关键词: 土壤重金属, 城市公园, 污染评价, 公园建设年限, 景观格局

Abstract:

Urban parks play a significant role in urban ecosystems and serve as vital venues for residents' relaxation. Soil pollution in these parks directly affects the physical and mental health of residents, whereas heavy metal pollution in urban park green spaces is often overlooked. With rapid urbanization, the health effects of urban parks on residents have attracted widespread social attention. In urban parks located in economically active and industrially dense areas of eastern China, the accumulation of heavy metals in the soil can pose a potential threat to the health of residents. There is relatively little research on the relationship between soil heavy metal content and the construction years of parks, as well as on the relationship with the landscape pattern of parks. Therefore, this study considered Ningbo City, Zhejiang Province, as the research area. Ningbo is one of the financial and economic centers of Zhejiang Province and a typical industrial city, making research on this city representative. Sampling points were set along the east-west and north-south directions from the city center, selecting 20 representative urban parks with different establishment years. Through field sampling and indoor experimental analysis, this study focused on the pollution characteristics, enrichment levels, and their relationship with the construction years of parks for six heavy metals (Cd, Ni, Cu, Zn, Cr, and Pb) in the soil of urban parks, and further explored the impact of park landscape patterns on soil heavy metal pollution. The results showed that 1) there was a significant difference in the heavy metal content in the soil of different urban parks. The contents of Cu, Zn, Cd, and Pb were significantly higher than the background values, 2.1, 2.2, 10, and 1.9 times the background values, respectively, with a proportion exceeding the background value by over 95% and a large coefficient of variation. The Cr and Ni contents were similar to soil background values. Principal component analysis of heavy metals in the soil of urban parks, combined with the level of pollution, indicated that the sources of Cu, Zn, Cd, and Pb in the soil were closely related to human activities. This is because Ningbo is one of the cities in China where the industry developed earlier. The research area is located in a dense transportation network with high motor vehicle traffic, and major industrial parks are nearby. These are the main reasons for the significant accumulation of Cu, Zn, Cd, and Pb in soil. Cr and Ni were mainly influenced by the soil parent material and were less affected by human activities. 2) The content of the heavy metals Zn, Cd, and Pb in the soil showed an increasing trend with an increase in the construction years of urban parks. Because heavy metals are difficult to degrade in the soil, the pollution of heavy metals in the soil has become more serious with the increase in park construction years. Therefore, to reduce the impact of soil heavy metals in parks on human health, it is necessary to rationalize the industrial layout, transfer industrial activities, promote clean production, reduce the emission of heavy metal pollutants, regularly assess the level of soil pollution, and adopt plant remediation in urban parks to reduce soil heavy metal content. 3) Landscape patterns affected the heavy metal content in the soil of urban parks. Although urban park green spaces weaken air pollution in the city and alleviate the pollution pressure of air particulates, the air particulates entering urban parks have an adverse effect on the park soil. The forest patches in the parks, with their larger canopy areas, change the local microclimate, enhancing their role as a “sink” for urban air particulates, which then settle into the soil, leading to an increase in the enrichment of Zn, Cd, and Pb in the soil. There was a significant positive correlation between the proportion of forest patches and heavy metal content in the soil of urban parks, with p-values of 0.021, 0.018, and 0.011 for Zn, Cd, and Pb, and r² values of 0.37, 0.38, and 0.41, respectively. Forest patches affect the capture of heavy metal particulates in the atmosphere by urban parks, thereby affecting the heavy metal content in the soil of urban parks. A reduction in the proportion of forest patches in parks would weaken the “sink” function of urban parks, thereby leading to a decrease in heavy metal particulates that settle on the ground. The rational layout of urban parks plays a significant role in reducing the accumulation of soil heavy metals and can also control sources, such as changing production methods, rationalizing the spatial distribution of industries, adopting more efficient dust removal measures, or increasing the area of green spaces to absorb air particulates from transportation, thereby effectively reducing air particulates entering urban parks. The contagion index showed that the heavy metal content was higher when the connectivity of the forest patches in parks was good. Therefore, in the planning and construction of parks, planning forest patches in a dispersed layout can reduce the capture of air particulates, thereby reducing the health risks posed by heavy metals in urban park soils. Future research can enhance the applicability of the study by investigating the impact of different tree species and their landscape patterns on the accumulation of heavy metals in parks and by conducting an in-depth analysis of the health risks of different types of human health, making the research more applicable and playing an important role in the pollution prevention of urban parks. This study combines landscape patterns and ecological processes to analyze the levels and sources of heavy metal pollution in parks of a typical industrial city, providing a scientific basis for the planning, construction, and transformation of urban parks. This helps to better understand the relationship between heavy metal pollution in the soil of urban parks and their ecological functions, which is of great significance for enhancing the ecological service functions of urban parks, promoting the sustainable development of urban ecosystems, and maintaining healthy living environments.

Key words: soil heavy metals, urban parks, pollution evaluation, park construction years, landscape pattern