Hydrogeological flow patterns and hydrochemical driving forces of groundwater in a typical coastal hilly region of the Jinjiang watershed, Southeast China: Recommendations for water pollution control and management

Abstract

Coastal groundwater (CGW) systems in rapidly urbanizing regions face critical challenges in achieving Sustainable Development Goal (SDG), where anthropogenic pressures intersect with hydrogeological vulnerability. This study employs coupled isotopic-hydrogeochemical analysis and geostatistics to unravel hydrochemical driving forces compromising groundwater quality in the Jinjiang Downstream Watershed (DJW), Southeast China. The results indicated that groundwater was predominantly recharged from local atmospheric precipitation and lateral recharge from the adjacent boundaries. Hydrochemical distributions exhibited a distinct pattern, transitioning from HCO₃-Ca to HCO₃·Cl-Ca, and then to Cl-Mg·Ca/Na·Ca, reflecting processes ranging from freshwater recharge to seawater intrusion (SWI). Elevated nitrates were primarily attributed to domestic sewage leakage and septic tank leaching. Additionally, preferential flow posed a risk to deep groundwater quality, by facilitating the rapid transport of contaminants through rock fractures. Key driving forces of hydrochemistry included silicate dissolution with local runoff paths, SWI, and human activities. The study advocates for a governance paradigm integrating electrochemical sensor networks with machine learning-driven contaminant prediction and phased membrane bioreactor deployment, which synergistically reduce nitrate fluxes while maintaining aquifer freshening processes. This integrated approach establishes a scalable model for SDG-aligned groundwater management in vulnerable coastal zones, demonstrating how process-based insights can bridge scientific discovery and water security implementation.

Keywords

Groundwater flow pattern / Atmospheric precipitation / Hydrochemistry / Nitrate / Driving forces / Seawater intrusion / Electrochemical sensor networks / Machine learning / Coastal area / Sustainable Development Goal (SDG) / Groundwater management / Hydrogeological survey engineering

References

[1] Amiri V, Sohrabi N, Li PY, Amiri F. 2023. Groundwater quality for drinking and non-carcinogenic risk of nitrate in urban and rural areas of Fereidan, Iran. Exposure and Health, 15(4), 807-823. doi: 10.1007/s12403-022-00525-w.

[2] Anaman R, Peng C, Jiang ZC, Liu X, Zhou ZR, Guo ZH, Xiao XY. 2022. Identifying sources and transport routes of heavy metals in soil with different land uses around a smelting site by GIS based PCA and PMF. Science of the Total Environment, 823, 153759. doi: 10.1016/j.scitotenv.2022.153759.

[3] Carretero S, Rodrigues Capítulo L, Dapeña C, Fabiano M, Kruse E. 2022. A chemical and isotopic approach to investigate groundwater dynamics in a coastal aquifer. Catena, 213, 106229. doi: 10.1016/j.catena.2022.106229.

[4] Chen JQ, Yan BZ, Xu TB, Xia F. 2023. Hydrochemical evolution characteristics and mechanism of groundwater funnel areas under artificial governance in Hengshui City, North China. Ecological Indicators, 148, 110059. doi: 10.1016/j.ecolind.2023.110059.

[5] Chen ZY, Qi JX, Zhang ZJ. 2010. Application of Isotope Hydrogeology Method in Typical Basins of North China. Beijing, Science Press, 24-25 (in Chinese).

[6] Cheng ZS, Su C, Zheng ZZ, Li Z, Wang LK, Wang EB. 2021. Grain size characteristics and genesis of the Muxing loess in the Muling-Xingkai Plain, Northeast China. Journal of Groundwater Science and Engineering, 9(2), 152-160. doi: 10.19637/j.cnki.2305-7068.2021.02.007.

[7] Chitsazan M, Aghazadeh N, Mirzaee Y, Golestan Y. 2019. Hydrochemical characteristics and the impact of anthropogenic activity on groundwater quality in suburban area of Urmia city, Iran. Environment, Development and Sustainability, 21(1), 331-351. doi: 10.1007/s10668-017-0039-1.

