Evidence for Bacterially Mediated P Release from Anoxic Sediments

In the classic Einsele-Mortimer model of anaerobic P release it was assumed that under anoxic conditions solid ferric (Fe 3§ minerals were reduced to ferrous ions (Fe 2+) with a co-release of P adsorbed to the ferric mineral. The released P could either be taken up by the biota or, could readsorb onto ferric oxyhydroxides particles (which were formed by the abiotic oxidation of ferrous iron), however, it is becoming evident that the anaerobic release of P from sediments is not simply an abiotic process but, can be the result (either directly or indirectly) of bacterial processes. In particular, three anaerobic bacterial processes sulphate reduction, dissimilatory iron reduction and poly-phosphate hydrolysis can potentially lead to the release of P under anaerobic conditions: viz:-