Managed aquifer recharge infiltration studies targeting nitrate removal: Raw sequence reads

We present results from field experiments linking hydrology,geochemistry, and microbiology during infiltration at a field site thatis used for managed aquifer recharge (MAR). These experiments measuredhow a horizontal permeable reactive barrier (PRB) made of woodchipsimpacted subsurface nitrate removal and microbial ecology. Concentrationsof dissolved organic carbon consistently increased in infiltrating waterbelow the PRB, but not in un-amended native soil. The average nitrateremoval rate in soils below the PRB was 1.5 g/m2/day NO3-N, despite rapidinfiltration (up to 1.9 m/d) and a short fluid residence time within thewoodchips (≤6 h). In contrast, 0.09 g/m2/day NO3-N was removed on averagein native soil. Residual nitrate in infiltrating water below the PRB wasenriched in δ15N and δ18O, with low and variable isotopic enrichmentfactors that are consistent with denitrification during rapidinfiltration. Many putative denitrifying bacteria were significantlyenhanced in the soil below a PRB; Methylotenera mobilis and generaMicrobacterium, Polaromonas, and Novosphingobium had log2 fold-changes of+4.9, +5.6, +7.2, and +11.8, respectively. These bacteria were presentbefore infiltration and were not enhanced in native soil. It appears thatthe woodchip PRB contributed to favorable conditions in the underlyingsoil for enhanced nitrate removal, quantitatively shifting soil microbialecology. These results suggest that using a horizontal PRB could improvewater quality during rapid infiltration for MAR.