Journal
FRESHWATER SCIENCE
Volume 31, Issue 4, Pages 1057-1069Publisher
UNIV CHICAGO PRESS
DOI: 10.1899/11-161.1
Keywords
nitrogen; wastewater treatment plant; stream; biofilm; stable isotopes; nitrification; denitrification
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Funding
- European Science Foundation [05_EDIV_FP065-COMIX]
- Spanish Ministry of Science and Innovation [CGL2008-05504-C02-02/BOS]
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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 NH(4)(+ )and NO(3)(- )concentrations and their 15N signatures along a stream reach downstream of a WWTP. We compared the delta N-15 signatures of epilithic biofilms with those of DIN to assess the role of stream biofilms in N processing. We analyzed the delta N-15 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 delta N-15 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 delta N-15 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.
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