[8] Clark ID, Fritz P. 2013. Environmental Isotopes in Hydrogeology. Boca Raton, CRC Press, 174-176.

[9] Craig H. 1961. Isotopic variations in meteoric waters. Science, 133(3465), 1702-1703. doi: 10.1126/science.133.3465.1702.

[10] Egbueri JC. 2020. Groundwater quality assessment using pollution index of groundwater (PIG), ecological risk index (ERI) and hierarchical cluster analysis (HCA): A case study. Groundwater for Sustainable Development, 10, 100292. doi: 10.1016/j.gsd.2019.100292.

[11] Ez-zaouy Y, Bouchaou L, Saad A, Hssaisoune M, Brouziyne Y, Dhiba D, Chehbouni A. 2022. Morocco’s coastal aquifers: Recent observations, evolution and perspectives towards sustainability. Environmental Pollution, 293, 118498. doi: 10.1016/j.envpol.2021.118498.

[12] Fu CC, Li XQ, Ma JF, Liu LX, Gao M, Bai ZX. 2018. A hydrochemistry and multi-isotopic study of groundwater origin and hydrochemical evolution in the middle reaches of the Kuye River basin. Applied Geochemistry, 98, 82-93. doi: 10.1016/j.apgeochem.2018.08.030.

[13] Fu TF, Qi C, Wang ZY, Li CZ, Liu WQ, Fu YS, Chen GQ, Su Q, Xu XY, Yu HJ. 2022. Hydrochemical characteristics and quality assessment of groundwater under the impact of seawater intrusion and anthropogenic activity in the coastal areas of Zhejiang and Fujian Provinces, China. Lithosphere, 2022, 1394857. doi: 10.2113/2022/1394857.

[14] Gaillardet J, Dupré B, Louvat P, Allègre CJ. 1999. Global silicate weathering and CO₂ consumption rates deduced from the chemistry of large rivers. Chemical Geology, 159(1-4), 3-30. doi: 10.1016/S0009-2541(99)00031-5.

[15] Gao ZJ, Han C, Xu Y, Zhao ZH, Luo ZJ, Liu JT. 2021. Assessment of the water quality of groundwater in Bohai Rim and the controlling factors—a case study of northern Shandong Peninsula, north China. Environmental Pollution, 285, 117482. doi: 10.1016/j.envpol.2021.117482.

[16] Gibbs RJ. 1970. Mechanisms controlling world water chemistry. Science, 170(3962), 1088-1090. doi: 10.1126/science.170.3962.1088.

[17] Giménez-Forcada E. 2014. Space/time development of seawater intrusion: A study case in Vinaroz coastal plain (Eastern Spain) using HFE-Diagram, and spatial distribution of hydrochemical facies. Journal of Hydrology, 517, 617-627. doi: 10.1016/j.jhydrol.2014.05.056.

[18] Han DM, Kohfahl C, Song XF, Xiao GQ, Yang JL. 2011. Geochemical and isotopic evidence for palaeo-seawater intrusion into the south coast aquifer of Laizhou Bay, China. Applied Geochemistry, 26(5), 863-883. doi: 10.1016/j.apgeochem.2011.02.007.

[19] Han DM, Currell MJ. 2022. Review of drivers and threats to coastal groundwater quality in China. Science of the Total Environment, 806, 150913. doi: 10.1016/j.scitotenv.2021.150913.

[20] Han DM, Song XF, Currell MJ, Yang JL, Xiao GQ. 2014. Chemical and isotopic constraints on evolution of groundwater salinization in the coastal plain aquifer of Laizhou Bay, China. Journal of Hydrology, 508, 12-27. doi: 10.1016/j.jhydrol.2013.10.040.

[21] Han DM, Song XF, Currell MJ. 2016. Identification of anthropogenic and natural inputs of sulfate into a karstic coastal groundwater system in northeast China: Evidence from major ions, δ¹³C-DIC and δ³⁴S-SO₄. Hydrology and Earth System Sciences, 20(5), 1983-1999. doi: 10.5194/hess-20-1983-2016.

