B. A. Helena, M. Vega, E. Barrado, R. Pardo, and L. Fernandez, “A case of hydrochemical characterization of an alluvial aquifer influenced by human activities,” Water, Air, and Soil Pollution, Vol. 112, No. 3, pp. 365-387, 1999.
 M. Vega, R. Pardo, E. Barrado, and L. Debán, “Assessment of seasonal and polluting effects on the quality of river water by exploratory data analysis,” Water Research, Vol. 32, No. 12, pp. 3581-3592, 1998.
 V. Simeonov, J. A. Stratis, C. Samara, G. Zachariadis, D. Voutsa, A. Anthemidis, M. Sofoniou, and T. Kouimtzis, “Assessment of the surface water quality in Northern Greece,” Water Research, Vol. 37, No. 17, pp. 4119-4124, 2003.
 K. P. Singh, A. Malik, and S. Sinha, “Water quality assessment and apportionment of pollution sources of Gomti river (India) using multivariate statistical techniques: A case study,” Analytica Chimica Acta, Vol. 538, No. 1-2, pp. 355-374, 2005.
 Ministry of Environmental Protection of China, “Planning of comprehensive water pollution control the Songhua River Basin,” 2006.
 D. A. Wunderlin, M. P. Diaz, M. V. Ame, S. F. Pesce, A. C. Hued, and M. A. Bistoni, “Pattern recognition techniques for the evaluation of spatial and temporal variations in water quality. A case study: Suquia river basin (Cordoba, Argentina),” Water Research, Vol. 35, No. 12, pp. 2881-2894, 2001.
 S. A. A. Wahab, C. S. Bakheit, and S. M. A. Alawi, “Principal component and multiple regression analysis in modelling of ground-level ozone and factors affecting its concentrations,” Environmental Modelling & Software, Vol. 20, No. 10, pp. 1263-1271, 2005.
 K. P. Singh, A. Malik, S. Sinha, D. Mohan, and S. Sinha, “Chemometric analysis of groundwater quality data of alluvial aquifer of Gangetic plain, North India,” Analytica Chimica Acta, Vol. 550, No. 1, pp. 82-91, 2005.
 C. W. Liu, K. H. Lin, and Y. M. Kuo, “Application of factor analysis in the assessment of groundwater quality in a Blackfoot disease area in Taiwan,” Science of the Total Environment, Vol. 313, No. 1, pp. 77-89, 2003.
 P. George, D. Gerasimoula, and L. Nicolaos, “A long-term study of temporal hydrochemical data in a shallow lake using multivariate statistical techniques,” Ecological Modelling, Vol. 193 No. 3, pp. 759-776, 2006.
 D. H. Wang, Y. Wang, and Z. Lin, “The control and damage of organic pollutant in Songhua River to the ecological environment,” Environmental Science and Management, Vol. 32, No. 6, pp. 67-69, 2007.
 S. H. Guo, X. L. Wang, Y. Li, J. J. Chen, and J. C. Yang, “Investigation on Fe, Mn, Zn, Cu, Pb and Cd fractions in the natural surface coating samples and surficial sediments in the Songhua River, China”. Journal of Environmental Sciences, Vol. 18, No. 6, pp. 1193-1198, 2006.
 X. Q. Li, J. W. Zhang, Q. J. Wang, H. F. Zhang, and N. Qiu, “Analysis of mechanism of water purification by nature and strategy of protection of water environment in Songhua River through Harbin city,” Urban Environment & Urban Ecology, Vol. 16, No. 6, pp. 233-235, 2003.
 J. R. Liu, H. W. Dong, X. L. Tang, X. R. Sun, X. H. Han, B. Q. Chen, C. H. Sun, and B. F. Yang, “Genotoxicity of water from the Songhua River, China, in 1994–1995 and 2002–2003: Potential risks for human health,” Environmental Pollution, Vol. 157, No. 2, pp.357-364, 2009.
 S. K. Jiang and H. Liu, “Analysis for the present situation and development trend of the water quality in the downstream of Nenjiang River,” Jilin Water Resources, Vol. 265, No. 9, pp. 1-2, 2004.