Freshwater biodiversity and water quality

Northward shift and changes in occurrence of selected freshwater species

Note: This indicator shows the evolution of the number of observations of Southern European dragonfly species in Flanders. Due to climate change the number of records of Southern European dragonflies increases in Flanders. Some species that were only occasional visitors in the past, such as Lestes barbarus now have permanent populations.

Data source:

Hickling, R.; Roy, D. B.; Hill, J. K. and Thomas, C. D., 2005. A northward shift of range margins in British Odonata. Global Change Biology 11 (3): 502506. (left) Biodiversity Indicators, 2006. Climate Change: Trend of Southern European dragonfly species . Research Institute for Nature and Forest, Brussels. www.natuurindicatoren.be (updated 08.05.2006). Available at www.natuurindicatoren. be/indicatorenportal.cgi?lang=en&detail=404&id_ structuur=25. (right)

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Model simulation of hydrodynamics and phytoplankton dynamics during three contrasting summers in Lake Nieuwe Meer (the Netherlands)

Note: (a) the cold summer of 1956, (b) the average summer of 1991, and, (c) the hot summer of 2003

Data source:

Jöhnk, K. D.; Huisman, J.; Sharples, J.; Sommeijer, B.; Visser, P. M. and Stroom, J. M., 2008. Summer heatwaves promote blooms of harmful cyanobacteria. Global Change Biology 14: 495512.

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The share of Trichoptera taxa sensitive to climate change in the European ecoregions

Note: Trichoptera taxa are species with restricted distribution ('endemic species'), species inhabiting the crenal zone (springs), that cannot move further upstream, and species adapted to low water temperatures (cold stenothermy) in European ecoregions

Data source:

• Ecoregions for rivers and lakes provided by  European Environment Agency (EEA)

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Past trends

Northward and upward movement
There are European examples of aquatic species (dragonflies, brown trout) that have shifted their ranges to higher latitudes (northward movement) and altitudes in response to climate warming. Thermophilic fish and invertebrate taxa will to a certain extent replace cold-water taxa. Examples include the brown trout in Alpine rivers (Hari et al., 2006), non-migratory British dragonflies and damselflies (Hickling et al., 2005; Figure 1 left), and south European Dragonflies in Belgium (Biodiversity Indicators, 2006, see Figure 1 right).

Change in species composition and abundance
Climate change will generally have a eutrophicationlike effect (e.g. Schindler, 2001), with enhanced phytoplankton blooms (Wilhelm and Adrian, 2008), and increased dominance of cyanobacteria in phytoplankton communities, resulting in increased threat of harmful cyanobacteria and enhanced health risks, particularly in water bodies used for public water supply and bathing (Johnk et al., 2008; Mooij et al., 2005; Figure 2). More frequent extreme precipitation and runoff events are also expected to increase the load of nutrients to waters and in turn result in more eutrophication.
Changes in temperature have already had profound impacts on the species composition of macrozoobenthos (fauna that spend most of their lives buried in sediments) in northern European lakes (Burgmer et al., 2007). Fish and invertebrate communities have been found to respond to increases in water temperature in the upper Rhone River in France (Daufresne et al., 2004, 2007).

Phenology changes
Changes in growth season, earlier ice break-up or periods above a certain temperature will change lifecycle events, such as an earlier spring phytoplankton bloom, appearance of clear-water phase (because large zooplankton will appear earlier), first day of flight of aquatic insects and time of spawning of fish. Prolongation of the growing season can have major effect on population abundances with an increased number of cell divisions or generations per year.
Phytoplankton and zooplankton blooms in several European lakes are occurring one month earlier than 30-40 years ago (Weyhenmeyer 1999; 2001; Adrian et al., 2006; Noges et al., in press). Manca et al. (2007) found that increasing temperatures at Lago Maggiore have resulted in earlier and longer zooplankton blooms. Hassall et al. (2007) found that British Odonata species over the period 1960 to 2004 changed their first day of flight by 1.5 day per decade.

Invasive freshwater species
Climate change is expected to result in biological invasions of species that originate in warmer regions. For example, the subtropical filamentous highly-toxic cyanobacterium Cylindrospermopsis raciborskii thrives in waters that have high temperatures, a stable water column and high nutrient concentrations: it has recently spread rapidly in temperate regions and is now commonly encountered throughout Europe (Dyble et al., 2002).
Its spread into drinking and recreational water supplies has caused international public health concerns due to its potential production of toxins. Fish species adapted to warmer waters, such as carp, may replace native species such as perch and trout in many regions (Kolar and Lodge, 2000).

Projections

Many species are projected to shift their ranges to higher latitudes and altitudes in response to climate warming. Southern species will move further north due to further increases of temperature. Species of colder regions will move north and towards higher altitudes or will disappear when their migration is hampered (e.g. due to habitat fragmentation). Some Arctic and alpine species may disappear.

• Increased eutrophication with enhanced algal blooms, also including new harmful invaders such as Cylindrospermopsis and Gonyostomum semen, is a possibility supported by several recent publications and observations (Findlay et al., 2005; Wilhelm and Adrian, 2008; Johnk et al., 2008; Battarbee et al., 2008; Willen and Cronberg, pers. com.), particularly in areas of Europe exposed to more heavy rains that can cause increased nutrient loading and reduced underwater light in lakes.
• A comparison of a large set of Danish shallow lakes with a corresponding one located in the colder climate of Canada (Jackson et al., 2007) suggests that warming will decrease winter fish-kills and enhance the overwintering success of planktivorous fish which, in turn, suppress Daphnia/zooplankton development. As a result of decreased zooplankton grazing pressure, there will be more phytoplankton biomass build up per unit total phosphorus in warmer climate. 
•  Where river discharges decrease seasonally, there may be negative impacts on Atlantic salmon. Walsh and Kilsby (2006) found that salmon in northwest England will be affected negatively by climate change by reducing the number of days with suitable flow depths during spawning time.
• In the ongoing European research project Euro-limpacs there has been an evaluation of the sensitivity of Trichoptera taxa (Caddisflies) to climate change (see Figure 3). The main results are that more than 20 % of the Trichoptera species are projected to be endangered due to climate change in southern Europe (droughts) and in the Alpine region (too high temperatures), whereas the impacts in other parts of Europe would be less pronounced (Hering et al., 2006).