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

The application of Fe(III), in combination with sediment oxidation by NO(3)(-), is an accepted procedure to manage stratified eutrophic lakes by controlling the phosphorus release from sediments into overlying water. Depox(R), a newly developed compound, consisting of Fe(III) and NO(3)(-), has a storage effect for NO(3)(-). NO(3)(-) is released slowly, hence the disadvantageous high solubility of NO(3)(-) in water can be retarded. The compound was added to water as a suspension which quickly flocculated and precipitated. Within 3 weeks, NO(3)(-) was desorbed from the Depox(R) compound in deionized water. After application in lakes, the NO(3)(-) 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. SO(4)(2-) consumption was significantly lower after Depox(R) addition, and CH(4) production was completely suppressed by Depox(R) treatment in the laboratory, whereas in the enclosures SO(4)(2-) and also CH(4) concentrations at the sediment water interface did not change significantly between treated enclosures and controls.