Environmental Engineering Reference
In-Depth Information
Figure 4.11
The impact of acid rain on the terrestrial environment
Source.
Compiled from data in Fernandez (1985); Shriner and Johnston (1985); Tomlinson (1985)
Episodic increases in acidity of this nature may
be likened to the spring flush in the aquatic
environment, although their intensity and
duration is usually less.
Once the acid rain enters the soil, its impact
will depend very much on the soil type and the
underlying bedrock. Soils derived from granite,
for example, will already be acidic, and therefore
vulnerable to further increases. In contrast, soils
developed over limestone, or some other calcium-
rich source, will have the ability to neutralize
large quantities of additional acid. Natural
processes, such as the decay of organic matter or
the weathering of minerals, increase the acidity
of many soils, and it is often difficult to assess
the contribution of acid rain to the total. Indeed,
it has been argued that the addition of
atmospheric acids may be relatively insignificant
compared with those from in-soil processes (Krug
and Frink 1983). The situation is further
complicated when such soils are developed for
agriculture. To maintain productivity, it is
necessary to make regular applications of
fertilizer and lime, which mask acidification.
Acidic water interferes with soil biology and
soil chemistry, disturbing nutrient cycles and
causing physiological damage to plant root
systems. Increased acidity inhibits the bacterial
activity which is instrumental in releasing
nutrients from dead or decaying animal and
vegetable matter; the ability of nitrifying bacteria
to fix atmospheric nitrogen may also be
restricted, leading to reduced soil fertility
(Ontario: Ministry of the Environment 1980).
