Characterizing Lignin Chemistry of Wetland Soil Profiles in the Atchafalaya and Barataria Basins.

Recent studies have indicated that organic carbon from the

deterioration of the Mississippi River deltaic plain wetlands could be

the additional source leading to the hypoxia in the northern Gulf of

Mexico along the Louisiana coast. In this study, wetland soil profiles

from two contrasting basins, Atchafalaya Basin and Barataria, were

characterized for degradation characteristics of lignin biomarkers

using a tetramethylammonium hydroxide (TMAH)-Pyrolysis gas

chromatography/mass spectrometry (PY-GC/MS) method. Various

ratios of lignin monomers were evaluated. The results showed that

ratios of guaiacols with intact C3 side chains to guaiacol (C3G/G)

soil profiles in Barataria Basin was much higher than those in the

Atchafalaya Basin soil profiles, suggesting generally less degradation of

organic matter in Barataria Basin. In addition, there was a general trend

of decreasing C3G/G ratio with soil depth in the freshwater marsh soil

profiles in the Barataria Basin, indicating more extensive degradation

of organic matter in the deeper layers. The range of change in ratios

of C3G/G and C3S/S among the three sites from inland toward ocean

in Atchafalaya Basin was relatively small, suggesting non-preferred

degradation between Syringyl and Guaiacol lignin monomers. These

results have important implications in interpreting soil/sediment

organic matter transformation in these different coastal basins.