Increased sea level rise accelerates carbon sequestration in a macro-tidal salt marsh

Area of Science:

• Environmental Science
• Climate Change Ecology
• Coastal Geomorphology

Background:

• Salt marshes are vital for climate mitigation via carbon sequestration.
• Accelerating sea level rise (RSLR) poses a threat to salt marsh function.
• Understanding OCAR response to RSLR is crucial for climate mitigation strategies.

Purpose of the Study:

• To investigate the impact of accelerated RSLR on organic carbon accumulation rates (OCAR) in salt marshes.
• To compare OCAR over four decades at two nearby sites with differing RSLR rates.
• To assess the influence of RSLR on sediment accretion rates (SAR) and carbon content.

Main Methods:

• Studied OCAR over 40 years at two adjacent Dutch salt marshes.
• One site experienced accelerated RSLR (9.7-11.7 mm yr⁻¹) due to subsidence; the other had low RSLR (2.0 mm yr⁻¹).
• Compared OCAR and SAR between sites and within different marsh zones (levees vs. basins).

Main Results:

• Accelerated RSLR sites showed OCAR twice as high as low RSLR sites.
• OCAR increased by 63% on levees and 27% in basins with accelerated RSLR.
• Increased OCAR was primarily driven by higher SAR due to increased tidal inundation and sediment supply.

Conclusions:

• Salt marsh carbon sequestration capacity increases with accelerated RSLR.
• Nature-based climate mitigation in salt marshes is sustainable long-term.
• Salt marsh effectiveness for climate mitigation may increase with future sea level rise.