Are Ephemeroptera, Plecoptera and Trichoptera traits reliable indicators of semi-urban pollution in the Tsitsa River, Eastern Cape Province of South Africa?

The taxonomy-based response pattern of macroinvertebrates to pollution gradient is well established, with tolerant taxa increasing in impacted conditions, while sensitive taxa increase with decreasing deterioration, typical of rural pollution. This study identified rural indicator and sensitive traits of Ephemeroptera, Plecoptera and Trichoptera (EPT) taxa by examining their trait distribution pattern in relation to rural pollution. Physicochemical parameters and EPT were sampled seasonally from August 2016 to April 2017. Eight sites were selected and categorised into three site groups. Site group 1 served as the least impacted site group and Site group 2 as the moderately influenced, whereas Site group 3 was the most impacted. Seven traits were selected and categorised into 27 trait modalities. The response of EPT traits to physicochemical parameters was analysed using the simultaneous analysis of the information contained in three tables: R (environmental characteristics of samples), L (taxa distribution across samples) and Q (species traits) (RLQ) and confirmed with fourth-corner analysis. Three trait attributes, large (10-20 mm), swimming, shredding, streamlined body shape and large body size (≥ 10-20), were considered tolerant signature traits of semi-urban pollution. These trait attributes were associated with the influenced Site group 3 and indicated a significant positive affinity with at least one physicochemical indicator of increasing semi-urban pollution (NH-N, NO-N, NO-N, PO-P, EC, turbidity, temperature and pH). Conversely, small body size (< 10 mm), operculate gills, spherical body shape and a preference for sediments were correlated with the least influenced Site group 1 and were considered sensitive traits of semi-urban disturbance. Overall, this study provided critical insights into EPT responses to disturbance, revealing that semi-urban activities influenced EPT traits differently in the Tsitsa River.