Date of Award
Open Access Dissertation
Doctor of Philosophy in Biological Sciences (PhD)
Administrative Home Department
Department of Biological Sciences
Committee Member 1
Committee Member 2
Committee Member 3
Denitrification and nitrogen fixation are nitrogen cycling processes that can occur simultaneously in streams but are rarely studied together. The overarching goal of this dissertation was to quantify temporal and spatial variation of these processes in streams across the USA, characterize the environmental drivers of that variation, and determine the role that denitrification plays in the carbon cycle. To characterize temporal variation in these processes, a 2-year study in the Pilgrim River in Michigan’s Upper Peninsula found no difference in rates among seasons but high day-to-day variation in rates of both processes (maximum daily change 4,390 μg N/m2/hr for denitrification and 39 μg N/m2/hr for nitrogen fixation) that was related to dissolved nitrogen concentrations. A second study characterizing spatial variation in rates in 12 streams distributed across 9 ecoregions found that denitrification ranged from 0 ± 0 to 10,355.8 ± 3,054.8 µg N/m 2/hr and nitrogen fixation ranged from 0 ± 0 to 155.4 ± 120.6 µg N/m2/hr (mean ± 95% CI) and co-occurred in 9 streams. Finally, we incorporated organic carbon removal via denitrification with carbon removal estimates from aerobic respiration in 23 streams across 12 ecoregions. In 13 stream/substrate combinations 100% of the carbon removal was due to denitrification. Overall, these studies show that denitrification and nitrogen fixation commonly cooccur in streams, that rates are more variable spatially and temporally than expected, and that this variation is not simply explained by environmental characteristics as commonly assumed.
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Nevorski, Kevin, "DENITRIFICATION AND NITROGEN FIXATION COMMONLY CO-OCCUR BUT RATES VARY THROUGHOUT THE YEAR AND IN DIFFERENT ENVIRONMENTS", Open Access Dissertation, Michigan Technological University, 2021.