Abstract. Although most field and modeling studies of river corridor exchange have been conducted a scales ranging from 10’s to 100’s of meters; results of these studies are used to predict their ecological and hydrological influences at the scale of river networks. Further complicating prediction, exchange are expected to vary with hydrologic forcing and the local geomorphic setting. While we desire predictive power, we lack a complete spatiotemporal relationship relating discharge to the variation in geologic setting and hydrologic forcing that are expected across a river basin. Indeed, Wondzell’s [2011] conceptual model predicts systematic variation in river corridor exchange as a function of (1) variation in discharge over time at a fixed location, (2) variation in discharge with location in the river network, and (3) local geomorphic setting. To test this conceptual model we conducted more than 60 solute tracer studies collected in a synoptic campaign in the 5th order river network of the H. J. Andrews Experimental Forest (Oregon, USA). We interpret the data using a series of metrics describing river corridor exchange and solute transport, testing for consistent direction and magnitude of relationships relating these metrics to discharge and local geomorphic setting. We confirmed systematic decrease in river corridor exchange space through the river networks, from headwaters to the larger mainstem. However, we did not find systematic variation with changes in discharge through time, nor with local geomorphic setting. While interpretation of our results are complicated by problems with the analytical methods, they are sufficiently robust for us to conclude that space-for-time and time-for-space substitutions are not appropriate in our study system. Finally, we suggest two strategies that will improve the interpretability of tracer test results and help the hyporheic community develop robust data sets that will enable comparisons across multiple sites and/or discharge conditions.

The lampricides 3-trifluoromethyl-4-nitrophenol (TFM) and 2',5-dichloro-4'-nitrosalicylanilide (niclosamide) are added to Great Lakes tributaries to target the sea lamprey, an invasive parasitic fish. This study examines the photochemical behavior of the lampricides in Carpenter Creek, Sullivan Creek, and the Manistique River. The observed loss of TFM in Carpenter and Sullivan Creeks (i.e., 34 and 19%) was similar to the loss of bromide in parallel time of passage studies (i.e., 30 and 29%), demonstrating that TFM photodegradation was minimal in both tributaries during the lampricide application. Furthermore, the absence of inorganic and organic photoproducts in the Manistique River demonstrates that TFM and niclosamide photodegradation was minimal in this large tributary, despite its long residence time (i.e., 3.3 days). Kinetic modeling was used to identify environmental variables primarily responsible for the limited photodegradation of TFM in the field compared to estimates from laboratory data. This analysis demonstrates that the lack of TFM photodegradation was attributable to the short residence times in Carpenter and Sullivan Creeks, while depth, time of year, time of day, and cloud cover influenced photochemical fate in the Manistique River. The modeling approach was extended to assess how many of the 140 United States tributaries treated with lampricides in 2015 and 2016 were amenable to TFM photolysis. While>50% removal of TFM due to photolysis could occur in 13 long and shallow tributaries, in most systems lampricides will reach the Great Lakes untransformed.