Assessing the effectiveness of Hyparrhenia hirta in the rehabilitation of the ecosystem of a gold mine dump

Abstract

The mining of gold is associated with several environmental challenges such as acid mine drainage, release of toxic metals which are associated to tailing sediments and have adversely impacted human health and the ecosystem. With increasing global population that is faced with limited land resources for agricultural activities, there is need for land restoration through effective rehabilitation of contaminated soils. The introduction of Hyparrhenia hirta, an indigenous grass specie as a phytoremediation technique for in situ rehabilitation of degraded soil is not only an economically viable approach but also environmentally friendly. Hyparrhenia hirta being a tufted and wiry perennial grass that is invasive with deep root system often aid in stabilizing the ecosystem owing to their self-fertile and drought resistant potentials that support that prevalence in harsh conditions at mine dump sites. In this study, mine tailings at Gold One Mine, Ekuhurleni, South Africa were assessed for heavy metal contents at the same time analysing the uptake of such heavy metals by Hyparrhenia hirta grass specie. The total metal mean concentrations was high (4023.67 mg/kg) for Hyparrhenia hirta which absorbed more of the following mean metal concentrations: 46.10 mg/kg for Cu; 40.08 mg/kg for Zn; 859.12 mg/kg for Pb; 618.26 mg/kg for Cr; 151.70 mg/kg for Co and 2308.41 mg/kg for Ni. The tailings were strongly acidic with a pH range of 3.86 – 4.34. These heavy metals despite the acidic environments were successfully absorbed by Hyparrhenia hirta grass specie. Along these lines Hyparrhenia hirta was discovered reasonable for re-vegetation of mine tailings dump as it has the capacity to hold together tailings sediments against wind and water erosion.

Tropical surface gold mining: A review of ecological impacts and restoration strategies

“…While phytoremediation species can sometimes naturally regenerate in contaminated sites, their growth may be too sparse for them to stabilize and effectively remediate the soil (Okereafor et al, 2020), and therefore usually need to be actively planted to achieve desired densities. However, we found very few field-based planting trials of potential phytoremediator species (see Annex C for species used in gold mine phytoremediation).…”

“…Studies indicate that without topsoil conservation, natural regeneration at former gold mines is significantly delayed (Ekyastuti et al, 2016; Román‐Dañobeytia et al, 2015; Sousa et al, 2008) compared to sites abandoned after less severe land conversions, such as agriculture. Tailings, eroded waste rock, and pit bottoms can remain unvegetated or hold standing water for years, if not decades, in both large‐scale (Mulligan et al, 2006; Okereafor et al, 2020; Rossouw et al, 2009) and ASGM sites (Peterson & Heemskerk, 2001; Schimann et al, 2012). The sparse recolonizing vegetation is often entirely herbaceous (Haagner et al, 2008; Salami et al, 2003; Weiersbye et al, 2006) and includes fewer woody species seedlings than nearby forest floors (Eludoyin et al, 2017; Peterson & Heemskerk, 2001).…”