When trends intersect: The challenge of protecting freshwater ecosystems under multiple land use and hydrological intensification scenarios
Introduction
Intensification is a key characteristic of many emerging global ‘megatrends’; trends that, on a global scale, will significantly shape the ecological, social, economic and cultural landscapes of the future (Hajkowicz et al., 2012). These include urbanisation, increasing mineral extraction and energy production and the requirement to obtain more resources from a declining natural resource base. A rising world population, forecast to be 9 billion people by 2043 (UNESA, 2012), increased wealth and changing dietary preferences suggest that global food production will need to increase by 70% by 2050 (Steduto et al., 2012). Potentially constraining this production is the threat of water scarcity. Vörösmarty et al. (2010), using a global geospatial framework, showed that pandemic impacts on both human water security and freshwater biodiversity were highly coherent, although not identical. Nearly 80% of the world's population (4.5 billion in 2005) was exposed to high levels of threat to water security, while 65% of global river discharge, and the aquatic habitats supported by river flows, were classified as moderately to highly threatened (Vörösmarty et al., 2010). The most serious impacts, which include watershed changes, pollution and water resource development, coincide in regions of intensive agriculture and dense human settlement. Already, the global agricultural sector accounts for 70% of withdrawals from freshwater systems and more than 90% of consumptive water use (Steduto et al., 2012). The direct and indirect competition for water resources associated with population growth will intensify both mild and moderate droughts.
Importantly, the impacts of land use intensification and increasing water demands have to be considered within the wider context of global climate change. Anthropogenically-driven climatic changes are already considered to pose a major threat to global biodiversity, including inland aquatic ecosystems and their species (Solomon, 2007, Woodward et al., 2010). Globally, freshwater ecosystems and biota are considered to be particularly vulnerable because of their physical fragmentation within terrestrial landscapes and relative isolation by catchment divides and saltwater barriers (Dudgeon et al., 2006). Many freshwater species will be unable to disperse to suitable habitats as temperatures increase and changes in precipitation disrupt migration and feeding and breeding patterns (Woodward et al., 2010). These climatically-driven changes will be accompanied by the direct and indirect effects of increasing human demands for water (Palmer et al., 2008). In regions where precipitation declines, surface and ground water resources and environmental flows will be increasingly contested. As a consequence, declining water availability will pose a significant threat to freshwater environments, as well as agriculture and human consumption. It is anticipated that by 2050, 2.3 billion people will be living in water basins experiencing severe water stress (OECD, 2012). The extent to which human communities will stay and adapt to declining conditions is difficult to predict. Most studies have focused on developing countries where mitigating circumstances, such as war and poverty, are present (Gemenne, 2011). Environmental extremes also cause hardships in developed countries, but the dynamic is likely to be different because of greater economic and political stability, and differences in agricultural technology.
The implications of the interacting trends of land use intensification and hydrological intensification for the management and conservation of freshwater ecosystems are the focus of this paper. We consider the evidence for hydrological intensification, the existing legacy of land use change on the water quality and hydrological regimes of Australian river systems, the likely interacting effects of land use and hydrological intensification and the need for proactive governance and adaptive management. We also suggest a set of priority research actions to integrate land use intensification into freshwater management and conservation.
Section snippets
Evidence for intensification of the global hydrological cycle
Associated with the broad trend in the expansion of the earth's population has been a major expansion of the global economy driven largely by the exploitation of fossil fuel resources and land clearing, resulting in an associated increase in carbon emissions (Canadell et al., 2007). The rate of growth in atmospheric emissions has increased from approximately 1.3% per year during the 1990s to 3.3% per year during the period 2000–2006 (Canadell et al., 2007). This trend is likely to continue
Australia as an exemplar study region
The large areal extent of the Australian continent provides an opportunity to compare the impacts of both land use and hydrological intensification across multiple biomes because the continental landmass spans equatorial, tropical, arid and temperate climatic zones (Fig. 2). Generally, Australia is characterised by water-limited conditions with high climatic variability and soils that are low in nutrients and high in salts (Diamond, 2005). However, the Great Dividing Range in eastern Australia
Impacts of land cover and land use change on Australian freshwater ecosystems
The changes in water quality, quantity and ecological health of Australian freshwater ecosystems resulting from changes in land use and land cover since European settlement have been profound (Boulton et al., 2014). These include sedimentation, eutrophication, salinisation, acidification, pollution (heavy metals and pesticides), altered flow regimes, degradation of urban streams, also known as the urban stream syndrome (Walsh et al., 2001), the loss and degradation of some types of aquatic
Predicted effects of land use intensification and hydrological intensification on Australian freshwater ecosystems
Land in Australia is being increasingly managed for multiple objectives, including the production of food, fibre, water supply, extraction of minerals and energy, biodiversity conservation, landscape amenity and in recent years, for carbon sequestration. Intensification of resource use is being driven by the need to increase productivity in response to growing demand from domestic and international markets (Lesslie and Mewett, 2013). Additionally, there is a declining resource base, in
Are some forms of land use intensification better than others?
Currently agriculture accounts for approximately 70% of all consumptive water use in Australia, mostly for irrigation. Irrigated agriculture covers less than 1% of the total landmass, but produces approximately one third of Gross Farm Product (GFP) (Lake and Bond, 2007). In contrast, grazing and dryland cropping cover 53% and 6% of the land-surface, respectively (Lake and Bond, 2007). Both forms of agriculture have had profound impacts on river systems, both in terms of altering hydrologic
Delivering environmental flows
Various mechanisms are already in place in many Australian regions to protect the environmental water share or deliver environmental flows during extended dry periods or droughts. Environmental flows are defined as “the quantity, quality and timing of water flows required to sustain freshwater and estuarine ecosystems and the human livelihoods and well-being that depend on these ecosystems” (Brisbane Declaration, 2007). Opportunities include limiting the volume of water pumped from a river over
The importance of improved governance in supporting freshwater ecosystems facing intensification
Managing land use and hydrological intensification and their impacts is a human endeavour. Hence, consistent with Pahl-Wostl et al. (2013), contemporary intensification challenges facing the world will enhance scrutiny on governance systems from global to local scales. Consequently, building healthy governance systems that address the causes and impacts of intensification are needed to create the foundations to establish a more sustainable future for freshwater ecosystems. Dale et al. (2–13)
Developing an understanding of long term ecosystem behaviour to support decision making
Despite a long history of palaeoecological research across Australia, there has been very little integration of this evidence into natural resource decision-making (Mills et al., 2013). Evidence from natural archives of change, such as wetland sediments, tree rings and speleothems can provide considerable insight into systems change including, but not limited to: (i) benchmark conditions; (ii) initiation of human impact; (iii) the magnitude of human impacts relative to benchmarks; (iv) recent
Conclusions
Land has been cleared across most of the temperate regions of Australia and large amounts of fresh water have been diverted and extracted for the production of food and fibre, resulting in major land use and water use legacies. These must be addressed if the nation is to avoid the loss of multiple ecosystem services and an accelerated decline in aquatic biodiversity. Although adaptive management processes are in place, much of the inland aquatic landscape is affected by humans; often in
Acknowledgements
This work was funded by the Department of Industry, Innovation, Science, Research and Tertiary Education (DIISRTE) via the Northern Futures Collaborative Research Network Program (CRN), the Australian Government's Stream 2 Climate Adaptation Program and ACEAS, the Australian Centre for Ecological Analysis and Synthesis. ACEAS is a facility of the Australian Government-funded Terrestrial Ecosystem Research Network (www.tern.gov.au), a research infrastructure facility established under the
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