Work

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

Year: 2023

Type: article

Abstract: The high contaminated shallow groundwater by nitrate (NO 3 -) and ammonium (NH 4 + ) 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 NO 3 -(maximum: 63.9 mg/L) and NH 4 + (maximum: 36.7 mg/L) concentrations were detected in shallow groundwater.NO 3 -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 NO 3 -from the unsaturated zone to the insides of the wells.The dual isotopic (δ 15 N and δ 18 O) NO 3 -approach suggested that sewer leakage is a major source of nitrogen contamination in shallow aquifers.In addition, the exponential increase in NO 3 --δ 15 N accompanied by NO 3 -reduction with the distinct δ 18 O/δ 15 N slopes of NO 3 -(~0.5)indicated denitrification.Finally, we established a negative nonlinear relationship between NO 3 -and the dissolved organic carbon, suggesting that organic carbon strongly affects denitrification reactions in shallow groundwater.

Source: Journal of Geography (Chigaku Zasshi)

DOI: 10.5026/jgeography.132.183

Authors: Takashi NAKAMURA, Ken'ichi OSAKA, Saroj Kumar CHAPAGAIN, Kei NISHIDA

Institutions: University of Yamanashi, University of Shiga Prefecture, Institute for Integrated Management of Material Fluxes and of Resources, United Nations University

Language: English

Topic: Groundwater and Isotope Geochemistry

Subfield: Geochemistry and Petrology

Field: Earth and Planetary Sciences

Domain: Physical Sciences

SDG: Clean water and sanitation

Open Access status: diamond