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Control mechanisms on the reactive silicate fluxes by using on board resuspension experiments in the eutrophicated coastal environment

Özkan Ebru Y., Buyukisik Hasan B.

Oceanological and Hydrobiological Studies

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2023

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Vol. 52, No. 3

343--365

EN

This study aims to differentiate bio-mediated and biogenic CO3-2precipitation or terrestrial CO3-2 input using on board incubation techniques, to investigate the effects of resuspension in the coastal environment and to increase our understanding of predicted relationships between silicate releases and other biogeochemical variables in resuspension events. Relationships between dark silicate flux and BSi, CO3-2, OrgC, Mn (manganese) according to the seasons were examined. The silica flux is controlled by the CaCO3 coating on the diatom skeletons due to the fact that diatom skeletonsact as crystallization nuclei in the calcite precipitation that is biologicallya ffected. The reduction in flux with BSi may be due to the reduction in thesurface areas of larger diatom species. The negative linear relationships observed between silica fluxes and CO3-2 is indicative of RSi fluxes constrainedby bio-mediated carbonate increase. Linear relationships which are the samein their slopes but differ in their intercepts, reveal the effect of the changein diatom size on silica flux. Smaller diatoms have more surface area perunit volume, meaning an increased silica flux. On the other hand, seeing different CO3-2 values at stations with the same orgC value have increased the confidence interval (CI) 95% in the linear relationship. The presence ofdifferent silica flux values in stations with the same carbonate value may beexplained both by different orgC values and by diatoms containing different group sizes. The silica flux is controlled by the CaCO3

2

Seasonal variations in the abundance and sinking flux of biogenic silica in Daya Bay, northern South China Sea

Zhao Xiufeng, Yang Weifeng, Ma Haoyang, Li Junjie, Chen Min, Fang Ziming, Zhang Xiao, Zeng Jian, Qiu Yusheng, Zheng Minfang

Oceanologia

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2019

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No. 61 (2)

239--251

EN

Coastal seas account for > 50% of the biogenic silica (BSi) production in marine environments. However, BSi sinking is poorly understood. Here, seasonal variations in the abundance and sinking flux of BSi were investigated in Daya Bay, in the northern South China Sea. The highest BSi concentrations occurred in summer, averaging 8.04 ± 5.48 μmol L-1 (±SD), followed by autumn (5.51 ± 3.11 μmol L-1) and spring (3.76 ± 3.06 μmol L-1). The lowest BSi concentration of 2.93 ± 1.34 μmol L-1 was observed in winter. Based on234Th/238U disequilibria, the average BSi sinking fluxes were 7.08 ± 8.62, 10.01 ± 13.95, and 8.30 ± 13.06 mmol Si m-2 d-1 in spring, summer, and autumn, respectively. The lowest flux of 4.19 ± 3.98 mmol Si m-2 d-1was measured in winter. Together with nitrogen fluxes, the Si:N sinking ratios were 0.8:1.0, 1.5:1.0, 1.6:1.0, and 1.4:1.0 in spring, summer, autumn, and winter, respectively, indicating that particle sinking induces the faster removal of Si compared to N in Daya Bay.

3

Identifying the main sources of silicate in coastal waters of the Southern Gulf of Valencia (Western Mediterranean Sea)

Sospedra J., Niencheski L. F. H., Falco S., Andrade C. F. F., Attisano K. K., Rodilla M.

Oceanologia

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2018

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No. 60 (1)

52--64

EN

Silicon is a major nutrient for siliceous primary producers, which can become a potential limiting nutrient in oligotrophic areas. Most of the silicon inputs to the marine environment come from continental discharges, from both superficial and ground waters. This study analyses the main sources of silicon and their dynamics along the southernmost 43 km of shoreline in the Gulf of Valencia (Western Mediterranean Sea). The salinity and silicate concentration in the different compartments (springs, freshwater wells, beach groundwater, surf zone and coastal waters) in this coastal area were determined. In addition, chlorophyll a and phytoplankton community were analyzed in the surf zone and coastal waters. Silicate concentrations in freshwater wells ranged between 130 and 150 μM, whereas concentrations of this nutrient declined to 49 μM in freshwater-seawater mixture transects. At the same time, there was a positive gradient in silicate for both freshwater and coastal waters southward. An amount of 18.7 t of dissolved silicate was estimated in the nearest first kilometre nearest to the coastline, 6 t of this silicate belonged to the background sea level. On the other hand, the sum of the main rivers in the area supplies 1.6 t of dissolved silicate per day. This implies that a large amount of the remaining 11.1 t must derive from submarine groundwater discharges, which would thus represent 59% of the coastal dissolved silicate budget. Overall, it is suggested that a subterranean transport pathway must contribute considerably to silicate concentrations throughout this zone, which is characterized as permeable.

