Abstract: Lake Wuliangsuhai is one of the representative inland freshwater lakes in grassland areas of China,and its shrinking and eutrophication is becoming more serious.The study on the ecological and environmental effects of the shrinking and eutrophication revealed that the total nitrogen (TN) content in the surface sediment of the lake had an obvious differentiation both in longitudinal and in latitudinal direction,and had a significant correlation with organic matter content.The mean C/N ratio of the sediment ranged from 12.07 to 19.95,which meant that the organic matter was mainly come from the hydrophytes of the lake,and the eutrophication of the lake was mostly caused by its internal load.Both TN and organic matter had a clear grainsize effect in different fractions of grain sizes of surface sediment,and their contents in IV (<63 μm) were as 3.1～7.6 and 2.5～8.0 times as those in I (>250 μm),respectively.

Key words: paddy soil, dissimilatory Fe(III)-reducing bacteria, enrichment culture, terminal-restriction fragment length polymorphism , (T-RFLP) technology