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

Abstract

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 150 km. 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 ± 0.62 mg L−1 and 25.7 ± 2.9 ‰, respectively) compared to upper-estuary concentrations (1.0 ± 0.2 mg L−1 and 9.3 ± 1.4 ‰, respectively). Nitrate concentration then decreased rapidly within 30 km down-estuary (to 0.8 ± 0.2 mg L−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 48 000 ± 5000 kg day−1 at the sewage treatment plant outfall to 23 000 ± 13 000 kg day−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.

Wastewater influences nitrogen dynamics in a coastal catchment during a prolonged drought

“…High uptake rates followed elevated concentrations in the Aransas River (Fig. ), suggesting that increased assimilatory WWTP N uptake was the primary response of river organisms to this WWTP input (Pennino et al ). However, the low uptake velocities of both (0.030 mm s −1 ) and (0.007 mm s −1 ) in the Aransas River, coupled with less relative denitrification, suggest that the N inputs of the WWTP overwhelmed the capacity of the river ecosystem to process N, reflected by sustained DIN export during the drought (Martí et al ).…”

“…The input of wastewater can increase N export and water quantity (Bowen and Valiela ; Carey and Migliaccio ; Iverson et al ). Additionally, the effects of WWTP inputs to rivers are enhanced during drought (Andersen et al ; Passell et al ) or seasonal low flow (Pennino et al ), because the effluent proportion of the river flow increases. High uptake rates followed elevated concentrations in the Aransas River (Fig.…”

Seasonal Drivers of Carbon Dioxide Dynamics in a Hydrologically Modified Subtropical Tidal River and Estuary (Caboolture River, Australia)

“…Estuaries receive high loads of dissolved and particulate carbon and nutrients from rivers (Borges & Abril, ). These input rates are generally elevated in waters receiving effluent from sewage treatment plants (STP) and catchments featuring heavily modified land use, which are often cleared of vegetation and lack riparian buffering (Pennino et al, ). Due to the availability of excess organic carbon entering the tidal river estuarine continuum, estuarine waters are generally supersaturated in CO 2 , which can lead to high CO 2 fluxes to the atmosphere (Staehr et al, ).…”

Nitrogen dynamics in a highly urbanized coastal area of western Japan: impact of sewage-derived loads

“…He confirmed that wastewater-derived dissolved inorganic nitrogen (DIN) significantly influenced phytoplankton biomass in the estuaries. Pennino et al (2016) examined the transformations of nitrogen derived from a wastewater treatment facility, based on the nitrogen mass balance and the δ 15 N and oxygen stable isotope ratios (δ 18 O) in the tidal Potomac River estuary from Washington, D.C., to the Chesapeake Bay. Estuaries and shallow bays are dynamic environments, influenced by tidal variations and inflow of freshwater from rivers and channels.…”