Internal eutrophication by sediment phosphorus release in a restored wetland

Phosphorus (P) availability tends to be regulated by sediment P sequestration, which in turn is strongly affected by periodic desiccation.  Work in Dutch fens shows that sediment desiccation re-oxidizes iron binding sites, causing net sediment P retention upon reflooding, whereas organic sediments of the Florida Everglades have shown net P release after drying and reflooding.  We monitored water and sediment chemistry before and after flooding at a wetland restoration.  Sediments had an average of 54% organic matter, 1225 ugP/gdw, and 0.74 mg HCl-extractable Fe/gdw.  Immediately after flooding, all surface waters had higher soluble reactive phosphate (SRP) concentrations than before.  Sites that had been inundated prior to flooding increased by 78 and 227%.  Sites that began the year inundated, but had dried prior to flooding increased by 99 and 711%.  Previously dry areas had SRPs of 300 and 747 ugP/L.  Duckweed and filamentous algae reached high abundances, likely in response to P release.  Three months after flooding, three of four previously wet sites continue to have higher SRP. Measurement of sediment P binding fractions before and after flooding is ongoing.  Reflooding historically drained wetlands for restoration is a common practice, but may cause sediment P release and internal eutrophication.