Environmental Engineering Reference
In-Depth Information
macro-invertebrate community in streams in Wales
(Wade
et al.
1989). In invertebrates in acid waters, espe-
cially crustaceans and gastropods, the transport of Na
+
,
Cl
−
and K
+
ions is upset and Na
+
in body fluids
decreases. In fish stressed by acidity, there may be a
decline in body Na
+
and Cl
−
contents.
Aluminium is toxic to fish in the pH range 5.0 -5.5
and Al
3+
ions interfere with the regulation by calcium
of gill permeability, with enhanced loss of sodium. Five
major functions that are adversely affected are: ion
regulation, osmoregulation, acid/base balance, nitro-
gen excretion and respiration (Brakke
et al.
1994). The
loss of Na
+
and a decrease in Cl
−
ions in the blood
plasma causes the body cells to swell and extracellu-
lar fluids to become more concentrated. Reports of
the death of Atlantic salmon (
Salmo salar
) in Norway
in the 1900s and of brown trout (
Salmo trutta
)
in mountain lakes in Norway in the 1920s and 1930s
were all attributed to an increase in acidity. The
numbers of such lakes doubled by 1986 (Henriksen
et al.
1989). In Finland, roach (
Rutilus rutilus
) were
reported to be the most sensitive species, disappear-
ing from many waters in the 1980s. Even the relat-
ively hardy species whitefish (
Core
go
nus peled
) and
perch (
Perca fluviatilis
) exhibited reproductive dam-
age. There are also reports of similar effects on fish
populations in several eastern provinces of Canada.
In conclusion, periodic mortality of fish during the early
stages of development and growth due to acid episodes
causes the populations to decrease and disappear.
Social aspects
Technological inputs
Nature of water use
(aquatic ecosystems)
RESTORATION
MEASURES
Problems
Scientific studies
Public awareness
Funding
Politics and economy
Fig. 12.4
Strategic principles of lake restoration. The
choice of restoration measures will depend both on
direct and indirect factors related to nature of water
use, problems relating to water quality and scientific
studies (thick arrows). From Gulati (1989); see also
Vollenweider (1987).
funding, scientific knowledge and restoration measures
on the other (Fig. 12.4; see Vollenweider 1987, Gulati
1989). Most lake-restoration methods are directed at
reducing external P inputs into lakes. The restoration
techniques invariably need to be applied simul-
taneously to ensure some success (see for example in
Ryding & Rast 1989, Cooke
et al.
1993). The choice
of lake-restoration or -recovery measures has to be
considered in the context of different human influ-
ences and the limnological characteristics of the lake
to be restored. For restoring eutrophic lakes we can
divide the measures into two main types:
external
and
in-lake
control measures (Fig. 12.5; Ryding
1981, Gulati 1989). The external control measures start
with the diversion of sewage and wastewater inputs
and the prevention of external nutrient-rich inputs into
the waterbody to be restored. The
in-lake
restoration
measures involve decreasing internal P loading by vari-
ous physico-chemical control measures (see below), by
the so-called biomanipulation of the lake's foodweb
structure and functioning, or by using both sets of
12.3 Techniques of lake restoration
Lake and reservoir management and restoration tech-
nologies developed rapidly during the 1980s in the USA,
Canada and Europe (Cooke
et al.
1993), especially in
the Netherlands, Denmark, Germany and the UK,
prompted by research into the nature of the problems
faced. The new developments have enabled discernible
changes in the perspectives of and approaches to
lake restoration. An important basis of the restoration
and management measures to be applied depends on
users' interests; that is, the economic and recreative
utility of the waterbody. Strategic principles of lake
restoration combine the social aspects and available
technology. They include the nature of water use, prob-
lems and public awareness on the one hand and
