Hydrochemical Evolution and Nitrogen Behaviors in Coastal Groundwater Suffered From Seawater Intrusion and Anthropogenic Inputs

Coastal aquifers play key roles in providing freshwater resources to maintain the social and economic development coastal areas. However, climate change human activities have dramatically affected quantities qualities of groundwater aquifers. In this study, stoichiometric analysis hydrogeochemistry, multivariate analysis, isotopic trancing techniques were used reveal local hydrochemistry characteristics, natural anthropogenic origins, major hydrochemical evolution a typical aquifer located Pearl River estuary. According hydrogeological conditions burial conditions, was divided into three zones, namely, semiconfined fissure (SFGW), recharged (RFGW), porous medium (PGW). Seawater intrusion, ion exchange, water–rock reaction, main controlling factors affecting characteristics groundwater, but there significant differences effects different zones. Among them, samples from SFGW severely by seawater contributions ranged 6% 97%. Obvious cation exchange process occurred during intrusion. The PGW RFGW mainly controlled interaction. addition, had further influence on which resulted elevated nitrate–nitrogen (NO 3 − –N). mean NO –N concentrations 6.58 3.07 mg/L, respectively. Furthermore, δ 15 N–NO 18 O–NO values these two regions +2.35‰ +27.54‰ +0.39‰ +18.95‰, respectively, indicating that input contributed increased nitrate. Redox dual nitrogen evidence indicated denitrification predominant biogeochemical RFGW. This study highlights impacts intrusion inputs behaviors provides scientific basis for management