Hydrology and Earth System Sciences
www.hydrol-earth-syst-sci.net
1027-5606
1607-7938
12
2
2008
10.5194/hess-12-371-2008
http://www.hydrol-earth-syst-sci.net/12/371/2008/
http://www.hydrol-earth-syst-sci.net/12/371/2008/hess-12-371-2008.html
http://www.hydrol-earth-syst-sci.net/12/371/2008/hess-12-371-2008.pdf
371
381
2008-03-05
Climate control on sulphate and nitrate concentrations in alpine streams of Northern Italy along a nitrogen saturation gradient
M. Rogora
m.rogora@ise.cnr.it
C. Arese
R. Balestrini
A. Marchetto
CNR Institute of Ecosystem Study, 28922 Verbania Pallanza, Italy
CNR Water Research Institute, Department of Hydrobiology Applied to Water Pollution, 20047 Brugherio, Milan, Italy
The role of meteorology, hydrology and atmospheric deposition on the
temporal pattern of SO<sub>4</sub> and NO<sub>3</sub> concentrations was investigated
for three streams draining alpine catchments in Northern Italy.
<br><br>
The study sites lie on a gradient of atmospheric fluxes of SO<sub>4</sub> and
NO<sub>3</sub> (from about 50 to 80 meq m<sup>−2</sup> y<sup>−1</sup>, and from 40 to
90 meq m<sup>−2</sup> y<sup>−1</sup>, respectively). As a consequence
of the increasing N input, the three catchments are also representative of
aggrading levels of N saturation. Different methods of statistical analysis
were applied to monthly data for the period 1997–2005 to identify which
variables (temperature, precipitation, hydrology, SO<sub>4</sub> and NO<sub>3</sub>
deposition) were the main predictors of water chemistry and its change in
time. Hydrological changes and snow cover proved to be the main confounding
factors in the response to atmospheric deposition in the River Masino
catchment. Its particular characteristics (small catchment area, rapid
flushing during runoff and thin soil cover) meant that this site responded
without a significant delay to SO<sub>4</sub> deposition decrease. It also showed
a clear seasonal pattern of NO<sub>3</sub> concentration, in response to hydrology
and biological uptake in the growing season.
<br><br>
The selected driving variables failed to model the water chemistry at the
other study sites. Nevertheless, temperature, especially extreme values,
turned out to be important in both SO<sub>4</sub> and NO<sub>3</sub> export from the
catchments. This result might be largely explained by the effect of warm
periods on temperature-dependent processes such as mineralization,
nitrification and S desorption.
<br><br>
Our findings suggest that surface waters in the alpine area will be
extremely sensitive to a climate warming scenario: higher temperatures and
increasing frequency of drought could exacerbate the effects of high chronic
N deposition.
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