《Table 1–Test results for the mutational years of water quality indicators in Tai lake.》

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《Three decades of changes in water environment of a large freshwater Lake and its relationship with socio-economic indicators》

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From 1980 to 2012，there are a significant linear relationships between water quality indicators（TN，TP，Ch1-a，COD，and BOD）and time，for which，all the R2values are greater than 0.5（p<0.01），revealing that the concentrations of water quality indicators were increasing（Fig.1）.Mean annual concentrations of TN increased significantly with fluctuations from 1980 to2004，followed by intermittent small-magnitude decreases from2004 to 2010 and increased again until 2012.Generally，concentrations of TN increased from 0.65 mg/L in 1980 to2.7 mg/L in 2012，more than quadrupling in 32 years.During the study period，four obvious peaks in concentrations of TN were observed in 1988，1992，1997，and 2004，with the greatest concentration（4.8 mg/L）in 2004.Mean annual increases were0.084 mg/L.However，this varied for different time intervals.From 1980 to 1990，the mean annual rate of increase was0.084 mg/L，rising to 0.13 mg/L during 1990–2000 and reaching the greatest value of 0.448 mg/L in 2004.Following that，concentrations of TN decreased at a rate of 0.26 mg/L until2012.Mean concentrations of TN were 1.6 mg/L，2.8 mg/L，and3.6 mg/L，during the 1980s（1980–1990），1990s（1990–2000）and2000s（2000–2012），respectively.The Mann-Kendall trend analysis revealed that concentrations of TN increased continuously throughout the 32 years considered during this study，without any sharp transitions（Table 1）.