Algal use of sedimentary phosphorus from an Amazon floodplain lake: Implications for total phosphorus analysis in turbid waters

Chemical forms of P and their availabilities to Selenastrum capricornutum were measured in sediments collected from Lago Calado, an Amazon floodplain lake. Postbioassay analysis confirmed that Selenastrum used ∼60– 70% of the P in the NaOH‐extracted fraction during a 9‐d incubation. No evidence for algal use of Ca‐bound P or organic P was found. Methodological comparisons revealed that persulfate digestion may not adequately recover algal‐available particulate P in waters high in inorganic turbidity. An average of 26% of the agal‐available P in Amazon River water was in particulate form.