Abstract
Trace metals can enter some natural regions with low human disturbance from atmospheric circulation, but little information is available regarding how the canopy can retained trace metals. Therefore, a representative sub-alpine spruce plantation was selected to investigate the net throughfall fluxes of eight trace metals (Fe, Mn, Cu, Zn, Al, Pb, Cd and Cr) of closed canopy and gap-edge canopy from August 2015 to July 2016. Over a one-year observational period, the annual fluxes of Al, Zn, Fe, Mn, Cu, Cd, Cr and Pb were 7.29 kg·ha-1, 2.30 kg·ha-1, 7.02 kg·ha-1, 0.16 kg·ha-1, 0.19 kg·ha-1, 0.06 kg·ha-1, 0.56 kg·ha-1 and 0.24 kg·ha-1, respectively, in the deposited precipitation. The annual net throughfall fluxes of these trace metals were 1.73 kg·ha-1, 0.9 kg·ha-1, 1.68kg·ha-1, -0.032 kg·ha-1, 0.04 kg·ha-1, 0.018 kg·ha-1, 0.093 kg·ha-1 and 0.087kg·ha-1, respectively, in the gap-edge canopy and -1.6 kg·ha-1, 1.13 kg·ha-1, 1.65 kg·ha-1, -0.10 kg·ha-1, 0.05 kg·ha-1, 0.03 kg·ha-1, 0.26 kg·ha-1 and 0.15 kg·ha-1, respectively, in the closed canopy. The closed canopy displayed a greater filter effect on the trace metals from precipitation than did the gap-edge canopy in the sub-alpine forest. In the rainy season, the net filtering ratio of trace metals ranged from -66%-89% in the closed canopy and from -52% to 25% in the gap-edge canopy. However, the net filtering ratio of all trace metals was greater than 50% in the closed canopy in the snowy season. Therefore, the results suggested that the most trace metals moving through the forest canopy are taken up rather than by rainfall leaching; moreover, the closed canopy can efficiently take up trace metals in the snowy season.