Salinity reduces coastal wetland potential for climate change mitigation

Coastal wetlands represent a vital component of the global carbon cycle due to the inherent capability of sequestering carbon in both biomass and sediments. Their future ability to act as carbon sinks largely depends on how plant communities will adapt to sea-level rise, and its most direct consequences: submergence and salinization. Although tidal ecosystems can actively contrast SLR through vertical and lateral soil accretion, the impacts of salinity on soil-plant-water interactions, species succession, and ecosystem productivity remain unaccounted for in carbon budget models.

Salinity is known to limit plants capability to uptake water, and as such, it is expected to have an impact on the ecosystem productivity, the soil water balance, and water table dynamics. Here, we model the response of coastal ecosystems to salt stress, and we show that salinity and plant salt tolerance exert a dominant control on how coastal plant communities interact with water table dynamics. We demonstrate that salinization and shifts in groundwater regimes may trigger abrupt successions from the highly productive salt-sensitive species dominating freshwater coastal wetlands, to the less productive salt-tolerant species now confined within the intertidal fringe. Our theoretical results explain recent eco-hydrological patterns observed in the Florida Everglades and indicate that shifts from salt-sensitive to salt-tolerant communities could cause a drastic reduction of coastal wetland productivity.