Wells, NaomiKappelmeyer, UKnöller, K2022-02-022018-06-132018-10-012018-06-020043-135429908465 (pubmed)https://hdl.handle.net/10182/14563Nitrogen fate and transport through contaminated groundwater systems, where N is both ubiquitous and commonly limits pollutant attenuation, must be re-evaluated given evidence for new potential microbial N pathways. We addressed this by measuring the isotopic composition of dissolved inorganic N (DIN = NH₄⁺, NO₂¯, and NO₃¯) and N functional gene abundances (amoA, nirK, nirS, hszA) from 20 to 38 wells across an NH₄⁺, hydrocarbon, and SO²₄− contaminated aquifer. In-situ N attenuation was confirmed on three sampling dates (0, +6, +12 months) by the decreased [DIN] (4300 - 40 μM) and increased δ¹⁵N-DIN (5‰–33‰) over the flow path. However, the assumption of negligible N attenuation within the plume was complicated by the presence of alternative electron acceptors (SO²₄−, Fe³⁺), both oxidizing and reducing functional genes, and N oxides within this anoxic zone. Active plume N cycling was corroborated using an NO₂¯dual isotope based model, which found the fastest (∼10 day) NO₂¯ turnover within the N and electron donor rich central plume. Findings suggest that N cycling is not always O₂ limited within chemically complex contaminated aquifers, though this cycling may recycle the N species rather than attenuate N.pp.373-382Print-Electronicen© 2018 Elsevier Ltd. All rights reserved.contaminated groundwaterstable isotopesnitritechemolithotropic N cyclingbiodegradationnitrate dual isotopesSulfatesOxygenNitrogenNitrogen IsotopesAmmonium CompoundsHydrocarbonsWater Pollutants, ChemicalEnvironmental MonitoringGenes, BacterialNitrogen CycleGroundwaterJournal Article10.1016/j.watres.2018.06.0051879-24482022-02-02