Climate change impacts and vulnerability in Europe 2016

Climate change impacts on environmental systems
4.3.6 Freshwater ecosystems and water quality
Key messages
• Coldwater species have been observed to move northwards or to higher altitudes in response to increased temperatures.
• Increasing water temperatures can lead to earlier and larger phytoplankton blooms and to species invasions. For
example, the recent rapid spread of the highly toxic cyanobacterium Cylindrospermopsis raciborskii throughout Europe
and into other temperate regions has caused international public health concerns.
• A warmer and wetter climate can lead to increased nutrient and dissolved organic carbon concentrations in lakes and
rivers, but management changes can have much larger effects than climate change.
This section presents selected information on the
impacts of changes in the indicators presented above
for freshwater ecosystems and water quality. This
information is not presented in the indicator format
because several different impacts are foreseen for
aquatic species and ecosystems, and the message
cannot be conveyed simply in one indicator. More
information can be found in the many reviews of climate
change impacts on freshwater (see, for example, Kernan
et al., 2011; Dokulil, 2013; Jeppesen et al., 2014; Vaughan
and Ormerod, 2014; Arnell et al., 2015).
Changes in the river flow regime
River flow regimes, including long-term average flows,
seasonality, low flows, high flows and other types of
flow variability, play an important role in freshwater
ecosystems. Thus, climate change affects freshwater
ecosystems not only through increased temperatures
but also through altered river flow regimes (van Vliet
et al., 2013).
Changes in phenology
Increasing temperatures will change the life-cycle
events and stimulate an earlier spring onset of various
biological phenomena, such as phytoplankton spring
bloom, clear water phase, the first day of flight for
aquatic insects and the time of spawning of fish.
Prolongation of the growing season can have major
effects on species. For example, British Odonata
dragonflies and damselfly species have changed their
first day of flight by 1.5 days per decade on average over
the period 1960 to 2004 (Hassall et al., 2007), and there
is growing evidence for an advancement of phenological
events in zooplankton (Vadadi-Fülöp et al., 2012).
Changes in species distribution
Increased water temperatures will favour warmwater
species, whereas coldwater species will become more
limited in their range. Examples of northwards-moving
species are non-migratory British dragonflies and
damselflies (Hickling et al., 2005) and south European
dragonflies (INBO, 2015). Species have also been
observed to move to higher altitudes, such as the
brown trout in Alpine rivers (Hari et al., 2006).
Facilitation of species invasions
Climate change is facilitating biological invasions
of species that originate in warmer regions.
For example, the sub-tropical cyanobacterium
Cylindrospermopsis raciborskii thrives in waters that
have high temperatures, a stable water column and
high nutrient concentrations. This highly toxic species
has recently spread rapidly in temperate regions and
is now commonly encountered throughout Europe
(Haande et al., 2008; Antunes et al., 2015). Its spread
into drinking and recreational water supplies has
caused international public health concerns (see also
Section 5.2.6).
Changes in algal blooms and water quality
Climate change is affecting water quality in various
ways. Higher temperatures stimulate mineralisation of
soil organic matter, which leads to increased leaching
of nutrients, especially nitrogen and phosphorus
(Battarbee et al., 2008; Jeppesen, Kronvang et al., 2010).
Decreases in stream flow, particularly in summer,
will lead to higher nutrient concentrations owing to
reduced dilution (Whitehead et al., 2009), whereas
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