Effect of Stirring Time on Sodium Silicate Synthesis From Mount Kelud Volcanic Ash

This study performed the synthesis of sodium silicate from the volcanic ash of Mount Kelud with various stirring time in the sodium silicate synthesis process. Synthesis of sodium silicate was carried out using alkaline extraction at low temperature. This method is based on the solubility of silica under alkaline conditions and is proven to be more effective than the smelting method. The dissolution of silica contained in the volcanic ash of Mount Kelud was carried out using NaOH solution to form a Na2SiO3 solution. This process also studied the effect of stirring time on the amount of dissolved silica, with the stirring time of 0.5; 1; 1.5; 2; 2.5; 3 and 4 hours. The dissolved silica levels were tested using AAS. The amount of dissolved silica increased sharply with the longer length of stirring time, however for a stirring time of more than 2.5 hours, the dissolution was slow. The study revealed that the optimal result time was obtained from the stirring time of 2.5 hours with dissolved silica content of 19.82%. Keywords: volcanic ash, silica, sodium silicate, stirring time

Global syndromes induced by changes in solutes of the world’s large rivers

Solute-induced river syndromes have grown in intensity in recent years. Here we investigate seven such river syndromes (salinization, mineralization, desalinization, acidification, alkalization, hardening, and softening) associated with global trends in major solutes (Ca2+, Mg2+, Na+, K+, SO42−, Cl−, HCO3−) and dissolved silica in the world’s large rivers (basin areas ≥ 1000 km2). A comprehensive dataset from 600 gauge stations in 149 large rivers reveals nine binary patterns of co-varying trends in runoff and solute concentration. Solute-induced river syndromes are associated with remarkable increases in total dissolved solids (68%), chloride (81%), sodium (86%) and sulfate (142%) fluxes from rivers to oceans worldwide. The syndromes are most prevalent in temperate regions (30~50°N and 30~40°S based on the available data) where severe rock weathering and active human interferences such as urbanization and agricultural irrigation are concentrated. This study highlights the urgency to protect river health from extreme changes in solute contents.

Canine Silica Urolithiasis in Mexico, Associated with the Concentration of Dissolved Silica in Tap Water

Silica urolithiasis is infrequent in dogs, but in Mexico represents 12.9%. Our hypothesis is the consumption of high amounts of silicates in the diet, especially that dissolved in tap water. The objective of this study was to determine the concentrations of silica in the tap water in different geographical areas and their relationship with cases of silicate urolithiasis in dogs. From 179 cases of silicate urolithiasis, 98.9% were from dogs within a geographic area called the Trans-Mexican Volcanic Belt, which represents a cross shaft to the center of the country. Silica concentrations in tap water ranged between 3 and 76 mg/L, with a range of 27 to 76 mg/L, a mean of 49.9 ± 12 mg/L within the Trans-Mexican Volcanic Belt, and a concentration from 3 to 30 mg/L, with a mean of 16.4 ± 7 mg/L outside this area; these were significantly different ( p < 0.001 ). These findings demonstrate that there is a geographic risk factor for silicate urolithiasis in urolith-forming dogs, related to the consumption of tap water with a high concentration of silica. Further studies are necessary to identify this same pathophysiological association in other species.

Impact of Holocene climate change on silicon cycling in Lake 850, Northern Sweden

Diatom-rich sediment in a small subarctic lake (Lake 850) was investigated in a 9400 cal. yr BP sediment record in order to explore the impact of Holocene climate evolution on silicon cycling. Diatom stable silicon isotopes ([Formula: see text]) and biogenic silica (BSi) indicate that high BSi concentrations in sediment throughout the Holocene are associated with a lighter Si isotope source of dissolved silica (DSi), such as groundwater or freshly weathered primary minerals. Furthermore, higher BSi concentrations were favoured during the mid-Holocene by low detrital inputs and possibly a longer ice-free period allowing for more diatom production to occur. The diatom [Formula: see text] signature shows a link to changes in regional climate and is influenced by length of diatom growth period and hydrological fluctuations. Lighter Si isotopic values occur during the mid-Holocene, when climate is inferred to be more continental and drier, with pronounced seasonality. In contrast, a heavier Si isotopic signature is observed in the early and late Holocene, when oceanic influences are thought to be stronger and the climate wetter. The [Formula: see text] values have generally lighter signatures as compared with other studies, which supports a light DSi source.

