Patterns in dissolved organic carbon quality in a New England coastal watershed: it’s relationship to urban and wetland sources and flow dynamics

Humans can affect the amount and quality of dissolved organic carbon (DOC) inputs to aquatic ecosystems by altering land use (e.g. by agricultural uses and impervious surfaces) and by the production of sewage and animal waste. These changes may affect stream ecosystem metabolism and contribute to the eutrophication of downstream ecosystems. The presence of wetlands in river networks, however, may dampen the human signal because wetlands are dominant sources of both labile and recalcitrant DOC. Little is understood about the relative importance of these sources of DOC quantity or quality in river networks. We assessed the relative importance of wetlands and urban sources of DOC using synoptic surveys and DOC quality measurements. Urban and wetland sites in the Ipswich River Watershed, (Plum Island Sound Long Term Ecological Research), MA, were sampled seasonally for inorganic nutrients, oxygen, and DOC quantity and quality. DOC quality was measured using 3D excitation and emission spectra (EEMs) on an HJY Fluoromax 3 Spectrofluorometer. Parallel factor analysis (PARAFAC), which determines dominant spectral characteristics will be presented. In addition to synoptic surveys, DOC quality dynamics were also captured through storm events downstream of urban and wetland centers. We find that wetlands are more important sources of DOC to the river network in terms of concentration; however DOC quality in urban systems is comprised of lower-molecular weight compounds and therefore potentially more labile. Thus, DOC from urban systems may be more important to overall stream metabolism. Results from storm sampling suggest that flood events lead to increased input of terrestrial carbon as flow-paths in riparian zones are activated.