Abstract: Heavy metals in sediments from Dongjiang River were detected by ICP-MS. The results showed that the distribution characteristics of these heavy metals, including Cu, Zn, Cd, Hg, were similar, and the sites with higher and lower value were approximately in accordance. Cu, Zn, Cd, Hg, Pb were the main heavy metal pollutants. The average contents of these heavy metals in the sediments were 157.29, 213.21, 0.98, 0.42, 50.77 mg·kg^-1 respectively, which exceeded the sediment background value in China. The degree of pollution was evaluated by the index of geoaccumulation and the index of the Hakanson ecological risk. The results showed that the geoaccumulation of the pollutants in Dongjiang River was in the order: Cd, Cu, Zn, Hg, Pb, while the ecological risk degree of the pollutants was in the order: Hg, Cd, Cu, Pb, Zn. On the whole, in Dongjiang River, the potential ecological risk of sediments from upstream (Heyuan) was at low level, middle stream (Huizhou) at relatively high level, and downstream (Dongguan) at very high level.

Key words: Free air CO₂ enrichment (FACE), Rice, Canopy energy balance