Grades 6–8 · Earth & Space
How can a salt marsh build its surface upward?
A salt marsh is flooded and drained by tides. Floodwater can carry fine sediment into the plants. When the stems slow the moving water, some particles settle and add material to the marsh surface.
In the diagramSediment and roots can build marsh elevationflood tide brings suspended sedimentroots add organic material below
Plants also contribute from below. Roots grow through the wet soil, and some organic material remains after roots die. This accumulation can help increase the volume and elevation of the marsh soil.
At the same time, decomposition, erosion and compaction can remove material or lower the surface. Whether the marsh gains height depends on the balance among these processes. A layer of deposited mud is only one part of that balance.
As local sea level rises, a marsh may need to build upward or spread into suitable land to maintain its position in the tidal zone. Sediment supply and space matter. Living vegetation can help shape a coastline, but its ability to adjust has physical and ecological limits.
About this explanation
Starting knowledge: Know that tides cover and uncover coastal wetlands and that plant roots add organic material to soil.
Sources
- NOAA National Centers for Coastal Ocean Science — Salt Marsh Ecology in an Era of Sea Level Rise