A PREMILINARY ASSESSMENT OF THE CHEMICAL AND HYDROLOGICAL INTERACTION OF ACIDIC SNOWMELT WATER WITH THE TERRESTRIAL PORTION OF A CANADIAN SHIELD CATCHMENT M.C.English I , D_S. Jefffies 1, N.W.Foster 2, R.G.Semkin 1, and P.W.Hazlett 2 1. National Water Research Institute, Canada Centre for Inland Waters, Environment Canada, 867 Lakeshore Rd. Burlington, Ontario, L7R 4A6, Canada 2. Great Lakes Forest Centre, Canadian Forestry Service, Agriculture Canada, 1219 Queen St E., Sault Ste Marie, Ontario, P6A 5M7, Canada ABSTRACT. This study examines certain aspects of the hydrological and chemical interaction of springmelt runoff with the terrestrial portion of a Canadian Shield catchRaent. Though NO 3- is the dominant anion in the snowpack for most of the winter, SO4 -~"deposition increa-ses at the end of the winter season (March) such that it is the dominant anion in snowpack meltwater runoff. Pronounced formation of~ce lenses in the snowpack are responsible for notable movement of H +, NO 3- and SO 4- ions downslope prior to contact with the ground. Subsurface melfwater flow through the lower portion of the slope is much more acidic ( pH 5.18 ) than that flowing within the subsurface in the upper slope ( pH 6.44 ). 1.Introduction Reports summarizing research conducted on acidic snowmelt runoff conclude that in order to understand the significance of the event to terrestrial ecosystems it is imperative to understand the details of meltwater runoff both within the snowpack and through the ground (Seip,1980;Overrein et al.,1981). Two factors combine to increase the significance of within-snowpack downslope transfer of water and ions. The first is that with prolonged runoff the effectiveness of the ice lenses to divert flow downslope prior to contact with the ground will decrease (Colbeck, 1977). Secondly, during the initial melt period when downslope diversion of water is most efficient there is a disproportionate exsolving of ions from the snowpack (Seip,1980). Till structure is such that the lower hillslope will receive a greater proportion of water than the upper portion. This hydrological pattern implies that weathering rates in the lower slope may become progressively greater from the top to the bottom of a hillslope. The two purposes of this research are: i) to quantify the downslope transfer of water and ions along ice lenses in the snowpack prior to ground contact and ii) to examine whether elevafional differences in soil percolate chemistry occur along a hillslope. 2.Methods The study is ongoing at the Turkey Lakes Watershed (,,TI;W) located 50 km north of O , O Sault Ste Marie, Ontario, Canada (47 2 14 N, 84 25 30 W).The study site is a Water, Air, and Soil Pollution 31 (1986) 27-34. © I986 by D. Reidel Publishing Company.