Development of an iron oxide-impregnated paper strip technique for the determination of bioavailable phosphorus in runoff

Bioavailable phosphorus (P) requires separate analysis because it is independent of physical and chemical P fractions present in runoff. Iron oxide-impregnated paper strips (P-i-strips) provide a simple technique for determining bioavailable P in aqueous samples. In this study, some controversial strip preparation procedures were examined and subsequently modified, and the efficiency of the technique was compared to the conventional physico chemical fractionation approach. P-i-strips prepared using Whatman 50 filter paper rapidly drawn through iron chloride solution then immersed in ammonium hydroxide solution produced the most accurate and precise results. A strong asymptotic relationship between P uptake and the duration of shaking, coupled with rapid intra-sample transformations between P fractions, indicated that shaking for 8 h was sufficient for complete P uptake from natural water samples and standard solutions (0-250 mu g P l(-1)). A single P-i-strip was used because multiple strips increased analytical error. The contribution to P-i-strips from adhering sediment particles was negligible for samples with low concentrations of solids but turbid samples (>0.75 mg l(-1) suspended solids) were noticeably influenced by P derived from particulate material. Fractionation of agricultural runoff demonstrated a strong relationship between the dissolved inorganic (MRP and P-i-strip fraction, but only 85% of the total dissolved fraction (TDP) was retained by the P-i-strip, suggesting not all soluble P was available for biological uptake. (C) 1998 Elsevier Science Ltd. All rights reserved.