CONTROLS ON TEMPERATURE IN SALMONID-BEARING HEADWATER STREAMS IN TWO COMMON HYDROGEOLOGIC SETTINGS, KENAI PENINSULA, ALASKA

Headwater streams are the most numerous in terms of both number and length in the conterminous United States and play important roles as spawning and rearing grounds for numerous species of anadromous fish. Stream temperature is a controlling variable for many physical, chemical, and biological processes and plays a critical role in the overall health and integrity of a stream. We investigated the controls on stream temperature in salmon-bearing headwater streams in two common hydrogeologic settings on the Kenai Peninsula, Alaska: (1) drainage-ways, which are low-gradient streams that flow through broad valleys; and (2) discharge-slopes, which are high gradient streams that flow through narrow valleys. We hypothesize local geomorphology strongly influences surface-water and groundwater interactions, which control streamflow at the network scale and stream temperatures at the reach scale. The results of this study showed significant differences in stream temperatures between the two hydrogeologic settings. Observed stream temperatures were higher in drainage-way sites than in discharge-slope sites, and showed strong correlations as a continuous function with the calculated topographic metric flow-weighted slope. Additionally, modeling results indicated the potential for groundwater discharge to moderate stream temperature is not equal between the two hydrogeologic settings, with groundwater having a greater moderating effect on stream temperature at the drainage-way sites.