The 5 principal sites used for these investigations are 25-40 km east of Sept-Iles, Quebec, Canada on the north shore of the Gulf of the St. Lawrence. A full account of these sites, the longitudinal trends as smaller streams coalesce into large rivers, and a summary of changes in organic carbon dynamics and community structure are described by Naiman et al. (1987). This subarctic, Precambrian Shield region is forested with typical boreal species: black and white spruce (Picea mariana and P. glauca; 47% of area), balsam fir (Abies balsamea; 44%), paper birch (Betula papyrifera), trembling aspen (Populus tremuloides), speckled alder (Alnus rugosa), and willow (Salix spp.). There is approximately 112 cm of precipitation annually, evenly distributed throughout the year, with mean monthly values ranging from 8.0 cm in April to 10.6 cm in September and December. Precipitation occurs mostly as snow from October to April. The mean annual temperature is 1 degree C, with a growing season of 105 d (i.e., mean daily air temperature >5.6 degree C). All stream sites are ice-covered from early November to mid April. Most streams are low gradient (<1.5% slope), have high concentrations of DOC (10-15 mg/L), low concentrations of nitrogen (NO sub(3):20-43 mu g/L) and phosphorus (PO sub(4):11-29 mu g/L), and have approximately 2100 degree-days annually ( degree C/y). There is a strong freshet in April and May when 50% of the annual discharge occurs. Minimum flows in January and February are only 3-5% of the annual maximum.