[Untitled]

China has numerous lakes within its territory. According to geographical location, genesis and topography, China can be divided into five lake regions: 1, East China plain lake region; 2,Yungui plateau lake region; 3, Monxin lake region; 4, North-east lake region; and 5, Qin-zan plateau lake region. Geographical location and environmental conditions exert an important effect on the nitrogen distribution in lakes. The lakes with serious pollution and eutrophication have a higher content of nitrogen, about 1.8 to 3.8% of the total nitrogen in water and 0.4–0.9% of the nitrogen in sediment. and the lakes that are closed or semi-closed or located in an arid or semi-arid area also have more nitrogen content (0.91% of nitrogen in water and 0.216% of nitrogen in sediment in Erhai lake). Four sources of nitrogen are contained within the lake sediment: 1, from terrestrial sources by erosion from the basin; 2, from pollution by the industry and waste water of urbanization; 3, by autochthonous plankton and algae and 4, from chemical deposition in a drought zone. The sediments derived from terrestrial plants have a high nitrogen content but also have a high C/N ratio, while nitrogen sources from autochthonous plankton have a high nitrogen content but have a low C/N ratio, as some lakes located near cities are eutrophied or hypertrophied.