Nitrate transformation and water movement in a wetland area

The NO₃ ⁻ transformation capacity of a riparian zone at Rabis stream, Denmark, was investigated for a period of 2 years. The riparian zone of 15–25 m received NO₃ ⁻-containing groundwater from the adjoining agricultural areas. The water flows as surface runoff along the surface of the wetland and in the root zone towards the stream. Changes in water chemistry, water balance and mass transport were investigated. The riparian zone acted as a buffer zone for NO₃ ⁻, PO₄ ³⁻ and dissolved Fe²⁺. The NO₃ ⁻-transformation capacity of the wetland was about 400 kg N ha⁻¹ y⁻¹, but varied seasonally. A simple rearrangement of drain systems in wetland areas can probably reduce the NO₃ ⁻ content of Danish surface waters by 20 000–50 000 t N y⁻¹.