Silicate In Seawater Research Articles

Utilization of rice husk ash as a potential catalyst for diatom growth and adsorbent for heavy metals in aquaculture systems

Many aquaculture environments suffer from significant silicon deficiencies and severe heavy metal contamination, posing substantial risks to both production and safety in aquaculture. This study aimed to assess the release of silicate from rice husk ash (RHA) and its impact on phytoplankton abundance and community composition, which are key factors affecting shellfish growth and survival. Additionally, the capacity of RHA to adsorb mercury (Hg2+) was examined using different modification methods. The results demonstrated that the concentration of dissolved silicate in seawater increased with higher RHA doses, reaching a maximum of 189.77 ± 45.61 μmol L−1 in the high RHA treatment (HR) with 1.0 g L−1 of RHA. Notably, the HR treatment group exhibited a significant increase in chlorophyll-a concentration for nano-phytoplankton (2–20 μm), with an up to eightfold rise in abundance compared to the control group. Moreover, the HR treatment resulted in a maximum diatom abundance of 4217 ± 741.98 cells L−1, benefiting diatom species such as Coscinodiscus sp., Nitzschia sp., and Cyclotella sp. These findings underscore the potential of RHA as a catalyst for diatom growth, which in turn supports the growth of shellfish. Furthermore, no concentrations of mercury (Hg), lead (Pb), cadmium (Cd), arsenic (As), copper (Cu), zinc (Zn), and chromium (Cr) were detected in any of the silicate enrichment treatments, confirming the safety of the RHA. The treatment of RHA with NaOH achieved an impressive removal efficiency of Hg2+, reaching up to 97.41 ± 0.33 %. This study highlights the promising application of agricultural waste RHA as a catalyst for diatom growth and an adsorbent for heavy metals in water systems relevant to aquaculture practices.

Autocalibration based on dilution of a single concentrated standard is used for the determination of silicate in sea water by the modified molybdenum blue method

The silicate (Si) molybdenum blue method was modified by combining oxalate and ascorbic acid into a single reagent and was used for determining Si in sea water samples. The first step of this automated assay protocol was designed to perform either a calibration by a single Si standard prepared in deionized (DI) water, or to dilute samples in the range of 0–160 μM Si to fit into 0–20 μM Si calibration range using a 20 cm flow cell. By designing the assay protocol to function in batch mode, the influence of salinity on calibration was eliminated, thus making the method suitable for analysis of samples collected in the open ocean, coastal areas, or rivers. Reproducibility and accuracy of this method were evaluated by analysis of certified sea water reference materials. Phosphate (P) does not interfere significantly if the Si:P ratio is 4:1 or larger. The limit of detection was 514 nM Si, r.s.d. 2.1 %, sampling frequency 40 s/h, reagent consumption 700 μL/sample, and using deionized water as the carrier solution.

Programmable flow injection: a versatile technique for benchtop and autonomous analysis of phosphate and silicate in seawater

High-resolution, autonomous monitoring of phosphate and silicate in the marine environment is essential to understand their complex dynamics and implications for the functioning of marine ecosystems. In the absence of dependable reagent-less sensors for these nutrients, leveraging established colorimetric techniques using miniaturized analyzers, such as programmable Flow Injection (pFI), offers the best immediate solution to meet oceanographic accuracy and precision standards. In this work, we further optimize the phosphomolybdate and silicomolybdate assays recently adapted for use with pFI, laying the groundwork for the technique’s use for long-term, autonomous operations. For both assays, we show that only a narrow range of acidities and molybdate concentrations can maximize sensitivity while minimizing salt effects. In addition, we demonstrate the stability of our optimized colorimetric reagent formulations, ensuring that analytical sensitivity remains within 10% of initial levels for at least 35 days of continuous use. We then applied our optimized protocols to produce oceanographically consistent phosphate and silicate profiles at the Hawaii Ocean Time Series (HOTS) and Southern Ocean Time Series (SOTS), respectively, which compared favorably against a reference method and historical data. Using certified reference materials for nutrients in seawater, we show that our pFI protocols, optimized for long-term operations, achieve a shipboard precision better than 6% and a relative combined uncertainty (k=1) of 4.5% for phosphate (0.45 - 2.95 µmol L-1) and 6.2% for silicate (2.2 to 103 µmol L-1). To demonstrate pFI’s potential as a versatile tool for autonomous monitoring, we report a five-day hourly phosphate time series at a coastal shore station in central California (n=121 analyses), examine phosphate uptake by seaweed at five-minute intervals at a seaweed aquaculture facility (n=103), and discuss a unique, high-resolution surface silicate transect spanning multiple frontal zones in the Australian sector of the Southern Ocean (n=249). These data, obtained using a commercially available pFI analyzer, confirm that pFI is a viable technology for autonomous monitoring of phosphate and silicate, paving the way for more ambitious, long-term deployments in a variety of settings.

