『Abstract
Karst watersheds are a major source of drinking water in the
European Alps. These watersheds exhibit quick response times and
low residence times, which might make karst aquifers more vulnerable
to elevated nitrogen (N) deposition than non-karst watersheds.
We summarize 13 years of monitoring NO3-,
NH4+, and total N in two forest
ecosystems, a Norway spruce (Picea abies (L.) Karst.) forest
on Cambisols/Stagnosols (IP I) and a mixed beech (Fagus sylvatica
L.) spruce forest on Leptosols (IP II). N fluxes are calculated
by multiplying concentrations, measured in biweekly intervals,
with hydrological fluxes predicted from a hydrological model.
The total N deposition in the throughfall amounts to 26.8 and
21.1 kg/ha/year in IP I and IP II, respectively, which is high
compared to depositions found in other European forest ecosystems.
While the shallow Leptosols at IP II accumulated on average 9.2
kg/ha/year of N between 1999 and 2006, the N budgets of the Cambisols/Stagnosols
at IP I were equaled over the study period but show high inter-annual
variation. Between 1999 and 2006, on average, 9 kg/ha/year of
DON and 20 kg/ha/year of DIN were output with seepage water of
IP I but only 4.5 kg/ha/year of DON and 7.7 kg/ha/year of DIN
at IP II. Despite high DIN leaching, neither IP I nor IP II showed
further signs of N saturation in their organic layer C/n ratios,
N mineralization, or leaf N content. The N budget over all years
was dominated by a few extreme output events. Nitrate leaching
rates at both forest ecosystems correlated the most with years
of above average snow accumulation (but only for IP I this correlation
is statistically significant). Both snow melt and total annual
precipitation were most important drivers of DON leaching. IP
I and IP II showed comparable temporal patterns of both concentrations
and flux rates but exhibited differences in magnitudes: DON, NO3-, and NH4+
inputs peak in spring, NH4+ showed
an additional peak in autumn; the bulk of the annual NO3-
and DON output occurred in spring; DON, NO3-,
and NH4+ output rates during winter
months were low. The high DIN leaching at IP I was related to
snow cover effects on N mineralization and soil hydrology. From
the year 2004 onwards, disproportional NO3-
leaching occurred at both plots. This was possibly caused by the
exceptionally dry year 2003 and a small-scale bark beetle infestation
(at IP I), in addition to snow cover effects. This study shows
that both forest ecosystems at Zobelboden（最初のoの頭に¨）
are still N limited. N leaching pulses, particularly during spring,
dictate not only annual but also the long-term N budgets. The
overall magnitude of N leaching to the karst aquifer differs substantially
between forest and soil types, which are found in close proximity
in the karstified areas of the Northern Limestone Alps in Austria.
Keywords: Nitrogen saturation; Nitrate leaching; Nitrogen deposition;
Snow melt; Long-term monitoring』
1. Introduction
2. Study site
3. Methods
3.1. Meteorological data
3.2. N concentrations
3.3. Bulk precipitation and throughfall
3.4. Seepage
3.5. Laboratory analysis
3.6. Water fluxes
3.7. N input-output budgets
4 Results
4.1. Hydrochemistry during the study period
4.2. N deposition in precipitation and throughfall
4.3. N in seepage water
4.3.1. IP I
4.3.2. IP II
4.4. Annual N budgets
4.5. Intra-annual variation in N fluxes
5. Discussion
5.1. Annual budgets, N status, and nitrate leaching
5.2. Inter-annual and intra-annual variation of N fluxes
5.3. Uncertainties
6. Conclusions
References