The impact of run-of-river hydropower projects on fish community: a case of Mpanga Hydropower Project

Abstract

Several studies have focused on the ecological impacts of large storage dams and less attention is given to small hydropower projects, especially run-of-river type, yet they are the commonest globally. This research, aimed at assessing the impact of run-of-river hydropower projects on aquatic ecology through determining the spatial and temporal variation of water quality, abundance and diversity of fish and the growth behaviour of fish along reaches affected by the operation of the project. Water quality was determined using a hand-held Palintest meter, while the fish abundance was through a count of fish caught using a minnow trap and, the fish growth behaviour was deduced through the length-weight relationship. The study found a significant reduction (p < 0.05) in the concentration of dissolved oxygen and oxidation-reduction potential in the reservoir reach in both dry and wet season, while in the midstream and downstream reach, there was an increase (p < 0.05) in the concentration of dissolved oxygen, oxidation-reduction potential in both dry and wet season. Furthermore, the pH in the midstream reach was significantly higher compared to the reservoir reach and the downstream reach in the wet season. On the other hand, there was no significant difference (p > 0.05) in the average temperature, electrical conductivity and total dissolved solids across all three reaches in both the dry and wet seasons. Similarly, the overall abundance and diversity of fish species were greater in the downstream reach (richness 11) and lowest in the midstream (richness 7) and reservoir reach (richness 7). There was a complete absence of rheophilic species such as Amphilius jacksonii and predominantly migratory fish such as Labeobarbus altianalis in the reservoir reach. Based on the length-weight relationship, the growth co-efficient of all fish species in the reservoir reach were found to be significantly less than the ideal growth co-efficient, thus they exhibited negative allometric growth. The study thus showed that the reservoir reaches tended towards hypoxia conditions and was thus very susceptible to eutrophication which in turn affected the fish abundance, diversity and growth. Notwithstanding the above, this study is the first of its kind in Uganda and therefore, further long-term study is needed.