The effects of habitat improvement techniques on invertebrate communities in two managed lowland rivers.

Most rivers and streams in England and Wales have been channelised for reasons of flood control, drainage of wetlands and channel improvement for navigation. Channelisation is one of the most dramatic aspects of man's impact on the riverine system. It involves the direct modification of the river channel and has impacts on the environment and ecosystem of the river. In order to decrease or ameliorate the impacts of channelisation and restore the riverine habitat, different restoration and rehabilitation techniques are used. Improvement structures in a river may produce many effects, but their overall function is to increase the diversity of the river habitat. Although the initial objectives of the installation of such structures are improvements to fish stocks and fisheries, they also improve biodiversity in invertebrates and plants and hence increase the conservation value. The effectiveness of two river habitat improvement techniques; artificial riffles and current deflectors, installed in two rivers. Harper's Brook and the River Smite were studied by comparing the macroinvertebrate communities of a control site on each river with those of channelised and improved sites by means of benthic kick-sampling. Eighty four samples from seven sites of Harper's Brook and 57 samples from five sites of the River Smite were collected in four seasons. One hundred and eight taxa with the total abundance of 210,045 from Harper's Brook and 101 taxa with the total abundance of 149,397 from the River Smite were identified. The results of ANOVA showed that the sites in Harper's Brook were significantly different in mean diversity (H') and in general the mean diversity of natural and two artificial riffles were greater whilst those of run sites were smaller. The natural riffle of the River Smite had also the greater mean diversity than the other sites. The results of DECORANA indicated that there was a clear separation between the riffle sites and run sites in all seasons in Harper's brook, and the separation of the natural riffle from the other sites in the River Smite. The results of TWINSPAN agreed with DECORANA, indicating that the two artificial riffles were associated with the natural riffle and the third with the run sites. The overall results showed that the riffle reinstatement was successful in improving the hydrology and biology of some sites close to or similar to that of a natural site. Current deflectors have also been successful in changing the hydrology of the river and creating pool and shoal sequences. Although the biology of the created shoal was not comparable to the natural riffle, it had a better biology compared with an unimproved site