Potentially mobile phosphorus in Lake Erken sediment

The amount of potentially mobile phosphorus (P) in Lake Erken sediments was determined by P release experiments, and forms of mobile P were identified by P fractionation. Amounts and forms of this P were compared to P released by sediment diagenesis. Calculated on the top 30 cm of a sediment core, the amount of potentially mobile P was 5 g/m2, consisting mainly of organic-P (NaOH-nrP) but also of P associated to iron (BD-P). P release experiments were performed by maintaining steep diffusion gradients in flow-through chambers under oxic or anoxic conditions. Using this method it took no longer than three weeks to release an amount of P from the main P mobile pools (NaOH-nrP, BD-P) corresponding to P naturally lost during sediment diagenesis, a process which normally takes years. Release rates as well as mobile amounts of P in the NaOH-nrP pool varied significantly depending on the redox status. In conclusion, the release method applied made it possible to determine potentially mobile P under specified conditions and to detect ecologically important P fractions in the surface sediments.