Ecosystem scale controls on the vascular plant component of dissolved organic carbon across a freshwater delta

In the context of global carbon cycling, rivers are typically modeled as spatial integrators of all sources and processes within the watershed. However, substantial evidence in many scientific fields, including soils science, ecology, and hydrology, indicate that spatial variation is significant at sub-watershed scales. Thus it is reasonable to assume that spatial heterogeneity also occurs with respect to carbon sources and dynamics, and that not all features within a watershed are equally important toward determining riverine carbon concentration and composition. Presented are the results of a fine scale investigation of lignin and DOC dynamics within the Sacramento-San Joaquin River Delta. Specifically, DOC concentration ranged from 1.3 to 39.9 mg/L (median 3.0 mg/L), with significant differences in concentration among ecosystems and sampling stations. Lignin concentration ranged from 3.0 to 110 μg/L (median 11.6 μg/L), with significant differences among ecosystems and sampling stations. Lignin carbon normalized yields ranged from 0.07 to 0.84 mg/100 mg OC (median 0.36 mg 100/mg OC), with significant differences among ecosystems. A simple mass balance model utilized lignin phenol ratio parameters to determine the ecosystem scale sources of lignin at the intake to the California State Water Project pumps. Results indicated temporal variation in source, with riverine source signatures predominating from early spring through early autumn, and wetland signatures predominating through the remainder of the year. Finally, Delta-derived sources of DOC appear to overwhelm upstream source signatures, potentially significantly influencing carbon export across the estuary.