Assessing Salt Marsh Vulnerability Using High-Resolution Hyperspectral Imagery

Abstract

Change in the coastal zone is accelerating with external forcing by sea-level rise, nutrient loading, drought, and over-harvest, leading to significant stress on the foundation plant species of coastal salt marshes. The rapid evolution of marsh state induced by these drivers makes the ability to detect stressors prior to marsh loss important. However, field work in coastal salt marshes can be challenging due to limited access and their fragile nature. Thus, remote sensing approaches hold promise for rapid and accurate determination of marsh state across multiple spatial scales. In this study, we evaluated the use of remote sensing tools to detect three dominant stressors on Spartina alterniflora. We took advantage of a barrier island salt marsh chronosequence in Virginia, USA, where marshes of different ages and level of stressor exist side by side. We collected hyperspectral imagery of plants along with salinity, sediment redox potential, and foliar nitrogen content in the field. We also conducted a greenhouse study where we manipulated environmental conditions. We found that models developed for stressors based on plant spectral response correlated well with salinity and foliar nitrogen within the greenhouse and field data, but were not transferable from lab to field, likely due to the limited range of conditions explored within the greenhouse experiments and the coincidence of multiple stressors in the field. This study is an important step towards the development of a remote sensing tool for tracking of ecosystem development, marsh health, and future ecosystem services.

Mapping barrier island soil moisture using a radiative transfer model of hyperspectral imagery from an unmanned aerial system

“…This study was part of a broader field campaign conducted in summers of 2018 and 2019 to study the beach and intertidal zone sediments 33 as well as to characterize and map the salt marsh ecosystem 69,70 in the southern portion of Hog island. The data collected for this study took place specifically along the shore on the southern tip of the island.…”

Aquatic ecosystems science using an imaging spectrometer

“…12 At the same time, coastal wetlands have experienced significant stress due to sea-level rise, encroachment, and nutrient loading, and many of these signs of salt marsh stress are detectable in hyperspectral data. 15 Wetland systems store carbon in both the above-ground biomass as well as the sediments, however, the large variance in estimates of global carbon sequestration in coastal wetlands reflects several inherent challenges. One is that variations in species between low-and high-marsh vegetation types can change rapidly with elevation since species composition varies with local micro-topography, contributing to difficulties in accurate estimates, especially when these variations are sub-pixel.…”