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

Abstract

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 o N) and Øygard in southwestern Norway (58 o 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 -1 yr -1 ), whereas the Øygard site has a more mild, humid climate with much larger N deposition (13-19 kg N ha -1 yr -1 ). Streamwater nitrate (NO 3 -) 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 µg N L -1 was reached just before snowmelt. At onset of the snowmelt flood, NO 3 -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 NO 3 -concentrations may indicate a relatively high NO 3 -leaching potential in this catchment. On average, the annual NO 3 -export was negligible at Dalelva (<0.1 kg N ha -1 yr -1 ), while at Øygard it amounted to 3.0±0.3 (±1 s.d.) kg ha -1 yr -1 , or nearly 20% of the annual N deposition. In addition to this relatively high annual N loss, elevated NO 3 -concentrations during the growing season further indicate that the N supply at Øygard is in excess of the combined plant and microbial demand.

Modelling impacts of climate and deposition changes on nitrogen fluxes in northern catchments of Norway and Finland

“…A snowmelt-induced spring flood in late April-May usually dominates the annual hydrological pattern, whereas less pronounced flow peaks often occur in autumn due to rainfall events. In these areas, a major fraction of the annual NO 3 loss occurs during these high flow periods (Kaste and Skjelkvåle, 2002;Rankinen et al, 2004). In low-lying nearcoastal areas of southern and southwestern Scandinavia, on the other hand, the climate is maritime and winters are often mild with little snow accumulation.…”

“…Site characteristics and climate at the study sites. The mean climatic data from Dalelva, Øygard and Simojoki cover the periods 19902000, 19932000, and 19712000, respectively (Kaste and Skjelkvåle, 2002;Drebs et al, 2002). vegetation zone (Fig.…”

“…N deposition data were obtained from the nearest monitoring stations in the Norwegian monitoring programme on long-range transported air pollutants (cf. Kaste and Skjelkvåle, 2002). The data are wet and dry deposition of total inorganic N (TIN), the sum of NO 3 and NH 4 + : the wet deposition is determined by the chemical composition and the amount of precipitation, whereas dry deposition is estimated from ambient air concentrations and dry deposition velocities for individual components (Tørseth and Semb, 1998).…”

“…The period 199395 was selected as the basis for the Norwegian INCA calibrations (Kaste, 2004 (Kaste and Skjelkvåle, 2002).…”

“…was six times that at Dalelva. The percentages of each land cover type modelled at the Dalelva and Øygard catchments were obtained from topographic maps, thematic maps and aerial photographs (Kaste and Skjelkvåle, 2002).…”