Macroinvertebrate Assemblages along the Longitudinal Gradient of an Urban Palmiet River in Durban, South Africa

SIMPLE SUMMARY: Rivers are the most threatened ecosystems globally. However, much attention has been directed to natural rivers as urban streams are regarded as unnatural with poor capacity to provide ecosystem services. This study was carried out to explore the capacity of an urban Palmiet River to provide refuge for aquatic biota and the importance of solid wastes in providing habitat for macroinvertebrates in severely disturbed urban rivers. The water was found to be of good quality in the upper reach/headwaters and polluted in the industrial area. However, the river showed the ability to self-purify as the water showed some improvement as it flows downstream. Various sensitive and tolerant groups of macroinvertebrates were found along the river. Although the current condition of the river can still support biodiversity and the functioning of the river, it is unclear if the system could endure further disturbance. Some sites with good-quality water showed low or absence of sensitive organisms due to poor habitat. It is evident that macroinvertebrate assemblages are influenced by the water quality and availability of physical habitat, and solid wastes may provide additional habitat in severely disturbed streams. These findings attest that urban river functioning does not differ from that of a natural river, and it should be appreciated as it provides important ecosystem services for local communities. ABSTRACT: Urban rivers are regarded as unnatural because they drain catchments characterized by impervious surfaces. The present study explored macroinvertebrate communities in relation to water and habitat quality along the longitudinal gradient of an urban Palmiet River in Durban, South Africa. Sampling was conducted across six sites along the river. The water quality has shown a significant variation (ANOVA, p < 0.05) across six sites. Good-quality water was observed at Site 6, whereas Site 5 exhibiting hypertrophic condition. Sites 4 to 1 were all eutrophic; however, nutrient levels showed to decrease from Site 4 down to Site 2 and increased again at Site 1. A similar trend was observed for habitat quality, with Site 6 showing excellent and Site 5 exhibited poor habitat. Coinciding with water and habitat quality, macroinvertebrate diversity and abundance showed significant differences across six sites. Sensitive palaemonids, notonemourids, and amphipods were only observed in the headwaters and have contributed over 50% of the variation in abundance between Site 6 and other sites. The non-metric multidimensional scaling (NMDS) plot has also shown clear discrimination (MANOVA, p < 0.001) for the Average Score Per Taxon (ASPT) across the six sites. Macroinvertebrate communities have shown a clear association between water and habitat quality. These findings affirm the ecological importance of urban rivers as they provide refuge to aquatic biodiversity, with anthropogenic litter providing additional habitats for other taxa. Despite the current conditions supporting biodiversity and the functioning of the river, it is unclear if the system could endure further disturbance.