E. Engelhaupt et Ts. Bianchi, Sources and composition of high-molecular-weight dissolved organic carbon in a southern Louisiana tidal stream (Bayou Trepagnier), LIMN OCEAN, 46(4), 2001, pp. 917-926
The composition and cycling of high-molecular-weight dissolved organic carb
on (HMW-DOC) were examined in a tidal stream (Bayou Trepagnier) with season
ally high DOC concentrations (1.0-5.6 mM). C-13 nuclear magnetic: resonance
(C-13 NMR) was used to examine the bulk chemical composition of natural HM
W-DOC from two field sites over 1.5 yr. The HMW-DOC at both sites was domin
ated by aliphatic (41%), carbohydrate (33%), and carboxyl (16%) carbon, wit
h relatively low aromatic carbon abundance (10%). A comparison of C-13 NMR
signatures of bayou HMW-DOC and leachate HMW-DOC collected from leaf litter
and soils revealed that plant litter leachate appears to be a more importa
nt source of HMW-DOM than soil. Dominant sources of HMW-DOC were likely all
ochthonous inputs of terrestrial plant litter with periodic inputs of soil
organic matter during flooding events. The low aromaticity of bayou HMW-DOC
may reflect the influence of low-oxygen conditions, which inhibit the deco
mposition of particulate aromatic macromolecules such as lignin and humic m
aterial to HMW-DOC. Lignin-phenol biomarker concentrations (A(6), in mg/100
mg OC) were much lower in HMW-DOC (1.2) than in plant (5.2) and soil (6.8)
organic matter, indicating that a significant fraction of this highly arom
atic material was not degraded to HMW-DOC. Finally, this study demonstrated
that lignin and other compounds from terrestrially derived organic matter
in sediments and adjacent soils are not a significant source of more solubl
e moieties that enter the HMW DOC pool of the bayou.