High-value chemicals from marine diatoms: a biorefinery approach

Nowadays, we are going a step forward into the new era for the sustainable production of industrial commodity products such as energy, fine-chemicals, active compounds and materials from renewable biomass. Marine diatoms offer great potential as an untapped living factory for the generation of valuable commodity chemicals. As a photosynthetic microorganism, diatoms contain pigments, which have a high market value in the cosmetic, pharmaceutical and food colorant industries. Their unique metabolism to utilize the soluble silicate in seawater for their porous silica cell wall (frustule) opens an opportunity for the nano-porous material industry. Diatom’s lipids consist fatty acids, which could be catalytically upgraded into high-quality fuels like fatty acid alkyl esters (biodiesel) or hydrocarbons (green diesel). In the analysis reported here, we present the potential of biorefinery pathways of valuable components in marine diatoms. Understanding the biochemistry of them and the application of their valuable chemicals are discussed to gain insights for the opportunities and the key barriers in the development of marine diatoms-based biorefinery.

A design of spectrophotometric microfluidic chip sensor for analyzing silicate in seawater

High quality and continuous in situ silicate data are required to investigate the mechanism of the biogeochemical cycles and the formation of red tide. There is an urgently growing need for autonomous in situ silicate instruments that perform determination on various platforms. However, due to the high reagents and power consumption, as well as high system complexity leading to low reliability and robustness, the performance of the commercially available silicate sensors is not satisfactory. With these problems, here we present a new generation of microfluidic continuous flow analysis silicate sensor with sufficient analytical performance and robustness, for in situ determination of soluble silicate in seawater. The reaction mechanism of this sensor is based on the reaction of silicate with ammonium molybdate to form a yellow silicomolybdate complex and further reduction to silicomoIybdenum blue by ascorbic acid. The minimum limit of detection was 45.1 nmol L-1, and the linear determination range of the sensor is 0-400 μmol L-1. The recovery rate of the actual water is between 98.1%-104.0%, and the analyzing cycle of the sensor is about 5 minutes. This sensor has the advantages of high accuracy, high integration, low water consumption, and strong anti-interference ability. It has been successfully applied to measuring the silicate in seawater in Jiaozhou Bay.

Silicon-based electrochemical microdevices for silicate detection in seawater

This paper describes the electrochemical characterisation of gold and platinum microdevices mass fabricated using silicon technology. Specific attention was paid to allow in situ electrochemical detection of silicate in seawater. Thus, using a silicon nitride (Si3N4) inorganic passivation layer patterned using Inductively Coupled Plasma Chemical Vapor Deposition (ICP-CVD), coupled with a non-aggressive lift-off based process, different electrodes were isolated electrically: one gold or platinum working electrode named “macroelectrode” (2mm of diameter), four gold or platinum working ultramicroelectrodes (UME) (15μm of diameter), one platinum counter electrode and one silver electrode which can be used as a reference electrode after its chlorination. Their small size and mass fabrication make them very promising for oceanographic applications. As some components of microdevices release silicate and contaminate the solution, after being immersed in seawater, these microdevices were inserted in a specific cell that only puts the electrodes in contact with the seawater solution. Gold has been tested as a possible material for working electrodes but its lack of adherence to the passivation layer in seawater solutions led to non-accurate measurements. On the contrary, passivation layer on platinum electrodes resists to the seawater corrosive medium. The analytical performances of the platinum microdevices has been tested through different silicate calibrations and shows an outstanding accuracy and reproducibility when measurements are performed, especially with the macroelectrodes which showed only 2.8% signal variation after four months of use and a limit of quantification of 0.50μmolL−1 suitable for oceanographic applications.

