We studied how the transition between unusually dry and wet years affected the hydrologic processes (like snowmelt and baseflow) and biological processes (such as nutrient uptake and assimilation) that regulate nitrogen dynamics in two mountain streams. Comparing a larger, open-canopy stream to a smaller, shaded stream in the Lake Tahoe Basin (California/Nevada, USA), we found the larger stream had higher metabolic rates and more efficient uptake of inorganic nitrogen. However, in the wet year, delayed baseflow sharply instream productivity and reduced nitrogen retention in both streams, leading to greater nitrogen export. These findings show that hydroclimate extremes can disrupt stream ecosystem function and highlight how stream-specific features shape biogeochemical responses to changing precipitation patterns.