Deep groundwater in the Kumamoto area affected by nitrate nitrogen with source origin by sterols

Summary, in English

Nitrate nitrogen contamination of groundwater is often related to agricultural production and is a common problem in many parts of the world, particularly in regions that depend on groundwater for water supply. Nitrate nitrogen concentrations in groundwater in the Kumamoto area have increased in recent years, and countermeasures are urgently needed. Identifying the causes and sources of contamination is important for counteracting such contamination. For this purpose, continuous groundwater monitoring was conducted over a period of more than one year, and nitrate nitrogen concentrations and sterol compounds were analyzed as indicators. Nitrate nitrogen concentrations ranged from 0.07 to 4.86 mg L⁻¹, with most sites remaining below the natural background threshold of 3 mg L⁻¹. Sterol ratios generally remained below the fecal contamination threshold of 0.3, except for 0.354, which was observed in February 2023. Principal component analysis was applied to characterize the variation patterns in sterol composition, revealing that β-sitosterol and cholesterol contributed most strongly to the first principal component, whereas coprostanol and cholestanol dominated the second principal component. Hierarchical cluster analysis further classified the samples into five clusters, identifying beef and dairy cattle manure as the primary sources of groundwater pollution. Although measuring sterols is useful for estimating the origin of nitrate nitrogen pollution and as an indicator of fecal contamination, observations must be continuous and not intermittent because of hydrophobicity and high adsorption rates in the solid phase. Therefore, it is necessary to continuously collect and measure water samples for longer periods, probably for at least one year.

• Author: Kei Nakagawa; Zhuolin Li; Takahiro Hosono; Yuji Takao; Ronny Berndtsson
• Department/s: MECW: The Middle East in the Contemporary World; Centre for Advanced Middle Eastern Studies (CMES); Division of Water Resources Engineering; LTH Profile Area: Water
• Publishing year: 2025-12
• Language: English
• Publication/Series: Journal of Hydrology
• Volume: 662
• Links: http://dx.doi.org/10.1016/j.jhydrol.2025.134101
• Document type: Journal article
• Publisher: Elsevier
• Topic: Oceanography, Hydrology and Water Resources
• Keywords: Biomarkers; Deep groundwater; Groundwater contamination; Nitrate nitrogen; Sterols
• Status: Published
• ISBN/ISSN/Other: ISSN: 0022-1694