[22] Hou QX, Zhang Q, Huang GX, Liu CY, Zhang Y. 2020. Elevated manganese concentrations in shallow groundwater of various aquifers in a rapidly urbanized delta, south China. Science of The Total Environment, 701, 134777. doi: 10.1016/j.scitotenv.2019.134777.

[23] Huang GX, Li LP. 2024. Groundwater Chemistry and Quality in Coastal Aquifers. Water, 16(14), 2041. doi: 10.3390/w16142041.

[24] Huang GX, Liu CY, Sun JC, Zhang M, Jing JH, Li LP. 2018. A regional scale investigation on factors controlling the groundwater chemistry of various aquifers in a rapidly urbanized area: A case study of the Pearl River Delta. Science of The Total Environment, 625, 510-518. doi: 10.1016/j.scitotenv.2017.12.322.

[25] Khan MR, Koneshloo M, Knappett PSK, Ahmed KM, Bostick BC, Mailloux BJ, Mozumder RH, Zahid A, Harvey CF, van Geen A, Michael HA. 2016. Megacity pumping and preferential flow threaten groundwater quality. Nature Communications, 7(1), 12833. doi: 10.1038/ncomms12833.

[26] Kurwadkar S, Kanel SR, Nakarmi A. 2020. Groundwater pollution: Occurrence, detection, and remediation of organic and inorganic pollutants. Water Environment Research, 92(10), 1659-1668. doi: 10.1002/wer.1415.

[27] Kwon HI, Koh DC, Cho BW, Jung YY. 2022. Nutrient dynamics in stream water and groundwater in riparian zones of a mesoscale agricultural catchment with intense seasonal pumping. Agricultural Water Management, 261, 107336. doi: 10.1016/j.agwat.2021.107336.

[28] Li CC, Gao XB, Li SQ, Bundschuh J. 2020. A review of the distribution, sources, genesis, and environmental concerns of salinity in groundwater. Environmental Science and Pollution Research, 27(33), 41157-41174. doi: 10.1007/s11356-020-10354-6.

[29] Li BJ, Liang X, Jin MG, Yang JL, Ma B, Ge Q. 2017. Origin and evolution of aquitard porewater in the western coastal plain of Bohai Bay, China. Groundwater, 55(6), 917-925. doi: 10.1111/gwat.12590.

[30] Li ZH, Li JF, Huang JO, Li YS. 2024. Nitrate contamination in groundwater and its health risk assessment: A case study of Quanzhou, a typical coastal city in Southeast China. Environmental Earth Sciences, 83(10), 331. doi: 10.1007/s12665-024-11608-z.

[31] Lin L, Pussella P. 2017. Assessment of vulnerability for coastal erosion with GIS and AHP techniques case study: Southern coastline of Sri Lanka. Natural Resource Modeling, 30(4), e12146. doi: 10.1111/nrm.12146.

[32] Lingle DA, Kehew AE, Krishnamurthy RV. 2017. Use of nitrogen isotopes and other geochemical tools to evaluate the source of ammonium in a confined glacial drift aquifer, Ottawa County, Michigan, USA. Applied Geochemistry, 78, 334-342. doi: 10.1016/j.apgeochem.2017.01.004.

[33] Liu CL, Zheng JH, Li ZH, Li YS, Hao QC, Li JF. 2021. Analysis on the situation and countermeasures of water resources supply and demand in the cities of small and medium-sized river basins along southeast coast of China —taking Xiamen City as an example. Journal of Groundwater Science and Engineering, 9(4), 350-358. doi: 10.19637/j.cnki.2305-7068.2021.04.008.

[34] Liu JT, Lou KX, Gao ZJ, Wang YB, Li Q, Tan MH. 2024. Comprehending hydrochemical fingerprint, spatial patterns, and driving forces of groundwater in a topical coastal plain of Northern China based on hydrochemical and isotopic evaluations. Journal of Cleaner Production, 461, 142640. doi: 10.1016/j.jclepro.2024.142640.

