9628368 Hornberger In many catchment-stream systems, the concentration and composition of dissolved organic material (DOM) is a critical water quality characteristic. Examples of processes controlled by DOM interactions are: 1) complexation of trace metals by the humic fractions of DOM which control both trace metal transport and bioavailibility; 2) enhancement of the solubility of hydrophobic organic contaminants; 3) formation of trihalomethanes in drinking water as a result of interactions between Chlorine and components of the DOM during water treatment; and 4) absorption of visible and UV radiation by DOM and generation of photoproducts. The DOM also can have indirect effects on water quality by influencing internal processes of aquatic ecosystems, e.g., photosynthesis and heterotrophic activity. In this proposal, we advance a plan of study to investigate in-stream processes and their interaction with catchment processes in determining the spatial and temporal patterns of quantity and quality of DOC in streams in the Rocky Mountains. The research tasks will include experimental additions of DOC-enriched water to stream segments to quantify interactions in the hyporheic zone, field monitoring to deermine synoptic spatial patterns along stream channels and in hillslope lysimeters of amounts and composition of DOC, and the extension of mathematical models to interpret the results. Studies of the in-stream processes will include continuing assessment of the roles of near-stream and catchment-scale processes.
