Comparative analysis of habitat structure and macroinvertebrate assemblages in headwater streams of Odzi sub-catchment, Chimanimani District, Zimbabwe, post Cyclone Idai-induced flooding

Abstract

Flooding results in short and long-term modifications of aquatic ecosystem structure and biodiversity. Cyclone Idai, which ravaged  through Zimbabwe in 2019, had devastating consequences on aquatic ecosystems. However, the extent of habitat modification and  consequent biodiversity shifts are unknown. This study focuses on the comparative analysis of (i) habitat structure and (ii)  macroinvertebrate assemblages in headwater streams of the Odzi sub-catchment, Chimanimani District, Zimbabwe, specifically  examining the conditions post-Cyclone Idai-induced flooding. Field sampling was conducted in the dry season (September−November)  2019 and wet season (January−March) 2020. Headwater streams of the Murare (first order), Umvumvumvu (first and second order) and  Nyanyadzi (first and second order) rivers were sampled. Habitat assessment was done following the Benthic Macroinvertebrate  Monitoring Protocol Implementation Plan. Selected water variables were measured using appropriate probes. Macroinvertebrate  assemblage data were collected using the South African Scoring System (SASS 5) protocol. Spatiotemporal variations in water quality,  habitat structure and macroinvertebrate metrics were assessed using two-way ANOVA, ANOSIM and SIMPER. Significant spatiotemporal  heterogeneity (p < 0.05) was detected in temperature, turbidity, conductivity and total dissolved solids, velocity and depth regimes, channel flow status, sediment deposition, channel alteration and frequency of riffles for the three rivers. Habitat quality ascending  hierarchical order was: Umvumvumvu > Murare > Nyanyadzi after Cyclone Idai induced flooding. The highest macroinvertebrate  composition diversity was detected in Murare River, the least flood-affected stream. The largest dissimilarity (ANOSIM, 75.3%) was  between the Umvumvumvu and Nyanyadzi rivers. Macroinvertebrate community structure differed significantly because of species  uniqueness and heterogenous tolerance to changes in environmental conditions after flooding. Flooding intensity and duration induces  dissimilar environmental tolerances and persistent macroinvertebrates communities in lotic systems across local catchment scales. Long- term assessment of water quality impairment, resilient functional feeder groups and rifflescale physical habitat structure are imperative   for optimised micro-scale conservation of macroinvertebrates in headwater streams prone to flash flooding.