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Article
Adapting to climate change: implications for freshwater biodiversity and management in the UK Stewart J. Clarke Senior Freshwater Ecologist, Natural England, Northminster House, Peterborough, PE1 2QP, UK. Email:
[email protected] Tel: 01733 455564 Received 27 May 2008; accepted 4 February 2009; published 8 May 2009
Abstract Current work on adaptation responses for conservation management in the face of predicted climate change has a distinctly terrestrial focus. Existing evidence for the potential impact of climate change on freshwater ecosystems indicates that it is the interaction between direct climate change and current anthropogenic pressures that is likely to define the way in which freshwater biodiversity is affected. A brief overview of the likely effect of climate change upon fresh waters is presented. In light of this review, possible actions to safeguard freshwater biodiversity in the face of climate change are discussed.
Management challenges and proposed responses are
presented at the level of individual sites, at the landscape scale and according to management policy drivers. Many of the principles underlying these proposed adaptation responses need a more extensive and robust evidence base and an attempt is made here to highlight the key research gaps. Keywords: Climate change; adaptation; biodiversity; management.
Introduction
with immediate and radical action, it is clear that we are committed to a period of warming and associated changes
The potential impacts of global climate change and
in weather patterns over the next 30–40 years (King, 2005;
associated social and economic responses are widely
IPCC, 2007).
recognised as a major threat to biodiversity (Hulme,
private companies and environmental managers are
2005; Sutherland et al., 2008). Climate change is rapidly
increasingly focused on adaptation strategies that will
emerging as one of the most significant issues facing
allow social, economic and natural systems to absorb and
biodiversity conservation and ranks alongside habitat
respond to the worst impacts of this climate change.
Consequently, governments, institutions,
loss/degradation and invasive non-native species as one
There is an increasing level of discussion around
of the main pressures influencing biodiversity loss and
appropriate adaptation strategies for natural systems and
increased research effort (Sutherland et al., 2006; Ferris,
for conserving biodiversity (Abramovitz et al., 2001; Hulme,
2007).
Climate-change mitigation through reductions
2005; Mitchell et al., 2006; Smithers et al., 2008). Guidance
in greenhouse gas emissions is now at the forefront
has recently been published in the UK to assist managers in
of the international political agenda.
deciding how land management and conservation policy
DOI: 10.1608/FRJ-2.1.3
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Clarke, S.J.
needs to change to ensure a secure future for biodiversity
synopses reflect this (Allan et al., 2005). However, the
(Hopkins et al., 2007). However, adaptation work to date
body of literature reporting climate-driven effects upon
has had a distinctly terrestrial focus. The premise of this
freshwater ecosystems is growing rapidly. No attempt is
discussion piece is that freshwater ecosystems and their
made here to review this comprehensively; the following
management are sufficiently distinct to warrant further
merely aims to outline the main impacts. There is a
analysis and may require specific consideration.
The
developing on-line bibliography and information resource
paper has been written with two broad aims: to investigate
(http://www.climate-and-freshwater.info, accessed 16 De-
the relevance and implications of general (or terrestrial)
cember 2008) created as part of the EU-funded
biodiversity
freshwater
Eurolimpacs project, which provides a useful summary of
ecosystems and to stimulate discussion, particularly
likely impacts on a range of freshwater ecosystem types.
adaptation
principles
for
between the research and the practitioner communities,
In addition to evidence from palaeolimnological
on the direction of freshwater science in this area.
studies, demonstrating the impact of past climate events, and established links between freshwater ecosystem
How will climate change affect freshwater ecosystems?
behaviour and major drivers of regional climate such as the NAO, there are several reasons why climate change may be expected to adversely affect freshwater
Predicting the likely impact of future climate change on
ecosystems: temperature is an important influence
natural and human systems is made difficult by both the
acting upon fresh waters; changes to precipitation will
complex nature of the earth’s climate system and also by the
affect hydrology (another important driver of freshwater
variety of responses (environmental and socio-economic)
system behaviour); fresh waters are profoundly affected
that might be expected to arise in the face of dramatic, or
by catchment land use (which in turn will be affected
even subtle, changes in temperature and precipitation
by climate change); fresh waters are already subject to a
patterns. These ‘feedback’ mechanisms may exacerbate or
range of pressures that will interact with climate change.