Nutrient chemistry and eutrophication risk assessment of the Ghaghara River, India

This study was carried out to evaluate the eutrophication risk associated with the nutrient flux from the Ghaghara river by using nutrient molar ratios and indicators for coastal eutrophication potential values. The concentration of ammonium (3–8 times), nitrate (3–10 times), and phosphate (3–4.5 times) in the Ghaghara river were higher than the reported value for the unpolluted rivers indicating the contribution from the anthropogenic sources. The dissolved nutrients concentration showed significant seasonal variations in the Ghaghara river system. The specific yield of nitrate-N, phosphate-P, and dissolved silica-Si from the Ghaghara river were 0.49, 0.03 and 0.96 tons km−2 yr−1 respectively. The average molar ratio for dissolved inorganic nitrogen (DIN)/Dissolved inorganic Phosphate (DIP) was above 16:1, indicated phosphate limitation in biological productivity. In contrast, an average molar ratio of Dissolved inorganic Silica (DSi)/DIN of 4.6 ± 4.4 favored the diatom growth in the Ghaghara river. The negative value of P-ICEP (-2.93 kg C. km−2day−1) indicated phosphate limitation in the Ghaghara river. The positive value of N-ICEP (1.71 kg C·km−2day−1) indicates an excess of nitrogen over silica transport from the Ghaghara river to the Ganga river, which can create an eutrophication problem in the Ganga river.

Spatial and seasonal variation in dissolved silica benthic fluxes in the shallow zones of the southern Baltic Sea

&lt;p&gt;Dissolved silica (DSi) is an important macronutrient in the marine environment, necessary for growth of many aquatic organisms. Yet, DSi marine cycle is still not fully recognized, especially in dynamic, coastal zones. Although DSi is mainly transported to the sea by rivers, benthic fluxes of DSi, which originate from dissolution of the siliceous remains in the sediments, can also represent an important source of bioavailable silicon in the ocean. Benthic DSi fluxes are mainly powered by diffusion, but their rates are strongly shaped by the benthic fauna. Still, the role of benthos in these processes is not fully recognized. The main goal of this study was to investigate how various environmental factors and benthic fauna may shape the coastal cycle of Si in coastal environments during different seasons.&lt;/p&gt;&lt;p&gt;Our study was conducted in the shallow coastal ecosystems of the southern Baltic Sea characterized by contrasting environmental conditions: shallow, brackish and enclosed Szczecin Lagoon (Oder river estuary), dynamic open waters near &amp;#321;eba with relatively low anthropogenic influence, enclosed Puck Bay and Vistula prodelta. We investigated both shore ecosystems (app. 0.5 m depth) and deeper areas (from 6 up to 60 m depth). DSi concentrations in the bottom waters and environmental characteristics (T, S, O&lt;sub&gt;2&lt;/sub&gt;, sediment organic matter) were investigated at 6 stations, during three seasons (winter, spring and autumn) in years 2019-2020 with s/y Oceania (IOPAN) and directly from the shore. Additionally, samples from shore stations were collected during summer. DSi benthic fluxes were determined at each station by performing &lt;em&gt;ex situ&lt;/em&gt; incubations of sediment cores (n = 4-5) with natural benthic assemblages. The benthic organisms in studied cores were collected, identified, counted, and weighed.&lt;/p&gt;&lt;p&gt;The lowest fluxes were measured at sandy stations while highest return fluxes were observed at muddy sites. High variability in DSi benthic fluxes along studied localities was observed, ranging from -1.11 mmol d&lt;sup&gt;-1&lt;/sup&gt;m&lt;sup&gt;-2&lt;/sup&gt; in summer at shore station in the Puck Bay and up to 6.79 mmol d&lt;sup&gt;-1&lt;/sup&gt;m&lt;sup&gt;-2&lt;/sup&gt; in Szczecin Lagoon in autumn. We used &amp;#160;Gaussian Generalized Linear Models (GLMs) to estimate the role of environmental conditions, benthic fauna characteristics &amp;#160;and interactions among them in the variability of DSi benthic flux across studied localities. The most important predictors for the fluxes were all pair-wise interactions of temperature, total organic carbon, the C/N molar ratio, and the density of benthic macrofauna. Both interaction terms that included C/N ratio, a measure of organic matter quality (i.e. low C/N ratio indicates higher quality), were associated with increased DSi uptake by the sediment. Further, the interaction term between T and benthic marcofauna density was also linked to negative benthic fluxes of DSi. In contrast, the interaction of T and TOC caused a strong increase in DSi return fluxes.&lt;/p&gt;

