Quantifying soil redistribution across Himalayan hillslope under the influence of topography and terrace abandonment using fallout-137Cs

Soil erosion poses a critical challenge in mountainous regions which threaten the ecosystem stability and agricultural productivity. Conventional erosion assessment methods often fail to capture the spatial heterogeneity and complex topography of the Himalayan landscape. However, the application of the Fallout Radionuclide (FRN) 137Cs technique offers a reliable and effective approach for quantifying long-term soil redistribution under such challenging terrain. This study evaluated soil erosion and deposition patterns on a representative steep Himalayan hillslope comprising both cultivated and abandoned terraced fields. The highest erosion rate (-34.6 ± 4.47 t ha⁻¹ yr⁻¹) was observed at the abandoned terraces located on the upper hillslopes, whereas the highest sediment deposition (+ 11.5 ± 3.00 t ha⁻¹ yr⁻¹) occurred at the lower and valley positions. Notably, regardless of the hillslope position, the hillslope shape exerted a significant influence on erosion and deposition dynamics, wherein convex slopes facilitated soil loss, while concave slopes promoted sediment accumulation. Abandoned terraces exhibited significantly higher soil erosion compared to cultivated fields emphasising the adverse consequences of land abandonment. Although, Well-maintained terraces at lower and valley hillslope positions effectively trap soil and sediment from upslope areas. The ¹³⁷Cs method effectively captured the spatial patterns of soil redistribution across the rugged terrain, it also demonstrated the pronounced variability in erosion and deposition driven by topographic heterogeneity. The findings underscore the need for regular terrace maintenance, enhanced vegetative cover, and integrated soil conservation strategies. Policy interventions promoting terrace preservation, sustainable land-use practices and preventing land abandonment are crucial for mitigating soil erosion and supporting resilient mountain agriculture in the Himalayan region.