Impact of flood intensity on aquatic insect communities in a Korean stream under monsoonal climate

Abstract

As a consequence of climate change, localized torrential rainfall has increased in intensity and frequency in Northeast Asia under the influence of the monsoonal climate. The purpose of this study was to evaluate the impact of flood intensity on aquatic insect communities in a Korean stream, where the summer monsoonal flood is normal. Quantitative sampling was conducted according to stream reaches (upstream, midstream, and downstream sites) in Gapyeong stream, located in the central Korean peninsula, during July 2008–October 2009. Sampling was conducted within 48 hours after every rain event during the rainy season, and flood intensity was evaluated using the total amount of precipitation for 3 days before sampling. Precipitation was categorized in 100 mm increments. Water velocity and Froude number (Fr) were measured, and mean species abundance and species richness were determined. Habitat orientation groups (HOGs) were analyzed. Data were analyzed using nonmetric multidimensional scaling (NMS) ordination and two‐way analyses of variance .As a result, the velocity increased as precipitation increased at all sites, and the Fr at the upstream and midstream sites were below critical flow for all precipitation categories. The EPT‐group (Ephemeroptera, Plecoptera, and Trichoptera) together with Diptera were >90% in abundance at all study sites. The mean abundance of some major taxa (i.e., Ephemeroptera and Plecoptera) decreased significantly as precipitation increased, particularly, at the downstream site. The mean abundance of all HOGs was more influenced by the relatively large amount of precipitation (e.g., >200 mm) at all sites. According to NMS ordination, the amount of precipitation was the major factor determining the composition of aquatic insect communities in the study stream. In conclusion, aquatic insect communities in the Gapyeng stream were significantly influenced by the intensity of precipitation, and the impact was intensified at the downstream site.