CORRELATION OF NITRATE PROFILES WITH GROUNDWATER AND SEDIMENT CHARACTERISTICS IN A SHALLOW SANDY AQUIFER

Sediment profiles of a shallow sandy aquifer in an agricultural area of Denmark can be characterized by a new term called total reduction capacity (TRC), quantifying the total amount of reduced compounds in the aquifer material (ferrous iron, reduced sulfur compounds, solid organic carbon). A distinct increase of TRC was observed at and below the oxidation-reduction front; in this study the front was a zone approximately 30 cm wide. Oxygen, nitrate and sulfate were present above the oxidation-reduction front but disappeared at the front. Detailed porewater profiles indicate that denitrification also takes place above the front, supposedly in anaerobic microenvironments not evident in the water samples from the small wells. The TRC profiles showed that some reduction capacity is still present above the oxidation-reduction front and is apparently able to support denitrification.