant to transformation into the equilibrium θ phase. The coarsening of θ′ proceeded through both lengthening and thickening, resulting in the continuing decline in YS at 300 °C from 93 MPa after 300 °C/100 h to 78 MPa after 300 °C/1000 h. Conversely, the θ′ precipitates in the alloy with high Si and Mn concentrations underwent almost complete transformation into deleterious θ after only 100 h at 300 °C, thus imparting a significantly lower YS of 69 MPa after 300 °C/100 h. The possible sources of these microstructure and property changes with the compositional variation were explored. This study has implications for strategic design of Al-Cu alloys for high-temperature applications.

The Yunmengshan iron formation at the end of the Paleoproterozoic era

Precambrian iron formations (IF) carry rich information on the interplay between the geosphere and the early biospheres. Here, we report mineralogical and petrologic characterizations of the Yunmengshan IF deposited at ~1.7 Ga, the transition between Paleoproterozoic and Mesoproterozoic eras. The IF contains granular hematite with evident oncoidal structures and lacks laminated structures, which are distinct to the typical banded iron formation (BIF) or granular iron formation (GIF) deposited early in the marine environments with high silica content. Based on observations of clastic sedimentary structures around the Yunmengshan IF, including parallel bedding, cross-bedding, asymmetric ripple mark, and mud crack, we deduce that the Yunmengshan IF was mainly deposited in a supratidal to intertidal zone. Electron microscopic observations show two types of hematite euhedral crystals: laminar hematite of 200–500 nm thick and 3-5 μm in diameter and granular hematite of 200–300 nm in diameter randomly distributed in the matrix. Stilpnomelane and minnesotaite, as Fe2+-silicates in the typical Archean- and the early Paleoproterozoic BIF, are identified but with extremely low abundance. The morphology and paragenetic association of these minerals imply that the Yunmengshan IF was probably deposited in an aquatic environment with low Si concentration. These results indicate that the Yunmengshan IF represents a transitional type of iron deposition between BIF/GIF and ironstone in the geological history of the iron cycle on the surface of Earth.

Transformation of Lowland Rainforest into Oil-palm Plantations and use of Fire alter Topsoil and Litter Silicon Pools and Fluxes

The effects of land use and fire on ecosystem silicon (Si) cycling has been largely disregarded so far. We investigated the impacts of land use and fire on Si release from topsoils and litter of lowland rainforest and oil-palm plantations in Jambi Province, Indonesia. Lower concentrations of Si in amorphous silica (ASi) were found in oil-palm plantation topsoils (2.8 ± 0.7 mg g− 1) compared to rainforest (3.5 ± 0.8 mg g− 1). Higher total Si concentrations were detected in litter from oil-palm frond piles (22.8 ± 4.6 mg g− 1) compared to rainforest litter (12.7 ± 2.2 mg g− 1). To test the impact of fire, materials were burned at 300 °C and 500 °C and were shaken with untreated samples in simulated rainwater for 28 h. Untreated oil-palm topsoils showed a significantly lower Si release (p≤ 0.05) compared to rainforest. The fire treatments resulted in an increased Si release into simulated rainwater. Si release from oil-palm topsoils and litter increased by a factor of 6 and 9 (500 °C), respectively, and Si release from rainforest topsoils and litter by a factor of 3 and 9 (500 °C). Differences between land use were related to initial ASi and litter Si concentrations, and to losses of soil organic matter during burning. We conclude that transformation of rainforest into oil palm plantations could be an important and immediate Si source after a fire event but may indirectly lead to a decrease in the long-term Si availability to plants.

Synthesis and Characterization of 12CaO\xb77Al2O3 Slags: The Effects of Impurities and Atmospheres on the Phase Relations

