Title: Developing a stream typology for wadeable streams in the Rwenzori sub region, Uganda

Author: Amon Aine

Supervising Institution: Univ. of Natural Resources and Life Sciences, Vienna - Institute of Hydrobiology and Aquatic Ecosystem Management

Year: 2023



Aquatic macroinvertebrates as primary processors play an integral role in cleaning water. They are diverse with a habitat specific community largely submerged. This study investigates the viability of using abiotic parameters and macroinvertebrates to define river types as a baseline for reliable assessment of stream integrity in Rwenzori subregion. Inspired by the EU Water Framework Directive which emphasizes reference-based, type- and stressor-specific methods, eight reference and six non-reference sites from rivers Dura and Mpanga were sampled considering longitudinal zonation, substrate composition, and stressor gradient. Physicochemical parameters, substrate composition and benthic macroinvertebrates were documented. Harmonizing abiotic parameters and macroinvertebrate communities, reference sites were clustered into rivers upstream (RU) with seven indicator taxa and rivers downstream (RD) with eight indicator taxa. Non-reference sites clustered into sandy sites (SS) with no indicator taxa and polluted sites (PS) with two indicator taxa (67.3%≤ indicator value ≤ 00%, P<0.05) respectively. Out of 16, eight metric showed significant differences (P < 0.05) between reference sites and PS but not between SS and RU. SS were best distinguished (P < 0.05) from PS by EPTOC-dominance. Hydropsyche sp., Diplecterona sp., Leptonema sp. and Simuliidae metrics were best for distinguishing RU and RD (P < 0.05). Apart from the RS – score, TARISS, SASS and ETHBios show highest ecological integrity in reference sites, moderate in SS and poor in PS. This study shows the need to define river types in Rwenzori subregion if benthic macroinvertebrates are to be reliably used in inferring stream ecological integrity amidst existing multiple stressors. We recommend taxonomic resolution at lowest level since river types were only distinct genus level, investigation of more reference sites, and testing seasonality in defining river types considering more catchments within the subregion.


Key words: Biomonitoring, assessment system, freshwater systems, Uganda, macroinvertebrates, stream ecological integrity