Silica In Sediments Research Articles

Efficient reactive adsorption of hexamethyldisiloxane on MCM-41 supported sulfuric acid

Volatile methyl siloxanes (VMSs), which are converted to silica sediments during biogas burning, are regarded as the most problematic VMSs in existing biogas cleaning systems. However, the majority of methods for VMS removal, including cryogenic condensation, physical absorption, chemical absorption and porous material adsorption have been constrained by these methods' intrinsic drawbacks. Here, we present an alternate method for removing VMS from gas streams that are based on the materials supported by H2SO4. Simple incipient wetness impregnation was used to create MCM-41-supported H2SO4 (SSA/MCM) materials, which showed high reactive adsorption property for hexamethyldisiloxane (L2) elimination in the temperature range of 80–160 °C with the peak reactivity at 100 °C. With maximum QB and Qm values of 191.3 and 365.6 mg g−1, respectively, dynamic adsorption findings showed the significance of altering the intake concentration, gas flow rate, adsorbent mass, relative humidity, as well as H2SO4 loading in determining the L2 removal efficacy. Furthermore, it was established that the L2 reactive adsorption was caused by the polymerization of L2 by supported H2SO4, which produced the creation of polysiloxane. The findings offer an important foundation for creating a cutting-edge biogas cleaning method.

Distribution and dissolution kinetics of biogenic silica in sediments of the northern South China Sea

The dissolution efficiency of sedssimentary biogenic silica (bSiO2) dramatically affects the regeneration of dissolved silicic acid (dSi) at the sediment-water interface, which is a crucial pathway to maintain Si balance and silicic productivity growth in marine environments. We conducted wet alkaline leach and flow-through experiments to explore the dissolution behaviors of sedimentary bSiO2 in the northern South China Sea (NSCS), one of the largest marginal sea continental shelves. The bSiO2 contents of surface sediments were 0.64 - 2.06%, with an average of 1.04 ± 0.35%, varying with isobath water depth. The solubility of bSiO2 in surface sediments ranged from 227 μmol L-1 to 519 μmol L-1, and the dissolution rate constants varied from 0.67 to 1.53 yr-1 under specific conditions in lab incubation. The correlation between the biogenic materials (bSiO2, OC, and TN) revealed a different preservation pattern of bSiO2 in finer (Φ > ~ 5.5) and coarser (Φ< ~ 5.5) sediments. The high concentration of Al in sea water and “Al – detrital – bSiO2” interactions in sediments significantly interfered with the apparent solubility and dissolution dynamics of bSiO2. We combined the regional characteristics (primary production, bottom current, and resuspension-deposition) and the reconstructed dissolution kinetics of bSiO2 explained the mismatch between the surface (diatom biomass)/(total phytoplankton biomass) ratio and the sedimentary bSiO2/OC ratio, and the mismatch between the surface bSiO2 primary productivity and the bSiO2 sediment records in the NSCS. The resuspension-deposition, the higher reconstructed rate constants (0.94 ± 0.13 yr-1), and the dissolution rate (0.20 ± 0.01 yr-1) were responsible for the lower bSiO2/OC ratio (0.45 ± 0.28) at the inner shelf, and the winnowing process at the outer shelf with the lower reconstructed reactivity (0.30 yr-1) and dissolution rate (0.001 yr-1) led to the good preservation of bSiO2 in the upper slope. Furthermore, through the comparison with other sea areas, the relatively lower reactivity (1.12 ± 0.3 yr-1) of bSiO2 in sediments supported the notion that the NSCS sediments may serve as an important silica sink in the world ocean silica cycle.

