SEASONAL TEMPERATURE PATTERNS IN AN ARCTIC AND 2 SUB-ARCTIC ALASKAN (USA) HEADWATER STREAMS

We investigated the thermal ecology of three Alaskan streams. Monument Creek (MC) and Little Poker Creek (LPC) are subarctic streams in interior Alaska; LPC is in a permafrost-dominated valley. Imnavait Creek (IC) is an arctic tundra beaded stream in the northern foothills of the Brooks Range. Water temperatures were recorded with automated dataloggers hourly (LPC) or bi-hourly (MC and IC). Records for MC extend through almost three entire years, while data from IC (three years) and LPC (one year) represent the majority of the ice-free season. We also collected winter water/ice temperatures from IC (1989-1990). Mean annual water temperatures were 1.1-degrees-C (LPC), 2.3-degrees-C (MC), and 2.9-degrees-C (IC), while maxima were 5.8-degrees-C (LPC), 13.0-degrees-C (MC), and 21.4-degrees-C (IC). Water temperature rose in the spring about twice as fast (both mean and maximum daily increase) in MC as in LPC, and again about twice as fast in IC as in MC. A similar pattern was observed during the autumnal decline in water temperature. Maximum daily amplitude followed a similar pattern, with MC (6.6-degrees-C) intermediate between LPC (4.1-degrees-) and IC (11.6-degrees). LPC accumulated approximately 400 degree-days above 0-degrees-C, MC approximately 950 degree-days, and IC approximately 1000 degree-days. Although it is about 450 km north of the other streams, the tundra stream (IC) accumulated more degree-days, had higher maximum and mean temperatures, greater daily temperature amplitude, and steeper slopes of vernal temperature rise and autumnal temperature decline than the subarctic streams (LPC and MC). The absence of a canopy of riparian plants, channel morphology, and continuous sunlight during the arctic mid-summer accounted for these higher temperatures. Beaded tundra streams provide a highly seasonal (< 120 d ice-free) and spatially and temporally complex thermal environment.