Keywords: 
• sediment

Abstract: Hasuhai Lake is one of the representative shallow lakes in grassland areas of China, and its eutrophication is becoming more serious. The study on the character of spatial distribution and pollution of the nitrogen forms and organic matter revealed that the content of the total nitrogen (TN), the organic nitrogen (OrgN), the ammonium nitrogen and the organic matter in the surface sediment of the lake had an obvious differentiation in longitudinal direction. The distribution characteristics of TN in surface sediments were mainly dominated by the distribution characteristics of OrgN, and TN had a significant correlation with organic matter content. In the sediment cores, the TN content and the organic nitrogen content both had the same trend that their content decreases with the increasing depth. The vertical distribution of ammonium nitrogen in the sediment core was various, but it was also enriched in the surface sediments. The organic nitrogen is the main exiting form of nitrogen in surface sediments and sediment core, and ammonium nitrogen is the main exiting form of inorganic nitrogen. There was very little TN mineralized in the diagenesis. The typical sources of organic matter in surface sediment of Hasuhai Lake may be macrophytes such as reed and terrestrial source. The pollution of nitrogen in the surface sediments of Hasuhai Lake has serious biology toxicity effect on the bottom biology communities and aquatic ecosystem.