Baseline assessment of benthic macroinvertebrate community structure and ecological water quality in Rwenzori rivers (Albertine rift valley, Uganda) using biotic-index tools

Abstract

The Rwenzori Mountains and Albertine Rift region of southwestern Uganda are part of a globally recognized biodiversity hotspot, but are currently facing pressures from intensified agriculture, mineral exploitation and hydroelectric power generation. This study was undertaken to assess the ecological water quality of Rwenzori rivers using biomonitoring metrics to determine the major factors shaping macroinvertebrate community structure in disturbed and undisturbed sites. We sampled macroinvertebrates at 66 sites along headwater tributaries and downstream areas of the Nyamwamba, Mubuku and Nyamugasani rivers, supplemented by five sites along the Kazinga channel and Lake George wetland, and identified a total of 32,579 macroinvertebrates to family level. Insecta was the most diverse taxon (45 families). Based on Average Score Per Taxon (ASPT) scores, sites were classified into four ecological water quality groups as excellent (40 sites), good (16), fair (7) and poor (8). Upstream sites had the highest abundance of pollution-sensitive families such as Caenidae and Hydropsychidae, while downstream sites had high numbers of Chironomidae. Lorenz curves revealed a low degree of evenness with Gini coefficient values ranging from 0.75 to 0.94. Ordination analysis revealed that total phosphorus, specific conductivity, chloride and chemical oxygen demand were key environmental variables contributing to variation among the sites. The majority of sites did show little to no anthropogenic influence with the exception of downstream sites. The results of this study provide useful baseline reference data, to assess and better manage the impacts of anthropogenic activities on the ecological integrity of the region’s aquatic systems. Furthermore, these datasets will advance the development of a regional family-level biotic index.