Abstract: Dissolved carbon flow from water in the alpine forest headwater streams is one of the essential components of carbon flux. A study on dissolved carbon output with water flow in the alpine headwater streams was carried out in a typical alpine forest in the eastern Qinghai-Tibet Plateau in July 2015. The output characteristics of dissolved carbon with water flow were investigated in the catchment covering an area of 4.31 km². The results are given as follows. The maximum annual output rate of dissolved carbon in unit area catchment was 12.99×10³ kg·km^-2. The output rates of the unit area of catchment were 3.56×10^-2 g·m^-2·d^-1 for total carbon, 2.12×10^-2 g·m^-2·d^-1 for inorganic carbon, and 1.43×10^-2 g·m^-2·d^-1 for organic carbon in the alpine forest headwater streams. In contrast, the output rates of the unit area of stream were 2.01×10³ kg·m^-2·d^-1 for total carbon, 1.20×10³ kg·m^-2·d^-1 for inorganic carbon, and 0.81×10³ kg·m^-2·d^-1 for organic carbon. For streams with length greater than 30 m, total carbon and inorganic carbon concentrations were higher in stream source than at stream end, but organic carbon concentration showed the opposite. Contrarily, for streams with length less than 30 m, the concentrations of total carbon, inorganic carbon, and organic carbon had larger values at stream end than in stream source. These results suggest that the water flow in the alpine forest headwater streams leads to a large amount loss of dissolved carbon. This study provides a new idea for further studies on the ecological linkage between the land system and water body under the climate change.

Key words: forest headwater streams, dissolved carbon loss, catchment, carbon source and sink