Field sampling
The Chishui River Basin in China is located on the border between the
Yunnan and Guizhou Plateau and the Sichuan Basin. Within its distinct
geographical context, this area has diverse topography, soil types,
various vegetation types, and rich biodiversity. A survey was conducted
in September 2021 covering an altitude range from 179–1433 m. A total
of 52 sampling points were selected based on the geographical
characteristics of the Chishui River Basin and the composition of fish
fauna, with the goals of accessibility and maximal coverage of different
habitats. The sampling points were distributed throughout five main
tributaries along the Erdao, Tongzi, Guling, Datong, and Xishui rivers.
The sampling points were divided across three reaches: 14 points in the
upstream reach (nos. 1–14), 20 in the middle (nos. 15–34), and 18 in
the downstream (nos. 35–52). The sampling point locations are shown in
Fig 1.
To obtain accurate data, GPS was utilized to determine altitude, a
handheld velocity radio (HZBP, Beijing, China) was used to measure flow
velocity, and an infrared rangefinder (Trueyard SP1500H, Nevada, USA)
was used to measure river width. A portable chlorophyll sensor
(YSI6920V2-2, Ohio, USA) was used to record the chlorophyll a
concentration in the water, and a multiparameter water quality analyzer
(YSI6920V2-2, Ohio, USA) was used to measure dissolved oxygen (DO), pH,
electrical conductivity (EC), and water temperature. The Chishui River
Basin survey encompassed a wide range of altitudes and sampling points,
providing valuable data on the diverse topography, soil types,
vegetation types, and biodiversity within the area.
Chishui River human Footprint (FPT) data were obtained from the human
footprint map of the area
(https://datadryad.org/stash/dataset/doi:10.5061/dryad.052q5) (Venter et
al., 2016). Additionally, Chishui River land-cover data from
high-resolution (10 m) land-cover maps were obtained from
http://data.ess.tsinghua.edu.cn/fromglc10_2017v01.html. Based on the
land use types used in a previous fish study (Zhang Q et al., 2022) and
considering the characteristics of this study area, we selected three
land types; farmland, forest, and impervious surface data were acquired
using ArcGIS 10.6. Values were extracted from an area of 1 km radius
around each sampling location, and each value was calculated as the
proportion of the relevant land cover type to the total terrestrial
area, excluding water areas. The land cover values at each sampling site
were averaged over three locations. In subsequent analyses, we used
generalized additive models (GAMs) to analyze the relationships between
land use types and fish diversity metrics.