Application of the DITAPH model coupling human activities and groundwater dynamics for nitrate vulnerability assessment: A case study in Quanzhou, China

To address the deficiencies in comprehensive surface contamination prevention strategies within China's nitrate-affected regions, this research innovatively proposes the DITAPH model - a systematic framework integrating groundwater nitrate vulnerability assessment and Nitrate Vulnerable Zones (NVZs) delineation through optimization of hydrogeological parameters. Based on detailed hydrogeological and hydrochemical investigations, the DITAPH model was applied in the plain areas of Quanzhou to evaluate its applicability. The model selected hydrogeological parameters (depth of groundwater, lithology of the vadose zone, topographic slope, aquifer water yield property), one climatic parameter (precipitation), and two anthropogenic parameters (land use type and population density) as assessment indicators. The results of the groundwater nitrate vulnerability assessment showed that the low, relatively low, relatively high, and high groundwater nitrate vulnerability zones in the study area accounted for 5.96%, 35.44%, 53.74% and 4.86% of the total area, respectively. Groundwater nitrate vulnerability was most strongly influenced by human activities, followed by groundwater depth and topographic slope. The high vulnerability zone is mainly affected by domestic and industrial wastewater, whereas the relatively high groundwater nitrate vulnerability zone is primarily influenced by agricultural activities. Validation of the DITAPH model revealed a significant positive correlation between the DITAPH index (DI) and nitrate concentration (ρ(NO₃⁻)). The results of the NVZs delineated by the DITAPH model are reliable and can serve as a tool for water resource management planning, guiding the development of targeted measures in the NVZs to prevent groundwater contamination.