Streamwater responses to reduced nitrogen deposition at four small upland catchments in Norway

Øyvind Kaste,Kari Austnes,Heleen A. de Wit

doi:10.1007/s13280-020-01347-3

Øyvind Kaste, Kari Austnes + Show 1 more

Open Access

https://doi.org/10.1007/s13280-020-01347-3

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Abstract

Reduced emissions of nitrogen (N) in Europe have resulted in decreasing atmospheric deposition since 1990. Long-term data (1988–2017) from four small Norwegian catchments located along gradients in N deposition, rainfall, and organic carbon (C) show different responses to 25–30% reductions in N deposition during the same period. At three sites the decreased N deposition caused reduced leaching of nitrate to surface water, whereas the westernmost site showed no decrease, probably due to thin soils with low C:N ratio, poor vegetation cover and high precipitation. The loss of total N to streamwater constituted 30–50% of the N deposition. Losses via denitrification are unknown but assumed to be low, as a major fraction of the catchments are well-drained. Hence, the study sites seem to continue to accumulate N, presumably mostly in soil organic matter. Although atmospheric N deposition has declined, ambient loads might still exceed long-term sustainable levels in these vulnerable ecosystems.

Highlights

Emissions of sulphur oxides (SOx), nitrogen oxides (NOx) and reduced nitrogen (NHx) in Europe have been reduced by approximately 90, 55 and 20%, respectively, since 1990 (EEA 2017)
Reduced deposition of sulphate (SO4) and sea-salts has resulted in an increase in dissolved organic carbon (DOC) in surface waters (Monteith et al 2007), a proxy for dissolved organic matter (DOM) which is a vector for transport of organic N
Concentrations of non-marine SO4 are highest at Birkenes (1.3 mg L-1) and somewhat lower in the other three catchments (0.6-0.7 mg L-1)

Summary

Introduction

Emissions of sulphur oxides (SOx), nitrogen oxides (NOx) and reduced nitrogen (NHx) in Europe have been reduced by approximately 90, 55 and 20%, respectively, since 1990 (EEA 2017). In Fennoscandia there were reports of increasing N concentrations in upland surface waters during the 1980s and 1990s (Agren 1983; Lepisto 1995; Kaste et al 1997). Many of these ecosystems are sensitive to acidification. They have thin soils and sparse vegetation and a limited capacity to retain N from atmospheric deposition

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