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Nitrate Dynamics in Two Streams Impacted by Wastewater Treatment Plant Discharge: Point Sources or Sinks?
Author(s) -
Rahm Brian G.,
Hill Nicole B.,
Shaw Stephen B.,
Riha Susan J.
Publication year - 2016
Publication title -
jawra journal of the american water resources association
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.957
H-Index - 105
eISSN - 1752-1688
pISSN - 1093-474X
DOI - 10.1111/1752-1688.12410
Subject(s) - nitrate , microcosm , denitrifying bacteria , effluent , denitrification , environmental science , wastewater , environmental chemistry , sulfate , sewage treatment , sink (geography) , streams , nitrogen , environmental engineering , chemistry , hydrology (agriculture) , computer network , cartography , organic chemistry , computer science , geography , geotechnical engineering , engineering
We examined nitrate processing in headwater stream reaches downstream of two wastewater treatment plant outfalls during low streamflow. Our objectives were to quantify nitrate mass flux before and after effluent discharge and to use field and laboratory techniques to assess the mechanism of nitrate uptake. Microcosm experiments were utilized to determine the location of nitrate processing, and molecular biomarkers were used to detect and quantify microbial denitrification. At one site, downstream nitrate mass flux was significantly ( p = 0.01) lower than sum of upstream and wastewater effluent fluxes, indicating rapid stream assimilation of incoming nitrate in the vicinity of the point source. Microcosm experiments supported the theory that nitrate processing occurs in sediments. Molecular assays for denitrifcation‐associated functional genes nosZ , nirS , and nirK , provided evidence that effluent contained enriched denitrifying communities relative to ambient stream water. Nitrate loss at the site with greater uptake was correlated with sulfate loss ( p < 0.01; r 2 = 0.86), suggesting a possible link between sulfate reducing bacteria and denitrifying bacterial communities. Results suggest there is an opportunity to better understand nitrate dynamics in cases where point sources may act as point sinks under specific sets of conditions.