[Impacts of Land Use and Landscape Patterns on Heavy Metal Accumulation in Soil]

Land use cover change (LUCC) is one of the most important human activities that drive the evolution of the environment. It has great effect on the accumulation, distribution, and migration of heavy metals in the environment. Vegetation can absorb heavy metals directly, and it can also change the physical, chemical, and biological properties of soil and then control the mobility and activity of heavy metals in soil, which will eventually cause pollution of heavy metals in soil. In addition, the migration of heavy metals in soil is also affected by changes of landscape element composition and landscape pattern at sample points, plots, watersheds, and regional scales. Based on the soil sampling data and land use data of Ningbo city in 2003 and 2013, the decision tree classification method based on classification and regression tree algorithm was used to classify the land use and cover type. Single-factor pollution index and Nemero composite pollution index were used to evaluate the soil heavy metal pollution status. The landscape pattern indexes were used to explore the change of landscape patterns under different degrees of heavy metal accumulation. Finally, redundancy analysis and partial redundancy analysis were used to identify those landscape pattern factors that had the most significant impacts on the soil heavy metal accumulation in the study area. The results showed that:①The eight soil heavy metal elements including As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn presented different degree of accumulation from 2003 to 2013 in the study area, of which Hg, Ni, and Cr had the highest degree of accumulation. Most of the study area has been polluted by heavy metals, and the pollution degree in the heavily polluted areas is still increasing. ②Higher accumulation degrees of heavy metals was not distributed entirely in areas where land use types have always been construction land, or in areas where other types of land use had been converted to construction land. A considerable proportion of heavy metals accumulated in areas where land use types have always been cultivated land or converted from other types to cultivated land. ③Heavy metal polluted areas have fragmented, complex, and aggregated landscape pattern, and the correlation between this kind of landscape pattern characteristics and soil heavy metal accumulation in arable land, residential land, and industrial land was the highest. ④The higher the aggregation degree of construction land patch, the higher the accumulation degree of most heavy metals. The accumulation degree of Cu, Hg, Pb, and Cd increased significantly with the increase of landscape diversity and shape complexity of agricultural land. The closer the distance to the mining site, the more obvious the effect on the increase of Cd content.