[35] Liu RN, Xie XJ, Hou QX, Han DY, Song JM, Huang GX. 2024. Spatial distribution, sources, and human health risk assessment of elevated nitrate levels in groundwater of an agriculture-dominant coastal area in Hainan Island, China. Journal of Hydrology, 634, 131088. doi: 10.1016/j.jhydrol.2024.131088.

[36] Liu Y, Jiao JJ, Liang WZ, Kuang XX. 2017. Hydrogeochemical characteristics in coastal groundwater mixing zone. Applied Geochemistry, 85, 49-60. doi: 10.1016/j.apgeochem.2017.09.002.

[37] Liu Y, Xue Q, Chang CW, Wang R, Liu ZY, He L. 2022. Recent progress regarding electrochemical sensors for the detection of typical pollutants in water environments. Analytical Sciences, 38(1), 55-70. doi: 10.2116/analsci.21SAR12.

[38] Lu YX, Zhang JM. 2010. Quanzhou: Red, yellow and blue division of groundwater resources and dynamic management measures. China Water Resources, 17, 36-38 doi: 10.3969/j.issn.1000-1123.2010.17.017. (in Chinese with English abstract).

[39] Luijendijk E, Gleeson T, Moosdorf N. 2020. Fresh groundwater discharge insignificant for the world’s oceans but important for coastal ecosystems. Nature Communications, 11(1), 1260. doi: 10.1038/s41467-020-15064-8.

[40] Luo MH, Zhang Y, Xiao K, Wang XJ, Zhang XL, Li G, Li HL. 2023. Effect of submarine groundwater discharge on nutrient distribution and eutrophication in Liaodong Bay, China. Water Research, 247, 120732. doi: 10.1016/j.watres.2023.120732.

[41] Marandi A, Shand P. 2018. Groundwater chemistry and the Gibbs Diagram. Applied Geochemistry, 97, 209-212. doi: 10.1016/j.apgeochem.2018.07.009.

[42] Matiatos I, Wassenaar LI, Monteiro LR, Venkiteswaran JJ, Gooddy DC, Boeckx P, Sacchi E, Yue FJ, Michalski G, Alonso-Hernández C, Biasi C, Bouchaou L, Edirisinghe NV, Fadhullah W, Fianko JR, García-Moya A, Kazakis N, Li SL, Luu MTN, Priyadarshanee S, Re V, Rivera DS, Romanelli A, Sanyal P, Tamooh F, Trinh DA, Walters W, Welti N. 2021. Global patterns of nitrate isotope composition in rivers and adjacent aquifers reveal reactive nitrogen cascading. Communications Earth and Environment, 2, 52. doi: 10.1038/s43247-021-00121-x.

[43] Morici S, Gagliano Candela E, Favara R, La Pica L, Scaletta C, Pecoraino G. 2023. Hydrogeochemical characterization of the alluvial aquifer of Catania Plain, Sicily (South Italy). Environmental Earth Sciences, 82(6), 144. doi: 10.1007/s12665-023-10816-3.

[44] Moussaoui I, Rosa E, Cloutier V, Neculita CM, Dassi L. 2023. Chemical and isotopic evaluation of groundwater salinization processes in the Djebeniana coastal aquifer, Tunisia. Applied Geochemistry, 149, 105555. doi: 10.1016/j.apgeochem.2022.105555.

[45] Peng C, Gan MF, Che JL, Zhang Y, Shi P. 2024. Study on the influence of water exchange in river hyporheic zone on nitrogen migration and transformation process. Acta Ecologica Sinica, 44(23), 10794-10806 doi: 10.20103/j.stxb.20240202029. (in Chinese with English abstract).

[46] Reyment RA, Davis JC. 1988. Statistics and data analysis in geology. Biometrics, 44(3), 918. doi: 10.2307/2531613.

[47] Richardson CM, Davis KL, Ruiz-González C, Guimond JA, Michael HA, Paldor A, Moosdorf N, Paytan A. 2024. The impacts of climate change on coastal groundwater. Nature Reviews Earth & Environment, 5(2), 100-119. doi: 10.1038/s43017-023-00500-2.