Synthesis of crystalline slags of 12CaO·7Al2O3 phase from the corresponding melt compositions in different atmospheric conditions and different purities is investigated. Observations using a thermogravimetry coupled with differential thermal analysis showed that the dehydration of a zeolitic 12CaO·7Al2O3 phase occur at 770 °C to 1390 °C before it congruently melts at 1450 °C. The X-ray diffraction pattern of the slag showed that a single 12CaO·7Al2O3 phase is produced from a mixture, which has small SiO2 impurity with a 49:51 mass ratio of CaO to Al2O3. A scanning electron microscope and electron probe micro-analyzer showed that a minor Ca-Al-Si-O-containing phase is in equilibrium with a grain-less 12CaO·7Al2O3 phase. Moreover, 12CaO·7Al2O3 is unstable at room temperature when the high-purity molten slag is solidified under oxidizing conditions contained in an alumina crucible. On the other hand, a high-temperature in-situ Raman spectroscopy of a slag that was made of a higher purity CaO-Al2O3 mixture showed that 5CaO·3Al2O3 phase is an unstable/intermediate phase in the the CaO-Al2O3 system, which is decomposed to 12CaO·7Al2O3 above 1100 °C upon heating in oxidizing conditions. It was found that 5CaO·3Al2O3 is present at room temperature when the 12CaO·7Al2O3 dissociates to a mixture of 5CaO·3Al2O3, 3CaO·Al2O3, and CaO·Al2O3 phases during the cooling of the slag at 1180 °C ± 20 °C in reducing atmosphere. It is proposed that low concentrations of Si stabilize 12CaO·7Al2O3 (mayenite), in which Si is a solid solution in its lattice, which is named Si-mayenite. Regarding the calculated CaO-Al2O3-SiO2 diagram in this study, this phase may contain a maximum of 4.7 wt pct SiO2, which depends on the total SiO2 in the system and the Ca/Al ratio.

Effect of Silicon Concentration on Melting Behavior of Scraps in Hot Metal

To clarify the effects of Si concentration, temperature, and time on melting of the silicon steel, three silicon steels with different Si concentrations were used to conduct an experimental investigation of the melting of scrap cylinders under natural convection. Thermodynamics and kinetics of scrap cylinder melting were revealed and analyzed based on the experimental results. Carbon diffusion between the cylinders and hot metal during melting was modeled using Thermo-Calc 2017b software to evaluate the mass-transfer coefficients. Results showed that a higher Si concentration and lower melting temperature led to slower melting of the silicon steel scrap cylinder. The mass-transfer coefficient of C during the melting decreased with an increase of Si concentration. At 1623 K (1350 °C), the mass-transfer coefficients were 1.322 × 10−4, 0.436 × 10−4, and 0.142 × 10−4 m s−1 for low (0.30 mass pct), medium (1.58 mass pct), and high (3.21 mass pct) Si concentrations in the scrap cylinders, respectively; at a melting temperature of 1723 K (1450 °C), the values of the respective mass-transfer coefficients were 1.370 × 10−4, 0.613 × 10−4, and 0.289 × 10−4 m s−1.

Formation of extracellular β-chitin nanofibers during batch cultivation of marine diatom Cyclotella sp. at silicon limitation

Diatoms are unicellular algae that make nanostructured biosilica shells called frustules possessing ordered pore arrays. Dissolved silicon (Si) in the form of Si (OH)4 is the required substrate for cell wall biosynthesis and cell division. The extracellular formation of β-chitin nanofibers by the centric diatom Cyclotella sp. was followed during batch cultivation of the cell suspension within a bubble-column photobioreactor at a low initial Si concentration (0.25 mM) leading to 1–2 cell divisions, and high Si concentration (1.7 mM) leading to 4–5 cell divisions. Fibers were excreted from 20 specialized pores (fultoportulae) lining the rim of each frustule valve face. In Si-limited batch cultivation, 80% of the fibers formed during the last cell division after dissolved Si was depleted from the medium. Within 24 h after the final cell division, fibers were nominally 56 nm diameter and 60 μm length, with 85% of the fibers between 20 and 80 μm, and one fiber per fultoportula was formed. After the final cell number density was maintained for 72 h, a second fiber per fultoportula was formed, presumably after breakage or scission of the first fiber from the cell. X-ray diffraction (XRD) analysis confirmed that isolated fibers were composed of pure β-chitin. The unprecedented length and purity of the β-chitin nanofibers suggest future advanced material applications.

