The influence of environmental and physical factors on the thermal patterns of headwater streams

Graduation date: 2004A case study was performed in 2000 and 2001 to characterize the thermal\ud pattern of four morphologically similar eastern Oregon streams and to identify the\ud physical and environmental factors that expressed significant and functionally\ud viable relationships with stream temperature (daily maximum, daily minimum and\ud daily rate of heating). Stream and environmental attributes were measured at\ud various locations along each stream to provide a data set comprised of variables\ud representing daily stream temperatures (minimum, maximum and rates of heating),\ud daily air temperatures (minimum and maximum), shade, elevation, elevation\ud change and length. Data from the 20 hottest days were analyzed using analysis of\ud variance and regression-based path analysis.\ud With the exception of those reaches that were influenced by groundwater or\ud subsurface flow, downstream reaches consistently experienced increases in the\ud daily maximum stream temperature. The most significant parameter with respect\ud to daily maximum stream temperature appeared to be reach elevation; expressed\ud through reach location in the watershed. Maximum air temperature also positively influenced maximum stream temperature however, only on streams that expressed\ud significant variation in maximum air temperature. The dominant influence of\ud groundwater on maximum stream temperature was also apparent.\ud Significant reach level variation in daily minimum stream temperatures was\ud not observed in this study, however most streams did record increases in the\ud downstream direction. Daily minimum air temperature was consistent across all\ud streams in expressing the most significant relationship with daily minimum stream\ud temperature.\ud With the exception of groundwater influenced reaches, all streams exhibited\ud obvious downstream increases in the daily rate of stream heating. Daily minimum\ud air temperature consistently exhibited a significant negative association with the\ud rate of heating and a relationship was also implied between reach elevation,\ud maximum stream temperature and minimum stream temperature and this stream\ud temperature response. Groundwater and subsurface flow, when present, also\ud appeared to influence the daily rate of stream heating.\ud Resource management activities should have little impact on the parameters\ud found, on these streams, to be associated with stream temperature. Location in the\ud watershed and climatic influence through both minimum and maximum air\ud temperatures emerged as the dominant factors with respect to stream thermal\ud patterns