Inferring Long Term Averaged Soil Redistribution Pattern using Meteoric 10Be

Soil loss is one of the major environmental threats the world is facing due to horizontal expansion of cities and increasing land abuse. It has been previously shown by workers that the abuse or improper use of land and soil had adversely affected early civilisations. Keeping into consideration the imminent threat, a number of methods have been proposed to estimate soil loss e.g. numerical models, monitoring-based field methods. However, these are either time-consuming or inherently carry a degree of uncertainty.

One method involves using environmental fallout nuclides as tracers of soil erosion and mapping areas of soil loss and accumulation. The commonly used nuclides in this technique are ¹³⁷Cs and ⁷Be. ¹³⁷Cs is a nuclear fission product and cannot be used to track soil dynamics older than 1940s, while ⁷Be has a very short half-life and is used to study soil dynamics in a seasonal scale.

In this study, we have proposed a method of using meteoric ¹⁰Be to trace long-term soil redistribution in a landscape. This cosmogenic nuclide is produced in the atmosphere and reaches the land surface by dry and wet fallout. Once it reaches the surface, it is adsorbed by the soil particles and it mobilizes along with the soil. Thus, higher concentrations indicate net soil accumulation, whereas, lower concentrations are due to net soil loss. The rate of delivery of ¹⁰Be flux estimated from global circulation models (GCMs) has been used to calculate rates of erosion.

We tested our method in Pranmati catchment, a small river catchment (~93 km²) in Uttarakhand, India and validated by comparing our findings with previously proposed geomorphic transport laws. Our results show that soil erodes from the high lying divergent (convex) topography and accumulates in the low lying convergent (concave) topography. The rates of erosion are also influenced by land cover – erosion in forests is much slower compared to grassland.