Phosphate seawater concentration

Annual mean surface seawater concentrations of (a) chlorophyll (b) nitrate, (c) phosphate, (d) silicate, and (e) iron. Data from Conkright, M., et al. (2002). World Ocean Atlas 2001 Vol. 4 Nutrients. Vol. NOAA Atlas NESDIS 52. U.S. Government Printing Office. Plots from M. Vichi, et al. (2007). Journal of Marine Systems 64, 110-134. (See companion website for color version.)... 

Figure 20. Rate of dissolution relative to the rate of dissolution in very low phosphate seawater (Rate ) after a half hour of reaction vs. surface phosphate concentration at Q = 0.8 and n = 0.5 (57)...

Isaeva [181] described a phosphomolybdate method for the determination of phosphate in turbid seawater. Molybdenum titration methods are subject to extensive interferences and are not considered to be reliable when compared with more recently developed methods based on solvent extraction [182-187], such as solvent-extraction spectrophotometric determination of phosphate using molybdate and malachite green [188]. In this method the ion pair formed between malachite green and phosphomolybdate is extracted from the seawater sample with an organic solvent. This extraction achieves a useful 20-fold increase in the concentration of the phosphate in the extract. The detection limit is about 0.1 ig/l, standard deviation 0.05 ng-1 (4.3 xg/l in tap water), and relative standard deviation 1.1%. Most cations and anions found in non-saline waters do not interfere, but arsenic (V) causes large positive errors. 

A commonly used procedure for the determination of phosphate in seawater and estuarine waters uses the formation of the molybdenum blue complex at 35-40 °C in an autoanalyser and spectrophotometric evaluation of the resulting colour. Unfortunately, when applied to seawater samples, depending on the chloride content of the sample, peak distortion or even negative peaks occur which make it impossible to obtain reliable phosphate values (Fig. 2.7). This effect can be overcome by the replacement of the distilled water-wash solution used in such methods by a solution of sodium chloride of an appropriate concentration related to the chloride concentration of the sample. The chloride content of the wash solution need not be exactly equal to that of the sample. For chloride contents in the sample up to 18 000 mg/1 (i.e., seawater),... 

Eberlein and Kattner [194] described an automated method for the determination of orthophosphate and total dissolved phosphorus in the marine environment. Separate aliquots of filtered seawater samples were used for the determination orthophosphate and total dissolved phosphorus in the concentration range 0.01-5 xg/l phosphorus. The digestion mixture for total dissolved phosphorus consisted of sodium hydroxide (1.5 g), potassium peroxidisulfate (5 g) and boric acid (3 g) dissolved in doubly distilled water (100 ml). Seawater samples (50 ml) were mixed with the digestion reagent, heated under pressure at 115-120 °C for 2 h, cooled, and stored before determination in the autoanalyser system. For total phosphorus, extra ascorbic acid was added to the aerosol water of the autoanalyser manifold before the reagents used for the molybdenum blue reaction were added. For measurement of orthophosphate, a phosphate working reagent composed of sulfuric acid, ammonium molyb-... 

Pruszkowska et al. [135] described a simple and direct method for the determination of cadmium in coastal water utilizing a platform graphite furnace and Zeeman background correction. The furnace conditions are summarised in Table 5.1. These workers obtained a detection limit of 0.013 pg/1 in 12 pi samples, or about 0.16 pg cadmium in the coastal seawater sample. The characteristic integrated amount was 0.35 pg cadmium per 0.0044 A s. A matrix modifier containing di-ammonium hydrogen phosphate and nitric acid was used. Concentrations of cadmium in coastal seawater were calculated directly from a calibration curve. Standards contained sodium chloride and the same matrix modifier as the samples. No interference from the matrix was observed. 

The final run 4-1 was the adsorption of phosphate from seawater to which 1 mM of phosphate was spiked. The concentration of NaCl in seawater is ca. 0.5 M, which is 500 times higher than the concentration of the spiked phosphate. Thus, it can be concluded electrolytes in seawater do not interfere with the adsorption of phosphate by Zr(FV) loaded CRP200 as in the case of arsenate uptake by Zr(IV) loaded phosphoric acid resin RGP.14... 

Speciation calculations can be performed for the weak acids and bases in a feshion similar to that presented earlier for Fe(III). The results of these calculations as a function of pH are shown in Figure 5.19. At the pH of seawater, the dominant species are carbonate, bicarbonate, ammonium, hydrogen phosphate, dihydrogen phosphate, and boric and silicic acid. In waters with low O2 concentrations, significant concentrations of HS can be present. 

