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Preliminary Investigations of Temporal Variability in the Concentration and Composition of DIC and DOC in Streams Abstract Diel concentration fluctuations of metals and other chemical species in streams have been well documented in the literature. Daily cycles of temperature, oxidation-reduction, photosynthesis and respiration, force chemical and physical changes in pH, alkalinity, dissolved oxygen, redox speciation, dissolved carbon dioxide, and dissolved and particulate element concentratons. It has been demonstrated that there is a significant and reproducible diel cycle in the carbon stable isotope composition of dissolved inorganic carbon (DIC, 13C-DIC) in both the Clark Fork (CFR) and Big Hole Rivers (BHR) in Montana. These changes are caused by the combined effects of photosynthesis and respiration of aquatic plants and microbes, and it is reasonable to expect diel changes in the total concentration and isotopic composition of the dissolved organic carbon (DOC, 13C-DOC) as it is influenced by changes in the sources of the organic carbon. DOC represents the single largest pool of reduced organic carbon in most aquatic systems; however, the presence of short-term temporal changes of the concentration of DOC have only been recently demonstrated. Both DOC and DIC have important roles in the natural processes that take place in streams. DIC can accumulate in surface waters from air-water gas exchange, community respiration, weathering of minerals or from groundwater contributions. Sources of DOC can include decomposition of organic matter and secretion by aquatic plants and microbes. However, little is known about the connection between these general classes of carbon reservoirs in natural systems. This current investigation is examining the connection on a diel (24-h) basis between DIC and DOC in several Montana rivers. It will also provide insight into the relationship between daily changes in DOC and transport of metals in these rivers. The objectives of this study are: 1) to measure the concentrations and 13C composition of DIC and DOC over a 24-h period, 2) to investigate and quantify the connection between the diel cycles of DIC and DOC, 3) to investigate the diel mobility of trace metals in the system in relationship to temporal changes in DOC concentration. Biography
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