Water Quality Characteristics and Integrated Assessment Based on Multistep Correlation Analysis in the Danjiangkou Reservoir, China

The Danjiangkou Reservoir is the water source for China’s South-to-North Water Transfer Project (Middle Route) which diverts water to the North China Plain for irrigation, industrial and domestic usages. Hence, water quality in the Reservoir is critical for public health and economic development in the reception area. In this study, spatial and temporal patterns of 13 water quality variables including nutrients, heavy metals, and trace elements from China’s Environmental Quality Standards for Surface Water (GB3838-2002) were investigated in 8 sites with 2 replicates in four seasons during 2007-2010. Afterwards, multistep correlation analysis based on grey theory was applied to assess water quality. The results indicated that there were dramatic increases in the concentrations of total nitrogen (TN), ammonium nitrogen (NH4+-N) and a few heavy metals such as chromium (Cr) and lead (Pb) during the sampling period. The major pollutants in the Reservoir were TN, Pb, and arsenic (As) with respective average concentrations of 4.6 mg/L, 210.4 μg/L, and 14.1 μg/L, while Pb and As also reached the maximum contaminant level of USEPA (15 μg/L and 10 μg/L for Pb and As, respectively). The Pb concentration increased 20 times compared to that (10.6 μg/L) in 2004-2006. Water quality in a sampling site varied and could be catego- rized from grade I to V based on the individual variable using the national standard (GB3838-2002). Integrated assessment using all sampled variables simultaneously revealed an overall water quality deterioration from grade I and II in 2007 to grade II and III in 2010 in the Reservoir. The application of multistep correlation analysis based on grey theory demonstrated its feasibility and effectiveness, and could provide a simplified indicator for water quality assessment.