Trait-based responses of Ephemeroptera, Plecoptera, and Trichoptera to sediment stress in the Tsitsa River and its tributaries, Eastern Cape, South Africa

Elevated instream fine sediment is one of the most important water quality stressors affecting both the structure and function of aquatic ecosystems. This study evaluates whether a predictable pattern of trait distribution of Ephemeroptera, Plecoptera, and Trichoptera (EPT) can be observed along a gradient of sediment stress in eight selected sites in the Tsitsa River and its tributaries. The sites were classified into four site groups according to their fine sediment loads. One-way analysis of variance was used to test differences in the relative abundance of traits across the site groups. A predictable pattern was observed in 13 of the 27 trait attributes tested, with most traits displaying low abundances in highly disturbed site groups. The relationship between EPT traits and fine sediment stress was analysed using the multivariate RLQ analysis, and the result showed that traits such as swimming, shredding, operculate gill, small body size, and sclerotized body were the dominant traits in the sediment influenced site groups. In the less disturbed site groups, filter feeding, crawling, filamentous gill, soft and exposed body, and large body size were the dominant trait attributes. These observed relationships between EPT traits and sediment stress provide support for the potential usefulness of EPT traits as indicators of fine sediment stress in riverine ecosystems.