Fallout radionuclides (FRNs) for measuring soil erosion in the Himalayan region: A versatile and potent method for steep sloping hilly and mountainous landscapes

The Himalayan hills and mountains are very fragile and being threatened by land degradation due to soil erosion by water, poses serious challenges to the soil ecosystem services and sustainability of natural resources. Reliable estimate of long-term soil erosion rate in various land use/land cover types and slopes are necessitated to suggest suitable conservation measures for managing the natural resources. The rugged terrain, inaccessibility, remoteness, and extreme weather events restrains in adopting conventional methods of soil erosion measurements. Fallout Radionuclides (FRNs) 137Cs provide a unique potential for reliable measurement of long-term soil erosion rate in the hilly and mountainous landscapes. This relies on underlying assumptions of uniform spatial distribution, strong binding to soil particles, negligble plant uptake, minimal leaching by water, no chemical migration as well as movement solely through physical processes and appropriate soil sampling designs. FRN based erosion measurements may compliment to the erosion models as well as serves as exclusive method for erosion estimation in the landscape. Erosion measurement over the hillslope positions will provide robust opportunity to understand the erosion processes in the Himalayan region on explicit manner. The present study underscores the shortcomings of conventional erosion methods and models in addressing the complexities of erosion processes over hillslopes in rugged terrains, often hindered by resource intensiveness and limitations in data acquisition. We deliver a comprehensive overview of the FRN method's potential and adaptability in measurement of long term soil erosion rate in higher elevation area with steep to very steep sloping complex topography of hilly and mountainous landscapes.