Improving soft magnetic properties in FINEMET-like alloys with Ga addition

Abstract The effect of partial substitution of Si by Ga on the microstructure and soft magnetic properties of FINEMET-like Fe73.5Si13.5−xNb3B9Cu1Gax (x = 0, 3, 6, 9, 12 at.%) alloys has been investigated. It was found that the primary crystallization of ribbons was gradually changed from α-Fe (Si) into α-Fe (Ga, Si) phase with the increase of Ga content. Besides, the Fe-Ga clusters were detected in the amorphous ribbon with x = 6, which could provide nucleation sites for the α-Fe (Ga, Si) phase. In such case, the crystallization temperature of the ribbons with Ga addition was lower than that of ribbon without Ga addition. For the ribbon with x = 6, the precipitation of Ga element was priority to that of Si, which leads to the ‘increase-decrease’ tendency for the changes of lattice parameter with the increase of annealing temperature. Meanwhile, compared to the α-Fe (Si) phase with enrichment of Si for x = 0 ribbon, the α-Fe (Ga, Si) phase with high Ga and low Si concentration for the x = 6 ribbon was obtained, together with fine grain size (11 nm) of α-Fe (Ga, Si) phase, resulting to the same low coercivity (0.24 A/m), higher saturation magnetization (1.37 T) and maximum permeability after annealed at 455 °C for 1 min.

Effect of carbon doping on threshold voltage and mobility of In-Si-O thin-film transistors

In this study, a co-sputtering method with In2O3 and SiC targets was used to fabricate carbon-doped In-Si-O (In1-xSixO1-yCy) as the channel material for oxide thin-film transistors (TFTs). Three types of In1-xSixO1-yCy channels, namely, In0.88Si0.12O0.99C0.01 (Si0.12C0.01), In0.76Si0.24O0.99C0.01 (Si0.24C0.01), and In0.60Si0.40O0.98C0.02 (Si0.40C0.02), were prepared. After annealing at 300 °C, the Si0.24C0.01 and Si0.40C0.02 films retained an amorphous structure, while the Si0.12C0.01 films exhibited a body-centered-cubic structure. However, all the In1-xSixO1-yCy films maintained a smooth surface with a root-mean-square roughness of approximately 0.28 nm, despite structural differences. Results showed that the conductivities of all the In1-xSixO1-yCy films were not sensitive to the O2 partial pressure during sputtering, indicating that In1-xSixO1-yCy films exhibit more stable electrical conductivity than other InOx-based oxides. The field-effect mobility (μFE) with respect to the Si concentration of In1-xSixO1-yCy and In1-xSixO TFTs showed very similar behavior. In contrast, the threshold voltage (Vth) behavior of the two types varied dramatically, with the In1-xSixO TFTs Vth value increasing drastically from −57.7 to 9.7 V with increasing Si concentration, and the Vth of In1-xSixO1-yCy TFTs increasing only gradually from −9.2 to 2.4 V. This indicates that incorporated carbon has a significant effect on Vth at a low Si concentration due to strong C—O bond formation. The highest bond dissociative energy occurs between O and C atoms in the In1-xSixO1-yCy channel. The amount of oxygen vacancy in Si0.12C0.01, Si0.24C0.01, and Si0.40C0.02 was 18.9%, 13.3%, and 12.9%, respectively. As a result, the Si0.12C0.01 TFT exhibited superior transistor properties of Vth = −9.2 V while maintaining a μFE of 32.4 cm2/Vs. Therefore, an In1-xSixO1-yCy film is significantly advantageous as a channel material for oxide TFTs given that it can result in mobility exceeding 30 cm2/Vs.

Two metasomatic events recorded in apatite from the ore-hosting dolomite marble and implications for genesis of the giant Bayan Obo REE deposit, Inner Mongolia, Northern China

In the Bayan Obo REE deposit in Inner Mongolia, Northern China, three major orebodies are hosted in dolomite marble of the Bayan Obo Group. There are carbonatite dikes in the ore district. Apatite is a common accessary mineral in the ore-hosting dolomite marble (DM apatite) and in carbonatite dikes (IC apatite). These two types of apatite are both fluorapatite, and have low SiO2, uniform P2O5, and variable CaO contents. Total REY (REEs + Y) contents are correlated with Na2O contents, indicating that REY of both types of apatite enter lattice via the substitution reaction: Na+ + (REY)3+ = 2Ca2+. These features, combined with high REY (6230–18,906 ppm) and Sr (9653–17,200 ppm) contents of DM apatite, indicate that DM apatite likely had a carbonatite origin. Some DM apatite grains are partially replaced by albite and quartz. Fluid inclusions crosscutting both apatite and albite or quartz indicate that they formed later than quartz and albite replacement. The back-scattered electron images show that DM apatite grains contain many micro-pores (fluid inclusions), and monazite inclusions formed from the fluid inclusions. However, no monazite inclusions are observed within quartz and albite, excluding the possibility that the monazite inclusions were precipitated directly from the fluids. The monazite inclusions were therefore formed during fluid-induced dissolution–reprecipitation processes, where DM apatite served as the source of LREEs. This also explains the depletion of some LREEs in DM apatite. The formation of monazite inclusions in apatite requires fluids with relatively low Na and Si concentrations, different from the fluids responsible for quartz and albite replacement. DM apatite was affected by two stages of fluid activities: the first stage of metasomatism by alkaline fluids that were likely derived from carbonatite magmas when the deposit first formed (represented by quartz and albite replacement), followed by a second stage of modification that caused LREEs depletion and the formation of new REE minerals. Thus, the Bayan Obo REE ore deposit was modified by a significant thermal event after the formation, which provided negligible or only small amounts of REEs.

