Fetch and distance from the bay control accretion and erosion patterns in Terrebonne marshes (Louisiana, USA)

Abstract

Wetlands in the Mississippi River Delta are rapidly degrading. Sea level rise and low sediment supply are widely recognized as the two main factors contributing to landto-water conversion. To determine what marsh areas are more resilient, it is fundamental to identify the drivers that regulate marsh accretion and degradation. In this study, a combination of field data and aerial images is used to determine these drivers in Terrebonne Bay, Louisiana, USA. We find that accretion and degradation patterns depend on whether the marsh is located inland in a sheltered area or facing open water. In the first case, the distance to the nearby channel is important, because during flooding of the marsh platform more sediment is deposited in the proximity of channel banks. The accretion rates of marshes facing open water are high and correlate to fetch, a proxy for the ability of waves to resuspend bottom sediment. These areas are more resilient to sea level rise, but waves are also the main mechanism of degradation, as these marshes tend to degrade by edge erosion. Consequently, we propose a bimodal evolution trajectory of the marshes in Terrebonne Bay: marshes close to the bay and facing open water accrete rapidly but are affected by lateral erosion due to waves, whereas sheltered marshes accrete slowly and degrade in large swathes due to insufficient sediment supply.

Using Normalize Difference Vegetation Index to Infer Wetlands Salinity and Organic Contribution to Vertical Accretion Rates

“…Spatial data of fractional floating vegetation (FAV) and fractional submerged vegetation (SAV) used to mask out areas that could be interpreted as wetlands were retrieved from the USGS website via (https://www.sciencebase.gov/catalog/item/606df312d34e-ae125e9c7647) (Couvillion, 2021a(Couvillion, , 2021b. Geomorphological data of distance from the channel, and distance from the bay used to derive the models were taken from Cortese and Fagherazzi (2022). Spatial data of leveed areas, which were masked out from the calculations can be downloaded via the National Levee Database (https:// levees.sec.usace.army.mil/).…”

Leveraging the Historical Landsat Catalog for a Remote Sensing Model of Wetland Accretion in Coastal Louisiana

“…Their results, then, are not easily transferrable to the regional scales that remote sensing data can address. Conversely, studies that incorporate spatial datasets to examine wetland changes typically do not employ direct inputs for sedimentation and bioproductivity to derive accretion rate estimates (e.g., Craft et al., 2009), instead relying on other spatial variables and proxies such as channel distance and fetch (a proxy for wave‐driven sediment resuspension) to capture accretionary processes (Cortese & Fagherazzi, 2022). Remote sensing offers the ability to accurately model and map these factors that drive wetland accretion rates and thereby provide more accurate assessments of blue carbon storage and sequestration dynamics at regional and global scales.…”

Storm Impacts on Mineral Mass Accumulation Rates of Coastal Marshes

“…The inorganic mass accumulation rates map is available via the ORNL DAAC Delta-X data portal at https://doi. org/10.3334/ORNLDAAC/2301 (Cortese & Fagherazzi, 2023). Data supporting the modeling are publicly Journal of Geophysical Research: Earth Surface 10.1029/2023JF007065…”