Abstract
Abstract. Although most field and modeling studies of river corridor exchange have been conducted at scales ranging from tens to hundreds of meters, results of these studies are used to predict their ecological and hydrological influences at the scale of river networks. Further complicating prediction, exchanges 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 is expected across a river basin. Indeed, the conceptual model of Wondzell (2011) predicts systematic variation in river corridor exchange as a function of (1) variation in baseflow 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 including a synoptic campaign in the 5th-order river network of the H. J. Andrews Experimental Forest (Oregon, USA) and replicate-in-time experiments in four watersheds. 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 main stem. However, we did not find systematic variation with changes in discharge through time or with local geomorphic setting. While interpretation of our results is complicated by problems with the analytical methods, the results 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 datasets that will enable comparisons across multiple sites and/or discharge conditions.
Highlights
Ecological functions and processes in the river corridor are influenced by the exchange of water, solutes, and energy between the surface stream and its catchment and regulate downstream water quality (e.g., Brunke and Gonser, 1997; Krause et al, 2011; Wondzell and Gooseff, 2014; Ward, 2015)
We set out to leverage novel datasets collected across a 5thorder basin to test the existence of systematic relationships linking river corridor exchange with temporal variation in discharge, spatial patterns in discharge, and local geomorphic setting
These findings reflect a high degree of heterogeneity on a reach-to-reach basis in space, likely overwhelming or obscuring river corridor exchange patterns that might emerge in more spatially continuous and larger-scale assessments, which would be a better test of the Wondzell (2011) model
Summary
Ecological functions and processes in the river corridor are influenced by the exchange of water, solutes, and energy between the surface stream and its catchment and regulate downstream water quality (e.g., Brunke and Gonser, 1997; Krause et al, 2011; Wondzell and Gooseff, 2014; Ward, 2015). Several recent studies have extended feature- and reach-scale findings to predict ecological functions of river corridors at basin scales relevant to resource management (e.g., Gomez-Velez and Harvey, 2014; Kiel and Cardenas, 2014; Gomez-Velez et al, 2015; Bertuzzo et al, 2017; Helton et al, 2018). These approaches require a scaling relationship to predict river corridor exchange across space and through time. To use discharge as a scaling factor to predict river corridor exchange, a more complete description of the exchange–discharge relationship is required
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