Nitrate decontamination in a low impacted aquifer

Groundwater reservoirs constitute important freshwater resources. However, these ecosystems are highly vulnerable to contamination and have to rely on the resident microbiota to attenuate the impact of this contamination. Nitrate is one of the main contaminants found in groundwater and denitrification is the main process that removes the compound. In this study denitrification rates in three groundwater samples from a low impacted Uruguayan aquifer were measured after nitrate, acetate and pyrite amendments. Results showed that denitrification is feasible under in situ nitrate and electron donor concentrations, although input of a readily utilizable carbon source would be necessary to attenuate higher nitrate concentrations. Stable-isotope probing (SIP), combined with amplicon sequencing of 16S rRNA, nirS and nirK genes, was used to identify the active denitrifiers present. In all three groundwater samples, members of the phylum Betaproteobacteria were the dominant denitrifiers, with different families being observed; members of the Neisseriaceae, in particular Vogesella genus, were key denitrifiers at one site, while the genera Dechloromonas (Rhodocyclaceae) or Comamonas (Comamonadaceae) were the main denitrifiers that responded to the nitrate and acetate input at the other two sites.