Abstract
In March 2003, a re-meandering experiment, connecting main channel with an oxbow lake, was implemented in Shibetsu River, located in eastern Hokkaido, northern Japan. The objective of this study is to examine the changes in distribution and structure of macroinvertebrate community before and after the re-meandering experiment in the alluvial lowland river. We investigated composition of macroinvertebrate community in straight reach, oxbow lake (pre-experiment), and re-meandering reach (post-experiment). After the oxbow lake was connected with the main channel, we set five transect lines for quantitative evaluation of macroinvertebrate at three study reaches (natural meandering, re-meandering and straight channel). The hypothesis we tested was that the re-meandering reach containing more diverse habitat environments has more diverse macroinvertebrate community than do straight channel. The study results showed that most lentic species were replaced with lotic species after the connection. Most taxa identified on transects, however, were found at shallow shorelines of point bar, which we did not expect before the experiment. Since taxa richness and abundance were negatively correlated with shear velocity, a low shear stress and resultant bed stability at the shorelines of point bar are responsible for a high abundance and richness of macroinvertebrate community. Those results indicated a role of point bar for keeping abundance and diversity of macroinvertebrate in alluvial lowland river. Taxa richness and abundance of macroinvertebrate community in re-meandering channel had once recovered to the level of natural meandering channel in June, but this recovery was not maintained until November. We believe that this is due to the continuous movement and changes of bed material as well as channel morphology. The re-meandering reach is still dynamic and we have to monitor the physical process as well as ecological response until it reaches to the stable phase.
