Multi-species measurements of nitrogen isotopic composition reveal the spatial constraints and biological drivers of ammonium attenuation across a highly contaminated groundwater system

WATER RESEARCH

卷:98

Article

Wells, Naomi S.¹  Hakoun, Vivien^2,3  Brouyere, Serge²  Knoeller, Kay¹ 

[1] UFZ Helmholtz Ctr Environm Res, Dept Catchment Hydrol, Theodor Lieser Str 4, D-06112 Halle, Saale, Germany

[2] Univ Liege, Dept ArGEnCo Hydrogeol & Geol Environm, Bat B52-3 Sart Tilman, B-4000 Liege, Belgium

[3] IDAEA CSIC Spanish Natl Res Council, Barcelona, Spain

关键词: Ammonium attenuation;    Groundwater;    Industrial pollution;    Nitrate reduction;    Nitrite reduction;    Stable isotopes;   

DOI  :  10.1016/j.watres.2016.04.025

来源: Elsevier

【 摘 要 】

Groundwater under industrial sites is characterised by heterogeneous chemical mixtures, making it difficult to assess the fate and transport of individual contaminants. Quantifying the in-situ biological removal (attenuation) of nitrogen (N) is particularly difficult due to its reactivity and ubiquity. Here a multi-isotope approach is developed to distinguish N sources and sinks within groundwater affected by complex industrial pollution. Samples were collected from 70 wells across the two aquifers underlying a historic industrial area in Belgium. Below the industrial site the groundwater contained up to 1000 mg N l(-1) ammonium (NH4+) and 300 mg N l(-1) nitrate (NO3-), while downgradient concentrations decreased to similar to 1 mg l(-1) DIN ([DIN] = [NH4+-N] + [NO3--N] [NO2--N]). Mean delta N-15-DIN increased from similar to 2 parts per thousand to +20 parts per thousand over this flow path, broadly confirming that biological N attenuation drove the measured concentration decrease. Multi-variate analysis of water chemistry identified two distinct NH4+ sources (delta N-15-NH4+ from-14 parts per thousand and +5 parts per thousand) within the contaminated zone of both aquifers. Nitrate dual isotopes co-varied (delta N-15: -3 parts per thousand - +60 parts per thousand; delta O-18: 0 parts per thousand- +50 parts per thousand) within the range expected for coupled nitrification and denitrification of the identified sources. The fact that delta N-15-NO2- values were 50 parts per thousand-20 parts per thousand less than delta N-15-NH4+ values in the majority of wells confirmed that nitrification controlled N turnover across the site. However, the fact that delta N-15-NO2- was greater than delta N-15-NH4+ in wells with the highest [NH4+] shows that an autotrophic NO2- reduction pathway (anaerobic NH4+ oxidation or nitrifier-denitrification) drove N attenuation closest to the contaminant plume. This direct empirical evidence that both autotrophic and heterotrophic biogeochemical processes drive N attenuation in contaminated aquifers demonstrates the power of multiple N isotopes to untangle N cycling in highly complex systems. (C) 2016 Elsevier Ltd. All rights reserved.

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