Geoscience Reference
In-Depth Information
CHAPTER 9
Understanding and Managing Climate
Change Effects on River Ecosystems
Stephen J. Ormerod
1
and Isabelle Durance
1,2
1
Cardiff School of Biosciences, Cardiff University, UK
2
Sustainable Places Institute, Cardiff University, UK
Introduction
estuarine and riparian ecosystems by supplying
water, energy and nutrients; and they represent
large cultural value, for example recreation,
tourism and simply as inspirational places (UK
National Ecosystem Assessment, 2011). Although
there is still very active debate about how such
use and exploitation can be harmonized with
the protection of biodiversity, this new emphasis
is likely to reposition many aspects of the
valuation, designation, protection, management
and restoration of rivers and their catchments.
The third key issue has major consequences for
these first two. Rivers are now considered to be
among the most sensitive of all ecosystems to
the effects of climate change, both directly and
indirectly through interactions with other stressors
(after Durance and Ormerod, 2007, 2009). As one
of the defining developments in river conservation
over the last 20 years, the reasons are increasingly
well rehearsed. River temperatures track rising air
temperature closely, particularly in headwaters,
as shown by unequivocal warming in rivers on
at least four continents (see below and Kaushal
et al.
, 2010). Large biological effects are likely
because most river organisms are ectotherms, while
metabolic activity, production, decomposition and
oxygen concentrations are temperature dependent.
All streams and rivers are also linked inextricably
to climatic effects on flow pattern and all related
Among the important issues for river conservation
and management that have developed since the
1990 York conference (Boon
et al.
, 1992), three
have gained particular prominence.
First, there is increasing evidence that rivers
contribute disproportionately to global biodiversity
measured by unit area or water volume (Strayer
and Dudgeon, 2010). This feature stems probably
from their physical complexity, the wide range of
river types found across the world and their natural
isolation in separate river basins. As rivers are also
'hotspots' for human activity, freshwater organisms
are at greater risk of extinction than their marine or
terrestrial counterparts (Hambler
et al.
, 2010).
Second, the 'ecosystem services' concept - the
idea that ecosystems provide utility and benefits to
people - is re-focusing attention on rivers as assets
with large, multiple values (Maltby and Ormerod,
2011; Everard, this volume). Among ecosystems
worldwide, rivers are considered increasingly to
be among the most important providers of goods
and services: they provide water for human use
and habitat for economically important species
such as Atlantic salmon (
Salmo salar
) and eels
(
Anguilla anguilla
); they regulate flooding, erosion,
sediment supplies, water quality and pollutant
disposal; they support adjacent wetland, floodplain,
