Fig. 4 Environmental factors and land-use types shaping microbial community composition in the river ecosystems during (a) autumn and (b) spring. Pairwise comparisons of environmental factors and land-use types are shown at the upper-right, with a color gradient representing Spearman’s correlation coefficients. Microbial community composition was correlated to each environmental factor or land-use type based on the partial Mantel’s test. The line width represents the partial Mantel’s r statistic for the corresponding correlation, and the line color represents the significance based on 999 permutations. T, water temperature; Turb, water turbidity; Cond, electrical conductivity; DO, dissolved oxygen; TP, total phosphorus; TN, total nitrogen; NH4+-N, ammonium nitrogen; NO3--N, nitrate nitrogen; NO2--N, nitrate nitrogen.