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How mangroves store carbon in their soil

Waterlogged mud keeps dead roots and leaves from rotting, so mangrove soils hold most of the ecosystem's carbon.

Intermediate 2 min read carbonblue carbonsoilclimate

A mangrove forest stores carbon in three places: the living trees, the dead wood and litter, and the soil. In most mangroves the soil holds the largest share, often more than half and sometimes more than three-quarters.

Why the soil is so rich

  1. Tides keep the mud waterlogged, so there is little oxygen.
  2. Without oxygen, the microbes that normally rot dead roots and leaves work very slowly.
  3. Roots and fallen leaves pile up as peat-like soil that can be metres deep.
  4. Tidal water also brings in sediment carrying carbon from rivers and the sea, which is trapped by the roots.

Orders of magnitude. Studies of mangroves worldwide report whole-ecosystem stocks averaging around 1,000 tonnes of carbon per hectare, with a very wide range from a few hundred to well over 2,000 depending on soil depth and the place. Atlas uses 400 / 700 / 1,000 tC/ha as an illustrative low / central / high bracket so results are conservative.

Why it matters for climate. If the forest is cleared or drained, soil carbon is exposed to air and can be released as CO₂ over years. A hectare of lost mangrove can therefore release far more carbon than a hectare of lost upland forest.

Limits. Soil carbon cannot be seen from space; it needs core samples. Atlas multiplies mapped area by an assumed stock until measured values are added.

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