Isotopic analyses of Ordovician–Silurian siliceous skeletons indicate silica‐depleted Paleozoic oceans

The Phanerozoic Eon marked a major transition from marine silica deposition exclusively via abiotic pathways to a system dominated by biogenic silica sedimentation. For decades, prevailing ideas predicted this abiotic-to-biogenic transition were marked by a significant decrease in the concentration of dissolved silica in seawater; however, due to the lower perceived abundance and uptake affinity of sponges and radiolarians relative to diatoms, marine dissolved silica is thought to have remained elevated above modern values until the Cenozoic radiation of diatoms. Studies of modern marine silica biomineralizers demonstrated that the Si isotope ratios (δ30 Si) of sponge spicules and planktonic silica biominerals produced by diatoms or radiolarians can be applied as quantitative proxies for past seawater dissolved silica concentrations due to differences in Si isotope fractionations among these organisms. We undertook 446 ion microprobe analyses of δ30 Si and δ18 O of sponge spicules and radiolarians from Ordovician-Silurian chert deposits of the Mount Hare Formation in Yukon, Canada. These isotopic data showed that sponges living in marine slope and basinal environments displayed small Si isotope fractionations relative to coeval radiolarians. By constructing a mathematical model of the major fluxes and reservoirs in the marine silica cycle and the physiology of silica biomineralization, we found that the concentration of dissolved silica in seawater was less than ~150μM during early Paleozoic time-a value that is significantly lower than previous estimates. We posit that the topology of the early Paleozoic marine silica cycle resembled that of modern oceans much more closely than previously assumed.

Excitation and Emission Properties of Adsorbed U(VI) on Amorphous Silica Surface

In the geochemical field, the chemical speciation of hexavalent uranium (U(VI)) has been widely investigated by performing measurements to determine its luminescence properties, namely the excitation, emission, and lifetime. Of these properties, the excitation has been relatively overlooked in most time-resolved laser fluorescence spectroscopy (TRLFS) studies. In this study, TRLFS and continuous-wave excitation–emission matrix spectroscopy are adopted to characterize the excitation properties of U(VI) surface species that interact with amorphous silica. The luminescence spectra of U(VI) measured from a silica suspension and silica sediment showed very similar spectral shapes with similar lifetime values. In contrast, the excitation spectra of U(VI) measured from these samples were significantly different. The results show that distinctive excitation maxima appeared at approximately 220 and 280 nm for the silica suspension and silica sediment, respectively.

Invasion of a Widespread, Non‐Native Grass Causes Downstream Reductions in Bioavailable Silica

AbstractThis study shows that riverine riparian (shoreline) zones — and plant management decisions made therein — can measurably influence the availability of silica delivered to lower reaches of rivers, estuaries, and some coastal oceans. The aims were to determine how much silica is sequestered by riparian vegetation in a river, and what processes govern that effect. We used the invasion and rapid spread of the non‐native grass Phragmites australis (common reed) in the Platte River (central United States) to quantify the biochemical and physical mechanisms by which silica is removed from the river flow and stored in sediments. Specifically, we measured bioavailable silica in sediment, native and non‐native vegetation biomass, and river water over a period of four years. The robust biomass production and high silica content of Phragmites led to biochemical production of amorphous silica particles (ASi) that was 1.5× higher than native willow and 2× higher than native Phragmites. And, the denser growth habit of non‐native Phragmites contributed to more rapid physical sequestration of ASi than with other vegetation. Altogether, the rapid vegetation change due to this invasion caused sequestered silica to increase 1.5× in this reach, which is ~7% of the Platte’s annual silica load. Subsequent Phragmites eradication efforts, wherein the plants were sprayed with herbicide and left physically intact, allowed rapid silica remobilization but it was highly variable.

Lake sedimentary biogenic silica from diatoms constitutes a significant global sink for aluminium

Diatoms play an important role in marine biogeochemical cycle of aluminum (Al), as dissolved Al is taken up by diatoms to build their siliceous frustules and is involved in the sedimentation of diatomaceous biogenic silica (BSi). The Al incorporation in BSi facilitates decreasing the dissolution of marine BSi and thus substantially influences the biochemical processes driven by diatoms, such as CO2 sequestration. However, the role of lake BSi in the terrestrial biochemical Al cycle has not been explored, though lakes represent the second-largest sink for BSi. By identifying the previously unexplored high Al/Si atomic ratios (up to 0.052) in lake BSi, here we show lake BSi is a large terrestrial Al pool due to its high Al content, and lake sedimentary BSi constitutes a significant global sink for Al, which is on the same magnitude as the Al sink in global oceans.

