密云库区1991～2011年水质变化趋势研究

运用多元统计方法分析密云库区1991~2011年17个指标3个监测点的水质时间变异特征.应用聚类分析划分年际尺度上的年际Ⅰ(1991~1993,1995年),年际Ⅱ(1994,1996~2000,2002~2006年),年际Ⅲ(2001,2007~2011年)和季节尺度上的非汛期(11~12月、1~4月),汛期(5-10月).基于此,运用判别分析阐释影响年际及季节水质变异的环境因素,最后运用因子分析识别不同年际段的污染来源和组成.密云水库21年间TP均值(0.03mg/L)略高于地表水Ⅱ类标准,TN均值(0.98mg/L)超过国家Ⅱ类标准的0.96倍,NO3--N是TN均值超标的主要原因,氮磷污染问题仍需要重点监测和治理;库区植物生长状况和密度不均等及人为排放的不固定性使得TP变异系数较大;NO3--N的较大变异系数体现在年际及季节变异性,非点源污染的控制(水土保持、化肥使用量减少、生活污水减少)和网箱养鱼的取消改善了库区21年水质,NO3--N浓度降低,其季节变异发生在特定季节;另外,年际尺度上,气候变化引起了库区T增加;酸性点源减少使p H升高;工业活动、化肥使用等人为影响的SO42-显著上升促进了碳酸盐岩溶解,使EC、Ca2+、Mg2+、SO42-、T-Hard、T-Alk浓度增加;内源污染减少致使BOD5浓度下降;季节尺度上,季节性气温变动促使非汛期T低于汛期;非汛期碳酸盐岩溶解使Mg2+浓度高于汛期.对比不同年际段的水体污染来源,点源-非点源复合污染转化为以非点源污染为主,21年间非汛期地下水补给过程中碳酸盐岩的溶解作用一直影响水体化学特性,汛期降水径流携带的污染物直接影响水质状况,氮素污染组成简化,以NO3--N为主.控制流域水土流失、畜禽养殖、化肥使用等非点源污染,增强水利流通性,及时清理底泥及沉积物,能够有效减少库区氮磷,有机物及离子污染.

The research of water quality trend in the Miyun Reservoir from 1991 to 2011

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.