WHOLE-STREAM METABOLISM IN ARCTIC TUNDRA STREAMS: A FEASIBILITY TEST AND INITIAL RESULTS

W. B. Bowden and C. Pruden. Landcare Research New Zealand

Tundra streams are subject to 24 h sunlight during the biologically active season (mid-May to mid-September). For this reason we assumed that whole-stream metabolism (WSM) estimates -- which are dependent on natural diurnal light/dark cycles -- would not work well at our sites (near Toolik Lake Alaska, 68° 38' N). However, at this latitude the sun's position does vary, even at the summer solstice. In addition, lower-order streams (which have become a recent focus of our work) are often incised and bank shading can promote low light levels at the stream bottom during portions of the day. Thus, we tested the feasibility of using a WSM approach in 3 low-order streams. For each stream we were able to measure substantial changes in DO over 24 h tests and observed significant changes in DO between stations. All 3 streams were strongly heterotrophic (P < < R). This is important because our chamber methods strongly favour autotrophic components of the community. Estimates of metabolism were highly sensitive to the values used for the re-aeration coefficient. We concluded that this approach to estimating stream metabolic activity in Arctic streams has merit, but that it will be necessary to carefully estimate the re-aeration coefficient for each experiment.