The Influence of Groundwater on Brook Trout Distribution in Small Streams

Groundwater plays a critical role in regulating temperature in small streams and is important for thermally sensitive species such as brook trout. Our study examined temperature in small boreal forest streams of Northwestern Ontario to 1) evaluate the spatial and temporal variability in stream temperature, 2) examine the influence of temperature variability of fish distribution among and within stream reaches and 3) develop GIS models to predict groundwater areas using local landscape characteristics.  Temperature was monitored at the substrate/water interface across transects spaced every 2 m throughout 50 m stream reaches.  During the summer, groundwater input resulted in temperature variability within a reach was as high as 12^oC.  Cooler streambed areas were consistently cooler throughout the summer and experienced less diurnal temperature fluctuation than surrounding areas.  During the summer, brook trout were more commonly located in stream reaches with higher thermal variability and within these reaches, density was higher in cooler areas. Groundwater inputs were consistently associated adjacent terrestrial areas that contribute shallow subsurface flow to the stream.  The location of contributing areas can be predicted with GIS models which can inform forest management planning in order to protect these important habitat features.