Risks of nutrients and metal(loid)s mobilization triggered by groundwater recharge containing reactive organic matter

The potential risk of multiple contaminants mobilization from sediment was evaluated under the infiltration of reactive organic matter (OM) during groundwater recharge. Significant NH4-N, PO4, As, Fe, and Mn release were observed which show elevated peaks in the initial stage (0-19 d) and declines afterwards until reach quite low and stable content (20-37 d). When re-oxidize with SO42 � (38-65 d), the reducing condition is stimulated to release more Fe and Mn however no As, NH4-N and PO4 3 � main driving force for NH4-N, PO4 , As, Fe, and Mn release. The NH4-N and PO4 passive mobilization from Fe/Mn oxides due to its dissolution. The cation exchange also works significantly on NH4+ release while desorption works on PO43 � as well. Microorganism responses to the infiltration reactive OM and further impacts the mobilization of multiple contaminants. The precipitation of secondary Fe/Mn minerals accompanied by co-precipitation and/or re-absorption lower down their aqueous levels. However, this aqueous contamination risk was hidden in solid reactive secondary minerals when oxidizer like SO42- perturbs the recurrence of Fe and Mn contamination occurs. This shows the perennial release of nutrients and trace elements should be paid attention in areas with reactive OM infiltration followed by redox/groundwater chemistry fluctuations, potentially in hyporheic zone of river/lake, managed aquifer recharge zone, etc.

Automated summary

The study evaluated the potential risk of multiple contaminants mobilization from sediment during groundwater recharge induced by reactive organic matter (OM) infiltration. Significant release of NH4-N, PO4, As, Fe, and Mn was observed initially, followed by a decline, reaching low and stable levels. Re-oxidization with SO42- stimulated the release of Fe and Mn, but had no effect on As, NH4-N, and PO4. NH4-N and PO4 were mobilized passively due to the dissolution of Fe/Mn oxides. Cation exchange played a significant role in NH4+ release, while desorption affected PO43-. Microorganisms responded to the infiltration of reactive OM and influenced the mobilization of contaminants. The precipitation of secondary Fe/Mn minerals and their co-precipitation and/or re-absorption lowered the aqueous concentrations. However, the risk of aqueous contamination was hidden in solid reactive secondary minerals, which were disturbed by oxidizers like SO42-. This highlights the importance of considering the perennial release of nutrients and trace elements in areas with reactive OM infiltration and redox/groundwater chemistry fluctuations, such as the hyporheic zone of rivers/lakes and managed aquifer recharge zones.