HR: 0800h
AN: B31A-0072    [Abstracts]
TI: Bacterial community structure and nitrogen transformation in hyporheic zones of arid-land streams
AU: * Zeglin, L H
EM: lzeglin@unm.edu
AF: University of New Mexcico, Department of Biology, MSC03 2020, Albuquerque, NM 87108, United States
AU: Crenshaw, C L
EM: chelsea1@unm.edu
AF: University of New Mexcico, Department of Biology, MSC03 2020, Albuquerque, NM 87108, United States
AU: Dahm, C N
EM: cdahm@sevilleta.unm.edu
AF: University of New Mexcico, Department of Biology, MSC03 2020, Albuquerque, NM 87108, United States
AU: Takacs-Vesbach, C
EM: cvesbach@unm.edu
AF: University of New Mexcico, Department of Biology, MSC03 2020, Albuquerque, NM 87108, United States
AB: Hyporheic zones of desert streams can be areas of high biological activity and consequent nutrient transformation, particularly where land use change increases nutrient concentrations in a stream. Does hyporheic bacterial community composition vary, and does this biotic heterogeneity covary with water and nutrient supply? Bromide (Br^-) and ¹⁵N-NO₃^- was injected for 24 hr in six streams (three "natural" reference streams, three streams in agricultural/urbanized catchments) in New Mexico and Arizona, USA. Four transects of 3 to 4 wells were placed along a longitudinal gradient within the study reach, and from these hyporheic water and gas samples were collected during and after each experiment. Gas samples were analyzed for O₂, ¹⁵N₂O, and ¹⁵N₂. Hyporheic water samples were analyzed for major cations and anions, DOC, ¹⁵NO₃^- and ¹⁵NH₄⁺. Bacterial diversity of hyporheic water was assessed using Denaturing Gradient Gel Electrophoresis (DGGE). There was high spatial and temporal variability in hyporheic bacterial community structure, connection with surface water and nutrient concentrations both within and among streams. For example, mean subsurface DGGE band richness per stream ranged from 9 to 21, and surface water comprised between 0 to 100 percent of hyporheic water in each well. There were strong differences in bacterial richness between streams (ANOVA, p < 0.001); however, this variability appeared related to salinity rather than differences in land use or nutrient concentration. ¹⁵NH₄⁺ levels were higher in modified stream than reference stream subsurface waters, suggesting dissimilatory nitrate reduction to ammonium (DNRA) may be an important process in these hyporheic sediments. Our results to date suggest that though hyporheic microbial community structure is highly heterogeneous, this biological variability may be due to different factors than variability in stream nitrogen cycling function. Further work will identify dominant sequences within these bacterial communities and investigate within-stream heterogeneity.
DE: 0408 Benthic processes (4804)
DE: 0410 Biodiversity
DE: 0439 Ecosystems, structure and dynamics (4815)
DE: 0465 Microbiology: ecology, physiology and genomics (4840)
DE: 0469 Nitrogen cycling
SC: Biogeosciences [B]
MN: 2007 Fall Meeting