CHARACTERIZING THE CASCADE EFFECT OF UPSTREAM HYPORHEIC EXCHANGE IN MOUNTAIN STREAMS

The characterization of hyporheic exchange in streams is important to understanding biogeochemical cycling in stream ecosystems. Previous hyporheic exchange investigations have generally focused on particular stream reaches. In this study, we investigate the cascade effect of hyporheic exchange in upstream reaches on hyporheic exchange in down stream reaches. We hypothesize that the residence time distribution of a conservative tracer in a down stream reach will be directly influenced by temporal scattering of input concentrations due to upstream hyporheic exchange, and therefore be characterized differently than if the downstream reach were isolated in a hyporheic exchange experiment. To test this idea, we performed two stream tracer experiments in a 4th order portion of Lookout Creek, Oregon, and simulated the observed data with a general residence time distribution solute transport model. The first experiment was done in the lower reach, LO411, and the second experiment was performed in the combined upper reach, LO410, and LO411. This study is a preliminary investigation in scaling up our understanding of hyporheic exchange from reach scale to basin scale.