Abstract

Understanding the chemical characteristics of sediments and the nutrient diffusion from sediments to the water body is important in the management of surface water quality. Changes in chemical properties and nutrient concentration of a submerged soil were monitored for 6 months using a microcosm with the thickness of 30cm for upland soil and 15cm of water thickness above the soil. The soil color changed from yellowish red to grey and an oxygenated layer was formed on the soil surface after 5 week flooding. The redox potential and the pH of the pore water in the microcosm decreased during the flooding. The nitrate concentration of the surface water was continuously
increased up to 8 mg^l-1 but its phosphate concentration decreased from 2 mg^l-1 to 0.1 mg^l-1 during flooding. However, the concentrations  of NH₄⁺, PO₄^3-, Fe and Mn in the pore water were increased by the flooding during this period. The increased NO₃^- in the surface water was due to the migration of NH₄⁺ formed in the soil column and the oxidation to NO₃^- in the surface water. The increased phosphate concentration in the pore water was due to the reductive dissolution of Fe-oxide and Mn-oxide, which scavenged phosphate from the soil solution. The oxygenated layer played a role blocking the migration of phosphate from the pore water to the water body.

Keywords microcosm, redox potential, nutrient, iron, manganese