Environmental variables
At each site, the annual mean temperature (T ) was used to
characterize the climate, and the dataset (unit: 0.1 °C, year: 2015,
resolution: 1 km) was obtained from the Resource and Environment Science
and Data Center (http://www.resdc.cn/). A water sample was
collected, and the total nitrogen (TN ), total phosphorus
(TP ), and chemical oxygen demand (COD ) were determined
using a Palintest 7500 Photometer (Palintest, UK). Trophic state indices
were calculated by the following equations: TLI(TP ) =
10(9.436+1.624 lnTP ), TLI(TN ) = 10(5.453+1.694
lnTN ), TLI(COD ) = 10(0.109+2.661 lnCOD ). Water
nutrient status (Nwater ) was the mean value of
TLI(TP ), TLI(TN ), and TLI(COD ) (Cao et al. 2021).
The water depth (Hquadrat ) in each quadrat was
measured by a pole and ruler, average water depth at each site
(Hsite ) was the mean value ofHquadrat s of all quadrats.
In addition, the linear distance
between the site location and the nearest town
(Lsite-town ) was determined to measure the
anthropogenic disturbance level (Gosper et al. 2015).