In-stream restoration (1): an assumption supported

Posted on March 9, 2011

It’s commonly assumed that the quality of riverine habitats can be improved by adding instream structures in the form of woody material or boulders, or by reconfiguring the stream channel.  There’s an expectation that additional physical complexity will lead to an increase in biodiversity.  However,  very few studies have tested this prediction, especially with respect to macroinvertebrates, and only 15-30% of instream restoration attempts have included post-project monitoring.  The results from 24 different studies have now been subjected to the first meta-analysis to be conducted in the field of instream habitat enhancement.  The main conclusions are that adding large woody debris to streams had a significant positive effect on the number of macroinvertebrate taxa, but almost no effect on macroinvertebrate density.  Adding boulders or reconfiguring the channel had a generally beneficial effect, but the outcomes were much less consistent than those with woody debris.  Typically, macroinvertebrate responses weren’t affected by the size of streams, but they were conditioned by land use patterns in the catchment, and forested reaches produced the most consistent positive results.  Improved understanding of these effects will depend crucially on improvements in the quantity and quality of monitoring data. 

Reference:  Miller, S.W., Budy, P. & Schmidt, J.C.  2010.  Quantifying macroinvertebrate responses to in-stream habitat restoration: applications of meta-analysis to river restoration.  Restoration Ecology 18(1), 8–19.