The Response of Coastal Wetlands to Sea-level Rise: Understanding how Macroscale Drivers Influence Local Processes and Feedbacks

Science Center Objects

The purpose of this work is to advance our understanding of how coastal wetland responses to sea-level rise (SLR) within the conterminous United States are likely to vary as a function of local, regional, and macroscale drivers, including climate. Based on our interactions with managers and decision makers, as well as our knowledge of the current state of the science, we propose to: (a) conduct a national evaluation summarizing coastal elevation change trends using surface elevation table (SET) data; (b) develop quantitative models of the relationships between climate drivers, wetland foundation species, and ecosystem properties; and (c) examine barriers and opportunities for landward migration of coastal wetlands.

Statement of Problem: Coastal wetlands provide many societal benefits. In addition to providing habitat for fish and wildlife, coastal wetlands offer storm protection, improve water quality, support seafood populations, and provide recreational opportunities. Therefore, wetland scientists are challenged to provide robust scientific information that can allow managers and decision makers to anticipate the possible responses of coastal wetlands to changes in sea level (SLR). Our assembled research team has, both recently and through the years, held and participated in a great many meetings with stakeholders along the Atlantic, Gulf, and Pacific coasts to better understand the knowledge gaps and critical science needs.

Combined with our knowledge of the scientific literature and the gaps therein, we identified several major critical research needs, which drive the tasks described in this work plan: (1) We need a broader view of the current condition and elevation trajectory of coastal wetland communities, especially their ability to keep up with rising sea levels. (2) We need to be able to anticipate the major changes expected in coastal wetland properties and processes and their responses to future climate scenarios. (3) We need to be able to predict the conditions that drive wetlands to migrate inland in response to rising sea levels.

 

Why this Research is Important: To anticipate future changes in our Nation’s coastal wetlands, research must look across biogeographic, geomorphic, and ecological boundaries. The need for this research is especially great since both changes in wetland type and changes in wetland productivity have major implications for wildlife habitat management and coastal protection. Most previous work has built on select coastal wetland examples. In the United States, almost no attention has been paid to the full suite of coastal wetland types that occur throughout the 12 biogeographic regions of the conterminous coastline (Osland et al. 2019, Figure 1).

 

map of U.S. showing the twelve biogeographic regions

Maps of the conterminous United States identifying the 12 assigned biogeographic regions (a) and the distribution of dominant plant groups in coastal wetlands (b) in relation to the Global Aridity Index (c) and winter temperature extremes (d). Within each biogeographic region, coastal wetland plant communities are generally dominated by a common set of foundation plant species. In panel b, blue indicates graminoid dominance (e.g. grass-like plants), red indicates mangrove dominance, yellow indicates succulent plant dominance, and black indicates primarily unvegetated wetlands (e.g., salt flats, salt pans) often dominated by algal mats. Whereas winter temperature extremes govern the transitions from mangrove to graminoid dominance (see red to blue transitions in panel b, which occurs in Florida), aridity and salinity tend to govern the transitions from graminoid to succulent dominance and the absence of vegetation (see transitions from blue to yellow or blue to black in panel b, which occur in Texas and California). The Global Aridity Index represents the ratio of precipitation to potential evapotranspiration. (Figure 1 in Osland et al., 2019)

(Credit: Michael J. Osland, USGS. Public domain.)

These biogeographic regions and associated plant community types result from a combination of the geomorphic setting of estuaries and existing geographic gradients that can be expected to shift with changes in climate. An understanding of how these processes interact to structure coastal wetlands is needed to develop a broader understanding of how coastal wetlands are likely to respond to changing environmental conditions in the future. This research aims to produce data on the relative roles of site-specific (local) processes, geomorphic settings, and climate drivers that influence the full range of coastal environments in the conterminous United States. These data are essential for a comprehensive assessment of coastal wetland response to changing sea level. The assessment will provide resource managers and policy makers with evidence to guide well-informed decisions related to protection, restoration, and adaptation of coastal wetlands at the National scale.

 

Objective(s):

  1. Synthesize coastal wetland elevation trends for the conterminous United States, identify potential abiotic and biotic drivers, and evaluate quantitative hypotheses about the network of factors controlling observed variations.
  2. Advance our understanding of the potential influences of climatic drivers and their interactions on coastal wetland ecosystem properties along the geographic gradients of the conterminous United States including their influence on wetland responses to accelerations in SLR.
  3. Examine the potential for landward migration of coastal wetlands in the conterminous United States in response to future climate change scenarios.
     

Methods: Analyses and modeling relevant to the listed objectives will be conducted using existing data.