Long-term trends in the Swedish boreal region show declines in total riverine nitrogen (N) export, likely due to the large-scale tightening of the N cycle caused by boreal forest management and climate change in an already N-limited environment. We used coupled measurements of whole stream metabolism and nitrate uptake in 8 boreal forest streams during summer (growing season) and autumn (during leaf abscission) to investigate the seasonal biological controls over in-stream N processing. Streams ranged in sub-catchment size, from 12 to 6790 ha. Nitrate uptake was measured using the Tracer Additions for Spiraling Curve Characterisation (TASCC) in order to quantify the influence of nitrate concentration on its biological uptake. Nitrate removal was observed at nearly all sites and appeared to be greater during the autumn than summer. This seasonal shift suggests that inputs of labile organic matter may play an important role in regulating nutrient use in these streams. Ongoing work is relating estimates of whole stream metabolism to rates of nitrate uptake. Overall, biological processes in streams draining forested boreal catchments appear to be N-limited during summer and autumn. Implications for boreal forest management and climate change are highlighted.