Abstract: 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_4^{2-} were the dominant anions in the streamwater in
this region. A significant difference of Ca^{2+},
HCO_3^- and SO_4^{2-} 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_4^{2-} 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). We suggest that the highly mobile capacity, rapid water
exchange between precipitation and discharge, and long-term export lead to this
observed pattern.
