Relationships between morphological quality and macroinvertebrate diversity in a degrading gravel-bed river following the magnitude 8.0 Wenchuan earthquake, China

The occurrence of earthquakes has the potential to significantly modify river morphology and cause notable effects on the aquatic ecosystem. Prior to the 2008 Wenchuan earthquake with a magnitude of 8.0, the Shiting River located in the upper basin of the Yangtze River was stable. Rapid bed incision or degradation has continued since the earthquake, and weirs and bank revetments were constructed to mitigate degradation. The impacts of channel morphology adjustment and human activities on biodiversity are not clear, which prohibits efficient river restoration. This paper evaluated the morphological quality of the Shiting River by employing the Morphological Quality Index (MQI), an approach recommended in the European Water Framework Directive. Macroinvertebrate diversity was analyzed in relation to the impacts of morphological adjustment and human activities based on field data collected in 2021. The results showed that the channel degraded and deepened after the earthquake, the planform changed from multi-threaded to single-threaded, and swamps on the floodplains disappeared. The quality of channel morphology in 2021 was evaluated using the MQI and was found to be ranging from poor to moderate. The diversity metrics of macroinvertebrates, specifically the Shannon, Simpson, and Evenness indices, exhibited a positive and significant correlation with four MQI sub-indices, which represented channel geomorphological functionality, artificiality, morphological pattern, and substrate, respectively. However, there was no significant correlation observed between the diversity metrics and the overall MQI score. The results imply that channels with superior morphological functionality, slower channel adjustment, and lower levels of anthropogenic disturbances tend to exhibit greater macroinvertebrate diversity. The study found a significant decrease in macroinvertebrate richness downstream of weirs and bridges. The community structures upstream and downstream of weirs and bridges were also significantly different. This study may help inform the ecological response of rivers to dynamic morphological changes and intense anthropogenic disturbances following disastrous earthquakes.