NATURAL REMOVAL OF ADDED N-NUTRIENTS, REACTIVE PHOSPHORUS, CRUDE-OIL,AND HEAVY-METALS FROM THE WATER PHASE IN A SIMULATED WATER-SEDIMENT SYSTEM

Water/sediment simulation systems were constructed by using an aquariu m (0.45 x 0.29 x 0.35 m(3)), filled with suitable amounts of water and sediment collected from three selected locations: Lan Hua Shan (LHS), Tai Hu (TH), and Loong Yu Tao (LYT) of the Zhujiang (Pearl River) Est uary of China in November 1992 at low-tide period. The salinities of t he water samples collected from LHS, TH, and LYT were found to be 0.2, 4.6, and 16.2 g L(-1), respectively. Known amounts of ammonium, nitra te, nitrite, reactive phosphorus, crude oil, arsenate (III), cadmium ( II), chromium (III), copper (II), and zinc (II) were added as pollutan ts into each of the water/sediment simulation systems. The rates of th e natural removal of each added pollutant in all water/sediment simula tion systems were studied by monitoring their concentrations at variou s intervals in the investigation period. Except for Cr (III) and react ive phosphorus in the water/sediment systems of the LHS, TH, and LYT s ites, and nitrate in the TH and LYTsites, the concentrations of the ad ded pollutants in the water phase of the studied systems under a flow- condition simulation were reduced to 8% or less of the corresponding a dded amount on or before the 12th day by natural processes. The rate o f self-purification and the estimated assimulative capacity of each ad ded pollutant in all water/sediment simulation systems is discussed.