Presenter Information

Nicholas Barnett CarpenterFollow

Presentation Type

Presentation

Faculty Mentor’s Full Name

Royce Engstrom

Faculty Mentor’s Department

Department of Chemistry and Biochemistry

Abstract

Abstract. All aquatic organisms must assimilate the essential nutrient, nitrogen, which can be done through different pathways, including assimilation of nitrate or the utilization of atmospheric nitrogen via nitrogen fixation. We examined the Upper Clark Fork River in Montana in order to determine the extent to which nitrogen fixation provides nitrogen to aquatic organisms during the summer months when nitrate becomes scarce. We used an established experimental technique known as acetylene reduction, in which the rates of acetylene reduction serve as a proxy for nitrogen fixation. Epilithic biofilms were collected via rocks covered in algae from 3 locations on the river, and incubated in the river for 2 hours in clear plastic chambers with air, river water, and acetylene gas. Headspace samples were then drawn from these chambers and analyzed for ethylene, the product of acetylene reduction, via the analytical technique known as gas chromatography. The results showed that nitrogen fixation did occur during the summer months coinciding with low nitrate levels. Concomitantly, as readily available nitrate was depleted during the productive summer months, we observed a shift in aquatic community composition from green algal species that are non-nitrogen fixing (i.e., Cladophora) to a known nitrogen-fixing species (Nostoc). This work ties important ecological function to community composition during progressive N limitation of primary production.

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Life Sciences

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Aquatic Community Composition Shift to Nitrogen Fixing Organisms

Abstract. All aquatic organisms must assimilate the essential nutrient, nitrogen, which can be done through different pathways, including assimilation of nitrate or the utilization of atmospheric nitrogen via nitrogen fixation. We examined the Upper Clark Fork River in Montana in order to determine the extent to which nitrogen fixation provides nitrogen to aquatic organisms during the summer months when nitrate becomes scarce. We used an established experimental technique known as acetylene reduction, in which the rates of acetylene reduction serve as a proxy for nitrogen fixation. Epilithic biofilms were collected via rocks covered in algae from 3 locations on the river, and incubated in the river for 2 hours in clear plastic chambers with air, river water, and acetylene gas. Headspace samples were then drawn from these chambers and analyzed for ethylene, the product of acetylene reduction, via the analytical technique known as gas chromatography. The results showed that nitrogen fixation did occur during the summer months coinciding with low nitrate levels. Concomitantly, as readily available nitrate was depleted during the productive summer months, we observed a shift in aquatic community composition from green algal species that are non-nitrogen fixing (i.e., Cladophora) to a known nitrogen-fixing species (Nostoc). This work ties important ecological function to community composition during progressive N limitation of primary production.