The Environmental Geochemistry Of Heavy Metals In Soils And Sediments In Typical Regions Of Jiangsu Coastal Zone, Eastern China

Coastal zone is the typical region, characterized by intensive human activity, strong sensitivity responding to global change, as well as the transition from one type of ecosystem to another. Land Ocean Interaction in the Coastal Zone (LOICZ), as the joint project of IGBP and IHDP, seeks to promote the integrative research of ocean and land in the earth surface system. Heavy metals, as the essential part of geochemical elements of soils and sediments, are of prime importance for the environment quality of soils and sediments due to their persistence and toxicity. The elevated contents of heavy metals in soils and sediments not only directly influence soil physical and chemical properties, but also pose a risk to human health through food chain. With the rapid development of agriculture and industry, heavy metals pollution has threatened the ecosystem, which has been become the common hotspot of geographical, environmental and marine sciences. Therefore, the assessment on the characteristics of heavy metals levels in coastal zone is essential, because it can serve as a reference for environmental quality assessment and management.Jiangsu coastal zone in eastern China is a traditional agricultural-based region, as well as a new arising industry-based region. Though Jiangsu coastal zone has a long history of development, the overall economical level significantly falls behind the southern region of Jiangsu. Since 2009, the development of Jiangsu coastal zone has been promoted to the national development strategy of China, which poses an opportunity on the Jiangsu coastal zone. However, the rapid development also brings large pressure on the ecosystem and environment. Systematic sampling was conducted in typical regions of Jiangsu Coastal zone, including coastal soils from Xiangshui to Rudong, coastal tidal flat, as well as surface sediments of radial sand ridge field; and Cd, Cr, Cu, Hg, Ni, Pb and Zn were determined. Geostatistics, multivariate analysis,210Pb dating and risk assessment methods were applied to examine the sources, spatial variability, sedimentary history, and environmental risk of heavy metals in soils and sediments of Jiangsu coastal zone. The results derived from this study were shown as follows.1) The mean contents of Cd, Cu, Hg, Pb and Zn in surface soils of Jiansgu coastal zone were higher than the background values of Jiangsu coastal plain, which indicated that there were obvious accumulations of these heavy metals in surface soils; while the mean contents of Cr and Ni were lower than the background values. Cr and Ni were controlled by parent material, and seemed to originate from a natural source. Cd, Cu, Pb, and Zn were associated with the combination of parent material and anthropic inputs. Hg was dominated by atmospheric deposition related to various human activities. The contents of Cd, Cr, Cu, Pb, Ni and Zn in soils originated from marine deposition were significantly lower than alluvium and lagoon facies deposition, as well as the Changjiang delta deposition. The human influences on heavy metals were exhibited on the northern, western and southern parts of study area.Spatial variation of heavy metals in surface soils of Jiangsu coastal zone was composed of nugget effect, an exponential structure with the range of 15 km (local scale), as well as a spherical structure with the range of 80 km (regional scale). Spatial variations of Cr and Ni were associated with natural geochemical sources at local and regional scales. Parent material influenced the basic spatial variations of Cd, Cu, Pb and Zn at both local and regional scales, but human activity also contributed to the spatial variations of these metals. Hg variation was dominated by human inputs at both scales.Overall, there was relatively fine environmental quality in surface soils of Jiangsu coastal zone. Cd and Hg were the most contaminated metals in study area, and had moderate ecological risk. Further works should focus on the raised Cd and Hg contents.2) The grain sizes of cores in tidal flat of Jiangsu followed the increasing trend from northern to southern parts The sedimentary rates of Guanhe river mouth, Doulonggang, and Rudong were 1.08, 1.42 and 1.54cm·a-1 respectively, which is consistent with the previous works. Cr and Ni had natural sources in the cores of tadial flat in Jiangsu zone, and the human influences were not found. The sources and sedimentary records of Cd, Cu, Hg, Pb and Zn varied from the sampling sites. There were significant human input influences on the sedimentary records of heavy metals in Guanhe and Doulong cores. The Cd, Cu, Hg, Pb, and Zn contents in Guanhe core and the Cd, Hg contents in Doulong core were affected by human activities. The human influences began since the mid-late 1980s, with the increasing enrichment factors of heavy metals. While Cd, Cu, Pb and Zn in Guanhe core and Cd in Doulong core exhibited decreasing enrichment factors since the early 2000s due to the implement of strict environmental governance. However, the enrichment factors of Hg in both cores did not present the decreasing trend since the early 2000s, which could be attributed to the rapid development of chemical industry.The significant human inputs on heavy metals were not observed in Rudong core. It can be seen that the amount of wastewater discharging sites is significantly less than other regions of Jiangsu coastal zone. Moreover, the sampling site of Rudong is located in the coastal sand ridge field with the relatively coarse sediments. Therefore, the heavy metals levels in Dudong core remained their natural background.3) The contents of Cd, Cr, Cu, Hg, Ni, Pb and Zn in surface sediments of radial sand ridge field varied within the natural background, and came from natural sources. Spatial distributions of heavy metals were controlled by grain sizes. The total spatial variation of seven metals in radial sand ridge field could be divided into nugget effect, an exponential structure with the range of 7 km (local scale), as well as a spherical structure with the range of 25 km (regional scale). At local scale, the spatial variations of metals were dominated by grain sizes of surface sediments, and the patches with high values were distributed in the northwestern and southeastern parts of radial sand ridge field. At regional scale, the spatial variations of heavy metals were controlled by mineral composition. The sediments of radial sand ridge field showed good environmental quality, and had little environmental risk. The relative high risk was merely located in the region with fine grain size.