Effect of heavy metals and physicochemical parameters on diversity of plants at a gold mine tailings dam in Ghana

This study focuses on the impact of physicochemical parameters and heavy metals concentrations in soil on abundance, richness and diversity of plants at Marlu tailings dam located near Bogoso, Ghana. The concentrations of heavy metals (mg/kg) in soil at the study area are as follows: Fe (10,528.9 - 7,873.0), Cu (224.9 - 177.4), Zn (51.6 - 42.7), Cd (3.0 - 2.6), As (2.4 - 1.7) and Mn (78.3 - 57.1). Soil nutrient levels (nitrate, phosphate and sulphates) were relatively low with most sites having acidic soils (6.4 - 5.3). A total of 2,055 plants composed of eighteen (18) different species were observed at the study area. Pennisetum purpureum was the most abundant plant species (46.8%), and Poaceae and Asteraceae were the predominant families with percentage abundance of 37 and 28.8%, respectively. Diversity of plants measured using Simpson and Shannon indices at sampling sites varied significantly between the different sampling sites but are relatively low compared to other similar sites in Ghana. Species richness and diversity of plants correlated positively with the low nutrient levels and soil acidity. Low plant abundance, species richness and diversity correlated with increased Copper (Cu) levels in soil. Cadmium (Cd) levels were correlated with low abundance of plants belonging to families Asteraceae and Fabaceae. The presence of heavy metals at concentrations above regulatory limits negatively impacted on abundance and diversity of plants at the decommissioned mine tailings dam. Increased concentrations of heavy metals and low nutrient levels in soil could account for reduced plant abundance, species richness and diversity at the mine tailings dam.