Nitrogen Contamination and Denitrification Occurrence in Shallow Groundwater of Urbanized Area at Kathmandu Valley, Nepal

Nakamura, Takashi, Osaka, Ken'ichi, Chapagain, Saroj Kumar and Nishida, Kei, (2023). Nitrogen Contamination and Denitrification Occurrence in Shallow Groundwater of Urbanized Area at Kathmandu Valley, Nepal. Journal of Geography (Chigaku Zasshi）　, 132(2), 183-196

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  • Sub-type Journal article
    Author Nakamura, Takashi
    Osaka, Ken'ichi
    Chapagain, Saroj Kumar
    Nishida, Kei
    Title Nitrogen Contamination and Denitrification Occurrence in Shallow Groundwater of Urbanized Area at Kathmandu Valley, Nepal
    Appearing in Journal of Geography (Chigaku Zasshi）　
    Volume 132
    Issue No. 2
    Publication Date 2023-01-18
    Place of Publication Japan
    Publisher Tokyo Geoscience Association
    Start page 183
    End page 196
    Language eng
    Abstract The high contaminated shallow groundwater by nitrate （NO3-) and ammonium （NH4+) in the Kathmandu Valley, Nepal were investigated along with their nitrogen sources and distribution mechanisms. Thirty-six shallow groundwater samples were collected from the tube- and dug- wells during the monsoon season （August） of 2009 and 2010. High levels of NO3- (maximum: 63.9 mg/L）and NH4 + (maximum: 36.7 mg/L） concentrations were detected in shallow groundwater. NO3- represented a significant contribution to the total dissolved inorganic nitrogen in most the dug wells; these wells were characterized by unprotected inner walls, indicating the possible influx of nitrified NO3- from the unsaturated zone to the insides of the wells. Thedual isotopic (δ15N and δ18O) NO3- approach suggested that sewerleakage is a major source of nitrogen contamination in shallow aquifers. In addition, the exponential increase in NO3--δ 15Naccompanied by NO3- reduction with the distinct δ18O/δ15N slopes of NO3-~0.5） indicated denitrification. Finally, we established a negative nonlinear relationship between NO3- and the dissolved organic carbon, suggesting that organic carbon strongly affects denitrification reactions in shallow groundwater.
    Keyword shallow groundwater
    urbanized area
    nitrogen contamination
    denitrification
    Kathmandu Valley
    Copyright Holder The Authors
    Copyright Year 2023
    Copyright type Fair use permitted
    ISSN 1884-0884
    DOI https://doi.org/10.5026/jgeography.132.183
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    Created: Thu, 20 Jul 2023, 08:57:50 JST by Věra Greschner Farkavcová on behalf of UNU FLORES