ABSTRACT: Bed temperatures in relation to hyporheic exchange patterns in a headwater stream, and response to forest harvesting.

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Abstract

Stream temperature is an important control on biogeochemical processes and on the growth and distribution of species in streams. Bed temperatures are similarly important in relation to benthic organisms. Studies have shown that reduction of canopy cover over streams due to logging increases stream temperatures throughout the summer by exposing the stream to solar radiation. However, the effect of harvesting on bed temperatures has not been studied in as much detail. This study examines the hypothesis that bed temperature variations in a headwater stream, and their response to forest harvesting, are influenced by hyporheic exchange patterns. Stream temperatures, bed temperatures, and hydraulic head measurements were made throughout the summers of 2004 and 2005 in two study reaches of a headwater stream in the southern Coast Mountains of British Columbia. Stream temperatures were also recorded in a control stream, for which the catchment remained unlogged through the experiment. The treatment catchment was logged in the fall of 2004. Principal component analysis showed that up-welling and down-welling zones of the stream exhibited different bed temperature patterns. A paired-catchment analysis showed that the daily maximum stream temperatures increased by up to 6慢 while daily maximum bed temperatures increased up to 2慢 in the summer of 2005. Areas of downwelling flow into the stream bed showed generally higher temperatures and slightly greater temperature increases than areas where the piezometers indicated upwelling flow. These results confirm that hyporheic exchange influences the bed temperature patterns in streams and their response to harvesting.

Bibliography of Canadian Geomorphology