River restoration success depends on the species pool of the immediate surroundings.

Previous studies evaluating the success of river restorations have rarely found any consistent effects on benthic invertebrate assemblages. In this study, we analyzed data from 24 river restoration projects in Germany dating back 1 to 12 years and 1231 data sets from adjacent river reaches that lie within 0-5, 5-10, and 10-15 km rings centered on the restored sites. We calculated restoration success and recolonization potential of adjacent river reaches based on stream-type-specific subsets of taxa indicative for good or bad habitat quality. On average, the restorations did not improve the benthic invertebrate community quality. However, we show that restoration success depends on the presence of source populations of desired taxa in the surrounding of restored sites. Only where source populations of additional desired taxa existed within a 0-5 km ring around the restored sites were benthic invertebrate assemblages improved by the restoration. Beyond the 5-km rings, this recolonization effect was no longer detected. We present here the first field results to support the debated argument that a lack of source populations in the areas surrounding restored sites may play an important role in the failure to establish desired invertebrate communities by the means of river restorations. In contrast, long-range dispersal of invertebrates seems to play a subordinate role in the recolonization of restored sites. However, because the surroundings of the restored sites were far from good ecological quality, the potential for improvement of restored sites was limited.

[1]  D. Tullos,et al.  Analysis of functional traits in reconfigured channels: implications for the bioassessment and disturbance of river restoration , 2009, Journal of the North American Benthological Society.

[2]  A. Lorenz,et al.  Hydromorphological restoration of running waters: effects on benthic invertebrate assemblages , 2011 .

[3]  J. Harding,et al.  Barriers to the recovery of aquatic insect communities in urban streams , 2006 .

[4]  M. Palmer,et al.  Stream insect occupancy-frequency patterns and metapopulation structure , 2007, Oecologia.

[5]  L. Alexander,et al.  Dispersal by terrestrial stages of stream insects in urban watersheds: a synthesis of current knowledge , 2009, Journal of the North American Benthological Society.

[6]  James R. Karr,et al.  On the Calculation of Information-theoretical Measures of Diversity , 1968 .

[7]  R. Briers,et al.  Riparian forestry management and adult stream insects , 2004 .

[8]  D. Lehmkuhl.  Change in Thermal Regime as a Cause of Reduction of Benthic Fauna Downstream of a Reservoir , 1972 .

[9]  C. Coutant.  Evidence for upstream dispersion of adult CAD disflies (Trichoptera: Hydropsychidae) in the Columbia River , 1982 .

[10]  D. Williams,et al.  The upstream/downstream movement paradox of lotic invertebrates: quantitative evidence from a Welsh mountain stream , 1993 .

[11]  S. Rundle,et al.  Population structure and dispersal in the Canary Island caddisfly Mesophylax aspersus (Trichoptera, Limnephilidae) , 2001, Heredity.

[12]  Anthony Ricciardi,et al.  Assisted colonization is not a viable conservation strategy. , 2009, Trends in ecology & evolution.

[13]  P. Shaw,et al.  Long-term recovery of macroinvertebrate biota in grossly polluted streams: Re-colonisation as a constraint to ecological quality , 2009 .

[14]  J. Hellmann,et al.  An Assessment of Invasion Risk from Assisted Migration , 2008, Conservation biology : the journal of the Society for Conservation Biology.

[15]  D. Hering,et al.  Assessing streams in Germany with benthic invertebrates: development of a practical standardised protocol for macroinvertebrate sampling and sorting , 2004 .

[16]  J. Meyer,et al.  Standards for ecologically successful river restoration , 2005 .

[17]  S. Ormerod,et al.  Insect dispersal does not limit the biological recovery of streams from acidification , 2007 .

[18]  J. M. Elliott,et al.  A comparative study of the dispersal of 10 species of stream invertebrates , 2003 .

[19]  Katie A. Barnas,et al.  Synthesizing U.S. River Restoration Efforts , 2005, Science.