Effect of humic acid on the sedimentation and transport of nanoparticles silica in water-saturated porous media

Nano silicon particles (nSiO2) is one of the most widely used industrial engineered nanomaterials (ENMs). The extensive applications of nSiO2 may pose potential risks to aquatic ecosystems and human health. Humic acid (HA) is a major component of soil and water that exists widely in the natural environment and adsorbs to the surface of nanoparticles, which affects the fate and transport of ENMs in soil. Therefore, it triggers the necessity to study the chemical reaction of HA controlling the sedimentation and transport of nSiO2. The sedimentation kinetics and transport breakthrough curves of nSiO2 with/without HA in water-saturated porous media were studied in two electrolyte (NaCl and CaCl2) solutions. The likely mechanisms were explored with both multiple technologies and numerical modeling including TEM-EDX, particle size distribution, zeta potentials, and the two-site kinetic attachment model (TSKAM). Our experimental results showed that the existence of HA generally increased the suspensivity and the transportability of nSiO2 in NaCl and CaCl2 solutions in packed sand columns at acidic pH. This result was attributed to the HA adsorption leading to the more negatively charged surface and the smaller size of nSiO2 aggregates. However, the formation of coordination complexes associated with larger cluster among nSiO2 between HA and Ca2+ contributed to the increased sedimentation of nSiO2 at alkaline pH. Subsequently, the presence of HA inhibited the transport of nSiO2 in CaCl2 solution at pH 9.0. Comparably, in NaCl at pH 9.0, HA showed the negligible effect on the nSiO2 deposition in sand. Both the attachment and detachment parameters, which were obtained from fitting the breakthrough curves of ENMs using the TSKAM, could be used to well describe the transport behavior of nSiO2 with HA under various conditions. In particular, the irreversible attachment parameters at site 2 on sand were positively related to the retention of nSiO2 with HA. The fate and transport of nSiO2 can be distinctly affected by HA depending on the ion composition, ion strength, and pH in soil. This study will provide insights for assessing the mobility of nSiO2 with HA in subsurface soil and aquatic environments.

In-site mineral geochemistry and whole-rock Fe isotopes of the quartz-magnetite-pyroxene rocks in the Wuyang area, North China Craton: Constraints on the genesis of the pyroxene-rich BIF

Quartz-magnetite-pyroxene (QMP) rocks with high Fe contents are of greatly economic and petrological importance and generally occur within the oldest and largest exposures of supracrustal rocks preserved on Earth. However, the chemical composition and genesis of QMP rocks remain unclear. To constrain the protolith and genesis, we present new whole-rock geochemistry and Fe isotopic data, mineral EPMA and LA-ICP-MS analysis and X-ray mapping for the QMP rocks in the Wuyang area, North China Craton. The Wuyang QMP rocks have undergone high-temperature metamorphism and have special mineral assemblages with coexisting magnetite, quartz, clinopyroxene and variable orthopyroxene. Pyroxenes of the Wuyang QMP rocks show very distinct major, trace and rare earth element (REE) compositions from those of the nearby pyroxene-marbles and pyroxenite intrusions. Such difference excludes a contact metamorphic origin for pyroxenes of the QMP rocks. X-ray elemental mapping suggests that Fe-poor carbonate minerals (dolomite and calcite) and quartz inclusions are well preserved in these pyroxene grains and no reaction phenomenon can be observed between them, indicating that these pyroxenes are not the product of metamorphic decarbonation reactions of pre-existing sedimentary silica and Fe-rich carbonate phase. Shale-normalized REE + Y patterns of the whole-rock samples and pyroxenes display geochemical features consistent with classic banded iron formations (BIFs), which show light REE depletion, positive LaSN, EuSN and YSN anomalies. This indicates that the geochemical features are compositionally inherited from their original pure chemical sediments. The Wuyang QMP rocks are therefore considered as pyroxene-rich BIF. Neotocite and hisingerite inclusions in pyroxene grains from the QMP rocks could be metamorphic products of some early Fe- and Mn-rich silicates before pyroxene. Moreover, the Wuyang QMP rocks are enriched in light iron isotopes similar to other Fe- and Ca-rich minerals in Archean BIFs. Therefore, we inferred that pyroxene from the QMP rocks could result from dehydration of initial sedimentary hydrous Ca-, Mg- and Mn-containing Fe(II)-silicate gel during diagenesis and re-crystallization in later metamorphism, providing a new interpretation for the origin of pyroxene-rich BIF.

