Methodology for priority control sequence of river water pollution mitigation and its application in the Haihe River Basin

Methodology for priority control sequence of river pollution control has been established and then applied in the Haihe Rvier Basin. By assessing oxygen consumption,eutrophication of river water,and ecological risk of heavy metals in the sediment,the priority control sequence of river pollution in the Haihe Rvier Basin was promoted. The results showed that about 36% of the total river length had a severe pollution of oxygen depletion,which mainly distributed in the Heilonggang,Ziya,and Tuhaimajia River System,with the percentage of 100,54,and 68,respectively. While eutrophication occurred 50%,52. 3% and 39. 7% for Ziya River System,Beisan Rvier System( the North Canal,Chaobai River and Jiyun River) and Tuhaimajia River System,respectively. The ecological risk of heavy metals in surface sediment for the Haihe River Basin was low,but was severe for Ziya River System,Luan River System and Zhangwei River System,accounting for 26. 5%,21. 6% and 28. 0% respectively. The total river length that above moderate pollution for oxygen depletion,eutrophication,and ecological risk in the Haihe River Basin was 8203 km,6927 km and 6733 km,respectively,posing that the priority control sequence of the Haihe River Basin was oxygen consumption controlling firstly,then eutrophication mitigation,followed by ecological risk preventing. As for sub-river-systems,oxygen depletion was still the primary pollution for Yongding,Daqing,Heilonggang,Ziya,and Tuhaimajia River System,while the mitigation of river eutrophication should be addressed first for Beisan River System. As for Luan,Haihe( main watercourse) and Zhangwei River System,heavy metal pollution control should be the first to take into account.