Using the RO/ED Method to Isolate Low-Ash Dissolved Organic Matter in High Yield along a Salinity Gradient

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The chemical characteristics of dissolved organic matter (DOM) are expected to be modified by an array of biogeochemical processes (sources, sinks, transformations) along a salinity gradient such as the river-estuary-ocean system. To quantify such changes in the quality and quantity of DOM, scientists have relied upon methods of isolation such as solid-phase extractions (SPE) and ultrafiltration (UF), for which yields of DOM typically decline substantially along the salinity gradient. Observed changes in the chemistry of isolated samples of DOM along a salinity gradient are the integrated result of biogeochemical processing and salinity-dependent fractionation of DOM as the retention characteristics of individual compounds are modified by increased salinity. Most prior work has interpreted measured compositional changes solely in terms of biogeochemistry. In this project, researchers at the Georgia Institute of Technology will conduct laboratory experiments to optimize a coupled reverse osmosis/electrodialysis (RO/ED) method to maximize the yield of DOM and minimize co-concentration of inorganic solutes. Field experiments along the full salinity gradients of the Satilla and Altamaha rivers in southeast Georgia will provide feedback to the design and optimization of the modified RO/ED method. High-quality, low-ash samples of DOM will be collected across a range of salinities and characterized chemically and spectroscopically (elemental analyses (CHONS), acid-base titrations, 13C NMR and FTICR spectrometry). The goals of the proposed research are: (1) to extend the range of water chemistries over which the RO/ED method can be applied, (2) to develop new capabilities for removing residual inorganic materials to obtain low-ash samples of marine DOM, and (3) to isolate DOM in high yield along several complete river-estuary-ocean salinity gradients and to test the hypothesis that DOM is not significantly fractionated by the RO/ED isolation method.. Broader Impacts: The project will provide financial support for the doctoral research of one graduate student. Knowledge gained during the project will be shared formally through publications in the peer-reviewed literature and presentations at national and international meetings and directly with current collaborators and other scientists who have requested the PI?s formal support in using the RO/ED method to isolate DOM from a variety of natural waters.