Nematode Community Response to Soil Restoration of a Mining-Affected Island in Southern Philippines

Abstract

Nematodes are widely used as bioindicators of ecological disturbances, including heavy metal pollution. However, their responses to soil recovery following restoration efforts in mining-impacted areas remains poorly documented. This study examines the response of nematode communities to restoration of mining-affected areas in Hinatuan island, southern Philippines. Specifically, we compared nematode communities in two rehabilitated sites with those from a Reference site and a Mined-out site between 2019 and 2021. Nematodes were collected in April 2019 and October of 2021, and identified to the genus level using morphology-based techniques. Basic soil characteristics (e.g., pH, OM, soil texture, N and P) and heavy metal concentrations (e.g., Ni, Cu, Zn, Pb and Cd) were analysed. The results showed minimal differences in soil characteristics and heavy metals across sites, except for Pb. Nematodes were absent from the Mined-out site during both sampling periods, likely due to topsoil removal and severe soil degradation caused by heavy machinery. However, nematodes started to flourish in the two rehabilitated areas, with abundances increasing with rehabilitation age (2012 Rehabilitation > 2015 Rehabilitation), though still lower than in the Reference site. An increase in nematode populations was observed between 2019 and 2021. In both years, Shannon index values were higher in the rehabilitated sites than the Reference site. Additionally, predators and omnivores - often considered less tolerant to soil disturbance - were present in both rehabilitated sites. The increasing nematode abundance, higher diversity index value and occurrence of sensitive nematode taxa in the rehabilitated areas suggest improving soil conditions due to ongoing restoration efforts. These findings underscore the importance of integrating effective soil restoration measures into post-mining land management to support long-term ecological sustainability.

Keywords: nematodes, fungi, rehabilitation, mining, southern Philippines