| Xiangjiang River is among the rivers most heavily polluted with heavy metals in China. In this study, we characterized heavy metal pollution and the ecological risk of sediments from the Hengyang section of the Xiangjiang River basin, including the mainstem and four important tributaries (Chongling River, Leishui River, Zhengshui River and Mishui River). The aim was to evaluate the effectiveness of treating heavy metal pollution in the study area and provide data to support continuing pollution control and treatment. The study was based on the monitoring results of nine heavy metal elements (Cd, As, Hg, Pb, Cu, Zn, Mn, V, Cr) in the sediments of 11 sampling transects in the study area from 2015 to 2019. Pollutant characteristics and ecological risk of the nine heavy metals were analyzed using the geoaccumulation index method and potential ecological risk index. Results show that Cd pollution was common and heavy in the mainstream and all four tributaries. As, Hg, Pb, Cu, Zn, Mn pollution has occurred at some sites to varying extents, and V and Cr pollution was absent or light to moderate. The potential ecological risk index shows that As, Cu in Chongling River and Cd, Hg in all the rivers presented high to extremely high ecological risk. The total potential ecological hazard index of the nine heavy metals in the study area was in the order, Chongling River (1316) > Leishui River (718) > Xiangjiang River mainstream (609) > Zhengshui River (515) > Mishui River (441). The ecological hazard of Chongling River, Leishui River and the main stem of Hengyang section was very high, and high in the Zhengshui and Mishui Rivers. To summarize, the geoaccumulation index and potential ecological hazard index both indicate that heavy metal pollution was most serious in Chongling River, followed by Leishui River and the Xiangjiang mainstream, and pollution in Zhengshui River and Mishui River was relatively light. Furthermore, heavy metal pollution in Chongling River, Leishui River, Mishui River and the mainstream of Xiangjiang River was lower in 2017-2019 than in 2015-2016. |
