Streamwater chemistry and flow dynamics along vegetation-soil gradient in a subalpine Abies fabri forest watershed, China

Streamwater chemistry and spatial flow dynamics from a subalpine Abies fabri forest in an experimental watershed located in the east slope of Gongga Mountain were analyzed to gain insights into the gradient effect of primary community succession on the stream biogeochemical process. Results showed that high sand content(exceeding 80%) and porosity in the soil(exceeding 20% in A horizon and 35% in B horizon), as well as a thick humus layer on the soil surface, made the water exchange quickly in the Huangbengliu(HBL) watershed. Consequently, no surface runoff was observed, and the stream discharge changed rapidly with the daily precipitation. The flow trends of base ions in the stream water were influenced by the Abies fabri succession gradient. Ca 2 , HCO - 3 and SO 2- 4 were the dominant anions in the streamwater in this region. A significant difference of Ca 2 , HCO - 3 and SO 2- 4 concentration exported between the succession stages in the watershed can be found. But they had the similar temporal change in the stream flow. Ca 2 , HCO - 3 and SO 2- 4 showed significantly negative correlations with the daily precipitation and the stream discharge. ;Concentrations of Cl -, Na , K , and Mg 2 were low in all streamwaters monitored and we observed no differences along the Abies fabri succession gradient. Low ratios of Na:(Na Ca) (range from 0.1 to 0.2) implied cations were from bedrock weathering(internal source process in the soil system) in this region. But, a variance analysis showed there were almost no differences between rainwater and streamwaters for Mg 2 , Na , K , and Cl - concentrations. This indicated that they might be come from rainfall inputs(external source). The highly mobile capacity, rapid water exchange between precipitation and discharge, and long-term export lead to this observed pattern were suggested.