Nitrate labelled with 15N was added for 2 years to a small Boreal Shield forested catchment to evaluate where new nitrogen (N) inputs are stored in this system in the short term. The landscape in the study catchment is a mosaic of Pinus banksiana Lamb. - Picea mariana (Mill.) BSP surrounded by of lichens, mosses, and grasses on exposed bedrock surfaces. After the second year of N addition, 10% of the added 15N was found in aboveground biomass, 27% in organic horizons, 6% in forest island mineral soil, 3% in soil underneath pillows, and 16% was lost through runoff. Despite covering a smaller proportion of the catchment and having only slightly larger N stocks, forest islands stored more 15N (31%) than pillows (15%). Preferential routing of water towards forest islands and a greater potential for biotic and abiotic N immobilization are hypothesized to favor N retention in forest islands. Thirty-eight percent of the 15N could not be accounted for. The comparison of a mass-balance...
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Lamontagne et al. (2000) studied this question.