a ATT = Microbial communities attached to in situ samplers.
b SUS = Microbial communities suspended in groundwater.
c Operational taxonomic units (OTUs) calculated using a cutoff of 97% average nucleotide similarity.
d The number of OTUs found in a randomized subset of n sequences where = the number of suspended samples. This was done to account for the greater number of ATT sequences among both bacteria and archaea.