Table 3.

Bacterial operational taxonomic units making the most significant contribution to variation between communities from the upstream and downstream sites

Operational taxonomic unitc	Relative abundance (%)a		P valueb	Contribution to variation (%)	Cumulative contribution to variation (%)	Taxonomic identificationd
	All upstream sites	All downstream sites
Otu4	0.16	4.35	0.043	2.51	2.51	Sphingobacteriales
Otu2	0.04	3.63	0.005	2.16	4.67	Gallionellaceae
Otu3	4.00	0.62	0.002	2.07	6.74	Crenothrix
Otu1	2.68	0.30	0.012	1.53	8.27	Dechloromonas
Otu42	0.38	2.73	0.002	1.41	9.69	Verrucomicrobia
Otu5	2.36	0.08	0.004	1.37	11.06	Thiobacillus
Otu8	2.97	0.71	<0.001	1.36	12.41	Desulfococcus
Otu39	0.10	2.10	0.272	1.22	13.64	Alteromonadaceae
Otu16	1.67	0.11	<0.001	0.94	14.58	Proteobacteria, unclassified
Otu33	0.87	2.09	0.003	0.86	15.44	Rhodobacter
Otu12	1.43	0.10	0.017	0.85	16.29	Comamonadaceae
Otu6	0.45	1.26	0.399	0.78	17.07	Deltaproteobacteria, unclassified
Otu10	0.00	1.26	0.106	0.76	17.83	Oceanospirillales
Otu7	0.03	1.23	0.239	0.73	18.55	Methylophilaceae
Otu9	0.02	1.17	0.321	0.70	19.25	Flavobacteriaceae
Otu15	0.00	1.06	0.331	0.63	19.89	Sphingobacteriales
Otu18	0.01	1.04	0.327	0.62	20.51	Methylophilus

^aEach data point is the mean value (n = 5).

^bP value based on ANOVA comparison of all upstream and all downstream samples.

^cOTUs were identified within a 16S tag pyrosequencing data set based on 97% sequence identity.

^dTaxonomic assignments were based on comparison to the SILVA-compatible bacterial alignment database.