9628166 Chin Natural organic matter (NOM) is an important component of soils, streams, lakes, ground waters, and estuarine waters, and it plays a key role in such diverse environmental phenomena as mineral growth and dissolution, cycling of trace metals, and the global biogeochemical C budget. Perhaps most importantly, NOM plays a crucial, though complex, role in the transport of organic and inorganic pollutants through porous media. On the one hand, NOM that is bound to mineral surfaces may remove trace metals, nonpolar organic compounds (NOCs ) and other pollutants from the water column. On the other hand, NOM that remains free or in colloidal form within the water column may increase the mobility of pollutants. Hence, understanding and quantifying the bulk partitioning of NOM between solid and dissolved phases is fundamental to a wide range of pollutant transport phenomena. Moreover, because NOM consists of a variety of hydrophobic and hydrophilic molecules with variable structure, functionality, and reactivity, we need to understand not only how NOM partitions but also how it fractionates upon sorption to mineral surfaces. For example, preferential sorption of the more hydrophobic components may increase the retardation of NOCs through porous media. Numerous field and laboratory studies have suggested that NOM fractionates upon sorption, and provided clues to fractionation processes. Nevertheless, many questions remain regarding the effects of NOM composition, solution characteristics, mineral surface properties and kinetic considerations on fractionation. Additionally, little is known about the effects of mineral dissolution, metal complexation, and NOM coagulation on apparent fractionation. Finally, much of our current understanding of fractionation is based on largely indirect evidence. For example, although observed kinetic effects on fractionation have been attributed by some to changes in conformations of sorbed NOM molecules, this hypothesis has not been tes ted directly. To better understand NOM fractionation processes, we propose a 3-year interdisciplinary research effort combining field sampling at a carefully chosen freshwater wetland watershed, McDonalds Branch basin in the New Jersey Pinelands, with newly developed molecular-level methodologies, to study NOM sorption and fractionation in a far more direct manner than previously has been possible. NOM samples will be collected from surface waters, soils, and shallow and deep ground waters in carefully documented recharge and discharge zones. Fractionation on sorption of McDonalds Branch and standard NOM samples will be quantified by characterizing solutions prior to and following adsorption, using a combination of analytical techniques, including: 13C NMR and 1H NMR; UV-Vis, fluorescence, and attenuated fourier transform infra-red (ATR-FTIR) spectroscopies; high pressure size exclusion chromatography (HPSEC); total organic carbon analysis (TOC); vapor pressure osmometry; potentiometric titration's; and elemental analysis. Scanning-tunneling and atomic-force microscopy (STM and AFM), including the new tapping mode AFM, will be used to determine the structure of sorbed organic molecules, and the role of structural changes in sorption and fractionation. High pressure liquid chromatogrphy (HPLC) and AA will be used to study oxide dissolution and NOM-metal binding phenomena. Surface FTIR will assist in deterring sorption mechanisms, and how they influence fractionation. We believe that this project is fundamental to many areas of water quality research, and that we have chosen a true end-member natural laboratory watershed to conduct the field investigation. The combination of state-of-the-art laboratory techniques listed above will allow us to tackle this problem in a far more quantitative, mechanistric manner than previously has been possible. Over the course of this research, new techniques of metal-complexation analysis will be refined, new methods of STM/AFM imaging of sorbed organic molecules will be furthered, and a new approach to integrating laboratory and field investigations of NOM structure, composition, and reactivity will be fostered. The proposed research will lay a strong foundation for a broad spectrum of additional research. For example, the approach may be expanded to encompass sampling at a greater diversity of watershed types, with different NOM characteristics. We anticipate that this research will enable a wide range of future studies of how NOM fractionation influences the transport of hydrophobic and hydrophilic pollutants. Finally, given the importance of freshwater wetlands, and the rapidity with which they are disappearing from our landscape, we feel that investigations involving NOM evolution in wetlands are crucial to further our understanding of such complex but fragile ecosystems.
