Title：
Revealing the mechanisms underlying high nitrate levels in a coastal groundwater system: An isotope and remote sensing-based study
Authors：
276:108187
Corresponding
Author：
Xu Yin, Wenlu Lan, Ke Pan, Junlin Shu, Yan Liu, Wenshi Zhang, Tianzhang Qiu, Zhongheng Yan, Li Li, Yanxia Zuo*, Hao Jiang*
Pubyear：
2026
Title of
Journal：
Ocean Coastal Manage
Paper
Code：
Volume：
276
Number：
Page：
108187
Others：
Classification：
Source：
Abstract：
Urban groundwater systems often exhibit high nitrate (NO3-) levels, leading to prominent environmental issues such as water quality deterioration and eutrophication. Although studies have been conducted worldwide, the NO3-sources and transformation processes in groundwater of densely populated coastal zones are not yet fully understood. Utilizing isotope tracing techniques combined with a Bayesian model, the spatiotemporal distribution characteristics of NO3--N in groundwater and its potential sources were analyzed in the Qinzhou Bay groundwater system. Furthermore, the anthropogenic impacts on the NO3- pollution were elaborated by linking land use types to the NO3- -N source. The isotopes revealed significant denitrification in the system. The source apportionment results demonstrated that the NO3--N originated primarily from non-point sources (soil and fertilizer), followed by domestic and industrial point sources, with atmospheric deposition making the smallest contribution. Seasonally, non-point sources contributed approximately 74% during high-flow periods and 54% during low-flow periods, with chemical fertilizer playing a dominant role. The source apportionment was further supported by the significant correlations among the land uses, isotopes, and the NO3--N sources. These findings collectively indicated that anthropogenic influences substantially outweighed natural impacts on the groundwater NO3--N in the coastal zone. The integrated methodology combining micro-scale isotopic analysis with macro-scale land-use assessment provided more precise and reliable NO3--N source apportionment, thus enabling a more in-depth understanding of coastal groundwater NO3--N pollution and targeted NO3--N source pollution control around the world.
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