[48] Rodell M, Famiglietti JS, Wiese DN, Reager JT, Beaudoing HK, Landerer FW, Lo MH. 2018. Emerging trends in global freshwater availability. Nature, 557(7707), 651-659. doi: 10.1038/s41586-018-0123-1.

[49] Rogers KM, van der Raaij R, Phillips A, Stewart M. 2023. A national isotope survey to define the sources of nitrate contamination in New Zealand freshwaters. Journal of Hydrology, 617, 129131. doi: 10.1016/j.jhydrol.2023.129131.

[50] Santoni S, Huneau F, Garel E, Celle-Jeanton H. 2018. Multiple recharge processes to heterogeneous Mediterranean coastal aquifers and implications on recharge rates evolution in time. Journal of Hydrology, 559, 669-683. doi: 10.1016/j.jhydrol.2018.02.068.

[51] Schroeter SA, Orme AM, Lehmann K, Lehmann R, Chaudhari NM, Küsel K, Wang H, Hildebrandt A, Totsche KU, Trumbore S, Gleixner G. 2025. Hydroclimatic extremes threaten groundwater quality and stability. Nature Communications, 16(1), 720. doi: 10.1038/s41467-025-55890-2.

[52] Su C, Zhang FE, Cui XS, Cheng ZS, Zheng ZX. 2020. Source characterization of nitrate in groundwater using hydrogeochemical and multivariate statistical analysis in the Muling-Xingkai Plain, Northeast China. Environmental Monitoring and Assessment, 192(7), 456. doi: 10.1007/s10661-020-08347-6.

[53] Su H, Li H, Chen H, Li Z, Zhang SH. 2023. Source identification and potential health risks of fluoride and nitrate in groundwater of a typical alluvial plain. Science of the Total Environment, 904, 166920. doi: 10.1016/j.scitotenv.2023.166920.

[54] UNESCO. 2022. Groundwater: Making the invisible visible. United Nations. In:The United Nations World Water Development Report 2022: Paris, UNESCO, 34-35.

[55] Wang D, Wu JH, Li PY, Li LX, Yang JY, Zhang PB, He S, Kou XM, Wang Y. 2024. Seasonal nitrate variations, risks, and sources in groundwater under different land use types in a thousand-year-cultivated region, northwestern China. Environmental Research, 251, 118699. doi: 10.1016/j.envres.2024.118699.

[56] Wang H, Ni J, Song QC, Li C, Wang FG, Cao YQ. 2021. Analysis of coastal groundwater hydrochemistry evolution based on groundwater flow system division. Journal of Hydrology, 601, 126631. doi: 10.1016/j.jhydrol.2021.126631.

[57] Wang SQ, Zhang ZX, Sprenger M, Wei SC, Zheng WB, Liu BB, Shen YJ, Zhang YZ. 2024. Seasonal recharge mechanism of the upper shallow groundwater in a long-term wastewater leakage and irrigation region of an alluvial aquifer. Journal of Hydrology, 629, 130424. doi: 10.1016/j.jhydrol.2023.130424.

[58] Wang ZY, Li YL, Pan JB, Xu MY, Xu JJ, Hua DB. 2023. Array electrochemiluminescence device with ultra-high sensitivity and selectivity for rapid visualized monitoring of trace radon in environment. Journal of Hazardous Materials, 453, 131449. doi: 10.1016/j.jhazmat.2023.131449.

[59] Wisitthammasri W, Chotpantarat S, Thitimakorn T. 2020. Multivariate statistical analysis of the hydrochemical characteristics of a volcano sedimentary aquifer in Saraburi Province, Thailand. Journal of Hydrology: Regional Studies, 32, 100745. doi: 10.1016/j.ejrh.2020.100745.

[60] Wu CC, Cai F, Wu JZ, Zhao GG. 2011. Topographic and morphologic features in the coastal zone of Quanzhou Bay and their controlling factors. Marine Geology and Quaternary Geology, 31(4), 75-81. doi: 10.3724/SP.J.1140.2011.04075.

