Impact of mining operation on the ecology of river Offin in Ghana.

Five sites in the Offin river basin were studied with respect to the quality of water and bottom sediment, as well as the community structure of both fish and phytoplankton along the river course to assess the effects of gold mining operations on the aquatic ecosystem. Turbidity, conductivity and concentrations of lead and cadmium in the water column showed a decreasing trend from the dredging area. Sediments upstream of and around the dredging area were sandy with low concentrations of organic (0.01-0.02% DW) and inorganic (e.g. CaCO3 1.1-1.2 mg g-1

DW; PO4, 1.2-3.5 mg g-1DW) materials, including trace metals (e.g. Hg<0.05 mg g-1DW, Pb<0.20 mg g-1DW, As<0.50mg g-1DW).  Fish  in  the  dredging  area  had accumulated higher mean concentrations of trace metals in their tissues  compared  to  those  from  the  non-impacted  sites.  Higher diversities of phytoplankton were recorded at sites where turbidity was lower. Autotrophs (blue-green and green algae) were virtually absent from sites with high turbidities. The structure of  the  fish  community  in  the  dredging  area  was  different  from other adjacent areas. However, the diversity and richness indices (0.56-0.67 and 1.12-1.67, respectively) of the fish communities along the river course were similar except for the most polluted site, which had the lowest indices. 

Dankwa, H.R., Biney, C.A. and deGraft-Johnson, A.A. 2003.  West Africa Journal of Applied Ecology, vol.7: 19-29