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Biogeosciences An interactive open-access journal of the European Geosciences Union
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Volume 13, issue 22 | Copyright
Biogeosciences, 13, 6211-6228, 2016
https://doi.org/10.5194/bg-13-6211-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 18 Nov 2016

Research article | 18 Nov 2016

Sources and transformations of anthropogenic nitrogen along an urban river–estuarine continuum

Michael J. Pennino1,a, Sujay S. Kaushal1, Sudhir N. Murthy2, Joel D. Blomquist3, Jeff C. Cornwell4, and Lora A. Harris5 Michael J. Pennino et al.
  • 1Department of Geology and Earth Systems Science Interdisciplinary Center, University of Maryland, College Park, MD, USA
  • 2DC Water, Office of the General Manager, Washington, D.C., USA
  • 3US Geological Survey, Maryland, Delaware, and District of Columbia Water Science Center, Baltimore, MD, USA
  • 4Center for Environmental Science, University of Maryland Horn Point Laboratory, Cambridge, MD, USA
  • 5Center for Environmental Science, University of Maryland Chesapeake Biological Laboratory, Solomons, MD, USA
  • anow at: US EPA, Office of Research and Development, National Health and Environmental Effects Research Laboratory, Corvallis, OR, USA

Abstract. Urbanization has altered the fate and transport of anthropogenic nitrogen (N) in rivers and estuaries globally. This study evaluates the capacity of an urbanizing river–estuarine continuum to transform N inputs from the world's largest advanced (e.g., phosphorus and biological N removal) wastewater treatment facility. Effluent samples and surface water were collected monthly along the Potomac River estuary from Washington D.C. to the Chesapeake Bay over a distance of 150km. In conjunction with box model mass balances, nitrate stable isotopes and mixing models were used to trace the fate of urban wastewater nitrate. Nitrate concentrations and δ15N-NO3 values were higher down-estuary from the Blue Plains wastewater outfall in Washington D.C. (2.25±0.62mgL−1 and 25.7±2.9‰, respectively) compared to upper-estuary concentrations (1.0±0.2mgL−1 and 9.3±1.4‰, respectively). Nitrate concentration then decreased rapidly within 30km down-estuary (to 0.8±0.2mgL−1), corresponding to an increase in organic nitrogen and dissolved organic carbon, suggesting biotic uptake and organic transformation. TN loads declined down-estuary (from an annual average of 48000±5000kgday−1 at the sewage treatment plant outfall to 23000±13000kgday−1 at the estuary mouth), with the greatest percentage decrease during summer and fall. Annually, there was a 70±31% loss in wastewater NO3 along the estuary, and 28±6% of urban wastewater TN inputs were exported to the Chesapeake Bay, with the greatest contribution of wastewater TN loads during the spring. Our results suggest that biological transformations along the urban river–estuary continuum can significantly transform wastewater N inputs from major cities globally, and more work is necessary to evaluate the potential of organic nitrogen and carbon to contribute to eutrophication and hypoxia.

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The results of this paper report the analysis of the fate and transport of wastewater and anthropogenic nitrogen along the Potomac River estuary, from Washington D.C. to the Chesapeake Bay. In conjunction with a mass balance approach, nitrate isotopes were used to estimate fluxes and trace the sources and transformations of N along the estuary. This study shows that estuaries have a large capacity to transform N inputs, but with large seasonal variability due to hydrological extremes.
The results of this paper report the analysis of the fate and transport of wastewater and...
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