Introduction to the Legacy Forest Small Streams Study: Runoff patterns and related biochemistry in the western portion of the Boreal Shield

The Forest Watershed and Riparian Disturbance (FORWARD) Project is an ongoing study initiated on the western Boreal Plain (northwestern Alberta) in 2001 to incorporate hydrologic processes into industrial forest management. Data collection and modelling focused on streamflow during the growing season (01 May to 31 October) in eight recently disturbed (>50% by total area) and six reference first- to fourth-order watersheds. In 2003, the Legacy Forest Small Streams (LFSS) study was launched in the western Boreal Shield (northwestern Ontario) to extend the geographical scope of the FORWARD Project. The objectives of my study were to provide a comparable baseline data set on stream flow dynamics for the modelling process within industrial forest management and in the context of a comparative study of storm driven patterns. Long-term intention is to apply controlled disturbance (ie. forest harvest) to a subset of the study watersheds. My study focused on five first- to third-order designated reference streams characterized between the 01 April to 31 October 2004 period. Mean total runoff in the small streams in the western Boreal Shield were >3 times higher than similarly sized reference watersheds in the western Boreal Plain (P<0.01). Long-term data from federally monitored rivers (Environment Canada 2006b) indicate that the timing and magnitude of peak flows differ between the Boreal Shield and Boreal Plain. During the long-term (25 yr) 01 April to 31 October period, an average of 30% of the runoff from Boreal Shield reference watersheds (Whitefish and Current rivers) occurred during snowmelt in April, compared to 16% in the Boreal Plain watershed (Sakwatamau River). Long-term mean total runoff (25 year) for the same period was twice as high in reference watersheds on the Boreal Shield (overall average 258 +/- 4 mm; mean +/- standard error) than the reference watershed on the Boreal Plain (129 +/- 10 mm). During the 01 April to 31 October 2004 period, an average of 65% of the runoff from LFSS watersheds occurred during snowmelt in April, compared to only 21% in FORWARD study streams on the Boreal Plain. Precipitation patterns were estimated to account for <30% of the disparity in snowmelt volume between the two study areas; the remainder was attributed to physiographic features that promote retention of the snowpack and limit infiltration. It is projected that forest disturbances (e.g. harvest) in LFSS watersheds will enhance sublimation of the snowpack, cause earlier snowmelt in cleared areas and reduce interaction of snowmelt water with soils. The focus on these western Boreal Shield streams will be primarily on response variables related to snowpack in contrast to runoff during the growing season.; A pilot project (Appendix A) was initiated to provide introductory baseline data on the presence and abundance of aquatic macro invertebrates and to determine rates of leaf pack (alder) decomposition prior to watershed disturbance. Leaf litter breakdown and associated invertebrate communities are sensitive to and ecologically-relevant measurements of land use impacts on stream ecological integrity (Gessner and Chauvet 2002). In four streams in the western Boreal Shield study, leaf pack loss was 3-fold higher and there was an indication that macroinvertebrate densities were higher in June compared to September deployment. One of the four streams, East Dog, had the fewest Plecoptera and Trichoptera among all four streams and the water had the highest color in June (306 and 356 TCU) and September (254 and 267 TCU) in both 2004 and 2005, respectively. Water in East Dog also had the tendency to have the lowest pH (min. 5.5) in both 2004 and 2005 while the other three streams had a minimum ranging from 5.9 to 6.0. Seasonal deployment (June vs. Sept.) and water quality characteristics (e.g. color, pH) likely influence leaf pack colonization by macroinvertebrates.; Key Words: boreal forest, watershed disturbance, runoff, forest harves...