Natural Processes – Efficient Reducers of Atmospheric Carbon

By Gray Merriam

Precambrian wetland carbon storage – Photo by Gray Merriam

Discover the added value of our wetlands

The amount of carbon dioxide in the atmosphere is the inescapable root of climate change. Anything affecting the rate of addition of carbon dioxide to the atmosphere is unquestionably related to climate change.

A small group of activists have recently tried to stimulate interest in natural processes as preferred alternatives to developing technical means of reducing the addition of carbon dioxide to the atmosphere. Their plea could be much stronger if ecological differences between major ecosystem types were clarified. So, for example, the storage of carbon in tropical forest is largely in the biomass of the plants, mainly the trees themselves, not in soil organic matter. In contrast, the majority of carbon storage in the boreal forest is in the organic matter of the soil and peat, not in the tree tissues.

The total area of boreal forest exceeds the area of tropical rain forest, and the carbon storage per square metre in the boreal can be twice that in the tropical forest. It also would strengthen this fresh look at ways to slow climate change if we made clear that wetlands are among the greatest storage depots created by natural processes.


Wetlands affect the rate of addition of carbon to the atmosphere because wetlands put significant amounts of carbon into long-term storage. This carbon is sequestered by being built into the organic matter that makes up aquatic plants, including algae, and the secondary organic production of tissues in herbivores that eat those plants. When that plant and animal matter dies, much of it sinks into the sediments in the beds of wetlands. The organic compounds containing that carbon do not decompose because they do not have access to oxygen. The water and the mucky sediments seal them away from the oxygen that is required for their decomposition.

Kennebec Wetland Complex

Some of this sequestered carbon can get back into the atmosphere by way of chemical changes that do not require oxygen. Some carbon is combined with hydrogen instead of oxygen and this forms methane – one carbon atom combined with four hydrogen atoms – sometimes called marsh gas. Methane can escape to the surface of a wetland and thus into the atmosphere where it acts as a greenhouse gas.

So the effect of the wetland on the rate of addition of carbon to the atmosphere depends on the net difference between the carbon that is kept in the sediments minus the carbon that escapes as methane.

For a number of measured temperate wetlands the carbon stored was from 100 to 200 grams of carbon per metre squared per year (g C/m2/y). The escape of methane for those wetlands was from 45 to 55 gC/m2/y.   Thus, these wetlands were putting into long-term storage about 100 grams of Carbon per square metre of wetland per year, net. Each acre of wetland stored about 40.47 Kg of carbon per year.   

When they are calculated, wetlands in the headwaters areas of both the Salmon and the Napanee Rivers will probably far exceed the carbon storage of forests.

Kennenec Wetlands