Ecological evaluation of weir removal based on physical habitat simulations for macroinvertebrate community

In Korea, rapid urbanization has changed the land use in rural areas, which has resulted in an increase in the number of weirs that are left untended in streams. Previously, changes in stream morphology and fishes were studied following the removal of such weirs. The present study was conducted to investigate changes in the habitat of the macroinvertebrate community after weir removal using physical habitat simulations (PHSs). The functional group approach was used in the PHSs for the macroinvertebrate community. In the functional group approach, macroinvertebrates are classified based on the traits of their food acquisition (i.e., the functional feeding group) or habitat selection (i.e., the functional habit group). In the present study, macroinvertebrate species were divided into the functional habit groups (FHGs) of swimmers, clingers, burrowers, and sprawlers. Hydraulic simulations and habitat simulations were carried out using the River2D model and habitat suitability curves (HSCs), respectively. The distributions of the composite suitability index (CSI) for the FHGs were obtained over the entire study area, and the changes in the suitability of the habitat for the target FHGs were evaluated. The simulation results indicated that habitat suitability for swimmers, clingers, and sprawlers was improved. However, habitat suitability for burrowers was degraded after the weir was removed. Consequently, the removal of the weir increased the diversity of the macroinvertebrate community, thus improving the health of the aquatic ecosystem.