How South Africa’s mangrove forests sequester carbon

Date:20 March 2020 Author: Leila Stein Tags:, ,

South Africa’s mangrove forests have been identified as possible ‘carbon sinks.’ This means they could absorb and use carbon dioxide effectively.

New research has shown that marine ecosystems are particularly interesting as potential carbon sinks or stores. Coastal wetlands like mangroves, salt marshes and seagrasses can store more carbon than terrestrial ecosystems.

This is because the waterlogged soils preserve the organic carbon and prevent decomposition. The soils also build up over time and if left undisturbed, this “blue carbon” can accumulate for thousands of years.

This new research studied carbon storage by the Nxaxo Estuary, on the coastline of the Eastern Cape and found that total ecosystem carbon storage in this estuary was 234.9 megagrams of carbon per hectare, or Mg C/ha.

This is less than the global average for mangroves, which has been recorded as 386 Mg C/ha by the International Union for Conservation of Nature (IUCN) Blue Carbon Initiative. But, according to the researchers, is similar to other southern hemisphere warm-temperate mangrove sites in Australia and New Zealand.

Despite its relative storage to these other sites, the researchers noted that the storage was relatively low in the Nxaxo Estuary.

“Like other mangrove sites around the world, the soil carbon pool made the largest contribution towards the total carbon storage. Soil carbon was positively related to soil organic matter, which increased with depth,” said Jaime Leigh Johnson and Jacqueline Raw, the two researchers on the project.

“As the soil carbon makes the largest contribution to the total ecosystem carbon stock, it is important that management objectives focus on preventing degradation. If soil carbon stocks are lost by conversion of mangroves through land-use changes, recovery of these stocks is not guaranteed,” they said.

In the next phase of their research, Johnson and Raw have recommended looking at mangrove forests in KwaZulu-Natal for their sequestering abilities. They explain that this will determine whether the mangroves in that region could be considered viable for carbon offset projects.

This article was originally published in The Conversation.

Image: Jaime Leigh Johnson and Jacqueline Raw

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