Fractionation of sediment phosphorus revisited: II. Changes in phosphorus fractions during sampling and storing in the presence or absence of oxygen

Abstract

The purpose of this study was to evaluate the sensitivity of a phosphorus (P) fractionation procedure on sampling practices and other sources of error in the characterization of the chemical status of P in noncalcareous sediments rich in humic compounds and iron (Fe). We investigated the effects of nitrogen gas (N2) shielding on the stability of various P fractions during sampling and various periods of sample storage on both oxic and reduced sediments. In addition, we studied storage‐induced changes in preserved or unpreserved extracts from different fractionation steps. Sampling and storage conditions were critical factors in P fractionation studies. During sampling, sample storage, and extraction, the N2 atmosphere (atm) protected samples from oxidation and consequent changes in P forms, especially in the redox‐sensitive form. Long‐term storage without N2‐shielding caused the most drastic changes in oxic sediment, whereas the reduced sediment protected with N2 experienced only minor changes. Extracts preserved with acid can be stored for at least 1 week without significant changes. The extraction results of P and other elements obtained with both oxic and reduced sediment samples supported the biogeochemical basis of the fractionation procedure, demonstrated by the behavior of Fe and Fe‐bound P in sediment originating from and treated in different oxygen (O2) conditions. Despite a few shortcomings, with careful laboratory work and avoidance of sample oxidation during sampling and storage, the fractionation procedure and working practices used seem to provide reliable results and valuable information on the chemical character of sediment P.