Nitrogen dynamics in runoff from two small heathland catchments representing opposite extremes with respect to climate and N deposition in Norway

Overview & Synopsis

Effects of contrasting climatic conditions and nitrogen (N) deposition levels on streamwater N dynamics are assessed at two small heathland catchments; Dalelva in northern Norway (69°N) and Øygard in southwestern Norway (58°N). The study comprises 11 years of data on climate, hydrology and N inputs/outputs from Dalelva and 8 years of corresponding data from Øygard. Both sites are comparable in catchment size, geology and land cover characteristics, but have large differences in climate and N deposition. Dalelva is characterised by a cold, arctic climate and low N deposition (2-3 kg N ha?1y?1), whereas the Øygard site has a more mild, humid climate with much larger N deposition (13?19 kg N ha?1yr?1). Streamwater nitrate (NO3?) concentrations at Dalelva generally were negligible during the growing season, but showed a steady increase during the dormant season until a maximum of 40-100 ?g N L?1 was reached just before snowmelt. At onset of the snowmelt flood, NO3? concentrations decreased momentarily to very low levels, suggesting that N eluted from the seasonal snowpack to a great extent was infiltrated and immobilised in the soils. At Øygard, flood peaks occurred frequently during all seasons, and usually there was no distinct spring flood. A lack of clear dilution effects from floods on streamwater N3? concentrations may indicate a relatively high NO3? leaching potential in this catchment. On average, the annual NO3? export was negligible at Dalelva (