N leaching from small upland headwater catchments in southwestern Norway

We investigated nitrogen leaching and input-output budgets from 12 small, upland headwater catchments with differing fractions of peat, heather and bare rock in SW Norway. A close relationship was found between annual inorganic nitrogen loss and the fractional cover bare rock explaining 74% of the variation. It was not possible to distinguish between the N leaching from the peat and heather dominated catchments in this investigation. Nitrate loss was negatively correlated to the C/N ratio of the soil organic horizon. Lowest soil C/N ratios of the soil organic surface horizon occurred in catchments receiving the highest amounts of N deposition. Our data for Norwegian moorland are in agreement with previous investigations relating soil C/N ratio and N leaching in forest soils. Runoff from the catchments showed a seasonal pattern in NO3- concentrations. The low values during the summer are presumably due to increased biological activity (plant uptake and immobilization by soil microbes). The winter and spring NO3- concentrations in 2001 in all catchments were much higher than in 2000, perhaps due to soil freezing.