mask the real impact of climate change. In very general terms, global climate models (IPCC, 2007) predict warmer
Thermal effects
and drier conditions for much of north-west Europe but this general pattern masks regional and seasonal shifts in
Water temperature is closely related to air temperature in
temperature and precipitation. Equally, it is not possible
rivers, streams and shallow lakes and ponds, and most
to foresee changes in the frequency and magnitude of
freshwater species, being scarcely able to regulate their
extreme weather events such as the rainfall and associated
own body heat, are sensitive to temperature variation.
floods experienced in England during summer 2007 and
There is already some evidence that rising temperatures
the extreme temperatures affecting continental Europe in
are affecting macroinvertebrate communities in streams
the summer of 2003.
(Durance & Ormerod, 2007), distributions of salmonid fish
It is already well established that freshwater ecosystems
are likely to change due to rising temperatures (Davidson
are influenced by large-scale climate drivers, such as
& Hazlewood, 2005) and fish communities are responding
the North Atlantic Oscillation (NAO) (Weyhenmeyer et
to warming and to other pressures (Daufresne & Boet,
al., 1999; George, 2000; Monteith et al., 2000; Bradley &
2007). At a simple level, many freshwater species might
Ormerod, 2001; Jennings & Allott, 2006) and, therefore, it is
be expected to be impacted by climate change in a similar
likely that changes to climate will have far-reaching effects.
manner to terrestrial species; ‘climate-space’ is equally
Yet freshwater ecosystems have generally received little
applicable to freshwater species. As elsewhere, a simple
attention from those modelling climate-change impacts
response involving range shifts to higher latitudes and
upon biodiversity (cf. Walmsley et al., 2007) and existing
altitudes may be anticipated. There is also the potential for
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Adapting to climate change
temperature increases to result in increases in productivity,
These hydrological changes may be expected to interact
which may be an issue for growths of nuisance algae.
with land-use practices (that might also arise in response
However, these temperature effects may be exacerbated,
to climate change pressures) to drive catchment and sub-
masked or mitigated by other pressures; for example, the
catchment responses of freshwater ecosystems, for example
degree of riparian shading may be a greater driver of stream
via reduced groundwater recharge. At the other end of the
temperature than changing air temperatures. In addition
scale changes to the hydrology of larger rivers and lakes
to direct effects upon freshwater species, temperature
will affect water retention times and nutrient cycling, and
increases will have consequences for a range of ecological,
may exacerbate problems with nuisance algae.
chemical and physical processes that are temperature controlled. In lakes, for example, the timing of spring
Interaction with other pressures
phytoplankton blooms (Thackeray et al., 2008), thermal stratification (Winder & Schindler, 2004) and chemical
Unlike many terrestrial habitats, fresh waters are strongly
processes, such as release of sediment phosphorus, may
influenced by activities in the wider landscape. Activities
each be affected.
and climate change effects acting within the catchment will therefore also impact upon fresh waters. These off-
Hydrological effects
site impacts upon rivers and lakes are already a major conservation challenge, with current legislation focusing
Changes in precipitation (quantity, intensity and timing),
on the water body itself (see Mainstone & Clarke,
combined with higher temperatures leading to increased
2008).
evapo-transpiration, have the potential to alter the water
events, climate change may lead to greater quantities of
cycle within catchments. For example, the UKCIP (UK
sediment and nutrients being transported from land to
Climate Impacts Programme) high CO2-emission scenarios
vulnerable freshwater ecosystems (Lane et al., 2007). As
predict a decreasing trend in summer precipitation of up to
a consequence of integrating landscape pressures in this
40 % and an increasing trend in winter precipitation of up
way, many freshwater ecosystems in north-west Europe
to 20 % for much of southern England (Hulme et al., 2002).
are already degraded, owing to human use and activities.
Elevated temperatures are likely to lead to increased evapo-
A significant proportion of rivers and lakes in north-west
transpiration rates, which could offset any net increase in
Europe are suffering from the effects of nutrient enrichment
precipitation. Arnell (2004) extrapolated climate-change
(see for example, Carvalho & Moss, 1995; Søndergaard &
predictions to river flows and suggested that mean summer
Jeppesen, 2007) and, in many areas of densely populated
flows in south-east England might be ~ 30 % lower than
regions, water supplies are already stretched to the limits
the 1961–1990 mean, and that extreme low flows (Q95)
of sustainable use. This is likely to compromise the ability
might be reduced by ~ 25 %; in contrast, mean winter
of these freshwater ecosystems to cope with, or absorb, any
flows are likely to increase. These hydrological changes
impacts of climate change.
