Wetland : A Carbon Sink

- By Mugdha Gaonkar

Carbon is the key building block of life on earth. The carbon cycle is the process by which natural system absorbs and releases carbon. Plants and animals use carbon to build their cell structure. Carbon can also be stored in the soil. Stored carbon is released in the atmosphere through various processes like respiration, decomposition, burning of fossils etc.

Industrial revolution in the early 1900’s led to overall economic development around the world but consequently the excessive burning of fossil fuels to run these industries which continue even today has adversely impacted carbon cycle. The imprudent burning of fossils for energy releases cocktail of toxic gases in the atmosphere than it can process naturally. By far, carbon dioxide is the most concerning among the other gases like carbon monoxide, various hydrocarbons, SOx, NOx, VOCs etc. The natural sequestration capacity of plants is reduced because of human activities like a clearing of forests, reclaiming wetlands etc. These carbon emissions are a major driver of the greenhouse effect and human-induced climate change.

Wetlands play a significant role in landscape function, including cycling of carbon, water purification, regulation of flows, food and fibre production, provision of habitats and tourism & recreation services. Wetlands play a dynamic and fundamental role in absorbing atmospheric carbon. According to the Ramsar Scientific and Technical Review Panel, wetlands cover just 9% of the planet’s land surface, yet are estimated to store 35% of terrestrial carbon.

Wetlands are centres of high productivity in the landscape, they have a high capability to sequester carbon. As depositional areas, wetlands can also store carbon-rich organic sediments. Generally, undisturbed or intact wetlands tend to act as ‘carbon sinks’ owing to their dense vegetation, algal activity, and soils. However, under anaerobic conditions, wetlands can also produce greenhouse gases such as methane and nitrous oxide but this is limited to saline conditions only. The capacity of wetlands to store carbon varies widely with the type of wetland, temperature, soil, and availability of water. Plants in the wetlands have a higher growth rate, which helps to store a large amount of carbon. The rise in temperature acts as a positive feedback system for wetlands to sequester carbon.

There are two prominent Green House Gases (GHGs), methane and nitrous oxide which are natural products of wetlands. Wetland is also a huge repository of methane. Wetland is a place where excess Nitrogen get fixed by the process of nitrification. Nitrogen fixation is processed in the aerobic zone of wetlands but at the same time in the anaerobic zone a complementary process also occurs, which is known as denitrification where nitrite is transformed to Nitrous oxide. Thus, the dual nature of wetlands is evident in terms of GHG sink and source.

There are many factors threatening the existence of wetlands. Some of the major ones which are usually caused by anthropogenic activities such as intensive agriculture, mining, encroachments, dumping, dam constructions, draining, and development etc.

Restoring and protecting wetlands boons an important opportunity for mitigating greenhouse gas emissions. Greater thought needs to be given to the roles of wetlands as carbon sources, sinks and storages when designing climate protection and natural resource programs.