Identifying factors that control nitrate flux from catchments is an important goal in ecosystem science.   Broadly viewed, fluvial N export is a product of climate, local hydrological conditions, current and historical N deposition, and terrestrial and lotic ecosystem processes. In this research, we applied K¹⁵NNO₃ and Na Br as simulated rainfall to a 0.25 hectare plot surrounding a headwater spring in the Upper Susquehanna Basin.  Zero tension lysimeters, tension lysimeters, near stream wells and stream channel stations were sampled through time to evaluate where along the soil to stream flowpath nitrate loss was greatest.  The experiment was replicated 3 times to capture spring, summer, and autumn conditions.  Preliminary results indicate that nitrate movement off the landscape and into the stream was greatest in the spring when runoff was highest.  In summer, tracer flux to the stream was minor following the initial application.  In all seasons, little of the conservative and reactive tracer penetrated to the depth of the tension lysimeters (50cm).  We use the ¹⁵N:Br ratio to assess the relative rates of nitrate immobilization along the terrestrial – stream flowpath and how those rates vary with season and carbon supply.