Impact of rainfall intensity on benthic macroinvertebrate communities in a mountain stream under the East Asian monsoon climate

As a consequence of the climate change, localized torrential rainfall has increased in intensity and frequency in Northeast Asia. This work aims at studying the effect of rainfall intensity on benthic macroinvertebrate communities in a mid-sized mountain stream in Korea, where the summer monsoon flood is prevalent. Sampling was conducted along reaches in Gapyeong stream (42 km in length), central Korean Peninsula, from a period of July 2008–October 2009. The sampling collection was carried out within 48 h after every major rain occasion and rainfall intensity was quantified by using the total rainfall amount for three days. Both water velocity and Froude number were found to increase with respect to the increase of rainfall at all study sites. As a consequence, the habitat environment and benthic macroinvertebrate communities were apparently affected by the rainfall intensity along the stream reaches. The species richness and abundance of benthic macroinvertebrates were significantly decreased at a rainfall over 200 mm, while much less decreased at a rainfall below 100 mm. Furthermore, the richness and abundance of species generally decreased with an increase of rainfall and their decrease was more evident at the downstream site, as compared to the upstream and midstream one.