[20]  R. Briers,et al.  Inter‐population dispersal by adult stoneflies detected by stable isotope enrichment , 2004 .

[21]  Stephen James Ormerod,et al.  Intensive sampling and transplantation experiments reveal continued effects of episodic acidification on sensitive stream invertebrates , 2006 .

[22]  J. Ciborowski,et al.  Inland dispersal of adult aquatic insects , 1996 .

[23]  P. Zwick.  Stream habitat fragmentation — a threat to biodiversity , 1992, Biodiversity & Conservation.

[24]  J. Lawton,et al.  Species interactions, local and regional processes, and limits to the richness of ecological communities : a theoretical perspective , 1992 .

[25]  J. Hughes.  Constraints on recovery: using molecular methods to study connectivity of aquatic biota in rivers and streams , 2007 .

[26]  David J. Thompson,et al.  Patterns of movement and dispersal in an endangered damselfly and the consequences for its management , 2007 .

[27]  R. Nichols,et al.  Landscape, habitat characteristics and the genetic population structure of two caddisflies , 2007 .

[28]  J. Layzer,et al.  Restoration and colonization of freshwater mussels and fish in a southeastern United States tailwater , 2006 .

[29]  G. Likens,et al.  Stable isotopes identify dispersal patterns of stonefly populations living along stream corridors , 2005 .

[30]  S. Kemp,et al.  Conservation implications of genetic variation between spatially and temporally distinct colonies of the endangered damselfly Coenagrion mercuriale , 2005 .

[31]  Phaedra Budy,et al.  Quantifying Macroinvertebrate Responses to In‐Stream Habitat Restoration: Applications of Meta‐Analysis to River Restoration , 2010 .

[32]  R. Nichols,et al.  Genetic population structure and neighbourhood population size estimates of the caddisfly Plectrocnemia conspersa , 2003 .

[33]  L. Meester,et al.  The Monopolization Hypothesis and the dispersal–gene flow paradox in aquatic organisms , 2002 .

[34]  O. Hoegh‐Guldberg,et al.  Assisted migration: part of an integrated conservation strategy. , 2009, Trends in ecology & evolution.

[35]  N. Bond,et al.  Linking ecological theory with stream restoration , 2007 .

[36]  W. Gurney,et al.  Emergence and lateral dispersal of adult Plecoptera and Trichoptera from Broadstone Stream, U.K. , 1999 .

[37]  S. Jähnig,et al.  River restoration success: a question of perception. , 2011, Ecological applications : a publication of the Ecological Society of America.

[38]  M. Schwartz,et al.  A Framework for Debate of Assisted Migration in an Era of Climate Change , 2007, Conservation biology : the journal of the Society for Conservation Biology.

[39]  S. Jähnig,et al.  Hydromorphological parameters indicating differences between single‐ and multiple‐channel mountain rivers in Germany, in relation to their modification and recovery , 2008 .

[40]  P. Haase,et al.  Testing different sorting techniques in macroinvertebrate samples from running waters , 2004 .

[41]  D. Jenkins,et al.  Ecological and evolutionary significance of dispersal by freshwater invertebrates , 2003 .

[42]  Margaret A. Palmer,et al.  Reforming Watershed Restoration: Science in Need of Application and Applications in Need of Science , 2009 .

[43]  R. Naiman,et al.  Freshwater biodiversity: importance, threats, status and conservation challenges , 2006, Biological reviews of the Cambridge Philosophical Society.

[44]  J. Olden,et al.  Process-Based Principles for Restoring River Ecosystems , 2010 .

[45]  M. Palmer,et al.  River restoration, habitat heterogeneity and biodiversity: a failure of theory or practice? , 2010 .

[46]  D. Williams,et al.  Invertebrate movements within a small stream: Density dependence or compensating for drift? , 2000 .

[47]  Stephen James Ormerod,et al.  Dispersal of adult aquatic insects in catchments of differing land use , 2004 .