In causing more extreme rainfall and runoff
may have dramatic consequences in small headwater
Increased nutrient and sediment loads, toxic pollution,
streams (Durance & Ormerod, 2007) as well as in ponds
invasive species and habitat modifications are all known to
which have small wetted areas and small contributing
affect adversely freshwater species diversity and all of these
catchments. Longer and more frequent periods of drought,
pressures are likely to increase and interact with a changing
combined with more intense rainfall and runoff events, are
climate. Palaeolimnological studies of past climate change
known to act as stressors of in-stream ecology (e.g. Wood
have often found that catchment changes are as, or more,
& Armitage, 2004; Lake, 2007). As well as direct effects,
important in determining lake ecology than climate (e.g.
there will be indirect effects resulting from the interaction
Dalton et al., 2005). Similarly, work investigating current
between flow and habitat or nutrient concentrations.
climate change, either through analysis of existing data
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Clarke, S.J.
(Durance & Ormerod, 2009) or experimental approaches
the managers of freshwater systems is to apply these
(Moss et al., 2003), has indicated that the effects of altered
adaptation principles to their own area of work.
water quality and fish communities are more important
working out what this means in practical terms, it may be
than temperature increases.
Climate change may
easiest to consider what changes we might need to make
exacerbate the impact of invasive non-native species by
to how we manage individual water bodies (including
increasing their potential reproductive range. Freshwater
species of conservation concern), how we manage the
ecosystems appear to be particularly suspectible to
landscape or catchment surrounding those waters and how
invasions of problem species and there are examples from
current management frameworks might need to change.
In
across a wide range of ecosystems and taxonomic groups. Climate change may release a number of species from
Management at the scale of the waterbody
current temperature constraints and increase their invasive tendencies.
Indeed, experiments simulating warmer
Climate change is now widely accepted as the most
conditions have already shown that the exotic invasive
pressing environmental problem facing us, and Planet
plant species Lagarosiphon major, which is already widely
Earth as a whole. However, moving away from this
distributed in the UK, was favoured by warmer conditions
global scale, it is clear that there are many other pressures
in small experimental ponds (McKee et al., 2002).
threatening biodiversity at the local scale. Given predictions
It is these interactions between climate change and
about the way that climate change may interact with these
other pressures that arise from the link between hydrology,
other pressures, it is important that we do not completely
temperature and ecological patterns and process,
shift our attention away from the small scale and from
which are most likely to have the greatest impact upon
local issues to focus solely on the global scale. It is also
biodiversity and, hence, require management responses.
important to recognise that local and global environmental problems are ultimately interlinked. It follows that the
How can we ‘climate-proof’ our freshwater conservation and management practices?
action we take to manage individual water bodies may help adapt freshwater biodiversity to climate change, as part of ‘safeguarding baseline biodiversity’ (Table 1). Current conservation effort is largely directed towards
Adaptation responses can be simply defined as those
‘protected areas’: in sparsely populated areas, large tracts
actions that we need to take to ensure that a sector (in this
of land may be given over exclusively to conservation but,
case freshwater biodiversity) is not adversely affected by
in more densely populated areas, it is often necessary to
climate change. Hulme (2005) argues that climate-change
integrate conservation with other land uses. The small-
adaptation strategies for natural systems should have three
scale, protected-area approach has proved moderately
broad aims:
successful where the major pressures are ‘on-site’, such as
a.
to increase the flexibility in management of
habitat loss or over-grazing, but has been less effective at
vulnerable ecosystems;
preventing deterioration due to external pressures, such
to enhance inherent adaptability of species
as nutrient enrichment (Mainstone, 2008).
and ecosystem processes within vulnerable
and wetland sites are particularly susceptible to these
ecosystems; and
external pressures and, in England, diffuse pollution from
to reduce trends in the pressures that increase
agriculture is a major cause of the unfavourable condition
vulnerability.
of protected freshwater habitats (English Nature, 2003).
b.
c.
