Assessing coastal wetland vulnerability to sea-level rise along the northern Gulf of Mexico coast: Gaps and opportunities for developing a coordinated regional sampling network.

Coastal wetland responses to sea-level rise are greatly influenced by biogeomorphic processes that affect wetland surface elevation. Small changes in elevation relative to sea level can lead to comparatively large changes in ecosystem structure, function, and stability. The surface elevation table-marker horizon (SET-MH) approach is being used globally to quantify the relative contributions of processes affecting wetland elevation change. Historically, SET-MH measurements have been obtained at local scales to address site-specific research questions. However, in the face of accelerated sea-level rise, there is an increasing need for elevation change network data that can be incorporated into regional ecological models and vulnerability assessments. In particular, there is a need for long-term, high-temporal resolution data that are strategically distributed across ecologically-relevant abiotic gradients. Here, we quantify the distribution of SET-MH stations along the northern Gulf of Mexico coast (USA) across political boundaries (states), wetland habitats, and ecologically-relevant abiotic gradients (i.e., gradients in temperature, precipitation, elevation, and relative sea-level rise). Our analyses identify areas with high SET-MH station densities as well as areas with notable gaps. Salt marshes, intermediate elevations, and colder areas with high rainfall have a high number of stations, while salt flat ecosystems, certain elevation zones, the mangrove-marsh ecotone, and hypersaline coastal areas with low rainfall have fewer stations. Due to rapid rates of wetland loss and relative sea-level rise, the state of Louisiana has the most extensive SET-MH station network in the region, and we provide several recent examples where data from Louisiana's network have been used to assess and compare wetland vulnerability to sea-level rise. Our findings represent the first attempt to examine spatial gaps in SET-MH coverage across abiotic gradients. Our analyses can be used to transform a broadly disseminated and unplanned collection of SET-MH stations into a coordinated and strategic regional network. This regional network would provide data for predicting and preparing for the responses of coastal wetlands to accelerated sea-level rise and other aspects of global change

Maps of the distribution of coastal wetland surface elevation change infrastructure.

<p>Maps show the distribution of surface elevation table-marker horizon (SET-MH) stations along the U.S. Gulf of Mexico coast across: (A) wetland types, (B) minimum air temperature, (C) mean annual precipitation, (D) elevation, (E) elevation relative to mean higher high water (MHHW), and (F) rate of relative sea-level rise.</p

The distribution of SET-MH stations across elevation and inundation gradients.

<p>(A) elevation, (B) elevation relative to mean higher high water (MHHW), and (C) rate of relative sea-level rise.</p

Maps of the distribution of coastal wetland surface elevation change infrastructure.

<p>Maps show the distribution of surface elevation table-marker horizon (SET-MH) stations along the U.S. Gulf of Mexico coast across: (A) wetland types, (B) minimum air temperature, (C) mean annual precipitation, (D) elevation, (E) elevation relative to mean higher high water (MHHW), and (F) rate of relative sea-level rise.</p

The temporal distribution of SET-MH station installations in U.S. Gulf of Mexico states.

<p>The temporal distribution of SET-MH station installations in U.S. Gulf of Mexico states.</p

The distribution of SET-MH stations across elevation gradients within eight tidal datum regions.

<p>The Pensacola, Florida tidal datum region is not shown because it does not have any SET-MH stations.</p

The distribution of SET-MH stations across ecologically-relevant climatic gradients.

<p>(A) minimum air temperature and (B) mean annual precipitation. SET-MH stations are shown via the vertical solid gray bars and left y axis. For interpretation within the context of coastal wetland transition zones, we also present established sigmoidal relationships between: (1) minimum temperature and the abundance of mangrove forests (solid black line and right y axis in A) [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0183431#pone.0183431.ref044" target="_blank">44</a>]; and (2) mean annual precipitation and the coverage of wetland plants (solid black line and right y axis in B) [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0183431#pone.0183431.ref045" target="_blank">45</a>]. Temperature and precipitation threshold zones are illustrated by the rectangles with light gray diagonal hatch lines in A and B, respectively.</p

The distribution of SET-MH stations within coastal wetland types and states.

<p>The distribution of SET-MH stations within coastal wetland types and states.</p