[Study on the stages of major sediments in Dianchi lake]

The statistical technique self-organizing maps (SOM) was applied for stages analysis of Lake Dianchi sediments, southwestern China. The dataset of nine pollutants, including Cd, Cr, Cu, Hg, Pb, Sn, Zn, TP and KN, was observed and collected for 10 monitoring sites from 1991 to 2010. The results show that the 20 years' study could be divided into 4 stages. In stage one (1991 to 1995) , concentrations of sediments are relativity low. In the second stage (1996 to 2001) , concentrations of most sediments are higher than the stage before and show increasing trends. In the following stage (2002 to 2006), majority of the observed sediments exhibit fluctuation characteristics. Nevertheless, different concentration patterns exist among different pollutants, the concentration climaxes of most pollutants have been observed during the year 1996 to 1999 and 2005 to 2007. According to the relevant information gathering from yearly lake pollution load, the national survey of pollution sources etc., the reason for the above stages and concentration patterns of observed sediments are analyzed. The result shows that sediment concentration is sensitive to human activities in the basin, such as pollution emission as well as controlling.