Spatial and temporal analysis of water quality from 1991 to 2011 in Miyun Reservoir

Abstract

Cluster analysis, discriminant analysis-DA, and principal component analysis/factor analysis were used to analyze temporal–spatial variations and sources of water quality from 1991 to 2011 in the Miyun Reservoir. Water quality analysis was conducted in three interannual (IA) groups: IA I (1991–1993, 1995), IA II (1994, 1996–2000, 2002–2006), and IA III (2001, 2007–2011); two seasonal clusters: non-flood season (NF, November–December and January–April) and flood season (FL, May–October); and two spatial clusters (MP-main part of Kuxi and Kudong and NH-Neihu), based on spatial I (I-Kudong, I-Kuxi, and I-Neihu), spatial II (II-Kudong, II-Kuxi, and II-Neihu), spatial III (III-Kudong, III-Kuxi, and III-Neihu), spatial NF (NF-Kudong, NF-Kuxi, and NF-Neihu), and spatial FL (FL-Kudong, FL-Kuxi, and FL-Neihu). Spatial variations between MP and NH were lower than those between seasonal and IA variations. IA DA showed that electrical conductivity (EC), Ca2+, Mg2+, T-Hard, and T-Alk were due to carbonate dissolution accelerated by SO42− both from fertilizer use and industrial activities. Effective control measures decreased BOD5 and NO3−-N. Spatial variations at spatial IA and seasonal scales showed that high levels of significant parameters in MP were mostly attributed to non-point pollution from watershed, whereas cage culture and sediment release in NH. The main pollution was comprised of nitrogen, phosphorus, organic, and other ion pollutants (Ca2+, SO42−, Mg2+, T-Alk, EC, and T-Hard). Future studies must focus on water circulation enhancement, timely sediment dredging, and decreasing non-point pollution in FL (water and soil loss, fertilizer use, and cage culture) and anthropogenic discharge in NF.