Distribution of land-use types and dynamics of environmental factors
PCoA biplots show that the land-use types of the Weihe River were markedly different from those of the Hanjiang River and Qinling tributaries, with the first axis explaining 87.88% of the variation in land-use type (Fig. 2a). In Weihe River, agricultural land was the primary land-use type, accounting for 61.22±12.58% of total land area. In addition, the area proportion of urbanized land in Weihe River was significantly higher than those in the other two regions (Fig. 2b). Forest was the main land-use type in the Hanjiang River and Qinling tributaries, accounting for 60.88±5.85% and 64.91±12.48% of total land area, respectively. According to the distributions of different land-use types, the river areas were dominated by agricultural or forest land. Specifically, the Weihe River area mainly comprised agricultural land, grassland, and urbanized land; the Hanjiang River area mainly hosted forest, agricultural, and shrub land; and the Qinling tributary area was dominated by forest and shrub land.