Abstract
: The increasing concentration of nitrogen compounds in the groundwater is of a growing concern in terms of human health and groundwater quality. Although an excess of nitrogen compounds in the groundwater of the Kathmandu Valley has been reported, the seasonal variations of the fate of the nitrogen compounds and their relationships to the subsurface sediments are unknown. In this study, spatially distributed shallow dug well samples were collected during both the dry and wet seasons of 2016, and the nitrogen compound, chloride (Cl−), and iron (Fe2+) concentrations were analyzed. Two shallow dug wells and one deep tube well were monitored monthly for 2 years. Although NH4-N concentrations were similar in the clay-dominated areas during both seasons (1 and 0.9 mg-N/L), they were lower in the gravel-dominated areas during wet season (1.8 > 0.6 mg-N/L). The NO3-N concentration differed depending upon the soil type which increased during the wet season (clay 4.9 < 13.6 mg-N/L and gravel 2.5 < 6.8 mg-N/L). The Fe2+ concentration, however, was low during the wet season (clay 2.7 > 0.4 mg/L and gravel 2.8 > 0.3 mg/L). Long-term analysis showed higher fluctuation of nitrogen compounds in the gravel-bearing areas than in the clay-bearing areas.
Highlights
Both developed and developing countries are experiencing serious issues due to anthropogenic groundwater contamination and recharge through leakage into the water supply network, municipal sewage, and onsite waste disposal [1,2,3,4]
This paper presents the spatial distribution of the nitrogen contamination and temporal effects regarding the persistence of nitrogen with respect to the spatial distribution of the subsurface soil types in Kathmandu Valley
The statistical values for the water table level and chemical parameters collected from the shallow groundwater are presented in Table 1 which is compared with Nepal Drinking Water Quality
Summary
Both developed and developing countries are experiencing serious issues due to anthropogenic groundwater contamination and recharge through leakage into the water supply network, municipal sewage, and onsite waste disposal [1,2,3,4]. These concerns are more severe in areas in which groundwater is the primary source of fresh water [5,6], as well as in the densely populated areas of developing countries due to improper infrastructure [7,8,9]. Among the numerous chemical and biological contaminants of groundwater, there is growing concern regarding the fate and transformation of nitrogen contaminants in groundwater [2,5,6].
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