Seasonal Variations in Water Quality and NOM Removal in Natural Bank Infiltration of Boreal Lake Water

Managed aquifer recharge (MAR) provides a means to improve water quality in drinking water production by natural organic matter (NOM) removal. We chose a natural bank infiltration site to investigate aquifer recharge over a much longer time scale than can be achieved by studying existing MAR sites or by column tests. The objective was to assess the long-term sustainability of MAR. Here we focus on the seasonal variation of NOM reduction and redox conditions during infiltration. To examine the NOM removal and its seasonal variability, lake and groundwater samples were collected, and total organic carbon, dissolved organic carbon, chemical oxygen demand, dissolved inorganic carbon, pH, dissolved oxygen, iron, manganese, conductivity, and stable isotopes of oxygen and hydrogen were measured. The lake infiltratefraction was estimated at each sampling location in the aquifer by the isotope tracers. NOM along the groundwater flow pathway was found to be removed by 80-90 %, which is higher than reported at Finnish MAR plants. Seasonal temperature dependent changes in oxygen and iron levels at the lake shoreline were observed, but the removal of NOM was constant during all seasons. The main conclusion was that an aquifer can sustainably remove NOM from infiltrating water, without losing its efficiency. However, the northern seasons trigger variations in the redox conditions.