Analysis of regime shift in Taihu Lake based on Mann-Kendall method

Basing on the rate of change of trends and tendencies, Mann-Kendall method, total nitrogen (TN), total phosphorus (TP) and chlorophyll a (Chla) were took as the key factors, and regime shift and mutation were analyzed in Taihu Lake among 1981~2008.The results showed that: (1) Significant increases in TN, TP and Chla were 0.05, 0.10 and 0.05 level respectively; (2) There were two TN mutations from 1990 to 1991 and 1994 to 1995.The TP mutation occurred between 1987 and 1988.Chla changes contained three stages: 1981~1989, the first stage had not yet mutated; 1990~1996: the second was mutation transitional stage; 1997~2008: the third was mutated stage; (3) Considering the mutation and the historical change sequence of TN, TP and Chla, the two mutations of regime shift were 1988 and 1997 in Taihu Lake. The lake regime was divided into three stages in Taihu Lake. The first stage was from 1981 to 1987, in which the TP concentration was 0.025 mg/L and it was called macrophytes-algae coexist stage which was closed to clear water steady state. The second stage was algae-macrophytes coexist state from 1988 to 1996, and the TP concentration was 0.086 mg/L. The third stage was algae-dominated turbid water state from 1997 to 2008, and the TP concentration was 0.103 mg/L. The results showed that Mann-Kendall method could be used for lake regime shift analysis. © 2015, Chinese Society for Environmental Sciences. All right reserved.