Abstract: An experimental engineering demonstration project of remedying eutrophicated waters through large scale confined growth of water hyacinth was carried out in Dongfeng Ba and Laogan Yutang, two tracts of relatively enclosed waters in Caohai of Lake Dianchi. In line with the project, growth and variation of nitrogen and phosphorus accumulation capacity of water hyacinth was monitored regularly and dynamic changes in water quality of the two tracts of waters were measured in the year after the water hyacinth was planted. Results show that growth rate of the water hyacinth in both tracts of waters peaked up to 759.3 and 601 g•m^-2•d^-1, in July and dropped almost to zero in December. The plants accumulated nitrogen and phosphorus from the water, reaching 1.95 and 0.17 kg•t^-1, respectively, in Dongfeng Ba and 1.74 and 0.14 kg•t^-1, respectively, in Laogan Yutang. Eutrophication degree of the water body was found to have a direct relationship with growth of the plants. Cultivation of water hyacinth in such a way obviously improved transparency of the water body, lowered the concentration of dissolved oxygen and pH in the water, which had no adverse effect on growth of the fish in the water, but beneficial effect on growth and propagation of water hyacinth. At the beginning of the project, waater hyacinth seedlings were released at a rate of 22.5 t•hm^-2, and their coverage of water surface was less than 10%. After 6 months (July to December) of cultivation, water hyacinth lowered the mean concentration of TN, TP and NH₄⁺-N by 7.79, 0.67 and 0.91mg?L^-1, respectively, in Dongfeng Ba and by 1.03, 0.08 and 0.09 mg?L^-1, respectively. in Laogan Yutang. The concentrations of TN and TP in the two water bodies did not show any rising trend and water quality varied smoothly after water hyacinth was harvested mechanically, indicating that the effect of large scale confined growth of water hyacinth remedying eutrophicated water is very effective.

Key words: water hyacinth, enclosed water body, eutrophication, water remediation, Lake Dianchi