[Seasonal occurrence characteristics of different forms of nitrogen in the sediments of Chaohu Lake].

Seasonal characteristics of the free nitrogen (FN), the exchangeable nitrogen (EN), the acid hydrolysable nitrogen (HN) and the residual nitrogen (RN) in the surface sediment of Chaohu Lake were analyzed by sequential extraction method. The correlations among the nitrogen fractions with the total nitrogen (TN) and the mineralizable nitrogen (MN) were discussed considering the seasonal variations of the TN and MN. The results show that the concentrations of FN, EN and TN are lower in summer and higher in autumn and winter, NH4(+)-N is the main fraction of FN and EN. TN concentrations are much higher in West Chaohu Lake with the maximum concentration of 2280.47 mg/kg in the west lake center than in the East Chaohu Lake. The seasonal order of mineralizable nitrogen (MN) content is winter> spring > autumn > summer. The bio-available nitrogen fraction varies with different seasons, which is the amino acid nitrogen (AAN) in spring, EN in summer and autumn, FN in winter. The study about seasonal occurrence characteristics of nitrogen fractions in sediment provided foundational data for lake ecological security evaluation and nitrogen release evaluation.