Environmental Engineering Reference
In-Depth Information
well as fix the atmospheric nitrogen, together with their
relatively poor edibility by zooplankton, allows them
to attain both high densities and biomass. They can
thus persist and dominate the phytoplankton of many
shallow lakes throughout the growth period, and
even overwinter. Lastly, several species of cyanobac-
teria can produce potent toxins, which are a matter
of great concern from the viewpoint of human and
animal health (Codd 2000, Chorus 2001).
Rast and Holland (1988) provide a scheme with a
sequence of decisions to be made in the development
and implementation of eutrophication measures in lakes
and reservoirs (Fig. 12.1). The scheme takes into
account the different concerns and cost-effectiveness
in the selection of feasible remedial measures. A
practical framework for the management of lakes and
reservoirs is to (i) assess the available information,
(ii) identify eutrophication problems for establishing
management strategies and control measures, (iii) ana-
lyse costs and expected benefits of alternative manage-
ment strategies and the adequacy of institutional and
regulatory frameworks for implementation of a given
strategy and (iv) select a control strategy and pub-
licity measures and evolve mechanisms to minimize
the recurrence of eutrophication problems..
Establish
Objectives
(based on desired use
of waterbody)
Institutional
concerns
Regulatory
concerns
Assess factors
affecting achievement
of objectives
Water demand
Problems/conflicts
Land usage
Water quality
Identify available
remedial measures
to achieve objectives
Sociological
concerns
Technical
concerns
Assess cost-effectiveness
of alternatives
in relation to
achieving objectives
Ecological
concerns
Economic
concerns
Selection of
most feasible
remedial measures
Implementation
of remedial
programmes
12.2.2 Acidification
Acidification is only second to eutrophication among
the most widespread anthropogenic changes in lakes,
reservoirs and streams. The regions most vulnerable
to acidification, where critical loads have been ex-
ceeded, are Scandinavia, North America and the UK.
In the first two regions, acidification has caused great
damage to fish populations in lakes (e.g. Henriksen
et al.
1989). Schindler (1988) documented the effects
of acid rains on freshwater ecosystems in a paper that
attracted a lot of attention. Precipitation in parts of
Europe and North America has a pH well below 4.7
(so-called acid rain), compared with a pH of
c
.5.6 for
pure rain water. The elevated acidity in the rain-
water is due mainly to polluted air masses containing
S and N compounds (SO
2
and NO
x
), released from the
burning of fossil fuels, transported by winds thousands
of kilometres away from the place of their origin -
across the national boundaries - and transformed by
photo-oxidation to sulphuric acid (
c
.70%) and nitric
Assessment
of results
Fig. 12.1
Schematic representation of the sequence of
steps involved in the decision-making process for the
selection and implementation of control programmes
in lakes. Note: the desired use of the waterbody, water
demand and socio-ecological concerns will determine
the choice of most feasible remedial measures. From
Rast and Holland (1988); in Mason (1996). Reproduced
by permission of Ambio.
acid (
c
.30%) before they eventually fall as acid rain.
These emissions are linked via the runoff from ter-
restrial ecosystems and via direct transport and de-
position to aquatic ecosystems (Fig. 12.2; see also
Steinberg & Wright 1994). In addition, in areas with