[61] Yang Y, Yuan YL, Xiong GY, Yin ZY, Guo Y, Song J, Zhu XB, Wu JF, Wang JG, Wu JC. 2024. Patterns of nitrate load variability under surface water-groundwater interactions in agriculturally intensive valley watersheds. Water Research, 267, 122474. doi: 10.1016/j.watres.2024.122474.

[62] Zamrsky D, Oude Essink GHP, Bierkens MFP. 2024. Global impact of sea level rise on coastal fresh groundwater resources. Earth’s Future, 12(1), e2023EF003581. doi: 10.1029/2023EF003581.

[63] Zhang AG, Liang Y, Ma R. 2024. Adsorption/desorption behavior of nh4-n under surface water-groundwater interaction and its impact on n migration and transformation. Earth Science, 49(10), 3761-3772 doi: 10.3799/dqkx.2023.188. (in Chinese with English abstract).

[64] Zhang B, Song XF, Han DM, Guo ZR, Xiao GQ, Yang JL. 2013. Seawater intrusion degree evaluation based on mathematical statistics and fuzzy mathematics in Qinhuangdao Yangdai River Plain. Scientia Geographica Sinica, 33(3), 342-348 doi: 10.13249/j.cnki.sgs.2013.03.342. (in Chinese with English abstract).

[65] Zhang F, Wang JL, Huang DK, Zhong QQ, Yu T, Du JZ. 2023. Fresh groundwater discharge as a major source of ⁹⁰Sr into the coastal ocean. Environmental Science and Technology, 57(32), 12033-12041. doi: 10.1021/acs.est.3c03597.

[66] Zhang HY, Han X, Wang GC, Mao HR, Chen XL, Zhou L, Huang DD, Zhang F, Yan X. 2023. Spatial distribution and driving factors of groundwater chemistry and pollution in an oil production region in the Northwest China. Science of The Total Environment, 875, 162635. doi: 10.1016/j.scitotenv.2023.162635.

[67] Zhang M, Huang GX, Liu CY, Zhang Y, Chen ZY, Wang JC. 2020. Distributions and origins of nitrate, nitrite, and ammonium in various aquifers in an urbanized coastal area, south China. Journal of Hydrology, 582, 124528. doi: 10.1016/j.jhydrol.2019.124528.

[68] Zhang Y, Chen ZY, Huang GX, Yang MN. 2023. Origins of groundwater nitrate in a typical alluvial-pluvial plain of North China plain: New insights from groundwater age-dating and isotopic fingerprinting. Environmental Pollution, 316, 120592. doi: 10.1016/j.envpol.2022.120592.

[69] Zhao HM, Mao X, Liu CL, Li YS, Liu LJ. 2023. Transgression-regression processes since the MIS 3 in the coastal zone of Quanzhou Bay, Fujian. Journal of Geomechanics, 29(4), 569-583 doi: 10.12090/j.issn.1006-6616.2023046. (in Chinese with English abstract).

[70] Zheng R, Sun ZL, Jiao JG, Ma QQ, Zhao LQ. 2024. Salinity prediction based on improved LSTM model in the Qiantang Estuary, China. Journal of Marine Science and Engineering, 12(8), 1339. doi: 10.3390/jmse12081339.

[71] Zhou J, Du Y, Deng YM, Tao YQ, Leng ZC, Ma T, Wang YX. 2022. Source identification of groundwater phosphorus under different geological settings in the central Yangtze River basin. Journal of Hydrology, 612, 128169. doi: 10.1016/j.jhydrol.2022.128169.

[72] Zhu JC, Wang SB, Zheng ZQ. 2018. The Geological Survey Report of Quanzhou City. Southeast Fujian Geological Brigade, 96-106 (in Chinese).

[73] Zhu YC, Yang HJ, Xiao Y, Hao QC, Li YS, Liu JH, Wang LW, Zhang YQ, Hu WX, Wang J. 2024. Identification of hydrochemical characteristics, spatial evolution, and driving forces of river water in Jinjiang Watershed, China. Water, 16(1), 45. doi: 10.3390/w16010045.