Effect of land use pattern on the bioavailability of heavy metals: A case study with a multi-surface model

In modern agricultural practice, the land use pattern has been changing due to economic reasons and related policies, which significantly affects the basic physical and chemical properties of soils, thereby influencing the speciation and distribution of heavy metals (HMs) in soils. In this study, we selected three typical types of land use patterns (vegetable field, paddy field and forest field) in Shaoguan City, Guangdong Province, to analyze the content and distribution of HMs, screen the sensitive physicochemical properties, and predict the phytoavailability of HMs under different land use patterns with the multi-surface model (MSM). The forest field had relatively lower levels of labile and free HM ions than both paddy and vegetable fields, which may be attributed to the lower HM content in forest field. The modeling results revealed that organic matter (OM) is the primary carrier of HMs, accounting for 0.19%-97.92% of labile HMs. The sensitivity of soil physicochemical properties to free HM ions followed the order of pH > SOM > goethite > clay. Besides, the conversion of paddy field into vegetable or forest field increased the environmental risk of HMs. Our results may help better decision making in agricultural restructuring to reduce the risk of HM-contaminated soils, as well as give a demonstration for the application of the MSM in predicting the phytoavailability of HMs as a powerful technique.