Assesement of Downstream Pollution Profiles of Tanneries Effulents Along Modjo Riverbed Sediments Using Benthic Macroinveretebrtes As Bioindicators

In this study of tannery pollution load along Modjo River, physico-chemical parameters were correlated with macroinvertebrate metrics. Out of eight study sites, Site 1 (site at which Modjo River joins with Lake Koka) values like biological oxygen demand, chemical oxygen demand, dissolved oxygen, sulfide, sulphate and total dissolved solids levels were higher in the site of tannery waste discharge. Values recorded highly exceeded the Maximum Permissible Limit in Environmental Protection Authority guidelines. At Site 4 the chromium concentration of 116mg/kg was significantly higher than the other studied sites. In another other investigation chromium concentrations from bed sediments in Site 1 were 209 times greater than the surface water results recorded at this site six years ago. A total of 4,088 macroinvertebrate individuals belonging to 38 families were collected from 8 study sites along Modjo River. These results showed that Modjo River is highly degraded and has alarming effect on Lake Koka. This study was performed in order to conserve and manage the biodiversity by evaluating the degree of tannery pollution on Modjo River using macroinvertebrate and physico-chemical parameters; and to predict the effect on Lake Koka. 

Key words: Macroinvertebrate; Modjo River