Conservation management of rivers and wetlands under climate change – a synthesis

Additional keywords: adaptive management, dam operation, environmental flow, protected areas, river regulation.

The world’s rivers and wetlands are degrading at an alarming rate, more than other ecosystems (Millennium Ecosystem Assessment 2005), seriously affecting biodiversity (Dudgeon et al. 2006; Vörösmarty et al. 2010) and human-subsistence communities dependent on river flows (Lemly et al. 2000). The causes are well known widespread threats, including habitat loss and degradation, invasive species, overharvesting and pollution (Allan and Flecker 1993; Dudgeon et al. 2006), whose impacts may be altered by climate change, which is predicted to change flow regimes to rivers and wetlands (Milly et al. 2005; Bates et al. 2008; Palmer et al. 2008). Cumulative evidence of degradation, loss of ecosystem services and increasing financial burdens of dealing with ecological freshwater problems (e.g. deteriorating water quality) are forcing communities and governments to consider strategies for conservation management. These are necessarily intertwined with water-management objectives for human requirements, often the cause of degradation.

Conservation-management objectives for freshwater ecosystems, particularly for highly regulated rivers where there is extraction, usually have to compete with a legacy of water-resource development for water supply and hydroelectricity generation from rivers, which continues to dominate decision-making on rivers (Vörösmarty et al. 2000). Inevitably, conservation management of rivers and wetlands needs to extend well beyond the traditional approach of management of protected areas, communities and species, including those with threatened status. It has to deal with protection or recovery of flow regimes, complicated by effects of climate change. Until recently, water management has assumed that rainfall fluctuates within historical limits of variability, an assumption that has demonstrably failed with climate change (Milly et al. 2008). Climate change is projected to alter runoff and water availability by 2050, increasing at high latitudes by 10–40% and decreasing over dry regions by 10–30%, as well as increasing extremes of dry and wet periods (IPCC 2007). This will particularly affect wetlands and rivers predicted to become drier and may also offer opportunities where runoff and water availability are predicted to increase. Regulated river basins are predicted to be affected more than free-flowing river basins (Palmer et al. 2008). Although other threats to freshwater ecosystems can be substantial, modification of flow regimes remains the most widespread problem for rivers and wetlands. In this special issue, 10 papers examine threats facing rivers and wetlands and outline conservation-management strategies, including recovery of flow regimes, alteration of dam operations, management of protected areas, and effective governance and adaptive management. Here, I synthesise the different perspectives on conservation-management strategies for wetlands and rivers, given increasing effects of climate change.

Temperatures are rising and contributing to a changing climate, altering relationships among rainfall, runoff and flows to surface and groundwater systems and increasing aridity of river basins (Milly et al. 2005; IPCC 2007). Predicted patterns in global rainfall patterns are considerably uncertain (Bates et al. 2008). In Mediterranean rivers, temperatures are increasing whereas rainfall is decreasing (Hermoso and Clavero 2011). The timing, magnitude and frequency of rainfall or snowmelt in many catchments is predicted to change (Bates et al. 2008; Milliman et al. 2008; Klausmeyer and Shaw 2009; Palmer et al. 2009; Viers and Rheinheimer 2011), with increasing temperatures predicted to augment flows early in spring as snowpacks melt and produce flow reductions in summer (Aldous et al. 2011). This inevitably increases availability of aquatic habitat downstream in spring, and reduces this habitat in summer.

Environmental envelopes or niches for biota will change with climate change. High temperatures and changes to hydrologic regimes may exceed tolerances of some aquatic biota (e.g. reduced perenniality, increased water temperatures of mountain streams, Palmer et al. 2009; Turak et al. 2011; Viers and Rheinheimer 2011). With reduced rainfall from climate change, there will be increased drying of rivers and wetlands (Herron et al. 2002), and this will be exacerbated by decreasing durations of flooding caused by rising air temperatures, compounding effects of flow reductions from regulation. Such effects will not be as severe as the impacts of river regulation (Lester et al. 2011). There are already major regime shifts in many aquatic ecosystems from changes to flow produced by river regulation (Gordon et al. 2008). Increased fragmentation provides opportunities for weed invasion. For example, the prostrate-growing plant lippia, Phyla canescens, has invaded and established almost mono-specific stands in parts of the Macquarie Marshes and Gwydir wetlands as a result of reductions in flooding (Whalley et al. 2010).

