A restoration paradox in a non-perennial river: Environmental flows improve macroinvertebrate richness but favour tolerant taxa

Full description

River regulation alters natural flow regimes, driving declines in the ecological integrity of non-perennial freshwater ecosystems. This study evaluates macroinvertebrate community responses to contrasting regulated flow regimes through spatial and temporal comparisons within the Darling-Baaka River system, Australia. Macroinvertebrate community data from contemporary (2024-2025) and historical (1994-2011) datasets were compared across two adjacent river reaches: the main channel and the Great Darling Anabranch (anabranch), which has received targeted environmental flows since 2007. Multivariate analyses suggest that macroinvertebrate communities across the region have become more homogeneous over time, characterised by reduced multivariate dispersion and increased similarity both between samples and between the two river reaches. However, the two river reaches had different trajectories over time. The main channel experienced a decline in total reach richness and a reduced frequency of collection for sensitive taxa. Conversely, the anabranch had a shift in total reach richness to levels comparable with historical main channel and regional richness. This reach level richness and per sample stability over time contrasted with the declines observed in the main channel. However, the community shift in the anabranch was primarily driven by the colonisation of disturbance-tolerant taxa rather than the re-establishment of more sensitive taxa. These findings highlight a restoration paradox: while targeted environmental flows can stimulate an initial increase in taxonomic richness, flow management alone is insufficient to overcome the loss of structural habitat and longitudinal connectivity. Reversing ecological degradation in regulated non-perennial rivers requires an integrated management framework that pairs environmental watering with physical habitat rehabilitation.