Differentiation of natural and anthropogenic contaminant sources using isotopic and microbial signatures in a heavily cultivated coastal area

• Published in: Environmental pollution (1987) 2021-03, Vol.273, p.116493-116493, Article 116493
• Main Authors: Kaown, Dugin, Koh, Eun-Hee, Mayer, Bernhard, Ju, YeoJin, Kim, Jaeyeon, Lee, Hye-Lim, Lee, Seong-Sun, Park, Dong Kyu, Lee, Kang-Kun
• Format: Article
• Language: English
• Subjects: Contaminant sources; Microbial community structure; Multiple isotopes; Nitrate; Seawater intrusion
• ISSN: 0269-7491; 1873-6424
• DOI: 10.1016/j.envpol.2021.116493

Hydrogeochemical and multiple isotope data for groundwater samples were obtained and interpreted to discriminate anthropogenic and natural contaminant sources in a coastal aquifer underlying a heavily cultivated watershed in Hwaseong, South Korea. The local aquifers are vulnerable to contamination, due to high anthropogenic N inputs and the location close to the ocean facilitating seawater intrusion. Thus, to effectively control the groundwater quality in the study area, it is necessary to differentiate between anthropogenic and natural contaminant sources. The concentrations of NO3–N in the groundwater ranged between 0.14 and 45.6 mg/L in August 2015 and 0.2–39.6 mg/L in March 2016. High concentrations of Cl− (388–1107 mg/L) and a high electrical conductivity (1027–2715 μS/cm) were observed in the study area, suggesting that the groundwater was affected by seawater intrusion. Furthermore, δ15N–NO3-, δ34S–SO42- values and 87Sr/86Sr of groundwater were determined to reveal the origins of the natural and anthropogenic contaminants and the groundwater mean residence times (MRT) and 87Sr/86Sr ratios were used to assess the hydrogeochemical processes along the flow path in the study area. Young groundwater was affected by an anthropogenic contamination source with contributions of 26–46% adding nitrate to the aquifer, whereas old groundwater was impacted by mixing with seawater with contributions of 10–20% with low concentrations of NO3–N, but elevated concentrations of chloride and sulfate. Recently recharged uncontaminated groundwater showed oxic conditions with a diverse microbial community structure, whereas young groundwater contaminated by anthropogenic sources showed a less diverse microbial community structure. The results of this study suggest that multiple isotopes combined with groundwater MRT and microbial data can be applied to distinguish natural and anthropogenic contaminant sources in a groundwater system. [Display omitted] •Novel approaches were uses to differentiate anthropogenic and natural contaminant sources.•A Bayesian mixing model was used to determine contributions of contaminant sources.•Groundwater MRT and microbial data were evaluated to differentiate contaminant sources.•Multi-isotope, microbial data and MRT were combined to assess contaminant sources. Multi-isotope and microbial data combined with groundwater mean residence times successfully revealed the origins of natural and anthropogenic contaminants.