PHOSPHORUS RETENTION AND RELEASE CHARACTERISTICS OF SEWAGE-IMPACTED WETLAND SEDIMENTS

Sediment deposited in traps positioned along a sewage-impacted wetland receiving phosphorus (P)-retaining reactants from natural wetland wat er was fractionated into different particle sizes, and the amount of P retained in these particle sizes was investigated. Subsamples of the sediments collected from different sites along the wetland system were also equilibrated with water at different water:sediment ratios and e quilibration periods to investigate the extent of P released from thes e sediments under aerobic and anaerobic conditions. Results obtained s howed that most of P deposited in sediments is in fine fractions (<16 mu m), particularly in sediments collected from confluence sites where water inflow from the natural wetland provides P-retaining reactants and from sites immediately below these confluence sites (postconfluenc e sites). The extent of P release from sediments depended on the aerob ic anaerobic conditions of the sediments, equilibration period, water: sediment ratio and the position of sites within the wetland. The rate of P released from sediments associated with an increase in equilibrat ion period tended to be higher under aerobic than anaerobic conditions . Water:sediment ratio was found to be a more important factor in cont rolling the release of P from sediments under anaerobic than aerobic c onditions. The amount of P released from the confluence and postconflu ence sites was higher than that from other sites over a range of equil ibration periods and water:sediment ratios under aerobic and anaerobic conditions.