Studying the dynamics and geochemical behavior of dissolved and particulate organic material is difficult because concentration and composition may rapidly change in response to aperiodic as well as periodic physical and biological forcing. Here we describe a method useful for quantifying fluxes and analyzing dissolved organic matter (DOM) dynamics. The method uses coupled optical and acoustic measurements that provide robust quantitative estimates of concentrations and constituent characteristics needed to investigate processes and calculate fluxes of DOM in tidal and other lotic environments. Data were collected several times per hour for 2 weeks or more, with the frequency and duration limited only by power consumption and data storage capacity. We assessed the capabilities and limitations of the method using data from a winter deployment in a natural tidal wetland of the San Francisco Bay estuary. We used statistical correlation of in situ optical data with traditional laboratory analyses of discrete water samples to calibrate optical properties suited as proxies for DOM concentrations and characterizations. Coupled with measurements of flow velocity, we calculated long-term residual horizontal fluxes of DOC into and out from a tidal wetland. Subsampling the dataset provides an estimate for the maximum sampling interval beyond which the error in flux estimate is significantly increased.

Suspended-sediment concentration data were collected by the U.S. Geological Survey in San Francisco Bay during water year 2005 (October 1, 2004-September 30, 2005). Optical sensors and water samples were used to monitor suspended-sediment concentration at two sites in Suisun Bay, three sites in San Pablo Bay, two sites in Central San Francisco Bay, and three sites in South San Francisco Bay. Sensors were positioned at two depths at most sites. Water samples were collected periodically and analyzed for concentrations of suspended sediment. The results of the analyses were used to calibrate the output of the optical sensors so that a record of suspended-sediment concentrations could be derived. This report presents the data-collection methods used and summarizes, in graphs, the suspended-sediment concentration data collected from October 2004 through September 2005. Calibration curves and plots of the processed data for each sensor also are presented.

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