Effects of simulated acid rain on soil acidification, availabilities and temporal and spatial variations of Cu and Pb in a vegetable field under natural conditions

Under natural conditions, a field trial was introduced to explore influences of soil acidification on availabilities of Cu and Pb and their transferences in soil vertical profiles. Four different levels of simulated acid rain (SAR) were sprayed to the field to acidify the soils so as to observe behaviors of available Cu and Pb. Soil samples were collected from four soil layers: 0~10, 10~20, 20~30 and 30~60 cm. Results indicated that SAR could effectively decrease soil pH of four layers. With the decline of soil pH, contents of available Cu and Pb increased generally and high SAR level resulted in greater increases. In terms of vertical distributions in soil profiles, soil available Cu rose with the depth, indicating a downward movement of Cu to deeper soil layers; while soil available Pb increased only in the layer of 20~30 cm, but decreased dramatically in the deep soil layer (30~60 cm). This suggested that the available Cu was easy to transfer and available Pb was relatively immobile, under the influences of soil acidification. The results also revealed, with the prolongation of soil acidification, contents of soil available Pb increased, whereas contents of soil available Cu decreased, which implied soil available Cu was inclined to be transferred out of soils into groundwater, posing a threat to groundwater system, and soil available Pb was easier to accumulate in soils and be taken up by plants, posing a threat to the food security.