The Phosphorus and Arsenic Compounds of Sea-Water

Abstract

THE first estimations of phosphate in sea-water, in which sufficiently accurate analytical methods .were adopted, were carried out more or less simultaneously by Matthews (1916Matthews ( , 1917 and by Raben (1916-20) working independently. Matthews used the colorimetric method of Pouget and Ohouchak (1909, 1911), and precipitated the phosphate from 500 C.c. of sea-water by means of ferric chloride. Pouget and Ohouchak checked their method using the gravimetric method of Posternak, weighing the barium phosphomolybdate obtained. Values similar to those obtained by Matthews were obtained in the Government Ohemist's Laboratory, London, upon samples sent from Plymouth, and the seasonal variation in the phosphate content of sea-water as found by one of us (1923) is in close agreement with the analyses recorded by Matthewsalthough an entirely different method was used, that of Deniges, which is colorimetric.Raben analysed sea-water from many sources and from various depths, but his results and those of his co-workers are uniformly much higher than those of Matthews andAtkins (1925, 1926) for surface water; moreover, these results as plotted by Brandt (1920) never indicate that lack of phosphate may set a limit to the algal plankton, for the minimum value found was close to 50 mg. of phosphate, as P 205per m.3, whereas Matthews and Atkins found the surface water to be almost entirely devoid of phosphate in summer. As has previously been pointed out by one of us (1926) a serious discrepancy exists, though Raben tested his analytical methods upon known minute amounts of phosphate in the presence of the salts of sea-water, and his results leave nothing to be desired so far as their accuracy is concerned and within the limits of the conditions of his test.Matthews, however, found that with the ammonium phosphomolybdate precipitate a little molybdic acid was liable to be thrown down, and he considered the colorimetric method to be the preferable. He also found

Dynamics of Dissolved Organic Phosphorus

“…Even worse, Atkins considered the observed increase in phosphate following permanganate oxidation to be an analytical artifact due to the presence of arsenite in seawater and concluded "much of what was formerly considered to be P in organic combination, in seawater, is in reality arsenic" (Atkins and Wilson, 1927). This inappropriate conclusion from one of the intellectual giants of those times was sufficient to preclude further investigations of DOP at Plymouth or elsewhere, for at least a decade, or more.…”

The Rate of Liberation of Phosphate in Sea Water by the Breakdown of Plankton Organisms

“…It was olear that about 40 mg. P per cubic metre was being rapidly set free from dissolved organic compounds present in the sea water. The results of Matthews (1917), Ibanez (unpublished), Kalle (1933) and Kreps (1934) show that sea water may contain 30-50 mg. of organic phosphorus per cubic metre which, however, may include some arsenic (Atkins andWilson, 1927, andRakestraw andLutz, 1933).…”

Seasonal Variations in the Phosphate and Silicate Content of Sea Water during 1926 and 1927 in Relation to the Phytoplankton Crop

“…As the season advanced the deeper water became at first very much poorer in phosphate and later on rather richer again, according as this salt was used up by the phytoplankton and then regenerated by the decay of animal and plant cells and by the excretion of animals. It was further shown by Atkins and Wilson (1927) that Brandt's curve did not indicate complete exhaustion of phosphate because the method of analysis employed included arsenic, originally present as arsenite, but oxidised to arsenate and precipitated with the phosphate. Reasons were adduced for the belief that the amount of arsenic present in the sea as arsenate is very minute and is all used up in summer by the algffi.…”