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| The research of water quality trend in the Miyun Reservoir from 1991 to 2011 |
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Abstract Multivariate statistical methods were used to analyze the temporal variations of water quality from 1991 to 2011 in the Miyun Reservoir. The dataset consisted of 17 variables monitored monthly at three sites. Clustering analysis showed that the water quality could be divided into three groups at interannual scale: IA Ⅰ(1991~1993, 1995), IAⅡ(1994,1996~2000,2002~2006), IAⅢ(2001, 2007~2011), and two groups at seasonal scale: non-flood season (November-December, January-April), flood season (May-October). Discriminant analysis (DA) was used to identify the primary parameters that resulted in the variation of water quality. Principal component analysis/factor analysis (PCA/FA) was used to extract the main sources/factors responsible for the pollution in IAⅠ, IAⅡ, IAⅢ. The results demonstrated that TN and TP exceeded national Ⅱ separately 0.96 times and 0.2 times. The high coefficient of variation for TP was attributed to the instability of wetland plants and human activities, and the great annual and seasonal variability resulted in the high coefficient of variation for NO3--N, the effective control of endogenous pollution such as conservation of water and soil, decreasing domestic wastewater and fertilize use and the countermand of cage culture improved water qualityduring 21 years, indicating the decreasing concentration of NO3--N; The seasonal variation of NO3--N took place in specific season. At interannual scale, water temperature increased with increasing air temperature; Dissolution of carbonate rock was accelerated due to increasing SO42- concentration affected by fertilizer use and industrial activities, which increased the concentrations of EC, Ca2+, Mg2+, SO42-, T-Hard, T-Alk; The concentrations of BOD5 decreased due to the internal pollution. At seasonal scale, the concentration of Mg2+ was higher in non-flood season than in flood season because of the dissolution of carbonate rock. At interannual scale, the pollution sources for IAⅠ, IAⅡ, IAⅢ changed from a combined point and non-point pollution to primarily non-point pollution. The water quality was affected by the dissolution of carbonate rock in non-flood season and was impacted by the rainfall runoff in flood season. In the Miyun Reservoir, nitrogen pollution was predominantly derived from NO3--N. Enhancing the water circulation, decreasing non-point pollution (water and soil loss, fertilizer use and cage culture), and timely sediment dredging, can effectively decrease the concentrations of nitrogen, phosphorus, and organic and ionic pollutants.
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Received: 18 October 2014
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