Biological nitrogen uptake and microbial transformations in aquatic ecosystems under conditions of rapid environmental change

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The nitrogen (N) cycle is one of the most complex and heavily perturbed global biogeochemical cycles on earth. Naturally, microorganisms "fix" gaseous atmospheric N into a form used by plants and subsequently other organisms. Other microorganisms can return this fixed N to the atmosphere in gaseous form through a series of transformations completing the cycle. Humans however are enriching the earth by artificially fixing large amounts of N through fertilizer synthesis resulting in widespread N pollution. Although N pollution to inland waters is a growing concern in Canada and around the globe, little is known about the microbial diversity and the mechanistic controls of the microbial N rate transformations of this critical nutrient cycle in freshwaters. Unbalanced N transformations within lakes may have negative repercussions on aquatic ecosystem health as the availability of different N forms within this complex cycle may regulate phytoplankton community structure, contribute to the proliferation of nuisance cyanobacteria and produce the potent greenhouse gas nitrous oxide. We propose to characterize multiple N metabolic rate transformations as well as the microbial diversity in the freshwater N cycle at different scales of inquiry across several different ecosystem types. This unique integrative look into the N cycle will be done by using a combination of several novel physiological, isotopic, taxonomical and molecular techniques, many of which have yet to be used in a systematic fashion in freshwaters. We will examine the spatial and temporal variation of N-fixation, nitrification, denitrification and algal N nutrition along a gradient of lake types and will characterise the processing of N, as a function of climate change, increased point and non-point source N pollution, from a perspective of changes in community structure and in relation to other major biogeochemical cycles like carbon. The findings of this innovative program are expected to alter our current paradigms of N cycling in freshwaters, supply evidence to help substantiate the need to control N pollution to inland waters and provide important insights in the variability of the different processes to help direct future oceanographic studies.