Freshwater
These aims are reflected in the six principles described
This characteristic of freshwater habitats means that a more
in recent UK guidance for policy makers and land managers
integrated approach to management, over a much larger
(Table 1, from Hopkins et al., 2007). A key challenge for
area of land, is likely to be required. Small protected sites
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Adapting to climate change Table 1. Climate change adaptation guidelines for biodiversity (from Hopkins et al., 2007).
1. Conserve the habitat and species baseline. 1a. Conserve Protected Areas and other priority habitats. 1b. Conserve range and ecological variability of habitats and species. 2. Reduce sources of harm not linked to climate. 3. Develop ecologically resilient landscapes. 3a. Conserve and enhance patch variation within the landscape. 3b. Make space for the natural development of rivers and coasts. 4. Establish ecological networks. 5. Make sound decisions based on analysis. 5a. Thoroughly analyse causes of change. 5b. Use adaptive conservation targets and priorities. 6. Integrate adaptation and mitigation measures into conservation management. are vulnerable to many pressures (e.g. one off pollution
and losers in freshwater habitats. Species for which there
events) and under a changing climate may lose their
are national and international conservation obligations
special value as rare species are forced to migrate to new
may see contractions or shifts in range. Those which are
climate space. As a result, there has been intense debate
particularly vulnerable are cold water species such as some
about the future role of protected sites in safeguarding
white fish (Coregonus spp.), which have survived in upland
biodiversity. However, there are many reasons for placing
lakes since the last ice age. For other species, a key question
high-quality rivers, lakes and wetlands at the heart of
will be the extent to which we can mitigate these impacts
any biodiversity adaptation approach, on the grounds of
by changing management (e.g. increasing riparian shading
having: high biodiversity or intrinsic value; low levels of
to reduce river water temperatures) or reducing pressures.
on-site pressures; action already in hand to reduce off-site
Many freshwater species are dependent on hydrological
pressures; controls on damaging activities and, frequently,
connectivity or animal vectors to enable them to disperse
a management framework in place. Furthermore, the
to new habitats. Increasing connectivity will require action
idea of protected sites is well understood and generally
across the landscape. A habitat-based approach that seeks
accepted. There is a general willingness to invest in high-
to minimise the level of each impact and activity to ensure
quality sites, which does not necessarily extend to the wider
good quality habitat, in the expectation that characteristic
environment. In the freshwater environment, where off-site
species will follow (Mainstone & Clarke, 2008), has benefits.
or catchment-scale pressures (e.g. diffuse pollution) may
However, species conservation is a central concept of
have continued to affect the condition of protected sites,
conservation and we must begin to consider the possibility
the catchments of such sites may provide the ideal focus
that certain species will be lost from a particular area. It is
for piloting novel (‘no risk and no regrets’) management
our duty to ensure that, where this does happen, it is not
schemes, using protected status as a driver for investment.
because we have failed to deal with all of the pressures
A greater challenge is how we might conserve
within our control. Finally, our perception of what is native
particular species in the face of a changing climate. Much
and characteristic of a given area may have to change. As
of the work on species response to climate change has
species are able to spread into areas of higher latitude due
focused on changes in climate space and species’ abilities
to warmer temperatures, concepts such as native and non-
to migrate or disperse to new habitat (cf. Walmsley
native will become more and more difficult to define. A
et al., 2007). It is clear that warmer temperatures and
more appropriate focus for such debates is whether a species
changing hydrology will result in there being winners DOI: 10.1608/FRJ-2.1.3
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Clarke, S.J.
is invasive or benign and whether it might arrive ‘naturally’,
and, thus, are likely to be most acceptable where they
using its own dispersal mechanisms, or via human agency.
are seen as enhancements to already-degraded systems
Reducing pressures arising from human activity may
or where they are part of a systematic restoration of
help minimise the impact that climate change will have
more natural conditions (e.g. riparian re-afforestation).
in the future. The idea of ecosystem resilience is gaining support as an integral part of climate change adaptation.
