Potential rates and environmental controls of denitrification and nitrous oxide production in a temperate urbanized estuary |
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| Affiliation: | 1. Institute of Biomedical Sciences (ICBAS), University of Porto, Laboratory of Hydrobiology, Largo Prof. Abel Salazar 2, 4009-003 Porto, Portugal;2. Centre of Marine and Environmental Research (CIIMAR), University of Porto, Rua dos Bragas, 289 4050-123 Porto, Portugal;3. Faculty of Engineering, University of Porto, Department of Chemistry, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal;1. Fujian Provincial Key Laboratory for Coastal Ecology and Environmental Studies, Xiamen University, Xiamen, China;2. Key Laboratory of the Coastal and Wetland Ecosystems, Ministry of Education, Xiamen University, Xiamen, China;3. College of the Environment and Ecology, Xiamen University, Xiamen, China;1. Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China, 266100 Qingdao, PR China;2. Qingdao Collaborative Innovation Centre of Marine Science and Technology, Ocean University of China, 266100 Qingdao, PR China;1. Centre for Ecology & Hydrology, Bush Estate, Penicuik, EH26 0QB, United Kingdom;2. The University of Edinburgh, School of GeoSciences, Crew Building, West Mains Road, EH9 3JN, Edinburgh, United Kingdom;3. SRUC, King''s Buildings, West Mains Road, Edinburgh, EH9 3JG, United Kingdom |
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| Abstract: | Denitrification may play a major role in inorganic nitrogen removal from estuarine ecosystems, particularly in those subjected to increased nitrate and organic matter loads. The Douro estuary (NW Portugal) suffers from both problems: freshwater input of nitrate and organic load from untreated wastewater discharges. To assess how these factors might control sediment denitrification, a 12-month survey was designed. Denitrification potential and nitrous oxide (N2O) production were measured at different locations using the slurry acetylene blockage technique. Denitrification rate ranged from 0.4 to 38 nmol N g−1 h−1, increasing towards the river mouth following an urban pollution gradient. N2O production, a powerful greenhouse gas implicated on the destruction of the ozone layer, was significantly related with sediment organic matter and accounted for 0.5–47% of the N gases produced. Additional enrichment experiments were consistent with the results found in the environment, showing that sediments from the upper less urban stretch of the estuary, mostly sandy, respond positively to carbon and, inversely, in organic rich sediments from the lower estuary, the denitrification potential was limited by nitrate availability. The obtained results confirmed denitrification as an important process for the removal of nitrate in estuaries. The presence of wastewater discharges appears to stimulate nitrogen removal but also the production of N2O, a powerful greenhouse gas, exacerbating the N2O:N2 ratio and thus should be controlled. |
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