An oceanic subduction origin for Archaean granitoids revealed by silicon isotopes

Modern oceanic crust is constantly produced at oceanic ridges and recycled back into the mantle at subduction zones via plate tectonics. An outstanding question in geology is whether the Earth started in a non-plate tectonic regime, and if it did, when the transition to the modern regime occurred. This is a complicated question to address because Archaean rocks lack modern equivalents to anchor interpretations. Here, we present a silicon isotopic study of 4.0–2.8-Gyr-old tonalite–trondhjemite–granodiorites, as well as Palaeozoic granites and modern adakites. We show that Archaean granitoids have heavier silicon isotopic compositions than granites and adakites, regardless of melting pressure. This is best explained if Archaean granitoids were formed by melting of subducted basaltic crust enriched in sedimentary silica through interaction with seawater. Before the appearance of silica-forming organisms 0.5–0.6 billion years ago, the oceans were close to silicon saturation, which led to extensive precipitation of cherts on the seafloor. This is in contrast to modern oceans, where silica biomineralization maintains dissolved silicon at low concentration. The unique heavy silicon isotope signature of cherts has been transferred to Archaean granitoids during an oceanic subduction process, which was probably responsible for the formation of felsic rocks on Archaean emerged lands. Archaean granitic rocks formed by melting of silica-enriched subducted basaltic crust through interaction with seawater, according to heavy silicon isotopes measured in Archaean samples.

Vertical and Horizontal Changeability of Chemical Features of Bottom Sediment in River and Lacustrine Sections in Lake-River System

Bottom sediment is regarded as an important element in water ecosystem, playing the role of a nutrient “trap” but also of the potential and practically inexhaustible source of nutrients. A various transformations of mineral and organic components (diagenesis, dehydration, recrystallization, cementation, chemical reactions) take place in sediment, leading to the migration of nutrients compounds from sediment to water. The bottom sediment is composed of mineral and organic substances removed from the water during the processes of precipitation, sorption and sedimentation. Bottom sediment, that fills river beds, is characterized by a completely different chemical composition comparing to lake sediment. This is caused by the constant flow of water in the river and its good oxygenation. The aim of study was analysis of chemical composition of riverine and lacustrine bottom sediment. Research of bottom sediment was carried in the lake - river system of upper Paslçka. The upper Paslçka basin is situated in the north-east of Poland. The river Paslçka flows into Vistula Lagoon. The total area of the upper Paslçka River basin is 246.7 km2, while the length of the upper part of the river is 40.5 km (total area of Paslçka catchment is 2294.5 km2, total length of river is 211 km). The average fall of the upper course of Paslçka is 1.70 %o. Paslçka River in upper course flows through the lakes with different morphometric properties: Paslçk, Wymój, Sarçg, Lçguty and Is^g. The surface of lakes ranges from 8.5 to 397.5 ha, and a maximum depth - 5.0 to 54.5 m. The research showed a clear spatial differentiation of the content of silica, organic matter and carbon dioxide in the bottom sediments of particular river and lakes sections. The percentage share of other bottom sediments components i.e. macroelements (Ca, Mg, Fe, Mn) and nutrients (P, N), was also various in river and lake sediment. The dominant component of river sediments was silica (56.9 to 96.7% d.w.). With the flow of the river, the share of silica in the sediment was higher. In lake sediment, silica was also predominant, but not in such a wide range as in the river (24.8 to 53.2% d.w.). The content of organic matter in river sediment did not exceed 27%. In the sediments of the lakes Paslçk and Sarçg organic matter was the second component of sediments and ranged from 19.5 to 30.1%. In other lakes the content of organic components ranged from 12.3 to 20.3%. In lake sediment a high proportion of carbon dioxide was noted - between 14.4 and 24.2%, while in river sediment, this component did not exceed 6.3%.

