Abstract:

 In this study, different nitrogen forms in the seven surface sediments of Nansi Lake were separated by means of sequential extraction, and their contents, distribution characteristics and related factors were analyzed. The transferable nitrogen can be divided into four forms, the ion exchangeable form(IEF-N), weak acid extractable form(WAEF-N), strong alkaline extractable form(SAEF-N) and strong oxidant extractable form(SOEF-N) and their contents, distribution characteristics and influencing factors were analyzed. The results indicated that the content of total nitrogen and different translate nitrogen fractions(except SAEF-N) in the upper Nansi Lake was higher than the lower lake district. The ratio of TTN and TN in the lower lake was higher than the upper Nansi Lake. Nitrogen mainly combined with grained sediments in Nansi Lake. There were no significance correlation of TN and NH₄+-N between sediments and water, which proved that most of the nitrogen came from its main inflow rivers. As a result, the N／P ratio in sediments was only about 1.5～4.5 below the Redfield index, while the N／P ratio in water was 13.7～24.1 higher than Redfield index, which farther illustrated that the nitrogen and phosphorus came from its main inflow rivers. Although the concentration of TN  has greatly decreased in the last decade, phosphorus was the most restricting nutritious element.

Key words: Nansi Lake; surface sediment; nitrogen form; distribution characteristic; N／P