Environmental Engineering Reference
In-Depth Information
Figure 18.9
Diagrammatic depiction of different restoration methods applied to lakes, illustrating also the predicted effects
of climate change on lake restoration measures. The possible restoration measures (as discussed in the text) are shown in
boxes and numbered. The circle on the right side of the fi gure shows how biomanipulation operates: it leads to reduction of
planktivorous fi sh (PL) and increase of piscivorous fi sh (PI). See text for its effects on the food web. Climate changes are likely
to negate effects of some of the restoration measures, especially nutrient reduction (increase in both nutrient release from the
bottom and external nutrient loading) and on the food web (positive effects on planktivore fi sh and inedible phytoplankton and
negative effects on piscivore fi sh in temperate waters), hence hampering biomanipulation efforts. These negative effects of the
climate change are portrayed as the three unhappy smileys.
know little about long-term climate change and its
consequences for hydrology and water management
practices (e.g. the impact of fl ooding or droughts, or
both, as well as of human water use on ecosystems).
However, several model studies predict that warming
will act as a catalyst for higher growth of cyanobacte-
ria in lakes at higher temperatures than other phyto-
plankters (Paerl & Huisman 2008). According to
Jeppesen
et al
. (2007b), global warming is expected to
intensify eutrophication and its symptoms, via nutri-
ent loading, increased rates of evaporation losses and
changes in water levels. For example, the fi sh commu-
nity structure could be affected by increases in tem-
perature, eutrophication and salinity. Both the life
history traits and the feeding behaviour of many
organisms are likely to be affected: changes in life
history of many fi sh species (like a shorter body size
and life span) will lead to changes in fi sh community
compositions in lakes. As a result of this, less predators
will be present which will benefi t herbivores, plankti-
vores and omnivores and, hence, a disruption of the
food chain may take place (see section 18.3.2). Together
with increasing temperature, these changes will lead
to greater predation pressure of fi sh on zooplankton
and macro-invertebrates. Such a scenario seems to be
especially valid for temperate lakes where temperature
rises are perhaps relatively easier to predict. Successful
biomanipulation will therefore probably be more diffi -
cult under a changing climate. Finally, the predicted
climate changes expected to intensify the negative
impact of eutrophication on water quality in temper-
ate waters (Mooij
et al
. 2005 ). Figure 18.9 illustrates
the different restoration measures as discussed in the
text, and shows which of these measures are negatively
impacted by climate change. Regarding tropical waters,
we do not have at present the basic information, espe-
cially on biological aspects of lake restoration, let alone
predicting the climate change effects for these waters.
Lake restoration plans nowadays typically envisage
near - natural restoration
, that is, allowing nature to take
its course, and emphasizing that a lake is an integral
part of a landscape comprising other aquatic, semi-
aquatic and terrestrial ecosystems (see papers in Nien-
huis & Gulati 2002) and taking climate change into
