Mangrove forest in Thailand. Image credits: Public Domain Pictures
Chuanyi Guo, Pei Sun Loh, Jianxiong Hu, Zengxuan Chen, Siriporn Pradit, Chantha Oeurng, Ty Sok, Che Abd Rahim Mohamed, Choon Weng Lee, Chui Wei Bong, Xixi Lu, Gusti Z. Anshari, Selvaraj Kandasamy, & Jianjun Wang. (2024). Factors influencing mangrove carbon storage and its response to environmental stress. Frontiers in Marine Science, 11. https://doi.org/10.3389/fmars.2024.1410183
The Impressive Abilities of Underwater Trees
Just like trees on land are essential to human survival, mangroves – trees that live immersed in salt-water – provide invaluable protection and resources to the underwater ecosystem. Mangroves are found on tropical coasts and are known for their incredible salt-tolerance. The forests they compose act as a barrier to the coast, mitigating storm surge, trapping litter, reducing wind and wave activity, and purifying water. Although they cover only 0.1% of the Earth’s land area, their impressively high carbon storage capacity makes them critical in mitigating climate change.
Image credits: Hayden Dunsel via Unsplash
The Abilities of Mangroves Are Threatened
The health of mangroves and their ability to effectively store carbon depends on several natural factors including pH, salinity, climate, tides, and surrounding vegetation types. Their health is also affected by sea level, temperature, erosion, and space, all of which have been impacted by climate change and human activities in recent years. For example, increases in coastal erosion and sea level rise have caused mangrove forests to move further inland and decrease in area by an alarming 3.4% between 1996 and 2020. Further, the destruction of mangrove forests for agricultural space has exacerbated the problem. This loss is especially concerning because as mangroves degrade or disappear, they release their stored carbon into the atmosphere, worsening the effects of climate change.
In order to understand just how big this problem has become, scientists in this study set out to measure how much mangroves’ carbon storage abilities have been impacted by different factors in recent years.
Mangroves in China
The study took place at the 8,715 ha mangrove reserve in Pearl Bay, Guangxi, China. Researchers collected two sediment cores from the reserve and analyzed each core’s carbon storage over time. They measured the factors that contribute to carbon storage, such as sedimentation rates, tidal ranges, and the origin of organic matter (OM). The goal of this research was to determine whether the forest’s carbon storage capacity has been impacted by climate change.
Mangrove Tree Park Shenzhen China. Image credits: Chris via Flickr Creative Commons
The Soil Revealed That…
In general, mangrove forests with lower tidal ranges and slower sedimentation rates were found to store more carbon in their soils. This is because lower tidal ranges reduce the likelihood of carbon being washed away, allowing it to accumulate in the sediments.
Mangroves with OM that came mostly from local sources, such as fallen leaves and other plant material, also had higher carbon stocks. This suggests that environmental factors like tidal range and sedimentation rate play a significant role in determining how much carbon mangrove ecosystems can store.
The results of this study were promising: mangroves in Pearl Bay that fit the criteria for high carbon storage (small tidal ranges, slow sedimentation rates, and locally-sourced organic matter) had larger carbon stocks. However, the sediments did reveal that the organic matter in the mangroves decreased over time, suggesting that the mangrove forests may have degraded between 1963 and 2020. The researchers estimated that the degradation took place from 2001 to 2020, likely due to human activities. Further, while mangroves are capable of adapting under pressures of sea level rise and an influx of wastewater, they may not be able to keep up as these threats accelerate.
A (Semi) Positive Future
This study emphasizes the importance of managing mangroves sustainably, a task that could be achieved through national policies that specifically target agriculture and aquaculture activities and generally limit activities that increase the rate of climate change. Luckily, the high storage capacity of the mangroves studied in Pearl Bay indicates that the threat of climate change on mangroves in the area is low and degraded mangrove forests can be restored. However, protecting these ecosystems is extremely important in not only helping preserve their carbon storage capacity but also preventing the release of stored carbon in the future.
I received my MPS in Marine Biology & Ecology from the University of Miami’s Rosenstiel School of Marine, Atmospheric, and Earth Sciences in May 2024. I plan to use my education and experience to pursue a career in science writing or film production to help communicate the importance of the ocean to the general public.