Spatial and temporal patterns of temperature in the Horsefly River

Water temperature influences the ecology of a stream. Management practices, such as dear-cutting and land clearing for agriculture, have been associated with increases in the expected summer stream temperature at a variety of spatial and temporal scales in other systems. As a result, landscape disturbances within the Horsefly River's Watershed would be expected to change the ecology of the Horsefly River. The major difference between this study and most other studies is that the Horsefly Watershed (-2300 km~ is at least five times larger than watersheds studied previously. This study assessed the temporal patterns of stream temperature by evaluating trends in the Horsefly River's weekly water temperature near the Horsefly Townsite from July 1 to September 30 over a 45- year period (1955 - 1999). Possible trends in ground and ground water temperatures within the Horsefly Watershed were also evaluated. Assessing the influence of landscape disturbances on the Horsefly River's temperature near the Horsefly Townsite were inferred from a high spatial and temporal resolution environmental survey conducted within the Horsefly Watershed from July 1 to September 30, 2000. Weekly averages of daily the stream temperature statistics (maximum, average, minimum, range) were decomposed into a meteorological component (weekly air temperature), a hydrological component (weekly stream discharge) and a yearly trend component using multiple linear regression analysis. There were discernible yearly trends in the Horsefly River's temperature near the Horsefly Townsite that were independent of the meteorological and hydrological components. There was also a potential trend in ground and ground water temperature (0.033\u2070C/year) within the Horsefly Watershed. The high-resolution environmental survey suggested that most (-95%) of the recent (post 1955) landscape disturbances did not affect the Horsefly River's water temperature near the Horsefly Townsite. As well, the trends in the weekly averaged daily stream temperature statistics could be explained by the potential increasing trend in ground and ground water temperature. All the results from this research are consistent with the hypothesis: annual changes in the Horsefly River's temperature near the Horsefly Townsite from 1955 to 1999 were a direct consequence of climate warming and not likely related to landscape disturbances within the Horsefly Watershed. Management of the Horsefly River should consider trends in long-term climate change as an indicator for changes in the ecology of the river.