Landscape and catchment management
Resilience is defined as the capacity of an ecosystem to tolerate disturbance without collapsing into a different
Much of the current discussion about climate change
state, controlled by a different set of processes, or the
adaptation for biodiversity questions the future role of
amount of disturbance that the system can absorb without
isolated protected sites in a landscape that must allow
experiencing a change in structure and composition
migration of species to new climate space. To what extent
(sensu Holling 1973; Carpenter et al., 2001). There are
does this reflect a terrestrial bias in nature conservation
examples of such ‘regime shifts’ in freshwater habitats,
theory and practice? Certainly one of the greatest risks
for example, switches between clear-water, plant-
of climate change for many terrestrial species may be a
dominated states and algal-dominated, turbid states in
contraction or shift in climate space and isolation due
shallow lake ecosystems (Scheffer et al., 1993). There is
to inhospitable countryside between protected sites
a suggestion that systems experiencing relatively low
(Walmsley et al., 2007). Given the need to think and act
levels of human disturbance (which are often those with
on a larger scale, there are sound reasons for the network
high conservation value) may have greater resilience.
of protected sites to be seen as the foundation for building
Conversely, ecosystems affected by high nutrient loads
resilience across the whole landscape (Hopkins et al.,
or introduced species may behave in unpredictable ways
2007).
to rising temperatures and altered hydrological regimes
A major focus of climate-change adaptation for
(Carpenter, 2003). This, largely theoretical, concept needs
terrestrial habitats and species is to increase ecological
to be underpinned by more evidence before it receives
connectivity, or ‘porosity’, within landscapes (e.g.
widespread support but initial indications suggest that it
Castellon & Sieving, 2006). River systems, together with
may hold true for some model systems (Moss et al., 2003).
their associated wetlands, naturally have a high degree
Given that reducing pressures has clear and direct benefits
of connectivity (Pringle, 2001). However, centuries of
for biodiversity, this approach may be considered a low-
habitat modification and land drainage have drastically
risk strategy that may deliver large gains irrespective of
reduced hydrological connectivity within the landscape;
climate change. The greatest challenge will arise where
the number of ponds and small water bodies capable of
reducing existing pressures is associated with significant
supporting key aquatic species has reduced considerably
(financial and opportunity) costs, and benefits can not
and even rivers, which have retained their longitudinal
be clearly quantified or expressed in financial terms.
connectivity, are often isolated from parts of their
As well as addressing pressures, there may be
floodplains, with much reduced lateral connectivity. Many
positive management actions that we could follow to help
threatened freshwater species have suffered as a result
individual ecosystems adapt to new flow regimes or
of this simplification of the landscape and in particular
temperatures. For example, rising water temperatures
the loss of high-quality habitat in which to disperse. For
could be counteracted by increasing the amount of
example, a number of rare aquatic plant species, such as
shade along rivers and around small waterbodies, or
grass-wrack pondweed (Potamogeton compressus L.) and
new, two-stage channels could be constructed to better
ribbon-leaved water plantain (Alisma gramineum Lej.),
accommodate reduced flows.
These interventionist
have life cycles dependent upon dynamic interactions
approaches will change the character of ecosystems
between the main river and associated backwaters and
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Adapting to climate change
wetlands. Reinstating hydrological connectivity between
of water bodies. It is therefore important that attempts to
river channel and floodplain wetlands is a critical step in
re-connect rivers with their floodplains are undertaken
ensuring the survival of disturbance dependent freshwater
in parallel with other activities such as improving water
species and the restoration of a landscape rich in temporary
quality and preventing the spread of non-native species.
and permanent water bodies will benefit a wide range of species, by providing refugia from extreme events
Management processes and frameworks
and stepping stones to aid migration into more suitable climate space.
Management of these rare freshwater
Many of our existing management processes, institutions
species needs to take account of the various dispersal
and legislative drivers may need to be adapted for a very
pathways (aquatic, terrestrial and atmospheric) and
different future. The term ‘adaptive management’ has been
vectors (floods, animals, terrestrial corridors) and integrate
used to describe a more iterative and reflective approach
understanding of these with restoring system function.
to management, where managers ‘learn by doing’ and
‘Landscape’ approaches are arguably already well
use their enhanced understanding to revise management
ingrained within freshwater conservation, where the
accordingly. It may be argued that the areas that need most
management of the catchment is widely recognised as
immediate attention are the direct drivers for management
fundamental to achieving conservation goals. Increasing
of freshwater biodiversity, and other allied activities which
connectivity – the links between areas of suitable habitat
may impact upon freshwater biodiversity (e.g. water
– is an important element of the landscape-scale approach
supply, flood defence, agriculture).
