Leaching of Nitrogen from Upland Forest-Regeneration Sites into Wetland Areas

Abstract

The concentration of nitrate and ammonium nitrogen in the groundwater was investigated one year before, and during seventeen years after, clear-cutting at the Pahalouhi experimental site at Kivesvaara, located in the middle-boreal coniferous forest zone in Finland (64°28 'N, 27°33 'E). The effect of natural regeneration of Norway spruce (Picea abies) and Scots pine (Pinus silvestris) has been investigated at the same experimental site since 2002, when the Pahalouhi experimental field was supplemented with the inclusion of natural regeneration. All the treatments caused a rise in nitrate nitrogen concentrations, but leaching during the first two years from natural regeneration was clearly less compared with that observed following clear-cutting and planting. Having been initially virtually zero, the concentrations of nitrate nitrogen continued to rise for 5–7 years, reaching 500–700 μg/1 at their highest, after which they began to fall. The concentrations were still high seventeen years after clear-cutting, which constituted a situation not observed earlier. Compared with nitrate, there was no corresponding ammonium nitrogen leaching.