Exploration and application of hydrochemical characteristics method for quantification of pollution sources in the Danjiangkou Reservoir area

The quantification of point source (PS) pollution and non-point source (NPS) pollution in different regions is needed so that targeted management strategies for water environment managers can be prepared. The aim of this study was to establish a method for quantifying PS and NPS pollution by measuring ion concentrations. The Danjiangkou Reservoir and its main tributaries were selected as the study area. The spatiotemporal variation in the concentration of nutrients and ions was analyzed. The results showed that the main ions did not display any distinct spatiotemporal variations on the reservoir, but spatiotemporal variations were evident in the tributaries: Mg2+, Na+, SO42- and Cl- were lowest in the wet season, K+ was highest in the dry-to-wet transition season, and Si was highest in the wet season. We selected Cl-/TN, SO42-/TN, and Na+/TN as PS pollution tracking indicators and K+/TN, Ca2+/TN, and Si/TN as NPS pollution tracking indicators. The mean contribution rate of NPS pollution calculated using Cl-/TN, Na+/TN, and Si/TN, and by the isotope approach, had a significant linear relationship (p < 0.01). Therefore, Cl-/TN, Na+/TN and Si/TN were used to quantitatively assess the pollution sources. The calculated results indicated the TN load was dominated by the NPS pollution, and the average contribution rates of NPS of TN in the tributaries from the dry season to the wet season were 79%, 83%, and 93%, respectively. The TN load of NPS was highest during the wet season with a maximum value over 400 x 10(-3) t a(-1) km(-2), while the TN load of PS was highest during the dry season with a maximum value of 39.3 t a(-1). This study provides a new approach to the quantitative analysis of pollution sources by using hydrochemical characteristic ion indicators.