Carbon sequestration is simply the capture and storage of carbon. This is important becuase carbon dioxide is the most common greenhouse gas, so storing carbon somewhere other than the atmosphere is one tool to help slow the rate of climate change.
Coastal wetlands sequester lots of carbon, much more than a mature forest of the same area. Why are salt marshes so good at this? First, the plants in a salt marsh do a lot of photosynthesis, the process by which plants use carbon dioxide and sunlight to make food. This is the carbon capture part, and it happens wherever there are plants making roots and stems with sunlight and nutrients. The storage part of carbon sequestration, however, is where coastal wetlands really shine.
When plants die they are eaten by decomposers - microorganisms, bugs, etc. The carbon in those decomposing plants is no longer stored and the CO2 locked up in plant roots and leaves goes back into the air. Salt marshes are such great carbon sequesters because this proces of decomposition is so slow. Those decomposer organisms need oxygen. Water holds much less oxygen than air and wetlands are, of course, inundated with water. And the salt in a coastal wetland slows decomposition even more. So dead plants in a salt marsh get buried in the wet, salty mud where that carbon is stored for a long time.
Next time you get a chance to walk into a salt marsh (Love Your Wetlands Day 2023!) notice how spongey the soil feels. That is because of all the organic matter in the mud - all those dead plants that have yet to decompose. And those dead plants are made up of carbon that is not in the atmosphere causing climate change. One more reason to love your wetlands!
