Environmental Engineering Reference
In-Depth Information
12
Restoration of freshwater lakes
Ramesh D. Gulati and Ellen van Donk
12.1 Introduction
The goal of ecosystem restoration is to emulate a
natural and self-regulating system that is integrated
within its ecological landscape (Berger 1990). In
practice, lake restoration is considered synonymous with
improvements in water quality defined in terms of
clarity, oxygen conditions and the amount of algae,
to improve lake conditions designated for human use:
recreation, fishing and water supply. Most restoration
projects aim at improving the important ecological
attributes of lakes, rather than at the return of lakes
to a pristine condition. Such attempts are focused prim-
arily on eradicating the undesirable consequences
of the man-induced disturbances. Lake-restoration
work in the USA and western and northern Europe
started in the early 1970s (e.g. Bjork 1972). By 1975
the US Environmental Protection Agency initiated
the Clean Lakes Program by amending the Federal
Pollution Control Act. Subsequently, more federal
funds were provided to clean more than 300 lakes
in 47 federal states. The restoration work on Lake
Trummen in Sweden that involved sediment removal
and fish manipulation is a classic example of lake
restoration in Europe (Bengtsson
et al.
1975,
Andersson 1988). Also, restoration of acidified lakes
by liming, as in the north-eastern USA, became a relat-
ively common practice in Scandinavia. Restoration is
steadily becoming an essential part of national and
international efforts to improve both water quality and
the ecology of freshwater ecosystems (NRC 1992), esp-
ecially in western Europe, the USA and Canada (Cooke
et al.
1993). Most of the national action plans to restore
the many threatened rivers, lakes and wetlands were
developed in the 1980s. Their execution not only
involved cooperation among scientists and engineers,
but also called for positive feedback from legislators,
The development of modern society, especially the
human population explosion and intense industrial
urban developments, in the last four decades has
caused inland surface waters to become heavily
enriched by agricultural fertilizers and toxic sub-
stances (Forsberg 1987). The man-made alterations
to freshwater aquatic ecosystems worldwide - lakes,
reservoirs, wetlands and rivers - have been both
severe and destructive. Despite the recent attempts to
restore ecosystems under stress, freshwaters continue
to be perhaps the most vulnerable of habitats. In the
Western world, lakes and reservoirs are recreation
attractions (for water sports such as swimming, boat-
ing and angling). In addition, they are major sources
of water for drinking purposes, irrigation, industry,
transport and floodwater storage. While the lakes act
as sinks for many of the products of human activity
in their catchments, rivers drain human and animal
wastes and other wastewater effluents into the sea.
Increasing demand for fresh water by humans has led
to the creation of storage reservoirs in the floodplains
of many river systems (Moss 1998). Management
strategies for these aquatic ecosystems, including
wetlands, often ignore their regional watershed con-
text, hydrology and economic relationships.
For sustained and long-term use, many aquatic
ecosystems need not only to be
protected
by abate-
ment of pollution but also
restored
or
rehabilitated
.
Several studies are under way in the USA and Europe
to facilitate the return of the disturbed ecosystems to
conditions prevailing prior to the disturbance (see
examples in Gulati & van Donk 2002, NRC 1992, Cooke
et al.
1993).
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