A five-year investigation of water quality and heavy metal mass flux of an industrially affected river

This study investigated the water quality parameters (dissolved oxygen, electrical conductivity, salinity, pH, and temperature) and the mass flux of eight heavy metals (As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn) in five years (2015-2019) of the Houjing River. The river flows through a heavily-industrialized zone in Kaohsiung City in southern Taiwan. The surface water was sampled 4 times per year from five sampling locations: upstream sites (H1 and H2), industrial wastewater discharge point sites (H3 and H4), and downstream (H5). Our findings show that the water quality parameters improved in the study period, especially dissolved oxygen. However, some parameters, such as electrical conductivity (mean = 1152.50 ± 414.21 μS cm -1 ), were still higher than the Taiwan water quality irrigation standards. The heavy metal pollution was investigated in the aspect of mass fluxes and sources contribution. The spatial variation of the total heavy metal mass flux increased gradually from upstream to downstream, with H5 having the highest total mass flux of 74.1 kg d -1 . H2, located near an industrial zone, had a total mass flux of 33.7 kg d -1 and contributed to the most Ni, Cr, Pb, Zn, and Hg fluxes. This study indicates that the water quality improvements observed are still not enough to meet the regulations. Stricter enforcement is required as well as further investigation to identify any illegal pollution sources.