Sampling sites are also referred to as station locations. For water column work, depth profiles are constructed from seawater samples collected at representative depths. Temperature and salinity are measured in situ with sensors. Remote-closing sampling bottles deployed from a hydrowire are used to collect water for later chemical analysis, either on the ship or in a land-based laboratory. The standard chemical measurements made on the water samples include nutrients (nitrate, phosphate, and silicate), dissolved O2, and total dissolved inorganic carbon (TDIC) concentrations. 

Changes in phosphate, nitrate, ammonia, and silicate concentrations associated with the biogenic production and destruction of POM can alter seawater alkalinities. These effects are usually so small in scale that they can be ignored. Since the largest biotic impact on alkalinity in oxic seawater is exerted by the formation and dissolution of... 

The concentration of uranium contained in phosphate rocks (50 200 ppm) is higher than that in seawater (see section 12.3.5). Even though economic recovery of uranium from phosphate rock is difficult, several phosphoric acid plants include operation of uranium recovery facilities. 

Note that the observed concentrations of La and Th in seawater are in fact near the values expected from the solubility of phosphates (La and Th are effectively fixed as phosphates in almyrolithic exchanges between biogenic sediments and seawater), but the concentrations of the remaining elements are far lower than the values dictated by the solubility products. 

Laboratory assessment of the composition of the blood plasma is often carried out in clinical chemistry. Among the electrolytes, there is a relatively high concentration of Na"", Ca and Cl ions in the blood in comparison with the cytoplasm. By contrast, the concentrations of IC, Mg "", and phosphate ions are higher in the cells. Proteins also have a higher intracellular concentration. The electrolyte composition of blood plasma is similar to that of seawater, due to the evolution of early forms of life in the sea. The solution known as physiological saline" (NaCl at a concentration of 0.15 mol L ) is almost isotonic with blood plasma. 

Sodium is the sixth most abundant element on earth. It comprises about 2.6% weight of the earth s crust. Its salt, sodium chloride, is the major component of seawater. The concentration of sodium in seawater is 1.08%. As a very reactive element, sodium is never found in free elemental form. It occurs in nature in many minerals such as cryolite, amphibole, zeolite, sodalite, and soda niter. Sodium chloride (NaCl) is the most common salt of sodium. Some other important salts are caustic soda (NaOH), soda ash (Na2C03), baking soda (NaHCOs), Chile saltpeter (NaNOs), borax (Na2B407 IOH2O), sodium thiosulfate (Na2S203), sodium sulfate (Na2S04), and sodium phosphates. 

As mentioned in Section II, arsenate is present in seawater at a fairly uniform concentration (about 0.5-2 ng As/liter), and in nutrient-deficient waters its concentrations may exceed that of the essential phosphate (146). In oxygenated seawater, the species exist predominantly as H2PO4 and H2As04, and algae may absorb arsenate because it is similar to the phosphate anion (147). In terrestrial plants and other organisms, arsenic is taken up by the phosphate transport mechanism... 

Primary production in the ocean is controlled by major nutrients, such as nitrate and phosphate, but also by certain trace metals. Dissolved iron was hypothesized (over 50 years ago) to be a key nutrient limiting primary production rates in the sea. However, credible data for the concentration of dissolved iron in seawater have only become available in the last 8 years. Iron is present in surface seawater at concentrations less than 0.5 nanomole per kilogram. These low concentrations of dissolved iron suggest that it is, in fact, a nutrient that can limit primary production in the ocean (Martin et al., 1989). The role of iron in limiting productivity of the ocean can be resolved only when measurements of dissolved iron at concentrations below 1 nanomole per kilogram become routine. There is evidence that other trace metals could also control phytoplankton growth. 

The thermodynamically favoured oxidation state of tin (Sb) is +V However, in contrast to the tetrahedral coordination of phosphate and arsenate, Sbv is present in octahedral coordination as Sb(OH) 5 over a wide range of pH. Sbm has been reported in seawater at concentrations in the order of less than or equal to 10% of Sbv. The dominant form of Sbm in seawater should be Sb(OH)3. While methylated Sb is observed in seawater, in contrast to As, monomethylated forms are more abundant than dimethyl forms. Monomethyl Sb should be strongly hydrolysed in solution, probably in the form of CH3Sb020H. ... 

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