Deciphering soil erosion dynamics in a fluvial island ecosystem of Northeast India: An integrated RUSLE-geospatial approach

Abstract

Soil erosion poses a critical threat to the sustainability of fluvial island ecosystems, particularly in dynamic and flood-prone regions such as Majuli, the world's largest inhabited river island in Northeast India. Despite its ecological and cultural significance, spatially explicit assessments of erosion dynamics remain limited. This study aims to (i) quantify the spatial distribution and severity of soil erosion across Majuli and (ii) evaluate the influence of key biophysical factors on erosion variability. We hypothesize that erosion risk exhibits significant spatial heterogeneity driven by rainfall, topography, soil properties, and land-use practices. An integrated Revised Universal Soil Loss Equation (RUSLE) model coupled with geospatial techniques was applied using 160 GPS-referenced soil samples collected from riverbank locations. Soil loss was estimated using five core RUSLE factors: rainfall erosivity (R), soil erodibility (K), slope length and steepness (LS), cover management (C), and support practices (P), alongside erodibility indices including clay ratio, silt–clay ratio, modified clay ratio, dispersion ratio, erosion ratio, and erosion index. Estimated annual soil loss ranged from 2.58 to 50.88 t ha⁻¹ yr⁻¹, with a mean of 17.72 t ha⁻¹ yr⁻¹ and standard deviation of 9.83 t ha⁻¹ yr⁻¹. Dispersion ratio (0.09–0.34), erosion ratio (0.03–0.25), and erosion index (0.05–0.46) indicate moderate to high erodibility across large areas. Approximately 40.32% of the island experiences moderately severe erosion, whereas only 0.02% falls under very low erosion. The results indicate pronounced spatial heterogeneity in erosion risk, highlighting priority zones for targeted conservation. The study demonstrates the robustness of integrating field-based measurements with GIS-enabled RUSLE modeling to support watershed planning, soil conservation strategies, and sustainable land management in vulnerable riverine environments.