Fig. 1: Topographic map of the mountain ranges around the Yellow River and Wei River systems.

a Topographic map showing the contour of the Yellow River and Wei River. b Topographic map showing the locations of the reservoirs, dams and sampling sites. c Field picture showing the Yellow River in Zhongwei. d Field picture showing the Wei River in Tianshui. U: upper Yellow River. M: middle Yellow River. L: lower Yellow River.