Urban Stormwater Runoff Drives Denitrifying Community Composition Through Changes in Sediment Texture and Carbon Content |
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Authors: | Shane E Perryman Gavin N Rees Christopher J Walsh Michael R Grace |
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Affiliation: | (1) Water Studies Centre, Monash University, Monash, VIC, 3800, Australia;(2) Murray-Darling Freshwater Research Centre, La Trobe University and CSIRO Land and Water, Wodonga, VIC, 3689, Australia;(3) Department of Resource Management and Geography, The University of Melbourne, Melbourne, VIC, 3010, Australia |
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Abstract: | The export of nitrogen from urban catchments is a global problem, and denitrifying bacteria in stream ecosystems are critical
for reducing in-stream N. However, the environmental factors that control the composition of denitrifying communities in streams
are not well understood. We determined whether denitrifying community composition in sediments of nine streams on the eastern
fringe of Melbourne, Australia was correlated with two measures of catchment urban impact: effective imperviousness (EI, the
proportion of a catchment covered by impervious surfaces with direct connection to streams) or septic tank density (which
affects stream water chemistry, particularly stream N concentrations). Denitrifying community structure was examined by comparing
terminal restriction fragment length polymorphisms of nosZ genes in the sediments, as the nosZ gene codes for nitrous oxide reductase, the last step in the denitrification pathway. We also determined the chemical and
physical characteristics of the streams that were best correlated with denitrifying community composition. EI was strongly
correlated with community composition and sediment physical and chemical properties, while septic tank density was not. Sites
with high EI were sandier, with less fine sediment and lower organic carbon content, higher sediment cations (calcium, sodium
and magnesium) and water filterable reactive phosphorus concentrations. These were also the best small-scale environmental
variables that explained denitrifying community composition. Among our study streams, which differed in the degree of urban
stormwater impact, sediment grain size and carbon content are the most likely drivers of change in community composition.
Denitrifying community composition is another in a long list of ecological indicators that suggest the profound degradation
of streams is caused by urban stormwater runoff. While the relationships between denitrifying community composition and denitrification
rates are yet to be unequivocally established, landscape-scale indices of environmental impact such as EI may prove to be
useful indicators of change in microbial communities. |
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