Indigenous ammonibacteria, nitrosobacteria, nitrifying bacteria and denitrifying bacteria were screened from natural water of Lake Jinshan. The effect of water purification was studied in the demonstration project of Lake Jinshan after immobilization of nitrogen cycling bacteria. The result showed that water quality was improved obviously after running a period of time. NH 4 + -N, NO 2 --N, NO 3 --N or TN concentration was in dynamic state respectively, and the trend of them was negative. NH 4

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... -N concentration had reached national Ⅱclass of water quality index, TN and COD had reached Ⅳand Ⅲ respectively. NO 3 --N was the main form of TN in the water of Lake Jinshan, which might be in relation to the water environment without aquatic plants. The microorganisms in immobilized nitrogen cycling bacteria area could diffuse in the water and root area of aquatic plants, the number of them was higher 1-3 degrees than that of the comparison group. It was significant that techniques of immobilized nitrogen cycling bacteria can remove NH 4 + -N, TN and COD in desertification water.