Dissolved organic carbon (DOC) is a significant organic carbon reservoir in many ecosystems, and its characteristics and sources determine many aspects of ecosystem health and water quality. Fluorescence spectroscopy methods can quantify and characterize the subset of the DOC pool that can absorb and re-emit electromagnetic energy as fluorescence and thus provide a rapid technique for environmental monitoring of DOC in lakes and rivers. Using high resolution fluorescence techniques, we characterized DOC in the Tualatin River watershed near Portland, Oregon, and identified fluorescence parameters associated with effluent from two wastewater treatment plants and samples from sites within and outside the urban region. Using a variety of statistical approaches, we developed and validated a multivariate linear regression model to predict the amount of wastewater in the river as a function of the relative abundance of specific fluorescence excitation/emission pairs. The model was tested with independent data and predicts the percentage of wastewater in a sample within 80% confidence. Model results can be used to develop in situ instrumentation, inform monitoring programs, and develop additional water quality indicators for aquatic systems.

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A radial diffusion model is adapted to describe the kinetics of the exchange of organic compounds between the gas and particulate phases in the atmosphere. A Crank-Nicolson finite difference scheme with variable time stepping is used in applying the model to polydisperse particle size distributions. Two sets of conditions are simulated: (1) airborne particles, as in the ambient atmosphere, and (2) filter-bound particles, such as those found in an air filtration apparatus. The time scale of the intraparticle diffusion reaction, TD, is greatly dependent upon the atmospheric partition coefficient of the compound, Kp (m3/pg), and the particle size distribution of the aerosol. For most compounds typically determined in atmospheric samples, sorption equilibrium with airborne particles is approached rapidly. Sorption reactions that take place on /in filters are controlled not only by TD but also by an equilibrium mass-transfer time scale, TM, which is a function of Kp, the amount of particulate mass, Mp, and the volumetric flow rate, /. The kinetics of sorption reactions on/in filters are predicted to play an important role in the determination of both the probability and the magnitude of sorption-related artifacts within field-derived values of Kp.

[1] The relative impact of a large upstream dam versus in-reach groundwater pumping on stream temperatures was analyzed for humid, semiarid, and arid conditions with long dry seasons to represent typical climate regions where large dams are present, such as the western United States or eastern Australia. Stream temperatures were simulated using the CE-QUAL-W2 water quality model over a 110 km model grid, with the presence or absence of a dam at the top of the reach and pumping in the lower 60 km of the reach. Measured meteorological data from three representative locations were used as model input to simulate the impact of varying climate conditions on streamflow and stream temperature. For each climate condition four hypothetical streamflow scenarios were modeled: (1) natural (no dam or pumping), (2) large upstream dam present, (3) dam with in-reach pumping, and (4) no dam with pumping, resulting in 12 cases. Dam removal, in the presence or absence of pumping, resulted in significant changes in stream temperature throughout the year for all three climate conditions. From March to August, the presence of a dam caused monthly mean stream temperatures to decrease on average by approximately 3.0°C, 2.5°C, and 2.0°C for the humid, semiarid, and arid conditions, respectively; however, stream temperatures generally increased from September to February. Pumping caused stream temperatures to warm in summer and cool in winter by generally less than 0.5°C because of a smaller pumping-induced alteration in streamflow relative to the dam. Though the presence or absence of a large dam led to greater changes in stream temperature than the presence or absence of pumping, ephemeral conditions were increased both temporally and spatially because of pumping.Citation: Risley, J. C., J. Constantz, H. Essaid, and S. Rounds (2010), Effects of upstream dams versus groundwater pumping on stream temperature under varying climate conditions, Water Resour. Res., 46, W06517,

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