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Saltmarsh sediments

When sediments shape coastal marshes… and their capacity to store carbon

Coastal marshes, and salt meadows in particular—which are situated within the tidal range—are particularly valuable coastal ecosystems. They protect the coastline from erosion, are home to remarkable biodiversity and constitute important natural carbon sinks. However, their ability to provide these services depends on their geomorphological evolution: a salt marsh must be able to advance towards the sea when conditions are favourable, but also gradually raise its surface through sediment accumulation in order to keep pace with rising sea levels.

 

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Understanding the mechanisms that govern this evolution remains challenging, as numerous factors come into play simultaneously: exposure to waves, frequency of flooding, availability of sediments, proximity to rivers, the geometry of the bays, and so on… To better distinguish the role of each of these factors, researchers from the CarboNium and CABESTAN projects compared three salt marshes in the Pertuis Charentais. These sites have comparable climate, tidal range and sea level rise, but differ in terms of their geomorphology, exposure to waves and sediment supply.
 

The results show that salt marshes best protected from waves can advance rapidly towards the sea, at speeds of up to 14 metres per year, whilst the most exposed areas experience much slower advance, or even erosion. Coastal geomorphology thus appears to be a key factor in the lateral evolution of salt marshes.

The study also reveals that the vertical elevation of the salt marshes depends primarily on the availability of sediments transported by coastal waters. In the Pertuis Charentais, which are particularly rich in suspended matter thanks to river inflows and intertidal mudflats, some areas accumulate more than one centimetre of sediment per year. This capacity enables them to maintain their elevation despite rising sea levels.

This sedimentary process directly controls carbon storage. In these mineral-rich macrotidal marshes, carbon is mainly buried within the sediments deposited by the tides. The sites that accumulate the most sediment are therefore also those that sequester the most carbon in the long term. Isotopic analyses also show that this carbon comes mainly from organic matter supplied by the marine environment rather than from local plant production alone.

These results highlight that preserving natural sediment inputs and allowing the marshes the space they need to evolve is a key strategy for strengthening their resilience to climate change, protecting the coastline and maintaining their role as carbon sinks.
 

Scientific publication :

 

Benjamin Amann

About the author of this scientific article: Benjamin Amann

 

Benjamin is part of the CABESTAN project

He is a postdoctoral researcher working on the sedimentary evolution of coastal marshes and carbon sequestration

"My research aims to gain a better understanding of the functioning and morphosedimentary evolution of coastal wetlands in response to the risk of marine inundation, and their importance in the long-term carbon cycle. The aim is to gain a better understanding of how environmental factors and the diversity of land uses influence the accumulation of sediments and organic carbon in coastal wetlands."

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Modification date: 09 July 2026 | Publication date: 01 July 2026 | By: FairCarboN