“Inland waters” are aquatic-influenced environments located within land boundaries. This includes those located in coastal areas, even where adjacent to marine environments. Inland water systems can be fresh, saline or a mix of the two (brackishwater). Terminology can confuse: inland water bodies include the Caspian Sea (freshwater) and the Dead Sea (hyper-saline), whereas the Baltic Sea (also largely freshwater) would be excluded by some. A large number of the wetlands in, for example, Australia’s deep interior are saline – whereas many wetlands within only a few metres of the ocean are freshwater. Location counts, not ecological character.
Rather than impose artificial boundaries, it is better to view inland waters from the perspective of the wider ecosystem of which they are part. Most coastal aquatic habitats are therefore best considered as the lower sections of river basins – not least because they are influenced greatly by rivers. Estuaries are transitional zones between rivers and the sea. In practice, “inland waters” considerations tend to focus on fresh water – partly because freshwater environments dominate inland waters – but mainly because of the important of fresh water globally. The programme of work on inland waters and that for marine and coastal biodiversity
collaborate for relevant coastal areas.
Inland waters include lakes, rivers, ponds, streams, groundwater, springs, cave waters, floodplains, as well as bogs, marshes and swamps, which are traditionally grouped as inland wetlands.
The CBD has adopted the Ramsar Convention's definition of “wetland." The Ramsar Convention takes a broad approach in determining the wetlands that come under its aegis. Under the text of the Convention (Article 1.1), wetlands are defined as:
"Areas of marsh, fen, peatland or water, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh, brackish or salt, including areas of marine water the depth of which at low tide does not exceed six metres."
For current purposes it is sufficient to note that this definition includes all possible kinds of inland water body or ecosystem, or components thereof, including groundwater. The depth limit applies only to marine areas and not to inland water bodies.
“Inland water ecosystems” include land. From the ecological, hydrological, environmental and socio-economic perspective, all land is an integral part of an inland water ecosystem because fresh water (usually from rain) runs off it into rivers, lakes and wetlands. “Inland water habitat” also includes land that is influenced directly by aquatic habitat. For example, the vegetation near water bodies (in the riparian zone), even if never submerged, is influenced greatly by proximity to water. The clearest example of land-water interactions is with seasonally flooded areas, e.g., river floodplains, which may be dry or submerged depending on flood conditions.
Inland water ecosystems are ecologically dynamic. They are not amenable to artificial conceptual boundaries. They are best considered from the landscape or ecosystem perspective.
Inland waters biodiversity
Simply put, it is biodiversity associated with inland waters. But since all terrestrial animals and plants depend on fresh water, the boundaries between aquatic and terrestrial are blurred. At the species level, inland water biodiversity generally includes all life forms that depend upon inland water habitat for things other than simply drinking (or transpiration in plants). Besides the obvious life living within water itself (e.g., fish), this also includes many “terrestrial” species of animals (e.g., waterbirds), semi-aquatic animals (e.g., hippopotamus, crocodiles, beaver) and plants (e.g, flooded forest, mangroves, vegetation associated with the margins of water bodies). The majority of amphibians, for example, breed in fresh water.
As for all biodiversity, for inland waters the concept includes diversity at the species, genetic and ecosystem level. Species which are restricted to inland waters (e.g., freshwater fish) cannot move easily between different areas. Inland waters are therefore characterized by high endemicity of freshwater species – for example between different lakes or the upper reaches of sub-catchments of rivers, often even where located physically close to each other. This is also reflected in high levels of genetic diversity. Most importantly, ecosystem diversity (including hydrological and physical diversity within the landscape) is an extremely important aspect of the biodiversity of inland waters. This ecosystem diversity is very complex and includes both aquatic and terrestrial (landscape) influences; maintaining it is critical to maintaining ecosystem services
. Also, human interventions in the ecosystem tend to deliberately reduce this diversity (e.g., by modifying the form, and therefore function, of river channels and/or hydrology).
Where do inland waters occur?
No river can return to its source, yet all rivers must have a beginning
(Native American proverb)
Inland waters are everywhere (except marine areas and arguably the polar ice-caps – which are nevertheless composed of fresh water but rarely in liquid form). Inland waters, and particularly rivers, are part of all landscapes. At the smaller scale, inland water bodies are also present in all terrestrial biomes – including grasslands, mountains, forests, islands, agricultural ecosystems, inland sections of coastal zones and dry and sub-humid lands (in deserts, for example, the presence of oases and seasonal or transient rivers is what sustains life, including humans, in surrounding drylands).