Thermal alteration of streams draining clearcut watersheds: Quantification and biological implications

Abstract

A quantitative evaluation of stream temperature alterations due to a commercial forest harvesting practice and a research treatment is presented. Summer maximum stream temperatures averaged 1 ° C higher in the commercial clearcut and 9 °C higher in the clearcut-herbicided watershed than in the forested control. The largest average monthly temperature increase on the commercial clearcut (2.2 °C) occurred during April; on the clearcut-herbicided basin it occurred during June (10.5 °C). Significant changes in stream temperature were observed on both watersheds as early as February and as late as November. Changes in minimum stream temperatures are presented in detail along with the impact on diel temperature fluctuations. Changes in the stream temperature regimes of the clearcut watersheds from the headwaters to the mouth of the watersheds are also given. Potential impacts of the stream temperature alterations on aquatic ecosystems are summarized in relation to stress limits for brook trout and other organisms.