Silicic acid nutrient

Silicic acid (H4Si04) is a necessary nutrient for diatoms, who build their shells from opal (Si02 H20). Whether silicic acid becomes limiting for diatoms in seawater depends on the availability of Si relative to N and P. Estimates of diatom uptake of Si relative to P range from 16 1 to 23 1. Dugdale and Wilkerson (1998) and Dunne et al. (1999) have shown that much of the variability in new production in the equatorial Pacific may be tied to variability in diatom production. Diatom control is most important at times of very high nutrient concentrations and during non-steady-state times, perhaps because more iron is available at those times. 

For silica an additional component of silicic acid generated by inorganic dissolution also occurs. One can estimate oxidized" Si as being 23/138 AOU, but discrimination between preformed Si and inorganic Si is not possible. Representative profiles of PO4, NO3, and Si are given in Fig. 10-19. Note that after subtracting the oxidative nutrients the preformed values are relatively constant. 

A single technique that preserves all three nutrients (N03, P04, and Si(OH)4) in a single matrix would be most desirable. If this proves impossible, it will be necessary to use different approaches to preserve and store different nutrients. For example, glass containers cannot be used to store a reference material for Si(OH)4 due to the slow dissolution of silica (Zhang et al., 1999), while the polymerization of silicic acid upon freezing eliminates that option for preserving stable Si(OH)4 levels (Zhang and Ortner, 1998). 

Franck, V. M., Bruland, K. W., Hutchins, D. A., Brzezinski, M. A. (2003). Iron and zinc effects on silicic acid and nitrate uptake kinetics in three high-nutrient, low-chlorophyU (HNLC) regions. Mar. Ecol. Prog. Ser. 252, 15-33. 

Since sponges and radiolarians are not great players in particle flux, the rise of the diatoms must have profoundly altered the partitioning of silicic acid between surface and deep. The familiar nutrient-type distribution may have only existed for the last 50-100 million years. The approximate 14-fold drop in silicic acid concentration also suggests that the residence time of silicon in... 

There is some evidence that chromium (Cr " ), silicic acid (Si(OH)4) or related silicon-based compounds, borate (8407 ), nickel (NP" ), and arsenate (AsOf ) are required inorganic nutrients. However, the available evidence tends to be not convincing to all researchers (Reeves, 1997). The functions of arsenate and nickel are not clear. There is some indication that arsenate is used in the metabolism of sulfur-containing amino acids. An experimentally induced deficiency in arsenate or nickel results in impaired growth. 

On the other hand, a nutrient-type trace metal like Zn attains a concentration of dissolved Zn that is approximately five times greater in the old, nutrient-rich deep waters of the North Pacific than they are in the young, nutrient-poor North Atlantic deep waters. Its distribution in both ocean basins is similar to that of silicic acid. The efficiency with which Zn is recycled in the ocean leads to its relatively long oceanic residence time. 

Concentrations of many trace element nutrients (zinc, cadmium, iron, copper, nickel, and selenium) increase with depth in the ocean, similar to increases observed for major nutrients (nitrate, phosphate, and silicic acid) (Figures 2—4). In the central North Pacific, filterable concentrations of zinc and cadmium increase by 80-fold and 400-fold, respectively, between the surface and 1000-m depth. The similarity between vertical distributions of these trace elements and major nutrients indicates that both sets of nutrients are subject to similar biological uptake and regeneration processes. In these processes, both major and trace element nutrients are efficiently removed from surface waters through uptake by phytoplankton. Much of these assimilated nutrients are recycled within the euphoric zone by the coupled processes of zooplankton grazing and excretion, viral lysis of cells, and bacterial degradation of organic... 

Sihcate, or silicic acid (H4Si04), is a very important nutrient in the ocean. Unlike other major nutrients such as phosphate and nitrate or ammonium, which are needed by almost all marine plankton, silicate is an essential chemical requirement only for certain biota such as diatoms, radiolarian, silicoffageUates, and siliceous sponges. But siliceous phytoplankton contributes significantly to the primary production in the world s oceans. More than 40% of the entire primary production is contributed by diatoms, which reveals a close coupling of silica and carbon in the ocean. Therefore, silicate cycling has received sig-... 

The preparation of silica gel plates for the cultivation of certain types of bacteria has been described by Muller and Holm (391). A silicic acid sol is made by adding a solution of sodium silicate to hydrochloric acid buffered at about pH 4.5. The gel is permitted to set in Petri dishes, washed, soaked in nutrient solution, and then autoclaved. For a purer medium, the intermediate sol may be dialyzed before it is permitted to set to gel (392). An improved procedure for incorporating nutrients directly into the acid, forming the gel under sterile conditions and eliminating dialysis, was developed by Sterges (393). A simplified method (394) is described as follows. Seven hundred milliliters of 0.5 N HCl is mixed with 300 ml of the mineral nutrient solution to be employed. To I volume of 0.5 N sodium silicate is added 1 volume of lime water, and to this 1 volume of the acid nutrient is added. The mixture is poured into Petri dishes, aged 2 hr, and placed in an oven at lOO C for 1 hr. The use of tetramethyl ester of orthosilicic acid is advocated by Ingelman and co-... 

There are a number of potential drug administration routes in which PSi can be used (Table 1). Some of the routes are not even explored yet. In biomedical applications, in addition to the nontoxic behavior of the carrier material and bioresorbability, it is important that the degradation products are also nontoxic. PSi degradates into monomeric silicic acid, which is the most natural form of silicon and an important nutrient for humans (Jugdaohsingh et al. 2004). 

Diatoms can multiply very rapidly and dominate in nutrient-rich marine waters. Their distinguishing feature is a hard mineral shell made by polymerized silicic acid. They float in the water column or attach to surface of sediment. Diatoms are major contributors to production, especially in spring blooms. 

The acidity of soils also strongly affects the availability of metal cations such as K, Mg, and Ca. Most soils contain significant amounts of clay, whose chemical composition is dominated by aluminosilicates. Silicates are anionic, and the anions can be neutralized either by accepting protons or by associating with metal cations. When soil is too acidic, protons replace these metal cations, and the soil becomes depleted in these essential nutrients. 

The first two components are the active surfactants, whereas the other components are added for a variety of reasons. The polyphosphate chelate Ca ions which are present (with Mg ions also) in so-called hard waters and prevents them from coagulating the anionic surfactants. Zeolite powders are often used to replace phosphate because of their nutrient properties in river systems. Sodium silicate is added as a corrosion inhibitor for washing machines and also increases the pH. The pH is maintained at about 10 by the sodium carbonate. At lower pH values the acid form of the surfactants are produced and in most cases these are either insoluble or much less soluble than the sodium salt. Sodium sulphate is added to prevent caking and ensures free-flowing powder. The cellulose acts as a protective hydrophilic sheath around dispersed dirt particles and prevents re-deposition on the fabric. Foam stabilizers (non-ionic surfactants) are sometimes added to give a... 

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