Effect of experimental conditions on phosphorus extracted from estuarine and marine sediments

Abstract

The effect of the ratio of sediment to extracting solution was determined on the amount of P extracted by the Bray-P1 extractant (0.03 M NH₄F in 0.025 M HCl) from 10 estuarine and marine sediments. Phosphorus extracted from the sediments by the Colwell extractant (0.5 M NaHCO₃ at pH 8.5) was also determined. Decreasing the ratio of sediment to Bray-P1 extractant from 1 :7 to 1 : 7000 caused a one-hundredfold increase in extractable P. The amount of Bray-P1 extractable P also decreased significantly (P < 0.001) as extraction pH increased, and extraction pH varied between sediments. Sediment CaCO₃ content alone could not explain the increase in extracting solution pH (i.e. neutralization of the acid in the extracting solution) that occurred during the extraction period, and the surface area of the CaCO₃ may be a factor in determining final extraction pH. Bray-P1 extractable P was not correlated with Colwell extractable P.

Because of the effect of the sediments on Bray extractant pH, it is concluded that this extractant is inappropriate for determining the P status of estuarine and marine sediments. The effect of the ratio of sediment to extracting solution on extractable P has implications for determining the P status of suspended sediments.

Extra keywords: Bray extractable P, Colwell extractable P