Fig. 4

Dependence plots based on Random Forest regression, showing the relationship of the hydraulic (a) and physicochemical (b) predictors, with freshwater mussel density, in Poyang Lake, China. Dissolved oxygen (DO; mg/L), hydrogen ions (pH), salinity (Sal; mg/L), turbidity (TURB; NTU), and water temperature (T; °C), chlorophyll-a (Chl-a; mg/L), water velocity (V; m/s), water depth (WD; m), Total nitrogen (TN; mg/L) and total phosphorus (TP; mg/L), D (mm), Sorting index (S_o, unitless), Bed roughness (k_s, mm), Froude number (Fr, unitless), Reynolds number (Re, unitless), Boundary Reynolds number (Re*, unitless), Shear velocity (V, m/s), Shear stress (τ, N/m²). Critical shear stress (τ_c, N/m²)