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

ventilated to the atmosphere and contribute to the formation of clouds, providing thus
a feedback mechanism to global warming.
The production of organic carbon from phytoplankton photosynthesis (reaction 2) is
enhanced, by an increase of atmospheric CO2 and water pCO2. In addition, the
fixation of inorganic carbon by algae is intimately coupled to the nutrient cycle and
light. Assuming that coastal water is not limited with inorganic carbon, any change in
climate directly affecting nutrient inputs and illumination will either stimulate or inhibit
primary production, and the growth of phytoplankton. It is commonly recognized that
organic production in most coastal systems is N-limited. In other words, a moderate
enrichment of coastal waters with nutrient, particularly N, from higher river runoff and
atmospheric deposition could sustain an optimal productivity of the ecosystem with
an efficient transfer of energy between all trophic levels up to fish species of
economical interests.
A recent study in Danish waters (Figure IV.C.8) showed that climate change could
have a significant impact of primary production through increases in nutrient loads,
as well as increases in the mean temperature in the growing season.
In contrast, some model simulations in the North Sea demonstrated that a 50%
reduction in the loads of N and P from river runoff reduces the primary production by
10 to 30% in the southern North Sea (Skogen et al. 2004). In other marine areas,
the loads of atmospheric N, which have continuously increased over the past three
decades from anthropogenic pollution (Paerl and Whitall 1999), represent a large
nutrient input in the marine system and can account for all measured new production
in the eastern Mediterranean Sea (Kouvarakis et al. 2001; Mace et al. 2003), driving
the area into a P-limited system. Increasing precipitation will also increase the
availability of rainwater DON to phytoplankton growth (Seitzinger and Sanders 1999).
Figure IV.C.8. Average changes in winter
concentrations (Jan. & Feb.) of inorganic
N (left) and daily primary production
(right)during the growth period (Mar.to
Sept.) in Danish coastal waters in response
to a simulated 50% increase in runoff
from Danish rivers. As part of the Danish
national research programme DECO
(1997-2000), a eutrophication module
has been coupled to a 3D hydrodynamic
“Farvandsmodel” to analyse the sensitivity
of Danish coastal waters to changes
in climatic parameters on the basis
of year-2075 scenario simulated by global
climate modes.(Source: K. Edelvang et al.
2001, with permission) .
An excessive and imbalanced concentration of nutrients can alter significantly
the ecosystem. Increasing N and P with respect to Si in river-dominated
coastal systems will reduce the growth of the Diatoms population in time and
space, rapidly substituted by other non-Si demanding species usually less
efficient in the vertical export flux of carbon and in the transfer of energy along
the classic food web phytoplankton-zooplankton-fish. Moreover, non-Diatom
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