Statistical analysis of macroinvertebrate assemblage structure in relation to river-health assessment of an urban river, Eastern Cape, South Africa

Urban rivers in developing countries, including South Africa, are increasingly being impacted by human activities. The Bloukrans and Palmiet Rivers, where the current study was undertaken, are no exception. The Bloukrans River, the main object of this study, was impacted by wastewater effluent discharges and run-off from informal settlements and agricultural activities. The present study was aimed at evaluating the ecological health of the Bloukrans River using macroinvetebrate-based biomonitoring approaches, including the biotic index (i.e. the South African Scoring System version 5), multimetric and multivariate analyses of the assemblage structure. 18 metrics were selected and their potential for discriminating between the control and impaired sites evaluated. Macroinvertebrates were sampled bi-monthly (April - August 2013) at one control site (i.e. Site 1) in the Palmiet River and four impaired sites (i.e. Sites 2, 3, 4, and 5) in the Bloukrans River. The Scoring index indicated that the river health condition at the control site was good, whereas apart from Site 5, conditions at Sites 2, 3 and 4 were either poor or critically modified. 12 metrics discriminated between Site 1 and the four impaired sites. Canonical correspondence analysis indicated that dissolved oxygen, electrical conductivity, nutrients and turbidity exerted the greatest influenced on the assemblage structure. Overall, the study indicated that pollution in the Bloukrans River had significant impact on the river health, influencing metrics in the diversity, composition and richness categories. The 12 metrics that proved sensitive to deteriorating water quality, enabling the discrimination of the control site from the impacted sites, could be used with the Scoring index to assess river health in the Bloukrans River. However, although using metrics in addition to the Scoring index provided greater understanding, where analytical resources are limited the summary biotic Scoring index can provide an acceptable rapid indication of river health.