日本地球惑星科学連合2023年大会

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[J] オンラインポスター発表

セッション記号 A (大気水圏科学) » A-HW 水文・陸水・地下水学・水環境

[A-HW23] 同位体水文学2023

2023年5月25日(木) 10:45 〜 12:15 オンラインポスターZoom会場 (7) (オンラインポスター)

コンビーナ:安原 正也(立正大学地球環境科学部)、浅井 和由(株式会社 地球科学研究所)、中村 高志(山梨大学大学院・国際流域環境研究センター)、大沢 信二(京都大学大学院理学研究科附属地球熱学研究施設(別府))

現地ポスター発表開催日時 (2023/5/24 17:15-18:45)

10:45 〜 12:15

[AHW23-P03] Potential Sources of High Level of Ammonium Contamination in Deep Groundwater of Kathmandu Valley, Nepal

*SITI IFFAH HANISAH BINTI MOHD ALI1、Bijay Man Shakya2、Anoj Khanal3、Sanjeev Bickram Rana3西田 継1中村 高志1 (1.山梨大学、2.Smartphones for water - Nepal、3.Kathmandu Valley Water Supply Management Board)

キーワード:地下水、アンモニウム、窒素の同位体

The source of ammonium-nitrogen (NH4-N) in Kathmandu Valley deep groundwater has not been widely researched, yet the elevated concentration continues to be a matter of concern. In this study, the potential sources of ammonium-nitrogen in deep groundwater of Kathmandu Valley were investigated by observing water quality and nitrogen isotope in the deep groundwater where contamination with high concentrations of ammonium was confirmed. Contamination of NH4-N exceeding the drinking water guideline value of 1.1mg-N/L was detected in 17 out of the 25 deep wells with the maximum value of 124.8 mg-N/L. The concentration was found to be increased gradually from the peripheral part to the central part of the basin and higher in the area overlain by a thick clay layer (aquitard). Meanwhile, nitrogen isotope from ammonia (δ15N-NH4) was found to be ranged between 0.9‰ to 3.8‰. The origin of high ammonium concentration in the deep groundwater is nitrogen is found to be derived from soil deposited in the basin. Similarly, the geological analysis also suggested the natural origin of high ammonium concentration due to nitrogen loading from thick clay layers containing rich organic matter. From the preliminary analysis, the NH4-N enrichment in the aquifer is anticipated from the percolation through thick clay. Thus, this study found a possible relationship between the thickness of the aquitard to the concentration of NH4-N. However, in order to understand the source of ammonium contamination in the groundwater, there require a detailed study on hydrogeochemical processes within the aquifer and aquitards.