Relating transient storage to channel complexity in streams of varying land use in Jackson Hole, Wyoming

Abstract

Transient storage processes are important to biogeochemical cycling in many streams and depend greatly upon stream fluvial structure. Fluvial geomorphic structure establishes patterns of surface water and subsurface head distributions, often driving hyporheic exchange through steps, riffles, and meanders, and controls the potential for in‐channel dead zone storage in side pools, eddies, etc. We performed stream tracer experiments and geomorphological assessments (topographic thalweg surveys, channel dimension measurement, and sediment size analyses) in six streams in Jackson Hole, Wyoming, two agricultural streams, two urban streams, and two reference streams surrounded by native vegetation, to relate stream water transient storage to channel complexity. We propose that the inclusion of agricultural and urban streams increases the range of channel complexity and transient storage response over an assessment of numerous reaches within a single land use type. Stream tracer experiments were performed in each of the six reaches with slugs of Rhodamine WT (RWT). Downstream RWT breakthrough curves (BTCs) were simulated with a one‐dimensional solute transport model, STAMMT‐L, capable of simulating several transient storage residence time distribution types. As an indication of transient storage, relative BTC residence times were compared to timescale of advection, tadv (taken to be the time of peak tracer concentration). Reference streams were geomorphically complex, agricultural streams were intermediate, and urban streams were least complex. Urban streams had the shortest total relative residence times (<5tadv) and short mean storage residence times (0.34 hour, n = 2), and reference streams consistently had the longest total relative residence times (13–20tadv) and the longest mean storage residence times (1.82 hours, n = 2). These results indicate that increased geomorphic complexity increases the potential for transient storage, likely both in the channel and in the subsurface, as demonstrated in reaches in a range of land use settings.