Mitigating Cadmium (Cd) Toxicity in Montane Forest Soils Using Biochar: Laboratory Trial for Soils from Horton Plains, Sri Lanka

Ranmalee Bandara,Kasun Lakmini,Mahina Senevirathne,Rasanjali De Silva,Niluka Ranasinghe,Priyantha Indralal Yapa

doi:10.4236/ojss.2021.1110025

Abstract

Horton Plains (HP), one of the two montane forests in Sri Lanka and habitat to many endemic species of plants and animals, has been severely affected by forest dieback. Past research has identified a direct link between soil pollution with Cadmium (Cd) and the phenomenon of forest dieback. As a consequence, forest dieback is increasing proportionately to the soil pollution. Hence, this study focuses on identifying a cost-effective remediation technique to neutralize soil Cd, and thereby reducing forest dieback. Soil samples were collected from HP, mainly Thotupolakanda site which shows more than 90% severity of forest die back, and bulked together. The soil was high (13.4) in organic matter and low (5.42) in pH, and three soil amendments were tested in this research as; bio char prepared using 1) rubber nut shells, 2) rice husk, and 3) dead wood from HP. Each sample was spiked with 20 ml of 5 ppm (parts per million) Cd solution, and four treatments a) soil + rubber-nut shell biochar (T1), b) soil + rice husk biochar (T2), c) soil + wood-from-HP biochar (T3), and d) soil only (T4), with five (05) replicates, were setup. During the first eight weeks after the application of treatments, it was observed that T1 showed the best performance, by showing a consistent trend in reducing the available soil Cd, with T2 following closely. The interesting observation was that the natural forest soil (T4) was also able to buffer the loading of Cd. At the close of the experiment, it was observed that the available soil Cd goes almost to zero, in less than 24 months.

Highlights

Skeletons of dead and dying large trees have become a common feature of most of the area in Horton Plains (HP), Sri Lanka
Past research has identified a direct link between soil pollution with Cadmium (Cd) and the phenomenon of forest dieback
Soil samples were collected from HP, mainly Thotupolakanda site which shows more than 90% severity of forest die back, and bulked together

Summary

Introduction

Skeletons of dead and dying large trees have become a common feature of most of the area in Horton Plains (HP), Sri Lanka. Death of trees and large scale destruction of the natural montane forest vegetation appears to have brought a massive destruction to this important natural resource. Through the interference with respiration and other crucial metabolic functions of the forest vegetation, death is inflicted to the plants by these toxic heavy metals [4]. Levels of concentration, depending on the soil pH, are termed as: 1) Reference level, 2) Research level, and 3) Priority intervention level. The reference level for agricultural soils is 90% of the heavy metal concentration of natural, non-polluted soils. This is the highest value permitted for non-polluted soils. The highest level of toxicity, the intervention level, indicates levels that are considered dangerous to soil, which needs priority remediation [6]

Methods

Results

Conclusion