A multi-scale method for identifying groundwater exchanges sustaining critical thermal regimes in streams

A holistic understanding of heterogeneous groundwater-induced thermal regimes was developed for a Southern Ontario creek using a multi-scale field approach. To better understand the habitat characteristics sustained by the groundwater and surface water exchanges, the relationship between groundwater inputs and stream temperatures were investigated at stream, segment, geomorphic-unit and micro-habitat levels. Continuous point temperature measurements at various locations along the main channel were used to determine seasonal and spatial stream temperature trends and to identify areas of possible groundwater contributions. Methods effective for quantifying and locating groundwater inputs were evaluated, including the velocity-area method, stream temperature surveys and sediment temperature measurements. Sediment temperature mapping of riffle-pool and plane-bed geomorphic units illustrated highly varied substrate temperatures in the plan-view of the creek. The potential application of thermal imaging was also explored and thermal images successfully illustrated a groundwater-sustained micro-habitat. The results demonstrated that these multi-scale field techniques allow for different groundwater-surface water exchange processes to be observed and more effectively capture the complexity of these exchanges than single-level field approaches.