Changes in dissolved organic carbon during artificial recharge of groundwater in a forested esker in Southern Finland

Sprinkling infiltration in a forested esker leading to artificial recharge of groundwater was studied in Southern Finland. Changes in dissolved organic carbon (DOC) and the molecular size distribution and chemical properties of the organic carbon were investigated during the infiltration process. Artificial groundwater was produced using sprinkling infiltration directly onto the forest floor. One result of lake water infiltration through the organic horizon and 1 m thick mineral soil layer was a slight net increase in the DOC concentrations from 9.4 mg/L in the infiltration water to 13.2 mg/L in percolation water. This indicates that the forest soil represents a potential input of organic matter into infiltration water. However, the DOC concentrations decreased by 27–38% as the infiltration water percolated down through the unsaturated soil layer into the groundwater zone. At a distance of 1450 m from the infiltration area, the mean DOC concentration in the groundwater was below the recommended value for drinking water in Finland of 2.0 mg/L. There was a strong reduction in the concentrations of hydrophilic and hydrophobic acids, but only a slight decrease in hydrophilic neutral organic compounds during the infiltration process. The DOC in the production well consisted of low molecular size fractions. Larger molecular size fractions were removed effectively from the water during the infiltration process.