Interaction of Climate Change and Acid Deposition - Climate Change Impacts on Freshwater Ecosystems - page 169

16 1800

1600
1400

14

12

1200

10

1000
800

8

6

600

4

400

2

200

0

0

Figure 7.14 Decline of DOC (circles, left axis) at the Gårdsjön experiment during 10
days of watering and sea-salt addition. Cl − concentration (dashed line, right axis) in
added water (F. Moldan unpublished data.)

12 mg l −1 to 8 mg l −1 (Fig. 7.14). pH decreased slightly from 4.4 to 4.2 and
inorganic Al increased from 3 m eq l −1 to 200

μ

eq l −1 . The ionic strength of the
stream water almost doubled. These results suggest that the DOC changes were
driven by ionic strength or acidity increase. Climate change through enhanced
sea salt input can, in coastal areas, suppress DOC runoff concentrations during
hydrological episodes.

Saharan dust

Inputs of dust from deserts of Northern Africa are important sources of alkaline
substances that act to neutralize acid deposition. Dust inputs are great enough
to play a major role in the acid-base balance in acid-sensitive catchments in
mountainous regions of Southern Europe, such as Northern Italian Alps
(Rogora et al . 2004) and the Spanish Pyrenees (Rodà et al . 1993) and even as
far north as the central Alps of Austria (Psenner 1999). Future climate change
may mean an increase in the frequency and severity of these episodes of Saharan
dust inputs; for acidified freshwaters, this means an improvement in the
acidification status (Rogora et al . 2004).

Effects of climate warming on soil chemical processes

An increase in soil temperature should, in theory, increase the rate of chemical
weathering of soil minerals. This mechanism has been postulated by Sommaruga-
Wögrath et al . (1997) to explain recent trends in acidity of remote high elevation
lakes in the Austrian Alps. This is further supported by palaeolimnological data