Geoscience Reference
In-Depth Information
Instead, one might use different geographical
areas or different media such as air, water and
soil. There is, however, a clear international trend
towards consideration of the 'health' of differ-
ent ecosystems (Bailey et al. 1985).
The majority of threats involve chemicals. A
set of ecological effect variables is expected to
reflect such threats and the extent to which they
affect the ecosystem. There is also a difference
between biological effects for individual ani-
mals or organs and ecological effects for entire
ecosystems. Practically useful, operational effect
variables should be measurable, preferably sim-
ply and inexpensively, clearly interpretable and
predictable by validated quantitative models,
internationally applicable, relevant for the given
environmental threat and representative for the
given ecosystem.
Ecosystem indices would have the advantage
of expressing the environmental status simply,
but they simultaneously pose problems in that
a great deal of valuable information is lost in
aggregating the individual measures. This dis-
advantage is reduced if it is known exactly what
an index represents, and if these individual com-
ponents can be accessed as required. Ideally, the
same basic framework would be used at both the
national and regional scales. As problems and
priorities cannot be completely congruent at
different levels, however, the framework may be
adapted to the different requirements of different
levels. The national level may address large-scale
threats, perhaps originating outside the country,
such as acidification of soil and water, whereas
the region can address more local problems, such
as the eutrophication of lakes (Case Study 4.3).
Case study 4.3 Impact of eutrophication/oligotrophication: Lake Miastro, Belarus
The following case study concerns Lake Miastro, Belarus (see Case Table 4.2 for lake data;
for further details about the scenario, see HÃ¥kanson & Boulion 2002) and uses the well tested
lake foodweb model, LakeWeb, for the simulations. The aim here is to illustrate both the
effect-load-sensitivity analysis and how changes in a critical load factor (the tributary con-
centration of total phosphorus, TP) will cause, first, changes in lake phosphorus concentrations,
in concentrations of suspended particulate matter (SPM) and in sedimentation. It also shows
how such changes will influence target operational effect variables in lake management, such as
Secchi depth (a measure of water clarity) and algal volume (a measure of lake trophic level). In
1990 a drastic and sudden change in agricultural land-use practices occurred in the catchment
area of this lake. The use of imported fertilizers was stopped as a result of political changes
related to the fall of the former Soviet Union.
The presuppositions for this scenario are given in Case Fig. 4.3a, with the 'modelled values'
curve illustrating the sudden change in tributary total phosphorus (TP) concentrations in week
261 (
January 1990; week 1 is the first week of 1985 and the simulation covers a period of
10 yr). There are good empirical data for this scenario (from Professor Alexander Ostapenia,
Belarus State University, Minsk) giving mean characteristic monthly values for the period 1985
to 1989 for lake TP concentrations (see Case Fig. 4.3b) and TP concentrations in sediments
(Case Fig. 4.3e). One can first note the good correspondence between modelled values of lake
and sediment TP concentrations and empirical data. The following question is addressed in this
scenario (from Case Fig. 4.3b), how will the changes in TP concentrations in the lake influence
important sedimentological variables?
From Case Fig. 4.3c, one can note that the oligotrophication would likely imply a decrease in
suspended particulate matter (SPM) concentrations because the algal volume would go down
(Case Fig. 4.3g). This would also mean that sedimentation of matter decreases (Case Fig. 4.3d)
=
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