The deep-time carbon pump
In the tidal mudflats of Myanmar's Ayeyarwady Delta, a powerful geological process is occurring at biological speed. Replanted mangrove forests are capturing atmospheric carbon and burying it in sediment at an accelerated rate. This "blue carbon" sequestration is important, as the carbon locked away in these coastal soils can remain there for centuries or even millennia. The process connects a contemporary ecosystem service with the long-term geological carbon cycle.
The Ayeyarwady Delta once hosted one of Asia's most extensive mangrove systems, with 29 confirmed species. Since the 1920s, however, huge areas were cleared for charcoal production and shrimp farming. Restoration efforts are now underway, and studies in these replanted forests reveal a surprising finding. Young, rapidly growing mangroves are far more efficient at carbon burial than their mature counterparts. This is largely because they invest heavily in creating extensive underground root networks in the bare, anoxic mud. As the roots and other organic matter get buried, the oxygen-poor conditions of the waterlogged soil prevent decomposition, effectively trapping the carbon. This buried organic material contributes to the sediment layer, building up the coastline at a rate of several millimeters per year.
Measuring the flux
Scientists quantify this carbon burial using sediment traps and by analyzing soil cores dated with radioisotopes like Lead-210. This research shows that the bulk of carbon storage—between 71% and 98% in some Indo-Pacific mangroves—is below ground. Studies on restored mangrove sites have measured carbon burial rates in the first five years of recovery at 290 to 610 grams of carbon per square meter per year (gC/m2/yr). This is double the rate found in mature forests, which averages around 120 gC/m2/yr.
The dominant mangrove species in this region's restoration projects, particularly fast-growing pioneers like Avicennia officinalis and Avicennia marina, are especially effective. Their complex aerial and sub-surface root structures are adept at trapping both autochthonous carbon (from the mangrove's own biomass) and allochthonous carbon (transported from elsewhere by tides). While a mature forest holds a larger total stock of carbon, the rate of new carbon sequestration is highest in the vigorous growth phase of a young, colonizing forest. After about 20 years, a planted mangrove forest can store around 70% of the carbon found in an intact, mature stand. This rapid accumulation demonstrates how ecosystem restoration can have a measurable impact on carbon fluxes in a relatively short time.