Interaction of Climate Change and Acid Deposition - Climate Change Impacts on Freshwater Ecosystems - page 168

4.5

Ambient DOC
Low DOC

4.4

4.3

4.2

4.1

4.0

3.9

3.8

1970 1980 1990 2000

Year

2010 2020 2030

Figure 7.13 Projected recovery of pH in streamwater at Lysina catchment, Czech Republic,
as simulated by the MAGIC model using two scenarios for DOC. (i) DOC was assumed
constant at 1993-4 levels ('Low DOC' scenario) and (ii) DOC observed between 1993 and
2007 was used for the modelling of the period 1994-2007 and an average of period
2006-7 for the period 2008-30 ('Ambient DOC' scenario). (From Hruška et al . 2009.)

(Fig. 7.13). With the level of DOC measured in 1993-4, predicted pH rose close
to 4.30 from the lowest value measured (3.88) and predicted for late 1980s.
When the measured increase of DOC (Fig. 7.13) was incorporated into the
MAGIC model, pH was predicted to rise to only 4.20 (Hruška et al . 2009).
Concentrations of DOC in streams typically increase during episodes of
high runoff. What is less well established, however, is the role of ionic strength
of the runoff on DOC. Theoretically, the higher ionic strength of the soil solution
should result in lower DOC concentrations owing to the lower solubility of
organic matter (Evans et al . 1988; Tipping & Hurley 1988). Under natural
conditions, it is difficult to discern the effects of hydrology or chemistry alone
since the changes in discharge and water chemistry typically occur at the same
time. To investigate the potential effect of high sea-salt episodes on DOC runoff
concentrations, a field-scale watering experiment was conducted in 2004 at the
experimental catchment G1 at Gårdsjön, Sweden (F. Moldan unpublished data).
The catchment was brought to field capacity; i.e. addition of water from the
sprinkling system was approximately equal to discharge rate. After reaching field
capacity, the catchment was watered for 4 days with distilled water, after which
sea salt was added to the sprinkling solution.
Sea salt was added first for 2 days at a level typical for ambient throughfall and
then at a high level observed during storms and periods of high winds. Experimental
addition of sea salt resulted in an immediate decrease of DOC in the stream from