and this may be delivered both through intervention
The major drivers for freshwater conservation in
or habitat creation and through a ‘hands-off’ approach,
Europe, the EC Water Framework Directive (European
allowing natural processes to take place. Habitats created
Parliament & Council, 2000) and the EC Habitats and
through natural processes such as flooding, deposition
Species Directive (European Council, 1992), are based on
and erosion might be expected to be more sustainable in
static definitions of habitat and, in the case of the Water
the medium to long term and will not be compromised
Framework Directive, on historic reference conditions.
by the limited understanding of links between form
Although the Habitats and Species Directive does define
and process that has sometimes confounded habitat
‘favourable conservation status’ (the ultimate objective
restoration in dynamic environments (Clarke et al.,
of the directive) in terms of ‘structure and function’, the
2003). An example of the way in which UK conservation
implementation of both directives will require a re-think
is becoming more large scale is the ‘Wetland Vision’
to take account of climate change. Fig. 1 shows how
(http://www.wetlandvision.org.uk/, accessed 16 December
climate change might be integrated into the process of
2008), an ambitious vision for a wetter English landscape
setting objectives for protected sites. In spite of the nature
and an attempt to identify the best places for new and re-
of these pieces of legislation, freshwater management has
created freshwater and wetland habitats. However, there
increasingly incorporated measures of abiotic variables
are risks associated with large scale reconnections: first,
(water chemistry, hydrology) that may approximate to
isolated high-quality wetlands and small fresh waters may
components of ecosystem functioning. It has been argued
be compromised by poor water quality in main rivers,
that, having already incorporated this more functional
which receive high loads of nutrients from point- and
approach, freshwater management is to some extent pre-
diffuse- inputs; secondly, increasing connectivity may
adapted to dealing with some aspects of climate change
favour and exacerbate the spread of non-native invasive
(Mainstone, 2008). In contrast, conservation of terrestrial
species, such asAustralian swamp stonecrop Crassula helmsii
sites has tended to focus on vegetation structure and
(Kirk) Cockayne and signal crayfish Pacifastacus leniusculus
composition and the management of these. Nevertheless,
Dana, which can have devastating impacts on the ecology
changing baselines (e.g. increasing temperatures and
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Clarke, S.J.
Fig. 1. A proposed adaptive management framework for managing important freshwater sites. Future climate and land use scenarios feed into a modelling framework defined by current knowledge. Resulting scenarios or possible futures help to refine conservation objectives and guide decision makers. Robust monitoring data help to refine predictions of the future and revise objectives.
changing flow regimes) may undermine current targets.
as a means of storing carbon, while innovative flood-risk
Fundamental relationships, upon which environmental
management projects may lead to significant areas of
targets and management principles are based, may no
wetland creation. Equally, climate change may encourage
longer hold true. A precautionary approach requires that
a more responsible attitude to water use, including the
existing targets for water quality and other parameters are
development of means to minimise water use. However,
upheld until there is robust evidence to support revision.
some responses to climate change, such as a widespread
The nature of fresh waters and the strong social and
switch to biomass crops or a hard-engineering response
economic drivers of their management (for reasons of
to increased flood risk (see Sutherland et al., 2008), could
water supply, waste water disposal, aquaculture and
have major implications for freshwater ecosystems.
recreation as well as flood risk management) is a further
Ensuring that biodiversity is not neglected when critical
complication. Climate-change mitigation and adaptation
decisions are made about managing water resource
responses for other sectors and even other habitats
demands or dealing with increased flood risk is certain
and species will bring both opportunities and risks for
to become a major challenge. The scale and severity of
freshwater biodiversity. For example, wetland restoration
potential climate-change impacts upon society means
or pond creation (Downing et al., 2008) may be promoted
that it is inevitable that policy makers and politicians will
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Adapting to climate change
pursue those solutions that minimise these risks and in the
Framework Directive. Furthermore, there is a need to
most cost-effective way. What is also clear is that there is
bring together work from all areas of water- and land-
a role for freshwater scientists and managers in informing
management on climate-change impacts and adaptation
these choices and demonstrating the potential for
responses.
