Introduction - Climate Change Impacts on Freshwater Ecosystems - page 9

Amazonic, rivers of the Rhine and Danube. Of course, other continents contain
an equal or greater variety, but Europe also offers the complication of major
biological barriers to animal and plant movements in the Mediterranean, the
Alps, the Baltic and the North Sea, the benefits of a long and sophisticated
tradition of research in freshwater ecology, and a large concentration of freshwater
scientists. Euro-limpacs, on which this topic is based, has been a European-Union-
funded, continent-wide research programme to further our understanding of the
potential effects of climate change on freshwaters. It has contributed to our
understanding of the direct physical and hydrological effects of warming in the
past (Chapter 2) and present day (Chapters 3 and 4) and on the interactions with
climate of nutrients (Chapter 6), acidity (Chapter 7) and toxic pollution
(Chapter 7). It has looked at the implications for monitoring and restoration
(Chapters 5 and 9) and the definition of reference conditions under the Water
Framework Directive. Moreover, it has sought to use the results of these studies
in modelling the future (Chapter 10) and in helping political organizations to
make decisions on management (Chapter 11).
Euro-limpacs has been far from the last word, but it has contributed important
advances, and its strength has been the wide range of approaches it has used.
There is a nexus of stages in investigating any general phenomenon and climate
change effects on freshwater systems are no exception. The first stage is simply
in establishing their existence. There can be no doubt now that climate change is
occurring and virtually no doubt that it has largely been caused by human activity.
There is then a plethora of studies showing consequent effects (e.g. Carvalho &
Kirika 2003; Berger et al . 2007), though, strictly speaking, it is rare for the
consequence to be rigorously demonstrated. We are dealing with an unreplicated
grand experiment with no control.
However, where changes occur in many different glaciers, rivers and lakes
and where these correlate closely with changing temperatures or precipitation
(Gerten & Adrian 2000; Straile 2002; Winder & Schindler 2004), there can be
some confidence in the link. Such correlation, however, is made difficult because
many other changes have occurred in freshwater systems over the same period
as climate change, and most changes are ultimately caused by the increasing size,
aspirations and technological development of human societies in the past 200
years or so.
The correlations of recent history can be placed in context by the reconstructions
of the more distant past through analysis of lake and wetland sediments. The
record is patchy and selective, and interpretations usually lack experimental
validation, but where sediment and direct records have been compared over the
past few decades, there is often a close relationship (Haworth 1980), and
sophisticated statistical approaches (Birks 1998; Battarbee 2000) have been used
to quantify the palaeoecological record.
For periods before the last few decades, or occasionally the last two centuries,
where diary and documentary evidence exists, the sediment record is the only
record and we must use it as efficiently as we can. The range of chemical and
biological remains that can now be counted and calibrated against contemporary
observations and sediments is very wide. It can be increasingly elaborated by the
techniques of resurrection ecology where resting stages of invertebrates can be