Identification of Nitrate Sources and Main Controlling Factors in Shallow Groundwater Based on MixSIAR and Random Forest Model

As the most common pollutant in global water resources, the identification of the main controlling factors and sources of NO₃⁻ is crucial to the control of NO₃⁻ pollution. Based on methods such as human health risk model, random forest model, isotope and MixSIAR model, this study analyzed the distribution characteristics and potential risks of shallow groundwater NO₃⁻ in Huazhou District, and revealed the main controlling factors and main sources of shallow groundwater NO₃⁻. The results show that the shallow groundwater NO₃⁻ concentration in Huazhou District is high in the west and low in the east, especially in the southwest. The NO₃⁻ concentration is as high as 271 mg/L. The main factors controlling NO₃⁻ concentration being EC＞ORP＞Ca²⁺＞Mg²⁺＞T＞TDS＞HCO₃⁻. The main sources of NO₃⁻ are soil nitrogen and manure & sewage. The manure & sewage contributes the most to the NO₃⁻ content (63.8%), followed by soil nitrogen (19%) and chemical fertilizer (12.7%). Long-term drinking of shallow groundwater with high NO₃⁻ concentration in the study area has potential risks to human health, especially for children, whose HHRA assessment risk is as high as 7.904.