Hydrology and Earth System Sciences
www.hydrol-earth-syst-sci.net
1027-5606
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5
3
2001
10.5194/hess-5-299-2001
http://www.hydrol-earth-syst-sci.net/5/299/2001/
http://www.hydrol-earth-syst-sci.net/5/299/2001/hess-5-299-2001.html
http://www.hydrol-earth-syst-sci.net/5/299/2001/hess-5-299-2001.pdf
299
310
0000-00-00
Trends in nitrogen deposition and leaching in acid-sensitive streams in Europe
R. F. Wright
C. Alewell
J. M. Cullen
C. D. Evans
A. Marchetto
F. Moldan
A. Prechtel
M. Rogora
Norwegian Institute for Water Research, P.O. Box 173 Kjelsås, N-0411 Oslo, Norway
Institute for Terrestrial Ecosystem Research (BITÖK), University of Bayreuth, D-95440 Bayreuth, Germany
Centre for Ecology and Hydrology, Wallingford, Oxon OX10 8BB, UK
Consiglio Nazionale delle Ricerche - Istituto Italiano di Idrobiologia, 28922 Verbania Pallanza (VB), Italy
Swedish Environmental Research Institute IVL, Box 47086, S-402 58 Göteborg, Sweden
Email for corresponding author: richard.wright@niva.no
Long-term records of
nitrogen in deposition and streamwater were analysed at 30 sites covering major
acid sensitive regions in Europe. Large regions of Europe
have received high inputs of inorganic nitrogen for the past 20 - 30 years, with
an approximate 20% decline in central and northern Europe
during the late 1990s. Nitrate concentrations in streamwaters are related to the
amount of N deposition. All sites with less than 10 kgN ha<sup>-1</sup>
yr<sup>-1</sup> deposition have low concentrations of nitrate in streamwater,
whereas all sites receiving > 25 kgN ha<sup>-1</sup> yr<sup>-1</sup>
have elevated concentrations. Very few of the sites
exhibit significant trends in nitrate concentrations; similar analyses on other
datasets also show few significant trends. Nitrogen
saturation is thus a process requiring many decades, at least at levels of N
deposition typical for Europe. Declines in nitrate
concentrations at a few sites may reflect recent declines in N deposition. The
overall lack of significant trends in nitrate concentrations in
streams in Europe may be the result of two opposing factors. Continued high
deposition of nitrogen (above the 10 kgN ha<sup>-1</sup> yr<sup>-1</sup>
threshold) should tend to increase N saturation and give
increased nitrate concentrations in run-off, whereas the decline in N deposition
over the past 5 – 10 years in large parts of Europe
should give decreased nitrate concentrations in run-off. Short and long-term
variations in climate affect nitrate concentrations in
streamwater and, thus, contribute "noise" which masks long-term
trends. Empirical data for geographic pattern and long-term
trends in response of surface waters to changes in N deposition set the premises
for predicting future contributions of nitrate to acidification
of soils and surface waters. Quantification of processes governing nitrogen
retention and loss in semi-natural terrestrial ecosystems is
a scientific challenge of increasing importance.</p>
<p style="line-height: 20px;"><b>Keywords:</b> Europe, acid deposition, nitrogen, saturation, recovery, water