Variability in distribution of major and trace elements in Lower Eocene siliceous sections of the Transuralian Region, Russia

This paper presents lithologic and geochemical data from the sequence of the Eocene Irbit formation siliceous rocks (Transuralian Region) outcropping in a quarry in the Irbit deposit (thickness of 15 m) and in a large natural outcrop, Belaya Gorka (thickness of 13 m). The data show that both outcrops are composed of diatomites and clayey diatomites, both characterized by a certain degree of lithologic heterogeneity around their chemical, granulometric, and mineralogical compositions; microstructural features; and degree of diatom preservation. The values of indices important for the classification of siliceous rocks and determination of prospects for their industrial application—SiO2, Al2O3, Fe2O3, and clay fraction content—ranged from 66% to 77%, 7% to 14%, 3.00% to 5.60%, and 23% to 50%, respectively. In all studied lithologic varieties, element abundances of V, Cr, Mn, Co, Ni, Cu, Zn, Ga, Ge, and Sb were two to three times higher than their respective abundances in the Earth’s crust. This is probably related to these elements’ involvement in the biological cycle and favorable conditions for transport. Rb, Cs, Ba, and Sr, as well as rare earth elements, are considered the most reliable indicators of lithologic and geochemical subdivision of a sequence of siliceous rocks, as they are associated mainly with clayey minerals. Variations in these indicators have recorded, with great probability, even short-term cycles and semi-cycles of silica sedimentation in the Transuralian Region, as well as tectonic regime and involvement of terrigenous influx.

N:P stoichiometry and transparent exopolymeric particles buffer ecological impacts of nutrients in the Ganga River: a mesocosm study

ABSTRACTWe investigated the possible drivers of the N:P stoichiometric shift and its relationship with micro-algal production of transparent exopolymeric particles (TEP) along a 35 km gradient of the Ganga River. The objective was to evaluate if the trade-off between N:P stoichiometry and production of TEP helps in maintaining water quality of the river. Mesocosm experiments were conducted to examine N:P-TEP linkages and its role in turbidity removal. In situ measurements did not show Si to be a limiting nutrient (N:Si < 1.3). The TEP production increased with decreasing N:P ratio and peaked at N:P::6:1 with dominance of Aulacosira granulata and Fragilaria intermedia. Settling efficiency, turbidity removal and sedimentation of TEP, biogenic silica (BSi) and biomass all increased with decreasing N:P ratio proportionately to the amount of TEP produced in the mesocosm. The study demonstrates that trade-off between N:P stoichiometry and the production of TEP generates feedback to buffer the ecological impacts of nutrient pollution.

Post-mortem oxygen isotope exchange within cultured diatom silica.

RationalePotential post‐mortem alteration to the oxygen isotope composition of biogenic silica is critical to the validity of palaeoclimate reconstructions based on oxygen isotope ratios (δ18O values) from sedimentary silica. We calculate the degree of oxygen isotope alteration within freshly cultured diatom biogenic silica in response to heating and storing in the laboratory.MethodsThe experiments used freshly cultured diatom silica. Silica samples were either stored in water or dried at temperatures between 20 °C and 80 °C. The mass of affected oxygen and the associated silica‐water isotope fractionation during alteration were calculated by conducting parallel experiments using endmember waters with δ18O values of −6.3 to −5.9 ‰ and −36.3 to −35.0 ‰. Dehydroxylation and subsequent oxygen liberation were achieved by stepwise fluorination with BrF5. The 18O/16O ratios were measured using a ThermoFinnigan MAT 253 isotope ratio mass spectrometer.ResultsSignificant alterations in silica δ18O values were observed, most notably an increase in the δ18O values following drying at 40–80 °C. Storage in water for 7 days between 20 and 80 °C also led to significant alteration in δ18O values. Mass balance calculations suggest that the amount of affected oxygen is positively correlated with temperature. The estimated oxygen isotope fractionation during alteration is an inverse function of temperature, consistent with the extrapolation of models for high‐temperature silica‐water oxygen isotope fractionation.ConclusionsRoutinely used preparatory methods may impart significant alterations to the δ18O values of biogenic silica, particularly when dealing with modern cultured or field‐collected material. The significance of such processes within natural aquatic environments is uncertain; however, there is potential that similar processes also affect sedimentary diatoms, with implications for the interpretation of biogenic silica‐hosted δ18O palaeoclimate records.

