“…There is some evidence for a reverse trend for archaea, which exhibited higher abundance and diversity in groundwater compared with sediment in one study (Flynn et al, 2013). In studies that directly compared sediment and groundwater communities from the same site, a trend of no more than 30% overlap in the bacterial communities was determined (Reardon et al, 2004;Flynn et al, 2008Flynn et al, , 2013. Gene surveys of 16 S rRNA provide, at best, species-level resolution, but most studies have focused on higher taxonomic levels, or, alternatively, tracked a few specific lineages of interest across samples (Reardon et al, 2004;Flynn et al, 2013;Longnecker & Kujawinski, 2013).…”