The ecology of riverine ecosystems in the eastern Canadian subarctic remains relatively unknown and, like their circumpolar counterparts, these systems are predicted to be vulnerable to climate-induced ecological changes that are likely to affect species composition, distribution, and overall ecosystem functioning. Thus, lotic systems in this area must be evaluated in order to begin long-term monitoring of climate-driven alterations to ecological structure and function. The aim of the present research was to assess contemporary patterns in stream structure and function within the Torngat Mountains National Park in subarctic Labrador and determine the environmental (physicochemical) drivers of these ecological patterns. In particular, the study examined the influence of environmental variables from multiple spatial scales on macroinvertebrate assemblage structure, consumer trophic diversity and dietary overlap, and cellulose decomposition rates. Environmental variables that were measured at the reach scale ( a 1-km buffer around study sites), which included the relative area of glaciers and various land cover types, produced the most variation in stream structure and function. Glacier-fed streams had the lowest consumer richness and abundance, the lowest trophic diversity and little dietary overlap, arid the lowest cellulose decay rates. Cellulose decay rates were highest where consumer richness, trophic diversity and dietary overlap were highest and where riparian input was greatest. Consumer diets consisted primarily of allochthonous carbon (53 - 95%) and cellulose decay was likely mediated primarily by shredder invertebrates, as microbial activity was not correlated with decay rates. The present study provides baseline ecological data for long-term stream ecosystem monitoring in the Park and suggests that changes in glacial extent, source water contribution, and quantity and quality of riparian vegetation may cause the greatest alteration in stream structure and function.
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