Abstract: The main objective of this study is to quantify the impacts of peaking flows on riparian habitat fragmentation and macroinvertebrate assemblage variations. Field surveys of the Mudan River were conducted in the autumn of 2014. We sampled its macroinvertebrate assemblages and collected the habitat variables in six selected drawdown pools in its two regulated reaches, and made comparison with the data collected in its natural channels. Redundant analysis (RDA) of the physical and chemical habitat variables is used to summarize total variations in the habitat data and to identify the major environmental gradients in the pools. Results indicate substantial differences in the habitat variables and macroinvertebrate assemblages between the pools and river channels. In the pools, dissolved oxygen and pH were significantly higher than the natural river; higher levels of ammonia nitrogen and total nitrogen were found; and diptera, Hemipteran, Gastropoda were dominant. The abundance, taxa richness, Shannon-Wiener index, and Margalef richness significantly decreased in the pools due to habitat isolation. Redundancy Analysis reveals that the key habitat variables affecting macroinvertebrate assemblages in the pools are dissolved oxygen, pH and total phosphorus.

Key words: ecohydraulics, peaking flow, macroinvertebrate communities, habitat fragmentation, dissolved oxygen, redundancy analysis, water quality