Sammendrag
Nitrogen deposition has a potentially eutrophying impact on oligotrophic freshwaters. Here we present a data analysis and a literature review with a joint focus on nitrogen (N) limitation in oligotrophic lakes and rivers. The data analysis consists of a Nordic
lake dataset where relations between algal biomass (chlorophyll a), water chemistry and N deposition are investigated, and an
analysis of element stoichiometry (nitrogen : phosphorus ratios) in Norwegian natural rivers. The literature review includes
international publications on N limitation from a wide variation of monitoring and experimental studies. The data analysis and
literature both support that N limitation exists in surface waters that receive low N deposition and that elevated N deposition can
shift an ecosystem from N to P limitation. The results are used to review and revise ranges of critical loads of nitrogen for surface
waters, as a contribution to the ongoing review and revision of empirical critical loads under the Convention on Long-range
Transboundary Air Pollution.
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