Potential deposition of biogenic silica source sediment in the Paleo-Yangtze Grand Underwater Delta estimated with satellite remote sensing

ABSTRACTBiogenic silica sediment constitutes one of the critical sources of particle income in the oceans. In this paper, satellite remote sensing of primary production, sinking flux, and molar ratio of Si/C were utilized to elucidate potential biogenic silica sediment in the Paleo-Yangtze Grand Underwater Delta. Primary production retrieval showed that daily primary production in the Paleo-Yangtze Grand Delta was 3.3–10.8 Mt d−1, with 5.8 Mt d−1 on average. Sinking flux, retrieved with in situ observations and satellite remote sensing, was within the range of 109–657 mg Cm−2 d−1, or about 23% of total primary production, on average. A molar ratio of Si/C of 0.11–0.45 interval was used in the area, for the Paleo-Yangtze Grand Delta was similar to coastal water and affected by many factors. Considering that phytoplankton in the Paleo-Yangtze Grand Underwater Delta is mainly diatom (80% on average), about 0.21–0.88 billion tons of biogenic silica source sediment is produced in the area annually. With the reduction of land source sediment occurring in recent years in the area, biogenic silica sediment may be one of the dominant sediment sources for maintaining the future stability of the Paleo-Yangtze Grand Underwater Delta.

Viscoelastic behaviour of flocculated silica sediments in concentrated monovalent chloride salt solutions

Silica sand and quartz represent the second most common mineral in the earth's crust. The silica-water interface is central to the processing of a large number of mineral systems and the flow properties of particulate suspensions. In particular, these flow properties define the upper limit to processing of tailings suspensions in the mining industry and, ultimately, the recovery of water. In some regions of the world, the scarcity of fresh water has pushed this industry to use seawater, either as is or partially desalinated. Here we analyze the impact of monovalent alkali metal chlorides that are typical of seawater on the viscoelastic behaviour of flocculated silica sediments at concentrations typical of thickening systems. The sediment samples were subject to creep-recovery tests. All sediments exhibit nonlinear viscoelastic behaviour, deduced from the compliance-applied stress relationship. Interestingly, creep recovery was observed to be related to the Hofmeister series, Cs+<K+<Na+<Li+, with Cs+ producing lower recoveries than Li+. The yield stress, critical strain, and critical strain energy of the sediments were observed to be higher in maker salts (Na+ and Li+) compared with breaker salts (Cs+ and K+), due to stronger bonds in the particle networks. Our model of viscoelastic behaviour (Goñi et al., 2015) satisfactorily reproduces all experimental strain-time curves. The work provides novel input to decisions about the use of seawater or partially desalinated seawater in minerals processing with direct implications for tailings transportation, handling and water recovery.

Distribution of Biogenic Silica in Sediments of the Yellow River (Upper and Middle Reaches)

An experiment is held to extract the biogenic silica from Yellow River sediments to explore how such four influencing factors as extraction time, the type and concentration of extracting agent, and solid-liquid ratio affect the content of biogenic silicon in the samples. Besides, the distribution characteristics of biogenic silica in sediments of the Yellow River (upper and middle reaches) are discussed based on the measured results. The experiment results demonstrate the optimal conditions for the extraction of biogenic silica in sediments of the Yellow River: weight 0.050g of sediment sample at 90°C and extract biogenic silica for 7 hours with 40mL 1.0mol/L Na2CO3 solution as the extracting agent. The biogenic silica content of the surface sediments in the upper and middle reaches of the Yellow River varies greatly from 0.07-3.06mg/g. In descending order, the samples are arranged as: MD1>XH2>BT9>WLT8>SSG7>SZS5>XG4>GD3>WH6. The highest content appears in Maduo segment at the source of the Yellow River, and the lowest content appears in Wuhai segment.

