Wetland as Carbon Sinks

MA Salam, Gunajit Oinam, Abdul Malik, Hemanta Pokhrel, LP Mudoi, Rajdeep Datta, SK Bhagabati *

Joining of two rivers - Nambul and Oinam and meet at Loktak :: Pix - Lamdamba Oinam

Wetland is an "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".

Wetlands are amongst the most productive ecosystems on the Earth and provide many important services to human society. However, they are also ecologically sensitive and adaptive systems. It exhibits enormous diversity according to their genesis, geographical location, water regime and chemistry, dominant species, and soil and sediment characteristics.

Globally, the area extent of wetland ecosystems ranges from 917 million hectares to more than 1275m ha with an estimated economic value of about US $ 15 trillion a year. They provide a potential sink for atmospheric carbon but if not managed properly, they become a source of greenhouse gases.

However, only limited studies have been conducted to assess the roles and potentials of wetlands in carbon sequestration. They are often termed as "Nature's Kidneys" of landscape because of their ability to store, assimilation and transform contamination lost from the land before they reach waterways.

Wetlands are also referred to as "Biological Supermarkets" because they have extensive food webs that attract animals species, they possess unique habit and they are also rich in biodiversity. Wetland soils contain a disproportionate share of the earth's total carbon.

Although they occupy only between 5% and 8% of the earth's total land surface, their soils hold 35% or more of the estimated 1500 gigatons (Gt, or billion metric tonnes) of organic carbon that is stored in soils. Despite their importance, wetland have been historically underappreciated, and an estimated 87% of global wetland area has been lost since 1700.

They ae threatened by pollution, transformation, water extraction, and modification. Such disturbance can undermine a wetland's ability to capture carbon, but critically, damage to wetlands can also release significant amounts of carbon that have already been stored.

CARBON SINKS

Carbon sinks absorb more carbon then they release acting like sponges that can soak up carbon compounds such as carbon dioxide. They are either a natural or artificial (man-made) reservoir that can store carbon for an indefinite period. The process through which carbon sinks can remove carbon dioxide from the atmosphere is called "carbon sequestration". Natural carbon sinks are plants, soil, and oceans.

Drainage and degradation of wetlands can release significant amount of this stored carbon back into the atmosphere in the form of methane and reduce the ability of wetlands to sequester additional carbon. Better management practices can help protect these stored of carbon and the ability of wetlands to sequester it.

Plants grab carbon dioxide from the atmosphere to use in photosynthesis; some of this carbon is transferred to soil as plants die and decompose. Combined the Earth's land and ocean sinks absorb about half of all carbon dioxide emission from human activities.

WHY ARE CARBON SINK IMPORTANT

Climate change is an immense challenge. The earth's climate is changing at an unprecedented rate. The effects of a changing climate are many and vary by location, with intensifying storm activity, rising sea levels and more frequent floods and droughts predicted. Internationally renowned experts have highlighted that to void the most serious impacts of climate change we need to limit global warming to 2 degree Celsius between now and 2100.

This is no easy task; it means that global greenhouse gas (GHG) emissions need to be reduced by 40 to 70 percent by 2050 and that carbon neutrality (i.e. Zero emissions) needs to be reached by the end of the century at the latest. Ways to mitigate climate change is very important and Carbon sinks could play a very important role.

Globally wetlands represent just three percent of total land area, but sequester 30 percent of all soil carbon. It has been estimated that different kinds of wetlands contain 350-535Gt C, corresponding to 20-25% of world's organic soil carbon.

MECHANISM OF CARBON STORAGE IN WETLAND

Wetland ecosystems have unique characteristics as they are the sources of cultural, economic and biological diversity. These unique characteristics affect carbon dynamics and there are few mechanisms that aid in carbon storage in wetland ecosystem.

Plants absorb carbon dioxide from the air via pores in their leaves, called stomata, and perform photosynthesis to convert this gas into carbon, stored in their bodily tissues like roots, stems and leaves.

Animals which consume plants called herbivores, transfer the stored carbon into the soil via their excreta. Plants and animals, on dying, are decomposed by soil microbes, which also release carbon. Soil carbon is stored in the form of decomposing plant and animal fragments, microbes such as nematodes, and fungi, and in the form of a mineral-carbon composite called humus.

Most of the carbon dioxide is sequestered in the oceans by plankton and aquatic plants which absorbed it via photosynthesis. When these die, they sink to the bottom and decompose, releasing carbon deposits.

FACTORS INFLUENCING CARBON DEPOSITION AND LONG-TERM STORAGE IN WETLANDS

The balance between carbon input (organic matter production) and output (decomposition, methanogenesis, etc.) and the resulting storage of carbon in wetlands depend on several factors such as
o The topography and the geological position of wetland
o The hydrological regime
o The type of plant present
o The temperature and moisture of the soil
o pH and the morphology

CARBON SEQUESTRATION IN VARIOUS TYPES OF WETLANDS AT A GLOBAL SCALE

Wetlands are critical to mitigation climate change through capture and storage of carbon. They have an important and underestimated role in both carbon storage and the regulation of greenhouse gas emissions.

The Expert Meeting on Water, Wetlands, Biodiversity and Climate Change, involving the Ramsar Secretariat, the Ramsar Scientific and Technical Review Panel (STRP) and the Secretariat of the convention on biological diversity (CBD), concluded that it is time for the international community to recognise that wetlands are more important as carbon stores than many other biomes and that efforts to protect them should be expanded.

There are still uncertainties about the overall carbon balance in wetland systems, and even about the global area of wetlands and their existing carbon stocks. The Ramsar STRP calculated in 2007 that there were 1280 million hectares of wetlands (9 per cent of the planet's land surface), but this may be an underestimate. It is estimated that they contain about 35% of the global terrestrial carbon.

Coastal and estuarine wetlands have one of the highest primary productivities on earth but are small in their total global area. Seagrass meadows cover anywhere less than 0.2% of ocean floor, but store about 10% of the carbon buried in the ocean each year. Seagrasses are being lost at the rate of 1.5% per year and have lost approximately 30% of historical global coverage.

Mangroves cover about 14-15 million hectares around the world but are steadily disappearing. These coastal forests trap an estimated 31 to 34 billion kilograms of carbon every year, making them carbon storage powerhouses. Peat covers about 3 per cent of the global land surface (4million km2) but is believed to contain the planet's largest store of carbon. Peatlands store about 30% of terrestrial carbon (400-700 Giga tons)

Floodplain areas are often the most productive in the landscape, and consequently the capacity for carbon storage is high. However, watering of floodplains may lead to anaerobic conditions and emissions of methane into the atmosphere.

CONCLUSION

Wetlands play an important role in landscape function, including cycling of carbon, water and nutrients, food and fibre production, water purification, regulation of flows, provision of habitats, support for animal migrations, and tourism and recreation services. Wetlands are centres of high productivity in the landscape and therefore have a high capacity to sequester and store carbon.

Because wetlands currently store significant amount of carbon, drainage and degradation of wetlands results in large emissions of atmospheric carbon. There hare synergies between programs to conserve wetlands for biodiversity conservation and climate change adaptation/mitigation.

Further information and research is required on wetlands, including inventories of wetland area and type, baseline carbon storage, sequestration and emission rates, and measurement/ modelling of carbon flows in different types of wetlands.


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