景观格局对农业表层土壤重金属污染的影响

Impacts of landscape patterns on heavy metal contamination of agricultural top soils in the Pearl River Delta,South China

景观格局是决定诸多生态过程的重要因素,但其对农业土壤重金属污染的影响尚未明确.鉴于此,本研究基于珠江三角洲2005年的300个表层土壤As、Pb、Cd、Ni样点数据和土地利用/覆盖图,使用地统计分析、景观格局分析、单因子污染指数和Pearson相关分析,揭示4种农业表层土壤重金属的污染特征及空间分布格局,探讨样点缓冲区内景观格局与农业表层土壤重金属污染的定量关系.结果显示:1)235个农业表层土壤样品中,As、Pb、Cd和Ni超过国家土壤质量二级标准的比例分别为3.8%、0.4%、17.0%和9.4%,高污染区主要位于广州、佛山和中山;2)耕地表层土壤样品中重金属的平均污染水平大于林地和果园,但除了Cd,其他3种重金属污染水平在不同农用地类型上的差异并不显著;3)缓冲区内水体的比例、平均斑块规模、破碎化程度、景观形状复杂度和聚集度/连接度与4种表层土壤重金属污染水平呈显著正相关;缓冲区内城市用地的部分景观格局与土壤Pb和Cd污染水平呈现类似的显著正相关.相反,缓冲区内林地的比例、平均斑块规模和聚集度越大,土壤Pb和Ni污染水平越低(呈显著负相关,P<0.05);4)距离工业用地越近,农业表层土壤Pb、Cd和Ni污染水平越高.景观多样性仅与土壤Cd污染呈显著正相关.研究结果可为珠江三角洲农业土壤重金属污染防治提供理论依据.

Landscape patterns are known to influence many ecological processes, but the relation- ship between landscape patterns and soil pollution processes is not well understood. Based on 300 top soil samples, land use and cover map for the Pearl River Delta （PRD） of 2005, this study ex- plored the characteristics and spatial pattern of heavy metal contamination of agricultural top soils and examined the impacts of landscape patterns on the heavy metal contamination in the buffers of soil samples. Research methods included geostatistical analysis, landscape pattern analysis, single- factor pollution indices, and Pearson correlation analysis. We found that. 1 ） out of the 235 agricul- tural soil samples, 3.8%, 0.4%, 17.0% and 9.4% samples exceeded the Grade Ⅱ national stand- ard for As, Pb, Cd and Ni concentrations respectively. High pollution levels were found in three cit- ies, Guangzhou, Foshan and Zhongshan; 2） soils in the farmland were more polluted than those in the forest and orchard land, and there were no differences among different agricultural land use types in contamination level of each heavy metal （except Cd） ; and 3） the proportion, mean patch area as well as the degree of landscape fragmentation, landscape-level structural complexity and ag- gregation/connectivity of water at the buffer zone were significantly positively correlated with the contamination level of each of the four heavy metals in agricultural top soils. Part of the landscape pattern of urban land in the buffer zone also positively correlated with Pb and Cd levels （P〈0.05）. On the contrary, the proportion, mean patch area and aggregation degree of forest land negatively correlated with soil Pb and Ni levels （P〈0.05） ; and 4） the closer to the industry land were the soil samples, the more polluted the soils were for Pb, Cd and Ni. Only landscape diversity was found to be positively correlated with soil Cd contamination. The study results provide new information and scientific basis for heavy metal pollution control and remediation, especially for agricultural soils in the PRD.