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Open AccessArticle

Spatial Characteristics of Groundwater Chemistry in Unzen, Nagasaki, Japan

1
Institute of Integrated Science and Technology, Nagasaki University, 1-14 Bunkyo-machi, Nagasaki 852-8521, Japan
2
Liberal Arts Education Center, Tokai University, 9-1-1 Toroku, Higashi-ku, Kumamoto 862-8652, Japan
3
Division of Water Resources Engineering & Centre for Advanced Middle Eastern Studies, Lund University, Box 118, SE-221 00 Lund, Sweden
*
Author to whom correspondence should be addressed.
Academic Editor: Frédéric Huneau
Water 2021, 13(4), 426; https://doi.org/10.3390/w13040426
Received: 4 January 2021 / Revised: 1 February 2021 / Accepted: 2 February 2021 / Published: 5 February 2021
(This article belongs to the Section Hydrology and Hydrogeology)
Nitrate pollution in groundwater is a serious problem in Shimabara Peninsula, Nagasaki, Japan. A better understanding of the hydrogeochemical evolution of groundwater in vulnerable aquifers is important for health and environment. In this study, groundwater samples were collected at 12 residential and 57 municipal water supply wells and springs in July and August 2018. Nitrate (NO3−N) concentration at eight sampling sites (12%) exceeded Japanese drinking water standard for NO3 + NO2−N (10 mg L−1). The highest nitrate concentration was 19.9 mg L−1. Polluted groundwater is distributed in northeastern, northwestern, and southwestern areas, where land is used for intensive agriculture. Correlation analysis suggests that nitrate sources are agricultural fertilizers and livestock waste. Dominant groundwater chemistry is (Ca+Mg)−HCO3 or (Ca+Mg)−(SO4+NO3) type. Groundwater with higher nitrate concentration is of (Ca+Mg)−(SO4+NO3) type, indicating nitrate pollution affecting water chemistry. Principal component analysis extracted two important factors controlling water chemistry. The first principal component explained dissolved ions through water–rock interaction and agricultural activities. The second principal component explained cation exchange and dominant agricultural effects from fertilizers. Hierarchical cluster analysis classified groundwater into four groups. One of these is related to the dissolution of major ions. The other three represent nitrate pollution. View Full-Text
Keywords: groundwater; nitrate pollution; water chemistry; principal component analysis; hierarchical cluster analysis groundwater; nitrate pollution; water chemistry; principal component analysis; hierarchical cluster analysis
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MDPI and ACS Style

Nakagawa, K.; Amano, H.; Berndtsson, R. Spatial Characteristics of Groundwater Chemistry in Unzen, Nagasaki, Japan. Water 2021, 13, 426. https://doi.org/10.3390/w13040426

AMA Style

Nakagawa K, Amano H, Berndtsson R. Spatial Characteristics of Groundwater Chemistry in Unzen, Nagasaki, Japan. Water. 2021; 13(4):426. https://doi.org/10.3390/w13040426

Chicago/Turabian Style

Nakagawa, Kei; Amano, Hiroki; Berndtsson, Ronny. 2021. "Spatial Characteristics of Groundwater Chemistry in Unzen, Nagasaki, Japan" Water 13, no. 4: 426. https://doi.org/10.3390/w13040426

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