Study area and sampling
The study area covers the Weihe River, Hanjiang River,
and
their tributaries in the Qinling
Mountains in Southern Shaanxi province, China (Fig. 1). The Weihe and
Hanjiang Rivers run on the north and south sides of the Qinling
Mountains, respectively. Weihe River passes through Baoji, Xianyang, and
Xi’an, which are densely populated cities. Hanjiang River passes through
the cities of Hanzhong and Ankang. The rivers have numerous tributaries
at high elevations, which are characterized by low anthropogenic
disturbance in the Qinling Mountains.
In October 2017 (autumn) and April 2018 (spring), water and sediment
samples were collected from 52 sites in 12 rivers (Fig. 1, Table S1).
The sampling sites span the north mainstem (Weihe River), south mainstem
(Hanjiang River), and 10
tributaries
(Luofu
River, Bahe River, Shidi River, Shitou River, Heihe River, Jinqian
River, Jinshui River, Xuhe River, Xushui River, and Yuehe River) in
Qinling Mountains. At each sampling site, water samples were collected
from 0.5-m depths with aseptic polyethylene bottles. The samples for
chemical analysis (2 L each) were preserved at 4°C before being
transported to the laboratory. The samples for DNA-based analysis (4 L
each) were filtered through 0.22-µm mixed cellulose ester membranes
(Millipore, Bedford, MA, USA) within 24 h. The membranes were stored at
–80°C until DNA extraction. Each sediment sample was collected for
microbial analysis.