Sediment treatment with a nitrate-storing compound to reduce phosphorus release

The application of Fe(III), in combination with sediment oxidation by NO3−, is an accepted procedure to manage stratified eutrophic lakes by controlling the phosphorus release from sediments into overlying water. Depox®, a newly developed compound, consisting of Fe(III) and NO3−, has a storage effect for NO3−. NO3− is released slowly, hence the disadvantageous high solubility of NO3− in water can be retarded. The compound was added to water as a suspension which quickly flocculated and precipitated. Within 3 weeks, NO3− was desorbed from the Depox® compound in deionized water. After application in lakes, the NO3− availability on the sediment surface was prolonged for 2 months. After treatment, P release from the sediment and microbial metabolism were investigated under laboratory conditions as well as in the mesocosm. P release was almost stopped in both cases during the experiment. SO42− consumption was significantly lower after Depox® addition, and CH4 production was completely suppressed by Depox® treatment in the laboratory, whereas in the enclosures SO42− and also CH4 concentrations at the sediment water interface did not change significantly between treated enclosures and controls.