Evaluation on Characteristics of Heavy Metal Spatial Pollution in Farmland Soils along the Bijiang River

摘要

Based on the farmland soils along the Bijiang River, a main tributary of the international Lantsang-Mekong River flowing through the Jinding Lead-Zinc Deposit, this dissertation makes analyses on the pollution characteristics of spatial variation in farmland soils by adopting the soil sampling and testing analysis and applying single-factor pollution index (SPI) evaluation and Nemerow composite pollution index (NCPI) evaluation. The results indicate that: (1) In accordance with Environmental Quality Standard for Soils (II), the content of Cd contained in the farmland soils has severely exceeded the standard in a large scale, followed by Pb and Zn. However, the content of As is maintained within the specified standard; (2)The SPI values of soils are in the following sequence: Cd＞Zn＞Pb＞As. The pollution level caused by the heavy metal "Cd" to the farmland soils is extremely heavy in a wide range, and a majority of the farmlands are heavily polluted by Zn. The farmlands with moderate pollution by Pb are centered at Plot 2 in the deposit, and only a few farmland soils are moderately polluted by As at Plot 2 in the deposit; (3) Based on the NCPI, the results indicate that the NCPI of the farmland soils has reached to the degree of heavy pollution; (4) It is indicated based on the RPI evaluation that the RPI values of As, Cd, Pb and Zn contained in the farmland soils have exceeded the standard in the following sequence: Pb＞Zn＞Cd＞As, which illustrates that during the development of Jinding Lead-Zinc Deposit in Lanping County, the heavy metals imposing the most profound influence on the soil pollution are Pb and Zn. The heavy metal pollution in the farmland soils from the upper reaches to the lower reaches of the Bijiang River is not only caused by the development of Jinding Lead-Zinc Deposit in Lanping County, but is also associated with its high soil background value; (5) There is a remarkable spatial variation of heavy metal pollution in farmland soils from the upper reaches to the lower reaches of the Bijiang River. Both the SPI and the NCPI values of heavy metals in the soils within the deposit at the upper reaches of the Bijiang River are the lowest; the pollution index of the soils closest to the deposit are the highest, and the pollution index of the soils with a certain distance from the deposit drops swiftly; the pollution index of Plot 4 rises to a certain degree at the middle reaches, and gradually ascends near the Yunlong County seat at Plot 5, however, with a comparatively small growth rates.