Observations Inform Improvements in Model Silicon Cycling in a Semi-enclosed Coastal Sea

&lt;p&gt;We have developed a coupled physical-biological model representing plankton and nutrient dynamics of the Strait of Georgia, a fjord-like semi-enclosed coastal sea on the west coast of Canada. The nutrient-phytoplankton-zooplankton-detritus (NPZD)-type biological model is based on nitrogen uptake and remineralization with a coupled silicon cycle and includes both diatom and non-siliceous phytoplankton functional groups. The Strait of Georgia exhibits an estuarine circulation driven by input from the Fraser River as well as many smaller rivers and streams. It has high levels of dissolved silica (can be &gt;50 &amp;#956;M even at the surface). Silicon-replete conditions shape key characteristics of the local ecosystem, which include heavily silicified glass sponge reefs as well as frequent diatom and occasional silicoflagellate blooms. We therefore consider the ability of the model to match observed silicon levels an indicator of the fidelity of its representation of local biogeochemistry. Silicon in the model may be in the form of dissolved silica, living diatoms, or particulate biogenic silica, and model diatom growth may be limited by nitrogen, light, or dissolved silica availability. We will discuss the challenges involved in accurately representing important drivers of the regional silicon cycle. These include accurately capturing the division of primary productivity between diatoms and non-siliceous phytoplankton functional groups, as well as uncertainties in the magnitude of terrestrial inputs and sediment fluxes. We will show how evaluating the model functional groups by comparison with phytoplankton community composition determined by high performance liquid chromatography (HPLC) has informed our interpretation of model results and provided direction for efforts at improving model performance. We will discuss the impact of targeted adjustments to model parameters on the model silicon cycle in light of comparisons to observations.&lt;/p&gt;

Ongoing biogenic silica diagenesis — Interstitial-water chemical signals

&lt;p&gt;Biogenic silica diagenesis leads to abrupt changes in the physical properties of host sediment across the depth of an opal-A to opal-CT transition zone. Predicting the present-day diagenetic state of this reaction boundary, i.e., active versus arrested&amp;#160;opal-A to opal-CT transition zones, is imperative to constraining the diagenetic factors that impact dramatic variations in the physical state of sediment. This study assesses whether there are present-day signatures of active silica diagenesis in the interstitial water, and corroborates the potential for pore-water chemistry for distinguishing between ongoing precipitation of diagenetic opal and arrested reaction fronts. Interstitial-water chemistry, mineralogy, and thermodynamic analyses of the Ocean Drilling Program Sites 794 and 795 demonstrate that solubility equilibrium is reached with respect to opal-CT in the transition zones accommodated by the Neogene biosiliceous sediments in the Sea of Japan. Even though the dissolution of biogenic opal is triggering reverse-weathering processes, the equilibrium reached with respect to diagenetic opal strongly suggests that the dissolved silica depression across the transition zones is essentially influenced by ongoing transformation of opal-A to opal-CT. Owing to abrupt petrophysical variations linked to opal-CT precipitation, the interstitial profiles of major ions and primary parameters have also been impacted by silica diagenesis. The extremely low dissolved-silica diffusion fluxes in the sediment, the very low permeability of the sediment capturing silica diagenetic transformations, and the marked pore-water loss at the depth of the transition zone all support the fact that the dissolved species have not been diffused in the sediment at rates comparable to those by pore-water advection due to sediment porosity drop. Advective and diffusive mechanisms, however, appear to have ceased recently because they have failed to smooth out the traces of ongoing biogenic silica diagenesis.&lt;/p&gt;