As Spartina alter~~iflora lignocellulose degrades, it contributes soluble degradation products to the bulk dssolved organic carbon (DOC) pool in salt marsh environments. Experiments with radlolabeled S. alterniflora hgnocelluloses show that during the initial 6 mo of decomposition, DOC accounts for 50 to 60% of the total degradation products (DOC plus CO2) of the lignin fraction of hgnocellulose; by contrast, only 20 to 30 '10 of the polysaccharide portion of S alterniflora lignocellulose accumulates as DOC during decomposition. The differences in net accumulation are most llkely due to dfferential rates of microbial utilization of the soluble compounds denved from these 2 fractions and not to differential rates of formation. As a result, although lignin comprises only 7 % of undegraded S. alterniflora lignocellulose, it may contribute as much as 30 % of the carbon in lignocellulose-derived DOC. Soluble compounds denved from hgnin show evidence of significant chemical modification, such that only a small fraction of Iignin-derived carbon is present as recognizable lignin phenols The long residence time of lignin-derived carbon in salt marsh DOC pools, relative to that for polysaccharidederived carbon, demonstrates a mechanism by which lignin may serve as a source of aquatic humlc substances and contribute to the bulk DOC pool of salt marshes in greater proportion than expected from the ratio of lignin. polysaccharides in undegraded plant material. Based on quantification of lignin oxidation products, we estimate that S. alterniflora lignocellulose, both the lignin and polysaccharide components, contributes 44 "b of the carbon in the bulk DOC pool of a Georgia salt marsh creek.