Geochemistry of magnetite and hematite from unmineralized bedrock and local till at the Kiggavik uranium deposit: Implications for sediment provenance

The petrography and mineral chemistry of magnetite and hematite from igneous, metasedimentary, and sedimentary bedrock in the area of the Kiggavik unconformity-related uranium deposit, and from till covering the deposit were investigated using optical microscopy, scanning electron microscopy (SEM), electron probe micro-analyzer (EPMA), and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The R-package rob-Compositions method was used to treat censored values in the EPMA and LA-ICP-MS geochemical data, and the results were transformed using a centered log-ratio transformation prior to data analysis using partial least squares-discriminant analysis (PLS-DA). The Kiggavik rock samples are from a wide range of lithologies including granite, leucogranite, syenite, metagreywacke, quartzite, and quartz arenite. The integration of petrography and mineral chemistry identifies four origins for iron oxides in the Kiggavik bedrocks: magmatic, hydrothermal, diagenetic, and weathering. The igneous bedrocks mainly contain magmatic magnetite replaced by mostly hydrothermal and rarely by weathering related hematite. Higher concentrations of trace elements such as Mg, Al, Ti, and Zr in hydrothermal hematite from leucogranite, granite and Martell syenite relative to parent magnetite suggest that hematite crystallized from high-temperatures hydrothermal fluids. By contrast, relative trace elements depletion in hematite replacing V-Cr-rich magnetite from Schultz Lake Intrusive Complex syenite may indicate hematite precipitation from low-temperature oxidizing fluids.The high U content (450ppm averagely), rounded shape, and altered edges of hematite grains from metagreywacke indicate that the iron oxide is detrital, originally precipitated from U-rich hydrothermal fluids. Quartzite also contains hydrothermal hematite. Distinct chemical compositions of hydrothermal hematite from Kiggavik metasedimentary and igneous basement demonstrate different compositions and temperatures of parental hydrothermal fluids, as well as different compositions of replaced minerals/host rocks.Magnetite rarely occurs in the Kiggavik sedimentary bedrocks as it has been partly or entirely replaced by hematite. The Thelon Formation quartz arenite contains detrital hematite mainly sourced from weathering of the Kiggavik igneous basement, and also diagenetic hematite that formed in situ replacing detrital magnetite, ilmenite, sulfides and/or Fe-bearing silicates.PLS-DA distinguishes different compositions of magnetite and hematite characterizing the various Kiggavik rock samples. The PLS-DA latent variable subspaces defined by the bedrock samples were used to classify the sources of iron oxides in Kiggavik till. The results show that magnetite and hematite from the till are mainly derived from local rocks, with a small proportion from unknown host rocks. PLS-DA identifies Si, Ca, Pb, Zr, Al, Ge, Nb, Ga, Mn, Mg, Ti, Co, Y U, V, Ni, and Cr as main discriminator elements. Their variable concentrations in iron oxides can be used to separate different Kiggavik rocks. PLS-DA also demonstrates that lower concentrations of Si, Ca, Al, Mn, Mg, Ti, Zn, Co and Ni discriminate Kiggavik iron oxides from magnetite from porphyry, iron oxide copper gold ore deposits (IOCG), Iron Oxide-Apatite (IOA), and Bayan Obo Fe-Nb-REE deposit types. Nickel enrichment and higher Ca values also differentiate magnetite from Ni-Cu, and from VMS deposits and VMS-related BIF, respectively, from Kiggavik iron oxides. The PLS-DA discrimination models suggest that volcanogenic massive sulfide (VMS)-related banded iron formations (BIF) are the potential source for some of the unclassified iron oxide grains in Kiggavik till.Retention of U contents by iron oxides during phase transformation or in detrital hematite indicates the ability of iron oxides to act as a long term repository of U. Overall, this study shows that magnetite and hematite are efficient minerals for provenance studies and mineral exploration in uranium rich environments, and also indicates that robust models for classification of indicator minerals origins in unconsolidated sediments can be established from PLS-DA of LA-ICP-MS data.

