Eco-geochemical Assessment of Agroecosystems: Cd in the Chengdu Economical Region, Sichuan, China

The cadmium (Cd) in the Chengdu Economic Region was studied as an example of eco-geochemical assessment on agroecosystems. Dry and wet atmospheric deposition samples, chemical fertilizers, irrigation water, and plants were collected. The concentrations of Cd and other elements in these samples were analyzed and the fluxes of input and output of the agroecosystem were calculated. The results indicated that the Cd was more concentrated in the surface soil than in the deep soil, and Cd concentration in some rice samples exceeded the upper limit of the pollution-free agricultural products. The input of Cd into the agroecosystem was 17.8 g·hm−2·y−1 on average, which accounted for 85.2% of the total input. Infiltration (2.34 g·hm−2·y−1) and harvest (1.87 g·hm−2·y−1) were the two most important Cd outputs. The average increase of Cd content in soil was 0.006 mg·kg−1·y−1, which was a result of sources outside of the agroecosystem. In the next 20 years, the area of the grade III soil will increase 2–3 times under the current input and output condition of Cd, which will lead to significant decrease of the arable land. The decrease of the pH in the study area was 0.106 y−1 because of fertilization and acid rain, of which 89.6% was from the contribution of chemical fertilizers. The present study indicates that, even though 95% of the rice production is safe, after 20 years, 70% of the safe soil will degrade, and the area of alarming soil will increase rapidly from 4% to 27% of the total cultivated area in the region.