Aquatic Ecosystems: Main Challenges and Key Opportunities

There is growing recognition for the need of a sustained global effort to meet the immense challenges of managing the Earth’s water resources. At the 2002 WSSD, participating countries committed themselves to halving the proportion of people who lack access to safe drinking water and sanitation by 2015 (Millennium Development Goal Target 10) and significantly reducing the rate of biodiversity loss in aquatic ecosystems by 2010. Reconciling these two goals constitutes a major challenge. The implementation of IWRM schemes on regional and local scales; the increasing use of ecosystem approaches focusing on river basins and their interaction with coastal zones; the decommissioning of dams in North America and Europe; and the many different river and wetland restoration projects taking place throughout the world all suggest that these commitments are starting to be taken seriously, although change is slow and not happening in every part of the world.

It is clear that if we continue to ignore ecosystem processes and functions, human activities will lead to the continuing degradation of coastal and freshwater ecosystems, as well as the loss of biodiversity and a consequential decline in human well-being. The purpose of this brief article is to address the current condition of freshwater ecosystems and their capacity to deliver an array of life-supporting ecosystem goods and services. It looks critically at several different management approaches and policies, and concludes by identifying some of the challenges that human society must face in attempting to achieve the Millennium Development Goals (MDGs) related to water resources and other international targets, such as those related to biodiversity and climate change.

Content Table

The Value (environmental and social) of Aquatic Ecosystems

The first United Nations World Water Development Report (WWAP, 2003) noted that a healthy and unpolluted natural environment is essential for human well-being and sustainable development, stressing that aquatic ecosystems and their dependent species are an integral part of our lives and provide a resource base that helps us to meet a multitude of human and ecosystem needs (WWAP, 2003). These goods and services include water for human consumption, food production, irrigation, energy generation, regulating services (e.g. flood mitigation, water filtration, aquifer recharge and nutrient cycling), and transport and recreational services (Constanza, R., D´Arge, R. ; de Groot, R. 1997). Their value is irreplaceable, and they are an important part of the water, energy, health, agriculture and biodiversity sectors, which are essential for poverty alleviation and socio-economic development. However, as WWDR1 shows, these ecosystems are under severe pressures that threaten their ability to meet the multiple and growing demands placed upon them.

Aquatic Ecosystems – Status and Trends

Aquatic ecosystems refer not only to coastal waters, rivers and lakes, but also to a complex and interconnected system of permanent and temporary habitats, with a high degree of seasonal variations. For instance, the term ‘wetland’ describes a particular group of aquatic habitats representing a variety of shallow, vegetated systems, such as bogs, marshes, swamps, floodplains, Coastal lagoons, estuaries, etc… where the shallowest sites are often transitional areas and can be seasonally or intermittently flooded (Revenga, C., Brunner, J., Hinninger N., Kassem K., Payne, R. 2000).

The majority of us live in temperate and subtropical regions centred around coastal or inland water systems. Coastal waters, rivers, lakes, wetlands, aquifers and other inland water systems such as swamps and fens have, as a consequence, been subjected to disproportionate humaninduced pressures (UNEP, 2002b). These include construction along coastlines for harbors and urban expansion, alteration of river systems for navigation and water storage, drainage of wetlands to increase farmland, overexploitation of fisheries, and multiple sources of pollution (IUCN 2003b). Human population growth and the expansion of economic activities are collectively placing huge demands on coastal and freshwater ecosystems. Water withdrawals, for instance, have increased sixfold since the 1900s, which is twice the rate of population growth (UN, 2000).

In addition, the quality of many water bodies is declining due to increased pollution from sources such as agriculture, industry, tourism, urban runoff and domestic sewage. Increased concentrations of suspended solids in coastal waters, rivers and lakes resulting from human activity can cause significant changes in habitats. Intensified agricultural practices that rely on the application of soluble fertilizers and pesticides can result in increased nutrient runoff–one of the major causes of deterioration in water quality (Gleick, P.H.; Singh, A. and Shi, H. 2001). Pressures on aquatic ecosystems have also caused a severe decline in the condition of species. Freshwater species are more threatened with extinction than in terrestrial or marine environments (Revenga, C. and Kura Y. 2003).

In addition to those pressures, there may be others, related to the current and likely future impacts of climate change on coastal and freshwater – which are as yet not fully understood and need to be fully investigated.

