Geography Reference
In-Depth Information
Figure 3.4
Areas currently experiencing problems due to acid precipitation and areas likely to develop
problems in the future.
Source:
Based on Rodhe and Herrera 1988.
acidified lake ecosystems; however, its impact is
short-lived, a product of treating symptoms rather
than the underpinning causes.
Research has also focused on the
identification of areas susceptible to acidification;
this has led to the formulation of the 'critical
load' concept. This is a measure of the amount of
acid deposition that can be absorbed by an
ecosystem or environment without causing
damage. Critical load is the central concept of
the Oslo Protocol signed in 1994. Signatories
pledged to reduce acidic emissions so as not to
exceed critical loads for vulnerable regions. Thus
the critical load concept is a management tool
and can be used to model future environmental
change in response to increased or decreased acid
precipitation. The determination of critical load
is, however, dependent on information about the
volume of acid deposition, the buffering capacity
of soils, bedrock, etc., vegetation type, and
hydrology. For example, Arp
et al
. (1996) have
used a steady-state mass-balance model for
calculating critical sulphur and nitrogen loads in
upland forests of southern Ontario, Canada. This
model used data on wet atmospheric deposition
of major cations and anions, the availability for
plant use of nitrogen, calcium, magnesium and
potassium in the rooting spaces of soils, nutrient
uptake and retention in the forest biomass,
estimates of soil weathering, mean annual air
temperature, precipitation, and evaporation. This
reflects the many factors involved in the
calculation of critical loads and the importance
of environmental monitoring stations to provide
the necessary baseline data.
One example of such a monitoring network
is that of the UK Acid Waters Monitoring
Network (AWMN), which was established in
1988 (Patrick
et al
. 1996). It consists of eleven
lake and eleven stream sites in acid-sensitive areas
of the UK. The chemical and biological
characteristics of these sites are monitored and
together with the palaeolimnological record of
the lake sediments and data from the UK
precipitation monitoring network, they can be
used to determine acidification trends. Such data
