| Summary: | Algae are the most common primary producers in stream ecosystems, contributing as much as 80 % of the total primary production. The production of these ecosystems is strongly influenced by the terrestrial habitats, which are in turn likely to be altered by climate change. In arctic ecosystems, where the effects of climate may be most pronounced, there are important unknowns about how abiotic factors such as light, temperature, nutrients, flow regimes interact to influence stream productivity. This study therefore aimed to understand what controls the rate of benthic algal growth in Arctic streams by measuring the accumulation of algal biomass on artificial surfaces across arctic stream types in Norrbotten, Sweden. Ceramic tiles were placed at 36 locations distributed across tundra and birch forest streams. Algal accumulation on tiles was then measured over 7 weeks using a fluorometer (Bentothorch) together with a number of likely controlling factors (light, temperature, dissolved nutrients and depth). I observed a significant difference in algal accumulation between the stream types (p<0.05), with nearly three times greater biomass in birch forest compared to tundra streams. However, these differences were not related to variation in light and water temperature. Dissolved nitrogen had a significant correlation with algal accumulation although with a lot of unexplained variation. Unmeasured hydrological aspects such as stream flow may have had large significance for differences in algal growth between the higher-gradient tundra and lower-gradient birch forest streams. Overall, I hypothesize that the productivity of these systems is limited by nitrogen or several parameters working together and/or that these systems are affected by an unmeasured parameter (e.g., grazing, hydrological disturbance). While my results did not clearly establish the factors regulating algal growth in these streams it suggests that dissolved nitrogen is an important factor. The observed differences between stream types suggest that ...
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