Table 3.

Spearman's coefficients (r) describing rank correlations between microbial community composition and environmental factors for two select sets of factors calculated with Bio-Env, and for all factors calculated with the BV-Step forward selection procedure (Primer 6.0)

River	r	r	r (BV-Step, all variables)
Mackenzie	0.66 (a375, Mg, NO3)	0.66 (Q, Temp)	0.74 (a375, DO14C, NO3, SO4, pH, Temp, Si)
Yukon	0.54 (a375, Mg)*		0.74 (SUVA, DOC, Cl, TDP, Si)†
Kolyma	0.77 (a375, Mg, NO3)		0.85 (a375, NO3, LP)‡
Lena	0.80 (a375, Mg, NO3)	0.59 (Q)§	0.88 (a375, LP, NO3, SO4, NH4, Temp)
Yenisey	0.89 (a375, Mg, NO3)	0.77 (Q, Temp)	0.91 (a375, NO3, SO4, Na, K, pH, DOC)
Ob	0.75 (a375, Mg, NO3)	0.54 (Q, Temp)	0.87 (NO3, Cl, Ca)

Note that some samples were excluded from analyses because of missing environmental data. River flow (Q) was not determined for the Yukon or Kolyma.

*NO₃ did not improve correlation.

^†Q, TSS, ΔDO¹⁴C are not included.

^‡Q are not included.

^§Temp did not improve correlation.