Direct Determination of Dissolved Phosphate and Silicate in Seawater by Ion Exclusion Chromatography Sector Field Inductively Coupled Plasma Mass Spectrometry

A method is described for the direct determination of dissolved phosphate and silicate in seawater using ion exclusion chromatography (IEC) coupled with sector field inductively coupled plasma mass spectrometry (SF-ICPMS). Dissolved silicate was determined by double isotope dilution using a (29)Si spike, whereas one point gravimetric standard addition with internal standard of the same (29)Si spike was employed to quantitate dissolved phosphate. Medium resolution was used for all measurements in order to resolve polyatomic interferences on Si and P isotopes. Concentrations of 1.670 ± 0.008 and 30.20 ± 0.09 μM (SD, n = 6) with precisions of 0.47 and 0.31% for the dissolved phosphate and silicate, respectively, were obtained in National Research Council Canada certified reference material MOOS-3 seawater, in good agreement with certified values of 1.60 ± 0.15 and 30.5 ± 0.8 μM (U, k = 2), respectively. The reported method is a rapid (10 min per run), simple, and accurate online technique that requires no sample pretreatment. Moreover, this procedure achieves <0.5% precision (at above analyte concentrations) and method detection limits of 0.006 and 0.004 μM (0.18 as P and 0.11 ng g(-1) as Si), respectively, using a of 100 μL injection of seawater. The proposed technique is robust and well-suited for the determination of dissolved phosphate and silicate in seawater.

Improved accuracy of determination of dissolved silicate in seawater using absorption spectrometry

We studied to develop a certified reference material of seawater for nutrient analysis whose relative combined standard uncertainty for dissolved silicate was <0.5 %. In order to precisely measure the content of dissolved silicate in seawater, widely used absorption spectrometry with the so-called molybdenum blue was investigated as one of the highly sensitive determination methods. For the absorption spectrometry, a batch mode and a continuous flow analysis (CFA) mode were used and the characteristics of the calibration curves in the both modes were examined in detail. The calibration curve in the batch mode could be explained by a first-order regression line, whereas that in the CFA mode fitted to a second-order regression line. Therefore, for measuring the silicate content of seawater whose matrix depends on its origin, a standard addition method in a batch mode is preferable, though strict control of the compositions of the solutions for the standard addition calibration curve are greatly important for getting good linearity of the curve. In addition, in the case of the standard addition method, it is important to measure the blank value including the background; in the present study, the origins related to the blank were discussed and evaluated. The relative combined standard uncertainty of 0.48 % could be achieved for the measurement of content of 28 μmol/kg silicate in seawater, providing that the volume ratio between each of the molybdenum blue colorimetric reagents and the seawater was kept constant among all the solutions for the standard addition calibration curve. The procedure was validated using artificial seawater with a known concentration of silicate. Such highly improved precision and trueness which reaches the recent target of the community related to analysis of nutrients in seawater is reported for the first time. The developed procedure will provide a good way of validation for the analysts who need measurement with high precision and trueness on the content of silicate in seawater and other samples.

Examination of silicate limitation of primary production in Jiaozhou Bay, China

Jiaozhou Bay data collected from May 1991 to February 1994, in 12 seasonal investigations, and provided the authors by the Ecological Station of Jiaozhou Bay, were analyzed to determine the spatiotemporal variations in temperature, light, nutrients (NO - 3 N, NO - 2 N, NH + 4 N, SiO 2- 3 Si, PO 3- 4 P), phytoplankton, and primary production in Jiaozhou Bay. The results indicated that only silicate correlated well in time and space with, and had important effects on, the characteristics, dynamic cycles and trends of, primary production in Jiaozhou Bay. The authors developed a corresponding dynamic model of primary production and silicate and water temperature. Eq.(1) of the model shows that the primary production variation is controlled by the nutrient Si and affected by water temperature; that the main factor controlling the primary production is Si; that water temperature affects the composition of the structure of phytoplankton assemblage; that the different populations of the phytoplankton assemblage occupy different ecological niches for C , the apparent ratio of conversion of silicate in seawater into phytoplankton biomas and D , the coefficient of water temperature's effect on phytoplankton biomass. The authors researched the silicon source of Jiaozhou Bay, the biogeochemical sediment process of the silicon, the phytoplankton predominant species and the phytoplankton structure. The authors considered silicate a limiting factor of primary production in Jiaozhou Bay, whose decreasing concentration of silicate from terrestrial source is supposedly due to dilution by current and uptake by phytoplankton; quantified the silicate assimilated by phytoplankton, the intrinsic ratio of conversion of silicon into phytoplankton biomass, the proportion of silicate uptaken by phytoplankton and diluted by current; and found that the primary production of the phytoplankton is determined by the quantity of the silicate assimilated by them. The phenomenon of apparently high plant nutrient concentrations but low phytoplankton biomass in some waters is reasonably explained in this paper.