Fracture Mode Transition in Nb–1Si Alloys Triggered by Annealing Heat Treatment

The concentration of Si plays a crucial role in the ductile‐brittle transition of Nb solid solution (NbSS) alloys, and an appropriate annealing treatment contributes to controlling the Si concentration in NbSS alloy. In this paper, Nb–1Si (at%) alloy is arc‐melted and annealed at different temperature (1300, 1400, and 1500 °C) for 10 h. After annealing, both the strength and ductility increase. Particularly, after annealing at 1300 °C, the fracture feature transforms from cleavage to dimples, and the alloy possesses good strength and retains decent ductility due to the low Si concentration and small‐sized intragranular Nb3Si particles precipitating in the NbSS. The significant effect of annealing on the fracture mechanism of Nb–1Si provides guidance for the design of Nb–Si based alloys.

Piecewise Structural Equation Model (SEM) Disentangles the Environmental Conditions Favoring Diatom Diazotroph Associations (DDAs) in the Western Tropical North Atlantic (WTNA).

Diatom diazotroph associations (DDAs) are important components in the world’s oceans, especially in the western tropical north Atlantic (WTNA), where blooms have a significant impact on carbon and nitrogen cycling. However, drivers of their abundances and distribution patterns remain unknown. Here, we examined abundance and distribution patterns for two DDA populations in relation to the Amazon River (AR) plume in the WTNA. Quantitative PCR assays, targeting two DDAs (het-1 and het-2) by their symbiont’s nifH gene, served as input in a piecewise structural equation model (SEM). Collections were made during high (spring 2010) and low (fall 2011) flow discharges of the AR. The distributions of dissolved nutrients, chlorophyll-a, and DDAs showed coherent patterns indicative of areas influenced by the AR. A symbiotic Hemiaulus hauckii-Richelia (het-2) bloom (>106 cells L-1) occurred during higher discharge of the AR and was coincident with mesohaline to oceanic (30–35) sea surface salinities (SSS), and regions devoid of dissolved inorganic nitrogen (DIN), low concentrations of both DIP (>0.1 μmol L-1) and Si (>1.0 μmol L-1). The Richelia (het-1) associated with Rhizosolenia was only present in 2010 and at lower densities (10-1.76 × 105 nifH copies L-1) than het-2 and limited to regions of oceanic SSS (>36). The het-2 symbiont detected in 2011 was associated with H. membranaceus (>103 nifH copies L-1) and were restricted to regions with mesohaline SSS (31.8–34.3), immeasurable DIN, moderate DIP (0.1–0.60 μmol L-1) and higher Si (4.19–22.1 μmol L-1). The piecewise SEM identified a profound direct negative effect of turbidity on the het-2 abundance in spring 2010, while DIP and water turbidity had a more positive influence in fall 2011, corroborating our observations of DDAs at subsurface maximas. We also found a striking difference in the influence of salinity on DDA symbionts suggesting a niche differentiation and preferences in oceanic and mesohaline salinities by het-1 and het-2, respectively. The use of the piecewise SEM to disentangle the complex and concomitant hydrography of the WTNA acting on two biogeochemically relevant populations was novel and underscores its use to predict conditions favoring abundance and distributions of microbial populations.

Silicon alleviates simulated acid rain stress of Oryza sativa L. seedlings by adjusting physiology activity and mineral nutrients.

Silicon (Si) has been a modulator in plants under abiotic stresses, such as acid rain. To understand how silicon made an effect on rice (Oryza sativa L.) exposed to simulated acid rain (SAR) stress, the growth, physiologic activity, and mineral nutrient content in leaves of rice were investigated. The results showed that combined treatments with Si (1.0, 2.0, or 4.0mM) and SAR (pH4.0, 3.0, or 2.0) obviously improved the rice growth compared with the single treatment with SAR. Incorporation of Si into SAR treatment decreased malondialdehyde (MDA) content; increased soluble protein and proline contents; promoted CAT, POD, SOD, and APX activity; and maintained the K, Ca, Mg, Fe, Zn, Cu content balance in leaves of rice seedlings under SAR stress. The moderate concentration of Si (2.0mM) was better than the low and high concentration of Si (1.0 and 4.0mM). Therefore, application of Si could be a better strategy for maintaining the crop productivity in acid rain regions.

