Quantifying fluxes and characterizing compositional changes of dissolved organic matter in aquatic systems in situ using combined acoustic and optical measurements

Abstract

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.

Cross-connection detection in Australian dual reticulation systems by monitoring inherent fluorescent organic matter

“…LED-based sensors are becoming increasingly available in lighter and smaller dimensions, at lower costs, higher efficiencies and at increasingly lower wavelengths to target previously inaccessible spectral areas [119]. Such developments have allowed the high sensitivity and specificity of fluorescence spectroscopy within water sciences to be demonstrated, and this has been highlighted more recently by its use with in situ spectrometers [67,120,121] for uses such as detecting river pollution by monitoring protein-like fluorescence and to monitor diurnal variability in river water DOM.…”

A temperature compensation method for CDOM fluorescence sensors in freshwater

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296As interest in the aquatic cycle of organic carbon (OC) has increased, the deployment of in situ optical sensors to measure CDOM fluorescence (chromophoric dissolved organic matter) as a proxy for OC concentration has become more common (e.g., Downing et al 2009;Sandford et al 2010). CDOM sensors typically use UV light (~350 nm) to excite the emission of blue light (~450 nm) from certain organic fluorophores, allowing investigators to distinguish CDOM from more commonly measured phytoplankton pigments.

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Recent Advances in Understanding Flow Dynamics and Transport of Water-Quality Constituents in the Sacramento–San Joaquin River Delta

“…This capability is particularly important in a tidal setting where tidal advection and dispersion continuously affect constituent concentrations. For example, Ganju et al (2005) and Downing et al (2009) used data from Browns Island to assess the minimum sampling frequency necessary to accurately calculate advective outflow is, so as to properly manage project (and gate) operations, the uncertainty is very large.…”

“…Optical sensors invented in the 1980s were first deployed in the Delta in the late 1990s to continuously measure suspended-sediment concentration (Wright and Schoellhamer 2005). Optical sensors that continuously measure carbon and nutrients were first deployed in the Delta in the 2000s (Bergamaschi et al 2012;Downing et al 2009;Pellerin et al 2013). When these instruments are deployed with sufficient density to enable several channels or locations to be observed simultaneously, continuous data streams that include all tidal fluctuations can be collected, and these data have led to improved understanding of flow and constituent transport in the Delta.…”