中国科学院南京地质古生物研究所机构知识库

In active mountains, landslides are the primary agent of erosion that readily generates materials with high weatherability. Understanding the linkage between landslide activity, erosion, and chemical weathering is critical for assessing how tectonic uplift affects the carbon cycle and Earth's climate. However, quantifying the contribution to chemical weathering and erosion fluxes from landslides remains challenging because of the lack of effective tracers related to landslide activities. Recent studies suggest that a suite of isotopic tracers, including the U, Sr and Be isotopes, have the potential to trace solutes and materials associated with landslide activities. Here we use three isotope ratios (U-234/U-238, Be-10/Be-9, Sr-87/Sr-86) to quantify the contribution to solid and solute fluxes from landslides in the tectonic-active eastern Tibetan mountains. We focus on 22 small catchments (drainage area < 50 km(2)) draining the epicentral region of the 2008 Wenchuan earthquake using samples collected in 2018 and 2019. Landslide seepage water and landslide sediment samples are used to constrain the landslide-weathering end-member. Tree branch and regolith topsoil samples are used to characterize the weathering end-member of regolith. We show that the U-Be-Sr isotopes can trace the solutes and solids sourced from landslide debris and quantify that landslides contribute 33.1 +/- 16.2% (1SE) to the riverine solutes and 43.4 +/- 20.8% (1SE) to the riverbed silt-sized sediment. These proportions are lower than the landslide-derived proportions in high-order catchments immediately (1 to 4 years) after the Wenchuan earthquake, which may relate to changes in landslide-material inputs across drainage networks and/or weathering processes over time. We also found that across 87 catchments with variable basin areas (from <1 km(2) to similar to 20,000 km(2)) draining the broad eastern Tibetan mountains, the U-234/U-238 activity ratio of river water silt-sized riverbed sediment shows distinct characteristics for the catchments grouped by mean slope angles (mean slope angles shallower versus steeper than a common threshold angle of 32 degrees). These findings suggest that U isotopes are a promising tracer of landslide-sourced solutes and materials. Overall, our work provides a case study showing that a multi-isotope approach can be used to quantify the impacts of landslides on erosion and weathering, providing new insights into how tectonic activities could affect the carbon cycle.