Final reference sites had TP < 0.10 mg/L, NH4 < 0.50 mg/L, CODMn < 4 mg/L, DO > 6 mg/L, conductivity < 300mS/cm and an HQI score > 60 (Table 2).
In ecoregion I2, we did not set a land use threshold because the sum of farmland percent, urban land percent and water surface percent reached 97.63% (Gao et al., 2012).
Instead, we set primary selection criteria as no industrial pollution and no municipal wastewaters in their 500 m riparian buffer zones, and the physical and chemical thresholds were set as: TP < 0.20 mg/L, NH4 6 mg/L, conductivity < 500mS/cm, and an HQI score > 60 (Table 2).