A new study looks at 26 restored river sites across Europe and finds little evidence that these projects have impacted the benthic invertebrate community - i.e. the worms, crustaceans, and other organisms that dwell on the bottom of freshwater systems.
Benthic invertebrates are often used as indicators of stream ecological health and play a critical role in the food chain of freshwater systems.
Sonja Jahnig and fellow researchers surveyed both restored and non-restored stretches in rivers in southern and central Europe in both lowland and mountainous settings. They looked at hydromorphological restoration projects that spanned several hundred meters to several kilometers.
Restoration activities included both active practices (e.g. removal of bank fixation material, initiating re-meandering) and passive approaches (e.g. abandoning river maintenance, excluding livestock).
The researchers found that both active and passive restoration projects had improved the metrics for habitat at the meso scale (for example - shoreline length) and at the micro scale (for example - water velocity, substrate) though these effects were greater in certain settings than others.
However, they found that the improvements did not translate into a significantly altered benthic invertebrate community.
These findings published in the Journal of Applied Ecology are in line with previous research. However, the results from this study are particularly compelling because rather than conducting a meta-analysis of past research, the scientists directly studied paired sites in a variety of settings using a standard methodology.
The findings may surprise stream restoration practitioners who assume that transforming habitat features will have a major impact on the biotic community.
The authors conclude that small-scale restoration projects like many of the ones they looked at in the study (i.e. several hundred meters or less) are unable to address the catchment-scale issues (e.g. poor water quality, limited source populations) that limit benthic invertebrate communities. They write,
"Actively improving aquatic habitats along a short river stretch may even come at the price of causing degradation of the riparian zone, e.g. facilitate earth moving, but will not necessarily enhance ecological quality. Rather, efforts at a larger scale, i.e. catchment wide, including more comprehensive measures and tackling all pressures are likely to have effects on the invertebrate community – eventually improving ecological form and functioning."
--by Rob Goldstein
Jähnig, S., Brabec, K., Buffagni, A., Erba, S., Lorenz, A., Ofenböck, T., Verdonschot, P., & Hering, D. (2010). A comparative analysis of restoration measures and their effects on hydromorphology and benthic invertebrates in 26 central and southern European rivers Journal of Applied Ecology DOI: 10.1111/j.1365-2664.2010.01807.x