For coastal rivers and wetlands, sea-level rises are likely to affect freshwater wetland systems, as intruding seawater tips low-lying coastal freshwater wetlands into an alternate state (i.e. from freshwater to estuarine or marine, Turak et al. 2011). Obligate freshwater species will be replaced by more marine-tolerant biota as the sea invades these freshwater ecosystems (Kingsford et al. 2011a). Impacts of pollution are also likely to increase if freshwater flows decrease to rivers and wetlands (Palmer et al. 2009; Hermoso and Clavero 2011). For example, acidity and salinity increased considerably above natural levels on the Ramsar-listed Coorong, Lower Lakes and Murray Mouth wetland of the Murray–Darling Basin, with reductions in freshwater flows (Kingsford et al. 2011a).

Conservation management should vary with the nature and scale of threats across a catchment. Effects of invasive species, pollution and overharvesting usually demand a local focus. Protection and rehabilitation of flow regimes represents the greatest challenge for conservation of most rivers and wetlands. Opportunities to protect free-flowing rivers and tributaries should be implemented wherever possible to increase catchment-scale resilience (Palmer et al. 2008; Pittock and Finlayson 2011; Viers and Rheinheimer 2011). Also, with burgeoning human populations and increased dry periods and more-severe flooding with climate change, demands to develop water resources will continue (e.g. Okavango River Basin, Milzow et al. 2009). Environmental impacts should be adequately assessed across ecological and socioeconomic dimensions (e.g. flooding of agricultural land; impacts on fisheries; Gleick 2003). Conservation-management strategies to improve flow regimes include recovery of flow regimes, alteration of dam operations, protected-area management, and governance and adaptive management (Table 1).

Table 1.  Description and scale of implementation of conservation-management strategies for addressing alteration of flow regimes for free-flowing to highly regulated rivers and wetlands in the face of climate change
Superscripts indicate which papers in the special issue discuss the strategies

River regulation by dams and weirs and floodplain earthworks has fragmented hydrological and ecological processes (Nilsson et al. 2005), often severing or restricting connectivity to rivers and wetlands (Lemly et al. 2000; Kingsford et al. 2006). Consequently, recovery of flow regimes has become a key strategy for conservation, partly recovered by increasing environmental flows (Arthington et al. 2006). At their minimum, environmental flows are defined as water remaining in rivers after extraction for human use (e.g. Mediterranean rivers, Hermoso and Clavero 2011); however, there is increasing understanding that most current environmental flows inadequately sustain downstream ecosystems in highly regulated river basins (Aldous et al. 2011; Kingsford et al. 2011a). Legal recognition of environmental flows remains an important first step, albeit not universally recognised (Hermoso and Clavero 2011).

Environmental flows need to be established in all regulated rivers and increased considerably to meet legislated conservation obligations (Table 1). For example, the Murray–Darling Basin Authority (MDBA) estimated that full ecological sustainability of the Murray–Darling Basin rivers would require increased annual environmental flows of an average of 7600 GL; however, MDBA recommended 3000–4000 GL because of the likely socioeconomic impact (MDBA 2010). Given the limited water for environmental flows available in many rivers, environmental flows will need to focus on key ecosystems and processes (Table 1). Sophisticated modelling tools, applicable at large spatial and long temporal scales, will be critical for decision-making, linking hydrology to ecology and socioeconomic indicators (Table 1). Such modelling is often constrained by relatively poor fine-scale climate-prediction models, with few river basins having adequate numerical models (Aldous et al. 2011).

Conservation-management strategies focussed on alteration of dam operations can improve environmental outcomes for rivers and wetlands (Palmer et al. 2008; Table 1). Flow regimes of regulated rivers are managed, largely through the operation of dam storage and release and downstream weirs, and by reregulating storages. Traditionally, the building of dams and their operation in the catchment have focussed on providing water for human uses and not for the environment. Increasingly, climate change, through predicted increased rainfall variability, intensification and reduction, will require evaluation of dam safety around the world, particularly assessing their ability to cope with increased frequency of large flood events (Bates et al. 2008). This may be a catalyst to re-examination of safety risks of dams, including operating air spaces and pre-releases (Pittock and Hartmann 2011). Many thousands of dams require maintenance each year as they age and lose efficiency and this provides an opportunity to assess whether such structures still meet their purposes through establishment of a relicensing framework (Pittock and Hartmann 2011). The Federal Energy Regulatory Commission in the USA operates ~1000 hydropower dams, with time-limited licensing and accompanying socioeconomic and environmental assessment (Pittock and Hartmann 2011; Viers and Rheinheimer 2011), resulting in dam removal and refurbishments to reduce environmental impacts. In the Klamath basin, a proposed restoration agreement provides for removal of four hydroelectric dams (Aldous et al. 2011).

