The load of organic carbon, nitrogen and phosphorus from two large drainage basins (River Kitka and River Oulanka) in NE Finland

Abstract

Leaching and transport of organic carbon, nitrogen and phosphorus were studied in two large drainage basins and river systems in northern Finland. Within three consecutive years, 1990-1992, leaching of organic carbon from the River Kitka drainage basin varied between 880-3623 kg C km-2, and from the River Oulanka between 1995-8002 kg C km-2. Leaching of nitrogen and phosphorus were 111-177 and 1.9-3.7 kg km-2 from the drainage basin of Kitka, and 101-265 and 2.9-6.3 kg km-2 from Oulanka. In both basins the variability of organic carbon was roughly twice that of nitrogen and phosphorus. In comparison with other studies, the leaching values were well within the range of variation, although in general at the lower end of the variability range. The annual transport of organic carbon, nitrogen and phosphorus by the river systems also varied widely, and due to its higher organic carbon concentration and discharge the River Oulanka had a TOC load more than 2.5 - times that of the River Kitka. Phosphorus transport by the River Oulanka was more than 1.5 times that of the River Kitka, but for nitrogen the transport was only 90 to 140 % of that of Kitka.

In both areas the annual leaching and transport of nutrients were highly dependent on the hydrological conditions.