Geography Reference
In-Depth Information
primary producers such as algae. Consequently,
primary productivity declines and so, in turn, does
secondary productivity. In this context, acid
precipitation is influencing the biogeochemical
cycle of aluminium. It can also affect the nitrogen
cycle; as pH declines to less than 5.7, the activity
of nitrifying bacteria is curtailed. This causes
ammonia, which is usually oxidised to nitrate by
these bacteria, to accumulate in the system.
Certain groups of algae can then utilise the
ammonia in a complex biochemical process that
results in the accumulation of additional hydrogen
ions and so compounds acidification.
The overall impact of acid precipitation in
terrestrial and aquatic environments is to reduce
biodiversity. It does this by altering
biogeochemical cycling and generating milieu in
which only acidophilous (acid-loving) species can
survive. In both terrestrial and aquatic
environments, there may also be an accumulation
of organic matter as grazing and decomposer food
chains/webs become less active as diversity
diminishes.
regional pollution histories and is examined below
in relation to the UK and the USA.
The spatial distribution of acid precipitation
depends on where high emissions of nitrous and
sulphurous gases occur; the spatial distribution of
the acidification of ecosystems also depends on
prevailing wind directions and the buffering
capacity of soils and bedrock in areas of deposition
(see above). Most of the industrialised world lies
in the temperate zone of the Northern
Hemisphere, so it is here that the problems of acid
precipitation and its deposition are most acute.
The regions so far identified (Figure 3.4) as those
with the most severe problems are Scandinavia,
parts of northern Europe and Russia, parts of
China, the northeast USA and eastern Canada.
Case studies from these regions are discussed
below. In part, the problems arise because these
areas are themselves major producers and/or
receivers of acid precipitation. The data given in
Tables 3.1 and 3.2 show that the major producers
of sulphurous and nitrous oxides are the USA,
China, Germany and the Russian Federation. As
industrialisation proceeds in developing countries,
and their consumption of fossil fuel increases, acid
precipitation and its deposition will become a
problem in tropical regions and in the Southern
Hemisphere, as shown in Figure 3.4.
The introduction of measures to curb
sulphurous emissions in Europe and North
America in 1985 (the '30 percent club') has
brought some rewards. As Table 3.1 shows,
sulphurous emissions from many countries have
declined. This is due partly to the use of less
sulphur-rich fuels, energy efficiency programmes,
and to the installation of desulphurisation
technology in power stations. There are also calls
for positive measures of a similar kind to curb
nitrous gas emissions, although in general these
have fallen as sulphurous emissions have fallen.
International agreements to curb carbon dioxide
emission through energy-efficiency programmes
will also cause acid emission to decline. The
reduction of sulphurous emissions has led to
ecosystem recovery in some regions, as is discussed
below. Amelioration on a short-term basis has also
proved successful. This involves the liming of
The geography of acid precipitation
Acid precipitation has varied temporally and
spatially. Temporally, it began on a large scale in
the mid-1700s as industrialisation intensified and
spread through Britain and Europe. In the
Northern Hemisphere, the impact and timing of
acid precipitation has varied according to the
buffering capacity of specific environments as well
as the location of industry in relation to prevailing
wind directions. Its widespread occurrence at the
hemispheric scale is reflected in polar ice core
records. Ice cores from the Arctic show a
substantial increase in acidity from
c
. 1800. In
addition, the record of nitrous oxide in
preindustrial times was c. 275 ppbv (Raynaud
et
al
. 1993) rising to
c
. 312 ppbv in 1994 (Houghton
et al
. 1996), although some of this increase is due
to biomass burning and nitrate fertiliser use (see
Mannion 1998). Further aspects of the temporal
dimensions of acid precipitation have been
revealed through studies of lake sediments and
peats. Such research provides a record of local and
