Water pollution characteristics and pollution sources of Bei Canal river system in Beijing

Based on the monthly monitoring data of 23 water quality indexes of the main streams and tributaries of Bei Canal river system in 2011, a comprehensive water quality evaluation was made using water quality category method and average comprehensive pollution index method. Principal components of water quality indexes and pollution sources were determined with principal component analysis (PCA) and system clustering analysis method (SCAM). The results showed that the surface water in Bei Canal river system was heavily polluted due to high pollution discharge. Except that the water quality of urban central rivers was in class III ~ IV, the water quality in other areas such as urban drainage rivers and outsuburb rivers was below class V. According to the PCA results, the first principal component of water quality involved COD, CODMn、BOD5, NH3-N, TP, TN. The second principal component was Hg. The third principal component included petroleum contaminants. The rivers were classified into 4 categories based on their water pollution characteristics. Category 1 was composed of rivers that had clean water sources and were located mainly in urban central areas; the river water was polluted primarily by non-point source pollution. Category 2 was comprised of rivers with renewable water sources, chiefly located in the upstream of urban sewerage and drainages; the urban sewage treatment plant drainage was identified as the primary pollution source. Category 3 consisted of rivers with blended water sources including renewable and sewage water, which were located in the downstream of urban sewerage and drainages as well as in the outskirt areas; pollution level of these rivers were high due to domestic and agricultural pollution sources. Category 4 was rivers with polluted water as source, located in the outsuburb; the major pollution source of these rivers included sewage discharged from agricultural practices.