“Water for ecosystems” is the new rallying cry of the hydrological and aquatic sciences. Many countries in the world have recently reformed water policy and legislation, or are in the process of doing so, to recognize the need to allocate and manage water for protection and maintenance of ecosystems. While the spirit is laudable, and there is considerable enthusiasm amongst policy-makers for the idea of water for ecosystems, nevertheless there is reluctance amongst affected water users to accept the inevitable reductions in their water allocations, skepticism amongst water managers as to how the concept can be implemented practically, and concern amongst scientists now being asked to quantify the water needed to protect an ecosystem and make recommendations on how to manage such an allocation.Reluctance and skepticism aside, the determination of water allocations for ecosystems poses some significant scientific challenges. We hope to explore supporting policies, scientific tools and current research results related to the determination of water allocations (water quantity and water quality) for ecosystems, and management of aquatic ecosystems.It is clear that if the principle of making water allocations for aquatic ecosystems is to be implemented with any real commitment by governments and stakeholders, then the water allocated to ecosystems should lead to enhancement of the quality of people’s lives, and should not prejudice the provision of basic water supply, sanitation and food security. However, since freshwater supplies are finite, water for ecosystems must, in almost all cases, be made available from existing water resources. This in turn means that existing water resources must be allocated and managed carefully, and excessive demands by offstream users should be reduced, in order to ensure that allocations can be made for aquatic ecosystems with a reasonable degree of assurance.Management of aquatic ecosystems requires that management activities take place within an aquatic ecosystem as well as in the surrounding catchment. One of the most important management factors is the allocation of sufficient water of an adequate quality to maintain the desired aquatic ecosystem functions. However, it is not sufficient simply to release water from dams or flow control structures to serve as allocations to aquatic ecosystems. It is necessary also to consider and manage land-based activities which impact on water resources, such as commercial forestry, which reduces available runoff at the head of a catchment; damage to riparian zones, which changes patterns of flow and erosion/deposition patterns; excessive groundwater abstraction, which can reduce baseflow to aquatic and terrestrial ecosystems. There are four necessary components to ensuring that appropriate water allocations are made for and actually reach aquatic ecosystems. As we find good examples or information on new developments, we will make them available on the feature page.Decision-making frameworks or processes which recognize aquatic ecosystems and the critical role they play, and which allow aquatic ecosystem functions to be identified and valued in the same context as offstream or direct water uses by people. These frameworks are primarily law- or policy-based.Appropriate scientific and technical tools for quantitatively determining the appropriate water allocations for maintenance of desired aquatic ecosystem functions.Appropriate management tools and measures which can be used to manage people’s demands and impacts on water resources so that water remains or is made available for aquatic ecosystems;A comprehensive strategy for implementation of the management measures which will support water allocations for aquatic ecosystems.- Heather MacKay