Climatic changes and resulting altered flow regimes can also force re-examination of river operations (Viers and Rheinheimer 2011), including modifying dams with structures to improve biodiversity conservation (Table 1). These can include building multi-level offtakes to overcome thermal pollution downstream (Pittock and Hartmann 2011; Viers and Rheinheimer 2011) and fishways to improve fish passage. Some dams (e.g. Burrendong Dam, Macquarie River, Australia) have limitations on the quantity of environmental flow that can be released, constraining environmental-flow management; this could be rectified by increasing the size of the outlet. Also, different dam and river operations (e.g. linking dams, aquifer storage) can deliver environmental benefits, more closely mimicking natural flow regimes without necessarily affecting allocations of water to consumers and the environment (Watts et al. 2011). Such flows can target geomorphic and ecological processes and aquatic species (Table 1). Reinstating connectivity to wetlands such as natural floodplains can also mitigate effects of floods (Table 1). For example, in the Savannah River (USA), bypassing the city of Augusta in times of high flow events could restructure and rehabilitate floodplain habitats and reduce flood damage (Aldous et al. 2011). Operational changes may require purchase of floodplain easements to allow for periodic flooding.

There may also be opportunities to reregulate flows to mimic the natural flow regime once water has passed through a sequence of dams for hydroelectricity generation, using the most downstream dam to reregulate towards a more natural flow regime (Table 1). Sometimes structural modifications to distributary systems and installation of pumps are required. For example, a large pump on the River Murray transfers water into slightly modified natural channels that deliver environmental flows to Hattah Lakes on the River Murray, whereas changes to weir levels can raise river heights sufficiently to allow inundation of downstream floodplain forests (Aldous et al. 2011).

Many protected freshwater areas are in decline, failing to meet basic objectives for conservation, largely because of effects of water-resource management (Hermoso and Clavero 2011; Kingsford et al. 2011a; Pittock and Finlayson 2011). Where climate change reduces flows, the problems will be exacerbated (Hermoso and Clavero 2011; Lester et al. 2011). The gazettal of protected areas, often accompanied by listing as wetlands of international importance under the Ramsar Convention, remains a core conservation strategy, applicable across rivers with flow regimes ranging from free-flowing to highly regulated. The key problem with protected-area management is the lack of control over the flow regime, which underpins a freshwater protected area’s resilience. Without protection of flows, resilience of freshwater protected areas will fail as upstream water-resource development increases or flow decreases further with climate change.

Traditionally, conservation management of ecosystems and biota has relied on a protected-area approach; however, there is increasing realisation that mitigation of catchment processes remains the fundamental challenge for effective conservation management of rivers and wetlands. Protected-area status ascribes conservation responsibility to government, usually through its conservation agency, with associated legislative responsibilities. Protected-area gazettal and management often represents the most obvious government commitment to conservation, even though inclusion of freshwater ecosystems may be incidental to scenic or terrestrial landscapes (Kingsford et al. 2011b; Viers and Rheinheimer 2011). After key freshwater habitats are identified, they can be protected formally or become targets for the management of threatening processes and environmental flows. Priorities for protection should be refugia, key habitats and dispersal corridors for aquatic species, given the projected impacts of climate change (Turak et al. 2011). On free-flowing rivers, protected areas can become an important node for assessing impacts of upstream development (Kingsford et al. 1998). Even where threat management is not effective (e.g. as a result of river regulation and extraction upstream), building evidence of degradation of freshwater protected areas can become a powerful incentive for governments to commit resources (e.g. Coorong, Lower Lakes and Murray Mouth, Kingsford et al. 2011a). Protected wetland systems have become the key focus for increased environmental flows in the Murray–Darling Basin (MDBA 2010; Kingsford et al. 2011a; Pittock and Finlayson 2011) where flow requirements may be defined by flooding requirements of ecosystem components (e.g. good condition of river red gum forests, Aldous et al. 2011; Pittock and Finlayson 2011).

