In recent years, the Harbin City Reach of the Songhua River system has been
heavily polluted by both point and non-point pollution sources due to rising population,
which has resulted in ecological destruction impacts. Most river segments in
the study area cannot meet targeted water quality goals set by the Environmental
Protection Bureau (EPB) of Heilongjiang Province. Indeed, the Songhua river system
was one of the key river basins identified as needing control of heavy pollution by
the Chinese major special project for water pollution control technology formulated
in 2012. In this river system, accurate load reduction is highly important for protecting
the regional water resource system. Within the study area, gutter and
polluted branches are important direct pollution sources for downriver water
quality besides conventional point and non-point sources. Hejia gutter (M1) and
Songbei sewage treatment plant (P1) are the main pollution sources from Zhushun
Village to Dongjiang Bridge (segment 1). Hejia gutter is the biggest sewage gutter in
Harbin City and receives most non-point pollution sources of this district. There are
three main pollution sources fromDongjiang Bridge to Dadingzi Mountain (segment
2), including the Taiping sewage treatment plant (P2), the Ashi river (M3), and the
Hulan river (M4). The Ashi river and the Hulan river are two polluted branches of the
Songhua River system that receive all point pollution sources and most non-point
pollution sources of this district. So in the above two segments, the defined loadings
(I) include point sources and most non-point sources of the study area, but
some non-point sources were ignored in the present study due to difficulty in
calculating the loadings.