Effects of river regulation on aquatic invertebrate communitycomposition: A comparative analysis in two southern Africanrivers

Abstract

While natural floods play a crucial role in shaping the composition of aquatic com-munities, the most rivers worldwide are regulated or dammed for anthropogenic pur-poses, resulting in alterations to the biological and chemical composition of theseecosystems. Studies have demonstrated various negative effects of river regulationon aquatic invertebrate communities globally. However, there is a scarcity of researchin Africa, despite its vulnerability to anthropogenic impacts. This study aimed to com-pare aquatic invertebrate communities in the Phongolo River, an impacted regulatedriver, and the Usuthu River, a less impacted unregulated river, in South Africa. It fur-ther aimed to ascertain whether Lake Nyamithi, a naturally saline lake receiving waterfrom both of the aforementioned systems, exhibited a stronger similarity to one of thetwo rivers in terms of its aquatic invertebrate composition. Aquatic invertebrate andwater samples were collected from 2012 to 2018 over several surveys. The UsuthuRiver demonstrated a diverse and sensitive aquatic invertebrate community, empha-sising its high conservation value. The Phongolo River demonstrated effects of an-thropogenic impact, with taxa more resilient to changes in water quality and flowcompared to the Usuthu River. Mismanagement and excessive water use may leadto the loss of any remaining sensitive aquatic invertebrate communities in this river.The presence of invasive molluscan in the Phongolo River and Lake Nyamithi alsoposes a threat to the native aquatic invertebrate communities. These invasive speciesare currently absent from the Usuthu River although other invasive species, such asthe Australian redclaw crayfish, are found in both river systems. Lake Nyamithi dis-played a unique aquatic invertebrate community, distinct from both rivers and theirfloodplains. This study provides important baseline infomation on the Usuthu River'saquatic invertebrates and emphasises the need to maintain adequate water flow inrivers and floodplains to protect biodiversity and sensitive species.