Climate Change and the European Water Dimension - Agri ...

vertical bars are a simple measure of water column stability. Algal blooms of this kind
are commonly regarded as a symptom of eutrophication. Here, the key factor
influencing the appearance of these summer blooms was the quasi-cyclical variation
in the intensity of wind mixing. In a warmer climate-changed world, algal blooms of
this kind will appear much earlier in the year and may also be more persistent if the
trend towards lower summer wind speeds is sustained in the Atlantic Region.
Aphanizomenon (de-trended)
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1955 1960 1965 1970
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Figure IV.B.6. Factors influencing blue-green algae growth in Esthwaite
Water, UK (George et al., 1990)
Besides direct effects on phytoplankton growth conditions, climate change may alter
the cascading top-down relations in the food chain (Scheffer et al., 2001). In a
warmer world the biggest increase in phytoplankton biomass due to released grazing
control can be expected in arctic lakes (Flanagan et al., 2003).
Macrophytes
An littoral zone experiment under different temperature regimes in Finland showed
that, during warmer conditions, macrophytes emerged earlier and developed faster,
which led to a two-fold higher above ground biomass. Additionally, an increase in
filamentous green algae in the littoral zone was recorded (Kankaala et al. 2000).
Very little is known about how macrophytes will be impacted by climatic change in
alpine lakes. From the few observations of temperature effects on submerged plants
it can be concluded that increase in water temperature will generally affect growth
and decay of plant material. Moreover, invasive plants will be favoured and already
endangered species might be lost (Dokulil et al., 1993).
Zooplankton
The combined effects of predation and the availability of food regulate the
zooplankton populations that dominate the open water communities of lakes. Most
weather-related effects are mediated by changes in the quantity and quality of food
(George et al, 1990). The consequences of a sustained change in the fish
community on the open water food-web are more difficult to predict but could include
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Temperature gradient ( o C m -1 )