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This article in SSSAJ

  1. Vol. 35 No. 2, p. 250-255
     
    Received: Aug 24, 1970
    Published: Mar, 1971


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doi:10.2136/sssaj1971.03615995003500020023x

Fractionation of Inorganic Phosphate in Calcareous Lake Sediments1

  1. J. D. H. Williams,
  2. J. K. Syers,
  3. R. F. Harris and
  4. D. E. Armstrong2

Abstract

Abstract

Inorganic orthophosphate (inorganic P) added with NH4F reagent to calcareous Wisconsin lake sediments was recovered in the NH4F (0–32%), citrate-dithionite-bicarbonate (18–23%), and first HCl (38–63%) reagents of an inorganic P fractionation scheme. Calcium fluoride, formed during NH4F extraction of calcareous materials, sorbed inorganic P, presumably resulting in the formation of a CaF2-orthophosphate complex; inorganic P was also sorbed by CaCO3 and CaF2 in an NaOH system. Consequently, the values of NH4F-P and first NaOH-P underestimated the amount of inorganic P released from secondary Al- and Fe-containing sediment components during the NH4F and first NaOH extractions, whereas the values for “reductant-soluble P” (citrate-dithionite-bicarbonate-extractable) overestimated the amount of P occluded within Fe oxides, and the P extracted subsequently by HCl overestimated the amount of acid-extractable Ca-P present. Because of the side reactions with CaCO3, the NH4F reagent was omitted in subsequent fractionation studies. Added inorganic P sorbed from 0.1N NaOH solution by CaCO3 in pure form or in calcareous sediments was essentially quantitatively recovered in a subsequent citrate-bicarbonate extraction. A proposed inorganic P fractionation scheme for calcareous materials, based on successive single extractions with NaOH, citrate-dithionite-bicarbonate, and HCl reagents, removed approximately 90% of the total inorganic P in the sediments. Native inorganic P released in the NaOH extraction originated from Fe- and Al-bound P but not from Ca-bound P, and P released in the subsequent citrate extraction was largely, if not wholly derived from P resorbed during the preceding NaOH extraction. Phosphorus released in the following HCl extraction was derived from Ca-bound P. Previous inorganic P fractionation schemes have underestimated nonoccluded Fe- and Al-bound P and overestimated Cabound P and, frequently, occluded Fe-bound P in calcareous soils and sediments.

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