4

Wpływ dodatków spoiw ceramicznych na proces spiekania krzemionki biogenicznej

Konopka K., Kubiak P., Bobryk E., Szafran M.

Kompozyty

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2010

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R. 10, nr 1

15-19

PL

Skała osadowa o nazwie ziemia okrzemkowa jest efektem nagromadzenia przez tysiące lat pancerzyków (szkieletów) okrzemek, określanych też nazwą z języka angielskiego diatomity. Diatomity to jednokomórkowe algi obecne w różnym środowisku wodnym o specyficznej strukturze ścian komórkowych, zbudowanych z bezpostaciowej krzemionki (SiO2) i wyróżniające się różnymi elementami szkieletów, jak wyrostki, żebrowania i nanorozmiarowe pory. Ziemia okrzemkowa jest również łatwo dostępnym i tanim surowcem, wykorzystywanym jako materiał w budownictwie, na elementy o zwiększonej odporności ściernej, a także jako materiały adsorpcyjne. Jest to także bardzo dobre źródło biogenicznej krzemionki, która może być traktowana jako surowiec wyjściowy do wytwarzania litych materiałów. W szczególności istotne jest opracowanie metod ich konsolidacji oraz dobór parametrów technologicznych procesu spiekania, aby możliwe było zachowanie naturalnie istniejących w pancerzykach okrzemek porów. Artykuł przedstawia wyniki eksperymentów konsolidacji diatomitów, a w szczególności analizowano wpływ dodatku spoiw ceramicznych na przebieg procesu spiekania z możliwością zachowania naturalnie występujących w pancerzykach diatomitów porów. Na podstawie przedstawionych badań można stwierdzić, że zastosowanie spoiw ceramicznych do krzemionki biogenicznej pozwala na uzyskanie spieków już w temperaturze spiekania 900°C. Mikrostruktury uzyskanych spieków potwierdzają zajście procesu spiekania, polegającego na konsolidacji pancerzyków diatomitu i częściowego pozamykania naturalnie istniejących w diatomitach porów. Jest to istotne z punktu widzenia technologicznego, ponieważ pozwala na prowadzenie spiekania w stosunkowo niskiej temperaturze, taniej, pochodzenia biogenicznego krzemionki w postaci ziemi okrzemkowej z jednoczesnym możliwym zachowaniem części naturalnie występujących porów w pancerzykach diatomitów.

EN

Diatomaceous earth is the sedimentary rock formed by sedimentation of diatoms frustules through thousands of years. Diatoms are unicellular eukaryotic algae, which can be found in almost all aqueous and humid environments. They have unique morphology of skeletons with the pattern such as pores, ridges, areoles and other forms, and their cell walls are made of silica (hydrated silicon dioxide). Because of this specific morphology, diatoms are considered in nanotechnology. On the other hand, the wide application of the diatomaceous earth as building and abrasive materials, fillers and materials used for filtration or insulation results from the fact that this sedimentary rock is available in nature in large quantities and at a low cost. This rock is also easy to posses source of biogenic silica. Because of that diatoms have to be processed and sintered. The paper presents results of diatoms consolidation experiments. Especially the attention was made of influence the ceramic bonds on sintering process, degree of consolidation and preservation of the nanopores that naturally exist in diatoms. The bulk materials obtained by pressing and sintering were examined by scanning electron microscopy (SEM), the porosity and strength were estimated. Results showed that ceramic bonds help in sintering diatoms, sintered samples obtained at 900°C. Some naturally existed pores in diatom's frustules were not closed. The results are important for the application of cheep biogenic silica.