Estimating Algal Available Phosphorus in Suspended Sediments by Chemical Extraction

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Abstract
The availability of sediment inorganic phosphorus (Pi) to algae was determined in 28 suspended stream sediments collected from an agricultural watershed in northeastern Indiana by short‐ (2‐d) and longerterm (14‐d) incubations. Unincubated sediment was also analyzed for dissolved molybdate reactive Pi (DMRP) and Pi extracted by: (i) sequential NaOH and HCl, (ii) sequential NH4F, NaOH, and HCl, (iii) nitrilotriacetic acid (NTA), (iv) hydroxy‐Al resin, and (v) total P. Available P (Paa) measured in sediments by 2‐d and 14‐d incubations with algae averaged 21 and 25% of total sediment P, respectively. Extraction of sediments with 0.1 M NaOH, 0.5 M NH4F, sequential 0.5 M NH4F + 0.1 M NaOH, NTA, and hydroxy‐Al resin removed an average of 36, 22, 31, 45, and 17% of the total P, respectively. Of the extractants tested, NaOH‐extractable Pi was significantly correlated with 2‐d and 14‐d Paa (r = 0.89*** and 0.95***, respectively) but NaOH extraction removed amounts of Pi that exceeded sediment Paa by a relatively constant amount. The results suggest that a single extraction with 0.1 M NaOH can be used to estimate both short‐ and longer‐term Paa in suspended stream sediments derived from noncalcareous soils in the Northcentral USA.

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