Effects of silicon on Oryza sativa L. seedling roots under simulated acid rain stress.

Silicon (Si) has an important function in reducing the damage of environmental stress on plants. Acid rain is a serious abiotic stress factor, and Si can alleviate the stress induced by acid rain on plants. Based on these assumptions, we investigated the effects of silicon on the growth, root phenotype, mineral element contents, hydrogen peroxide (H2O2) and antioxidative enzymes of rice (Oryza sativa L.) seedling roots under simulated acid rain (SAR) stress. The results showed that the combined or single effects of Si and/or SAR on rice roots depend on the concentration of Si and the pH of the SAR. The combined or single effects of a low or moderate concentration of Si (1.0 or 2.0 mM) and light SAR (pH 4.0) enhanced the growth of rice roots, and the combined effects were stronger than those of the single treatment. A high concentration of Si (4.0 mM) or severe SAR (pH 2.0) exerted deleterious effects. The incorporation of Si (1.0, 2.0 or 4.0 mM) into SAR with pH 3.0 or 2.0 promoted the rice root growth, decreased the H2O2 content, increased the Si concentration and the superoxide dismutase (SOD), catalase (CAT), peroxidase (POD) and ascorbate peroxidase (APX) activities, maintained the balance of mineral element (K, Ca, Mg, Fe, Zn, and Cu) concentrations in the roots of rice seedlings compared with SAR alone. The alleviatory effects observed with a moderate concentration of Si (2.0 mM) were better than the effects obtained with a low or high concentration of Si (1.0 or 4.0 mM). The observed effects were due to disruptions in the absorption and utilization of mineral nutrients and impacts on the activity of antioxidant enzymes in roots, and this conclusion suggests that the degree of rice root damage caused by acid rain might be attributed to not only acid rain but also the level of Si in the soil.

Comparison of phosphorus fraction distribution and influencing factors of suspended and surface sediments in the Tiaoxi watershed, China.

Suspended and surface sediments from the Tiaoxi watershed, fed by the Xitiaoxi and Dongtiaoxi rivers, were analyzed for total phosphorus (TP) and the inorganic P fractions of loosely adsorbed P that were extractable with NH4Cl (NH4Cl-P), reductant P (BD-P), metal oxide-bound P extractable with NaOH (NaOH-P), and calcium-bound, HCl-extractable P (HCl-P), while other physicochemical compositions were also determined. The spatial variations of P fractions in these sediments were investigated, and the major factors influencing the various fractions were explored by multivariate statistics. Compared to surface sediments, suspended sediments contained considerably higher concentrations of total nitrogen, TP, organic matter, Al, Fe, Mn and biologically available P (BAP, given as NH4Cl-P, BD-P and NaOH-P combined) and lower concentrations of Si, Ca and HCl-P in the studied catchments. Dongtiaoxi sediments had higher TP, inorganic phosphorus and HCl-P concentrations and a lower BAP content compared with Xitiaoxi sediments, trends that were associated with local geological backgrounds, landscapes and anthropogenic characteristics. The results of principal component analysis showed different effects of sediment properties on P fraction distributions for Xitiaoxi and Dongtiaoxi sediments. The sediment components and structure exert a strong influence on BAP in Xitiaoxi sediments, in contrast to Dongtiaoxi sediments, where P fractions are mainly affected by urbanization and other anthropogenic activities such as shipping.

Seed-induced Hydrothermal Synthesis of Tobermorite from Municipal Solid Waste Incinerator Fly Ash

Resource recovery of municipal solid waste (MSW) incinerator fly ash is widely concerned. Tobermorite, an important but rare naturally mineral, could not be directly hydrothermal synthesized from it owing to its high content of Ca but low concentration of Si and Al. The selected external silicon-aluminum additives including coal fly ash (CFA), bentonite, kaolin and diatomite were solely or combined added. With the addition of 30% mass composite additive in which the ratio of quality for CFA and diatomite is 1:1, tobermorite could be synthesized most effectively in 48h at 150°C, mainly attributing to the proper element proportion adjusted by additives. Tobermorite seed added could not only promote the large formation of tobermorite, but also inhibit the production of hibschite and kaotoite. Since Ca/(Si + Al) = 1.20 and Al/(Si + Al) = 0.20, addition of 30% mass of composite additive and 3% mass of tobermorite seed would be the recommended technological parameter.