Assistant Professor Cedric Fichot’s advisee Josh Harrington receives the NASA FINESST fellowship

Joshua Harrington, advisee of Assistant Professor Cedric Fichot recently received the NASA FINESST fellowship. Cedric Fichot will be the PI and Joshua Harrington the FI of “Quantifying the Fat of Dissolved Organic Carbons from Stable and Degrading Marshes in the Mississippi River Delta Using Airborne Imaging Spectroscopy and Export Modeling”

Overview: Carbon export through coastal marsh-estuaries is an important, but poorly constrained, component of the global carbon cycle. Globally, many coastal marshes are unstable, their extent shrinking due to erosion, subsidence, and sea level rise. Research has indicated that organic matter export from coastal marshes and within-estuary dissolved organic carbon (DOC) degradation can significantly influence global carbon budgets. However, the size of these influences is not precisely known due to challenges in determining the fate of estuarine carbon. Estuarine geochemical processes are difficult to quantify using conventional in-situ methods, because they can vary on small spatial and temporal timescales – tens of meters and hours to days, respectively. Advances in imaging spectroscopy (hyperspectral remote sensing) provide opportunities to map distributions of DOC, and determine the fate of carbon across estuarine systems with improved resolution and coverage.

Here, I propose to combine remotely sensed information and models to determine the fate of DOC in two contrasting marsh-estuary systems located in the Atchafalaya River Delta, a major distributary of the Mississippi River. These contrasting systems will be used to examine the differences in DOC transformations, export fluxes, and fate between: 1) Terrebonne Bay, a rapidly eroding coastal-marsh system, and 2) Fourleague Bay, a nearby bay where riverine sediment inputs are thought to help marsh accretion keep up with sea level rise. I will use hyperspectral, in-situ measurements to develop and test different types of local algorithms for inferring water column inherent optical and geochemical properties from remote sensing reflectance. The best performing of these algorithms will be applied to imagery from the NASA JPL Airborne Visible/Infrared Imaging Spectrometer Next Generation instrument (AVIRIS-NG) to infer concentrations of DOC across the marsh-estuary systems. AVIRIS-NG imagery will be collected as part of the upcoming NASA Earth Ventures Delta-X investigation, which seeks to forecast changes to the Mississippi River Delta using remote sensing, hydrodynamic modeling, and field sampling to model and understand deltaic soil accretion. I will use remote-sensing-derived maps of estuarine DOC with the output of hydrodynamic models, and with in-situ measurements of flow in marsh channels to calculate lateral export fluxes of DOC to the ocean. These export rates will be combined with models of microbial and photochemical DOC remineralization in order to compare the fate of DOC between the different estuaries. Modeled DOC remineralization rates will leverage laboratory incubation experiments to determine photochemical and microbial DOC reactivities. These reactivity rates will be applied across the estuaries to estimate fractions of DOC remineralized within each estuary or exported to the ocean.

These estimates of DOC export fluxes to the continental shelf and DOC degradation within the estuary will help understand the fate of organic carbon in rapidly degrading coastal marshes. The objectives of this project are relevant to the Carbon Cycle and Ecosystems focus area of the NASA Earth Science SMD, which prioritizes understanding “ecosystems as they are affected by human activity, as they change due to their own intrinsic biogeochemical dynamics, and as they respond to climatic variations and, in turn, affect climate.”