DENITRIFICATION AND NITROGEN-RETENTION IN A FARMLAND STREAM IN SOUTHERN SWEDEN

Nitrogen retention in a small stream, River Raan in southern Sweden, w as studied by mass-balance calculations along a 7-km reach with runnin g water and in a small pond. In addition, denitrification activity and limiting factors for the denitrification were analyzed with the acety lene blockage method in different types of sediments from the stream a nd the pond at different times of the year. The total annual nitrogen retention was less than 3% of the total nitrogen transport in the stre am. The retention in the pond was greater than in the rest of the rive r. Significant nitrogen retention (20-50%) occurs only during low flow periods in the summer. On such occasions, the denitrification losses correspond to more than half of the total nitrogen retention. On an an nual basis denitrification was responsible for 30-40% of the total ret ention in Raan. The discharge was by far the most critical factor dete rmining nitrogen retention both in running water and the pond.