Environmental Engineering Reference
In-Depth Information
environmental protection agencies and industry. In
addition, feedback from citizen groups seemed to
have been essential for propagating public aware-
ness. During the last three decades some 25 lake-
restoration techniques have been developed and tested
for their overall effectiveness, type and intensity of
recurring problems, cost per unit area, required fre-
quency of employment and range of applicability, etc.
Since the early 1980s a biological means of lake
restoration, so-called
lake biomanipulation
, has be-
come extremely popular, both in Europe (Benndorf
1987; see references in Gulati
et al.
1990; see also the
review by Gulati & van Donk 2002) and North
America (Shapiro
et al.
1975, Lynch & Shapiro 1981,
Shapiro & Wright 1984). Lake restoration is now
among the major environmental focal points relating
to water management in general (Gulati & van Donk
2002; see also Nienhuis & Gulati 2002).
We present a state-of-the-art résumé of the
methods of aquatic ecosystem restoration in progress
in Europe and the USA: especially in north-west
Europe. We assess the types of disturbance, identify
the problems and main symptoms, discuss briefly the
lake-restoration techniques in use and draw some
conclusions.
12.2.1 Eutrophication
Eutrophication is a natural ageing process of lakes that
causes a steady increase in biological production due
to a gradual accumulation of nutrients and a slow
decrease in lake depth. In classical terms, eutrophica-
tion is the enrichment of water by inorganic plant
nutrients, especially N and P. The increasing eutroph-
ication in the early 1970s of the Great Lakes and other
lakes and reservoirs in the United States, Canada and
western Europe (Vollenweider 1968, Schindler 1974,
Vollenweider & Kerekes 1981) raised widespread pub-
lic concern. General recognition of P enrichment and
the related eutrophication problems led to large-scale
research funding by the state agencies. Whole-lake
experiments in eutrophication (e.g. Schindler 1974)
and development of eutrophication models provided
insight into the quantitative relationships between
nutrient loading rates and algal biomass and pro-
duction (Vollenweider 1987). The eutrophication
definition has been expanded to include the loading
with silt and dissolved and particulate organic mat-
ter (Cooke
et al.
1993). Human activities typically alter
the hydrology and increase the nutrient loads into lakes,
thereby accelerating the eutrophication processes.
The main causal factors for eutrophication are direct,
point discharge of human and animal wastes and non-
point, agricultural runoff from the catchment into these
lakes. Consequently, the rates of algal production and
nutrient accumulation in the lake sediments rise,
leading to an increase in loading from in-lake pro-
cesses (Rast & Thornton 1996), so that the effects of
eutrophication persist and build up over time.
In temperate regions the spring-time increases in light
and water temperature in eutrophic lakes generally
result in enhanced algal production, dominated by
filamentous cyanobacteria, formerly called blue-green
algae. Consequently, the turbidity of the water rises
and the underwater light climate deteriorates. Many
genera of filamentous cyanobacteria (e.g.
Oscillatoria
,
Anabaena
and
Aphanizomenon
) and the colony-
forming cyanobacterium
Microcystis aeruginosa
, a
cosmopolitan species, dominate the phytoplankton of
eutrophic lakes. These cyanobacteria reach bloom
conditions that may persist during the growing
season. The ability of cyanobacteria to grow better than
other algae over a wide range of nutrient levels as
12.2 Ecosystem disturbances
Several studies have dealt with restoration or rehab-
ilitation of aquatic ecosystems during the last three
decades (Cooke
et al.
1993; see references in Gulati
& van Donk 2002). It is now well known that
increases in nutrient input, organic matter, silt and con-
taminants to lakes and reservoirs cause a deteriora-
tion of water quality. The stressed water bodies
manifest themselves with an increased growth of
algae, water plants or both, causing reduced water
transparency and even a marked decrease in water
volume due to the accumulation of organic matter
including detritus. The most obvious, persistent and
widespread water-quality problems related to human
use of lakes and reservoirs are
eutrophication
and
acidification
. These two issues have received world-
wide attention since the 1970s. In this chapter, while
recognizing that there are many other disturbance and
stress factors, we focus on the main causes and
symptoms of these two major disturbances.
