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Exploring Community Dynamics of Denitrifying Bacteria in the Cahaba River Corianne Tatariw, Elise Chapman, Dr. Jennifer Edmonds Department of Biological Sciences University of Alabama, Tuscaloosa

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Acidification/ eutrophication of freshwater systems Loss of biodiversity Images from NOAA Harmful algal blooms Eutrophication/ hypoxia in coastal systems

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Goal: evaluate denitrification as a meaningful nitrate sink in large rivers How does denitrifier community structure respond to environmental parameters? What is the effect of these changes in denitrifier community structure on rates of denitrification?

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High diversity of microorganisms suggests functional redundancy, but Denitrifier communities respond differently to environmental conditions, affecting rates of denitrification (Cavigelli and Robertson 2000)

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NO 3 - NO 2 - NO N 2 O N 2 nirS /nirK gas Heterotrophic facultative anaerobes Dissolved Oxygen (DO) affects distribution of nirS and nirK denitrifiers (Graham et al 2010, Knapp et al 2009) nirK denitrifiers can function under fluctuating DO conditions nirS denitrifiers found in consistently anoxic environments

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Measured as porosity: Fraction of void space in a volume of sediment Greater surface area: volume in smaller sediments Affects movement of DO through sediment

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Valley Ridge (VR) Fall Line (FL) Coastal Plain (CP) VR FL CP

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Birmingham

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NirS and nirK denitrifiers will have distinct community structures within each geophysical province due to changes in sediment size and channel slope. Dominance of nirS vs. nirK will vary due to spatial and seasonal variations in DO

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Three subsamples taken from homogenized sediment in field Spring, Early Summer, Late Summer, Winter 2 locations per geophysical province (VR, FL, CP) TRFLP of nirS and nirK nirS: cd3aF/R3cd-HEX nirK: FlaCu-FAM/R3Cu Restriction enzyme: MspI Analysis of Similarity: Primer v.6

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No significant difference by geophysical province or date nirS dominates in anoxic environments which may have less variable conditions Valley Ridge Fall Line Coastal Plain Global R = 0.157 p = 0.03 2D Stress = 0.14

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Global R = 0.223 p = 0.001 Valley Ridge Fall Line Coastal Plain Coastal Plain different from Valley Ridge and Fall Line No significant seasonal difference CP has finer, sandy substrate compared to VR and FL 2D Stress = 0.22

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Denitrification rates will vary among geophysical provinces in response to changes in denitrifier community composition. Highest rates of denitrification will coincide with high primary productivity as carbon limitation is alleviated

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Sediment samples collected with microbial samples Acetylene block method to measure denitrification potential rates

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Denitrification Rate ( mol N 2 g -1 hr -1 ) a ab b p