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Investigations of Diel Changes in the Concentration of Metals and Sediment-Water Interactions Abstract Diel concentration changes of metals have been shown to occur in a variety of streams. Photosynthesis and respiration of aquatic plants and microorganisms drive the diel pH cycle in a “healthy” river. However, temperature and pH dependent sorption to surfaces play a significant role in the concentration cycles of both anions and cations in the river system. Since the transport and fate of chemical species within a river can have a significant impact on the health of the aquatic system and the surrounding environment, a better understanding of the of the mechanisms affecting diel concentration cycles will lead to a better fundamental understanding of river systems and water quality within natural waters. Previous examination of the Clark Fork River has demonstrated diel concentration changes in dissolved and particulate forms of Mn, Zn, Fe, Al, and Cu. These concentrations may be effected by daily biogeochemical processes in the benthic biofilm surfaces. It was additionally observed that the concentration of dissolved Mn and Zn cycles were in phase, suggesting that the cycles are linked by a common dependence to temperature, pH, photoperiod, and possibly hydrological cycles. A model has been proposed that links these diel concentration changes to the dissolution and precipitation in association with biofilm and algal populations through a daily solubility and redox cycle. Initial results of laboratory and in situ experiments will be presented that are intended to further investigate the role that benthic surfaces have in the diel concentration cycles of metals in streams. Fieldwork on the Clark Fork River will include the use of “flux” chambers to isolate benthic surfaces from the flowing water column. A comparison of the concentration changes of Mn and Zn within these isolation chambers will be compared to the water column to better identify the sources of the metals and the cause of the cyclic phenomena. Biography
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