Geoscience Reference
In-Depth Information
Second, climate change poses risks to the
ecological restoration and management of rivers
- for example, to fulfil the aims of the EC Water
Framework Directive (WFD; Council of the
European Communities, 2000). By changing
temperature and discharge patterns and by
interacting with other pressures on rivers, climate
change might affect organisms in ways that hinder
progress to 'good ecological status'. Examples
would be where increased discharge exacerbates
problems from sewage treatment overflows,
or where elevated temperatures, drought and
reduced nutrient dilution amplify the effects of
eutrophication (Wilby
et al.
, 2006). However, there
is also a potential opportunity. Climate change was
not a major concern when the WFD was being
drafted in the late 1980s and early 1990s, but the
legislation now represents an important policy
instrument for reducing adverse effects from other
pressures that would otherwise be exacerbated
under warmer conditions with more variable flow.
Third, the detection of ecological change and
status based on river bioassessment might be
confounded by climatic effects, for which exact
influences on communities are not yet clear. So far,
these issues have been explored more fully in North
America than in Europe. For example, Hamilton
et al.
(2010) showed that invertebrate sensitivity to
temperature and organic pollution are significantly
correlated, and attempts are now under way to
partition warming effects and isolate changes from
other causes (Stamp
et al.
, 2010). The resulting
tools are likely to be more effective where the
identification of traits, genera or species are precise
enough to reflect warming effects, discharge effects
or both (Lawrence
et al.
, 2010).
Fourth, climate change effects also imply
potential risks to those ecosystem services for
which rivers are most important - not least
the provision of water supply, the regulation
of flooding and support for biodiversity both
intrinsically and in adjacent ecosystems. At present,
knowledge of interactions among climate change,
ecosystem processes in rivers and ecosystem service
provision is insufficiently well developed to know
exactly how any impairments might arise. Equally,
better knowledge is required to know how to
optimize
ecosystem services are maintained (Everard, this
volume).
Knowledge gaps and research
priorities
All the issues discussed previously imply a
clear need for considerable deepening of how
well climate change effects on rivers and their
catchments are understood. We therefore identify
the following three research priorities.
Climatic effects on ecological
mechanisms and processes
So far, many indications of climate change effects
on river ecosystems are based on speculation,
review or prediction, or from assessments of long-
term change that correlate either with varying
discharge or rising temperature. At the very least,
there is a need to ensure that other confounding
aspects of global change are not responsible for
such trends (Durance and Ormerod, 2009). Far
more important, there is a clear need to move from
describing patterns of change to understanding
the mechanisms responsible. This is a crucial step
in predicting and managing effects. Changes in
fundamental river characteristics such as thermal
or discharge regime are likely to cause equally
fundamental changes to many ecological processes
including community metabolism, primary
production, nutrient cycling, decomposition, litter
retention, predator-prey interaction, food webs,
life-history strategy, phenology, altered behaviour,
inter-specific competition, the incidence of
parasites or diseases and dispersal or invasion and
population genetic composition (Traill
et al.
, 2010).
So far, however, these explicitly ecological and
evolutionary aspects of climate change have been
very poorly considered in the available research
and yet could be of crucial importance. For
example, Durance and Ormerod (2010) showed
how inter-specific competition almost certainly
interacted with extreme climatic variation in a
local extinction event in Wales, while Woodward
et al.
(2010b, c) have drawn attention to the effects
of climate change on the emergent properties of
food web character, trophic dynamics and other
management
actions
to
ensure
that
