Characteristics of Chemical Weathering in Small Mountainous Watersheds, Taiwan

Abstract:

Chemical weathering plays an important role in regulating the long-term atmospheric CO_2. Oceania, featured by small mountainous watersheds, has long been thought as a hotspot of CO₂ consumption but rarely documented. One of the high-standing islands, Taiwan, has attracted much attention for extreme sediment discharge; nonetheless, the concomitant chemical weathering is still unclear. This study compiled 29 watersheds around the island to investigate the controls of runoff, uplift, and physical erosion on chemical weathering. Results showed a strong statistical link between chemical weathering rate and runoff could be hold in high annual precipitation larger than 2000mm. Besides, both chemical weathering and physical erosion harmoniously (simultaneously) respond to uplift rate showing a tendency towards equilibrium between uplift and denudation. Interestingly, the proportion of chemical weathering over chemical weathering and physical erosion decreases with the increase of uplift indicating chemical weathering becomes minor, though its amount increases. The huge unweathered sediments transported to downstream implies the possibility of considerable downstream chemical weathering. Meanwhile, the chemical weathering rate and CO₂ consumption in Taiwan are ~319.7 t km^-2 yr^-1 and ~32.55 10⁵mol km^-2 yr^-1, respectively. Both values are approximately 13 and 16-fold higher than the global mean of 24.0 t km^-2 yr^-1 and 2.42 10⁵mol km^-2 yr^-1. Compilation with other studies in Oceania showed that the total CO₂ consumption here may be ~86 Mt C yr^-1, much higher than the previous estimation of ~30 Mt C yr^-1. In this regard, the Oceania islands may account for ~25.4% of the global consumed CO₂.