Re-Meandering of Lowland Streams: ignoring hydraulics and geomorphology have ecological consequences

We evaluated the restoration of physical habitats and its influence on macroinvertebrate community structure in 18 Danish lowland streams comprising six restored streams, six streams with little physical alteration and six channelized streams. We hypothesized that physical habitats and macroinvertebrate communities of restored streams would resemble those of natural streams, while those of the channelized streams would differ from both restored and near-natural streams. Physical habitats (substrate composition, depth, width and current velocity) were surveyed and macroinvertebrates were sampled along 100 m reaches in each stream. Restoration significantly altered the physical conditions and affected the interactions between stream habitat heterogeneity and macroinvertebrate diversity. The substrate in the restored streams was dominated by pebble, whereas the substrate in the channelized and natural streams was dominated by sand. Macroinvertebrate community structure was comparable among the three stream types. The analyses however revealed, a direct link between substrate heterogeneity and macroinvertebrate diversity in the natural streams. A similar relationship was not found in either the channelized or the restored streams, which we attribute to a de-coupling of the natural relationship between benthic community diversity and physical habitat diversity. Our study results suggest that restoration should aim at restoring the natural biotic communities through a regeneration physical structural and dynamic complexity in the streams.