The dynamics and influence of temperature in stream ecosystems of the Great Lakes Basin, Ontario

Many of the streams in Ontario have been modified by human activities. These modifications have occurred even though some of the basic properties of streams, including water temperature, are not fully understood. Temperature affects the overall productivity of stream ecosystems, yet the lack of long-term and geographically broad-scale data has limited the understanding of stream temperatures. The objectives of this thesis were to: (1) examine the influence of temperature on stream fish communities, (2) assess the broad-scale patterns in stream temperatures, (3) determine the factors influencing those temperatures, and (4) provide tools to assess in-stream temperatures. In Chapter 1, air temperature and groundwater discharge potential, surrogates for water temperature, were related to coldwater and warmwater fish distributions throughout southern Ontario watersheds. In Chapter 2, three characteristic thermal regimes were identified for 90 stream sites throughout the Great Lakes Basin. The centroids for regimes 1, 2 and 3 have maximum temperatures of 26.4°C, 28.4°C and 23.5°C and spring warming rates of 0.20°C·d-1, 0.12°C·d-1 and 0.10°C·d -1, respectively. The regimes were related to surrounding riparian forest, mean annual air temperature, upstream ponds and lakes as well as groundwater discharge potential. The spatial variability of the regimes, elevation, flow, wetland area, sparse forest cover and industrial stress were associated with fish community composition. In Chapter 4, a simple methodology was developed to estimate the thermal classification of stream sites from summer air and water temperature measurements. The ability of existing ecological classifications to represent the spatial variability in temperatures was assessed in Chapter 5, and suggested that certain attributes from existing classifications can be used to develop an aquatic ecological classification for Ontario streams. The results suggest that researchers and managers need to think of temperature in terms of regimes, much like the approach used for flow. Traditional, static water quality standards for temperature are inadequate as they ignore the variability in temperatures that influences stream ecosystems. Long-tens and broad-scale monitoring programs are needed to improve our understanding of stream temperatures and manage streams in the face of climate change and increasing anthropogenic activities.;Key words: stream temperature, thermal regime, fish communities, Great Lakes Basin, Ontario...