mutually beneficial approaches – the ‘ecosystem services’
focuses on the implications for flood alleviation and water
argument (Millennium Ecosystem Assessment, 2005).
companies focus on the implications for water supply
For example, current flood-risk analysis
In the UK, one of the greatest threats to freshwater
and treatment; there will be overlap between these areas
biodiversity may be the result of decisions taken at the
of work, such as changes to land management, to reduce
coast. There are extensive freshwater and brackish ditch
runoff and flood risk while improving water quality and
systems in south-east England that support a range of rare
increasing water-storage capacity. Engaging the public in
plant and invertebrate communities, and these are often
discussions about climate change and possible adaptation
protected by artificial (sea walls) and artificially maintained
responses is vital because of the range of threats, perceived
(replenished beaches or shingle barriers) structures.
and real, that accompany increasing temperatures
Many of these grazing-marsh systems have high species
and altered hydrological regimes, for example: floods,
richness and are the last refuge for many aquatic plant and
droughts and waterborne diseases, such as West Nile
invertebrate species; accordingly, many are internationally
virus. Pilot projects such as the BRANCH project, which
important conservation sites. Communities characteristic
considered how spatial planning will need to change to
of floodplain wetlands (ox-bows, backwaters, ponds),
ensure that biodiversity can adapt to climate change, are a
have been squeezed down to poor value land at the coast
useful way of raising awareness, of stimulating discussion
by hundreds of years of river modification, drainage and
and of testing approaches (BRANCH Partnership, 2007).
flood defence. The threat of sea level rise has combined with concerns about the economic viability of a continued hard-engineering approach in coastal flood-defence policy
What gaps in evidence do we need to address?
(Defra, 2005). A more sustainable coastal management policy would deliver a more naturally functioning
Central to any response to the threat of climate change to
coastal ecosystem but may lead to changes to or loss
freshwater ecosystems is a better understanding of likely
of important freshwater habitat, with up to 32 000 ha
impacts and the consequences of particular management
of protected wetland deemed vulnerable (Defra, 2007).
options. Any attempt to define research needs in such a
Proposals to recreate these habitats in more sustainable
broad area would be open to debate and, consequently,
locations may be constrained by land availability and by
I will consider only broad themes and offer these as the
our ability to create high-quality ecosystems. Sustainable,
stimulus for discussion: species and habitat requirements;
longer-term solutions for these communities will depend
processes and interactions; modelling capability; and
on restoring major river systems and their floodplains.
monitoring.
Finally, a key challenge is to bring together the
Research to understand the basic ecology of species and
range of land- and water- managers and users to make
species assemblages has largely fallen out of favour, losing
informed decisions about management of the catchment.
out to more holistic systems-based work. While more
Understanding the importance of the linkages between
multi-disciplinary, system-level approaches are critical,
land and water management and making management
understanding the impact of climate change does require
decisions will be, accordingly, an important part of
knowledge of basic relationships, such as the thermal and
climate-change adaptation for fresh water, and across the
hydrological preferences of particular species. This basic
EU integrated catchment management should be given
understanding is vital, not just in predicting which species
greater impetus with the implementation of the EC Water
or assemblages are likely to lose or gain under a changing
DOI: 10.1608/FRJ-2.1.3
Freshwater Reviews (2009) 2, pp. 51-64
60
Clarke, S.J.
climate, but also as an input to models that might help
is important as a means of understanding impacts but also
identify management options. It is also important that we
in testing adaptation responses. Scenarios, particularly
have a good understanding of the way in which species–
where these can be visualised (as maps or composite
environment relationships and ‘ecosystem processes’ (such
images), are also a valuable way in which to communicate
as nutrient cycles, energy flows and trophic interactions)
options to society and to inform decision making.
work now and how they might change under future climate.
Some gaps in our understanding may be addressed
By establishing relationships between biological and
through the establishment of a well-designed monitoring
physical or chemical parameters (including those driven by
network. Indeed, many of the impacts that have been
climate) and understanding how these may be modified by
linked to climate change have been detected through
human activity, it will be possible to link to climate change
existing monitoring schemes designed for other purposes
models and develop scenarios for the future (see Fig. 1).
