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

factors including an appropriate substrate and an adequate flow regime. In addition,
the presence of certain fish species is necessary to transport the larval stages of the
mollusk upstream for development and recruitment of new adults. No general
agreement exists on whether new flow regimes fostered by climate change are
compatible with survival of the mussel in the main river channel.
Reduced flows will result in a diminished diluting power in the Ebro. Thus freshwater
quality could decrease as a consequence of decreasing flow and/or increasing
discharges from agricultural fields and from treatment plants in the Ebro River.
Decreased flows would also lead to increasing salt wedge at the river delta. Such
effect could be compensated by accurately gauging releases of freshwater from
upstream dams. However, no consensus exists on the estimate of appropriate
releases. Current knowledge supports the idea that there will be a further increase in
salinity in winter and spring months and an increase in phosphorous (from
agricultural fields) as a consequence of the decrease in spring flows, fostering an
increase of primary production (phytoplankton or macroalgae) in the lower reaches of
the river.
Increased salinity in the spring may affect survival of some macroinvertebrates,
especially the clam Margaritifera and the ephemeroptera Ephoron. The effects on
fish fauna may be even more dramatic: the native species are adapted to the
fluctuations of the river hydrology, while the invasive species are more adapted to
constant flow and eutrophic waters; a switch towards latter conditions may cause the
definite disappearance of the today much reduced native fish populations. In
summary, climate-change-driven decreasing flows in the Ebro River will have a
further detrimental effect on the ecological status of the lower part of the watershed.
Transport of dissolved organic matter (DOM) from terrestrial ecosystems to
freshwater and, eventually to coastal waters is also an important factor in maintaining
the equilibrium of coastal ecosystems. Hejzlar et al. (2003) have investigated the
effects of climate change on the concentration of DOM. They report a negative
correlation between DOM concentration and temperature in well drained soils,
whereas in poorly drained soils, DOM concentration tends to increase independent of
temperature. Scenarios of possible future climate change related to double
atmospheric CO2 concentration suggests an increase in DOM concentration of about
7%, resulting from a complex of not yet well understood processes.
The productivity of the coastal waters in the region of the Ebro is closely linked to
both the total flow volume of water discharged into the sea and the amount of
particulate matter and DOM. In general, it is suggested that decreasing flow in the
river would have an impact on the productivity of the contiguous coastal areas.
Satellite images of chlorophyll a biomass in the Mediterranean Sea show how areas
of high productivity overlap with the run-off of the main rivers: the Rhone, the Ebro,
the Po and the Evros. In particular the area overlapping with the wide continental
shelf off the Ebro River mouth has large populations of foraging seabirds, whether or
not associated with industrial fishing vessels (Abelló et al. 2003), and is one of the
main spawning areas of small pelagics in the western Mediterranean.
Sea level rise
The deltaic body of the Ebro River has developed its present 50 km of sandy
shoreline over the last five centuries. The main morphological features are two
sandy spits that protrude to form lagoon areas. The delta is a biologically rich and
diverse environment (waterfowls, fisheries, vegetation), and supports a large
economic system based on tourism, agriculture, hunting, fishing and aquaculture.
The existence of the delta area is dependent of the steady supply of sediments
179