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| Titel |
Effects of nitrogen deposition and climate change on nitrogen runoff at Norwegian boreal forest catchments: the MERLIN model applied to Risdalsheia (RAIN and CLIMEX projects) |
| VerfasserIn |
R. F. Wright, C. Beier, B. J. Cosby |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 2, no. 4 ; Nr. 2, no. 4, S.399-414 |
| Datensatznummer |
250000640
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| Publikation (Nr.) |
 copernicus.org/hess-2-399-1998.pdf |
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| Zusammenfassung |
The catchment scale-experiments of the RAIN and CLIMEX
projects conducted on boreal forest ecosystems at Risdalsheia, southernmost Norway, provide a unique set of data
on the flux of nitrogen (N) in runoff following changes in N deposition, carbon dioxide (CO2)
level and temperature. MERLIN (Model of Ecosystem Retention and Loss of Inorganic Nitrogen), a
recently-developed model that focuses on N leaching, provides a means by which these data
can be placed into a quantitative framework.
The features of the N flux in runoff at Risdalsheia to be explained include (1) leaching
of about 30-50 mmol m-2 yr-1 (30-40% of N deposition) during the period
1985-1997 at reference catchments, (2) rapid and dramatic reduction in N leaching following experimental
reduction in N deposition in 1985 at KIM catchment, (3) increased flux of about 5 mmol m-2
yr-1 following onset of 3-5°C warming and increased CO2 in 1995 at KIM catchment, and (4) increased flux
of about 12 mmol m-2 yr-1 following 3-5°C warming of soil in 1995
at EGIL catchment.
One set of calibrated model parameters is sufficient to simulate the changes in N runoff
at both experimental catchments for both of the manipulations. The model support the conceptual
picture of the soil as the major sink for N inputs from deposition with N accumulating in both the
forest floor (labile organic matter LOM) and the bulk soil (refractory organic matter ROM). As
the molar carbon/nitrogen (C/N) ratio of LOM decreases to below 23, progressively less N is
immobilised and more goes to runoff. The model also supports the conceptual picture of
increased rate of decomposition of old soil organic matter in response to higher
temperature. An increase of 5% is sufficient to produce the
5-12 mmol m-2 yr-1
increase in N flux in runoff observed at the 2 experimental catchments. The MERLIN simulations
are consistent with
measurements of increase in net mineralisation rates (per catchment area by
70 mmol m-2 yr-1) and N contents in foliage in treated and reference
areas before and after onset of treatment.
Runoff provides a very sensitive indicator of changes in N cycling within the ecosystem.
Small changes in key processes such as N mineralisation give rise to large relative changes in N
flux. Uncertainties in measurements are generally much larger than changes indicated by the
model calibration. |
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