Heavy metal output and content of headwater streams in an alpine forest in the upper reaches of the Yangtze River.

Heavy metal in headwater streams can not only directly influence the ecological processes of forest ecosystems, but also play an accumulated role in polluting downstream water, but little information is available. Therefore, the heavy metal output, and the concentrations and contents of copper (Cu), cadmium (Cd), lead (Pb) and zinc (Zn) from stream head to end were investigated in twelve headwater streams of a typical alpine forest in the upper reaches of the Yangtze River. The output rates of per square meter from streams and watersheds were 0.5191 mg/d m(2) and 0.065 mg/d m(2) for Zn, 0.1640 mg/d m(2) and 0.0025 mg/d m(2) for Cu, 0.0944 mg/d m(2) and 0.0118 mg/d m(2) for Pb, and 0.0201 mg/d m(2) and 0.0205 mg/d m(2) for Cd, respectively. Although the output rates of these four heavy metals displayed increase tendencies with the increase of stream length, but the output rates of Cd, Pb and Cu were statistically related to stream flow velocity. Both the concentrations and contents of Zn and Pb generally decreased from stream head to end, but those of Cu and Cd showed relative steady trends in all streams. This indicated an obvious self-purification capacity for Zn and Pb in these head water streams, showing that the shorter streams have the higher self-purification capacity. The results provided efficient data and new idea in controlling river heavy metal contamination.