The overarching objective of an ecosystem approach, and thus of any regime for maintaining environmental flows, centers around the ecosystem services concept, which aims to promote understanding of the nature and value of socially beneficial services provided by natural ecosystems and to provide a methodology for their valuation and consideration within legal decision-making processes. The 2005 Millennium Ecosystem Assessment provides an essential typology of ecosystem services,69 which can assist in transboundary water cooperation by providing watercourse states with a common understanding of the costs and benefits for each state of measures for the utilization and protection of shared watercourse ecosystems.
In this way, the ecosystem services concept can improve the prospects for agreement over benefit-sharing arrangements amongst watercourse states, potentially leading to both optimized utilization and more effective protection of shared watercourse ecosystems.70 Accepted methodologies for valuing ecosystem services might also facilitate consideration of state responsibility for transboundary ecological harm.71 In either role, the ecosystem approach can function to facilitate the avoidance and resolution of interstate water disputes.
Despite a “lack of attention to ecosystem services within the context of transboundary freshwater ecosystems and law,” such methodologies are increasingly commonly employed in the practice of transboundary water cooperation.72 The Mekong River Commission, for example, has developed an approach to ecosystem management that involves “an assessment of the ecosystem components and/or an assessment of the ecosystem services that are derived from the interaction of those components in support of human well-being.”73
Guidance on water resources management for the maintenance of ecosystem services has also been developed under the auspices of the Ramsar Convention74 and the Convention on Biological Diversity (CBD).7? The CBD “Strategic Plan for Biodiversity 2011-2020” confirms that a key purpose of biodiversity conservation is that of safeguarding ecosystem services essential for human well-being, and includes a number of targets relating to the ecosystem services provided by inland waters.76 An emerging legal obligation to maintain ecosystem services is supported by recent statements of the UN special rapporteur on human rights and the environment framing the issue as a human right of access to ecosystem services.77
Discussion of ecosystem services often includes consideration of the role of payment for ecosystem services (PES) and, though this concept is not extensively developed in international legal practice,78 key actors in the field of transboundary water management provide some guidance on how such payment systems might work.79 PES can inform interstate engagement over transboundary waters because “[t]his linkage between the upstream provision of services...and the downstream utilisation of services thus provided (often water-related) has now become widely recognised and can be seen to operate on very large, often transboundary scales.”80 PES arrangements may be utilized as one element of integrated benefit-sharing arrangements, involving some sort of redistribution or compensation, to provide a potentially useful means of rebalancing competing state interests in a shared watercourse.81