Estuarine Ecosystems
Despite playing a critical role in the functioning of the planet, estuarine ecosystems are threatened by the growing intensity of human activity in the world’s coastal regions. These pressures are further amplified by growing demands on the planet’s limited supplies of freshwater—causing inflows to estuaries to be polluted, reduced, or stopped altogether.
What is an Estuary?
Estuaries are semi-enclosed coastal bodies of water which have a free connection with the open sea and within which sea water is mixed with freshwater from land drainage. There are two basic types of estuaries—river mouth estuaries and lagoonal estuaries. Both types of estuary provide important ecological goods and services to people.
The Ecological Goods and Services of Estuaries
Estuaries are among the most productive ecosystems in the world for plant and animal production. They are critical habitats to many species of fish, shellfish, birds and marine mammals. They are nurseries for many species of fish that are harvested in the open sea. In temperate regions, some three-quarters of all commercially important marine fish depend upon estuaries at some stage in their life cycle. Communities living near estuaries around the world depend on them for their food security and livelihoods. Estuaries therefore not only play a critical role in the generation of fish and shellfish, but also form the basis of many local and regional economies.
Estuaries are waste processors. The plants, animals and bacteria that are found in estuaries quickly break down and recycle organic matter. This leads to the very high productivity of plants and animals that is typical of estuaries. The mixing and recycling of organic matter enables estuaries to absorb part of the human wastewater and byproducts of surrounding cities and towns. Estuaries thus serve as a filter between terrestrial and oceanic systems, capturing and processing the many different substances that flow from the land to the ocean.
Estuaries, and their associated wetlands, serve as storm buffers that absorb wave energy and rising tidal waters during storms. The rich soils and abundant freshwater in the deltas of rivers also make for some of the world’s best farmland. Estuaries are central to commerce and trade in many regions and have traditionally been a place for human settlement. As places of great beauty, estuaries strongly influence the high value of waterfront property and provide for a diversity of economically important recreational activities. They provide valuable open space in coastal towns and cities.
The Threats to Estuarine Ecosystems
Complicated interconnections exist between the quality, quantity and timing of freshwater inflows and the health of estuaries. All of the goods and services that estuaries provide are threatened when freshwater inflows are changed. Even a small change in the flow of freshwater may affect the fundamental functioning of an estuary, which in turn will have ramifications on the animals and plants, as well as on human populations dependent upon the estuary. In many cases, upstream alterations to the volume, timing and quality of freshwater inflows have resulted in catastrophic destruction of downstream habitats, loss of species and degradation of ecosystems adapted to a certain range of freshwater inflows.
The Urgent Need for Effective Management of Inflows to Estuaries
There is an urgent need for estuarine management that effectively addresses threats to the health of estuarine ecosystems. Effective estuarine management begins by recognizing the need to allocate sufficient freshwater to sustain rivers and estuaries as healthy ecosystems and then making allocations for additional human needs. Any effort to do so necessitates the integration of science with the effective governance of freshwater flows to estuaries. For more information on estuarine management, see Managing Freshwater Inflows to Estuaries: A Method Guide (3.14MB PDF).
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