Direct Impacts of Climate Change on Freshwater Ecosystems - Climate Change Impacts on Freshwater Ecosystems - page 38

3
Direct Impacts of Climate Change
on Freshwater Ecosystems
Ulrike Nickus, Kevin Bishop, Martin Erlandsson, Chris D. Evans,
Martin Forsius, Hjalmar Laudon, David M. Livingstone, Don
Monteith and Hansjörg Thies
Introduction
Before the 1990s, most environmental scientists considered climate - in spite of
its variability - to exert a relatively constant influence on freshwater ecosystems.
In recent years, however, it has become very clear that climate change exerts
additional stress to surface waters and that it interacts with other drivers such as
hydromorphological change (Chapter 4), eutrophication (Chapter 6), acidification
(Chapter 7) and toxic substance contamination (Chapter 8). The main impacts of
climate change on freshwater ecosystems result from changes in air temperature,
precipitation and wind regimes. Freshwater systems respond by changes in their
physical characteristics including stratification and mixing regimes of lake water
columns, catchment hydrology or changes in ice-cover which, in turn, may induce
chemical changes in habitats, e.g. alterations to oxygen concentration, nutrient
cycling and, possibly, water colour. Biological responses include changes in the
phenology and species distribution of most organism groups. Links between
changes in climate and freshwater ecological responses have already been reported
and are predicted to continue under a projected future climate. However, the
modelling of this behaviour is complicated by likely non-linearities; responses
may be punctuated, with abrupt shifts occurring as thresholds are crossed.
This chapter focuses on the direct impacts of climate change that are
independent of other human-induced drivers such as land-use change, nutrient
enrichment, acid deposition and the input of toxic substances. We first briefly
describe how climate has changed during the past few decades, globally and in
Europe, and show, using selected Global and Regional Climate Models, how
climate is expected to change in future under different emission scenarios. We
then outline some of the principal physical and chemical responses of freshwater
ecosystems to climate change that have been revealed by recent research.