RELATING TRANSIENT STORAGE TO VARIED GEOMORPHIC, DISCHARGE, AND HYPORHEIC CONDITIONS IN ARCTIC TUNDRA STREAMS

Transient storage of solutes in either hyporheic zones or other slow moving waters of stream channels plays a significant role in the ecology and biogeochemical processes of streams. Rhodamine WT was used as a conservative tracer to assess the transient storage as well as other hydrologic characteristics of five morphologically diverse tundra streams in Arctic Alaska, during the summer thaw season (May-August) of 2004. To assess how the hydrologic conditions of these streams varied throughout the thaw season repeated stream tracer injections were performed. More specifically, at the onset of these experiments, it was predicted that transient storage would increase in these streams throughout the thaw season as the potential for a hyporheic zone increased with growth of the thaw zone below the channel. Across all studied streams, sub-channel thaw depths increased throughout the experiments, while discharges and velocities varied dramatically with minimum shifts of eight-fold and four-fold, respectively. Modeling of the tracer experiments show that the mean storage residence time, a measure of the average time that a solute spends in a storage zone, has an exponential inverse relationship with discharge. However, no relationship between transient storage and depth of sub-channel thaw was determined. Understanding the role of the increasing hyporheic potential on transient storage is not possible from these experiments because the influence of discharge confounds any such interpretation. This study indicates that across various stream morphologies, discharge is the first-order control on the transient storage dynamics of a stream.