Abstract: Samples of waters and deposits were collected from algae-dominated Meiliang Bay and macrophyte-dominated East Lake Taihu for in-lab determination of DIN(dissolved inorganic nitrogen) transformation potentials within 20 days.Results demonstrate that rapid nitrifications existed in the sediments and waters of the two lake zones,and there was remarkable negative correlation between NH₄⁺-N and NO₃^--N(P<0.05 or P<0.01).The nitrification rate in the algae-dominated zone was a little higher than in the macrophyte-dominated zone in the microcosm under the same condition,and the higher the initial NH₄⁺-N concentration,the higher the nitrification rate.Nitrification rates decreased gradually with time when no extraneous nitrogen was added.Denitrification was also stronger in the Meiliang Bay than in the East Lake.After 20 days in lab,TN declined by 3.7%(on average) in the sediments,by 26.7% in the water from the East Lake,and by 42.2% in the water from the Meiliang Bay,suggesting that sediment was the most important place for denitrification.Transformation potential of DIN within a short period of time reflects not only nitrogen transformation rate,but also effects of water bodies different in eco-type on cycling of nitrogen in the lake.