Geoscience Reference
In-Depth Information
Hg content
(ng g
−
1
ds)
0 800 1600
0
20
40
60
80
100
1970
1930
Vardsatra
Bay
1890
LAKE
EKOLN
1850
River
Fyris
Mercury content
(ng g
−
1
ds)
1600 -2000
1200 -1600
800 -1200
400 -800
200 -400
0-200
Graneberg
Bay
N
Hg content
(ng g
−
1
ds)
0 400
0
20
40
60
80
1970
1930
1890
1850
Fig. 4.16
Sediments as a historical archive
illustrating both the areal and the temporal
perspectives of ongoing changes, here
exemplified by the mercury contamination in
Lake Ekoln, Sweden. The sediment age has been
determined from data on sedimentation in
sediment traps. The main tributary to this lake
is River Fyris and mercury is transported to the
lake from different sources (hospitals, dentists,
laboratories, etc.) mainly from the city of
Uppsala. (Modified from Håkanson &
Jansson 1983.)
Hg content
(ng g
−
1
ds)
0 400
1970
1890
20
40
60
0 1.5
km
threats as a basis for action, but to have a more
objective approach. There is a growing aware-
ness that much better individual 'indicators'
and aggregated 'indices' of environmental health
are necessary because they alone can provide
a rational structure for decision-making in
the environmental sciences (Bromberg 1990;
OECD 1991). An index (an aggregated measure)
is generally distinguished from an indicator
(a single variable), and an ecosystem (a single
instance, such as a lake or a field) from an eco-
system type (the summation of several to many
ecosystems).
A frame of reference is required to assess
the status of the environment. Since 1987, many
countries have accepted 'sustainable develop-
ment' as a goal for environmental and economic
policy. The term was introduced in the final
report of the Commission for Environment and
Development (the Brundtland Commission). This
phrase is empty, however, unless it is defined in
terms of operationally measurable properties,
desired goals and relevant data. There are altern-
atives to choosing ecosystems as the basis for
environmental typology (Mackay & Paterson
1982; O'Neill et al. 1982; Cairns & Pratt 1987).
