Year of Award


Document Type


Degree Type

Master of Science (MS)

Other Degree Name/Area of Focus

Microbiology, Microbial Ecology

Department or School/College

Division of Biological Sciences

Committee Chair

Jim Gannon

Commitee Members

Bill Holben, Bonnie Ellis


biofilm, hyporheic, nutrient ratios, stoichiometry


University of Montana


The work presented herein is part of the Microbial Observatory Project in the Nyack Floodplain. The Nyack Valley Floodplain is a glacier-carved floodplain in the Middle Fork of the Flathead River on the south west border of Glacier National Park and north of the Great Bear Wilderness in northwest Montana. The study focuses on the bacterial diversity including elemental stoichiometry along a hyporheic flowpath underlying the Nyack floodplain. We isolated and characterized 44 bacterial strains, sampled microbial biofilm communities across the floodplain, characterized the bacterial isolates and determined elemental ratios (C:N:P). We tested the hypothesis that while the elemental stoichiometry of freshwater benthic bacteria is mostly homeostatic (doesn’t change significantly when nutrient feed ratios change), the range can vary and is dependent on the taxa. We were able to show homeostasis with respect to C:N ratios (3.7:1 – 8.1:1) and these did not depend on taxa, however, with respect to N:P (0.8:1 – 77.3:1) and C:P (5.1:1 – 323:1) ratios, these bacteria were not homeostatic and there was a difference with respect to taxa. In a floodplain context and from a “flow path” perspective, we hypothesized that the residence time of the hyporheic water in the aquifer, the distance of the well from the main channel and the water quality (DOC, STN and SP) influence the elemental content of sediment biofilm. This elemental content would vary in part by influencing microbial community structure as well as entrainment of nutrients of varying carbon, nitrogen and phosphorous content. The only significant correlation found was between the DOC content of the hyporheic water and the carbon content of the biofilm (p=0.02). Across seasons DOC, STN and SP were not correlated with distance from the main channel or residence time. The C:N ratio of the microbial biofilm might be driven by the dominant species of microbial community rather than by the water quality, distance from the river or the residence time of the water.



© Copyright 2010 Alejandra Valenzuela