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Spatial Heterogeneity of Denitrification Genes in a Highly Homogenous Urban Stream

Lookup NU author(s): Dr Charles Knapp, Professor David Graham


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Human modification of natural streams by urbanization has led to more homogeneous channel surfaces; however, the influence of channel simplification on in situ microbial distribution and function is poorly characterized. For example, denitrification, a microbial process that reduces soluble nitrogen (N) levels, requires peripheral anoxic zones that might be lost in artificial channels such as those with a concrete lining. To examine how microbial function might be influenced by channel simplification, we quantified denitrification rates and conditions in microbial mats within an urban concrete channel. We quantified spatial and diurnal patterns of nitrate uptake, diurnal dissolved oxygen (DO) levels, and nutrient conditions, along with the spatial distribution of DO, solids, chlorophyll a, and genes associated with denitrification (nirS and nirK), ammonia-oxidizing bacteria (AOB), cyanobacteria, and algal chloroplasts. Despite the channel being superficially homogeneous, nir genes were distributed in a patchy manner. Two types of gene patches were observed: one associated with nirK, which had diurnally variable DO levels and high nocturnal nitrate uptake rates, and the other associated with nirS, which had elevated AOB genes, thicker layers of mud, and an apparent 24 h nitrate uptake. All active nir patches had elevated microbial photosynthetic genes. Results imply that even artificial channels, with reduced macroscale heterogeneity, can sustain significant rates of denitrification, although the responsible communities vary with space and time. This patchiness has significant

Publication metadata

Author(s): Knapp CW, Dodds WK, Wilson KC, O'Brien JM, Graham DW

Publication type: Article

Publication status: Published

Journal: Environmental Science and Technology

Year: 2009

Volume: 43

Issue: 12

Pages: 4273-4279

ISSN (print): 1382-3124

ISSN (electronic):

Publisher: Springer Netherlands


DOI: 10.1021/es9001407


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Funder referenceFunder name
Kansas Technology Enterprise Corporation
National Science Foundation
MEXT-CT-2006-023469EU Marie Curie Excellence Programme