Understanding the effect of tidal wetlands on DOC concentrations and the chemical composition in the Sacramento-San Joaquin Delta (Delta) waters is important because DOC fuels the base of the Estuary foodweb and because it forms deleterious by-products when water is treated for potable use. The concern is that planned large scale wetland restorations may affect DOC concentration and quality at the regional scale. We report here the results of a study to measure fluxes and chemical composition of wetland-derived DOC from Brown's Island, a natural tidal wetland in the western Delta. We have paired ADCP discharge measurements with in situ measurements of optical properties - spectral properties of absorbance, fluorescence - to elucidate fluxes and changes in DOC concentration and composition, to differentiate among sources of DOC, and as proxies for geochemically-related substances, including nitrate, MeHg, and others. Optical properties are readily measured in situ, yet also contain a large amount of useful information related to sources and geochemical processes. DOC composition and flux varies on tidal, spring-neap, and seasonal timescales in response to regional and local conditions. We will present how results of such measurements offer powerful new quantitative insights into sources and geochemical processes in tidal wetlands.

Bergamaschi, B.A., B.D. Downing, J.A. Fleck, E. Boss, 2007. Quantifying Seasonal Changes in DOC Composition and Flux from a Tidal Wetland Using In-situ Optical Measurements. 10th International Symposium on Biogeochemistry of Wetlands, April 1-4, Annapolis, MD.