Coastal wetlands - A hope in the path of carbon storage

Carbon dioxide or CO2 is an atmospheric gas ideally found in trace amounts (<1%). However, it is more famous as a GHG or Greenhouse gas these days owing to its overall potential in accelerating global warming. At the moment when this article gets generated, atmospheric CO2 is at ~410.25ppm or 3204 Gigatonnes circulating around and another 500g extra as our laptop’s contribution. CO2 is so beyond threshold in the atmosphere that it needs to be sequestered as carbon into soil or elsewhere, as, its anthropogenic emissions need to be reduced. Carbon sequestration generally occurs across all biomes above and below the ground naturally. Yet below the ground storage of carbon is the most efficient and wetlands are undeniably the best after sea.

What is carbon sequestration in wetlands?

Like numerous ecosystem services (benefits obtained to people from ecosystems), carbon sequestration in wetlands is inevitable and probably a highest need of the hour. It refers to the transference of CO2 from the atmosphere into wetlands’ soil carbon pool as soil organic matter. For every activity however useful they might be, trade-offs are obvious; the sequestered carbon overtime shall remain in the soil and benefit living organisms only with an input-output balance of carbon/forms. There are higher chances, the organic matter gets disintegrated into soluble inorganic matter, through a process called mineralization and eventually emit CO2 and also a more global warming potent gas, methane or CH4, which might hinder the capacity of wetlands to act as a net carbon sink. Global methane emissions from fresh or comparatively less saline wetlands range between 150 - 42g m-2 y-1 however in coastal wetlands its hardly 1g m-2 y-1.

Unlike other wetlands, coastal wetlands are high in salinity and are known as polyhaline since salinity in them range above 18ppt. These wetlands are well exposed to an anion called sulfate (abundant in seawater) which allows sulfate-reducing bacteria to outperform methanogens (methane-producing bacteria) for energy, thereby reducing methane production and acting as an effective net carbon sink.

Terrestrial biomes like forest and tundra consist of enormous carbon aboveground, while wetlands, on the other hand, stock carbon underground and holds its largest reserve till date despite its lesser area worldwide. With just around 8 million km2, wetlands sequester more than 500 Pg C (1Pg C= 1015g) underground alone, when with more than 18 million km2, forest sequester just around 300 Pg C above and underground combined.

Scope of Vembanad wetlands as an effective carbon sink for Peninsular India

Vembanad wetland covers an area of ~2033.02km2 with coastal wetlands alone holding atleast 65-70% of the area. Considering the total land area of Kerala, which is roughly 38,863 km², Vembanad covers almost 5% of it, making latter the biggest blue carbon (carbon stored in marine and coastal ecosystems) sink in India. With an overall carbon emission of over 2,299 million tonnes in 2018, Indian emissions are on a rise by almost 4.8%. At present India, is the fourth largest carbon emitter after China, US and the EU, though growing faster lately that US and China. Places like Vembanad had been under constant threat of reclamation owing to developmental pressures and have lost around 63.62km2 of water spread until 1970; this excludes wetland reclamations.

Being the largest wetland and Ramsar site (wetland site designated to be of international importance under the Ramsar Convention) Vembanad holds huge potential as an effective blue carbon sink. In the aeon, when UN general assembly have declared the decade of restoration between 2021 – 2030, its high time to focus of wetland restoration alongside afforestation drives. Since biogeochemistry of carbon sequestration in wetlands are comparatively well-studied and restoration strategies are better established, actions could be taken with promising results.

ATREE (Ashoka Trust for Research in Ecology and the Environment) is a global NGO, based in Bangalore, working towards generation of interdisciplinary knowledge in informing policy and practise for conservation and sustainability. ATREE runs a wetland conservation program at Vembanad, Alappuzha, Kerala in the name of CERC (Community Environmental Resource Centre) aimed at identification of capacity gaps and its development for better institutional networks that shall lead to an integrated participatory management of Vembanad wetlands. CERC in its decade long work in the system have identified and is still in the process of deciphering critical threats affecting the wetland in getting reclaimed at a much faster rate.

Despite, strong legislations in the country, wetlands get reclaimed no matter what. The main culprit to be blamed is science itself. Understandings about the service wetlands provide are still unknown to majority of the masses, who believe these are just wastelands, as, it’s some sans “so called” development area and tend to reclaim it expecting monetary benefits. With a global hunger index at 103, India’s clear need of the hour is survival, any conservation effort forgetting this fact is a clear doom. Wetland conservation proves not just to be a mere climate action, more than a carbon sink, it is also a nutrient sink. It distributes organic as well as inorganic matter to nearby lands via the waterbodies within the vicinity. Coastal wetlands since are balanced carbon sinks, tend to mitigate radiative forcing of climate change. However, ongoing studies at CERC is of the opinion that change in hydrological regimes of the wetland mainly due to reclamations could increase the amount of air in soil leading to “priming effect”. This effect happens when aeration of soil activates enzyme activities that accelerate mineralization of organic matter, subsequently increasing CO2 emissions. However, this also leads to an increase in new carbon to the soil as well as nearby running waters, which could support plant life. On the retrospect, post heavy demineralization, a surge in nitrogen fertilization shall also lead to decreased root growth in wetland plants, decelerating carbon sequestration.

Words of Caution

UN Intergovernmental Panel on Climate Change (IPCC) in 2018 through its SR15 (Special Report on Global Warming of 1.5 °C), had warned a 12-year cap for acting against climate change to keep the rising temperature below 1.5°C since pre-industrial era. To stabilize or at worst lower global temperature, we have to attain a balance in sources and sinks (2S’s) of carbon. With a net zero between the 2S’s, at carbon neutrality, the CO2 emissions shall decline and reach a new equilibrium, stabilizing global temperature for centuries ahead.

At least a fair percentage of global population have already started facing the heat of climate change at various level. Take water scarcity, between 2000s and 1900s, there had been a whopping 44% increase in global population facing this threat. Extreme hydrological events have already started hitting, and Kerala is the best example to spot, with respect to 2018 floods, following drought, and repeat floods in 2019 almost the same time as the former. The alarming decrease in projected water quality is evident from various studies; albeit, they are from developed countries with comparatively better quality than developing. If global warming continues and the proposed targets of 1.5˚C or atleast 2˚C is not attained, water scarcity might get tripled or even worse. Floods could go up anywhere from 150% of present to ~580% with a followed soil erosion and drought. Similar would be case with plant productivity, an initial increase in metabolism with temperature rise wouldn’t be the after effect of global temperature crossing 1.5˚C, instead might succumb to heat and simply die off.

Limiting global warming to 1.5˚C with no or limited overshoot is the best to do for a projected hope control climate change. However, it requires steep decrease in CO2 emissions as stated within Paris Agreement 2016. Since climate change has the potential to affect all sectors of life, it is high time to move towards urgent steps towards carbon neutrality.

The Author is Anu Radhakrishnan , a senior program officer at ATREE CERC.