Nitrogen cycling in a forest stream determined by a ¹⁵N tracer addition

Abstract

Nitrogen uptake and cycling was examined using a six-week tracer addition of ¹⁵N-labeled ammonium in early spring in Waer Branch, a first-order deciduous forest stream in eastern Tennessee. Prior to the ¹⁵N addition, standing stocks of N were determined for the major biomass compartments. During and after the addition, ¹⁵N was measured in water and in dominant biomass compartments upstream and at several locatiogs downstream. Residence time of ammonium in stream water (5-6 min) and ammonium uptake lengths (23- 27 m) were short and relatively constant during the addition. Uptake rates of NH₄ were more variable, ranging from 22 to 37 µg N·m^-1·min^-1 and varying directly with changes in streamwater ammonium concentration (2.7-6.7 μg/L). The highest rates of ammonium uptake per unit area were by the liverwort Porella pinnata decomposing leaves, and fine benthic organic matter (FBOM), although epilithon had the highest N uptake per unit biomass N.

Citation

Mullholland, Patrick J.; Tank, Jennifer L.; Sanzone, Diane M.; Wollheim, Wilfred M.; Peterson, Bruce J.; Webster, Jackson R.; Meyer, Judy L. 2000. Nitrogen cycling in a forest stream determined by a ¹⁵N tracer addition. Ecological Monographs. 70(3). 2000. p. 471-493