A tracer investigation of nitrogen cycling in a pristine tundra river

The fate of nitrogen (N) in drainages depends in part on N storage and transformation within the river network. The addition of an [N-15]NH4+ isotopic tracer to a tundra river provided information on the uptake, food web transfer, and ecosystem retention of N. The fourth-order Kuparuk River ecosystem took up 60% of the NH4+ within 1 h and 1 km of the point of tracer addition. Long-lived biota and epilithon retained measurable amounts of the added N-15 for UP to 2 years. These transformations and storages within rivers exert control over the timing of N export, the chemical form of exported N, and, consequently, its ecological impact on downstream aquatic ecosystems.