Coastal marsh responses to rising seas: Surface elevation dynamics in coastal marshes along the northwestern Gulf of Mexico
Coastal marshes provide critical ecosystem services, making them one of the most valuable ecosystems on the planet. Coastal marshes store carbon, support fisheries, improve water quality, provide wildlife habitat, protect coastal communities, and offer popular recreational opportunities. However, due to their position at the interface between land and ocean, coastal marshes are threatened by accelerating sea-level rise.
Maintaining and enhancing the ecological and economic contributions of coastal wetlands in the face of rising seas requires information regarding surface elevation change dynamics, as these dynamics underpin the stability of wetland ecosystems. In a recent collaboration, scientists at the U.S. Fish and Wildlife Service and U.S. Geological Survey worked together to examine surface elevation change within coastal marshes in Texas along the northwestern Gulf of Mexico coast. The primary objective of the research was to assess coastal marsh vulnerability to rising seas.
The work was led by Jena Moon, a biologist at the U.S. Fish and Wildlife Service with decades of experience working along the Texas coast and was conducted in 14 coastal marshes within five National Wildlife Refuges between 2014–2019.
There are several factors that make coastal wetlands in Texas particularly vulnerable to sea-level rise. These include comparatively high rates of subsidence and relative sea-level rise, small tidal ranges, and anthropogenic land-use changes that have reduced freshwater and sediment delivery to the coast. At most of the study sites, vertical accretion (that is, the accumulation of sediment and organic material on the soil) was found to offset subsurface losses due to shallow subsidence (that is, decreases in elevation beneath the soil surface). However, net elevation gains were often lower than recent relative sea-level rise rates, and much lower than rates expected under future sea-level rise. This means that these marshes are not keeping pace with recent sea-level rise and are unlikely to be able to adjust to future accelerations.
Collectively, the study shows how climate change threatens Texas coastal marshes and the ecological and economic services they provide. By characterizing the status and potential loss of coastal marshes, the study reinforces the importance of identifying local changes that can inform landscape-level adaptive management strategies in response to climate change. Coastal marshes can adapt to sea-level rise via two primary mechanisms: (1) vertical adaptation via surface elevation gains, which can be facilitated with sediment additions (e.g., beneficial use of dredged sediment); and (2) horizontal adaptation via landward migration into adjacent upslope and upriver ecosystems, which can be facilitated with land acquisition and targeted management.
The paper, “Surface elevation change dynamics in coastal marshes along the northwestern Gulf of Mexico: building knowledge to better anticipate effects of rising sea-level and intensifying hurricanes” was recently published in the journal Wetlands.