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28 August 2012 Nitrogen processing and the role of epilithic biofilms downstream of a wastewater treatment plant
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Abstract

We investigated how dissolved inorganic N (DIN) inputs from a wastewater treatment plant (WWTP) effluent are processed biogeochemically by the receiving stream. We examined longitudinal patterns of NH4 and NO3 concentrations and their 15N signatures along a stream reach downstream of a WWTP. We compared the δ15N signatures of epilithic biofilms with those of DIN to assess the role of stream biofilms in N processing. We analyzed the δ15N signatures of biofilms coating light- and dark-side surfaces of cobbles separately to test whether light constrains functioning of biofilm communities. We sampled during 2 contrasting periods of the year (winter and summer) to explore whether changes in environmental conditions affected N biogeochemical processes. The study reach had a remarkable capacity for transformation and removal of DIN, but the magnitude and relevance of different biogeochemical pathways of N processing differed between seasons. In winter, assimilation and nitrification influenced downstream N fluxes. These processes were spatially segregated at the microhabitat scale, as indicated by a significant difference in the δ15N signature of light- and dark-side biofilms, a result suggesting that nitrification was mostly associated with dark-side biofilms. In summer, N processing was intensified, and denitrification became an important N removal pathway. The δ15N signatures of the light- and dark-side biofilms were similar, a result suggesting less spatial segregation of N cycling processes at this microhabitat scale. Collectively, our results highlight the capacity of WWTP-influenced streams to transform and remove WWTP-derived N inputs and indicate the active role of biofilms in these in-stream processes.

The Society for Freshwater Science
Miquel Ribot, Eugènia Martí, Daniel von Schiller, Francesc Sabater, Holger Daims, and Tom J. Battin "Nitrogen processing and the role of epilithic biofilms downstream of a wastewater treatment plant," Freshwater Science 31(4), 1057-1069, (28 August 2012). https://doi.org/10.1899/11-161.1
Received: 23 November 2011; Accepted: 1 June 2012; Published: 28 August 2012
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