Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Data Files
• Related Publications
• Parameters
• Instruments
• Project Information
• Funding

Triplicate core samples were collected at three different distances from the island’s edge at sites on the North, East, South, and West sides of the island. These core samples were then broken down into 10 centimeter (cm) sections and these sections were then further divided into two subsets. The samples in the first subset were used for the soil physiochemical analysis. The samples in the second set were centrifuged to yield pore water samples that were spectroscopically analyzed.

Sample Collection: Thirty-six cores, which were 0.5 – 1 meters long, were collected on four sides (cardinal directions) of the island with a manual push-coring method using an acrylic tube (1.7 m long x 7.6 cm diameter). On each side, cores were extracted in triplicates at 16 m outland, the edge of the marsh (0 m), and 2 m inland. Upon extraction in the field, each core was sectioned in 10 cm sections, sealed in polyethylene bags, and stored on ice during transportation back to the lab, where they were stored at 4 degrees C in the dark until analysis.  

Surface water samples were collected 10 cm below the surface at the edge of the marsh and 16 m outland following the procedures in Haywood et al. (2018).

Soil Physiochemical Analysis: The 10 cm sections were homogenized and weighed prior to analysis to determine gravimetric moisture content, bulk density, percent organic matter, and total carbon.

Gravimetric Moisture Content: The entire 10 cm section (~30 grams) was oven-dried at 60 degrees C until constant weight was achieved.

Bulk Density: The total weight of the dried 10 cm section of core was divided by the volume of the 10 cm section (385 cm3)

Percent Organic Matter: 1 gram of the dried 10 cm section of core was ground using a mortar and pestle. It was combusted in a Thermolyne furnace (Thermofischer Scientific, Waltham, MA) at 550 degrees C for 4 hours. After cooling, the sample was weighed. The difference in weight following combustion determined percent organic matter.

Total Carbon: 8 milligrams (mg) of the dried 10 cm section of core was used to determine total carbon. These samples were placed into a Shimadzu Total Organic Carbon Analyzer with SSM-5000 A (Shimadzu, Columbia, MD) and combusted at 900 degrees C for 13 minutes.

Porewater Analysis: To remove pore water from the wet soil samples, samples were centrifuged at 2578 g for 10 minutes. The pore water was decanted and filtered through a 0.45-micrometer x 22-millimeter Nylon syringe filter. After filtration, the pore water was stored at 4 degrees C in the dark until analysis. To determine the dissolved organic carbon, a Total Organic Carbon Analyzer (TOC-L) (Shimazdu, Columbia, MD) was used. A Cary 100 Spectrophotometer (Varian Inc., Palo Alto, CA) was used to collect UV–Vis absorbance spectra, and a Spex Fluorolog-3 spectrofluorometer (HORIBA Scientific, Edison, NJ) was used to collect fluorescence, methods based on Haywood et al. (2018).

The UV–Vis absorbance spectra were collected from 200 to 600 nm using a 0.5 nm bandpass and a 1 cm quartz cell, on a Cary 100 spectrophotometer.

Fluorescence EEMs were collected using a 1 cm quartz cell with excitation wavelengths of 250 to 550 nm and emission wavelengths of 250 to 600 nm with 5 nm increments for both on a Spex Fluorolog-3 spectrofluorometer. Along with sample EEMs, blank EEMs of Milli-Qnwater were collected daily.

To minimize temperature effects, samples were allowed to reach room temperature and shielded from light prior to analysis.

Analysis of Variance (ANOVA) was performed on R (Version 3.5.3; R Foundation for Statistical Computing, Vienna, Austria). The Tukey HSD method with Bonferonni correction was applied to the significant level (alpha = 0.003). The plots were created using ggplot2 (Wickhm, 2016) in R, too.

PCA analysis was performed in JMP (SAS Institute, Cary, NC).

For parallel factor analysis (PARAFAC) the pre-processed sample data were arranged into a three-way array with 114 samples, 61 excitation wavelengths in 5 nanometer (nm) increments ranging from 250 to 550 nm, and 71 emission wavelengths in 5 nm increments ranging from 250 to 600 nm. The fluorescence intensity was converted from arbitrary unites (A.U.) to Raman unites (R.U.) be-fore PARAFAC analysis. The PARAFAC analysis was performed with MATLAB R2015a (Math Works, Inc., Cambridge, MA) software program, utilizing open source drEEM toolbox version 2.0. The appropriate number of components for the dataset was determined using outlier identification and method validation techniques (i.e., least square fit and split-half analysis) following methods outlined in, with the best fit model having an explained variance of N95%. The identities of the components determined in the model were verified through comparison to previously identified component models using OpenFluor (DOM fluorescence spectral database).

BCO-DMO processing description:
- Adjusted field/parameter names to comply with BCO-DMO naming conventions
- Added a conventional header with dataset name, PI names, version date
- Converted dates to ISO date format (yyyy-mm-dd)
- Rounded columns to the hundredths place

Description from NSF award abstract:
Coastal Louisiana is currently experiencing net sea level rise at rates higher than most of the world's coastlines and within the global range predicted to occur in the next 65 - 85 years, making Louisiana an ideal site to study potential future impacts of rising sea level on coastal systems. This project will use field collection and controlled tank experiments to study the changing organic carbon cycle resulting from erosion of marsh soils along with its impact on associated biogeochemical processes. The hypothesis tested in this study is that the majority of eroded soil organic carbon is converted to carbon dioxide (CO2) and released to the atmosphere, representing an addition to the anthropogenic input of CO2. This process has not been quantified and could be an important missing component in predictive models of atmospheric CO2 changes. While this process may be of only regional importance today in comparison to other sources of CO2, this study of the Louisiana coast will greatly enhance our full understanding of the potential impacts on the global carbon cycle that may result from coastal erosion as global sea level continues to rise.

The project will train graduate and undergraduate students in interdisciplinary research involving marine and wetland biogeochemistry, microbiology, and ecological modeling. It will also fund development of an interactive, educational display on the loss of coastal wetlands for the Louisiana Sea Grant's annual Ocean Commotion educational event attended by area middle and high school students, teachers, and parents. Results from this study may also inform community planners both regionally and worldwide as they prepare for sea level rise in coastal communities.

Eustatic sea level rise and regional subsidence have created a much greater rate of coastline loss in Louisiana than is being experienced in most of the world's coastal regions, reaching global rates that are predicted to occur worldwide in 65 - 85 years. This provides a unique potential to extrapolate data from Louisiana's changing coastal carbon cycle to both regional and global models of the future impact of sea level rise and coastal erosion. By quantifying and modeling the importance of CO2 emissions resulting directly from mineralized soil organic matter from eroding coastlines, a missing element can be added to climate change models. The PIs here plan to investigate the fate of the coastal wetland carbon pool as it erodes using field sampling, laboratory analysis, mesocosm manipulations, and the creation of a coupled physical-biogeochemical model for the basin being studied. Beyond quantifying increased CO2 emission, the PIs will also address the potential for increased eutrophication due to input of nutrients from eroded soils, as well as the potential for future contribution to existing hypoxic zones in the northern Gulf of Mexico that result from excessive nutrient input from the Mississippi River watershed.