Anoxic nitrogen cycling in a hydrocarbon and ammonium contaminated aquifer. (1st October 2018)

• Record Type: Journal Article
• Authors: Wells, Naomi S.; Kappelmeyer, Uwe; Knöller, Kay
• Is Part Of: Water research. Volume 142(2018)
• Page Start: 373
• Page End: 382
• Publication Date: 2018-10-01
• Subjects: Contaminated groundwater -- Stable isotopes -- Nitrite -- Chemolithotrophic N cycling -- Biodegradation -- Nitrate dual isotopes; Water -- Pollution -- Research -- Periodicals; 363.7394
• DOI: 10.1016/j.watres.2018.06.005
• Languages: English
• ISSNs: 0043-1354

Abstract

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 SO4 2− 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 δ 15 N-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 (SO4 2−, Fe 3+ ), 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. Graphical abstract: Highlights: Redox-driven groundwater ammonium attenuation confirmed by nitrate and ammonium isotopes. Functional gene and isotopes show active nitrogen recycling within the 'inert' anoxic plume. Nitrite δ 18 O and δ 15 N are a sensitive tool for evaluating nitrogen cycling in anoxic environments.