Climate Change and the Hydrology and Morphology of Freshwater Ecosystems - Climate Change Impacts on Freshwater Ecosystems - page 65

4
Climate Change and the Hydrology
and Morphology of Freshwater Ecosystems
Piet F.M. Verdonschot, Daniel Hering, John Murphy,
Sonja C. Jähnig, Neil L. Rose, Wolfram Graf, Karel Brabec
and Leonard Sandin
Introduction
This chapter focuses on existing knowledge and new data, as well as hypotheses,
on how climate-hydromorphological interactions might alter freshwater
ecosystems in future. We include projected changes in climate and land use, and
their effects at the catchment, reach and habitat scales. The emphasis is on streams
and rivers, although some aspects of lake hydromorphology are also considered.
We focus on streams and rivers mainly because more knowledge exists on the
small-scale effects of climate change on stream and river hydrology and
morphology and ultimately on their biological effects, compared with lakes.
Finally, we discuss how climate change might affect attempts to restore stream
and river ecosystems.
Climate affects freshwater ecosystems indirectly through societal and economic
systems, such as land management, as well as directly by temperature and
precipitation. In many cases, climate change is an additional stressor adding to
the impacts of human activity. Freshwater biodiversity, for example, is at present
affected by the over-exploitation of natural resources, water pollution, flow
modification, habitat degradation and by invasive alien species (Dudgeon et al .
2006). In future, however, the effects of climate change are expected to become
more prominent, especially if the magnitude and rate of climate change are at the
higher end of the projected range (cf. Solomon et al . 2007; European Environ-
mental Agency 2008), which, on current evidence, seems likely. The principal
changes expected in Europe are described in Chapter 3. For streams and rivers,
changes in precipitation and discharge regimes are as important as changes in
temperature. Already there is evidence for an increase in annual river discharge
in eastern Europe and a decrease in southern Europe, and annual discharge is
also projected to decline strongly in southern and south-eastern Europe in future