Application of Single Factor and Multi-Factor Pollution Indices Assessment for Human-Impacted River Basins: Water Quality Classification and Pollution Indicators

Anthropogenic activities are most likely to alter the natural composition of waters. Extensive phosphate mining in Huangbaihe River Basin (HRB), China, has resulted in the reduction of the self-purification capacity of freshwater reservoirs in the basin. Based on a three-year (2014-2016) water quality monitored data and the application of three pollution index assessment (PIA) methods: Single Factor Pollution Index (SFPI), Nemerow’ Pollution Index (NPI), and Water Quality Index (WQI), the main objective of this study was to determine the water quality standards of surface water in the river basin. Research findings indicated that a holistic approach, a combination of a single factor and multi factor pollution indexes (MFPIs) method was able to distinguish pollutant characteristics and used to classify water quality of the river system. Comparison of the results showed that the SFPI classification is more conservative and highly influenced by the worst evaluated index. On the other hand, the MFPIs: the NPI and the WQI methods classified the water quality into a more reasonable grade because they integrate the effects of different impacting factors. The most impaired pollutants affected the water quality classification were total phosphorus (TP) and total nitrogen (TN). Application of the PIA result for the water quality management purpose in the basin showed that there is a direct causal relationship between the TP concentration and water quality of reservoir water; low water quality reservoirs were correlated with high TP. On the other hand, the reservoir water quality did not show any significant dependence on TN. A linear regression equation was proposed to determine WQI of reservoirs’ water using measured TP. The equation may be used to characterize the pollution level of reservoir water for prioritizing water quality management measures in HRB.