Construction and Evaluation of the Health Indicator System for Black Soil Environmental Quality

The study covered seven demonstration zones, including Hailun, Da'an, Changchun, Sanjiang, Dahewan, Qiqihar, and Shenyang, and collected 1,350 soil samples to establish a dataset of heavy metals and antibiotic resistance genes (ARGs) in farmland soils of the Northeast black soil region. The details are as follows: (1)Construct an evaluation index system for black soil environmental quality. This technical system adopts the minimum data set method of principal component analysis to select five heavy metal elements: Co, Cu, Ni, Cr, and Cd.

On this basis, 4 first-level indicators (heavy metals, organic matter, antibiotic resistance genes, soil fertility) and 38 second-level indicators were established. (2)Based on single-factor, Nemerow, and potential ecological risk assessments, Cd, Ni, and Cr were identified as the primary risk factors, with potential ecological risks ranging from low to moderate. Heavy metal sources were categorized into natural (e.g., Co, Cu, Zn contributed by parent soil materials) and anthropogenic (e.g., Cd, Pb, Ni from industrial emissions, fertilizer application, and wastewater irrigation).

Anthropogenic sources were particularly prominent in old industrial bases, with atmospheric deposition, chemical fertilizers, and organic fertilizers being the main pathways for heavy metal input. Cd, Pb, and As exhibited a net accumulation trend overall. （3）The ARGs health risk index shows that the soil risk of rice is significantly higher than that of dry fields, and is positively correlated with pathogen diversity (ρ=0.38).

Rice soil is a "hotspot" area for ARGs health risk, and the diversity of pathogenic bacteria is significantly positively correlated with the health risk index (ρ=0.38, P=0.0086). The contribution analysis of the random forest model shows that high-intensity application of fertilizers and pesticides is the core geographical driving factor. The model prediction reveals that the southern part of the Songnen Plain and the eastern part of the Sanjiang Plain are high-risk areas.

(4) The soil environmental quality in the black soil area of farmland is mainly composed of high-quality and safe areas, as well as low to moderate potential ecological risk areas. The key monitoring areas and pollution factors have obvious spatial concentration characteristics, and there are significant spatial differences between different regions. Typical black soil areas have better soil preparation for agricultural production suitability.

The soil environmental quality of farmland changes relatively slowly in the short term, but the cumulative effects in the medium and long term cannot be ignored. Continuous optimization of agricultural management measures and pollution source control should be carried out to ensure the safe and sustainable development of agriculture. (5) The migration activity of Cd between aggregates increases with the number of freeze-thaw cycles.

The cumulative release of Cd in soil increases with the number of freeze-thaw cycles, and is positively correlated with the disintegration and aggregation of soil aggregates under the influence of freeze-thaw action. Seasonal freezing and thawing promote the migration of Cd in the soil plant system, with higher Cd concentrations in the leaves than in the roots, which has a significant inhibitory effect on plant growth.

(6) The spatiotemporal prediction of heavy metals based on the XGBoost model (R²>0.65) indicates that geographic coordinates and climate factors are the main controlling factors of heavy metal spatial patterns, and human activities exacerbate pollution risks. The SSP-RCP scenario prediction shows that Pb and Cd will rapidly diffuse under the SSP5-8.5 high emission pathway, while pollution expansion is limited under the SSP1-2.6 sustainable pathway.