LINKING THE THERMAL REGIMES OF STREAMS IN THE GREAT LAKES BASIN, ONTARIO, TO LANDSCAPE AND CLIMATE VARIABLES

The lack of geographically broad-scale temperature data has limited our ability to classify stream temperatures and assess the processes affecting them. Continuous data (1 July 2005-30 June 2006) from 90 sites throughout the Great Lakes Basin (GLB) were used to classify and model the thermal regimes of streams in Ontario. Existing and newly developed temperature metrics were used to characterize the data for each site. The 90 sites clustered into three thermal regimes based on maximum weekly maximum temperature (degrees C) and spring rate of change (degrees C . d(-1)). The centroids of regime 1, 2 and 3 had temperatures of 26.4, 28.4, 23.5 degrees C and warming rates of 0.20, 0.12 and 0.10 degrees C . d(-1), respectively. There was a regional pattern in the thermal regimes; most sites in the north were regime 1 and most sites in the south were regime 2 but neither regime was limited to those areas. Regime 3 sites were found throughout the study area. Discriminant function analysis indicated that per cent riparian forest, mean annual air temperature, per cent surface water and groundwater discharge potential influenced the thermal regimes at the sites, and demonstrated how variables at three spatial scales influence stream temperatures. This study provides a framework for thermal assessments elsewhere and demonstrates how anthropogenic activities such as riparian deforestation, groundwater withdrawal, stream regulation and climate change will all affect the main drivers of thermal regimes in streams. Copyright (C) 2009 John Wiley & Sons, Ltd.