Groundwater Targeted Locus (Loci). groundwater metagenome

Anthropogenic additions of nitrogen to estuaries contributes to the eutrophication of coastal ecosystems. Permeable reactive barriers (PRBs) are one design strategy that reduces anthropogenic nitrogen inputs from groundwater. PRBs consist of trenches filled with woodchips that are positioned to intercept nitrate-laden groundwater before it enters estuaries. The woodchips in the PRB provide a carbon source that promote the growth of denitrifying bacteria, and facilitate the removal of nitrate. This large supply of carbon, however, likely supports additional bacterial metabolisms. Thus, PRBs provide a unique opportunity to examine microbial community structure under carbon-replete conditions in a coastal aquifer. Our results indicate that a brackish PRB provided sufficient carbon to drive the aquifer anoxic and to remove excess nitrate. Analysis of 16S rDNA indicated that the microbial community in the PRB was rich in anaerobic bacteria and had particularly high abundances of bacteria thought to have low energy yielding metabolisms. By contrast, the bacteria that were active in the PRB, as indicated by the abundance of 16S rRNA, were more similar to bacteria found in adjacent reference locations, suggesting that active bacteria growing directly on the woodchips, rather than in groundwater, are responsible for the barrier geochemistry. Among the environmental variables analyzed, dissolved oxygen levels explain the largest portion of the bulk microbial community structure. There was no significant effect of measured environmental parameters on the active microbial community, suggesting that common predictors of microbial community structure included here are not large contributors to microbial communities in coastal aquifers.