Carbon and nitrogen dynamics in forested and clearcut boreal soils: Implications for shoreline forest management

The establishment of shoreline buffer zones is an important component of forest management in Ontario. Research has identified scientific uncertainty as to the suitable width or even the need for buffer zones to protect aquatic systems from potential nutrient loading associated with forest harvesting. This thesis examines soil inorganic-N production and consumption, terrestrial ecosystem C and N storage, and shallow soil water C and N concentrations in boreal spruce forest at the Esker Lakes Research Area in northeastern Ontario. The objectives of this research were to determine (1) gross and net transformations for organic and mineral soils from clearcut and unharvested sites and to examine the role of fine logging slash, (2) shoreline and upland forest C and soil C and N storage for boreal lake watersheds, and (3) the influence of catchment slope, and forest and soil characteristics on C and N leaching in riparian zones. Full-tree harvested F horizons and 0-5 cm depth mineral soil layers had increased rates of nitrification compared to unharvested soils, and 12-year-old clearcut F horizons (1220 mug NO3--N g soil-1) released more NO3- than 2-year-old clearcuts (257 mug NO3--N g soil -1). This increased production has the potential to increase N leaching to aquatic systems. Amending F horizon from unharvested stands with black spruce foliage increased microbial biomass N and decreased inorganic-N production. Net mineralization rates for F horizons were negatively correlated to gross NH4+ consumption. Shoreline forests had similar overstory vegetation C storage, larger forest floor and smaller mineral soil C and N contents than upslope forests. Full-tree harvesting in shoreline buffers would remove a greater proportion of ecosystem C than current harvesting in upslope stands. Modelled terrain properties, including slope were not significantly related to nutrient concentrations of shallow soil water collected in riparian zones. Steep slopes, as determined by field measurements within 30 m of lake shorelines, had higher soil water DOC and DON concentrations compared to shallow slopes, but DIC, NO3- and NH4 + concentrations were similar between slope types. Forest species composition and soil N concentrations were important factors determining C and N concentrations in shallow soil water.