Abstract
This paper compares the ecological response of reaches treated with traditional (check dams, CDs) and morphologically based (artificial steps, ASs) grade-control works installed in a mountain river, where an unmodified reach provided reference conditions. Coarse particulate organic matter (CPOM) retentiveness was measured at the reach scale using artificial leaf release experiments. Macroinvertebrate sampling was carried out by a Surber net at pool- and run-type morphological units within the three reach types, and hydraulic and sediment characteristics were measured at each Surber sampling site. In addition to calculating a variety of parameters to describe hydrodynamic and macroinvertebrate characteristics within reaches and morphological units, biotic (Extended Biotic Index, IBE) and ecological (Fluvial Functionality Index, IFF) index scores were also calculated. Results averaged at the reach scale show that CPOM retention, macrobenthos taxa richness and diversity were higher in the presence of a natural bed morphology, whereas both types of grade-control works alter CPOM dynamics and macroinvertebrate communities. However, ASs showed CPOM retention dynamics and macroinvertebrate richness and diversity that were closer to the unmodified reach than CDs. Analysis at the unit scale demonstrated strong links between hydraulic variables and macroinvertebrate parameters such as abundance, diversity and proportion of shredders (SHR). Overall, ASs seem to provide a good trade-off between the need to limit channel incision whilst maintaining aquatic ecosystems.