Physical dynamics in rivers, wetlands, and estuaries drive important geochemical processes, yet our ability to measure these processes is hampered by an inability to resolve complex sources or to sample at temporal or spatial scales appropriate for the system. We have used in situ measurements of optical properties -- spectral properties of absorbance, fluorescence � at high temporal and spatial resolution to elucidate changes directly in nitrate concentration and dissolved organic carbon concentration and composition. We have also used these measurements as proxies for geochemically-related constituents such as Hg, MeHg, and as surrogates for disinfection byproduct formation potential in drinking water quality management.  Optical properties are readily measured in situ, yet also contain a large amount of useful information related to sources and geochemical processes. We present examples of how such measurements can offer powerful new insights into biogeochemical processes. Examples will include deployments in rivers, streams, estuaries, and wetlands, but the focus will be largely on estuaries. Measurement of biogeochemical variation and constituent mass flux in estuarine environments where tidal dynamics dominate is impractical over the diurnal to spring-neap time- scales necessary to accurately quantify flux. We used in-situ optical instrumentation to quantify constituent fluxes as well as examine changes in sources over daily to seasonal scales in tidal marshes and channels.Figure 1. Time series of nitrate concentration (middle black line, in uM, left axis) at Liberty Island in San Francisco estuary, California, USA. Stage height shown in upper panel (blue line). Cumulative tidal flux of nitrate shown in orange (in moles, right axis).

Use of optical measurements for understanding and quantifying biogeochemical processes

248th National Meeting (2014)

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