Use of biogenic silica in sediment to record diatom density and their responses to environmental change in Sanggou Bay maricultural area over the past 200 years

Two sediment cores (S1 and S2 from shellfish and kelp cultivation areas, respectively) were collected from the Sanggou Bay maricultural area for the analysis of biogenic silica (BSi), an ideal proxy for the reconstruction of diatom density. The results show that prior to the advent of mariculture, the maximum diatom density in the two cores were observed in the 1880s before the first industrial revolution, and the maximum densities were 6500 × 104 ind m−3 and 5300 × 104 ind m−3 for S1 and S2, respectively. The diatom density was primarily affected by natural factors, such as the sea surface temperature (SST), the East Asian Winter Monsoon Index (EAWM), and the wild shellfish feeding pressure. The diatom density was affected by different cultivation methods and maricultural density during the maricultivation period. The diatom density decreased to 2800 × 104 ind m−3 in the shellfish cultivation area (S1) in 1996, and the diatom density was only 3600 × 104 ind m−3 in the kelp cultivation area (S2). Subsequently, a shellfish-kelp polyculture approach was implemented and diatom density started to continuously increase. The total diatom densities in S1 and S2 were restored to 3700 × 104 ind m−3 and 4200 × 104 ind m−3 in 2006, respectively. Nonetheless, the total diatom density in core S1 was only 55% of the density in the 1880s. This observation indicates that additional efforts are required to promote modifications to improve the cultivation environment and establish an environmentally-friendly cultivation model.

Simulating the modern δ30Si distribution in the oceans and in marine sediments

AbstractThe δ30Si of biogenic silica ( ) in marine sediments is a promising proxy for the reconstruction of silicic acid utilization by diatoms in the geological past. The application of this proxy, however, requires an understanding of the modern δ30Si distributions and their controlling mechanisms. Here we present results from a modern climate simulation with a coupled ocean‐sediment model that includes a prognostic formulation of biogenic silica production with concurrent silicon isotopic fractionation. In agreement with previous studies, biological fractionation combined with physical transport and mixing determines the oceanic distribution of simulated δ30Si. A new finding is a distinct seasonal cycle of δ30Si in the surface ocean, which is inversely related to that of silicic acid concentration and mixed layer depth. We also provide the first simulation results of sedimentary δ30Si, which reveal that (1) the distribution in the surface sediment reflects the exported signal from the euphotic zone and (2) the dissolution of biogenic silica in the sediment acts as a source of relatively light δ30Si into the bottom waters of the polar oceans, while it is a source of heavier δ30Si to the subtropical South Atlantic and South Pacific.

Do sediment type and test durations affect results of laboratory-based, accelerated testing studies of permeable pavement clogging?

Previous studies have attempted to quantify the clogging processes of Permeable Interlocking Concrete Pavers (PICPs) using accelerated testing methods. However, the results have been variable. This study investigated the effects that three different sediment types (natural and silica), and different simulated rainfall intensities, and testing durations had on the observed clogging processes (and measured surface infiltration rates) of laboratory-based, accelerated PICP testing studies. Results showed that accelerated simulated laboratory testing results are highly dependent on the type, and size of sediment used in the experiments. For example, when using real stormwater sediment up to 1.18mm in size, the results showed that neither testing duration, nor stormwater application rate had any significant effect on PICP clogging. However, the study clearly showed that shorter testing durations generally increased clogging and reduced the surface infiltration rates of the models when artificial silica sediment was used. Longer testing durations also generally increased clogging of the models when using fine sediment (<300μm). Results from this study will help researchers and designers better anticipate when and why PICPs are susceptible to clogging, reduce maintenance and extend the useful life of these increasingly common stormwater best management practices.

The Southern Ocean silica cycle

The Southern Ocean is a major opal sink and plays a key role in the silica cycle of the world ocean. So far however, a complete cycle of silicon in the Southern Ocean has not been published. On one hand, Southern Ocean surface waters receive considerable amounts of silicic acid (dissolved silica, DSi) from the rest of the world ocean through the upwelling of the Circumpolar Deep Water, fed by contributions of deep waters of the Atlantic, Indian, and Pacific Oceans. On the other hand, the Southern Ocean exports a considerable flux of the silicic acid that is not used by diatoms in surface waters through the northward pathways of the Sub-Antarctic Mode Water, of the Antarctic Intermediate Water, and of the Antarctic Bottom Water. Thus the Southern Ocean is a source of DSi for the rest of the world ocean. Here we show that the Southern Ocean is a net importer of DSi: because there is no significant external input of DSi, the flux of DSi imported through the Circumpolar Deep Water pathway compensates the sink flux of biogenic silica in sediments.