Evolution and phosphorus fractionation in saline Spolic Technosols flooded with eutrophic water

Purpose: The aim of this study was to evaluate the behaviour of P in saline Spolic Technosols flooded with eutrophic water, with and without plant rhizosphere, in order to assess the role of these soils as sinks or sources of this nutrient. Materials and methods: Samples were taken from basic (pH ~7. 8), carbonated and acidic (pH ~6. 2), de-carbonated soils of salt marshes polluted by mine wastes. Three treatments were assayed: pots with Sarcocornia fruticosa, pots with Phragmites australis and pots without plants (bare soil). The pots were flooded for 15 weeks with eutrophic water (PO43- ~6. 92 mg L-1) and pH, Eh and water-soluble organic carbon and PO43- concentrations were monitored in the soil solution. A soil P fractionation was applied before and after the flooding period. Results and discussion: The PO43- concentration in the soil solution decreased rapidly in both soils, with and without plant, being diminished by 80-90 % after 3 h of flooding. The Fe/Mn/Al oxides and the Ca/Mg compounds played an important role in soil P retention. In pots with S. fruticosa, the reductive conditions due to flooding induced P release from metal oxides and P retention to Ca/Mg compounds. In turn, P. australis may have favoured the release of P from carbonates, which was transferred to Fe/Mn/Al compounds. Conclusions: The retention of P by the soil was the main mechanism involved in the removal of PO43- from the eutrophic flooding water but to evaluate the capacity of these systems as long-term P sinks, the combined effect of metals, Ca/Mg compounds and specific plant species should be considered. © 2012 Springer-Verlag.