Experimental and observational studies of radiolarian physiological ecology, 6. Effects of silicate-supplemented seawater on the longevity and weight gain of spongiose radiolarians Spongaster tetras and Dictyocoryne truncatum

Radiolaria occur abundantly in surface water with low silicate concentrations (ca. 1 μM), yet they construct remarkably robust siliceous skeletons. This indicates they compete very effectively for the available silicate. To examine the effects of variation in silicate concentration on skeletal growth and vitality, two spongiose radiolarians Spongaster tetras and Dictyocoryne truncatum, collected in surface plankton tows near Barbados, West Indies, were maintained in plastic tissue culture dishes, each well of the dishes containing ca. 15 ml seawater emended with additional sodium silicate of 0 μM (control), 50 μM, 100 μM and 150 μM. Their longevity and skeletal weight gain, the latter calculated from equations relating skeletal weight to a linear dimension of the skeleton, are reported with descriptions of their living features. The addition of silicate up to 100 μM had no statistically significant effect on the weight of silicate deposited per shell for either S. tetras or D. truncatum. However, noticeable detrimental effects resulted in earlier death in both S. tetras and D. truncatum at 150 μM. Early death was more frequent in D. truncatum. Spongaster tetras that grew skeletons may survive longer when cultured in 50 μM silicate-enriched seawater compared to 150 μM enriched seawater, but not longer than those cultured in unsupplemented seawater. D. truncatum has the longest longevity in unsupplemented seawater. In addition, scanning electron microscopy of shells collected from individuals that grew in culture revealed no evidence of enhanced skeletal growth or structures with silicate enrichment of the culture medium. These data add further evidence that S. tetras and D. truncatum are capable of competing very effectively for silica in ambient seawater concentrations of approximately 1.0 μM, and also that changes in seawater silicate may not have a dramatic effect on longevity, skeletal size, or weight of some radiolarians. Thus other environmental variables, such as variations in temperature and salinity, may more likely impress a relatively more salient signal in the microfossil record. Daily mean weight gain values at the four treatments ranged from 4.3 ng to 6.3 ng in S. tetras and from 19.7 ng to 27.1 ng in D. truncatum. For the control group, mean total weight gain was 0.035 μg in S. tetras and 0.083 μg in D. truncatum. Compared to the previously published results for S. tetras, using larger glass vials, the weight gain values seem to be significantly smaller. However, estimated silicate consumption ratios with respect to the available amount in the culture vessel by S. tetras agree substantially with each other. This suggests that observed radiolarian skeletal growth in the previous and present experiments was rather substantially affected by other environmental factors, such as available micronutrients, related to the water volume used in the culture vessel.

Determination of silicate in seawater by inductively Coupled Plasma Atomic Emission Spectrometry

Inductively Coupled Plasma Atomic Emission Spectrometry (ICP) was adopted for direct analysis of silicate in seawater, eliminating necessity for pre-treatment. Via this method, the determination of silicate is rapid and easy compared with conventional methods of colorimetry. In seawater analysis, a decrease of sensitivity of about 24% was observed due to interference by coexisting elements, mainly Na. Examination of the analytical conditions revealed a detection limit of 0.3 μM Si, and precisions of approximately 3.2, 2.0 and 1.3% for Si levels of 4, 15 and 94 μM, respectively. Using this method, silicate determination in the East China Sea was attempted.

