Geography Reference
In-Depth Information
is only a short-term solution because it treats
symptoms rather than underlying causes.
What is perhaps of equal concern to the
problem of acid precipitation itself is the
likelihood of additional affects caused by global
warming, as Wright and Schindler (1995) have
discussed. They suggest that increases in
temperature predicted by general circulation
models (GCMs) for the boreal zone could cause
increased mineralisation of nitrogen and the
oxidation of organic compounds, including those
containing sulphur. Thus, despite emission
reductions, acidification would continue; the acids
produced through mineralisation would continue
to mobilise aluminium. Numerous factors may
also conspire to allow the penetration of radiation,
including the harmful ultraviolet-B (UV-B), to
greater than usual depths, where it may have
adverse ecological impacts (see discussion in
Schindler et al. 1996). In addition, it has recently
been suggested that declines in dust production,
especially that containing bases (e.g. calcium
carbonate and magnesium carbonate), may negate
the impact of emission controls (Hedin and Likens
1996). The lack of such bases in the atmosphere,
due to legislation on air quality, seems likely to
cause a decline in neutralisation between acidic
and basic components. Thus, despite curbs on acid
emissions their environmental impact may be
intensified. These issues reflect the complex
interplay between numerous biogeochemical
cycles and between different forms of pollution.
Box 3.1 The reconstruction of lake pH using
diatom analysis
1 Diatoms are unicellular algae that are abundant in
most aquatic environments. They form the basis of
food chains/webs and many species are particularly
sensitive to water pH.
2 The frustules, which are the structural component of
diatoms, are composed of silica, which is resistant
to decay. Consequently, these frustules become
incorporated into lake sediments when the
organisms die. As sediments accumulate, a sample
of the diatom population is preserved. Changes in
the assemblages reflect, among other factors,
changes in pH. On the basis of the pH sensitivities
of their modern counterparts, the fossil diatoms
provide a means of reconstructing the pH history of
the lake waters.
3 This has been undertaken for many lakes in acid-
sensitive areas, data from some of which are given
in Table 3.3. The detailed pH reconstruction of one
of those lakes, Round Loch of Glenhead (Battarbee
et al . 1988) is illustrated below:
The impact of acid precipitation on terrestrial
ecosystems: forests and peatlands
The impact of acid precipitation on terrestrial
ecosystems occurs directly and indirectly. The
direct effect involves wet and/or dry and occult
deposition on vegetation, which may impair its
capacity for photosynthesis and cause a loss of
biodiversity as only those least acid-sensitive
species survive. Indirect effects are caused by the
influence that acid precipitation has on soils,
especially on their chemistry and microbiology.
Moreover, and as suggested above, other forms of
pollution such as ozone accumulation in the
the region have lower concentrations of
aluminium, heavy metals and sulphate and higher
pH than they did in the 1970s; in some cases, trout
have even been re-established. Moreover, where
liming of lakes or catchment soils has been
undertaken, rapid improvement in pH can occur.
This is illustrated by the work of Blette and
Newton (1996) on Woods Lake in the Adirondack
Mountains of the northeast USA and by the work
of Dixit et al . (1996) on the Aurora trout lakes of
Sudbury, Canada. In the latter, water quality in two
lakes was improved to such an extent that aurora
trout were reintroduced in 1990. However, liming
 
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