Temporal variation of chemical weathering rate, source shifting and relationship with physical erosion in small mountainous rivers, Taiwan

Temporal variation of the chemical weathering rate (CWR) versus physical erosion rate (PER) and the shift of the sources of dissolved solids during rainstorms are explored in two small mountainous rivers, Northern Taiwan. The ionic hydrochemistry of streamwater, rainwater, soil water, and groundwater were collected to quantitatively demonstrate the sources of the dissolved solids and the coupling effect between CWR and PER during typhoon and non-typhoon periods. Results indicate that silicate cation weathering (CWR_SC) varies between 33 and 37 t km⁻² yr⁻¹, which is ~7 times the global mean, and the annual PER is ~81–166 t km⁻² yr⁻¹, similar to the global mean of ~137 t km⁻² yr⁻¹. The rainstorm periods only account for 1% of a year but are responsible for 10% of the CWR_SC and over 80% of the sediment flux, highlighting the importance of storm events. Silicate cation concentrations present a simple dilution process during rainstorms indicates the high connectivity between hillslopes and streams during rainstorms is established and forces the soil water into streams rapidly. Besides, the coupling between CWR_SC and PER becomes less relevant during rainstorms. The coupling between CWR_SC and PER is non-linear with flow regime dynamics, and the estimates of CWR_SC derived from non-typhoon day are as largely biased as one order of magnitude. High-resolution water chemistry data on the variations in ion production and physical erosion is more valuable than previously thought for characterizing the CWR and PER of active mountain belts.