Variations in river chemistry in Taiwan’s mountainous rivers: Influences of landslides and weathering

With climate change, extreme rainfall events are expected to occur more frequently, leading to more landslides triggered by climate incidents. Landslide processes in a dynamic environment in Taiwan play a crucial role in driving physical erosion and chemical weathering, facilitating the water-rock interaction and the transport of terrestrial dissolved and particulate materials through river systems, thereby affecting elemental chemistry and carbon cycling. This relationship between physical erosion and the resultant weathering affects the sequestering of carbon dioxide through silicate weathering and further links between erosion in the landslide-active catchment area and climate change. However, our knowledge of the effects of landslide weathering on river water chemistry, weathering processes, and the relationship with carbon cycling remains limited, and the absence of reliable chemical indicators to evaluate these processes necessitates further study. Here, we address the effects of landslide-related weathering on water chemistry (elements and isotopes) and carbon cycling in Taiwan. Major and trace elements, related isotopes, and carbon concentration were analyzed in the water samples from the river water beside landslides and leakage from landslide deposits. This study aims to characterize variations in river chemistry associated with landslide-affected settings and explore potential chemical and isotopic indicators to evaluate landslide-related weathering processes. The preliminary results show that the waters influenced by landslides can show distinct chemical characteristics relative to nearby river water. Silicate weathering dominates the dissolved load (>80%), while sulfate appears to co-vary with the total dissolved solids, suggesting an additional sulfate-linked control on hydrochemical variability.  Dissolved uranium isotopes reflect the degree of physical erosion, and show a negative correlation with the silicate chemical weathering, which reflects a weathering limited condition in our study area. This study will help refine chemical indicators for assessing landslide weathering signals and improve understanding of the mechanism of landslide-weathering-river chemistry linkages, as well as the carbon export in mountainous rivers under a changing climate.