Interaction of Climate Change and Acid Deposition - Climate Change Impacts on Freshwater Ecosystems - page 166

Plastic inflow No.1

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Figure 7.12 Sulphate concentrations in streamwater at Plastic Lake, Ontario, showing
the pulses following drought. The breaks in the curve are due to droughts; at these
times there was no flow in the stream, thus no water samples were collected. (Updated
from Dillon et al . 1997.)

in soils and flushing of the sulphate with the first runoff. The drought causes
lowering of the water table and exposes anoxic soils and peats to oxygen. The role
of drought-induced acid episodes is particularly well-illustrated in the long-term
record from lakes and streams in the Muskoka-Haliburton area of southern Ontario
(Dillon et al . 1997; Eimers et al . 2008) (Fig. 7.12). Similar sulphate-driven acid
episodes have been reported at many other sites, including Birkenes, Norway
(Wright 2008), Sweden (Laudon & Bishop 2002a; Laudon 2008) and the United
Kingdom (Hughes et al . 1997; Adamson et al . 2001).

Dissolved organic carbon (DOC)

Dissolved organic carbon (DOC) in surface waters gives rise to weak organic
acids, complexes many toxic components and thus affects the chronic and acute
toxicity of acidic water to aquatic organisms, in particular, fish. In boreal lakes
and streams, DOC levels typically show a clear seasonal pattern, with low levels
in winter and spring and higher levels in late summer and autumn. This pattern
is climate-driven and related to biological activity in catchment vegetation and
soils, as well as in-lake processes (mainly driven by UVA radiation) that degrade
DOC in the water (Gennings et al . 2001). It can thus be expected that future
climate change will affect the annual mean levels and seasonal patterns of DOC
concentrations in surface waters (Laudon & Buffam 2008). This issue has already