Environmental Engineering Reference
In-Depth Information
18.1
INTRODUCTION
improve lake conditions designated for human use and
health such as recreation, fi shing, water supply, nature
conservation and biodiversity protection. As is done
throughout this topic, we use the term 'restoration' in
a general sense, while recognizing that most lake res-
toration projects aim primarily at improving the most
important functional attributes rather than a hypo-
thetical return to some kind of pristine ecological con-
dition. In practice, most such attempts focus primarily
on eliminating undesirable consequences of human-
induced disturbances.
Restoration is steadily becoming a critical part of
national and international efforts to improve both
water quality and the ecology of freshwater ecosys-
tems (NRC 1992), especially in western Europe, the
United States and Canada (Cooke
et al
. 2005 ). Lake
restoration work in the United States and western and
northern Europe started in the early 1970s (e.g. Bjork
1972). By 1975, the US Environmental Protection
Agency had initiated the Clean Lakes Program by
amending the Federal Pollution Control Act. Subse-
quently, more federal funds were provided to clean
more than 300 lakes in 47 federal states. Restoration
of acidifi ed lakes by liming, as in the north-eastern
United States, became a relatively common practice in
Scandinavia. In Europe, the Water Framework Direc-
tive (WFD) was established in 2000 (European Union
2000). It requires that in European member states all
inland and coastal waters within defi ned river basin
districts achieve at least a 'good ecological status' by
2015. Moreover, an important aim of the WFD is to
initiate water pollution control by reducing emissions
of harmful substances into waters (see papers in
Solheim & Gulati 2008 ).
Since 1975, some 25 lake restoration measures and
techniques have been developed worldwide and tested
for their effectiveness, cost per unit area, required fre-
quency of employment, range of applicability, etc. (see
in Cooke
et al
. 2005). Since the early 1980s,
lake
biomanipulation
as a tool for lake restoration has
often been used, both in Europe and in North America
(see section 18.3.2). Lake restoration is now one of the
key topics of water management (Gulati & van Donk
2002 ; Nienhuis & Gulati 2002 ).
In this chapter, we present an overview of published
results of ongoing studies of aquatic ecosystem resto-
ration and rehabilitation projects of the past four
decades, especially those in north-western Europe and
North America. Particular emphasis is paid to shallow
lakes, which are particularly susceptible to eutrophica-
The development of modern society, including the
demographic explosion and intense industrial and
urban developments of the past 150 years, but espe-
cially of the last half a century, has caused inland
surface waters to become heavily enriched by agricul-
tural fertilizers and toxic substances. The human-made
alterations to freshwater aquatic ecosystems world-
wide - not only lakes but also reservoirs, various kinds
of wetlands and rivers of all sizes - have been severe
and destructive. Despite recent attempts to restore
some lakes and other bodies of freshwater, these eco-
systems are arguably among the most damaged and
vulnerable of all (Schindler 2006, among others). In
the western world, lakes and reservoirs are recrea-
tional sites and tourist attractions (for swimming,
boating, fi shing etc.). In addition, they are major
sources of water for drinking, irrigation, industry and
transportation, and sink areas for fl oodwater storage.
Whereas lakes and lagoons also act as fi nal sinks for
many of the waste products of human activity, rivers
carry human and animal wastes, and other wastewa-
ter effl uents (urban, industrial and agricultural), down
to the sea. For better or worse, this is a service that
society demands of lakes, lagoons, wetlands and rivers.
Increasing demand for fresh water has also led to the
creation of storage reservoirs in the fl oodplains of
many river systems (Moss 1998). All too often, conven-
tional management plans for these aquatic ecosystems
ignore their regional watershed context, their hydrol-
ogy, and the socio-economic systems of which they
are part.
For sustained and long-term use, many aquatic eco-
systems should be not only protected by abatement of
pollution, but also restored or rehabilitated. Several
restoration studies have been carried out in the United
States and Europe on how to facilitate or accelerate the
return of disturbed wetland ecosystems to functional-
ity similar to the conditions prevailing prior to major
disturbance (e.g. National Research Council (NRC)
1992 ; Cooke
et al
. 2005). The goal of
ecosystem res-
toration
is to emulate or reconstitute a more or less
natural and self-regulating system that is integrated
within its ecological landscape (SER 2004; see also
Chapter 2). In practice, however, what is often called
'lake restoration' is in fact
rehabilitation
. It tends to
focus on improvements in
water quality
(using para-
meters such as water clarity, dissolved oxygen condi-
tions and the amount and species of algae present) to