On the Silicate in Sea Water

On the Silicate in Sea Water

Determination of reactive silicate in seawater by flow injection analysis

Dosage du silicate dans l'eau de mer par la methode au bleu de molybdene. Analyse de 80 echantillons a l'heure

Studies on the phytoplankton ecology of the trondheimsfjord. III. Dynamics of phytoplankton blooms in relation to environmental factors, bioassay experiments and parameters for the physiological state of the populations

Quantitative phytoplankton sampling was carried out at weekly intervals at one station in the central part of the Trondheimsfjord and at irregular intervals at one station near Trondheim Harbour during March–October, 1970 and 1971. Various developmental stages of diatom blooms have been observed, which have been related to variations in freshwater discharge, hydrography, nutrients (nitrate, orthophosphate, and reactive silicate in sea water and river water), light, the results of bioassay experiments, parameters for the physiological state of natural phytoplankton populations, and to data on phytoplankton and hydrography collected during 1963–1969. Two spring blooms of diatoms are persistent from year to year in the area. The first one starts in March, triggered by an increase in the incident radiation and culminates in early April. It develops analogously to a batch culture and is nourished mainly by nutrients accumulated during the winter. The second takes place in brackish waters during May–June concomitant with floods in rivers. The magnitude of its populations corresponds to discharge maxima unless disturbed by hydrographical irregularities and heavy grazing by Calanus finmarchicus (Gunnerus). This bloom is analogous to a continuous culture and is nourished by nutrients in entrainment water and to a lesser extent by those in the river water. Furthermore, the unpredictable development of diatom blooms in the autumn seems to follow peaks in the discharge unless prevented by too low salinity and poor incident light. In autumns of little discharge and with turbulence in the upper 5–10 m dinoflagellates predominate. In high salinity waters nitrogen seems generally more limiting than phosphorus for phytoplankton growth The N/P atomic ratio of such waters with no phytoplankton growth was 10–12 in contrast to 13–18 in the phytoplankton. Due to the high N/P ratio of 40–50 in river water, phosphorus was more limiting than nitrogen in some brackish waters. On two occasions trace metals seemed to be the most limiting.

An investigation of some methods used for the determination of silicate in sea water

Methods of filtration and storage of sea-water samples intended for silicate analysis have been investigated. The desirability in some circumstances of filtering water samples before analysis has been demonstrated. The behaviour of three recommended methods for the analysis of silicate in sea water has been compared by inter-calibration studies.

On the Variation of Silicate Content in Sea Water during its Storage

As the first step in the investigation of silicate in sea water, dissolution of silicate from various kinds of containers and from organic remains during the storage was studied.The amount of dissolution of silicate from glass bottles during its storage was fairly large, which was more than 105 μg-atoms/L on an average about a month later from the collection of samples, though the effect was different with different nature of glass materials of each bottle.Rapid dissolution of silicate from plankton diatoms was also found when sea water contained plankton diatoms of more than 105in cell numbers per liter.By these reasons it is recommended that silicate determination in oceanographic research should be done on board soon after sampling. If this is impossible, sea water should be filtered off and stored in paraffine coated bottles.

The determination of silicate in sea water

Silicon in sea water may be present in suspension, in particles of clay or sand, as a constituent of diatoms, etc., or in solution. Some silicon in solution occurs in the form of silicate. This is usually estimated by the colorimetric method of Diénert &amp; Wandenbulcke (1923), which makes use of the yellow colour of the silicomolybdic acid which is formed when ammonium molybdate and sulphuric acid are added to the water (Atkins, 1923). The colour may be compared with that of standard solutions of picric acid (Diénert &amp; Wandenbulcke, 1923) or potassium chromate (Swank &amp; Mellon, 1934). The method is simple but the colour in sea water is often faint and is not easy to match visually, nor is its intensity strictly proportional to the concentration of silicate. Less colour is produced in sea water than in standard solutions made with distilled water and this ‘salt error’ must be allowed for (Brujewicz &amp; Blinov, 1933; Wattenberg, 1937; Robinson &amp; Spoor, 1936).

Photometric determination of silicate in sea water

Photometric determination of silicate in sea water