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. 2018 Oct 1;142:373-382.
doi: 10.1016/j.watres.2018.06.005. Epub 2018 Jun 13.

Anoxic Nitrogen Cycling in a Hydrocarbon and Ammonium Contaminated Aquifer

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Anoxic Nitrogen Cycling in a Hydrocarbon and Ammonium Contaminated Aquifer

Naomi S Wells et al. Water Res. .

Abstract

Nitrogen 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 SO42- 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 (SO42-, 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.

Keywords: Biodegradation; Chemolithotrophic N cycling; Contaminated groundwater; Nitrate dual isotopes; Nitrite; Stable isotopes.

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