Chemistry 121 



procedure outlined by Williams et al. (1971a); however, Barrow sediments 

 are high in iron and the phosphorus from both NH4F and first NaOH 

 fractions was apparently tied up by excess iron before the extractions were 

 completed and then released in the following reductant soluble extraction. 

 The correction equations were therefore expanded to include this 

 additional resorption. 



The Chang and Jackson soil phosphorus fractions are usually 

 interpreted as follows: the NH4F-P fraction is considered to be composed 

 of Al phosphates such as variscite; the first NaOH-P fraction is composed 

 of Fe phosphates such as strengite, or of loosely sorbed phosphorus on 

 hydrated iron oxides; reductant soluble-? and the second NaOH-P 

 fraction is made up of phosphate occluded within matrices of more highly 

 crystalline iron minerals; and acid extractable-P is made up of calcium 

 phosphates such as apatite. However, Fife (1959) and Williams et al. 

 (1971b) have suggested that some phosphorus sorbed on hydrated iron 

 oxides appears in the NH4F extraction, and Syers et al. (1973) have 

 speculated that the distribution of phosphorus among NH4F, NaOH, and 

 reductant soluble fractions in some cases may be a reflection of the 

 phosphate-binding strength of a single retaining complex against the 

 individual extractions. 



Total inorganic phosphorus in the sediment was calculated from the 

 sum of the above Chang and Jackson inorganic phosphorus fractions. 

 Organic phosphorus was calculated as the difference between this summed 

 total and the total derived from the perchloric-nitric acid digest. 



Within one pond basin, interstitial DRP, DTP, and DUP (Table 4-17) 

 do not appear to differ greatly. Neither presence nor absence of active 

 roots nor oxidized or reduced sediments could be correlated significantly 

 with phosphorus concentrations. However, between ponds the limited data 

 suggest that there was a real difference in interstitial DRP; Pond J 

 concentrations were significantly higher than the single values measured 

 for Ponds A and C. Sediment phosphorus, iron, and phosphate sorption 

 isotherm data discussed later support this observation. Interstitial DRP 

 concentrations are 3- to 5-fold higher than DRP in the Pond J water 

 column; however, the situation is reversed in Ponds C and A where water 

 column concentrations are almost twice interstitial concentrations. The 

 DRP concentrations (Table 4-17) also vary between ponds and the DUP 

 concentrations are 2- to 10-fold higher than those in the water column 

 above. 



Results of the chemical fractionation of the sediments indicate that 

 retention of the inorganic P is by sorption of phosphate on hydrous iron 

 oxide rather than by formation of distinct iron, aluminum (clay), or 

 calcium phases. Evidence for this comes from experiments where ^"P04 

 was added to Barrow sediment samples prior to fractionation or anion- 

 exchange resin equilibration. After correction for resorption in 

 fractionation experiments, 98.5% of the added '"^P was found in the NH4F 

 and first-NaOH pools. The specific activities of these two pools were 



