Characterization of heavy metal pollution in agricultural soils and the driving mechanism of nutrient factors in the intermountain basin area

Yang Zhengyu^1,2Song Zhen^1,2*Zhou Huanzhan^1,2Ma Yonghong^1,2Geng Baili^3,4*Zhao Yuan^1,2Xiao Yuexin^1,2,5

• ¹Huangshan Observation and Research Station for Land-water Resources, Huangshan, China
• ²China Geological Survey Changsha General Survey of Natural Resources Center, Changsha, China
• ³Ministry of Natural Resources Observation and Research Station of Land-Sea Interaction Field in the Yellow River Estuary, Yantai, China
• ⁴China Geological Survey Yantai Center of Coastal Zone Geological Survey, Yantai, China
• ⁵Key Laboratory of Natural Resource Coupling Process and Effects, Beijing, China

To clarify the characteristics of heavy metal pollution (Hg, As, Cd, Cu, Zn, Pb, Ni, Cr) in farmland and explore the influence mechanism of soil nutrient factors (SOC, pH, TN, TP, TK) and C:N:P stoichiometric ratios on heavy metal pollution, this study collected 300 soil samples from the Huangshan section of the Xin'an River. Results indicate: (1) Overall, most (over 75%) of the study area's farmland has slight or no heavy metal pollution. Kriging interpolation shows that soil heavy metal pollution is mainly concentrated east of Xidi Town and west of Lan Tian Town, with notable levels of Cr, Cu, Zn, and Cd in these areas. (2) Positive matrix factorization reveals that the atmosphere contributes the most to Hg (72.8%); industry is the main source of As (73.9%); natural sources are the primary contributors to Cr, Ni, and Cu (52.5%, 51.7%, and 41.8%, respectively); soil Zn originates mainly from natural and traffic sources (31.0% and 42.8%); agricultural activities contribute the most to Cd (83.9%); and natural sources and solid waste are the main sources of Pb (40.9% and 43.1%, respectively). (3) Redundancy analysis shows that nutrient factors explain 21.5% of heavy metal pollution, with TN contributing the most (63.4%). ( 4) The results of linear regression and structural equation modeling both show that C:P has a significant negative correlation with the comprehensive heavy metal pollution index of soil (p < 0.05). This may be due to the fact that farmland in mountainous basin areas has a higher proportion of P compared to the average C:N:P ratio of subtropical farmland, and P can effectively bind with heavy metals (Cu, Cd, Pb, Ni, Zn) to form a stable state. This study systematically evaluates the heavy metal pollution in the Huangshan section of the Xin'an River from contamination assessment, source analysis, and impact mechanisms, offering a theoretical basis for preventing and controlling heavy metal pollution and ensuring land safety in similar regions.