12.4.5 Wetlands and aquatic ecosystems
Climate change may significantly impact northern peatlands (Vasiliev et al., 2001). The common hypothesis is that elevated temperature will increase productivity of wetlands (Dorrepaal et al., 2004) and intensify peat decomposition, which will accelerate carbon and nitrogen emissions to the atmosphere (Vasiliev et al., 2001; Weltzin et al., 2003). However, there are opposing results, reporting decreasing radiative forcing for drained peatlands in Finland (Minkkinen et al., 2002). Loss of permafrost in the Arctic (ACIA, 2004) will likely cause a reduction of some types of wetlands in the current permafrost zone (Ivanov and Maximov, 2003). During dry years, catastrophic fires are expected on drained peatlands in European Russia (Zeidelman and Shvarov, 2002; Bannikov et al., 2003). Processes of paludification are likely to accelerate in northern regions with increasing precipitation (Lavoie et al., 2005).
Throughout Europe, in lakes and rivers that freeze in the winter, warmer temperatures may result in earlier ice melt and longer growing seasons. A consequence of these changes could be a higher risk of algal blooms and increased growth of toxic cyanobacteria in lakes (Moss et al., 2003; Straile et al., 2003; Briers et al., 2004; Eisenreich, 2005). Higher precipitation and reduced frost may enhance nutrient loss from cultivated fields (Eisenreich, 2005). These factors may result in higher nutrient loadings (Bouraoui et al., 2004; Kaste et al., 2004; Eisenreich, 2005) and concentrations of dissolved organic matter in inland waters (Evans and Monteith, 2001; ACIA, 2004; Worrall et al., 2006). Higher nutrient loadings may intensify the eutrophication of lakes and wetlands (Jeppesen et al., 2003). Streams in catchments with impermeable soils may have increased runoff in winter and deposition of organic matter in summer, which could reduce invertebrate diversity (Pedersen et al., 2004).
Inland waters in southern Europe are likely to have lower volume and increased salinisation (Williams, 2001; Zalidis et al., 2002). Many ephemeral ecosystems may disappear, and permanent ones shrink (Alvarez Cobelas et al., 2005). Although an overall drier climate may decrease the external loading of nutrients to inland waters, the concentration of nutrients may increase because of the lower volume of inland waters (Zalidis et al., 2002). Also an increased frequency of high rainfall events could increase nutrient discharge to some wetlands (Sánchez Carrillo and Alvarez Cobelas, 2001).
Warming will affect the physical properties of inland waters (Eisenreich, 2005; Livingstone et al., 2005). The thermocline of summer-stratified lakes will descend, while the bottom-water temperature and duration of stratification will increase, leading to higher risk of oxygen depletion below the thermocline (Catalán et al., 2002; Straile et al., 2003; Blenckner, 2005). Higher temperatures will also reduce dissolved oxygen saturation levels and increase the risk of oxygen depletion (Sand-Jensen and Pedersen, 2005).