Increasing the number of rivers and wetlands in the protected-area network should be a priority (Table 1), given their under-representation in the protected-area network (Kingsford et al. 2004; Aldous et al. 2011; Hermoso and Clavero 2011). Thus, a key aim must be to produce a comprehensive, adequate, representative and efficient protected-area system where conservation objectives are maximised (Fitzsimons and Robertson 2005; Nel et al. 2009, 2011). Conservation-planning tools exist to determine the effectiveness of current and future protected-area networks in protection of biodiversity; however; increased investment is required to build the biological databases that underpin these quantitative approaches (Table 1). For example, limited data on the spatial and temporal distribution of freshwater biodiversity limit application of conservation planning in Sierra Nevada (Viers and Rheinheimer 2011). Traditionally, divergent scientific and assessment fields have existed for environmental-flow management and protected-area identification and designation; however, conservation-planning algorithms can also link to flow assessments (Nel et al. 2011).

Ultimately, political will and successful integration of the plethora of legislative tools and responsibilities for river and wetland management will determine whether there is improved conservation management of freshwater ecosystems. Increasingly, governments are engaged in major freshwater-rehabilitation initiatives (e.g. Murray–Darling Basin in Australia (MDBA 2010; Kingsford et al. 2011a; Pittock and Finlayson 2011) and European rivers through the Natura 2000 network (Hermoso and Clavero 2011)). The watershed or catchment scale for management remains the key spatial framework, although some strategies can apply within sub-basins (Table 1). Catchments often transcend political boundaries, increasing the number of institutions and legislative instruments water-management interests, including competing water-resource development and conservation objectives which are seldom resolved (Kingsford et al. 2011a; Hermoso and Clavero 2011; Viers and Rheinheimer 2011). Further, laws and regulations for conservation management of freshwater ecosystems are often badly implemented (Viers and Rheinheimer 2011) or poorly developed (Hermoso and Clavero 2011). For effective conservation management, implementation of existing legislation related to protection of free-flowing rivers, adequate environmental assessment and reduction of impacts of regulatory structures are critical (Table 1). Ultimately, integration of different governance, legislative and regulatory frameworks is essential for effective conservation (Table 1). Strategic adaptive management planning offers some opportunities; however, these have seldom been realised (Poff et al. 2003; Kingsford et al. 2011b).

High-level conservation objectives usually exist for protected areas and some river systems; however, it is often difficult to determine whether these are achieved and so there is a lack of accountability. Strategic adaptive management provides a useful framework that provides for stakeholder engagement and involvement. It links high-level objectives to targets, indicators and thresholds of potential concern to management, promoting transparency and accountability in management, underpinned by ongoing learning (Biggs and Rogers 2003; Kingsford et al. 2011b; Table 1). A key objective for improving conservation is increased cooperation among scientists, managers and other stakeholders (Poff et al. 2003), although performing experiments at the catchment scale remains largely unachievable (Kingsford et al. 2011b). Strategic adaptive management should begin with stakeholders involved in determining the desired condition for a particular river and wetland and then deriving objectives for its long-term planning and management (Kingsford et al. 2011b). Such a framework can also be applied to dam operations (Viers and Rheinheimer 2011; Watts et al. 2011). It also aims to avoid tipping points for alteration of states, potentially by predicting change using available data and models and effecting appropriate management. Effective implementation requires commitment by managing organisations and rigorous application of hierarchical planning, testing of management and reporting on effectiveness by measuring and modelling ecosystem responses to conservation management (Table 1).

There are many factors degrading rivers and wetlands; however, the most pervasive and deleterious is alteration of flow regimes, primarily driven by appropriation of freshwater for human use, considerably exceeding any effects of climate change on flow regimes (Vörösmarty et al. 2000, 2010; Lester et al. 2011). Predicted climate-change impacts offer increased challenges for drying systems and prospects for flow improvements where flows may increase.

Recovery of environmental flows and alteration of dam operations provide clear opportunities for proactive conservation of rivers and wetlands, given the uncertainties around impacts of climate change. Protected-area management will remain a key conservation strategy for influencing conservation management; however, long-term resilience depends ultimately on ensuring that flow regimes are improved or protected. The governance and adaptive management frameworks remain the key mechanism providing the institutional impetus for improving conservation management, accompanied by improved modelling of scenarios. Strategic adaptive management can provide practical mechanisms for implementation involving stakeholders, integrating legislative and policy tools, engaging science and imposing accountability on management. The conservation strategies outlined in this special issue can improve the poor state of the world’s rivers and wetlands; however, implementation will require considerable effort and focus.