(cf. Rosenzweig et al., 2008). A changing and potentially
A better understanding of processes is a fundamental
unpredictable environment does place increased emphasis
part of understanding ‘resilience’, which is widely
on monitoring and analysing ecosystem behaviour, and
acknowledged to be central to successful adaptation. An
on using this information to appraise and revise targets
important argument for the conservation lobby is that
and management approaches in light of new knowledge
high-quality freshwater systems are more resilient than
or understanding (Fig. 1). The unpredictability of climate
degraded ones and that functional (if not taxonomic)
change and its impacts presents particular challenges for
diversity, intact nutrient cycles and energy flows might
establishing monitoring programmes and it is possible
confer greater stability. However, this hypothesis remains
that future management will require information on
untested in freshwater systems; and even in better studied
parameters or ecosystem elements that we did not
systems, where considerable experimental effort has been
have the foresight to include within programmes.
employed, results are not clear (e.g. Balvanera et al., 2006).
Consequently, it is likely that long term monitoring
Even if further work is required to characterise the link
programmes that focus on a range of parameters in an
between biodiversity and resilience, the ‘precautionary
attempt to characterise the breadth of a system will be of
principle’ suggests we should continue to invest effort in
considerable value. At the very least a series of long term
preventing further freshwater species and habitat loss.
monitoring sites should be established or existing schemes
Knowledge of the way in which freshwater systems
such as the UK Environmental Change Network (Bealey
operate under current conditions is required to drive
et al., 1998) should be expanded to provide analogue
models and predictions of the future.
Linking this
sites and contextual information which may explain
understanding to models of future climate and land use
observed patterns in data from sites without such records.
will enable us to consider the range of possible ‘scenarios’ following different management options. Models might be
Conclusions
conceptual, numerical (e.g. Elliot & May, 2008) or physical (e.g. Moss et al., 2003) but they need to be underpinned by
It is evident that many of the general biodiversity
sound understanding of driving processes. Freshwater
adaptation principles (Hopkins et al., 2007) are applicable
ecosystems may be subject to extreme events (floods,
to management of freshwater ecosystems.
droughts) beyond our current experience and such events
differences in ecosystem characteristics, management
are particularly difficult to include in models. Predicting
spheres and our level of understanding have the result
future ecosystem behaviour and response depends
that adaptation for freshwater conservation may require
upon models being able to account for these stochastic
a different emphasis.
and unprecedented events; ultimately this may prove
freshwater management may focus more on restoring
impossible. This ability to model future system behaviour
lost hydrological and geomorphological processes and
© Freshwater Biological Association 2009
However,
For example, aspirations for
DOI: 10.1608/FRJ-2.1.3
61
Adapting to climate change
linkages than on creating new connecting habitats. A
Acknowledgments
shift towards managing function and process (rather than focusing on taxonomic components) should be easier for
The initial ideas expressed in this paper were presented at
freshwater managers due to the long history of focus on
a Eurolimpacs conference, ‘Climate Change and Aquatic
abiotic parameters such as water quality and hydrology.
Ecosystems in Britain: Science, Policy and Management’,
The very nature of freshwater habitats is such that
held at University College London in May 2007 and
management is already relatively holistic in approach with
published in proceedings from this event.
conservation bodies working with a number of functions
The author has benefited from discussion with colleagues
in the environmental protection agencies (water quality,
in Natural England, in particular Alastair Burn, Chris
water resources, flood management) (Mainstone & Clarke,
Mainstone and John Hopkins, and the comments of two
2008).
anonymous reviewers. The views expressed are those of
The general messages from the research literature and proposed adaptation principles are that the conservation
the author and do not necessarily reflect those of Natural England.
sector needs to continue working to reduce the wide range of pressures acting on the environment. By reducing
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Author Profile Stewart is Senior Freshwater Ecologist with Natural England, leading on standing water and aquatic plant conservation. He took up the post (originally with English Nature) after completing a PhD in river plant ecology at Queen Mary, University of London. His work is focused on providing advice and guidance on the management of protected lakes, canals and ditch systems. Recently he has worked with colleagues in a number of UK agencies on climate change impacts on freshwaters. He is currently a member of the FBA council. © Freshwater Biological Association 2009
DOI: 10.1608/FRJ-2.1.3
