Source Apportionment of Groundwater Quality Deterioration in a Highly Disturbed Riparian Zone of the Lower Yellow River Using Positive Matrix Factorization and Hydro-Chemical Analysis

Groundwater quality is jointly regulated by natural geological processes and anthropogenic activities. However, in regions subject to intense human disturbance, the quantitative identification of pollution sources remains poorly constrained. Taking the groundwater of the Shandong section of the lower Yellow River as the study object, this research systematically revealed regional groundwater quality characteristics and pollution sources by integrating hydrochemical analysis with the positive matrix factorization (PMF) model. Results indicate that groundwater in the study area has been significantly impacted by human activities, with the proportions of samples exceeding standards for Mn, TH, Fe, TDS, SO42−, Cl−, and NO3− reaching 66.0%, 63.8%, 42.6%, 38.3%, 29.8%, 25.5%, and 12.8%, respectively. The dominant hydrochemical type is HCO3·SO4·Cl-Na·Ca·Mg, signifying the superimposed effects of evaporation–concentration, water–rock interaction, and anthropogenic inputs. The PMF model identified three pollution sources: a composite source of agricultural runoff and industrial wastewater (44.7%), a mixed source of domestic sewage and carbonate dissolution (32.1%), and a source dominated by evaporite and fluorite dissolution (23.3%). Quantitative source contribution analysis shows that the industrial–agricultural composite source contributes 81.4%, 56.1%, 67.7%, 42.7%, and 42.3% of Mn, COD, K+, NO3−, and TH, respectively. The evaporite and fluorite dissolution source accounts for 84.5% of SO42− and 53.1% of F−. The domestic sewage and carbonate dissolution source contributes 40.4%, 44.3%, and 43.1% of Na+, Cl−, and NO3−, respectively. This study identifies the sources of groundwater quality deterioration and quantifies the relative contributions of natural processes and human activities, thereby providing a scientific basis for groundwater resource protection and pollution control in the Yellow River Basin and regions with similar geological settings.