Relating Hydrogeomorphic Attributes to Nutrient Uptake in Alluvial Streams of a Mountain Lake District

Stream form and hydrologic processes may indirectly drive nutrient uptake, however developing predictive relationships has been elusive. Problems in establishing such relationships may lie in the sets of streams analyzed, which often span diverse channel-sizes, geology, and regions, or are too geomorphically similar. We collected field data on stream geomorphology and hydrologic and nutrient transport processes using solute injections at 22 alluvial stream reaches in the Sawtooth Mountains, Idaho, USA. Many of these streams occur near lakes, which create contrasting fluvial form and functions that we hoped would produce a broad geomorphic dataset to compare to hyporheic and dead-zone transient storage and NO3 and PO4 spiraling metrics. Preliminary results suggest that storage zone residence time (Tsto) was best predicted by sediment D50, wood abundance (CWD), and discharge (r2=0.84, p<0.01) and relative hyporheic zone size was best related to D16 and channel width/depth ratio (W/D) (r2=0.48, p=0.05). Among site variation in NO3 uptake velocity (Vf) was best explained by CWD, W/D, and Tsto (r2=0.71, p=0.05) and PO4-Vf was best explained by bed mobility and Tsto (r2=0.96, p<0.01). If and by what mechanisms these models represent true geomorphic drivers of stream transient storage and nutrient cycling processes should be further considered and investigated.