Conservative solute transport processes and associated transient storage mechanisms: a comparison of streams with contrasting channel morphologies, land use, and land cover

2021 Summer.Includes bibliographical references.Land use within a watershed impacts stream channel morphology and hydrology and therefore in-stream solute transport processes. In this study, I selected two stream sites with contrasting channel morphology, land use and land cover: Como Creek, CO, a relatively undisturbed, high-gradient, forested stream with a gravel bed and complex channel morphology and Clear Creek, IA, an incised, low-gradient stream with low-permeability substrate draining an agricultural landscape. At these sites, I performed conservative stream tracer experiments to address the following questions: 1) How does solute transport vary between streams with differing morphologies and watershed land use?, and 2) How does solute transport at each stream site change as a function of discharge? I analyzed in-stream tracer time series data and compared results quantifying solute attenuation in surface and subsurface transient storage zones. I found significant differences in solute transport metrics between sites and significant trends in these metrics with varying discharge conditions at the forested site but not at the agricultural site. In the relatively undisturbed, forested stream there was a broad range of transport mechanisms and evidence of substantial exchange with both surface and hyporheic transient storage. In this forested site, changing discharge conditions activated or deactivated different solute transport mechanisms and greatly impacted advective travel time. Conversely, in a simplified, agricultural stream there was a narrow range of solute transport behavior across flows and predominantly surface transient storage at all measured discharge conditions. These results demonstrate how channel simplification resulting from land use change inhibits available solute transport mechanisms across varying discharge conditions