Ecosystem services can persist in drowning macrotidal salt marshes

Area of Science:

• Coastal ecology
• Salt marsh ecosystems
• Sea-level rise impacts

Background:

• Salt marshes are vital for coastal protection against sea-level rise (SLR).
• Marshes are vulnerable to drowning if SLR outpaces sediment supply, leading to increased inundation.
• Understanding marsh response to SLR is crucial for coastal management.

Purpose of the Study:

• To investigate changes in salt marsh composition and ecosystem services under simulated SLR.
• To assess the effects of SLR on sediment oxygen, vegetation growth, and decomposition in different marsh zones.

Main Methods:

• A 28-month mesocosm experiment simulating 50 and 100 years of SLR (1 cm/year).
• Evaluated sediment oxygen, vegetation growth, wave attenuation traits, community composition, and litter decomposition (Teabag Index).
• Compared responses in high marsh (Elymus athericus) and low/pioneer marsh (Spartina anglica) zones.

Main Results:

• No significant plant mortality or impact on wave attenuation traits observed across marsh elevations.
• Low marsh vegetation was largely unaffected; high marsh growth reduced by 22% under SLR treatments.
• Wetter treatments reduced litter decomposition and increased carbon persistence; higher plant diversity in high marsh over time.

Conclusions:

• Meso- and macrotidal marsh ecosystem services can persist long-term under gradual SLR.
• Sub-lethal impacts on vegetation allow for monitoring and management before erosion causes marsh loss.
• Marsh resilience is high, but eventual erosion remains a threat under rapid SLR scenarios.