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Wetlands

Wetlands are ubiquitous on Earth, and provide with a number of "services" for life on Earth - including human beings' ones. Their observation is thus an important stake for all. 

Strictly speaking, wetlands are wherever water meets land, including lakes and rivers, estuaries, deltas and coastal areas but also swamps and marshes, wet grasslands, peatlands, oases, floodplains and flooded forests, mangroves, man-made fish ponds, rice paddies and salt pans, etc. They are found everywhere around Earth, under every climate and altitude. Mostly, when talking wetland, though, rivers and lakes proper may not be the main topic, more swamps and marshes, or flooded areas. 

 

Sentinel-2A optical image of an area near Selestat (Alsace, France) with wetlands. (Credits Sertit/Icube)
Sentinel-2A optical image of an area near Selestat (Alsace, France) with wetlands. (Credits Sertit/Icube)
Photo of the Selestat wetlands (Credits H. Yésou, Sertit/Icube)
Photo of the Selestat wetlands (Credits H. Yésou, Sertit/Icube)

Wetlands'services

Wetlands provide a number of services, for everydays' life. They help in water resources control, disaster reduction, flood wave control, filter of pollutants, limiting wave erosion along shorelines. They are thus important for Economy, all the more since they also provide livelihoods for local indigenous people: fertile soils, fish, grazing (millions of people are concerned, one way or the other). 

They are also support to remarkable level of biodiversity. The combination of shallow water, high levels of nutrients, and high primary productivity (the amount of biomass produced) is ideal for the development of organisms, so they are breeding grounds for birds, fish, shellfish and amphibians. Migratory birds frequently have stops in them. This can lead to ecotourism, and so Economy and people's livelihood.

And, last but not least, wetlands have a huge impact on climate. They regulate carbon exchanges with the atmosphere via CO2 and CH4(carbon dioxide and methane) evasion. The Arctic wetlands, in particular, store enormous amounts of those greenhouse gases.

Credits Global Carbon Project
Credits Global Carbon Project

Observations & monitoring

Observing wetlands depends on the size and latitude of them. Optical observation by satellite (eg with Sentinel-2) is one of the priviledged means of measuring their extent.

Altimetry is helping to better know what is controlling the flow, water paths, and the water exchange either between rivers or between river and wetlands. Swot will provide with both extent and height at high resolution all over Earth (up to 77° in Latitude North and South).

Sentinel-2B optical image of an area near Noviy Urengoy city. This is a typical artic wetland (Credits Sertit/Icube)
Sentinel-2B optical image of an area near Noviy Urengoy city. This is a typical artic wetland (Credits Sertit/Icube)
Picture of the area (near Noviy Urengoy city), taken from an airplane. (Credits E. Zakharova/A. Kouraev)
Picture of the area (near Noviy Urengoy city), taken from an airplane. (Credits E. Zakharova/A. Kouraev)

Wetlands'stakes

All this means that threats to wetlands have impact on those domains. And since they have been much disparaged as source of epidemics, lands wasted for agriculture, etc., they were often dried out in the past. Inland wetlands declined by 70-75% and coastal ones by 62-63% in the XXe century. The disappearance of a marsh will threatened biodiversity. Climate change is having also an effect on Arctic swamps, leading to methane emission. On the other side, small lakes and ponds are now built for flood control, and natural wetlands are more and more made nature preserves. 

 

References

C.J. Vorosmarty, P.B. McIntyre, M.O. Gessner, D. Dudgeon, A. Prusevich, P. Green, S. Glidden, S.E. Bunn, C.A. Sullivan, C. Reidy Liermann, and P.M. Davies,  Global threats to human water security and river biodiversity, Nature 467, 555-561 (30 September 2010) doi:10.1038/nature09440

Global estimate of threats to river biodiversity (Credits riverthreat.net)
Global estimate of threats to river biodiversity (Credits riverthreat.net)

On this topic:

Higher resolution knowledge of flooded areas over the whole Earth
Waiting for Swot, knowledge of wetlands and flooded areas can be computed from the wealth of satellite observation already available, combining them in all possible ways. It will provide with validation data when Swot will be launched
Groundwater from altimetry
In the Amazon plain, the groundwater level is about the same than the rivers' and lakes', which can be measured by altimetry
Melting in the Kara Sea
AltiKa data over the Kara Sea enable to distinguish there the effects of ice melting and also the presence of polylinias.
Ob bogs and wetlands
Saral is giving very promising results, especially for wetlands and more generally inland waters. The measurements over the Ob basin area are providing with a mean to discriminate between water, ice and dry lands.
Missing: water
Altimetry enable to monitor wetland surfaces in Siberia as well as river run-offs. Comparisons between those and precipitation lead to look for water missing to balance the water budget.
Altimetry in Mesopotamia
Altimetry can be used to monitor the level of the numerous reservoirs and lakes, as well as the marshes of the Tigris-Euphrates basin.
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