Seasonal groundwater variations in the coastal plain under intense human activities: Hydrochemical evolution, quality degradation, and health risk assessment

Abstract

Coastal regions play an important socio-economic and ecological role, yet the spatio-temporal drivers of groundwater quality remain poorly understood. This study integrates hydrogeochemical analysis, positive matrix factorization, Entropy Water Quality Index, Human Health Risk Assessment, and Monte Carlo Simulation to develop a framework for identify main factors and processes affecting groundwater quality and its spatio-temporal variations in Pinghu City (PHC). Hydrochemical evolution of groundwater driven by water-rock interactions, evaporation, and ion exchange. Over 65 % of groundwater samples are classified as “good” or better, with TDS, Na⁺, Cl⁻, NO₃⁻ and As significantly impact groundwater quality. Seawater intrusion severely affects some southwestern sampling points, with EWQI values reaching 150.54–190.97, more than twice the limit. Groundwater degradation is primarily influenced by seawater intrusion, heavy metal pollution, and human activities, collectively explaining up to 60.77 % of quality deterioration. Four key factors identified in the positive matrix factorization: Cr-containing chemical agent discharges (25.88 %), natural sources (29.81 %), industrial sources (26.58 %), agricultural sources (17.73 %). As, Cd, and Cr are identified as the main carcinogenic risk factors, with Factors Ⅰ and Ⅱ contributed 81.31 % of the carcinogenic risk. The carcinogenic risk of As is concentrated in central PHC, while Cd and Cr risks are prevalent in the western and southwestern regions, exhibiting seasonal variations. This study fills a gap in groundwater quality assessments in southeastern China, offering insights into the processes driving groundwater contamination.