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

looms has significantly increased, extending to the Baltic proper and Gulf of Finland
(Finni et al. 2001; Poutanen and Nikkilä 2001), presumably in response to
anthropogenic eutrophication of the coastal waters. However, the fact that
cyanobacteria populations could be part of the natural system indicates that optimal
physical and meterological conditions are also required for their growth. Peperzak
(2003) showed the importance of increasing temperature and stratification in
doubling the growth rate of harmful algae, concluding that the risk of HABs due to
climate change scenarios as suggested by IPCC (2001) will rather increase than
decrease. Belgrano et al. (1999) related the occurrence of toxic phytoplankton
blooms in the Skagerrak to changes in the phase of the NAO, suggesting an
important role of climate forces in HABs formation.
Figure IV.C.9. Global maps of the distribution of organisms associated with the
production of the toxic syndrome Paralytic Shellfish Poisoning (PSP). The increasing
occurrence of this toxic material from 1970 (upper panel) to 2000 (lower panel) indicates a
stronger impact in the northern hemisphere, and polluted coastal areas. (Source: GEOHAB
Science Plan. http://www.jhu.edu/~scor/GEOHAB_2001.pdf).
Increasing nutrients, higher productivity and increased stratification due to freshwater
inflow have also lead to a drastic decrease in the oxygen content of the water
column, establishing a hypoxic or even anoxic subsurface layer causing mass
mortalities in the benthic and demersal communities. The combination of N fertilizer
applications, land-use changes and increase in runoff on the Mississippi river basin
has lead to the occurrence and extension of a low oxygen ‘dead zone’ in the Gulf of
Mexico bottom waters which can extend as far as 130 km offshore (Rabalais et al.
1996; Turner and Rabalais 1991)
Eutrophication is also a widespread problem in European coastal waters, favoring the
occurrence of hypoxic conditions in sensitive areas such as enclosed or semienclosed
seas. Permanent anoxic conditions are well-known in the Black Sea. In
other regions such as the Baltic, the frequency of anoxic periods has been increasing
(Figure IV.C.10) as a result of eutrophication, as well as a reduction in the intrusion
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