Policy and Management Responses:

This article has summarized some of the most serious problems facing the world’s coastal and freshwater ecosystems, from both a social and an environmental perspective (Rast, W. and Holland M.M. 2003). While recent improvements in some areas suggest that the situation is far from hopeless, failure to address these problems will have immediate social and economic costs and long-term – in some cases irreversible – impacts on biodiversity. It is perhaps not too alarmist to talk about a crisis currently facing water resources management. The following section considers some of the current and potential responses to this crisis.

IWRM and the ecosystem 

It is becoming increasingly accepted that the most effective management approach to the sustainable use of aquatic ecosystems is embodied in the concept of IWRM (Integrated Water Resources Management). A primary difference between the traditional sectoral approach to water management and IWRM is that the latter makes the link between water resources and human activities throughout the hydrological cycle and allows ecological and socio-economic issues to be considered within an ecosystem approach. IWRM specifically considers the relationships between freshwater and coastal zones, along with other interactions between freshwater, land use and development. It seeks to reduce the negative impacts of development in a river basin through, for example, the use of alternative land-use practices that mitigate damage while maintaining economic and social benefits (GWP, 2000).

Accepted indicators, such as trends in the status of biodiversity, and pollution measurements, such as BOD and nitrate concentrations in water, indicate the continuing deterioration of our coastal and freshwater aquatic ecosystems. In addition, global indicators of river fragmentation and flow regulation show that most of the large river systems are strongly or moderately affected by dams and altered flows.

Some challenges

For the past decade, despite efforts to minimize or reverse these trends, aquatic ecosystems have continued to deteriorate – with freshwater systems declining at an even faster rate than marine or terrestrial ecosystems. Some specific habitats, such as freshwaters in arid areas and semi-enclosed seas, have been particularly affected. Policy measures should include the IWRM and ecosystem approaches, however, this requires a shift from the traditional sectoral approach to water management. It also requires a better understanding of ecosystem functioning. However, due to a widespread lack of comprehensive and coordinated monitoring programmes, our understanding of the status of many of these ecosystems remains poor or incomplete. Indeed, very little information is available on the extent and quality of aquatic ecosystems. If the international community is serious about monitoring indicators that accurately describe the status of these ecosystems, habitats, species and their protection, in order to evaluate progress towards the WSSD’s and Convention of Biological Diversity’s 2010 target of reducing the rate of biodiversity loss, considerable improvements in the data quality, formats and geographical coverage are urgently required. Indeed, the ecosystem indicators presented today are only ever as good as the data that supports them.


Constanza, R., D´Arge, R. ; de Groot, R. 1997. The value of the world’s ecosystems services and natural capital. Nature 387: 253–60.

FAO, 2003. Review of the state of world fishery resources: inland fisheries FAO Fisheries Circular No. 942, Rev. 1 Rome.

Gleick, P.H.; Singh, A. and Shi, H. 2001. Threats to the world’s freshwater resources. Pacific Institute for Studies in Development, Environment, and Security, Oakland, California.

Global Water Partnership. 2000. Integrated water resources management. Global Water Partnership, Technical Advisory Committee Background Paper No. 4, Stockholm.

IUCN 2003b. Flow: The Essentials of Environmental Flows. M. Dyson, G. Bergkamp, and J. Scanlon (eds). IUCN, Gland, Switzerland and Cambridge, U.K.

Rast, W. and Holland M.M. 2003. Sustainable freshwater resources: Achieving secure water supplies. In: Holland, M.M., E.R. Blood and L.R. Shaffer (eds.), Achieving Sustainable Freshwater Resources, A Web of Connections, Island Press, Washington. p. 283-315.

Revenga, C., Brunner, J., Hinninger N., Kassem K., Payne, R. 2000. Pilot Analysis of Global Ecosystems: Freshwater Systems. Washington DC, World Resources Institute.

Revenga, C. and Kura Y. 2003. Status and Trends of Biodiversity of Inland Water Ecosystems.Secretariat of the Convention on Biological Diversity, Montreal, Technical Series

UN. 2000. UN Millennium Development Goals (MDG), United Nations, New York (

UNEP, 2002b. Vital Water Graphics- An overview of the State of the World’s Fresh and Marine Waters. UNEP, Nairobi, Kenya. ISBN: 92-807-2236-0.

WWAP, 2003. Water for people, water for life. World Water Development Report, UNESCO,

World Water Assessment Programme, Berghhan Books, London.

WWAP, 2006. Water, a shared responsability. World Water Development Report 2, UNESCO,

World Water Assessment Programme, Berghhan Books, New York.


This article was authored by Salif Diop, in collaboration with Neeyati Patel from DEWA (UNEP, Division of Early Warning and Assessment).

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