Phosphorus uptake by suspended sediments from a heavy eutrophic and standing water system in Suzhou, China

Phosphorus (P) uptake by suspended sediments, from a heavy eutrophic canal system with high P concentration, was conducted in the lab. Addition of KH2PO4 into the parallel operated experimental units were made similar to the external P input into the canal and carried out periodically. Results of P uptake after 39 days show that added P with the amount of 19.97 mg and 13.61 mg disappeared from the overlying water to 200 g wet sediments under intermittent disturbance and static conditions, respectively. Sequential fractionation indicated that P adsorption by Ox-Fe and Ox-Al might be the dominant P removal mechanism in the system. After P uptake under intermittent disturbance conditions, P adsorption experiment shows that the sediment was saturated with P very slowly (17.49%), compared with the sediment under static conditions (31.60%). Moreover, this sediment exhibited lower values for the constants K and S0. It was attributed to the redistribution of different P forms in the sediment. Therefore, the sediment was expected to present a lower P release potential than that under static conditions. After 6 weeks of anoxic incubation, the percentages of the P cumulative release from both sediments to the incorporated P confirmed this. It was suggested that sediment disturbance enhanced P retention in the sediment.