Introduction

Overview:

This research was funded by the National Academies of Sciences Gulf Research Program under their 2015 Healthy Ecosystems Data Synthesis grant. The team integrated and synthesized existing historical aerial photography and satellite imagery with fragmentation analysis, as well as existing biophysical and CO₂ flux data with biophysical process and mechanistic simulation models to better understand the trajectory and implications of sea-level rise (SLR) on coastal marshes in the northern Gulf of Mexico

This research builds on existing projects by the key personnel including: Patrick Biber (PI) – salt marsh restoration through improved plant propagation approaches and techniques, coastal vegetation habitat mapping and fragmentation analysis; Greg Carter (co-PI) – historical change analysis of barrier island vegetation, developing novel methods for historical image analysis; Deepak Mishra (co-PI) - developing Moderate Resolution Imaging Spectroradiometer (MODIS) and Landsat based biophysical models from field productivity monitoring using consistent protocols; and Wei Wu (co-PI) – modeling vegetation dynamics, hydrological and biogeochemical cycles, and the impact of SLR on coastal marshes in the northern Gulf. While many similar research activities may be ongoing in various locations in the region, the unique multi-disciplinary team we have developed that spans botany, ecology, geography and mathematical modeling with long-time series data analysis and scenario projections is unparallaled.

Objectives and Output:

The overall goal of the funded research was to analyze and synthesize the long-term health and productivity trends of coastal wetlands in the northern Gulf and to develop a better mechanistic understanding of their current and historical extent, condition, productivity, and function. We achieved this by combining existing data from (1) archives of aerial photography and satellite imagery with geospatial mapping and fragmentation analysis, (2) existing in-situ vegetation monitoring data, and (3) new biophysical and mechanistic process models at multiple spatial scales to improve future predictions for coastal salt marshes.

The specific objectives of this project were to:

• Collate and synthesize existing historical imagery from 1940s to present and develop georeferenced vegetation classes for coastal marshes
• Undertake a change analysis of selected marsh habitats over time and a fragmentation analysis of key vegetation types using FRAGSTATS
• Develop prototype weekly and bi-weekly composite salt marsh biophysical products from MODIS 250-m and 500-m and Landsat data including distributions of chlorophyll content, vegetation fraction, and leaf area index, and green biomass using field monitoring data collected from 2000 to 2015
• Develop a biophysical parameter-centered gross primary productivity (GPP) model and prototype 8-day composites of salt marsh GPP using MODIS 250 and 500-m data
• Develop a robust hierarchical Bayesian (HB) model to simulate GPP by coherently assimilating multiple spatial scales and then analyze the overall trend in productivity and carbon sequestration
• Assimilate mapping and biophysical data to develop and calibrate a mechanistic model which integrates vegetation, hydrology, and sediment dynamics to project future change in selected coastal marshes

The final products developed included (1) a time-series of historical maps showing change in salt marsh extent, composition, and fragmentation, overlayed with (2) biophysical process rates (productivity, canopy traits, plant biomass) for selected dominant plant species, and (3) future scenario simulations of salt marsh extent and function. The result of this mapping data analysis and modeling synthesis is a comprehensive protocol for salt marsh structural and biophysical characteristics that can be used for assessing the success of future restoration projects, identifying areas of degradation from oil and energy related activities in the coastal zone, and in evaluating the productivity of marshes that are impacted by anthropogenic development activity and SLR. The resultant products can be broadly applicable to inform plans for preservation, restoration, and the future viability of the numerous ecosystem services provided by coastal marshes to human communities.