Document: JEN-3-73-9

Nitrogen cycling in a subarctic stream in Iceland: Results from a ¹⁵N tracer addition.

TANK, J.L.* ¹ and D.M.SANZONE ²

University of Illinois, Urbana, IL, 61801 USA ¹
University of Georgia, Athens, GA, 30602 USA ²

Abstract:
We used a ¹⁵N tracer addition to quantify nitrogen cycling through the food web of a small subarctic stream in Northern Iceland. Beginning after snowmelt, we added ¹⁵N-NH₄Cl continuously for 4 weeks and followed the flow of ¹⁵N into the stream food web. Despite low stream temperatures (mean = 6.9 C), N uptake was rapid; ammonium uptake lengths ranged from 122-130m. By day 4 of the release, all food web compartments were labeled with tracer ¹⁵N. After 21 days, filamentous green algae had the highest tracer ¹⁵N values in the food web. Fine benthic organic material (FBOM) was less labeled than the bulk epilithon indicating that FBOM may have been a mixture of sloughed algae and other detritus. ¹⁵N uptake in the two groups of chironomids (Diamesinae and Orthocladiinae) was similar and chironomids were more highly labeled than the larger bodied blackfly (Neosimulium vittatum). Blackflies appeared to feed on the epilithic biofilm and associated fine particles as tracer ¹⁵N in blackflies was similar to that in bulk epilithon and FBOM. In contrast, the tracer ¹⁵N in chironomids fell between that of epilithon and green algae indicating that chironomids may be feeding on both resources. Adult chironomids captured in emergence traps placed over the stream had similar tracer ¹⁵N values as larvae collected from the benthos indicating that N uptake and export to the riparian zone was rapid.

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This abstract is being presented at: 12:00 PM in session:
Oral Session #55: Invertebrates in Streams: Foodwebs.