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WITHIN-REACH VARIATION IN NITRIFICATION AND DENITRIFICATION RATES IN STREAMS OF THE UPPER PENINSULA OF MICHIGAN

Variation of nitrogen transformation rates among channel geomorphic units within a stream is assumed to be small, but has been seldom quantified. We asked whether nitrification and denitrification rates varied among randomly selected pools within a 200m reach from three streams in the Upper Peninsula of Michigan. Nitrification rates, quantified using nitrapyrin-inhibition, and denitrification rates, quantified using acetylene block, were significantly lower in the smallest (discharge = 4.5 L/s) than in the largest (2700 L/s) stream, but were similar to those in an intermediate sized stream (30 L/s). There was greater variation in rates among pools in the smallest stream (coefficient of variation (CV) = 2.0 for nitrification, 6.3 for denitrification) than within the other two streams or across all pools in the study (CV = 0.2 to 1.6). Across all streams, denitrification and nitrification were positively correlated (r = 0.69, p < 0.001), but not correlated to ammonium, phosphate, or sediment organic matter. Our findings suggest that rates of nitrogen transformations may be highly variable among channel units and therefore may not be well estimated by a single study site per reach.

Michelle Kelly (Primary Presenter/Author), Michigan Technological University, mckelly1@mtu.edu;


Kevin Nevorski ( Co-Presenter/Co-Author), Michigan Technological University, kcnevors@mtu.edu;


Amy Marcarelli ( Co-Presenter/Co-Author), Michigan Technological University, ammarcar@mtu.edu;