Coastal wetlands are dynamic ecosystems that exist along a continuum from tidal freshwater forested wetlands (TFFW) to salt marshes. Zonation of these habitats is primarily controlled by flooding and salinity, and as sea-level rise (SLR), storm surge, and drought continue to impact these ecosystems, plant communities will shift along this continuum. Climate change-induced shifts in wetland community composition will alter not only ecosystem structure, but also ecosystem function and resilience. To successfully restore these dynamic ecosystems, it is critical to understand and plan for changes in ecological function and ecosystem services in anticipation of climate change.
As sea-level rises, how will shifts from fresh to salt-tolerant plant communities impact ecological function and resilience? Do long-term, plant-mediated, effects of SLR differ from short-term, direct, effects of salinity and flooding? To better understand the landscape-scale responses of coastal wetlands to climate change, we measured ecological functions along salinity gradients that incorporated transitions from TFFW to polyhaline marsh. We measured carbon cycling processes, such as primary production and decomposition, to assess ecological function, and we measured surface elevation change to assess wetland resilience to SLR.
Results/Conclusions
We used field studies and structural equation models to identify direct and indirect effects of elevated flooding and salinity on coastal wetland function. Our results indicate that as sea level rises, initial direct effects of salinity will stimulate decay of labile carbon, but over time, as plant communities shift from fresh to polyhaline marsh, litter decay will decline, yielding greater potential for long-term carbon storage. Furthermore, within-habitat responses to acute and chronic flood disturbances varied among wetland community types. Alternate scenario tests predicted no significant changes in decomposition in TFFWs impacted by long-term SLR, storm surge, or drought. In contrast, the model predicted greater decomposition following drought or storm surge in the oligohaline marsh. Resilience to long-term SLR, as indicated by wetland elevation change, was greater in the oligohaline marsh compared to the TFFWs. Additionally, the processes that contributed to resilience varied among habitats; elevation change in the TFFW was heavily influenced by root zone and other subsurface processes, whereas surface accretion dominated marsh elevation change. These changes have important implications for management activities that aim to restore or conserve resilient systems, and long-term restoration planning should account for habitat transitions that will impact ecological function, resilience, and ecosystem services.